Ultrastructure of Nerves

The nervous system allows us to perceive, understand, and respond to our environment. It comprises two different types of cells:

Nerve cells (neurones) – these form the functional basis of the nervous system, responsible for transmitting signals as electrical or chemical signals.

Glial cells – these provide functional and structural support for the neurones. One example is a Schwann cell, which produces the lipid sheath of peripheral neurones.

In this article, we will focus on the ultrastructure of nerves. We will look at the general structure of nerves, their layers of connective tissue and finish by considering some conditions that arise when the normal structure is lost.

Neuronal Structure

There are several different types of neurones found in the nervous system. They all contain the same key structural components – the cell body, dendrites, the axon and the axon terminals.

Cell Body

The cell body holds the nucleus. It is the site of protein synthesis, which occurs on small granules of rough endoplasmic reticulum called nissl substance.

In the nervous system, many neuronal cell bodies can group together to form a distinct structure. In the CNS, this is known as a nucleus, and in the PNS as a ganglion.

Dendrites

The dendrites are elongated portions of the cell body. They extend outwards, receiving input from the environment and from other neurones.

Axons

The axon is a long, thin structure down which action potentials (the nerve impulse) are conducted. Whilst neurones have many dendrites, most cells only have one axon.

Each axon is coated in myelin – a layer of insulating lipid. Myelin is formed by cells wrapping themselves around the nerve axon. In the CNS, this is performed by oligodendrocyte cells. In the PNS, Schwann cells are responsible for this action.

There are gaps between the myelin sheaths formed by different cells. These gaps are known as nodes of Ranvier. They allow for saltatory conduction of impulses.

Axon Terminals

The axon terminal is the most distal part of the axon. It is from here that the neurone sends chemical signals to other cells – usually via neurotransmitter release. To facilitate the secretion of neurotransmitters, the axon terminals contain a large number of mitochondria.

Fig 1.0 – The components of a typical neurone.

Coverings

Fig 1.1 – Connective tissue layers of a nerve cell.

In the peripheral nervous system, the axons of neurons are grouped together to form nerves. The axons are enclosed by several connective tissue layers:

Endoneurium – Surrounds the axon of an individual neurone.

Perineurium – Surrounds a fascicle, which is a collection of neurones.

Epineurium – Surrounds the entire nerve, which is formed by a collection of fascicles. It contains numerous small blood vessels, which supply the nerve fibres. Epineurium appears on the nerve as it exits the intervertebral foramen. It is created by the fusion of arachnoid and pia mater, which are layers of the meninges.

Classification

Neurones can be classified by structure or by function. Neurones with different functions have differing structures, which is visible histologically.

Structural Classification

Fig 1.2 - Structural classification of neurones.

Neurones can be either unipolar, pseudounipolar, bipolar or multipolar.

Unipolar – Here the cell body is at one end of a single unbranched axon, and there are no dendrites. These can be found in the cochlear nucleus of the brain.

Pseudounipolar – They have one axon which is divided into two branches by the presence of the cell body. Sensory neurones are all pseudounipolar.

Bipolar – These neurones have two processes arising from a central cell body – typically one axon and one dendrite. These cells are found in the retina.

Multipolar – They have one axon and many dendrites, with a cell body displaced to one side of the axon. Motor neurones are a prime example of this.

Functional Classification

There are three broad functional classifications of nerves – sensory (afferent), intermediate and motor (efferent). There are key structural differences between these three types:

Sensory nerves – small axons and psuedounipolar structure.

Motor nerves – larger axons and multipolar structure.

Intermediate neurones – central cell body and many dendrites.

Sensory and motor nerves are located within the PNS, whereas intermediate nerves are found in the CNS.

Clinical Relevance: Disorders of Nerve Tissue

Multiple Sclerosis

Fig 1.3 - Photomicrograph of ademyelinating MS-Lesion.

In multiple sclerosis, the myelin covering of neurones in the central nervous system is lost. This means that the relay of action potentials between sensory and motor neurones is affected. This can lead to visual, motor and auditory problems.

The etiology of Multiple Sclerosis (MS) is still uncertain. However, the causes are thought to either be as a result of autoimmune destruction of myelin, or the failure of oligodendrocytes to myelinate the interneurons.

Motor Neurone Disease

Motor Neurone Disease describes a group of conditions that include Amyotrophic lateral sclerosis, better known as ALS. In these diseases, motor neurones become damaged for reasons that are not entirely clear, but are thought to include dysfunctional mitochondria.

The damage to the motor neurones is progressive, making this a degenerative disease. It often begins with damage to peripheral nerves, and works its way up through the limbs until the central nervous system is compromised. This disease is fatal, with a median survival length of 3-5 years post diagnosis.

Ultrastructure of Blood Vessels

The average man has approximately six litres of blood in his body. This blood is carried by several different types of blood vessels, each of which are specialised to play their role in circulating blood around the body.

There are three major types of vessels; arteries, veins and capillaries. Arteries (with the exception of the pulmonary artery) deliver oxygenated blood to the tissues. At the tissues, the oxygen and nutrient exchange is carried out by the capillaries.

 The capillaries also return deoxygenated blood to the veins, which bring it back to the heart (with the exception of the pulmonary veins).

In this article, we shall follow the path that blood takes around the body, examining the structure and function of the major types of blood vessels.

Vessel walls can largely be split into three sections; tunica intima (innermost), tunica media, and tunica adventitia. Each must be considered.

The Arterial System

As a whole, the arterial system takes oxygenated blood from the heart, and delivers it to the capillaries, where oxygen and nutrient exchange can occur.

There are four main types of artery in the body, each with a distinct structure and function. 

We shall look at each in more detail (in order of decreasing size).

Large Elastic (Conducting) Arteries

These are the largest arteries found in the body, and are found closest to the heart. They function to ‘conduct’ blood from the heart to regions of the body, where it can be distributed.

Elastic arteries include most of the named vessels surrounding the heart, such as the aorta and pulmonary arteries.

Tunica Intima: Endothelial cells with a thin subendothelium of connective tissue and discontinuous elastic laminae.

Tunica Media: The tunica media is comprised of 40-70 fenestrated elastic membranes with smooth muscle cells and collagen between these lamellae. It is the thickest part of an elastic artery.

Tunica Adventitia: Thin layer of connective

 tissue containing minor vasa vasorum, lymphatics and nerve fibres.

Medium Muscular (Distributing) Arteries

From the large elastic arteries, blood enters smaller distributing arteries. 

