Overview The nervous system is the control and communication system of the body. Its job is to

send messages to and receive messages from various parts of the body . It is divided anatomically into two parts: Central Nervous system- Brain & Spinal Cord (the control center) Peripheral Nervous System- consists of the nerves and ganglia outside of the CNS and

functions in the capacity of a viaduct between organs and limbs of the body and the CNS.

The tools of trade for the peripheral nervous system are 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Cranial nerves, so called because they exit the skull via the cranium are components of the peripheral nervous system that originate in the brain.

They innervate body parts and organs of the body with sensory (afferent) or motor (efferent) neurons or both.

Ref O1

Overview Cont’d When stimulated nerve fibers transmit impulses to the

brain to be interpreted and relay responses back to the effector organs.

In the brain these fibers are seen as white matter.

White matter therefore is a general term referring to large axon tracts in the brain and spinal cord i.e. axons entering the cortex of the cerebral hemisphere, the cerebellum and the hippocampus, as well as those leaving it, form white matter.

Ref O2

White Matter of the Brain ( Ref O3.)

White matter The neuronal tracts of white matter are grouped according to

their directional course. Association tracts (fibers)- connect fibers of different

regions in cerebral cortex e.g. superior and inferior longitudinal fibers

Commissure fibers- connect fibers from the

R to L hemisphere e.g. corpus collusum

Projection tracts (fibers)- connects the cerebral cortex to

other masses of gray matter e.g. ‘Internal capsule’ Ref O4

Internal Capsule The internal capsule if described in terms of finance is one pricey

piece of brain real estate!

It separates the caudate nucleus and the thalamus from the lenticular nucleus and contains both ascending and descending axons.

It contains all of the pathways that allow information to be transferred between the cerebral cortex and the spinal cord, brainstem, and subcortical structures (i.e. thalamus, basal ganglia).

It’s subdivisions are the anterior limb, posterior limb, and the genu

(i.e. the area where the anterior and posterior limbs meet).

Ref O2

Location of Internal Nucleus Ref O3

Internal capsule Thalamus

Lentiform nucleus

Caudate nucleus

Passage

Of Neurons

Through

Internal

Capsule

Ref O3.

Fibers of The capsule

Anterior Limb The anterior limb of the internal capsule contains:

1) Frontopontine fibers project from frontal cortex to pons;

2) thalamocortical fibers connect the medial and anterior nuclei of the thalamus to the frontal lobes.

Genu1)Part of superior thalamic radiation

2)Frontopontine

3)Corticonuclear

Posterior Limb

1)Superior thalamic radiation2)Frontopontine3)Corticonuclear (corticobulbar)4)Corticospinal5)Extrapyrimidal

Ref O4

Fibers of the Capsule

Retrolenticular The retrolenticular segment contains fibers from the optic

system, coming from the lateral geniculate nucleus of the thalamus.

More posteriorly, it becomes the optic radiation

Sublentiform

The sublenticular part contains fibers connecting with the temporal lobe which includes auditory radiations and temporopontine fibers.

Ref O4

Connections to internal Capsule

Corticonuclear fibers- connects cerebral cortex to the brainstem

Corticopontine fibers- connections from the cortex to the pontine nuclei. Motor centers from the gyrus to the nuclei of CN V, V11 & X11

Thalamocortical fibers connects cortex and thalamus . These are concerned with sensory information

Ref O4

Brain

M.G.B. L.G.B. V.P.L. V.P.M. V.A/V.L.

( Ref O4)

Thalamus

Ref 4. Netter Atlas

Origins of Cranial Nerves Ref O3

Note:

While CNI and CNII are direct emergence of the brain (cerebrum) all other Cranial Nerves have their origins on the Brain stem

Olfactory Nerve - CN1Foramen: Cribriform Plate (Ethmoid bone)

Fiber Type: special sensory

Function: Smell

Branches: olfactory filaments

Embryo: CNS ectoderm

Ref 4.

Anatomy of the Nose It is a prominent structure between the eyes that serves as the

entrance to the respiratory tract and contains the olfactory organ.

It provides air for respiration, serves the sense of smell, conditions the air by filtering, warming, and moistening it, and cleans itself of foreign debris extracted from inhalations.

The nose has two cavities, separated by a piece of cartilage called the septum.

The external openings are known as nares or nostrils. The roof of the mouth and the floor of the nose are formed by the palatine bone.

Ref A-1

Anatomy Cont’d The forward section, within and above each nostril, is

called the vestibule.

Behind the vestibule and along each outer wall are three elevations, nasal concha or turbinate.

The olfactory system lies in the uppermost concha of the nasal cavity

Ref A-1

Nasal Cavity

Nasal Fossae

Contains three conchae, Superior, Middle and Inferior conchae.

The middle and inferior projections are covered with respiratory epithelium.

The superior conchae are covered with a specialized olfactory epithelium.

Respiratory Epithelium - ciliated pseudostratified columnar epithelium that contains a rich population of goblet cells. Typical respiratory epithelium consists of five cell types.

Psuedostratified Columnar cellsmucous goblet cellsbrush cellsBasal (short) cells small granule cell

Distribution of Olfactory Epithelium Ref P-6

Olfactory MembraneThe receptors for the sense of smell are located in a modified form of respiratory epithelium called olfactory epithelium in the nasal cavity.

Olfactory epithelium is very tall, pseudostratified columnar in form and contains cells of three types: olfactory receptor cells, supporting epithelial (sustentacular) cells and basal epithelial cells.

Characteristics of Olfactory Epithelium

Olfactory Cells – Bipolar NeuronsA single dendritic process extends from the cell body to the free surface where it terminates as a small swelling, the olfactory knob, which gives rise to about a dozen extremely long modified cilia. The cilia are the sites of interaction between odiferous substances and the receptor cells.

Sustentacular Cells – are elongated with their tapered bases resting on the basement membrane. Many long microvilli extend from their luminal surfaces to form a tangled mat with the cilia of the receptor cells.

Basal Cells – are small, conical cells which appear to be stem cells for both olfactory and sustentacular cells.

Ref – P-1.

