Spinal cord and peripheral nerve

CHAPTER 2CHAPTER 2SPINAL CORD AND PERIPHERAL SPINAL CORD AND PERIPHERAL

NERVESNERVES

By Hermizan Bin HalihanafiahBy Hermizan Bin Halihanafiah

Is a long, thin, tubular bundle of nervous system and support cell that extends from the brain.

The brain and spinal cord together make up the central nervous system.

Main pathway for information connecting the brain and peripheral nervous system.

Divide into two: External anatomy Internal anatomy

Protected by: Bony vertebrae Adipose tisue Spinal meninges Cerebrospinal fluid

The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.

MENINGES 3 layers: dura mater, arachnoid mater

and pia mater.1.Dura mater: outer layer, is tough, single

layered membrane is deep to the epidural space and superficial to the archnoid mater.

2.Arachnoid mater: middle layer, made of collagen fibers and some elastic fibers.

3.Pia mater: inner layer, transparent connective tissue layer that adhere to the surface of the spinal cord and brain

Epidural space is found within the space between vertebrae and the meninges which contain roots of the spinal nerves, the vertebral plexus of veins, small arteries, lymphatics and the epidural fat.

Subdural space is located between dura and arachnoid mater which contains interstitial fluid.

Subarachnoid space is located between the pia mater and arachnoid mater that contains cerebrospinal fluid.

EXTERNAL ANATOMY

In adults, it extend from the medulla oblongata, the inferior part of the brain to the superior border of the second lumbar vertebra.

In newborns it extend to the third or fourth lumbar.

The length is 42-45 cm and 2 cm diameter in the midthoracic region, larger in the lower cervical and midlumbar regions and smallest at the inferior tip.

EXTERNAL ANATOMY cont.. Inferior to lumbar enlargement, the spinal

cord terminates as a tapering, conical structure called the conus medullaris which ends at the level of intervertebral disc between the 1st and 2nd lumbar vertebra in adult.

From conus medullaris, arises filum terminale.

EXTERNAL ANATOMY cont.. Spinal cord is shorter than the vertebral

column, nerves that arise from the lumbar, sacral, coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exit the cord.

The roots of these spinal nerves angle inferiorly in the vertebral cavity form the end of the spinal cord like wisps of hair it is collectively called “cauda equina”

EXTERNAL ANATOMY cont.. Spinal nerves are the paths of

communication between the spinal cord and the nerves supplying specific regions of the body.

31 pairs of spinal nerves emerge at regular interval from intervertebral foramina.

There are:◦ 8 pairs of cervical nerves◦ 12 pairs of thoracic nerves◦ 5 pairs of lumbar nerves◦ 5 pairs of sacral nerves◦ 1 pairs of coccygeal nerves

EXTERNAL ANATOMY cont.. 2 bundles of axons called roots, connect

each spinal nerve to a segment of the cord.

The posterior (dorsal) root contains only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles and internal organs into the central nervous system

The anterior (ventral) root contains axons of motor neurons, which conduct nerve impulses from the CNS to effector organs and cells.

2 grooves penetrate the white matter of the spinal cord and divide it into right and left sides.

The anterior median fissure is a deep, wide groove on the anterior (ventral) side.

The posterior median sulcus is a shallower, narrow furrow on the posterior (dorsal) side.

The gray matter of the spinal cord is shaped like the letter H or butterfly and is surrounded by white matter.

INTERNAL ANATOMY

INTERNAL ANATOMY cont..

The gray matter consists of dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.

The white matter consists of primarily bundles of myelinated axons of neurons.

In the center of the gray matter is a small space called the central canal; it extends the entire length of the spinal cord and is filled with cerebropinal fluid (CSF).


Gray matter: Sensory nuclei receive input from sensory

receptors via sensory neurons, and motor nuclei provide output to effector tissues via motor neurons.

The gray matter on each side of the spinal cord is subdivided into regions called horns.

The posterior (dorsal) gray horns contain somatic and autonomic sensory nuclei.

The anterior (ventral) gray horns contain somatic motor nuclei, which provide nerve impulses for contraction skeletal muscles.


Between the anterior and posterior gray horns are lateral gray horns, which are present only in the thoracic, upper lumbar, and sacral segments of the spinal cord.

The lateral horns contain autonomic motor nuclei that regulate the activity of smooth muscle, cardiac muscle and glands.


White matter:

The white matter is organized into regions. The anterior and posterior gray horns

divide the white mater on each side into 3 broad areas called columns:◦Anterior (ventral) white ◦Posterior (dorsal) white◦Lateral white

Each column contains distinct bundles of axons having a common origin or destination and carrying similar information.

INTERNAL ANATOMY cont.. These bundles which may extend long

distances up or down the spinal cord, are called tracts.