They distribute the blood to sub-regions of the body.

Medium muscular arteries are similar in structure to large elastic arteries.

Tunica Intima: Consists of an endothelium, a subendothelial layer and a thick elastic lamina.

Tunica Media: Consists of around 40 layers of smooth muscle connected by gap junctions in order to allow coordinated contraction.

Tunica Adventitia: Thin layer of connective tissue containing minor vasa vasorum, lymphatics and nerve fibres.

Arterioles

Arterioles are part of the microcirculation. They carry blood from the muscular arteries to the metarterioles.

Structure:

Arteries with a diameter of less than 0.1mm are classed as arterioles. They generally have around 3 layers of smooth muscle cells and the internal elastic lamina is absent. The external elastic lamina is only present in larger arterioles.

Metarterioles

Arteries that supply capillary beds are known as metarterioles.

Instead of having a continuous layer of smooth muscle cells, intermediate rings of smooth muscle are located at certain points. These rings are known as known as precapillary sphincters, which contract to control blood flow to the capillary bed.

Clinical Relevance: 

Precapillary Sphincters Precapillary sphincters are very important in the control of tissue perfusion. When the body performs certain actions, these structures are able to restrict blood flow to certain regions and encourage it to others.

For example, when running, skeletal muscle requires a lot more blood than it usually would. In order to accommodate for this, precapillary sphincters in skeletal muscle relax in order to increase blood flow

The Capillaries

Capillaries consist of one layer of endothelium and its concordant basement membrane.

They are specially adapted to provide a short diffusion distance for nutrient and gaseous exchange with the tissues they supply.

There are three types of capillaries; continuous, fenestrated and sinusoidal, each of which have variably sized gaps between the endothelial cells.

These gaps act as a sieve, controlling which molecules and structures can leave the capillary. For example, in continuous capillaries (located in skeletal muscle), only water and certain ions can leave. In sinusoidal capillaries (located in the liver), larger structures such as cells and proteins are able to exit.

The Venous System

As a whole, the venous system takes deoxygenated blood from the capillaries, and delivers it to the heart (with the exception of the pulmonary veins). From the heart, blood can be pumped to the lungs and re-oxygenated.

Like the arterial system, the venous system is comprised of different vessel structures. We shall look at each in more detail (in order of ascending size, as we move away from the capillaries).

Postcapillary Venules

A postcapillary venule receives blood from capillaries and empties into venules. In addition, the surrounding tissue fluid tends to drain into them, as their pressure is lower than that of capillaries or the tissue.

Structure:

The wall is an endothelial lining with associated pericytes and a diameter of 10-30 micrometres. This is similar to the structure of capillaries, but postcapillary venules are more permeable, making them the preferred site of white blood cell migration (e.g. to sites of infection).

Clinical Relevance: Inflammation and Postcapillary Venules

During inflammation pressure in the venules actually becomes higher than that of the surrounding interstitium. This allows fluid to leak into the site of inflammation along with inflammatory cytokines and white blood cells.

Venules

Venules are continuous with the post-capillary venules. They continue to move blood away from the capillary beds. Many venules unite to form a vein.

Structure:

The endothelium is associated with pericytes or thin smooth muscle cells (the beginning of a tunica media) to form a very thin wall. Venules can have a diameter of up to 1mm. They also contain valves that press together to restrict retrograde transport of blood.

Veins

Veins are the major vessels of the venous system. They are the final step in the return of blood to the heart.

Structure:

Veins generally have a larger diameter and a thinner wall than the accompanying artery. The vessel wall contains more connective tissue, with less elastic and muscle fibres.

Veins vary slightly in structure according to their size:

Small and medium veins have a well developed tunica adventitia and a thin tunica intima and media.

Large veins have diameters greater than 10mm and a thicker tunica intima. They have well developed longitudinal smooth muscle in the tunica adventitia. The media has circular smooth muscle, which is usually not prominent, except for the superficial veins of the legs.

Veins contain valves that primarily prevent the back-flow of blood. They also act together with muscle contraction, squeezing the veins to propel blood towards the heart.

Fig 3 – Structure of a vein wall.

Venae Comitantes

Venae comitantes are deep paired veins wrapped together with an artery in one sheath. The pulsations of the artery promote venous return within the paired veins.

Ultrastructure of Bone

Bone is a specialised type of connective tissue. It has a unique histological appearance, which enables it to carry out its numerous functions:

Haematopoiesis – the formation of blood cells from haematopoietic stem cells found in the bone marrow.

Lipid and mineral storage – bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals.

Support – bones form the framework and shape of the body.

Protection – especially the axial skeleton which surrounds the major organs of the body.

In this article, we shall look at the ultrastructure of bone – its components, structure and development. We shall also examine how disease can affect its structure.

Protection – especially the axial skeleton which surrounds the major organs of the body.

In this article, we shall look at the ultrastructure of bone – its components, structure and development. We shall also examine how disease can affect its structure. 

Components of Bone

Bone is a specialised form of connective tissue. Like any connective tissue, its components can be divided into cellular components and the extracellular matrix.

Cellular Components

There are three types of cells in bone:

Osteoblasts – Synthesise uncalcified/unmineralised extracellular matrix called osteoid. This will later become calcified/mineralised to form bone.

Osteocytes – As the osteoid mineralises, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate bone mass.

Osteoclasts

– Derived from monocytes and resorb bone by releasing H+

ions and lysosomal enzymes.

They are large and multinucleated cells.

The balance of osteoblast to osteoclast activity is crucial in the maintenance of the tissue’s structural integrity. 

It also plays a role in conditions such as osteoporosis.

Extracellular Matrix

The extracellular matrix (ECM) refers to the molecules that provide biochemical and structural support to the cells.

The ECM of bone is highly specialised.

 In addition to collagen and the associated proteins usually found in connective tissue, bone is impregnated with mineral salts, in particular calcium hydroxyapatite crystals. These crystals associate with the collagen fibres, making bone hard and strong. 

This matrix is organised into numerous thin layers, known as lamellae.

Fig 1 – Cellular components of bone and their functions.

Structure of Bone

Under the microscope, bone can be divided into two types:

Woven bone (primary bone) – Appears in embryonic development and fracture repair, as it can be laid down rapidly. It consists of osteoid (unmineralised ECM), with the collagen fibres arranged randomly. It is a temporary structure, soon replaced by mature lamellar bone.