Additionally there are supporting loose vascular tissue, afferent nerve fibers and numerous serous glands called Bowman's glands.

Olfactory System

The olfactory system consists of the olfactory epithelium, bulbs and tracts along with olfactory areas of the brain collectively known as the rhinencephalon.

Ref P-6

Mechanism of Excitation of the Olfactory CellsInhaled aromatic molecules dissolve in the moisture lining the olfactory epithelium and stimulate its chemoreceptors. An action potential is then initiated and impulses transmitted to the olfactory bulb and eventually are decoded by the frontal lobe.

Ref P-5

Olfactory Nerve CNI

Neural Connections of Olfactory System

Pathways

1. medially into the medial olfactory area of the brain stem

2. laterally into the lateral olfactory area.

The olfactory tract enters the brain at the anterior junction between the mesencephalon and cerebrum and divides into two pathways.

The medial olfactory area feed into the hypothalamus and other primitive portions of the brain’s limbic system. This is the brain area most concerned with basic behavior.

Signal pathways from the lateral olfactory area feeds into almost all portions of the limbic system, especially into less primitive portions such as the hippocampus.

Ref P-1

The Optic Nerve CNII

Cranial Nerve II The optic nerve, also

called cranial nerve II

The optic nerve develops embryologically as an outgrowth of the primitive forebrain, and thus the optic nerve is invested by the meninges.

The dura mater becomes continuous with its developmental equivalent, the sclera, while the pia-arachnoid continues into the eye as the uveal tract .

Function (sensory) - transmits visual and pupillary reflex from the retina to the brain.

Ref A- 2

Anatomy of the Eye The eyes are the peripheral organ of vision located on either side of

the nose in the orbital fossas of the cranium.

It is spherical and embedded in occular fat; this provides protection as well as attachment points for its extrinsic muscles.

It consists of tunica, optical and neural structures.

The tunica forms the outer and inner walls of the eyeball. It consists of three layers:

• Fibrous -sclera and cornea• Vascular- choroid, ciliary body and iris• Neural- retina; the inner most layer of the eye it is attached at the back to

the optic disc and at the front to the ora serrata. This layer contains the photoreceptors of the eye- Rods &Cones

Ref A-1

Anatomy Cont'd

Ref A-2

Retinal layers

Ref: A-2

Retinal Photoreceptors- (Rods & Cones)

Ref: A-2

Physiology – How do we see The membrane-bound pumps in the inner rod segment actively

pump sodium ions out.

In a dark rod, as fast as Na ions are pumped out, the outer rod segment brings them back in, completing the circuit.

However, the transport of sodium back into the outer segment becomes disrupted and the outer segment becomes hyperpolarized.

The interference with sodium transport into the rod outer segment is mediated by the cyclic decomposition and recomposition of rhodopsin.

Ref P-3

Physiology Cont'd The hyperpolarization response to light is

proportional to lights intensity and thus the brighter the light the greater the hyperpolarization.

The net change in the overall membrane charge is perceived by the integrating neurons of the retina, specifically the horizontal and bipolar cells. They in turn pass the information (with suitable inhibitory and/or excitatory signals of their own) to the ganglion cells.

Ganglion cells, then send their axons out via the optic nerves.

Ref P-3

Path of Light

Ref O-2

The transduction process involves the interaction of light with rhodopsin molecules which promotes a conformational change in the rhodopsin molecule, thus initiating an action potential. The action potential then passes inwards along the dendrite and axon to the layer of integrating neurones

Ref O-12

Phototransduction Phototransduction in rod photoreceptors. (A) The molecular structure of rhodopsin, the pigment in rods.

Rhodopsin is a G-protein coupled receptor consisting of opsin (a seven transmembrane domain protein) and 11-cis-retinal (a covalently bound chromophore).

(B) The second messenger cascade of phototransduction. 1. Light stimulation of rhodopsin in the receptor disks leads to the activation of a G-protein (transducin). 2. The GTP-bound alpha subunit of transducin activates a phosphodiesterase (PDE). 3. The activated phosphodiesterase hydrolyzes cGMP into GMP, reducing its concentration in the outer segment and leading to the closure of sodium channels in the outer segment membrane. Ref P-7

Phototransduction in rod photoreceptors

Ref:

Pathway of the Nerve The signals are then carried via the optic nerves, (which travels

posteromedially from the eye to exit the orbit. The fibers then unite at the optic Chiasm.

At the optic chiasm 1/2 of the fibers from each optic nerve cross at the midline and exit the chiasm in the opposite optic tract.

The fibers of the optic tracts later continue posteriorly to the midbrain with most synapsing in the lateral geniculate nucleus of their respective thalamus.

A small portion of the fibers enter the midbrain and participate in the pupillary light reflex.

From here the impulse proceeds to the visual center of the brain for interpretation

Emergence of Optic Nerve

OPTIC CANAL

Ref 4

CNII

It leaves the orbit via the optic canal, running postero-medially towards the optic chiasm, where there is a partial crossing of fibres from the nasal visual fields of both eyes.

Visual Fields

The visual field refers to the total area in which objects can be seen in the side (peripheral) vision while you focus your eyes on a central point.

Ref 0-13

Clinical Correlation

Damage to the medial aspect of the optic chiasm, as is often seen with a pituitary gland tumor, may compromise the decussating fibers from both nasal hemiretinas.

The loss of peripheral vision in both eyes is called bitemporal hemianopia.

Cra

nia

l Ner

ve I

II

Cranial Nerve III - Occulomotor The oculomotor nerve is the third of twelve paired cranial nerves.

Function (Motor)- responsible for lid retraction, pupil constriction, and lens thickening (i.e. accommodation).

This nerve is composed of motor axons arising from the oculomotor nuclei ( pair) and the edinger-westphal nucleus in the rostral midbrain located at the superior colliculus level.

The Edinger- Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).

Ref O-2

Position of CNIII

Ref O7

Pathway of the Nerve On emerging from the brain, the nerve is invested with a sheath of pia

mater, and enclosed in a prolongation from the arachnoid.

It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process( of sphenoid bone).

It runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the carvernous plexus( collection of thin walled veins) of the sympathetic, and a communicating branch from the ophthalmic division of the trigeminal Nerve

Ref o2

Pathway of the Nerve

It then divides into two branches, which enter the orbit through the superior orbital fissure, between the two heads of the lateral rectus.

Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve RefO2

Occ

ulo

mo

tor

Ner

ve

(CN

III)

The oculomotor nerve is the third of twelve paired cranial nerves.

Function (Motor)- responsible for lid retraction, pupil constriction, and lens thickening (i.e. accommodation).

This nerve is composed of motor axons arising from the oculomotor nuclei ( pair) and the edinger-westphal nucleus in the rostral midbrain located at the superior colliculus level.

The Edinger- Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation). Ref O-2

Cranial Nerve III Occulomotor

The remaining extraocular muscles, the superior oblique and lateral rectus muscles, are innervated by the Trochlear nerve and Abducens nerve respectively.

Ref O7

Components of CNIII

Somatic Motor(General Somatic Efferent)

Supplies four of the six extraocular muscles of the eye (the superior rectus, inferior rectus, medial rectus, and the inferior oblique muscles) and the levator palpebrae superioris muscle of the upper eyelid.

Visceral motor(general visceral efferent)

Parasympathetic innervation of the constrictor pupillae and ciliary muscles.

Action of eye muscles

On emerging from the brain, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid.

It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process( of sphenoid bone).

It runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the carvernous plexus( collection of thin walled veins) of the sympathetic, and a communicating branch from the ophthalmic division of the trigeminal Nerve

It then divides into two branches, which enter the orbit through the superior orbital fissure, between the two heads of the lateral rectus.

Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve

RefO2

Pathway of the nerve

Pathway of the nerve

Propagation of action potential

The receptors become excited and signal a change in membrane potential which allows ions to diffuse more or less throughout the membrane and thus change the transmembrane potential.When the recptor potential arises above the threshold for eliciting an action potential in the nerve fibre attached to the receptor, then an action potential occurs.The greater the receptor potential rises above the threshold the greater the action potential frequency.

Ref P-1

The ciliary muscles of the eyeball consist of 2 sets of smooth muscle fibers-

1. meridonial fibers

2. circular fibers. The meridonial fibers extend from the ends of the

suspensory ligament to the corneoscleral junction. When these muscles contract, the lens ligament relaxes,

making the lens thicker and increasing the refractive power. Relaxation of these muscles produces the opposite effect.

Accomodation of the lens and this mechanism is regulated by negative feedback and contraction of the smooth ciliary muscles helps the eyes to focus on distant and close objects.

Physiology of pupillary constriction

Ref P-1

Clinicals Syndromes:

The following collection of signs and symptoms, known as oculomotor ophthalmoplegia

Downward, abducted eye on the affected side due to the unopposed actions of the superior oblique and lateral rectus muscles.

Strabismus (the inability to direct both eyes toward the same object) as a result of extraocular muscle paralysis. This leads to diplopia (double vision).

Ptosis (eyelid droop) on the affected side due to inactivation of levator palpebrae superioris muscle and the unopposed action of the orbicularis oculi muscle (innervated by CN VII). The patient may compensate for the ptosis by contracting the muscles of the forehead to raise the eyebrow and lid.

Dilation of the pupil on the affected side due to decreased tone of the constrictor pupillae muscle.

Loss of the accomodation reflex on the affected side.

Cranial Nerve IV

Ref O6

Characteristic A motor nerve that innervates the superior

oblique muscle of the eye. It is the smallest nerve in terms of the number of

axons it contains which has the greatest intracranial length.

Along with CNII, it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.

It is the only cranial nerve that exits from the dorsal aspect of the brainstem.

The human trochlear nerve is derived from the basal plate of the embryonic midbrain.

Ref 0-7

Anatomical features It emerges from the dorsal aspect of the brainstem at the

level of the caudal mesencephalon, just below the inferior colliculus.

It circles anteriorly around the brainstem;

runs forward toward the eye in the subarachnoid space.

It passes between posterior cerebral artery and superior cerebellar artery, and then pierces the dura just under the free margin of the tentorium cerebelli,

It enters the cavernous sinus and joined by CNIII, CNV, CNVI and internal carotid artery.

Finally, it enters the orbit through superior orbital fissure and innervates the superior oblique muscle.

Ref 0-7

Ref A- 4

Location of Superior Oblique Muscle The superior oblique muscle ends in a tendon

that passes through a fibrous loop, the trochlea, located anteriorly on the medial aspect of the orbit.

exerts pressure through a pulley-like structure. This structure explains the nerve's name, trochlear, which means "pulley" in Latin.

The body of the superior oblique muscle is located behind the eyeball while the tendon approaches the eyeball from the front.

Ref A-10

Ref A-9

Action of Superior Oblique Muscle Rotation in a vertical plane – looking down and up

(depression and elevation)

The tendon attaches to the top of the eyeball at an angle of 51 degrees with respect to the primary position of the eye. The force of the tendon’s pull therefore has two components:

A forward component that tends to pull the eyeball downward and a medial component that tends to rotate the top of the eyeball toward the nose (intorsion).

Rotation in the plane of the face – Intorsion (the inward

convergent rotation of the upper pole of the vertical meridian of each eye) and Extorsion (the outward divergent rotation of the upper poles of the vertical meridian of the cornea of each eye)

When the eye is adducted (looking toward the nose), the force of depression increases. When the eye is abducted (looking away from the nose), the force of intorsion increases, while the force of depression decreases. Ref A-9

Clinical correlation Torsional Diplopia

Weakness of intorsion results in torsional diplopia, in which two different visual fields, tilted with respect to each other, are seen at the same time.

To compensate for this, patients tilt their heads to the opposite side, in order to fuse the two images into a single visual field.

Ref a-9

CN

V-T

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Overview Trigeminal nerve is the largest cranial nerve It has both sensory and motor components and has three main branches:

V1- the ophthalmic

V2- maxillary

V3- mandibular branches. The ophthalmic and maxillary nerves are purely sensory

(Touch,Pressure,Temperature and Pain)

The mandibular nerve has both sensory and motor functions.

