2022

MASWA DISTRICT HOSPITAL

The scalp extends from the external occipital protuberance and superior nuchal lines to the supraorbital margins.

The scalp consists of 5 layers

Skin,

Connective tissue,

Epicranial Aponeurosis,

Loose areolar tissue, and

Pericranium.

The first 3 layers are bound together as a single unit.

This single unit can move along the loose areolar tissue over the pericranium, which is adherent to the calvaria.

The skin of the scalp is thick and hair bearing and contains numerous sebaceous glands.

As a result, the scalp is a common site for sebaceous cysts.

CONNECTIVE TISSUE (SUPERFICIAL FASCIA)

The superficial fascia is a fibrofatty layer that connects skin to the underlying aponeurosis of the occipitofrontalis muscle and provides a passageway for nerves and blood vessels.

Blood vessels are attached to this fibrous connective tissue.

The epicranial aponeurosis is a thin, tendinous structure that provides an insertion site for the occipitofrontalis muscle.

Posterolaterally, the epicranial aponeurosis attachment extends from the superior nuchal line to the superior temporal line.

Laterally, the epicranial aponeurosis continues as the temporal fascia.

Anteriorly, the subaponeurotic space extends to the upper eyelids due to the lack of a bony insertion.

This loose areolar tissue provides a potential subaponeurotic space that allows fluids and blood to pass from the scalp to the upper eyelids.

Areolar tissue loosely connects the epicranial aponeurosis to the pericranium and allows the superficial 3 layers of the scalp to move over the pericranium.

Scalp flaps are elevated along a relatively avascular plane in craniofacial and neurosurgical procedures.

However, certain emissary veins traverse this layer, which connects the scalp veins to the diploic veins and intracranial venous sinuses.

The pericranium is the periosteum of the skull bones.

Along the suture lines, the pericranium becomes continuous with the endosteum.

A subperiosteal hematoma, therefore, forms in the shape of the skull bones.

The occipitofrontalis muscle consists of 2 occipital bellies and 2 frontal bellies.

The occipital bellies arise from the superior nuchal lines on the occipital bone.

The frontal bellies originate from the skin and superficial fascia of the upper eyelids.

The occipital and frontal bellies insert into the epicranial aponeurosis.

Each occipital belly is innervated by the posterior auricular branch of the facial nerve, and each frontal belly is innervated by the frontal branch of the facial nerve.

The frontal bellies can raise the eyebrows.

Sensory supply

The following 6 sensory nerve branches of either the trigeminal nerve or the cervical nerve supply the scalp

Supratrochlear nerve – A branch of the ophthalmic division of the trigeminal nerve; this nerve supplies the scalp in the medial plane at the frontal region, up to the vertex

Supraorbital nerve – Also a branch of the ophthalmic division of the trigeminal nerve; this nerve supplies the scalp at the front, lateral to the supratrochlear nerve distribution, up to the vertex

Zygomaticotemporal nerve – A branch of the maxillary division of the trigeminal nerve; it supplies the scalp over the temple region

Auriculotemporal nerve – A branch of the mandibular division of the trigeminal nerve; it supplies the skin over the temporal region of the scalp

Lesser occipital nerve – A branch of the cervical plexus (C2); it supplies the scalp over the lateral occipital region

Greater occipital nerve – A branch of the posterior ramus of the second cervical nerve; it supplies the scalp in the median plane at the occipital region, up to the vertex

The frontal branch of the facial nerve supplies the frontal bellies of the occipitofrontalis muscle, and the auricular branch of the facial nerve supplies the occipital bellies of the muscle

The normal anatomy of the cervical spine consists of 7 cervical vertebrae separated by intervertebral disks and joined by a complex network of ligaments.

These ligaments keep individual bony elements behaving as a single unit

The first two cervical vertebrae, the atlas and the axis, are atypical.

The first cervical vertebra, the atlas, is the bone on which the skull rests. Below the atlas is the axis, the second cervical vertebra (C2).

The atlas articulates superiorly with the occiput (the atlanto-occipital joint) and inferiorly with the axis (the atlantoaxial joint).