Lamellar bone (secondary bone) – The bone of the adult skeleton. It consists of highly organised sheets of mineralised osteoid. This organised structure makes it much stronger than woven bone. Lamella bone itself can be divided into two types – compact and spongy.

In both types of bone, the external surface is covered by a layer of connective tissue, known as the periosteum. A similar layer, the endosteum lines the cavities within bone (such as the medullary canal, Volkmann’s canal and spongy bone spaces).

Lamellar bone can be divided into two types. The outer is known as compact bone – this is dense and rigid. The inner layers of bone are marked by many interconnecting cavities and is called spongy bone.

Compact Bone

Compact bone forms the outer ‘shell’ of bone. In this type of bone, the lamellae are organised into concentric circles, which surround a vertical Haversian canal (which transmits small neurovascular and lymphatic vessels). This entire structure is called an osteon and is the functional unit of bone.

The Haversian canals are connected by horizontal Volkmann’s canals – these contain small vessels that anastomose (join) with the arteries of the Haversian canals. The Volkmann’s canals also transmit blood vessels from the periosteum.

Osteocytes are located between the lamellae, within small cavities (known as lacunae). The lacunae are interconnected by a series of interconnecting tunnels, called canaliculi.

Spongy Bone

Spongy bone makes up the interior of most bones and is located deep to the compact bone. It contains many large spaces – this gives it a honeycombed appearance.

The bony matrix consists of a 3D network of fine columns, which crosslink to form irregular trabeculae. This produces a light, porous bone, that is strong against multidirectional lines of force. The lightness afforded to spongy bone is crucial in allowing the body to move. If the only type of bone was compact, they would be too heavy to mobilise.

The spaces between trabeculae are often filled with bone marrow. Yellow bone marrow contains adipocytes and red bone marrow consists of haematopoietic stem cells.

This type of bone does not contain any Volkmann’s or Haversian canals

Ossification and Remodelling

Ossification is the process of producing new bone. It occurs via one of two mechanisms:

Endochondral ossification – Where hyaline cartilage is replaced by osteoblasts secreting osteoid. The femur is an example of a bone that undergoes endochondral ossification.

Intramembranous ossification – Where mesenchymal (embryonic) tissue is condensed into bone. This type of ossification forms flat bones such as the temporal bone and the scapula.

In both mechanisms, primary bone is initially produced. It is later replaced by mature secondary bone.

Remodelling

Bone is a living tissue and as such constantly undergoes remodelling. This is the process whereby mature bone tissue is reabsorbed, and new bone tissue is formed. It is carried out by the cellular component of bone.

Osteoclasts break down bone via a cutting cone. The nutrients are reabsorbed, and osteoblasts lay down new osteoid. Remodelling occurs primarily at sites of stress and damage, strengthening the areas affected

Clinical Relevance – Disorders of Bone

Bone has a unique histological structure, which is required for it to carry out its functions. Alterations to this structure, secondary to disease, can give rise to several clinical conditions.

Osteogenesis imperfecta is a condition in which there is abnormal synthesis of collagen from the osteoblasts. Clinical features include fragile bones, bone deformities and blue sclera. It is a rare disease and genetic in aetiology, with an autosomal dominant inheritance pattern. The fragility of the bones predisposes them to fracture – this has a medicolegal importance, as in children it can be mistaken for deliberate injury.

Osteoporosis refers to a decrease in bone density, reducing its structural integrity. This is produced by osteoclast activity (bone reabsorption) outweighing osteoblast activity (bone production). The bones are fragile, and at an increased risk of fracture. There are three types:

Type 1: Postmenopausal osteoporosis – Develops in women after the menopause, due to decreased oestrogen production. Oestrogen protects against osteoporosis by increasing osteoblast and decreasing osteoclast activity.

Type 2: Senile osteoporosis – Usually occurs above the age of 70.

Type 3: Secondary osteoporosis – Where osteoporosis occurs due to co-existing disease (e.g. chronic renal failure).

Risk factors include age, gender, diet (vitamin D and calcium), ethnicity, smoking and immobility. It is usually managed by bisphosphonates which are taken up by osteoclasts causing them to become inactive and undergo apoptosis. This limits further degradation of bone

Rickets is Vitamin D or calcium deficiency in children with growing bones. This means that the osteoid mineralises poorly and remains pliable. The epiphyseal growth plates can then become distorted under the weight of the body, potentially leading to skeletal deformities.

Osteomalacia is a Vitamin D or calcium deficiency in adults with remodelling bones. Here the osteoid laid down by osteoblasts is poorly mineralised leading to increasingly weak bones, increasing their susceptibility to fracture.

Note: Vitamin D deficiency can be due to poor diet, lack of sunlight or a metabolic disorder. For example, kidney failure could interfere with the second hydroxylation of vitamin D or an intestinal disorder may prevent sufficient absorption. A calcium deficiency can be caused by diet or low vit. D.

Joint Stability

The stability of joints is a topic of great clinical importance; it explains why some joints are more prone to dislocation and injury than others. It also underlies the clinical basis of treating joint injuries.

In this article we shall look at the various factors that contribute towards joint stability.

Shape, Size and Arrangement of Articular Surfaces

The joints of the body come in all shapes and sizes. The most important factor to consider here is the relative proportion of the two articulating surfaces.

For example, in the shoulder joint, the humeral head of the upper arm is disproportionately larger than the glenoid fossa of the scapula that it sits in – making the joint more unstable, as there is less contact between the bones.

In contrast, the acetabulum of the pelvis fully encompasses the femoral head, and this makes the hip-joint far more stable. However, whilst the hip is more stable, the shoulder has a greater range of movement. Each joint has this trade-off that is particular to its function.

Fig 1 – The articulating surfaces of the shoulder joint. Note how the humeral head is disproportionately larger than the glenoid fossa of the scapula.

Ligaments

The ligaments of a joint prevent excessive movement that could damage the joint. As a general rule, the more ligaments a joint has, and the tighter they are, the more stable the joint is.

However, tight ligaments restrict movement, and this is why extra stability of a joint comes at the cost of loss of mobility. If disproportionate, inappropriate or repeated stress is applied to ligaments, they can stretch, tear or even damage the bone they attach to – this is why sportspeople are more susceptible to ligament injuries.

Tone of Surrounding Muscles

The tone of the surrounding muscles contributes greatly to the stability of a joint. A good example of this is the support provided by the rotator cuff muscles, which keep the head of the humerus in the shallow glenoid cavity of the scapula. If there is a loss of tone, such as in old age or stroke, the shoulder can dislocate.

