Peripheral Nervous System. Cranial Nerves – Part 1

1. The Department of Human anatomy
Peripheral nervous
system.
The Cranial Nerves Part - 1

2. Plan
 The peripheral nervous system-
Structural Organization
 spinal nerves
 cranial nerves
 ganglia

3.  The peripheral nervous system (PNS) consists
of the nerves and ganglia outside of the
brain and spinal cord. The main function of the
PNS is to connect the central nervous
system (CNS) to the limbs and organs. Unlike
the CNS, the PNS is not protected by the bone
of spine and skull, or by the blood–brain barrier,
leaving it exposed to toxins and mechanical
injuries. The peripheral nervous system is
divided into the somatic nervous system and the
autonomic nervous system.

4. Nervous System: Structural
Organization
Structural subdivisions of the nervous system:
 Central nervous system (CNS)
 brain and spinal cord
 Peripheral nervous system (PNS)
 cranial nerves (nerves that extend from the brain)
 spinal nerves (nerves that extend from the spinal
cord)
 ganglia (clusters of neuron cell bodies (somas)
located outside the CNS)

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7. Functional Organization of the PNS
Figure 14.1

8. Spinal Nerves
 31 pairs – contain thousands of nerve
fibers
 Connect to the spinal cord
8 pairs of cervical nerves (C1-C8)
12 pairs of thoracic nerves (T1-T12)
5 pairs of lumbar nerves (L1-L5)
5 pairs of sacral nerves (S1-S5)
1 pair of coccygeal nerves (Co1)

9. Spinal Nerves
Posterior View
Figure 14.9

10. Spinal Nerves
 Posterior root– contains
sensory fibers
 Anterior root– contains
motor fibers
 Just outside the spinal
cord there is a spinal
ganglion consisting of
nerve cells
 Anterior and posterior roots join
to form mixed spinal nerve
 Outside the intervertebral
foramen the spinal nerve divides
into :
1. Ramus communicans (white
and gray)
2. Ramus dorsalis
3. Ramus ventralis
4. Ramus meningeus

13. Innervation of the Skin:
Dermatomes
 Dermatome – an area of skin
Innervated by cutaneous branches of a single
spinal nerve
 Upper limb – skin is supplied by nerves of
the brachial plexus
 Lower limb
Lumbar nerves – anterior surface
Sacral nerves – posterior surface

14. Map of Dermatomes – Anterior
View
Figure 14.17a

15. Map of Dermatomes – Posterior
View
Figure 14.17b

16. The plexuses
Forms by ventral rami
 Cervical plexus
 Brachial plexus
 Lumbar plexus
 Sacral plexus
 Coccygeal plexus
 Thoracic ventral rami
do not form nerve
plexuses

17.  Cervical plexus (C1-C4)
innervates the muscles and
skin of the neck and
shoulder
most important:
Its phrenic nerve* (C3-C5)
is the sole motor supply of
diaphragm: one reason
why neck injuries are so
dangerous – can be lethal
(respiratory arrest = stop
breathing)

19. Brachial plexus
 Serves upper limbs
and shoulder girdle
 Arises primarily from
C5-T1
 Main nerves:
 Musculocutaneous – to
arm flexors
 Median – anterior
forearm muscles and
lateral palm
 Ulnar – anteromedial
muscles of forearm and
medial hand
 Axillary – to deltoid and
teres minor
 Radial – to posterior
part of limb

20. Musculo-
cutaneous
Median
Ulnar
Axillary
Radial

21. Lumbar plexus
 L1-L4
 Lies within the psoas major muscle
 Innervates anterior and medial muscles of
thigh through femoral and obturator
nerves respectively
 Femoral nerve also innervates skin on
anterior thigh (including quads) and
medial leg

23. Sacral plexus
 L4-S4
 Supplies muscles
and skin of
posterior thigh
and almost all of
the leg
 Main branch is
the large sciatic
nerve,

24. Coccygeal plexus
 This plexus is formed by
the fifth sacral nerve
(with a contribution from
S4) and the
coccygeal nerve. It gives
rise to the
anococcygeal nerve
(provides sensory
innervation to the skin
over the coccyx)

25. Names of cranial nerves
 Ⅰ Olfactory nerve
 Ⅱ Optic nerve
 Ⅲ Oculomotor nerve
 Ⅳ Trochlear nerve
 Ⅴ Trigeminal nerve
 Ⅵ Abducent nerve
 Ⅶ Facial nerve
 Ⅷ Vestibulocochlear nerve
 Ⅸ Glossopharyngeal nerve
 Ⅹ Vagus nerve
 Ⅺ Accessory nerve
 Ⅻ Hypoglossal nerve

26. Classification of cranial nerves
 Sensory cranial nerves: contain only afferent (sensory)
fibers
 ⅠOlfactory nerve
 ⅡOptic nerve
 Ⅷ Vestibulocochlear nerve
 Motor cranial nerves: contain only efferent (motor) fibers
 Ⅲ Oculomotor nerve
 Ⅳ Trochlear nerve
 ⅥAbducent nerve
 Ⅺ Accessory nerv
 Ⅻ Hypoglossal nerve
 Mixed nerves: contain both sensory and motor fibers---
 ⅤTrigeminal nerve,
 Ⅶ Facial nerve,
 ⅨGlossopharyngeal nerve
 ⅩVagus nerve

27. Cranial Nerve I: Olfactory
 Arises from the olfactory epithelium
 Passes through the cribriform plate of the ethmoid bone
 Fibers run through the olfactory bulb and terminate in the
primary olfactory cortex (uncus)
 Functions solely by carrying afferent impulses for the sense of
smell
 Lesions result in ANOSMIA