The atlantoaxial joint is responsible for 50% of all cervical rotation

The atlanto-occipital joint is responsible for 50% of flexion and extension.

The atlas is essentially a ring of bone, with no distinct body or spinous process, although it has two short transverse processes.

It possesses two flattened facets that articulate with the occipital bone; these are condyloid joints and they permit nodding of the head.

The axis sits below the atlas, and has a small body with a small superior projection called the odontoid process

The 7th cervical vertebra, C7, is also known as the vertebra prominens.

It possesses a long spinous prominence terminating in a swollen tubercle, which is easily felt at the base of the neck.

Provides a strong bony protection for the delicate spinal cord lying within it.

The pedicles of adjacent vertebrae form intervertebral foramina, one on each side, providing access to the spinal cord for spinal nerves, blood vessels and lymph vessels.

The numerous individual bones with their intervertebral discs allow movement of the whole column.

It supports the skull.

The intervertebral discs act as shock absorbers, protecting the brain.

It forms the axis of the trunk, giving attachment to the ribs, shoulder girdle and upper limbs, and the pelvic girdle and lower limbs.

The paired arteries supplying the head and neck are the common carotid arteries and the vertebral arteries

Carotid arteries

The right common carotid artery is a branch of the brachiocephalic artery.

The left common carotid artery arises directly from the arch of the aorta.

They pass upwards on either side of the neck and have the same distribution on each side.

The common carotid arteries are embedded in fascia, called the carotid sheath.

At the level of the upper border of the thyroid cartilage each divides into an internal carotid artery and an external carotid artery.

This artery supplies the superficial tissues of the head and neck, via a number of branches:

The superior thyroid artery supplies the thyroid gland and adjacent muscles.

The lingual artery supplies the tongue, the lining membrane of the mouth, the structures in the floor of the mouth, the tonsil and the epiglottis.

The facial artery passes outwards over the mandible just in front of the angle of the jaw and supplies the muscles of facial expression and structures in the mouth.

The occipital artery supplies the posterior part of the scalp.

The temporal artery passes upwards over the zygomatic process in front of the ear and supplies the frontal, temporal and parietal parts of the scalp.

The maxillary artery supplies the muscles of mastication and a branch of this artery, the middle meningeal artery, runs deeply to supply structures in the interior of the skull.

This is a major contributor to the circulus arteriosus (circle of Willis) which supplies the greater part of the brain.

It also has branches that supply the eyes, forehead and nose.

It ascends to the base of the skull and passes through the carotid foramen in the temporal bone.

The greater part of the brain is supplied with arterial blood by an arrangement of arteries called the circulus arteriosus or the circle of Willis.

Four large arteries contribute to its formation: the two internal carotid arteries and the two vertebral arteries

Anteriorly, the two anterior cerebral arteries arise from the internal carotid arteries and are joined by the anterior communicating artery.

Posteriorly, the two vertebral arteries join to form the basilar artery. After travelling for a short distance the basilar artery divides to form two posterior cerebral arteries, each of which is joined to the corresponding internal carotid artery by a posterior communicating artery, completing the circle.

The circulus arteriosus is therefore formed by

2 anterior cerebral arteries

2 internal carotid arteries

1 anterior communicating artery

2 posterior communicating arteries

2 posterior cerebral arteries

1 basilar artery.

The venous blood from the head and neck is returned by deep and superficial veins.

Superficial veins with the same names as the branches of the external carotid artery return venous blood from the superficial structures of the face and scalp and unite to form the external jugular vein

The external jugular vein begins in the neck at the level of the angle of the jaw.

It passes downwards in front of the sternocleidomastoid muscle, then behind the clavicle before entering the subclavian vein.

The superior sagittal sinus carries the venous blood from the superior part of the brain.

It begins in the frontal region and passes directly backwards in the midline of the skull to the occipital region where it turns to the right side and continues as the right transverse sinus.

The inferior sagittal sinus lies deep within the brain and passes backwards to form the straight sinus.