Dislocations of the shoulder joint can tear the rotator cuff muscles, making the patient more susceptible to further injuries.

Similarly, the tone of muscles around the knee are crucial to its stability. Through inappropriate or unbalanced training, the knee can be made prone to injury through muscle imbalance. This can lead to chronic pain.

Fig 2 – The rotator cuff muscles, which act to stablise the shoulder joint.

Structures of a Synovial Joint

A synovial joint is characterised by the presence of a fluid-filled joint cavity contained within a fibrous capsule.

It is the most common type of joint found in the human body, and contains several structures which are not seen in fibrous or cartilaginous joints.

In this article we shall look at the anatomy of a synovial joint – the joint capsule, neurovascular structures and clinical correlations

Key Structures of a Synovial Joint

The three main features of a synovial joint are: (i) articular capsule, (ii) articular cartilage, (iii) synovial fluid

Articular Capsule

The articular capsule surrounds the joint and is continuous with the periosteum of articulating bones.

It consists of two layers:

Fibrous layer (outer) – consists of white fibrous tissue, known the capsular ligament. It holds together the articulating bones and supports the underlying synovium.

Synovial layer (inner) – a highly vascularised layer of serous connective tissue. It absorbs and secretes synovial fluid, and is responsible for the mediation of nutrient exchange between blood and joint. Also known as the synovium

Articular Cartilage

The articulating surfaces of a synovial joint (i.e. the surfaces that directly contact each other as the bones move) are covered by a thin layer of hyaline cartilage.

The articular cartilage has two main roles: (i) minimising friction upon joint movement, and (ii) absorbing shock.

Synovial Fluid

The synovial fluid is located within the joint cavity of a synovial joint. It has three primary functions:

Lubrication

Nutrient distribution

Shock absorption.

Articular cartilage is relatively avascular, and is reliant upon the passive diffusion of nutrients from the synovial fluid.

Accessory Structures of a Synovial Joint

Accessory Ligaments

The accessory ligaments are separate ligaments or parts of the joint capsule.

They consist of bundles of dense regular connective tissue, which is highly adapted for resisting strain. This resists any extreme movements that may damage the joint.

Bursae

A bursa is a small sac lined by synovial membrane, and filled with synovial fluid.

Bursae are located at key points of friction in a joint. They afford joints greater freedom of movement, whilst protecting the articular surfaces from friction-induced degeneration

They can become inflamed following infection or irritation by over-use of the joint (bursitis).

Innervation

Synovial joints have a rich supply from articular nerves.

The innervation of a joint can be determined using Hilton’s Law – ‘the nerves supplying a joint also supply the muscles moving the joint and the skin covering their distal attachments.’

Articular nerves transmit afferent impulses, including proprioceptive (joint position) and nociceptive (pain) sensation

Vasculature

Arterial supply to synovial joints is via articular arteries, which arise from the vessels around the joint. The articular arteries are located within the joint capsule, mostly in the synovial membrane.

A common feature of the articular arterial supply is frequent anastomoses (communications) in order to ensure  blood supply to and across the joint regardless of its position.

 In practice this usually means arteries are above and below a joint, curving round each side of it and joining via small connecting vessels.

The articular veins accompany the articular arteries and are also found in the synovial membrane.

Clinical Relevance: Osteoarthritis

Osteoarthritis is the most common form of joint inflammation (arthritis). It stems from heavy use of articular joints over the course of many years, which can result in the wearing away of articular cartilage, and often the erosion of the underlying articulating surfaces of bones as well.

The changes which occur are irreversible and degenerative. This results in the decreased effectiveness of articular cartilage as a shock absorber and lubricated surface, as well as the roughened edges causing further damage.

As a result of this degeneration, repeated friction can cause symptoms of joint pain, stiffness and discomfort. This condition usually affects joints that support full body weight, such as the hips and the knees.

Arthritis can also come about through other causes, including;

 (i) as a result of infection, due to the ease with which blood (and any associated bacteria) can enter the joint cavity via the synovial membrane; 

(ii) due to autoinflammatory causes, as in rheumatoid arthritis, or; 

(iii) as a result of infection but not involving infection of the joint itself, as in reactive arthritis.

Ultrastructure of Muscle Cells

Muscle tissue has a unique histological appearance which enables it to carry out its function. 

There are three main types of muscle:

Skeletal – striated muscle that is under voluntary control from the somatic nervous system.

 Identifying features are cylindrical cells and multiple peripheral nuclei.

Cardiac – striated muscle that is found only in the heart. 

Identifying features are single nuclei and the presence of intercalated discs between the cells.

Smooth – non-striated muscle that is controlled involuntarily by the autonomic nervous system. 

The identifying feature is the presence of one spindle-shaped central nucleus per cell.

In this article, we will look at the histology of skeletal muscle – its composition, histological appearance and clinical correlations.

Composition of Skeletal Muscle

A muscle cell is very specialised for its purpose.

 A single cell forms one muscle fibre, and its cell surface membrane is known as the sarcolemma.

T tubules are unique to muscle cells. These are invaginations of the sarcolemma that conduct charge when the cell is depolarised.

Muscle cells also have a specialised endoplasmic reticulum – this is known as the sarcoplasmic reticulum and contains a large store of calcium ions.

Muscles also have an intricate support structure of connective tissue. Each muscle fibre is surrounded by a thin layer of connective tissue known as endomysium.

 These fibres are then grouped into bundles known as fascicles, which are surrounded by a layer of connective tissue known as perimysium. 

Many fascicles make up a muscle, which in turn is surrounded by a thick layer of connective tissue known as the epimysium.

Ultrastructural Appearance of Skeletal Muscle

The striated appearance of skeletal muscle fibres is due to the organisation of two contractile proteins:

 actin (thin filament) and myosin (thick filament).

The functional unit of contraction in a skeletal muscle fibre is the sarcomere, which runs from Z line to Z line. A sarcomere is broken down into a number of sections:

Z line – where the actin filaments are anchored.

M line – where the myosin filaments are anchored.

I band – contains only actin filaments.

A band – the length of a myosin filament, may contain overlapping actin filaments.

H zone – contains only myosin filaments.

A useful acronym is MHAZI – the M line is inside the H zone which is inside the A band, whilst the Z line is inside the I band.