28. Cranial Nerve II: Optic
 Arises from the retina of the
eye
 Optic nerves pass through the
optic canals and converge at
the optic chiasm
 They continue to the thalamus
where they synapse
 From there, the optic radiation
fibers run to the visual cortex
 Functions solely by carrying
afferent impulses for vision

29. Cranial Nerve III: Oculomotor
 Fibers extend from the ventral midbrain, pass
through the superior orbital fissure, and go to the
extrinsic eye muscles
 Functions in raising the eyelid, directing the
eyeball, constricting the iris, and controlling lens
shape
 The latter 2 functions are parasympathetically
controlled
 Parasympathetic cell bodies are in the ciliary
ganglia

30. Cranial Nerve III: Oculomotor
Figure III from Table 13.2

31. Cranial Nerve IV: Trochlear
 Fibers emerge from the dorsal midbrain
and enter the orbits via the superior orbital
fissures; innervate the superior oblique
muscle
 Primarily a motor nerve that directs the
eyeball

32. Cranial Nerve IV: Trochlear
Figure IV from Table 13.2

33. Cranial Nerve V: Trigeminal
 Composed of three divisions
 Ophthalmic (V1)
 Maxillary (V2)
 Mandibular (V3)
 Fibers run from the face
to the pons via the
superior orbital fissure
(V1), the foramen
rotundum (V2), and the
foramen ovale (V3)

34.  Ophthalmic nerve
 Sensory from the eyes,
conjunctiva and orbital
contents including the
lacrimal gland
 Maxillary nerve
 Sensory branches from
anterior and middle
cranial fossa,
nasopharynx, palate,
nasal cavity, teeth of
the upper jaw, maxillary
sinus, skin of the side
of the nose, lower
eyelid, cheek, upper lip
 Mandibular nerve
 Motor fibers innervate
muscles of mastication,
tensor tympani, anterior
belly of digastric
 Sensory fibres from the
skin of the lower face,
cheek, lower lip, ear,
external auditory
meatus and temporal
region, anterior two
thirds of the tongue,
teeth of the lower jaw,
mastoid air cells,
mucous membrane and
dura in the middle
cranial fossa

35.  Lesion involves loss of
sensation, weakness in
chewing, Jaw deviation towards
the affected side
 (Tic douloureux) or trigeminal
neuralgia
 - Most excruciating pain
known
 - Caused by inflammation of
nerve
 - In severe cases, nerve is
cut; relieves agony but results
in loss of sensation on that side
of the face

36. Cranial Nerve VI: Abducens
 Fibers leave the inferior pons and enter the orbit
via the superior orbital fissure
 Primarily a motor nerve innervating the lateral
rectus muscle (abducts the eye; thus the name
abducens)

37. Cranial Nerve VII: Facial
 Fibers leave the pons, travel through the internal
acoustic meatus, and emerge through the
stylomastoid foramen to the lateral aspect of the face
 Motor functions include;
 Facial expression
 Transmittal of parasympathetic impulses to
lacrimal and salivary glands (submandibular and
sublingual glands)
 Sensory function is taste from taste buds of anterior
two-thirds of the tongue

38. Cranial Nerve VII: Facial
Figure VII from Table 13.2

39. Facial Nerve (CN VII)
 Bell’s palsy: paralysis of facial
muscles on affected side and loss
of taste sensation
 Caused by herpes simplex I virus
 Lower eyelid droops
 Corner of mouth sags
 Tears drip continuously and eye
cannot be completely closed (dry
eye may occur)
 Condition may disappear
spontaneously without treatment

40. Cranial Nerve VIII:
Vestibulocochlear
 Fibers arise from the hearing and equilibrium
apparatus of the inner ear, pass through the
internal acoustic meatus, and enter the
brainstem at the pons-medulla border
 Two divisions – cochlear (hearing) and
vestibular (balance)
 Functions are solely sensory – equilibrium and
hearing

41. Cranial Nerve VIII: Vestibulocochlear
Figure VIII from Table 13.2

42. Cranial Nerve IX:
Glossopharyngeal
 Fibers emerge from the medulla, leave the skull
via the jugular foramen, and run to the throat
 Nerve IX is a mixed nerve with motor and
sensory functions
 Motor – innervates posterior 1/3 of the tongue
and pharynx, and provides motor fibers to the
parotid salivary gland
 Sensory – fibers conduct taste and general
sensory impulses from the tongue and pharynx

43. Cranial Nerve IX: Glossopharyngeal
Figure IX from Table 13.2

44. Cranial Nerve X: Vagus
 The only cranial nerve that extends beyond the
head and neck
 Fibers emerge from the medulla via the jugular
foramen
 The vagus is a mixed nerve
 Most motor fibers are parasympathetic fibers to
the heart, lungs, and visceral organs
 Paralysis leads to hoarseness
 Total destruction incompatible with life

45. Cranial Nerve X: Vagus

46. Cranial Nerve XI: Accessory
 Formed from a cranial root emerging from the
medulla and a spinal root arising from the
superior region of the spinal cord
 The spinal root passes upward into the
cranium via the foramen magnum
 The accessory nerve leaves the cranium via
the jugular foramen
 Innervates the trapezius and sternocleidomastoid,
which move the head and neck

47. Cranial Nerve XI: Accessory
Figure XI from Table 13.2

48. Cranial Nerve XII: Hypoglossal
 Fibers arise from the medulla and exit the
skull via the hypoglossal canal
 Innervates both extrinsic and intrinsic
muscles of the tongue, which contribute to
swallowing and speech
 If damaged, difficulties in speech and swallowing;
inability to protrude tongue

49. Cranial Nerve XII: Hypoglossal
Figure XII from Table 13.2