section 5, chapter 11

Cranial and Spinal Nerves

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The PNS consists of

31 pairs of Spinal nerves arising from the spinal cord

Peripheral Nervous System

Sensory fibers relay information from receptors to CNS

Somatic (voluntary) fibers connecting to the skin and skeletal muscles

Autonomic fibers connecting to viscera (involuntary)

12 pairs of Cranial nerves arising from the brain

Structure of a Peripheral Nerve

Peripheral nerves consist of bundles of nerve fibers encased by connective tissue.

Connective Tissue Coverings1.Epineurium – outermost layer

2.Perineurium – Surrounds fasicles

3.Endoneurium – surrounds individual nerve fibers

Fasicle – organized bundle of nerve fibers.

Blood vessels pass through perineurium and epineurium. Capillaries within endoneurium provide oxygen and nutrients to the neurons.

Figure 11.24. Scanning electron micrograph of a peripheral

nerve. Nerve fibers are organized into bundles, called fascicles.

Structure of a Peripheral Nerve

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Nerve and Nerve Fiber Classification

• Sensory nerves - conduct impulses into brain or spinal cord

• Motor nerves - conduct impulses to muscles or glands

• Mixed (both sensory and motor) nerves• Contain both sensory nerve fibers and motor nerve fibers• Most nerves are mixed nerves• ALL spinal nerves are mixed nerves (except the first pair)

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Cranial Nerves (CN) I - IV

Olfactory nerves (CN I) transmit impulses associated with smell

Optic nerves (CN II) transmit impulses associated with vision

Oculomotor nerve (CN III) Motor impulses to muscles that move the eyes, the eyelids, iris, and the lens

Trochlear nerve (CN IV) Motor impulses to muscles that move the eyes (superior oblique)

Cranial Nerve V

Trigeminal nerve (CN V) - Motor to muscles of mastication (chewing)

3 BranchesOphthalmic branch – sensory around eyes

Maxillary branch – sensory of upper jaw & teeth

Mandibular branch – sensory of lower jaw & teeth

Cranial Nerves VI and VII

Abducens nerve (CN VI) - motor impulses to lateral rectus muscles of eye = eye movement

Facial nerve (CN VII) - sensory from taste receptors and motor to muscles of facial expression

Figure 11.27 the facial nerves are associated with taste receptors on the tongue and with

muscles of facial expression.

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Cranial Nerves VIII and IXVestibulocochlear nerve (CN VIII)

Vestibular branch - Sensory from equilibrium receptors of ear

Cochlear branch - Sensory from hearing receptors

Glossopharyngeal nerve (CN IX)Sensory of tongue - taste

Motor to salivary glands

Motor to pharynx - swallowing

Cranial Nerve X

• Vagus nerve (CN X) “Wandering”Mixed nerve

• Somatic motor to muscles of speech and swallowing

• Autonomic motor to viscera of thorax and abdomen

• Sensory from pharynx, larynx, esophagus, and viscera of thorax and abdomen

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Figure 11.28 the vagus nerves extend from medulla downward through thorax and abdomen to supply many organs

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Cranial Nerves XI and XII

Accessory nerve (CN XI)• Motor to muscles of soft palate, pharynx and larynx

•Motor to muscles of neck and back

Hypoglossal nerve (CN XII)• Motor to muscles of the tongue

Cranial NervesCranial Nerves

I. OlfactoryII. OpticIII. OculomotarIV. TrochlearV. TrigeminalVI. AbducensVII. FacialVIII.VestibulocochlearIX. GlossopharyngealX. VagusXI. AccessoryXII. Hypoglossal

I. OhII. Once III. One IV. Takes V. The VI. AnatomyVII. Final VIII.Very IX. Good X. Vacations XI. Are XII. Heavenly

Pneumonic Device for remembring the 12 pairs of cranial nerves

The 12 pairs of cranial nerves

Cranial NervesCranial Nerves

Spinal Nerves

• ALL are mixed nerves (except the first pair)

• 31 pairs of spinal nerves:

• 8 cervical nerves (C1 to C8)

• 12 thoracic nerves (T1 to T12)

• 5 lumbar nerves (L1 to L5)

• 5 sacral nerves (S1 to S5)

• 1 coccygeal nerve (Co or Cc)

Nerve Plexuses

A Nerve plexus is a complex network formed by anterior branches of spinal nerves• The fibers of various spinal nerves are sorted and recombined• There are three (3) nerve plexuses:

Cervical plexus• Formed by anterior branches of C1-C4 spinal nerves• Lies deep in the neck• Supply to muscles and skin of the neck• C3-C4-C5 nerve roots contribute to phrenic nerves bilaterally

Phrenic Nerves conduct motor impulses to the diaphragm

(C3,4, and 5 keep the diaphragm alive)

(2) Brachial plexusFormed by C5-T1 spinal nervesLies deep within shoulders

Branches include: 1. Radial Nerve • extensor muscles of forearm, wrist, and fingers• May be damaged with crutches

2. Ulnar Nerve • Intrinsic muscles of hand• Funny bone

3. Median Nerve • Flexor muscles of forearm, wrist, and fingers• Inflamed with carpal tunnel syndrome

Brachial Plexus

Figure 11.33 Nerves of the brachial plexusFigure 11.33 Nerves of the brachial plexus

Lumbosacral Plexus

• (3) Lumbosacral plexus• Formed by T12-S5

• Branches include: 1. Obturator nerve

• Supply motor impulses to adductors of thighs

2. Femoral nerve• Supply motor impulses to muscles of anterior thigh and sensory impulses from skin of thighs and legs

3. Sciatic nerve• Supply muscles and skin of thighs, legs and feet

Figure 11.34 Nerves of the lumbosacral plexus.

Figure 11.32. The ventral branches of spinal nerves give rise to three plexuses. In the thoracic region spinal nerves give rise to intercostal nerves.

The thoracic spinal nerves give rise to intercostal nerves

• Supply intercostal muscles

• Supply muscles of upper abdominal wall

• Receive sensory from skin of the thorax and abdomen

Thoracic Spinal Nerves

End of section 5, chapter 11