Download Anatomy and Physiology I – Fall 2014 Lecture 17 – Nervous System

Anatomy and Physiology I – Fall 2014
Lecture 17 – Nervous System 3
I.
Two Components of PNS
A. Nerves
B.
II.
Ganglia (ganglion = singular)
1.
Dorsal root ganglia
2.
Vertebral ganglia – sympathetic
3.
Terminal ganglia - parasympathetic
4.
Collateral ganglia - visceral
Nerve Groupings and Coverings
A. Nerve fibers (axon) surrounded by endoneurium (conn. tis)
B.
Fascicle; surrounded by perineurium (connective tissue)
C.
Nerve; surrounded by epineurium (connective tissue)
Sensory nerves = axons conducting sensory info. from receptors
to brain or spinal cord
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Motor nerves = axons carries messages away from brain or spinal
cord to effector structures (muscle or glands)
Mixed nerves - both sensory and motor nerve fibers
III.
Cranial Nerves
12 pairs of nerves from brain to head/face/thoracic/abdominal cavities
Olfactory (I) – sense of smell
Optic (II) – vision
Oculomotor (III) – eye movement
Trochlear (IV)
Trigeminal (V)
Abducens (VI)
Facial (VII) – taste and facial expression
Vestibulocochlear (Auditory) (VIII) – hearing and balance
Glossopharyngeal (IV)
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Vagus (X) – voice, swallowing, slowing of heartbeat,
speeding up movement of food through gut
Accessory (XI)
Hypoglossal (XII)
IV. Spinal Nerves
31 pairs of nerves from spinal cord branch out to trunk and limbs
C1-C8 from cervical region
T1-T12 from thoracic region
L1-L5 from lumbar
S1-S5 from sacrum
CX from coccyx
Sensory impulses enter through dorsal root of spinal cord
Motor impulses leave via ventral root
Two roots unite to form spinal nerve, leaves vertebrae column
through intervertebral foramina
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SOMATIC NERVOUS SYSTEM
Transmits impulses for voluntary actions; 1 neuron carries signal
from brain to skeletal muscle
AUTONOMIC NERVOUS SYSTEM
Transmits impulses for involuntary actions; 2 neurons carry signal
from brain to: 1) cardiac or smooth muscle, 2) glands, 3) gut
Consists of motor neurons
I.
Functions
Involuntary activity - heart rate, movement of food through
digestive tract, secretions by glands
II.
Divisions
A. Sympathetic
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III.
B.
Parasympathetic
C.
Visceral
Anatomy – autonomic neurons function as 2- neuron relays
A. Preganglionic neurons
Cell bodies and dendrites in gray matter of spinal cord/brain
Axons end in ganglia; synapse with dendrites of
postganglionic neurons
B.
Postganglionic neurons
In ganglion, dendrites synapse with axon of
preganglionic neurons
Carry impulse to cell body found in ganglion. Impulses
pass out axon to cardiac/smooth muscle or gland
II.
Sympathetic Nervous System
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A.
Anatomy of Sympathetic Nervous System
Dendrites and cell bodies of sympathetic preganglionic
neuron in the lateral gray horns of spinal cord
Axon exits through ventral root of spinal nerve, then
enters sympathetic vertebral ganglion found along 2 chains
near the spinal cord. Vertebral ganglion + fibers connecting
them = sympathetic trunks
In vertebral ganglion, axon of preganglionic
sympathetic nerve synapses with dendrites of several
sympathetic postganglionic neurons. Axon may instead
synapse with postganglionic neuron in the collateral ganglia
Since they synapse with several neurons, sympathetic
nerves have wide-spread effects on several organs and can
coordinate them
Very long axons of postganglionic neurons then pass to
muscle or gland; uses norepinephrine for neurotransmitter
B.
Functions of Sympathetic Nervous System
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Used during “fight-or flight” responses, heavy exercise,
strong emotions, other stresses
Increased heart and breathing rate
Increased blood pressure
Blood vessels in muscles enlarge to provide them with
more energy
Sweat glands and adrenal glands turned on
Decreased digestive activity
Closes urinary and rectal sphincters
Dilates eye to let in more light
Contracts arrector pili muscle to give goose pimples –
look larger and more intimidating
III.
Parasympathetic Nervous System
A. Anatomy
Dendrites and cell bodies of parasympathetic
preganglionic neurons in brainstem or spinal cord
Axons extend long distance to parasympathetic
terminal ganglia in head, thoracic, or abdominal cavities
near structures stimulated where they synapse with dendrites
of parasympathetic postganglionic neurons
In terminal ganglia, message passes to: 1) cell body, 2)
axons and out to muscle/gland. Short postganglionic axons
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Differences with anatomy of sympathetic nervous system:
1) P.S. preganglionic neuron only synapses with ONE
postganglionic neuron
2) One P.S. neuron controls only ONE organ/gland
3) P.S. ganglia FAR from spinal cord
4) Axon of P.S. postganglionic neuron is SHORT
5) P.S. postganglionic neuron uses ACh rather than
norepinephrine as neurotransmitter
B.
Functions
Parasympathetic system acts under normal conditions:
1) Slows heart rate
2) Increase movement of food and secretion of
enzymes to aid digestion
3) Opens sphincters for urination and defecation
4) Constricts pupil to let in less light
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IV. Visceral Nervous System
Innervates gut organs
Uses collateral ganglion near gut organs – far from spinal cord
Uses additional neurotransmitters to norepinephrine and
acetylcholine used by sympathetic and parasympathetic
V.
Neurotransmitters of Autonomic Nervous System
A. Cholinergic Fibers – release acetylcholine; parasympathetic
actions
Two types of cholinergic receptors
1.
Muscarinic receptors – slow responding
excitatory action
2.
B.
Nicotinic receptors (also bind nicotine) - rapid
excitatory response
Adrenergic Fibers – use norepinephrine; sympathetic
actions
Two receptor types – α (alpha) and β (beta) with
differing effects
VI. Interactions of the Autonomic Nervous System
Sympathetic and parasympathetic branches of autonomic
nervous system often antagonistic; act together maintain
homoeostasis
Autonomic nervous system influenced by limbic system that
controls emotions. Example – fear or anger increase sympathetic
innervations and increase heart rate
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