Fig 1 – A sarcomere is measured from Z line to Z line

Sliding Filament Model

The sliding filament model describes the mechanism of skeletal muscle contraction

Actin and Myosin

Muscle fibres are formed from two contractile proteins – actin and myosin.

Myosin filaments have many heads, which can bind to sites on the actin filament. Actin filaments are associated with two other regulatory proteins, troponin and tropomyosin. 

Tropomyosin is a long protein that runs along the actin filament and blocks the myosin head binding sites.

Troponin is a small protein that binds the tropomyosin to the actin. 

It is made up of three parts:

Troponin I – binds to the actin filament.

Troponin T – binds to tropomyosin.

Excitation-Contraction Coupling

Excitation-Contraction Coupling

The unique structure of troponin is the basis of excitation-contraction coupling:

When depolarisation occurs at a neuromuscular junction, this is conducted down the t-tubules, causing a huge influx of calcium ions into the sarcoplasm from the sarcoplasmic reticulum.

This calcium binds to troponin C, causing a change in conformation that moves tropomyosin away from the myosin head binding sites of the actin filaments.

This allows the myosin head to bind to the actin, forming a cross-link. 

The power stroke then occurs as the myosin heads pivots in a ‘rowing motion’, moving the actin past the myosin towards the M line.

ATP then binds to the myosin head, causing it to uncouple from the actin and allowing the process to repeat.

Hence in contraction, the length of the filaments does not change. However, the length of the sarcomere decreases due to the actin filaments sliding over the myosin. 

The H zone and I band shorten, whilst the A band stays the same length. This brings the Z lines closer together and causes overall length of the sarcomere to decrease.

Hence in contraction, the length of the filaments does not change. However, the length of the sarcomere decreases due to the actin filaments sliding over the myosin. 

The H zone and I band shorten, whilst the A band stays the same length. This brings the Z lines closer together and causes overall length of the sarcomere to decrease.

Fig 2 – The sliding filament model of muscle contraction.

Clinical Relevance – Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is a a recessive X-linked genetic disorder in which dystrophin, a protein which anchors the sarcolemma to the myofilaments, is not produced.

This leads to the muscle fibres tearing themselves apart on contraction, causing progressive muscle weakness and wasting.

It has an early onset, with patients often being wheelchair-dependent by the age of 12.

The lymphatic system

The lymphatic system is a series of vessels and nodes that collect and filter excess tissue fluid (lymph), before returning it to the venous circulation. It forms a vital part of the body’s immune defence

In this article, we shall look at the components of the lymphatic system, their structure and their clinical correlations.

Lymph Organs

There are a number of organs that contain lymphatic tissue. They are involved in blood filtering and the maturation of lymphocytes.

Spleen

– Functions mainly as a blood filter, removing old red blood cells. It also plays a role in the immune response.

Thymus

– Responsible for the development and maturation of T lymphocyte cells.

Red bone marrow – Responsible for maturation of immature lymphocytes, much like the thymus.

In addition, some lymphatic tissue is located in the tonsils, appendix, and in the walls of the gastrointestinal tract.

Lymph Nodes

Lymph nodes are kidney shaped structures which act to filter foreign particles from the blood, and play an important role in the immune response to infection. On average, an adult has around 400 to 450 different lymph nodes spread throughout the body – with the majority located within the abdomen.

Each node contains T lymphocytes, B lymphocytes, and other immune cells. They are exposed to the fluid as it passes through the node, and can mount an immune response if they detect the presence of a pathogen. This immune response often recruits more inflammatory cells into the node – which is why lymph nodes are palpable during infection.

Lymph fluid enters the node through afferent lymphatic channels and leaves the node via efferent channels. Macrophages located within the sinuses of the lymph node act to filter foreign particles out of the fluid as it travels through.

Lymph Vessels

The lymphatic vessels transport lymph fluid around the body. There are two main systems of lymph vessels – superficial and deep:

Superficial vessels – arise in the subcutaneous tissue, and tends to accompany venous flow. They eventually drain into deep vessels.

Deep vessels – drain the deeper structures of the body, such as the internal organs. They tend to accompany deep arteries.

The drainage of lymph begins in lymph channels, which start as blind ended capillaries and gradually develop into vessels. These vessels travel proximally, draining through several lymph nodes.

Eventually the vessels empty into lymphatic trunks (also known as collecting vessels) – and these eventually converge to form the right lymphatic duct and the thoracic duct.

The right lymphatic duct is responsible for draining the lymph from the upper right quadrant of the body. This includes the right side of the head and neck, the right side of the thorax and the right upper limb. The thoracic duct is much larger and drains lymph from the rest of the body. These two ducts then empty into the venous circulation at the subclavian veins, via the right and left venous angles.

Lymph Fluid

Lymph is a transudative fluid that is transparent and yellow. It is formed when fluid leaves the capillary bed in tissues due to hydrostatic pressure. Roughly 10% of blood volume becomes lymph.

The average adult produces between 3-4 litres of lymphatic fluid each day, although this can vary in illness.

Clinical Relevance – Lymphoma

A lymphoma is one of a group of tumours developing from lymphatic cells. They make up around 3-4% of all cancers worldwide and typically have a 5-year survival rate of 70-85%, depending on the subtype. The two main subtypes are Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), with roughly 90% of lymphomas being NHLs. Risk factors for these lymphomas include:

Infection with Epstein-Barr virus (HL)

Autoimmune diseases (NHL)

HIV/AIDs (NHL)

Eating a large amount of meat and fat (NHL)

A diagnosis is reached following a lymph node biopsy, if histological features of lymphoma are found, further tests such as immunophenotyping can be carried out to determine the subtype.

Symptoms of lymphoma often include:

Lymphadenopathy – swelling of lymph nodes

Fever

Night sweats

Weight loss

Loss of appetite

Itching

Fatigue

 شارك معي هذا  البحث المتواضع اقدمة لكم من مدونتي مدونة تعليم اون لاين لنتعلم ونبحث ونشارك افكارنا استقبل اقتراحاتكم عبر البريد الإلكتروني او على ابط حسابي الواتس او فيسبوك

CLASSIFICATION AND DIAGNOSIS OF DIABETES

Classification

Diabetes can be classified into the following general categories

1. Type 1 diabetes (due to autoimmune b cell destruction usually leading to absolute insuln deficiency

including latent autoimmune diabetes of adult hood

 

 

2. Type 2 diabetes (due to a progressive loss of b-cell insulin secretion frequently on the background of insulin resistance)

 

.Specific types of diabetes due to other cause,monogenic diabetes syndromes (such as neonatal di-

abetes and maturity-onset diabetes of the young), diseases of the exocrine pancreas (such as cystic fibrosis and pancreatitis), and drug- or chemical induced diabetes (such as with glucocorticoid use,

in the treatment of HIV/AIDS, or after organ

transplantation)

4.Gestational diabetes mellitus (GDM; diabetes diagnosed in the second or third trimester of pregnancy that was not clearly 

overt diabetes prior to gestation)

 

The classification of diabetes type is not always straight-forward at presentation, and misdiagnosis may occur.  Therefore, constant diligence and sometimes reevalua- 

tion is necessary. Children with type 1diabetes typically

present with polyuria and polydipsia, and approxi-mately half present with diabetic ketoacidosis (DKA).

