NEUROANATOMY

Lecture : 8

Peripheral Nervous SystemAnatomy of the Cranial Nerves (I, II, III, IV, VI)

Prepared and presented by:

Dr. Iyad Mousa Hussein ,

Ph.D in Neurology

Head of Neurology Department

Nasser Hospital

1. Classification of the Peripheral Nervous System.

2. Structures of the Peripheral Nerve, and Nerve Fibers.

3. Classification of the Cranial Nerve.

4. Function of the Olfactory Nerve, and Pathway of the Smell.

5. Lesion of the Olfactory Nerve.

6. Function of the Optic Nerve, and Pathway of the Vision.

7. Lesion of the Optic Nerve.

8. Function, Branches, and Lesion of the Oculomotor Nerve.

9. The actions of the ocular muscles.

10. Function, and Lesion of the Trochlear Nerve.

11. Function, and Lesion of the Abducent Nerve.

LECTURE OBJECTIVES:

The peripheral nervous system (PNS) formed of the:

1. Somatic (voluntary or craniospinal) NS: which

controls the skeletal muscles:

a. Cranial nerves.

b. Spinal nerves.

2. Autonomic NS: which controls the smooth and

cardiac muscles:

a. Sympathetic nervous system.

b. Parasympathetic nervous system.

Classification of the Peripheral Nervous System

The peripheral nervous system consists of the cranial and

spinal nerves and their associated ganglia.

There are 12 pairs of cranial nerves, which leave the brain

and pass through foramina in the skull.

There are 31 pairs of spinal nerves, which leave the

spinal cord and pass through intervertebral foramina in

the vertebral column.

The Peripheral Nervous System

Definition: it is an axon or a dendrite of a nerve cell.

Structure of the Nerve Fiber:

1. Schwann cell.

2. Node of Ranvier.

3. Myelin sheath.

4. Mesaxon.

The Nerve Fibers

Definition: The cranial nerves are consist of 12 pairs of

nerves that arise from the brain.  They exit/enter the

cranium through openings in the skull.

The Cranial Nerves

The olfactory, optic and vestibulocochlear nerves are purely v

sensory nerves (128).

The oculomotor, trochlear, abducent, accessory and

hypoglossal nerves are purely motor nerves.

The trigeminal, facial, glossopharyngeal and vagus nerves

are mixed nerves (1975).

There are three cranial motor nerves (III, IV, & VI nerves),

which supply the muscles of the eye.

There are three cranial mixed nerves (VII, IX, & X nerves),

which have the same plan: each contains three types of fibers:

motor, sensory and parasympathetic.

Classification of the Cranial Nerves№NameFunctionSite of nucleusOpening in skull

1OlfactorySmell Temporal LobeCribriform plate

2OpticVision Occipital lobeOptic canal

3OculomotorMotorMidbrainSuperior orbital fissure

4Trochlear MotorMidbrainSuperior orbital fissure

5Trigeminal:

Ophthalmic

Maxillary

Mandibular

MixedMidbrainSuperior orbital fissure

Foramen rotundum

Foramen ovale

6AbducentMotorPonsSuperior orbital fissure

7FacialMixedPonsInternal acoustic meatus, Facial

canal, Stylomastoid foramen

8Cochleo-Vestibular Hearing and balance PonsInternal acoustic meatus

9Glosso-pharyngealMixedMedulla oblongata Jugular nerve

10VagusMixedMedulla oblongata Jugular foramen

11 Spinal AccessoryMotor C1-C4 AHC

of spinal cord

Jugular nerve

12 HypoglossalMotorMedulla oblongata Hypoglossal canal

Olfactory Nerve: (Latin for "to smell").

Function: Special sensory nerve (smell).

Olfactory nerve located in the anterior cranial fossa and

attached to the under surface of the frontal lobe.

The Olfactory Nerve (I)

Pathway of the Smell

From receptors in olfactory mucous membranes of the nasal

cavity → Fibers of olfactory nerve (consist of about 20 small

filaments on each side → The cribriform plate of the ethmoid

bone → Olfactory groove → olfactory bulb → Olfactory tract

→ direct and indirect (around corpus callosum) to terminate

in olfactory sensory area ( in the uncus of temporal lobe).

Note: Smell as well bilateral represented.

1. Unilateral anosmia.

2. Bilateral anosmia.

3. Parosmia (Smell hallucination)

4. Cacosmia (bad smell in chronic sinusitis).

5. Olfactory agnosia (higher-order loss of

olfactory discrimination).

Lesion of the Olfactory Nerve

Optic Nerve: (Latin for "to see").

Function: Special sensory nerve (Sense of vision).

The Optic Nerve (II)

Receptors of light are rods and cones of retina → Optic

nerve → Optic canal of the sphenoid bone → Optic chiasma

(the nasal or medial fibers decussate to the opposite optic

tract, while the temporal or lateral fibers continue in the

same optic tract → Optic tract → Relay in the lateral

geniculate body → Posterior limb of internal capsule →

Optic radiation → End in area 17, 18, 19 of occipital lobes.