Tracts are bundles of axons in the CNS; recall that nerves are bundles of axons in the PNS.

Sensory (ascending) tracts consist of axons that conduct nerve impulses to the brain.

Descending tracts consis of axons that carry nerve impulses from the brain to motor neuron.

Sensory and motor tracts of the spinal cord are continuous with sensory and motor tracts in the brain.

1. Connecting between brain and peripheral nerves (CNS and PNS)

2. Serve as a center for coordinating certain reflexes.

The 12 pairs of cranial nerves arise from the brain inside the cranial cavity and pass through various foramina in the bones of the cranium.

Divides into 3 functions: - Sensory nerves- Motor nerves and - Mixed nerves

Olfactory nerve (I) Optic nerve (II) Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Facial nerve (VII) Vestibulocohlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII)

Hermizan Halihanafiah

Sensory nerve Contain axons that

conduct impulses for olfaction, the sense of smell.

The olfactory epithelium occupies the superior part of the nasal cavity, covering the inferior surface of the cribriform plate and extending down along the superior nasal conchae.



The olfactory receptors within the olfactory epithelium are bipolar neuron.

Each has a single odor sensitive dendrite projecting from one side of the cell body and an unmylinated axons extending from the other side.

Bundle of axons of olfactory receptors extend through about 20 olfactory foramina in the cribriform plate of the ethmoid bone.


Olfactory nerves end in the brain in paired masses of gray matter called the olfactory bulbs. Two extensions of the brain that rest on the cribriform plate.

Within the olfactory bulbs, the axon terminals of olfactory receptor form synapses with the dendrite and cell bodies of the next neurons in the olfactory pathway.

The axons of these neuron make up the olfactory tract, which extend posteriorly from the olfactory bulbs.

Axons in the olfactory tract end in the primary olfactory area in the temporal lobe of the temporal cerebral cortex.


Sensory nerve Contains axons that conduct nerve impulses

for vision. In the retina, rods and cones initiate visual

signals and relay them to bipolar cells, which transmit the signals to ganglion cells.

Axons of all ganglion cells in the retina of each eye join to form an optic nerve, which pass through the optic foramen.



Posterior to the eyeball, the two optic nerves merge to form the optic chiasm.

Within the chiasm, axons from the medial half of each eye cross to the opposite side, axons from the lateral half is remain on the same side.

Posterior to the chiasm, the regrouped axons, some from each eye, form the optic tracts.

Most axons in the optic tracts end in the lateral geniculate nucleus of the thalamus.


There, they synapse with neuron whose axons extend to the primary visual area in the occipital lobe of the cerebral cortex.

A few axons pass through the optic chiasm and then extend to the superior colliculi of the midbrain.

They synapse with motor neurons that control the extrinsic (move the eyeball) and intrinsic eye muscles (control light intensity).



Motor nerve Oculomotor nerve extends anteriorly and divides

into superior and inferior branches, both of which pass through the superior orbital fissure into the orbit.

Axons in the superior branch innervate the superior rectus (extrinsic eyeball muscle) and the levator palpebrae superioris (muscles of upper eyelid).


Axons in the inferior branch supply the medial

rectus, inferior rectus and inferior oblique

muscles (all extrinsic eyeball muscles).

Theses somatic motor neurons control

movements of the eyeball and upper eyelid.

The inferior branch of the oculomtor nerve

also provides parasympathetic innervation to

intrinsic eyeball muscles, which are smooth

muscles.


They include the ciliary muscles of the eyeball and the circular muscles (sphincter pupillae) of the iris.

Parasympatethic impulses propagate from oculomotor nucleus in the midbrain to the ciliary ganglion, a relay centre of the autonomic nervous system.

From the ciliary ganglion, parasympathetic axons to the ciliary muscles, which adjust the lens for near vision.

Other parasympathetic axons stimulate the circular muscles of the iris to contract when bright light stimulate the eye, causing decrease in the size of the pupil (constriction).


Proprioceptive sensory axons from the extrinsic eyeball muscles begin their course towards the brain in the oculomotor nerve but eventually leave the nerve to join ophthalmic branch of trigeminal nerve.

They do not return to the brain in the oculomotor nerve.

The cell bodies of the sensory axons reside in the trigeminal ganglion, and they enter the midbrain via trigeminal nerve.

These axons convey nerve impulses for proprioception, the nonvisual perception of the movements and position of the body, from extrinsic eyeball muscles.


Motor nerve Smallest cranial nerve Arises from posterior part of the brainstem.


The motor neurons originate in the trochlear nucleus in the midbrain, and axons from the nucleus pass through the superior orbital fissure of orbit.

These somatic motor axons innervate the superior oblique muscles of the eyeball. (extrinsic eyeball muscle that control movement of the eyeball)

Proprioceptive sensory axons from the superior oblique muscle begin their course toward the brain in the trochlear nerve but eventually leave the nerve to join ophtalmic branch of the trigeminal nerve.