 

Adults with type

 

1 diabetes can be diagnosed at any age

and may not present with classic symptoms. They may

have temporary remission from the need for insulin.

The diagnosis may become more obvious. over time and should be reevaluated if 

there is concern

Screening and Diagnostic Tests for Prediabetes and Type 2 Diabetes

The diagnostic criteria for diabetes and prediabetes are shown in Table 2.2/2.5. Screening criteria for adults and children are listed in Table 2.3 and Table 2.4, respectively. 

Screening for prediabetes and type 2 diabetes risk through an informal assessment of risk factors

 

Adapted from Tables 2.2 and 2.5 in the complete 2023 Standards of Care. *

 

For all three tests, risk is continuous, extending below the lower limit of the range and becoming disproportionately greater at the higher end of the range.

 

†In the absence of unequivocal hyperglycemia, diagnosis requires two abnormal test results from the same sample or in two separate samples.

 

‡Only diagnostic in a patient with classicsymptoms of hyperglycemia or hyperglycemic crisis.

The nail unit

 The nail unit is a complex structure located on the dorsal surface of the fingers and toes. It has two main functions:

Protection – protects the digits from trauma

Sensation – assists with tactile sensation

In this article, we shall look at the anatomy of the nail unit – its component parts and clinical correlations.

 Adobe Stock, Licensed to TeachMeSeries Ltd

Fig 1 – Anterior view of the nail unit.

Components of the Nail Unit

The nail unit consists of the nail plate and the surrounding soft tissues:

Nail plate – outer portion of the nail unit, formed by layers of keratin. It forms a hard,

yet flexible, translucent plate.

Nail folds – skin that surrounds and protects the proximal and lateral margins of the nail plate

Nail bed (sterile matrix) – lies underneath the nail plate, attaching it to the distal phalanx. The nail bed provides a smooth surface for the growing nail plate to slide over (it does not contribute to plate growth itself).

Germinal matrix – area of soft tissue proximal to the sterile matrix. Cells within the germinal matrix divide and become keratinised to form the nail plate. Continuous cell division within the matrix ‘pushes’ the nail plate over the bed as it matures.

Hyponychium – the area distal to the nail bed, situated underneath the free edge of the nail plate.

Eponychium (cuticle) – layer of stratum corneum which extends between the skin of the finger and proximal nail plate.

Lunula – white ‘half-moon’ appearance of the germinal matrix through the proximal nail plate.

 Adobe Stock, Licensed to TeachMeSeries Ltd

Fig 2 – Lateral view of the nail unit.

Clinical Relevance: Nail Bed Injury

A nail bed injury refers to damage to the soft tissue underneath the nail plate – the nail bed and germinal matrix.

There are two main mechanisms of injury:

Crush – e.g. finger caught in door or direct blow from a hammer

Laceration – e.g. circular saw injury

An x-ray of the affected finger is required to assess for any bony injury (these injuries are often associated with a fracture of the distal phalanx).

In cases where the nail bed is lacerated, surgical repair can be carried out to improve the cosmetic appearance of the new nail growing through. The nail is removed, and the laceration repaired with absorbable sutures.

Following a nail bed repair, it takes approximately 6 months for the new nail to fully grow through and the finger can be sensitive to cold during this time.

المصطلحات التشريحية للحركة

المصطلحات التشريحية للحركة

1. Abduction and Adduction

2. Medial and Lateral Rotation

3. Flexion and Extension

4. Elevation and Depression

5. Pronation and Supination

6. Dorsiflexion and Plantarflexion

7. Inversion and Eversion

8. Opposition and Reposition

9. Circumduction

10. Protraction and Retraction

Anatomical terms of movement are used to describe the actions of muscles upon the skeleton. Muscles contract to produce movement at joints, and the subsequent movements can be precisely described using this terminology

The terms used assume that the body begins in the anatomical position. Most movements have an opposite movement – also known as an antagonistic movement. We have described the terms in antagonistic pairs for ease of understanding

• Flexion and extension are movements that occur in the sagittal plane They refer to increasing and decreasing the angle between two body parts

Flexion refers to a movement that decreases the angle between two body parts. Flexion at the elbow is decreasing the angle between the ulna and the humerus. When the knee flexes, the ankle moves closer to the buttock, and the angle between the femur and tibia gets smaller

Extension refers to a movement that increases the angle between two body parts. Extension at the elbow is increasing the angle between the ulna and the humerus. Extension of the knee straightens the lower limb

Abduction and Adduction

Abduction and adduction are two terms that are used to describe movements towards or away from the midline of the body

Abduction is a movement away from the midline – just as abducting someone is to take them away. For example, abduction of the shoulder raises the arms out to the sides of the body

Adduction is a movement towards the midline. Adduction of the hip squeezes the legs together.

In fingers and toes, the midline used is not the midline of the body, but of the hand and foot respectively. Therefore, abducting the fingers spreads them out

Elevation and Depression

Elevation refers to movement in a superior direction (e.g. shoulder shrug), depression refers to movement in an inferior direction

Pronation and Supination

This is easily confused with medial and lateral rotation, but the difference is subtle. With your hand resting on a table in front of you, and keeping your shoulder and elbow still, turn your hand onto its back, palm up. This is the supine position, and so this movement is supination.

Again, keeping the elbow and shoulder still, flip your hand onto its front, palm down. This is the prone position, and so this movement is named pronation.

These terms also apply to the whole body – when lying flat on the back, the body is supine. When lying flat on the front, the body is prone.

Dorsiflexion and Plantarflexion

Dorsiflexion and plantarflexion are terms used to describe movements at the ankle. They refer to the two surfaces of the foot; the dorsum (superior surface) and the plantar surface (the sole).