Trigeminal nerve exits the brain on the lateral surface of the Pons.

The three branches converge on the trigeminal ganglion that is located within Meckel’s cave and contains the cell bodies of incoming sensory nerve fibers.

Different types of sensory receptors

Sensation from the skin, muscles, bones, tendons, and joints is termed somatic sensation and is initiated by a variety of somatic receptors.

A variety of mechanoreceptors in the skin leads to a wide range of touch pressure experiences including hair bending, deep pressure, vibrations and superficial touch.

Mechanism of action of receptors

Generally the nerve endings are linked to collagen-fiber networks within the capsule.

These networks transmit the mechanical tension in the capsule to ion channels in the nerve endings and activate them.

Ref – Human physiology. The Mechanisms of body function 8th ed. Vander

Pathway The trigeminal ganglion is analogous to the dorsal root

ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body.

From the trigeminal ganglion, a single large sensory root enters the brainstem at the level of the pons. Immediately adjacent to the sensory root, a smaller motor root emerges from the pons at the same level.

Motor fibers pass through the trigeminal ganglion on their way to peripheral muscles, but their cell bodies are located in the nucleus of the fifth nerve, deep within the pons.

Emergence of CN V in the Cranium

Foramen Rotundum(Maxillary)

Superior Orbital fissure (Ophthalmic)

Foramen Ovale(Mandibular)

Innervations of sensory fibers

1.Ophthalamic branch

Innervates upper face including conjunctiva, cornea, forehead, eyelid, and the bridge of the nose

2. Maxillary branch

Innervates upper jaw, cheeks, nasal cavity

3. Mandibular branch

Innervates lower jaw, teeth gums, anterior 2/3 of tongue.

Innervations of CN V

Ref: A 4

Distribution of trigeminal nerve

Innervations of trigeminal nerve

CN VI- Abducens

Superior Orbital Fissure

Ref O5

Overview CN VI known as Abducens has only a somatic motor

(general somatic efferent) component

( innervates muscles)

Function : It innervates the lateral rectus muscle of the ipsilateral orbit.

Ref O7

Innervation of Abducens

Ref O7

Action

The abducens nerve innervates the lateral rectus muscle of the ipsilateral orbit.

The lateral rectus muscle is responsible for lateral gaze,its contraction causes the eye to be abducted.

Ref O7

Pathway of Nerve The fibers of the abducens nerve originate from the abducens nucleus

located in the caudal pons.

The nucleus is located just ventral to the fourth ventricle near the midline.

Axons of CN VII (facial nerve) loop around the abducens nucleus and give rise to a bulge in the floor of the fourth ventricle - the facial colliculus.

Fibers leaving the abducens nucleus travel ventrally to exit the brainstem at the border of the pons and medullary pyramids.

Ref O7

Ref O7

Ref O7

Pathway Upon exiting the brainstem, the abducens nerve

climbs superiorly along the ventral surface of the pons. On reaching the apex of the petrous portion of the temporal bone the nerve makes a sharp turn anteriorly to enter the cavernous sinus.

The abducens nerve travels along the lateral wall of the cavernous sinus with CNS III, IV, and V.

RefO7

Pathway From the cavernous sinus, the abducens nerve enters

the orbit through the superior orbital fissure.

It passes through the tendinous ring of the extraocular muscles and innervates the lateral rectus muscle on its deep surface.

RefO7

Ref O7

Clinical correlation

Lower Motor Neuron Lesion

Damage to the abducens nucleus or its axons results in weakness or paralysis of the ipsilateral rectus muscle.

CN VI paralysis is the most common isolated palsy due to the long peripheral course of the nerve.

RefO7

Overview The facial nerve is the seventh (VII) of twelve paired cranial nerves. It is composed of motor and sensory fibers

It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.

It also supplies preganglionic parasympathetic fibers to several head and neck ganglia.

(ref.A 4)

Facial Nerve

Functions Major motor nerve of facial expression Autonomic control of tear glands, nasal & palatine glands; submandibular &

sublingual salivary glands Sense of taste

Origin Motor fibres arise from lower pons Sensory fibres arise from taste buds on anterior two thirds of tongue

Ref. A- 12

Facial Nerve

Ref. 3

Click icon to add picture

Motor & Sensory branches of Facial Nerve

Ref. 3

Click icon to add pictureSurface anatomy of

The Branchial branches of Facial

Nerve

Five major branches include Temporal, Zygomatic, Buccal, Mandibular and Cervical branches

Motor fibres lead to posterior belly of digastric, stapedius muscle of middle ear, & muscles of facial expression

Autonomic fibres lead to submandibular & sublingual salivary glands

Gustatory (taste) fibres lead to genticulate ganglion and then to pons Motor fibres enter temporal bone via internal acoustic meatus, run through

middle-ear and emerge by way of stylomastoid foramen near parotid salivary gland anterior to the ear

Motor fibres then give rise to five major branches

Ref. 12

Facial Nerve

The facial muscles are like elastic sheets that are stretched in layers over the cranium, facial bones, the openings they form, and the cartilage, fat, and other tissues of the head.

They are skeletal in nature acting singly or in combination.

Branchial Motor : Muscles of Facial expression

Facial muscles

Organization of Skeletal muscle

Skeletal muscles fibers are innervated by large myelinated nerve fibers from the motor end plate of the spinal cord.

The nerve forms a terminal on the surface of the muscle fiber-motor end plate The invaginated membrane is called the synaptic gutter/trough The space between the space between the terminal and fiber is called the

synaptic cleft The muscle at the bottom of the gutter is folded to increase surface area In the axon terminal, mitochondria supply ATP for synthesis of acetylcholine-

the excitatory neurotransmitter

Acetylcholine is released and excites the muscle fiber membrane- action potential

Voltage gated calcium channels open and ca is released resulting in contraction of the muscle fiber

Physiology

Motor End Plate

Anatomy, Physiology & Histology of Lacrimal gland Paired almond-shaped glands, one for each eye. Secretes aqueous layer of tear film. Situated in the upper, outer portion of each orbit, in the lacrimal fossa of the frontal bone. It has 2 sections:

1.Smaller palpebral portion- lies close to the eye, along the inner surface of the eyelid. 2.Orbital portion- contains fine interlobular ducts that unite to form 3 - 5 main excretory ducts. Tears are secreted and collected in the fornix conjunctiva of the upper lid, and pass to the lacrimal puncta-

small holes found at the inner corner of the eyelids. These pass the tears on to the lacrimal sac then to the nasolacrimal duct, which dumps them out into the nose. The lacrimal gland is a compound tubuloacinar gland, made up of many lobules separated by connective tissue,

each lobule contains many acini.