They do not return to the brain in the trochlear nerve.

The cells body of sensory neurons reside in the trigeminal ganglion, and they enter the midbrain via trigeminal nerve.


Like those of the oculomotor nerve, these axons convey nerve impulses for proprioception, the nonvisual perception of the movements and position of the body, from extrinsic eyeball muscles.


Mixed nerve Largest cranial

nerve 2 roots from

venterolateral of the pons

Have large sensory root and small motor root


Large sensory root◦Has swelling part –

trigeminal ganglion◦Trigeminal ganglion

located in the fossa inner surface of petrous portion.

◦The trigeminal ganglion contain cell bodies of most of the primary sensory neurons.

Small motor root◦Originate from nucleus

in the pons


Consists 3

branches

◦Ophtalmic

◦Maxillary

◦Mandibular


Ophthalmic Branch

◦Smallest branches of T.N

◦Enter orbit through superior orbital fissure

◦Contain sensory axon from; (1) skin over

upper eyelid, (2) eyeball, (3) lacrimal gland,

(4) upper part of nasal cavity, (5)side of the

nose, forehead, anterior half of the scalp.


Maxillary Branch

◦ Intermediate in size

◦Enter the foramen rotundum of sphenoid

◦Contain sensory axon from; (1)mucosa layer

of the nose, (2) palate, (3) part of the

pharynx, (4) upper teeth, (5) upper lips, (6)

lower eyelid.


Mandibular Branch◦Largest T.N ◦Exits through the foramen ovale of sphenoid◦Contain sensory axons from : (1) anterior 2/3

tongue, (2) cheek and mucosa deep into it, (3) lower teeth, (4) skin over the mandible and side of the head anterior to the ear, (5) mucosa of the floor of the mouth.

The sensory axons from 3 branches enter the trigeminal ganglion and terminate in the nuclei in the pons.

The trigeminal nerve also contain sensory fiber from proprioceptors located in the muscles of the mastication


Somatic motor axons of the trigeminal nerve

are part of the mandibular nerve and supply

muscles of mastication.

Masseter, temporalis, medial and lateral

pterygoid, anterior belly of digastric,

mylohyoid and tensor tympani.

Important control chewing movements.



Motor nerve

Origin – abducens nucleus of the pons


Proprioceptive sensory axons from the lateral rectus muscle begin their course toward the brain in the abducens nerve but eventually leave the nerve to join ophtalmic branch of the trigeminal nerve.

They do not return to the brain in the abducens nerve.

The cells body of sensory neurons reside in the trigeminal ganglion, and they enter the midbrain via trigeminal nerve.

These axons convey nerve impulses for proprioception, the nonvisual perception of the movements and position of the body, fro extrinsic eyeball muscles.


Mixed nerve Sensory axons extend from the taste buds of

the tongue (anterior 2/3) through the geniculate ganglion (a cluster of cell bodies of sensory neuron that lies beside facial nerve, and end in the pons)

Sensory portion of the facial nerve also contain axons from proprioceprors in muscles of the face and scalp and from skin in the ear canal.


Axons of somatic motor

neurons arise from nucleus

in the pons, pass through

petrous portion of temporal

and innervate facial, scalp

and neck muscles.

Innervations this axons

cause contraction of facial

expression muscles, plus

stylohyoid, posteriorbelly of

digastric, and stapedius in

the ear.


Axons of parasymapthetic

neuron that are part of

the facial nerve end in 2

parasymapthetic ganglia;

pterygopalatine and

submandibular ganglion.

From this 2 ganglia, other

parasympathic axons

extends to the lacrimal

gland, nasal gland,

palatine gland, sublingual

and submandibular gland.


Acoustic @ Auditory nerve Sensory nerve Has 2 branches; vestibular and cochlear branches.


Vestibular branch◦ Carry impulses fro equibilirium◦ Sensory axons in the vestibular branch arise from

semicircular canals, the saccule, and the utricle of the inner ear.

◦ Then extend to the vestibular ganglion, where the cell bodies are located.

◦ And end in the vestibular nuclei in the medulla oblongata.

◦ Some sensory axons enter the cerebellum via the inferior cerebellar peduncle.


Cochlear Branch

◦ Carry impulses for hearing

◦ Sensory axons in the cochlear branch arise in the

spiral organ (Organ of Corti) in the cochlea of the

inner ear.

◦ The cell bodies of cochlear branch sensory neurons

are located in the spiral ganglion of the cochlea.

◦ From there axons extend to cochlear nuclei in the

medulla oblongata.


