Chapter 11, Section 5
Cranial and Spinal Nerves
Peripheral Nervous System • 12 pairs of Cranial nerves arising from the brain • 31 pairs of Spinal nerves arising from the spinal cord
•Sensory fibers relay information from receptors to CNS • Somatic (voluntary) fibers connecting to the skin and skeletal muscles • Autonomic fibers connecting to viscera (involuntary)
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Structure of a Peripheral Nerve Peripheral nerves consist of bundles of nerve fibers encased by connective tissue.
Fasicle – organized bundle of nerve fibers. Connective Tissue Coverings 1. Epineurium – outermost layer 2.
Perineurium – Surrounds fasicles
3.
Endoneurium – surrounds individual nerve fibers
Structure of a Peripheral Nerve 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.
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 nerve (CN I) • Fibers transmit impulses associated with smell
• Optic nerve (CN II) • Fibers 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
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Cranial Nerve V • Trigeminal nerve (CN V) • “Three (3) twins” • Motor to muscles of mastication (chewing) • 3 Branches • Ophthalmic 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 • 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.
Cranial Nerves VIII and IX • Vestibulocochlear nerve (CN VIII) • Aka auditory nerve • Sensory nerve •Two (2) branches: • Vestibular branch • Sensory from equilibrium receptors of ear
• Glossopharyngeal nerve (CN IX) • Sensory of tongue - taste • Motor to salivary glands •Motor to pharynx - swallowing
• Cochlear branch • Sensory from hearing receptors
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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 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
• Hypoglossal nerve (CN XII) • Motor to muscles of the tongue
•Motor to muscles of neck and back
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Cranial Nerves
The 12 pairs of cranial nerves I. Olfactory II. Optic III. Oculomotar IV. Trochlear V. Trigeminal VI. Abducens VII. Facial VIII.Vestibulocochlear IX. Glossopharyngeal X. Vagus XI. Accessory XII. Hypoglossal
Pneumonic Device for remembring the 12 pairs of cranial nerves I. Oh II. Once III. One IV. Takes V. The VI. Anatomy VII. Final VIII.Very IX. Good X. Vacations XI. Are XII. Heavenly
Cranial 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
• Nerve plexus • Complex networks formed by anterior branches of spinal nerves • The fibers of various spinal nerves are sorted and recombined • There are three (3) nerve plexuses:
• (1) 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)
Brachial Plexus • (2) Brachial plexus • Formed by C5-T1 • Lies 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 Figure 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.
Thoracic Spinal 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 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.
End of Chapter 11, Section 5