The straight sinus runs backwards and downwards to become the left transverse sinus.

The transverse sinuses begin in the occipital region. They run forward and medially in a curved groove of the skull, to become continuous with the sigmoid sinuses.

The sigmoid sinuses are a continuation of the transverse sinuses.

Anteriorly only a thin plate of bone separates the sinus from the air cells in the mastoid process of the temporal bone.

Inferiorly it continues as the internal jugular vein.

The internal jugular veins begin at the jugular foramina in the middle cranial fossa and each is the continuation of a sigmoid sinus.

They run downwards in the neck behind the sternocleidomastoid muscles.

Behind the clavicle they unite with the subclavian veins, carrying blood from the upper limbs, to form the brachiocephalic veins.

The brachiocephalic veins are situated one on each side in the root of the neck.

Each is formed by the union of the internal jugular and the subclavian veins.

The left brachiocephalic vein is longer than the right and passes obliquely behind the manubrium of the sternum, where it joins the right brachiocephalic vein to form the superior vena cava

In addition to the complex vascular network, the head and neck have an equally vast nervous supply.

The main nerves of those regions originate from two main sources

Cranial nerves

Cervical plexus

There are twelve cranial nerves in total: olfactory, optic, oculomotor, trochlear, trigeminal, abducent, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves.

The first two originate from the anterior part of the brain, while the remaining ten come from the brainstem.

The cervical plexus is formed by the C1 to C5 spinal nerves, giving off sensory and motor branches to the head and neck:

Sensory branches: lesser occipital, greater auricular, transverse cervical, supraclavicular

Motor branches: ansa cervicalis, phrenic nerve, nerve to rhomboids, nerve to serratus anterior

Sensory nerve.

Sense of smell.

Olfactory cells converge to become olfactory nerve.

Sensory nerve.

Ganglion cells in the retina of each eye join to form an optic nerve.

Nerve of vision.

Motor cranial nerve.

Originates in the midbrain.

Supply extrinsic eye muscles to control movements of the eyeball and upper eyelid.

Motor cranial nerve.

Smallest of the 12 cranial nerves.

Origin: midbrain.

Controls movement of the eyeball.

Largest cranial nerve.

Mixed nerve.

Three branches: opthalmic, maxillary and mandibular.

Deal with sensation of touch, pain and temperature.

Motor axons supply muscles of mastication.

Motor cranial nerve.

Originates from the pons.

Cause abduction of the eyeball (lateral rotation).

Mixed cranial nerve.

Sensory portion extends from the taste buds of the anterior two-thirds of the tongue.

Motor portion arises from the pons and deal with facial expression.

Sensory cranial nerve.

Originates in the inner ear.

Vestibular branch carries impulses for equilibrium.

Cochlear branch carries impulses for hearing.

Mixed cranial nerve.

Sensory axons carry signals from the taste buds of the posterior one-third of the tongue.

Motor neurons arise from the medulla and deal with the release of saliva.

Mixed cranial nerve.

Distributed from the head and neck into the thorax and abdomen.

Sensory neurons deal with a variety of sensations such as proprioception, and stretching.

Motor neurons arise from the medulla and supply muscles of the pharynx, larynx, and soft palate that are involved in swallowing and vocalization.

Motor cranial nerve.

Divided into cranial accessory and spinal accessory nerves.

Supplies sternocleidomastoid and trapezius muscles to coordinate head movements.

Motor cranial nerve.

Conduct nerve impulses for speech and swallowing.

There are several clusters, or aggregations, of lymph nodes in the neck and head.

They are important in draining lymph and for the proper functioning of the immune system.

In the head, the lymph nodes are organized into groups

Fascial group

Submandibular group

Parotid group

Submental group

Sublingual group

Mastoid group

Occipital group

The lymph nodes of the neck are also clustered together. However, rather than being organized in groups, they form three major chains:

Upper horizontal chain

Lateral cervical group: superficial group, deep group

Anterior cervical chain

Similar to the head, each set drains the neighbouring structures.

