chapter 011
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The Human Body in Health and Illness, 4th edition
Barbara Herlihy
Chapter 11:Nervous System: Spinal Cord and
Peripheral Nerves
Lesson 11-1 Objectives
• Describe the anatomy of the spinal cord and list its three functions.
• List five components of the reflex arc.
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Spinal Cord Structure
• Continuation of the brain stem
• Tubelike structure located in the spinal cavity
• Extends from foramen magnum to L1
• Diameter similar to the thickness of the thumb
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Lumbar Puncture
• CSF withdrawn from subarachnoid space between L3 and L4
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Spinal Cord Cross Section
• Gray matter– Inner H zone– Central canal
• White matter– Location of tracts
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Spinal Cord Tracts
Ascending: Sensory• Spinothalamic: Pain
pathway• Dorsal column• Spinocerebellar
Descending: Motor• Pyramidal: Major motor
tract• Extrapyramidal
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Spinal Cord Injuries
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Nerve Attachment to Spinal Cord
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Spinal Cord Function
• Sensory pathway• Motor pathway• Reflex center
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Reflex Arc: Five Components
• Receptor• Afferent neuron• Integrating
center• Efferent neuron• Effector organ
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Examples of Reflexes
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Lesson 11-2 Objectives
• List and describe the functions of the 12 pairs of cranial nerves.
• Identify the classification of spinal nerves.• List the functions of the three major plexuses.
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Nerve vs. Neuron
• Neuron: A single nerve cell
• Nerve: Bundles of neurons with fascia and blood supply
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Peripheral Nerves: Two Classification Systems
• Structural classification: Origin of the fiber– Cranial nerves– Spinal nerves
• Functional classification: Where nerves go and what they do– Somatic afferent nerves– Somatic efferent nerves– Autonomic nervous system (ANS)
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Cranial Nerves
• 12 pairs• Classification:
Sensory, motor, mixed
• Naming system: CN + Roman numeral (CN IV, CN V, CN X)
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Cranial Nerves (cont’d.)
• CN I: Olfactory nerve (smell)• CN II: Optic nerve (sight)• CN III: Oculomotor (most movements of
eyeball, eyelid, and pupil size)• CN IV: Trochlear (movement of eyeball)
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Cranial Nerves (cont’d.)• CN V: Trigeminal (chewing; sensations in face,
scalp, cornea, teeth)– Sensory arm of corneal reflex– Trigeminal neuralgia
• CN VI: Abducens (eyeball movement)• CN VII: Facial nerve (facial expression,
salivation, taste, tearing, and blinking)– Motor arm of corneal reflex– Bell’s palsy
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Cranial Nerves (cont’d.)
• CN VIII: Vestibulocochlear (hearing, balance)– Vestibular branch—balance– Cochlear branch—hearing– CN IX: Glossopharyngeal (swallowing, secretion of
saliva; taste)• Gag and blood pressure reflexes
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Cranial Nerves (cont’d.)
• CN X: Vagus (“wanderer” nerve) innervates many thoracic and abdominal organs and voice box; sensory arm of baroreceptor reflex
• CN XI: Accessory (head movement and shrugging shoulders, swallowing)
• CN XII: Hypoglossal (speech and swallowing)
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Spinal Nerves: 31 Pairs
• Cervical—8• Thoracic—12• Lumbar—5• Sacral—5• Coccygeal—1• Cauda equina
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Spinal Nerve: Plexuses
• Cervical – C1 to C4
• Brachial – C5 to C8, T1
• Lumbosacral – T12, L1-L5, S1-S4
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Some Important Spinal Nerves• From cervical plexus
– Phrenic
• From brachial plexus– Axillary– Radial, ulnar, median
• From lumbosacral– Femoral, obturator,
sciatic, tibial, common peroneal
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Examples of Nerve Involvement
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Dermatome• Area of skin
innervated by a spinal nerve
• Each named for the nerve serving it
• Used diagnostically to determine location of nerve damage
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