It's all about anatomy of spinal cord and peripheral nerves

1. CHAPTER 2CHAPTER 2
SPINAL CORD AND PERIPHERALSPINAL CORD AND PERIPHERAL
NERVESNERVES
By Hermizan Bin HalihanafiahBy Hermizan Bin Halihanafiah

2.  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.

4. Divide into two:
 External anatomy
 Internal anatomy

5.  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.

6. 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

7.  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.

11. 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.

13. 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.

14. 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”

17. 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

19. 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.

23.  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

25. 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).

27. INTERNAL ANATOMY cont..
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.

30. INTERNAL ANATOMY
cont..
 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.

31. INTERNAL ANATOMY cont..
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.

33. 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.

35. 1. Connecting between brain and peripheral nerves
(CNS and PNS)
2. Serve as a center for coordinating certain
reflexes.

37.  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

38.  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)

40. 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.

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 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.

43. Hermizan Halihanafiah
 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.

44. Hermizan Halihanafiah
 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.

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 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.

47. Hermizan Halihanafiah
 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).

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 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).

50. Hermizan Halihanafiah
 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.

51. Hermizan Halihanafiah
 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).

52. Hermizan Halihanafiah
 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.

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

54. Hermizan Halihanafiah
 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.

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 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.

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 Mixed nerve
 Largest cranial nerve
 2 roots from
venterolateral of the
pons
 Have large sensory
root and small motor
root

57. Hermizan Halihanafiah
 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

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 Consists 3
branches
◦ Ophtalmic
◦ Maxillary
◦ Mandibular

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 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.

60. Hermizan Halihanafiah
 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.

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 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

62. Hermizan Halihanafiah
 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.

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64. Hermizan Halihanafiah
 Motor nerve
 Origin – abducens nucleus of the pons

65. Hermizan Halihanafiah
 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.

66. Hermizan Halihanafiah
 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.

67. Hermizan Halihanafiah
 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.

68. Hermizan Halihanafiah
 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.

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

70. Hermizan Halihanafiah
 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.

71. Hermizan Halihanafiah
 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.

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 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

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 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.

74. Hermizan Halihanafiah
 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.

75. Hermizan Halihanafiah
 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.

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 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.

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 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.

78. Hermizan Halihanafiah
 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.

79. Hermizan Halihanafiah
 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.

80. Hermizan Halihanafiah
 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.

81. Hermizan Halihanafiah
 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.

82. Hermizan Halihanafiah
 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.

83.  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.

84.  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.

86.  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.

87.  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.

88. Definition
 The simplest type of nerve pathway.
 Implies an automatic, unconscious, protective
response to a situation in an attempt to maintain
body homeostasis.

90. Consists 5 components:
 Sensory receptors
 Sensory neuron
 Integrating center
 Motor neuron
 Effector

92.  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