Peripheral Nervous System
Chapter 14
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
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•
•
•
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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
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)
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):
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–
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Cervical plexus (C1-C4)
Brachial plexus (C5-T1)
Lumbosacral plexus (L1-S4)
Coccygeal plexus (S5 & coccygeal nerve)
Dermatomes & Myotomes
Dermatomes
• Dermatome: a skin surface area supplied by
sensory fibers of a given spinal nerve
Myotome
• Myotome: a skeletal muscle or group of
muscles that receives motor axons from a
given spinal nerve
Cranial Nerves
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
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
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
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’
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
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
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
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
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
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
Quiz yourself on a sheet of paper
Match 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
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?