Ref, 8&9

Facial Nerve- Visceral Motor Component

The acini contain only serous cells and produce a watery serous secretion. Each acinus consists of a grape-like mass of lacrimal gland cells with their

apices pointed to a central lumen. The central lumen of many of the units converge to form intralobular ducts,

and then unite to from interlobular ducts. The gland lacks striated ducts. The parasympathetic secretomotor fibers branch of the zygomatic nerve,

join with the lacrimal branch of the ophthalmic division of CN V, to supply sensory innervation to the lacrimal gland along with the eyelid and conjunctiva.

The nasal glands are innervated with secretomotor fibers from the nasopalatine and greater palatine nerve. Palatine glands are innervated by

the nasopalatine, greater palatine nerve and lesser palatine nerves. Ref. 8&9

Facial Nerve

Ref. 3

Lacrimal Gland

Anatomy & Histology of the Sublingual gland The sublingual glands are salivary glands in the mouth. They lie anterior to the submandibular gland under the tongue, beneath the mucous

membrane of the floor of the mouth. They are drained by 8-20 excretory ducts called the ducts of Rivinus. The largest duct, the sublingual duct (of Bartholin) joins the submandibular duct to drain

through the sublingual caruncle. The sublingual gland consists mostly of Mucous acini capped with serous demilunes and is

therefore categorized as a mucous gland. The chorda tympani nerve (from the facial nerve via the submandibular ganglion) is

secretomotor to the sublingual glands.

Ref. 7

Facial Nerve

Paired submandibular glands (submaxillary glands) are located beneath the floor of the mouth.

Lying superior to the digastric muscles, each submandibular gland is divided into superficial and deep lobes, which are separated by the mylohyoid muscle

Superficial portion- smaller portion, the mylohyoid muscle runs below it. Deep portion- comprises most of the gland.

Secretions are delivered into the Wharton's ducts on the superficial portion after which they hook around the posterior edge of the mylohyoid muscle and proceed on the superior surface laterally.

Facial Nerve – Anatomy, Physiology & Histology of the Submandibular gland

Ref A-7

Facial Nerve

Lobes • Submandibular Gland

Lobules

Adenomeres

•Secretory Unit•Made of acini or alveoli•Acini contains secretory cells•Some have lysozyme activity

Ref O-7

Submandibular glands are branched tubuloacinar glands.

Because the secretory cells are of both serous and mucous types, the submandibular gland is a mixed gland, though it is mostly serous.

The mucous cells are most active and therefore the major product of the submandibular glands is saliva.

Ref. A- 6

Facial Nerve

Parasympathetic innervation to the submandibular glands is provided by the superior salivatory nucleus via the chorda tympani, a branch of the facial nerve that synapses in the submandibular ganglion after which it follows the Lingual nerve leaving this nerve as it approaches the gland.

Ref P-1

Facial Nerve

The sympathetic nervous system regulates submandibular secretions through vasoconstriction of the arteries that supply it. Increased sympathetic activity reduces glandular bloodflow, thereby decreasing salivary secretions and producing an enzyme rich mucous saliva.

Facial Nerve

Ref A-6

Anatomy & Physiology of the Tongue Muscular hydrostat on the floor of the mouth which

manipulates food for mastication. Primary organ of taste, as much of the upper surface of

the tongue is covered in papillae and taste buds. The tongue provides a natural means of cleaning one's

teeth. A V-shaped line - the sulcus terminalis, divides the

tongue into an anterior 2/3 and a posterior 1/3. The mucosa covering the upper surface of the tongue is

thrown into numerous projections called the lingual papillae in the anterior 2/3rd of the tongue.

In the posterior 1/3rd, there are no papillae, but there are lots of lymphoid follicles present.

Facial Nerve- Special Sensory

Ref A-5

The three types of papillae are: fungiform (mushroom like) filiform (filum - thread like) Circumvallate

Taste for the anterior 2/3 of the tongue is supplied by the Facial nerve (Chorda tympani, CN VII). General sensation of the anterior 2/3 is supplied by the Lingual nerve which is a branch of V3 of the Trigeminal nerve CN V.

Taste as well as general sensation for the posterior 1/3 is supplied by the Glossopharyngeal nerve (CN IX) .

Facial Nerve

Ref A-5

The sensory receptors for the sense of taste are located in taste

buds. Taste buds are embedded in epithelium primarily on

the tongue .

Many lie along the walls of the papillae,

the small elevations on the tongue that are visible to the

naked eye.

Isolated taste buds are also present on the hard

palate, the pharynx, and the epiglottis. We have at least four

primary types of taste, but the taste buds for each are located

throughout the tongue.

Taste – Special Sensory

Ref P-1

Physiology- Taste

Ref P-6

General Sensory-Skin

Ref P-6

Skin Receptors

Ref P-6

Facial Nerve Disorders There are numerous causes of facial nerve disorder: Trauma: such as birth trauma, skull base fractures, facial injuries, middle

ear injuries, or surgical trauma. Nervous system disease: including Opercular syndrome, Millard-Gubler

syndrome. Infection: of the ear or face, or herpes zoster of the facial nerve

(Ramsey-Hunt syndrome). Metabolic: diabetes mellitus or pregnancy. Tumors: acoustic neuroma, schwannoma, cholesteatoma, parotid

tumors, glomus tumors. Toxins: alcoholism or carbon monoxide poisoning. Bell's palsy: Also called idiopathic facial nerve paralysis

(ref A. 1&2)

Clinical Correlation

Ref. A 3

Click icon to add picture

Signs of impaired Facial Nerve

CN VIII

Ref A-2

CN VIII - VESTIBULOCOCHLEAR NERVE

CN VIII is a purely sensory nerve

-It emerges from the medulla oblongata and exits the inner skull via the internal acoustic meatus.

