Peripheral Nervous System Chapter 14. Spinal Nerves 31 pairs of spinal nerves are connected to the...
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Transcript of Peripheral Nervous System Chapter 14. Spinal Nerves 31 pairs of spinal nerves are connected to the...
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Peripheral Nervous System
Chapter 14
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Spinal Nerves
• 31 pairs of spinal nerves are connected to the spinal cord– Numbered according to the portion of the vertebral
column at which they exit• 8 cervical nerve pairs• 12 thoracic nerve pairs• 5 lumbar nerve pairs• 5 sacral nerve pairs• 1 coccygeal nerve pair
– All spinal nerves carry both motor and sensory fibers so they are designated as mixed nerves
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Structure of Spinal Nerves• Ventral and dorsal roots join to form spinal
nerves• Each spinal nerve branches into a dorsal
ramus and ventral ramus. (plural = rami)
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Nerve Plexuses• The ventral rami subdivide to form complex
networks call plexuses– All spinal nerves except T2-T12
• Each nerve that emerges from a plexus contains all the nerve fibers that innervate a particular region of the body
• Four major subdivisions (Table 14-1):– Cervical plexus (C1-C4)– Brachial plexus (C5-T1)– Lumbosacral plexus (L1-S4)– Coccygeal plexus (S5 & coccygeal nerve)
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Dermatomes & Myotomes
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Dermatomes• Dermatome: a skin surface area supplied by
sensory fibers of a given spinal nerve
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Myotome• Myotome: a skeletal muscle or group of
muscles that receives motor axons from a given spinal nerve
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Cranial Nerves
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Cranial Nerves• Olfactory Nerve (I)
– Sensory– Sense of smell
• Optic Nerve (II)– Sensory– vision
• Oculomotor Nerve (III)– Motor– Eye movements, regulation of pupil size
• Trochlear Nerve (IV)– Motor– Eye movements
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Cranial Nerves• Trigeminal Nerve (V)
– Mixed– Sensations of head and face, proprioception– Chewing movements
• Abducens Nerve (VI)– Motor– Abduction of eye
• Facial Nerve (VII)– Mixed– Taste– Facial expressions, secretion of saliva & tears
• Vestibulocochlear Nerve (VIII)– Sensory– Balance, equilibrium, hearing
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Cranial Nerves• Glossopharyngeal Nerve (IX)
– Mixed– Sensations of tongue, reflex control of blood pressure & respiration– Swallowing movements, secretion of saliva
• Vagus Nerve (X)– Mixed– Sensations and movements of organs supplied (ex: slows heart,
increases peristalsis, contracts muscles for voice production)• Accessory Nerve (XI)
– Motor– Shoulder movements, turning head movements, movement of
viscera, voice production• Hypoglossal Nerve (XII)
– Motor– Tongue movements
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Cranial Nerves Acronyms
• Names:On Old Olympus’ Tiny Tops, A Friendly Viking Grew Vines And Hops
• Functional Classification:Some Say ‘Marry Money’; But My Brother Says ‘Bad Business, Marry Money’
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Reflexes
• A reflex is the action that results from a nerve impulse passing over a reflex arc– A predictable response to a stimulus– Conscious or unconscious– Somatic Reflexes• Skeletal muscle contraction
– Autonomic Reflexes• Contraction of smooth or cardiac muscle; glandular
secretion
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Somatic Reflexes of Clinical Importance
• In certain diseases or after trauma to the nervous system certain reflexes may be abnormal
• Testing of reflexes is a valuable diagnostic tool
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Stretch Reflexes
• Knee jerk or patellar reflex– Extension of lower leg in response to tapping
patellar tendon– L2-L4 segments of the spinal cord
• Ankle jerk or Achilles reflex– Plantar flexion of the foot in response to tapping
the Achilles tendon– S1-S2 segments of the spinal cord
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Stretch Reflexes
• Biceps Reflex– Flexion at the elbow in response to tapping the
brachii tendon– C5-C6 segments of the spinal cord
• Triceps Reflex– Extension at the elbow in response to tapping
proximal to the elbow– C6-C7 segments of the spinal cord
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Cutaneous Reflexes• Cutaneous reflexes result from stimulation of the
skin receptors• Babinski Reflex– Reflex in response to stimulation of the outer portion of
the sole of the foot (make a ‘J’ from the heel along the lateral edge through the ball of the foot)
– Infant (to 1 ½ yrs): extension and fanning of toes– Children & adults: plantar flexion– Change in response due to corticospinal tract becoming
fully myelinated– A + babinski’s in an adult means destruction to the
corticospinal tract
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Cutaneous Reflexes
• Abdominal Reflex– Drawing in of the abdominal wall in response to
stroking the side of the abdomen– T9-T12 spinal nerves and segments of the spinal
cord
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Quiz yourself on a sheet of paperMatch the following cranial nerve with the correct
function (write it out)• Olfactory A. taste, facial expression• Vagus B. hearing, balance• Facial C. sensation of head/face;
chewing movements
• Vestibulocochlear D. sense of smell• Trigeminal E. sensation/movement of
organs
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Quiz yourself on a sheet of paper Warm Up:1. What are the 3 parts of the diencephalon? Name one
function for each part.2. Differentiate between a dermatome and myotome.3. What are the 5 sections of spinal nerves? How many
spinal nerve pairs are in each section?