The brain and spinal cord are completely covered by three membranes, the meninges lying between the skull and the brain, and between vertebrae and the spinal cord.

These are

Dura mater

Arachnoid mater

Pia mater

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The arachnoid and pia mater are separated by the subarachnoid space, containing cerebrospinal fluid.

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The cerebral dura mater consists of two layers of dense fibrous tissue.

The outer layer takes the place of the periosteum on the inner surface of the skull bones, and the inner layer provides a protective covering for the brain.

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The dura mater forms several structures that separate the cranial cavity into compartments and protect the brain from displacement.

These are

The falx cerebri separates the hemispheres of the cerebrum

The falx cerebelli separates the lobes of the cerebellum

The tentorium cerebelli separates the cerebrum from the cerebellum

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The superior sagittal sinus that runs across the top of the brain is formed by falx cerebri and the tentorium cerebelli forms the straight and transverse sinuses.

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If there is hemorrhage in the brain, blood may collect here.

The subdural space is another potential space that may exist between the dura mater and the middle layer of the meninges, the arachnoid mater.

When bleeding occurs in the cranium, blood may collect here and push down on the lower layers of the meninges.

If bleeding continues, brain damage will result from this pressure.

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This is an extension of the inner layer of the cerebral dura mater and is separated from the vertebrae and ligaments within the neural canal by the epidural or extradural space.

Dyes, used for diagnostic purposes, and local anaesthetic or analgesic to relieve pain may be injected in the epidural space.

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The arachnoid or arachnoid mater is the middle layer of the meninges.

In some areas, it projects into the sinuses formed by the dura mater.

These projections are the arachnoid granulation or arachnoid villi.

They transfer cerebrospinal fluid from the ventricles back into the bloodstream.

The subarachnoid space lies between the arachnoid and pia mater.

It is filled with cerebrospinal fluid.

All blood vessels entering the brain, as well as cranial nerves pass through this space.

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This is a fine connective tissue containing many minute blood vessels.

It adheres to the brain, completely covering the convolutions and dipping into each fissure.

It continues downward covering the spinal cord.

Beyond the end of the cord it continues as the filum terminale, pierces the arachnoid tube and goes on, with the dura mater, to fuse with the Periosteum of the coccyx.

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The cerebrum is divided by a deep cleft, the longitudinal cerebral fissure, into right and left cerebral hemispheres.

Deep within the brain the hemispheres are connected by a mass of white matter (nerve fibres) called the corpus callosum.

The falx cerebri is formed by the dura mater.

It separates the two hemispheres and penetrates to the depth of the corpus callosum.

The superficial (peripheral) part of the cerebrum is composed of nerve cell bodies or grey matter, forming the cerebral cortex, and the deeper layers consist of nerve fibres or white matter.

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The exposed areas of the folds are the gyri or convolutions.

These are separated by sulci or fissures.

These gyri or convolutions greatly increase the surface area of cerebrum.

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The superficial area of the cerebral cortex is composed of grey mater (nerve cell bodies).

While the inner layer is formed by white matter (nerve fibres or tracts).

Within the cerebrum the lobes are connected by masses of nerve fibres or tracts which make up the white matter of the brain.

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These include

Projection fibres (internal capsule)

Commissural fibres (e.g. corpus callosum)

Association (arcuate) fibres

Internal capsule (projection fibres) connects the cerebral cortex with grey matter of lower parts of the brain and with spinal cord, e.g. the internal capsule.

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Association fibres connect different parts of a cerebral hemisphere by extending from one gyrus to another, some of which are adjacent and others distant.

Commissural fibres connect corresponding areas of the two cerebral hemispheres; the largest and important commissure is the corpus callosum.

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These are the central, lateral and parieto-occipital sulci

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The entire blood supply of the brain and spinal cord depends on two sets of branches from the aorta.

The vertebral arteries arise from the subclavian arteries, and

The internal carotid arteries are branches of the common carotid arteries.

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The posterior cerebral arteries arise at this confluence

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Conjoining the two major sources of cerebral vascular supply via the circle of Willis presumably improves the chances of any region of the brain continuing to receive blood if one of the major arteries becomes occluded.

