ap #14 PNS

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ap #14 PNS

spinal nerves

1. 31 pairs
2. Cauda equina
3. Structure
a. Ventral root & Dorsal root
b. Ramus (rami)
i. Dorsal ramus
1. Supplies somatic motor and sensory fibers muscles and skin of the posterior surface of the head, neck, and trunk
ii. Ventral ramus
a. Innervate muscles and glands in the extremities and lateral and ventral portions of neck and trunk
b. Autonomic motor fibers split from the ventral ramus
iii. Sympathetic rami

Ventral root

...

dorsal root

...

Ramus

1. Ramus (rami)
a. Dorsal ramus
1. Supplies somatic motor and sensory fibers muscles and skin of the posterior surface of the head, neck, and trunk
b. Ventral ramus
1. Innervate muscles and glands in the extremities and lateral and ventral portions of neck and trunk
2. Autonomic motor fibers split from the ventral ramus
c. Sympathetic rami

cervical plexus

1. Innervate the muscles and skin of the neck, upper shoulders, and part of the head
2. Phrenic nerve

brachial plexus

1. Innervate the lower part of the shoulder and all of the arm

lumbar plexus

1. Innervates thigh and leg
2. Femoral nerve

Sacral plexus and coccygeal plexus

1. Supply nearly all the skin of the leg, posterior thigh muscles, and leg and foot muscles
2. Sciatic nerve

Dermatomes & Myotomes

1. Dermatome-region of skin surface area supplied by afferent (sensory) fibers of a given spinal nerve
2. Myotome-skeletal muscle(s) supplied by efferent (motor) fibers of a given spinal nerve

Cranial nerves - Olfactory nerve

1. Sensory nerve
2. Carries information about sense of smell

Cranial nerves - Optic nerve

1. Sensory nerve
2. Unite to form optic chiasma
3. Carries visual information from the eyes to the brain

Cranial nerves - Vestibulocochlear Nerve

1. Sensory nerve
2. Vestibular nerve fibers
a. Originate in the semicircular canals
b. Carry the impulses of the sense of equilibrium
3. Cochlear nerve fibers
a. Originate in the organ of Corti
b. Carry the impulses of the sense of hearing

Cranial nerves - Vagus Nerve

1. Mixed nerve
2. Sensory fibers supply pharynx, larynx, trachea, heart, carotid body, lungs, bronchi, esophagus, stomach, small intestine, and gallbladder
3. Somatic motor fibers innervate the pharynx and larynx
4. Sensation & movement of organs supplied

Somatic motor nervous system

1. Includes all voluntary motor pathways outside the CNS
2. Effectors are skeletal muscles
3. Neurotransmitter is acetylcholine
4. Somatic reflexes
a. Knee jerk (also known as patellar reflex)
i. Extension of the lower leg in response to tapping the patellar tendon
b. Ankle jerk (also known as Achilles reflex)
i. Extension of the foot in response to tapping the Achilles tendon

Plantar reflex

Plantar flexion of all toes and a slight turning in and flexion of the anterior part of the foot in response to stimulation of the outer edge of the sole

Babinski reflex

1. Abnormal plantar reflex
2. Extension of great toe, with or without fanning of other toes, in response to stimulation of outer margin of sole of foot
3. Over 1-1/2 years of age, a positive Babinski reflex is one of the pyramidal signs indicating destruction of corticospinal fibers

Other reflexes - Corneal reflex

Winking in response to touching the cornea

Other reflexes - Abdominal reflex

1. Drawing in of the abdominal wall in response to stroking the side of the abdomen
2. Decreased or absent reflex may involve lesions of pyramidal tract upper motor neurons

Autonomic reflexes

1. May be spinal (e.g., urination and defecation) or modified by higher brain structures.
2. The thalamus, hypothalamus and brain stem are in charge of multiple reflexes - HR, BP, breathing, eating, osmotic balance, temperature, vomiting, gagging, sneezing.

Somatic nervous system vs. autonomic nervous system

Somatic nervous system:
1. Voluntary
2. Skeletal muscle
3. Single efferent neuron
4. Axon terminals release acetylcholine
5. Always excitatory
6. Controlled by the cerebrum

Somatic nervous system vs. autonomic nervous system

Autonomic nervous system
1. Involuntary
2. Smooth, cardiac muscle; glands
3. Multiple efferent neurons
4. Axon terminals release acetylcholine or norepinephrine
5. Can be excitatory or inhibitory
6. Controlled by the homeostatic centers in the brain - pons, hypothalamus, medulla oblongata

autonomic nervous system - functions

1. Major functions
a. To regulate heartbeat
b. Smooth muscle contraction
c. Glandular secretions
d. To maintain homeostasis
Two efferent divisions - sympathetic division and parasympathetic division

autonomic nervous system - 2 efferent divisions

sympathetic division and parasympathetic division

autonomic nervous system - pathways

1. Two neurons in the effector pathway.
2. 1st neuron is preganglionic neuron
a. Cell body in gray matter of brain or spinal cord.
b. Synapses with postganglionic neuron
3. 2nd neuron is postganglionic neuron
a. Cell body in autonomic ganglion
b. Synapses with effector

Function of ANS

1. Regulates visceral effectors in ways that tend to maintain or quickly restore homeostasis
2. Sympathetic and parasympathetic divisions often exert antagonistic influences on visceral effectors
3. Major function of sympathetic division is that it serves as an " emergency" system-the flight or fight reaction
4. Parasympathetic division is the dominant controller of most autonomic effectors most of the time - Rest and restore reaction

Enteric nervous system

1. Third division of ANS
2. Extensive network in digestive tract walls
3. Complex visceral reflexes coordinated locally
4. Roughly 100 million neurons
5. Intrinsic set of nerves - "brain of gut"
6. Neurons extending from esophagus to anus
7. 2 plexuses
a. Myenteric plexus - GI tract motility
b. Submucosal plexus - controlling secretionsEnter

Enteric nervous system - 2 plexuses

a. Myenteric plexus - GI tract motility
b. Submucosal plexus - controlling secretionsEnter

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