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most spinal and cranial nerves
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nerves that contain both somatic and autonomic (visceral) motor fibers
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most spinal and cranial nerves
nerves that contain both somatic and autonomic (visceral) motor fibers
somatic effectors
innervates skeletal muscles
autonomic effectors
innervates cardiac muscle, smooth muscle and glands
somatic efferent pathways
1 motor neuron links CNS to effector; cell body in CNS; axon thick and heavily myelinated
autonomic efferent pathways
usually 2 motor neurons link CNS to effector; preganglionic and postganglionic
preganglionic motor neuron
cell body in CNS; axon thin and lightly myelinated
postganglionic motor neuron
cell body in PNS (ganglion); axon thin and unmyelinated
somatic neurotransmitters
all motor neurons release ACh; effect is always excitatory
autonomic neurotransmitters
preganglionic motor neurons release ACh; postaganglionic motor neuron's release ACh (parasympathetic) and Norepinephrine (sympathetic) can be excitatory or inhibatory
parasympathetic division
promotes maintenance functions (digestion, defecation, urination); conserves energy
sympathetic division
fight or flight; mobilizes body for action (exercise, excitement, emergency, embarrassment) most organs have dual innervation (innervated by both divisions); exception-smooth muscle blood vessels, adrenal medulla, sweat glands
parasympathetic division
craniosacral; preganglionic neurons emerge from brain stem and sacral region of spinal cord; preganglionic neurons are long; postganglionic neurons are short; most ganglia are terminal ganglia (located near effector)
sympathetic division
thoracolumbar; preganglionic neuron cell bodies located in lateral horns of T1-L2 spinal cord; preganglionic neurons are short; postganglionic neurons are long; ganglia are located in the sympathetic trunk
visceral reflexes
autonomic; mediated by the brain stem or spinal cord; pupillary light reflex, ciliospinal reflex, salivary reflex, referred pain
pupillary light reflex
receptor-retina; sensory neurons travel via optic nerve; integration center-midbrain; motor neurons travel via oculomotor nerve; effector-smooth muscle of the iris
parasympathetic division
mediates ipsilateral and contralateral constriction of pupils
referred pain
pain felt at a site other than area of origin; occurs because visceral sensory neurons travel along same pathways as somatic sensory neurons; brain interprets visceral stimuli coming from somatic pathway
cholinergic neurons
release acetylcholine; all parasympathetic motor neurons; all sympathetic preganglionic motor neurons
adrenergic neurons
release norepinephrine; most sympathetic postganglionic motor neurons
response of visceral organs
inhibitory/stimulatory; depends on type of neurotransmitter, type of receptor organ
ACh
binds to nicotinic or muscarinic receptors
norepinephrine
binds to alpha or beta receptors
specific drugs
can be used to target specific receptors to obtain the desired effect; ex.-circular muscles of iris have muscarinic receptors-atropine blocks these receptors-causes dilation of pupils
most organs
receive dual innervation, effects are usually antagonistic
cooperative effect
occurs on external genitalia; parasympathetic causes erection, sympathetic causes ejaculation
blood vessels
primarily under sympathetic control-exhibit sympathetic (vasomotor) tone
heart, digestive, and urinary tract
organs primarily under parasympathetic control-exhibit parasympathetic tone
parasympathetic
effect on smooth muscle of blood vessels; only coronary blood vessels
cranial parasympathetic neurons
innervate circular muscles of iris-constricts pupil;pancreas- increase secretion; salivary glands- stimulates watery secretion (contains digestive enzymes); heart muscle- decrease rate of contraction; coronary vessels-weakly dilates (only innervated parasympathetic);lung-constricts bronchioles; digestive organs- increase motility and secretion; relaxes sphincters; gallbladder-contracts to release bile
sacral parasympathetic neuron
innervate: bladder/urethral-contracts smooth muscle of bladder and relaxes urethral sphincter, promotes voiding; sigmoid colon and rectum- increases motility and relaxes sphincter; penis-causes erection (vasodilation); clitoris-causes erection (vasodilation)
PNS
has no effect on arrector pili muscles or most blood vessels
Sympathetic neurons
innervates: radial muscles of iris- dilates pupil; pancreas-decrease secretion; salivary glands-stimulates viscous secretion; heart muscle-increase rate and force of contraction; digestive organs-decrease motility and secretion, contracts sphincters; gallbladder-decrease release of bile; bladder/urethra-relaxes smooth muscle of bladder and constrict urethral sphincter; penis-causes ejaculation; vagina-causes contraction of vagina, increase mucus secretion; blood vessels-vasoconstriction of most (increase blood pressure and divert blood to brain, heart, and muscles), vasodilation of skeletal muscle vessels during exercise; kidney-decrease urine output; sweat glands-increase sweating arrector pili muscles-produces goose bumps; adrenal medulla- releases epinephrine into blood stream
adrenal medulla
releases epinephrine into blood stream causing: vasodilation of coronary vessels; dilation of bronchioles; liver to release glucose to blood; increase cellular respiration; stimulates lipolysis (breakdown of fat) for use as fuel
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