The major branches that arise from the internal carotid artery, the anterior and middle cerebral arteries, form the anterior circulation that supplies the forebrain.

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Each gives rise to branches that supply the cortex and branches that penetrate the basal surface of the brain, supplying deep structures such as the basal ganglia, thalamus, and internal capsule.

The posterior circulation of the brain supplies the posterior cortex, the midbrain, and the brainstem; it comprises arterial branches arising from the posterior cerebral, basilar, and vertebral arteries.

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The Precentral (Motor) Area

This lies in the frontal lobe immediately anterior to the central sulcus.

The cell bodies are pyramidal shaped (Betz’s cells) and they initiate the contraction of skeletal muscles.

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This lies in the frontal lobe immediately anterior to the motor area.

The cells are thought to exert a controlling influence over the motor area, ensuring an orderly series of movements.

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In the lowest part of premotor area just above the lateral sulcus there is a group of nerve cells known as the motor speech (Broca’s) area which controls the movements necessary for speech.

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This extends anteriorly from the premotor area to include the remainder of the frontal lobe.

It is associated with reasoning, planning, emotions, behavior and problem solving.

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Post central (sensory) area: this is the area behind the central sulcus.

Here sensations for pain, temperature, pressure and touch, knowledge of muscular movement and position of joints are perceived.

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This lies behind the post central and includes the greater part of the parietal lobe of the cerebrum.

Its function is associated with obtaining and retaining accurate knowledge of objects.

The object can be recognized by touch alone because of the knowledge from the past experience (memory) retained in this area.

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This is situated in the lower part of the parietal lobe and extends into the temporal lobe.

Spoken words are perceived here

Auditory Area

This receives and interprets impulses transmitted from the inner ear by the cochlear, auditory part of the 8th cranial nerve

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This lies behind the parietal-occipital sulcus and includes the greater part of the occipital lobe.

The optic nerves pass from the eye to this area which receives and interprets as visual impressions.

Olfactory (Smell) Area

This lies deep within the temporal lobe where impulses from the nose via the olfactory nerves (1st cranial nerves) are received and interpreted.

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This is the area where impulses from special nerve endings in the taste buds in the tongue are perceived as a taste.

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Two masses below the corpus callosum.

Sensory input from the skin, viscera and special sense organs is transmitted to the thalamus before redistribution to the cerebrum.

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It has connections to the cerebral cortex and thalamus.

It forms part of the extrapyramidal tracts and are thought to be involved in initiating muscle tone in slow and coordinated activities.

If control is inadequate or absent, movement are jerky, clumsy and uncoordinated.

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It is composed a number of groups of nerve cells.

It is linked to the posterior lobe of the pituitary gland by nerve fibres and to the anterior lobe by a complex system of blood vessels.

Through these connections, the hypothalamus controls the output of hormones from both lobes of the gland.

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It occupies posterior cranial fossa.

It has two hemispheres separated by a narrow strip called vermix.

It is concerned with the coordination of voluntary movement, posture and balance.

Impulses from the cerebellum influence the contraction of skeletal muscle so that balance and posture are maintained.

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This is formed by

Midbrain,

Pons and

Medulla oblongata

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This consists of groups of cell bodies and nerve fibres (tracts) which connect the cerebrum with the lower parts of the brain and with the spinal cord.

The cell bodies act as relay stations for the ascending and descending nerve fibres.

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It consists mainly of nerve fibres which form a bridge between the two cerebella hemispheres and fibres passing between the higher levels of the brain and spinal cord.

There are groups of cells within the pons which act as relay stations and some of these are associated with cranial nerves.

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It is the outer aspect is composed of white matter, and centrally the grey matter.

In its deeper structure lie vital centres

Cardiac centre

Respiratory centre

Vasomotor centre

Reflex centres of vomiting, coughing, sneezing and swallowing

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Decussation of the pyramids

Motor nerves from the cerebral cortex to the spinal cord cross from one side the other, so that the left hemisphere of the cerebrum controls the right half of the body.