Dorsiflexion refers to flexion at the ankle, so that the foot points more superiorly. Dorsiflexion of the hand is a confusing term, and so is rarely used. The dorsum of the hand is the posterior surface, and so movement in that direction is extension. Therefore we can say that dorsiflexion of the wrist is the same as extension.

Plantarflexion refers extension at the ankle, so that the foot points inferiorly. Similarly there is a term for the hand, which is palmarflexion

Inversion and Eversion

Inversion and eversion are movements which occur at the ankle joint, referring to the rotation of the foot around its long axis.

Inversion involves the movement of the sole towards the median plane – so that the sole faces in a medial direction.

Eversion involves the movement of the sole away from the median plane – so that the sole faces in a lateral direction.

Opposition and Reposition

A pair of movements that are limited to humans and some great apes, these terms apply to the additional movements that the hand and thumb can perform in these species.

Opposition brings the thumb and little finger together.

Reposition is a movement that moves the thumb and the little finger away from each other, effectively reversing opposition

Circumduction

Circumduction can be defined as a conical movement of a limb extending from the joint at which the movement is controlled.

It is sometimes talked about as a circular motion, but is more accurately conical due to the ‘cone’ formed by the moving limb.

Protraction and Retraction

Protraction describes the anterolateral movement of the scapula on the thoracic wall that allows the shoulder to move anteriorly. In practice, this is the movement of ‘reaching out’ to something.

Retraction refers to the posteromedial movement of the scapula on the thoracic wall, which causes the shoulder region to move posteriorly i.e. picking something up.

Introduction to Medical Terminology

I. Introduction to Medical Terminology الطبیة للمصطلحات مقدمة

1. Concepts of Medical Terminology الطبیة المصطلحات مفاھیم

2. Prefixes  السوابق

3. Suffixes  اللواحق

4. Combining Forms المؤ

لفة الصیغ

5. Cells, Tissues and Organs  الأعضاء و الأنسجة و الخلایا

6. Body Structure الجسم تركیب

II. Disease and Treatment  العلاج و المرض

7. Disease  المرض

8. Diagnosis and Treatment; Surgery  الجراحة العلاج؛ و التشخیص

9. Drugs  الأدویة

III. Body Systems  الجسم أجھزة

10.The Cardiovascular and Lymphatic Systems  الجھاز و القلب جھاز

اللمفاوي

11. Blood and Immunity  المناعة و الدم

12.The Respiratory System  الجھازالتنفسي

13. The Digestive System  الجھازالھضمي

14. The Urinary System  الجھازالبولي

15.The Male Reproductive System  للذكر الجھازالتناسلي

16.The Female Reproductive System  للأنثى الجھازالتناسلي

17. The Endocrine System  الصماء الغدد جھاز

18. The Nervous System العصبي الجھاز

19. The Senses الحواس

20. The Skeleton  العظمي الھیكل

21. The Muscular System  العضلي الجھاز

22. The Skin  الجلد

ملاحق Appendixes

1. Abbreviations  الإختصارات

2. Symbolsالرموز

3. Specialties and specialists الأخصائیون و التخصص

Classification of Joints

 Classification of Joints

A joint is defined as a connection between two bones in the skeletal system

Joints can be classified by the type of the tissue present (fibrous cartilaginous or synovial), or by the degree of movement permitted (synarthrosis, amphiarthrosis or diarthrosis

In this article, we shall look at the classification of joints in the human body

Fibrous Joints

A fibrous joint is where the bones are bound by a tough, fibrous tissue. These are typically joints that require strength and stability over range of movement.

Fibrous joints can be further sub-classified into sutures,gomphoses and syndesmoses

Sutures

Sutures are immovable joints (synarthrosis), and are only found between the flat, plate-like bones of the skull

There is limited movement until about 20 years of age, after which they become fixed and immobile. They are most important in birth,as at that stage the joints are not fused, allowing deformation of the skull as it passes through the birth canal

Gomphoses

Gomphoses are also immovable joints. They are found where the teeth articulate with their sockets in the maxilla (upper teeth) or the mandible (lower teeth

The tooth is bound into its socket by the strong periodontal ligament

Syndesmoses

Syndesmoses are slightly movable joints (amphiarthroses

They are comprised of bones held together by an interosseous membrane.

 The middle radioulnar joint and middle tibiofibular joint are examples of a syndesmosis joint

Cartilaginous

In a cartilaginous joint, the bones are united by fibrocartilage or hyaline cartilage.

There are two main types: synchondroses (primary cartilaginous) and symphyses (secondary cartilaginous).

Synchondroses

In a synchondrosis, the bones are connected by hyaline cartilage

These joints are immovable (synarthrosis

An example of a synchondrosis is the joint between the diaphysis and epiphysis of a growing long bone

Symphyses

Symphysial joints are where the bones are united by a layer of fibrocartilage. They are slightly movable (amphiarthrosis

Examples include the pubic symphysis, and the joints between vertebral bodies

Synovial

A synovial joint is defined by the presence of a fluid-filled joint cavity contained within a fibrous capsule

They are freely movable (diarthrosis) and are the most common type of joint found in the body

Synovial joints can be sub-classified into several different types,depending on the shape of their articular surfaces and the movements permitted

Hinge – permits movement in one plane – usually flexion and extension

E.g. elbow joint, ankle joint, knee joint

Saddle – named due to its resemblance to a saddle on a horse’s back. It is characterised by opposing articular surfaces with a reciprocal concave-convex shape

E.g. carpometacarpal joints

Plane – the articular surfaces are relatively flat, allowing the bones to glide over one another

E.g. acromioclavicular joint, subtalar joint

Pivot – allows for rotation only. It is formed by a central bony pivot,which is surrounded by a bony-ligamentous ring

E.g. proximal and distal radioulnar joints, atlantoaxial joint

Condyloid – contains a convex surface which articulates with a concave elliptical cavity. They are also known as ellipsoid joints

E.g. wrist joint, metacarpophalangeal joint, metatarsophalangeal joint

Ball and Socket – where the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. It permits free movement in numerous axes

E.g. hip joint, shoulder joint

لتحميل المقالة السابقة كتاب الكتروني مترجماضغط هنا

Anatomical Terms of Location

Anatomical Terms of Location

المحاضرة اربعة

The anatomical terms of location are vital to understanding and

using anatomy. They help to avoid any ambiguity that can arise

when describing the location of structures

المصطلحات التشريحية للموقع حيوية لفهم واستخدام التشريح. فهي تساعد على

تجنب أي غموض يمكن أن ينشأ عند وصف موقع الهياكل.