-This nerve consists of the cochlear nerve (supplies the cochlea), carries information about hearing; and the vestibular nerve (supplies the vestibule) which carries information about balance.

Ref A-7

Ref. A4

THE BEGINNING OF THE EAR

The ear consists of three parts: the internal, middle and external

The internal ear originates from the otic vesicle, which detaches from the surface ectoderm.

This vesicle divides into a ventral component, which gives rise to the saccule and cochlear duct and a dorsal component, which gives rise to the utricle, semicircular canals, and endolymphatic duct .

Transverse section through the rhombencephalon showing formations of otic vesicle Ref. A14

THE BEGINNING OF THE EAR

The cochlear duct, which forms the organ of Corti, is derived from membranous labyrinth.

Ref. A14 & 6

THE HISTOLOGY OF THE EAR

The Organ of Corti is located within the scala media

It consists of 2 types of cells: hair cells & support cells (pillar & phalangeal cells)

These cells are supported by the basilar membrane

The tectorial membrane is a flaplike mass of glycosaminoglycans, overlying sensory cells and within which sterocillia are embeddedRef. A 6

MECHANISM OF HEARING Sound waves are funneled

into the external acoustic meatus, after which impinges on the tympanic membrane, which in turn vibrates

These vibrations travel to the ossicles, where the amplitude is enhanced

Vibrations are conducted to the perilypmph of the vestibule & pressure waves pass into the cochleaRef.P-1

MECHANISM OF HEARING Pressure waves are then conducted

directly to the endolymph of the scala media

Vibrations are induced in the basilar membrane & organ of Corti

The hair cells are then activated & initiates afferent sensory impulses

This occurs when vibrations reach the sterocillia of the hair cells, causing them to be depolarized & in turn excites sensory nerves & synapse with them

These impulses then pass to the auditory cortex of the brainRef.P 1

MECHANISM OF BALANCE

The vestibular nerve goes to the semicircular canals via the vestibular ganglion.

It receives positional information.

Axons of the vestibular nerve synapse in the vestibular nucleus on the lateral floor and wall of the fourth ventricle in the pons and medulla.

Ref A 6 &8

SYMPTOMS OF CN VIII DAMAGE Hearing loss

Vertigo (a feeling of motion when one is stationary)

False sense of motion

Loss of equilibrium

Motion sickness (is a condition in which a disagreement exists between visually perceived movement and the vestibular system's sense of movement) RefA 6&8

Glossopharyngeal

Nerve – CN IX

Overview The glossopharyngeal nerve contains both motor and sensory fibers,

and is distributed, as its name implies, to the tongue and pharynx.

It is the nerve of ordinary sensation to the mucous membrane of the pharynx, fauces, and palatine tonsil, and the nerve of taste to the posterior part of the tongue

It is attached by three or four filaments to the upper part of the medulla oblongata, in the groove between the olive and the inferior peduncle.

It exits the brainstem out from the sides of the upper medulla just rostral (closer to the nose) to the  vagus nerve and exits the cranium via the jugular foramen, anterior to cranial nerves X and XI which also exit the skull via the jugular foramen.

Ref O8

Branches of CN IX

Ref O8

Branches of CN IX

Ref O7

Components of the Glossopharyngeal Nerve General sensory-

Provides general sensory information from the skin of the external ear, internal surface of the tympanic membrane, upper pharynx, and the posterior one-third of the tongue.

Special sensory (special afferent)

Provides taste sensation from the posterior one-third of the tongue.

RefO7

Components of CNIX

Visceral sensory (general visceral afferent)

Carries visceral sensory information from the carotid sinus and body.

Visceral motor (general visceral efferent)

Parasympathetic innervation of the smooth muscle and glands of the pharynx, larynx, and viscera of the thorax and abdomen.

Brancial motor (special visceral efferent)

Supplies the stylopharyngeus muscle.

Ref O7

Visceral Sensory Component

This component of CN IX innervates the baroreceptors of the carotid sinus and chemoreceptors of the carotid body.

Sensory fibers arise from the carotid sinus and carotid body at the bifurcation of the common carotid artery, ascend in the sinus nerve, and join the other components of CN IX at the inferior glossopharyngeal ganglion

The cell bodies of these neurons reside in the inferior ganglion.

The carotid sinus contains baroreceptors that monitor arterior blood pressure. The carotid body contains chemoreceptors that monitor the CO2 and O2

concentration of the body.

Ref O7

Visceral sensory componet continued The cell bodies for this pathway are in the inferior

glossopharyngeal ganglion -- information is subsequently transmitted to the

nucleus of the solitary tract (abbreviated as NTS, remember this as the 'nucleus of taste sensation)

Ref O7

General Sensory Ref O2

Ref A-2

Branchial Motor Component

The branchial motor component of CN IX elevates the pharynx during swallowing and speech.

It originates from the nucleus ambiguus (ambiguous nucleus) in the medulla and receives innervatiom directly via the corticobulbar tract.

Upon exiting the skull the branchial motor fibers descend deep to the styloid process and wrap around the posterior border of the stylopharyngeus muscle before innervating it. ( Ref O8)

Visceral Motor Component The glossoglossopharyngeal nerve also

innervates the parotid gland, which causes salivation. This component originates in the inferior salivatory nucleus and passes through the otic ganglion

Ref A-1

Visceral Motor Component

It enters the cranium via the jugular foramen, within which lies two glossopharyngeal ganglion that mediate the sensation

Before exiting the foramen the tympanic nerve enters the petrous portion of the temporal and ascends forming a plexus on the surface of the promontory of the middle ear to provide general sensation.

The visceral motor fibers pass through this plexus and merge to become the lesser petrosal nerve.

The lesser petrosal nerve re-enters and travels through the temporal bone to emerge in the middle cranial fossa just lateral to the greater petrosal nerve. It then proceeds anteriorly to exit the skull via the foramen ovale along with the mandibular component of CN V (V3). Ref O7

Clincal Application Sensation supplied by the glossopharyngeal nerve

is different in

quality to that supplied by the trigeminal. To demonstrate this one can place a finger on the

anterior part of the tongue (V) and then the posterior part (IX).