Mix nerve Sensory axons of GN arise from :

◦Taste buds and somatic sensory receptor on the posterior 1/3 of tongue

◦Proprioceptors in swallowing muscles supply by motor portion

◦Baroreceptors in the carotid sinus◦Chemoreseptor in the carotid body


The cell bodies of these sensory neurons are located in the superior and inferior ganglia.

From these ganglia, sensory axons pass through the jugular foramen and end in the medulla oblongata.


Axons of motor neurons in GN arise in nuclei of the MO and exit the skull through the jugular foramen.

Somatic motor neuron innervate the stylopharyngeus muscle and autonomic motor neurons (parasympathetic) stimulate the parotid gland to secrete saliva.

Some of the sell bodies of parasymapthetic motor neuron are located in the otic ganglion.


Mixed nerve Sensory axon arise from:

◦ Skin of the external ear

◦ A few taste bud in the epiglottis and pharynx

◦ Proprioceptors in muscles of the neck and throat

◦ Baroreceptor in the arch of aorta

◦ Chemoreceptor in the aortic bodies

◦ Visceral sensory receptors in the most organs of thoracic and abdominal cavities.


These axons pass through the jugular foramen and end in the MO and pons

The soatic motor neurons, arise from nuclei in the MO and supply muscle of the pharynx, larynx, and soft palate that used in swallowing and vocalization.


Axons autonomic motor neuron

(parasympathetic) in the vagus nerve

originate in nuclei of MO and end in the lungs

and heart.

Vagal parasympathetic axons also supply

gland of GIT and smooth muscles of

respiratory tract, esophagus, stomach,

gallbladder, small intestine and most of the

large intestine.


Motor nerve Motor axons arise in the anterior gray of the 1st

5 segments of the cervical portion of the spinal cord.

The axons from the segment exit the spinal cord laterally and come together, pass through the foramen magnum and exit through the jugular foramen along with the vagus nerve.


The AN convey motor impulses to the sternocleidomastoid and trapezius muscles to coordinate head movement.

Sesnory axons in the AN originate from proprioceptors in the muscles supplied by its motor neurons begins their course toward the brain in the AN but eventually leave the nerve and to join the cervical plexus.


From cervical plexus, they enetr the spinal cord via the posterior root of the cervical spinal nerve to pass to and end in the MO.

The sensory axon do not return to the barin in the AN and, like all sensory axon, have their cell bodies in posterior root ganglion.


Motor nerve Somatic motor axons originate in the

hypoglossal nuclei in the MO, pass through the hypoglossal canal, and supply the muscles of the tongue.

These axons conduct impulses for speech and swallowing.


Sensory axons that originate from proprioceptors in the tongue muscles begin their course towards the brain in the hypoglossal nerve.

They leave the nerve and join cervical spinal nerve and end in the MO, again entering the CNC via posterior root of cervical spinal nerve.

The sensory axons do not return to the brain in the hypoglossal nerve.

Spinal nerve are the path of communication between the spinal cord and the specific region of the body

31 pairs Spinal nerve follows the name of

corresponding vertebra column. Consists cervical spinal nerve, thoracic

spinal nerve, lumbar spinal nerve, sacral spinal nerve and coccyx spinal nerve.

Emerge from spinal cord and through the intervertebral foramina.

Spinal nerves:1. 8 pairs of cervical spinal nerves

2. 12 pairs of thoracic spinal nerves

3. 5 pairs of lumbar thoracic nerves.

4. 5 pairs of sacral spinal nerves

5. 1 pairs of coccygeal spinal nerves.

Cervical and thoracic spinal nerves arise and leave at corresponding vertebra .

Because the spinal cord are shorter than vertebra column, nerve that arise from lumbar, sacral and coccyx region of spinal cord do not leave the vertebra column at the same level where they exit the cord.

The root of these spinal nerves angle inferiorly in the vertebral canal from the end of spinal cord like wisps of hair.

These root of this nerve, collectively called cauda equina.

Typical spinal nerve has 2 connection to spinal cord; posterior and anterior root.

Posterior and anterior root unite to form spinal nerve at intervertebral foramina.

Since posterior root contain sensory axons and anterior root contain motor axons, spinal nerves is classified as a mixed nerve.

Posterior root contain posterior root ganglion which cell bodies of sensory neuron is located.

Definition The simplest type of nerve pathway. Implies an automatic, unconscious,

protective response to a situation in an attempt to maintain body homeostasis.

Consists 5 components: Sensory receptors Sensory neuron Integrating center Motor neuron Effector

Types of reflexes

◦ Visceral (autonomic) reflex Involve responses of smooth muscle, cardiac

muscles and gland.

◦ Somatic reflex Involve contraction of skeletal muscles.

Types of somatic reflexes:◦ Stretch reflex◦ Tendon reflex◦ Flexor (withdrawal) reflex◦ Crossed extensor reflex

Health & Medicine

Spinal cord and peripheral nerve