In this article, we shall look at the basic anatomical terms of

location, and examples of their use within anatomy

Note: There are some anatomical terms that are specifically used

in embryology

في هذه المقالة ، سننظر إلى المصطلحات التشريحية الأساسية للموقع ، وأمثلة على

استخدامها داخل التشريح.

ملاحظة: هناك بعض المصطلحات التشريحية التي تستخدم على وجه التحديد في علم

الأجنة

Medial and Lateral

Imagine a line in the sagittal plane, splitting the right and left

halves evenly. This is the midline. Medial means towards the

midline, lateral means away from the midline

الوسيط والجانبي

تخيل خطًا في المستوى السهمي ، وتقسيم النصف الأيمن والأيسر بالتساوي. هذا هو

خط الوسط. الوسيط يعني نحو خط الوسط ، الجانبي يعني بعيدا عن خط الوسط.

Examples

.The eye is lateral to the nose

.The nose is medial to the ears

The brachial artery lies medial to the biceps tendon

أمثلة:

العين جانبية للأنف.

الأنف هو الوسيط للأذنين.

يكمن الشريان العضدي في الوسط إلى وتر العضلة ذات الرأسين

Anterior and Posterior

Anterior refers to the front and posterior refers to the back Putting

this in context, the heart is posterior to the sternum because it lies

behind it. Equally, the sternum is anterior to the heart because it

lies in front of it 

الأمامي والخلفي

يشير الأمامي إلى الأمام والخلف يشير إلى الخلف وضع هذا في السياق ، و

القلب هو الخلفي من القص لأنه يكمن وراء ذلك. وبالمثل ، فإن القص هو

أمام القلب لأنه يكمن أمامه

Examples

.Pectoralis major lies anterior to pectoralis minor

The triceps are posterior to biceps brachii

The patella is located anteriorly in the lower limb

Pectoralis الرئيسية يكمن أمام pectoralis طفيفة.

العضلة ثلاثية الرؤوس هي الخلفية إلى العضلة ذات الرأسين brachii.

تقع الرضفة في الطرف السفلي

Superior and Inferior

These terms refer to the vertical axis. Superior means higher

inferior means lower. The head is superior to the neck; the

umbilicus is inferior to the sternum

Here we run into a small complication, and limbs are very mobile

and what is superior in one position is inferior in anothe

Therefore, in addition to the superior and inferior, we need another

descriptive pair of terms

فوق وأقل

تشير هذه المصطلحات إلى المحور الرأسي. متفوقة يعني أعلى

أدنى يعني أقل. الرأس أعلى من الرقبة ؛ سرة البطن أقل شأنا من عظمة

القص

هنا نواجه تعقيدًا صغيرًا ، والأطراف متنقلة جدًا

وما هو متفوقة في موقف واحد هو أدنى في اخر

لذلك ، بالإضافة إلى اعلى وأقل شأنا ، ونحن بحاجة إلى زوج وصفي آخر

من المصطلحات

Examples

.The nose is superior to the mouth

.The lungs are superior to the liver

The appendix is (usually) inferior to the transverse colon

الأنف أعلى من الفم.

الرئتين اعلى من الكبد.

التذييل (عادة) أدنى من القولون المستعرض

Proximal and Distal

The terms proximal and distal are used in structures that

are considered to have a beginning and an end (such as

the upper limb, lower limb and blood vessels). They

describe the position of a structure with reference to its

origin – proximal means closer to its origin, distal means

.further away

قريب وبعيد

يتم استخدام المصطلحات القريبة والبعيدة في الهياكل التي تعتبر أن لها

بداية ونهاية (مثل الطرف العلوي والأطراف السفلية والأوعية الدموية). أنها

تصف موقف هيكل مع الإشارة إلى أصله-قريب يعني أقرب إلى أصله ،

البعيدة يعني أبعد من ذلك

:Examples

.The wrist joint is distal to the elbow joint

.The scaphoid lies in the proximal row of carpal bones

The knee joint is proximal to the ankle joint

أمثلة:

مفصل المعصم بعيد عن مفصل الكوع.

يقع scaphoid في الصف القريب من عظام الرسغ.

مفصل الركبة قريب من مفصل الكاحل

لتحميل المقالة السابقة كتاب الكتروني اضغط على الرابط ادناهتنزيل الكتاب

Anatomical Planes

الطائرة هي شريحة 2D من خلال مساحة 3D ، والتي يمكن اعتبارها ورقة زجاجية. الطائرات التشريحية هي خطوط مختلفة تستخدم لتقسيم جسم الإنسان. سوف تراهم عادة عند النظر إلى النماذج التشريحية والأقسام. استخدام الطائرات التشريحية يسمح لوصف دقيق للموقع ، ويسمح أيضا للقارئ لفهم ما هو الرسم البياني أو. الصورة تحاول أن تظهر
هناك ثلاث مستويات شائعة الاستخدام ؛ .sagittal و coronal و transverse
المستوى السهمي - خط عمودي يقسم الجسم إلى قسم يسار وقسم يمين
الطائرة الإكليلية - خط عمودي يقسم الجسم إلى الجزء الأمامي (الأمامي) والجزء الخلفي (الخلفي
طائرة عرضية - خط أفقي يقسم الجسم إلى الجزء العلوي (المتفوق). وقسم (أدنى
على سبيل المثال ، يمكن تسمية الرسم البياني على أنه قسم عرضي ، ينظر إليه بشكل ممتاز. يشير هذا إلى أنك تنظر إلى الأسفل إلى قسم أفقي من الجسم

A plane is a 2D slice through 3D space, which can be thought of as a glass sheet. The anatomical planes are different lines used to divide the human body. You will commonly see them when looking at anatomical models and prosections. Using anatomical planes allows for accurate description of a location, and also allows the reader to understand what a diagram or picture is trying to show.

There are three planes commonly used; sagittal, coronal and transverse.

Sagittal plane – a vertical line which divides the body into a left section and a right section.

Coronal plane – a vertical line which divides the body into a front (anterior) section and back (posterior) section.

Transverse plane – a horizontal line which divides the body into an upper (superior) section and a lower (inferior) section.

For example, a diagram may be labelled as a transverse section, viewed superiorly. This indicates that you are looking downwards onto a horizontal section of the body.