The gag reflex is mediated by the glossopharyngeal (afferent limb) and the vagus (efferent limb).

It is a functional test of both nerves. Ref O7

The vagus nerve : CN X

The Wandering Nerve

Vagus Nerve Name derived from Latin meaning “wandering”

Longest cranial nerve in the body.

Function: both motor and sensory innervations of the viscera

Is also called the pneumogastric nerve since it innervates both the lungs and the stomach.

Arises from the medulla and exits the cranium via the jugular foramen

Then passes into carotid sheath between the common carotid artery and internal jugular vein below the head to the neck, chest and abdomen where it contributes to the innervation of body organs.

Ref A-4

Origin of Vagus NerveRef A-3

- Ref A-15

Branches of the Vagus Nerve

Auricular nerve Pharyngeal nerve Superior laryngeal branch Superior cervical cardiac branches Inferior cervical cardiac branches Recurrent laryngeal nerve Thoracic cardiac branches Branches to the pulmonary plexus Branches to the eosphageal pleuxus Anterior vagal trunk Posterior vagal trunk Hering-Breuer reflex in alveoli

Ref A-4

Ref A-1

Ref A-15

Ref A-15

Ref A-3

Pathway The right vagus nerve gives off the right recurrent laryngeal

nerve(right of subclavian artery).It ascends into the neck between the trachea and esophagus.

It then crosses anteriorly to the right subclavian artery and runs posterior to the superior vena cava and descends posterior to the right main bronchus and contributes to cardiac, pulmonary, and esophageal plexuses.

It forms the posterior vagal trunk at the lower part of the esophagus and enters the diaphragm through the esophageal hiatus.

Ref O8

Pathway The left Vagus nerve enters the thorax

between left common carotid artery and left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve.

This further gives rise to thoracic cardiac branches, pulmonary plexus and esophageal plexus before entering the abdomen as the anterior vagal trunk via in the esophageal hiatus. ( Ref O8)

Innervation Two sensory ganglion are associated with the Vagus Nerve- Inferior

and Superior The branchial motor component provides voluntary control of the

following:

1. Striated muscle of the pharynx.

2. Striated muscle of the larynx, except for the stylopharyngeus muscle (CN IX) and the tensor veli palatini muscle (CN V).

3. Palatoglossus muscle of the tongue (other tongue muscles are innervated by CN XII).

It gives rise to 3 branches : Pharyngeal branch

Superior laryngeal nerve

Recurrent laryngeal nerve Ref O8

Visceral Motor Component

The parasympathetic (secretomotor) component of the vagus nerve consists of efferent fibers which innervate the smooth muscle and glands of the pharynx, larynx, and thoracic and abdominal viscera down to the splenic flexure.

It produces a “rest & digest” response leading to:

1. Increased secretion from glands and smooth muscle contraction.

2. Cardiac - Slows heart rate

3. Lungs - Stimulates increased bronchiolar secretions and bronchoconstriction

4. GI tract- Stimulates increased secretions and motility ( RefO8)

Clinical Application

The parasympathetic innervation of the heart is controlled by the vagus nerve. The right vagus innervates the Sinoatrial node and lowers heart rate( bradycardia)

The left vagus when hyperstimulated predisposes the heart to Atrioventricular blocks

Ref A-4

Cranial Nerve XI-Accessory Nerve

Ref A-3

REF O-4

Accessory Nerve The spinal accessory nerve (SAN) is formed by 2 parts. The spinal or motor portion includes fibers that originate in the ventral

horn of the upper 4 or more cervical segments of the spinal cord. The fibers may originate from as low as the fifth and rarely the seventh

cervical segment. These fibers ascend lateral and parallel to the spinal cord, entering the

skull through the foramen magnum. These fibers join the second or accessory component of the SAN that

originates in the nucleus accumbens brain stem nucleus of the medulla oblongata in the posterior fossa.

The 2 parts of the SAN, now joined, leave the skull through the jugular foramen. The nerve passes through the jugular foramen and then divides variably into the 2 original components.

Cell bodies of spinal accessory motor neurons are in the lateral part of the ventral grey horn of the cervical cord in, apparently, a caudal extension of the nucleus ambiguus.

Ref O-7

Accessory Nerve The superior branch, also known as the accessory or internal branch, joins the

vagus either directly or through the ganglion nodosum and then contributes to the pharyngeal, laryngeal, and cardiac sympathetic fibers.

The inferior branch, also known as the spinal or lateral branch, is essentially a pure motor nerve and innervates the sternocleidomastoid (SCM) and trapezius muscles.

It passes beneath the posterior belly of the digastric and the upper end of the SCM muscle along the internal jugular vein. It may travel either anterior or posterior to the occipital artery, and it communicates with the second cervical nerve before it enters the SCM.

The nerve emerges from the posterior border of the SCM and obliquely crosses the posterior cervical triangle downward before entering the trapezius.

The length of the SAN can vary from 4-5 cm when it is lax (chin pointing forward) to 9-10 cm when it is extended (chin pointing to the opposite shoulder).

In essence this nerve controls head rotation and shoulder shrugging (via trapezius muscle)

Ref O-7

Location of CN XI in Posterior TriangleRef A-2

Location of CN XI in Posterior TriangleRef A-2

Accessory Nerve

Ref A-2

Clinical notes The accessory nerve is vulnerable in the posterior

triangle as it crosses the roof. Such injuries result in paralysis of trapezius (but not

sternocleidomastoid which it has already supplied) and thus shoulder abduction beyond 90° involving scapular rotation is impaired (hair grooming, etc.).

The accessory nerve may be damaged in dissection of the neck for malignant disease, in biopsy of enlarged lymph nodes in and around the posterior triangle, or in penetrating injuries to this region.Ref A-2

Clinical testing of spinal accessory 1. Ask the patient to shrug the shoulders (trapezius)

against resistance.