Pathway of the Vision

1. Lesion in the optic nerve or retina: ipsilateral loss or

decrease of vision (blindness).

2. Lesion in the optic chiasma: bitemporal hemianopsia.

3. Lesion in the optic tract: contralateral homonymous

hemianopsia with preserved direct and indirect light reflexes.

4. Lesion in the lateral geniculate body, internal capsule and

optic radiation: contralateral homonymous hemianopsia with

preserved direct and indirect light reflexes.

5. Lesion in the occipital lobe:

a. Irritative: Visual hallucination.

b. Destructive: contralateral homonymous hemianopsia

with macular sparing and visual agnosia (the patient can see

but does not recognize objects).

Lesion in the Vision Pathway

Oculomotor nerve: (Latin for "eye" and "moving").

Function:

1. Motor function: movement of the eye ball.

2. Autonomic (parasympathetic): pupillary reaction.

Site of nucleus: it lies in the tegmentum of midbrain.

The oculomotor Nerve (III)

The nucleus of oculomotor nerve formed of 3 main parts:1. The Edinger-Westphal nucleus: parasympathetic function which supplies two intra-ocular muscles:

a. Constrictor pupillae muscles → Miosis.b. Ciliary muscles → Responsible for light and accommodation reflexes.

2. The lateral cell mass (motor function): which is divided into five parts which supplies five extra ocular muscles which are from above downwards:

a. Levator palpebrea superior.b. Superior recti muscles.c. Medial recti muscles.d. Inferior oblique muscles.e. Inferior recti muscles.

3. The central nucleus of Perlia: motor function which supplies the medial recti muscles of the two eyes allowing to contract together when both eyes converge to look to a near object.

Structure of oculomotor Nuclei

The oculomotor nerve supplies all the intra- and extraocular

muscles except:

1.Superior oblique muscles → from the trochlear nerve – IV.

2.Lateral recti muscles → from the abducent nerve –VI.

3.Dilator pupillae muscles → from the sympathetic fibers.

1. The Lateral Rectus Muscle: abducts (laterally) the eye ball.

2. The Medial Rectus Muscle: adducts (medially) the eye ball.

3. The Superior Rectus Muscle: elevates, adducts and rotates medially.

4. The Inferior Rectus Muscle: depresses, adducts and rotates medially.

5. The Superior Oblique Muscle: depresses, adducts and rotates

laterally.

6. The Inferior Oblique Muscle: elevates, adducts and rotates laterally.

The Actions of the Ocular Muscles

The oculomotor nerve emerges from a groove on the

medial aspect of midbrain (ventral surface).  

The nerve passes through the two layers of the dura

mater including the  lateral wall of the cavernous sinus and

then enters the superior orbital fissure to access the orbit.

1. Superior division: which supplies the:

a. Levator palpebrea superior.

b. Superior rectus muscles.

2. Inferior division: which supplies the:

a. Medial rectus.

b. Inferior rectus.

c. Inferior oblique muscles.

d. Sphencter pupillae muscle.

e. Ciliary muscle.

Branches of the Oculomotor Nerve:

1. Ptosis: paresis of the levator palpebrea superior muscle.

2. Diplopia: occurs only on elevation of eye lid.

3. Squint: divergent paralytic.

4. Mydriasis: dilated fixed pupil.

5. Loss of light and accommodation reflexes.

Lesion of the Oculomotor Nerve:

The trochlear nerve is so called because superior oblique

muscle (which it supplies) is arranged as a pulley (Latin:

trochlea – pulley).

Function: motor nerve → movement of the eye ball →

supplies the superior oblique muscles.

Site of the nucleus: it lies in the tegmentum of the midbrain.

The Trochlear Nerve (IV)

It is the smallest cranial nerve.

The trochlear nerve is purely a motor nerve.

The trochlear nerve emerges from the posterior surface of

the midbrain.

The nerve travels in the lateral wall of the cavernous sinus

and then enters the orbit via the superior orbital fissure of

the sphenoid bone where it supplies the superior oblique

muscle of the eye that controls downward and lateral

movement of the eyeball.

The Trochlear Nerve

Lesion of the Trochlear Nerve

1. Diplopia on looking down and out.

2. Limitation of movement during examination for eye

movement down and out.

Abducent nerve: (Latin for "abduction").

The abducent nerve is so called because lateral rectus

muscle (which it supplies) abducts the eyeball.

Function: motor nerve → movement of the eye ball →

supplies the lateral recti muscles (abduction).

Site of the nucleus: it lies in the lower part of the ventral

surface of pons.

The Abducent Nerve (VI)

The abducent nerve is purely a motor nerve.

The abducent nerve emerges from the lower border of

the pons (between the pons and medulla oblongata).

The abducent nerve travels the medial wall of the

cavernous sinus and then enters the orbit via the

superior orbital fissure of the sphenoid bone where it

supplies the lateral rectus muscle of the eye that

controls abduction of the eye.

The Abducent Nerve

1. Diplopia on looking out wards.

2. Limitation during examination of eye movement in the

outward direction.

3. Convergent paralytic squint.

Lesion of the Abducent Nerve