Sensory decussating

Also occurs at the medulla, although some sensory nerves cross over at lower levels of the spinal cord.

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Ventricles of the Brain

Within the brain there are four irregular shaped cavities containing cerebrospinal fluid.

They are called ventricles, these are

Right and left lateral ventricles

The midline third ventricle and fourth ventricle

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These cavities lie within the cerebral hemispheres, one on each side of the median plane just below the corpus callosum.

They are separated from each other by a thin membrane, the septum lucidium, and are lined by ciliated epithelium.

They open into the 3rd ventricle through the interventricular foramina (of monro).

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It is a cavity situated below the lateral ventricles between the two parts of the thalamus.

It is a slit-like cavity between the right and the left halves of the diencephalon are continuous with the cerebral aqueduct a narrow channel in the midbrain connecting the 3rd and 4th ventricles.

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It is situated below and behind the third ventricle, between the cerebellum and pons.

It communicates with the subarachnoid space by 3 foramina in its roof, and continuous below with central canal of the spinal cord.

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CSF drains from the 4th ventricle through a single median aperture and paired lateral apertures into the subarachnoid space.

These apertures are the only means by which CSF enters the subarachnoid space.

If they are blocked, the ventricles distend, producing compression of the cerebral hemispheres.

At certain areas, mainly at the base of the brain, the arachnoid and pia mater are widely separated by large pools (cisterns) of CSF.

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Cerebellomedullary cistern, the largest of the cisterns, located between the cerebellum and the medulla

Pontocerebellar cistern (pontine cistern), an extensive space ventral to the pons and continuous inferiorly with the spinal subarachnoid space.

Interpeduncular cistern (basal cistern), located between the cerebral peduncles of the midbrain.

Chiasmatic cistern, inferior and anterior to the optic chiasm.

Quadrigeminal cistern (cistern of the great cerebral vein), located between the posterior part of the corpus callosum and the superior surface of the cerebellum.

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CSF is a clear liquid produced within spaces in the brain called ventricles.

It is also found inside the subarachnoid space of the meninges which surrounds both the brain and the spinal chord.

In addition, a space inside the spinal chord called the central canal also contains CSF

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CSF is formed by choroidal epithelial cells of the choroid plexuses in the lateral, 3rd, and 4th ventricles.

CSF is secreted continuously at a rate of 0.5mL per minute, 720mls per day.

The amount around the brain and spinal cord remains fairly constant at about 120mls, which means that absorption keeps pace with secretion.

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It consists of

Water

Mineral salts

Glucose

Plasma proteins: small amount of albumin and globulin

Small amount of creatinine, urea

A few leukocytes

It is slightly alkaline

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It circulates through the system in a specific pattern, moving from the lateral ventricle to the third, and then from the third to the fourth.

From the fourth ventricle, the CSF passes into the subarachnoid space where it circulates around the outside of the brain and spinal cord and to the superior sagittal sinus via the arachnoid granulations also called arachnoid villi.

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The main site of CSF absorption into the venous system is through the arachnoid granulations, protrusions of arachnoid villi into the walls of dural venous sinuses, especially the superior sagittal sinus and its lateral venous lacunae.

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CSF from the lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space or central canal.

CSF is reabsorbed into the blood by arachnoid villi.

CSF protects the brain by providing a cushion against blows to the head.

The CSF provides the buoyancy that prevents the weight of the brain from compressing the cranial nerve roots and blood vessels against the internal surface of the cranium.

Brings nutrients to the brain and spinal cord at the same time keeping them moist

Removes waste from the system

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NAME OF FORAMEN

FROM

TO

Right and left interventricular

foramina (Monro)

Lateral ventricles

Third ventricle

Cerebral aqueduct (Sylvius)

Third ventricle

Fourth ventricle

Median aperture (Magendie)

Fourth ventricle

Subarachnoid space/cisterna magna

Right and left Lateral aperture

(Luschka)

Fourth ventricle

Subarachnoid space/cistern of great cerebral vein

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