2. Ask the patient to put hand on head (trapezius: shoulder abduction beyond 90°).

3. Ask the patient to move the chin towards one shoulder against resistance (contralateral sternocleidomastoid).

Ref A-2

Cranial Nerve XII

Origin

Ref A-8

Hypoglossal Nerve

Arises from the Hypoglossal Nucleus (hypoglossal trigone in the floor of the fourth ventricle) and passes through the Hypoglossal Canal.

It exits the cranium via the hypoglossal foramen in the posterior cranial fossa.

Spirals behind the Vagus Nerve and passes between the Internal Caratoid Artery and Internal Jugular Vein lying on the Carotid Sheath.

It then passes deep to the posterior belly of the Digastric Muscle and then the Submandibular region to enter the Tongue

(Ref A-4)

Hypoglossal Nerve Fiber Type- Motor Only

Ref A-3

Hypoglossal Nerve Palsy

Damage to the Hypoglossal nerve produces unilateral palsy of the Tongue musculature. The tongue deviates to the weaker side upon protrusion. Ref A-4

Summary

There are 12 prs of craniall nerves. CN I, II & VIII – sensory CN III, IV, VI, XI & XII- Motor CN V, VII, IX & X- mixed They form part of the peripheral

nervous system but have their origins in varying nuclei of the brain

Mnemonic RefA4

Other Reference 1.Campbell et al (1999) 5th edition Chapter 48; (pp. 976-988).

2. Monkhouse, Stanley; Cranial Nerves Functional Anatomy

3.http://en.wikipedia.org/wiki/internal capsule

1. http://slideshare.com

4.Netter Atlas -physiology

5.Guyton& Hall ; textbook of Medicl physiology

6.Aol:www.Students consult.com

7. Yale medical school online AOl:www. Yalemedicine.com

8. www.wikipedia .com

9. http://www.en.wikipedia.org/wiki/Facial_nerve

10.http://www.google.gy/imgres?imgurl=http://www.missionforvisionusa.org/anatomy/uploaded_images/lacrimalglandnumb

11. Henry Gray (1821–1865).  Anatomy of the Human Body.  1918.

12. http://openwetware.org/wiki/BIO254:Phototransduction

Reference - Anatomy

1. Students Study Guide Anatomy

2.www.googleimages

3.Monkhorse, Stanley; Nerves Functional Anatomy

4.http://emedicine.medscape.com/article/835585-overview65. http://dermatology.about.com/cs/skinanatomy/a/anatomy.htm

http://www.nuskin.com/en_ZA/corporate/company/science/skin_care_science/skin_anatomy_andphysiology.html

6. Wheater’s fundamentals of Histology – Atext and colour Atlas 5 th Ed.7. Kenneth S. Saladin; Anatomy & Physiology, unity of form and Function 10 th Ed.

8.Clinically Oriented Anatomy, Moore, Dalley & Agur.9. "eye, human."Encyclopædia Britannica. 2010. Encyclopædia

Britannica 2010 Ultimate Reference Suite DVD 201010 .A. R. Ten Cate (1998). Oral Histology: Development, Structure, and Function (5th edition ed.). Saint

Louis: Mosby-Year Book.11. Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner,

David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1.

12. Kliniska Färdigheter: Informationsutbytet Mellan Patient Och Läkare, LINDGREN, STEFAN, ISBN 91-44-37271-X

13. http://www.nlm.nih.gov/medlineplus/ency/article/003879.htm

14. Langman’s Medical Embryology, 11th edition

15.Aclands video-human anatomy

Reference _Physiology1.Guyton &Hall(2011) ; Textbook Medical Physiology ; 12th Ed .

2.www.studentsconsult.com

3. A. R. Ten Cate (1998). Oral Histology: Development Structure, and Function (5th edition ed.). Saint Louis: Mosby-Year Book.

4. www.http://education.vetmed.vt.edu/Curriculum/VM8054/EYE/PHYSIO.HTM-basic physiology of vision

5. Lehniger Biochemistry 5th Ed.

6.

Reference –Histology 1. 1.Constanzo , Linda S.; Physiology 3rd Edition

2. 2.Guyton &Hall(2011) ; Textbook Medical Physiology ; 12th Ed .

3. 3.Wheater’s Functional Histology- A text and colour Atlas

4. 4.www.http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab11/Eye/EXAMPLES/EXCNJNCT.HTM

Vascular • Central Nervous

Supply • System

Base of brain and cerebral arterial circle

Grant’s Atlas of Human Anatomy 12th ed.

The brain is supplied with arterial blood that arrives through four vessels. These vessels eventually unite on the inferior surface of the brain. This arrangement termed the circle of Willis, ensures alternate blood supplies to the brain.

The four vessels are paired internal carotid arteries and the paired vertebral arteries.

Cerebral Arterial Circle (Circle of Willis)

Grant’s Atlas of Human Anatomy 12th ed.

Schematic representation of the Circle of Willis. Circle of Willis is an arterial arrangement that ensures alternate paths for arterial blood supply to the brain. The value of four separate vessels coming together at one location is that if one becomes occluded, the three alternate routes may still provide an adequate blood supply to the brain.

Venous DrainageThe venous drainage of the brain occurs through a complex system of deep and superficial veins. These veins possess no valves and have thin walls devoid of muscular tissue. They pierce the arachnoid mater and the inner layer of the dura mater to open into the dural venous sinuses

Ref. Gray’s Anatomy 39ed.

Veins of the Brain Stem

The veins of the brain stem form a superficial venous plexus deep to the arteries.Veins of the medulla oblongata drain into the veins of the spinal cord or the adjacent dural venous sinuses, or into variable radicular veins which accompany the last four cranial nerves to either the inferior petrosal or occipital sinuses, or to the superior bulb of the jugular vein.

.The external (superficial) cerebral veins of the left hemisphere

Veins of the Cerebellum

The veins of the cerebellum drain mainly into sinuses adjacent to them or, from the superior surface, into the great cerebral vein. The cerebellar veins course on the Cerebellar surface, and comprise superior and inferior groups.

The internal (deep) cerebral veins, viewed from above after removal of the central portion of the corpus callosum Ref Gray’s anat 39thed