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The Autonomic Nervous System (Sensory arm of the ANS (controls body's…
The Autonomic Nervous System
Parasympathetic (Craniosacral) Division
Anatomy of the Parasympathetic Divison
CN III, VII, IX, X and lateral horns of S2-S4 in the spinal cord
preganglionic fibers are long, postganglionic fibers are short
pre synapse in either intramural (if in wall of effector organ) or terminal (if ganglia close to effector organ) ganglia
synapse with effector cells in the local area
Parasympathetic Responses
"rest and digest" - relaxation, food processing, and energy conservation.absorption
SLUDD
decreased HR, bronchoconstriction, and constriction of the pupils
preganglionic neuron synapses with only one postganglionic neuron, and ACh is quickly destroyed by AChE
Sensory arm of the ANS
located in blood vessels, walls of heart, GI tract, and bladder
interoceptors
chemoreceptors (changes in chemical composition)
mechanoreceptors (changes in stretch)
controls body's visceral function (involuntary)
cardiac muscle
glands
smooth muscles
visceral reflex arc
receptors (in viscera or skin)
sensory neuron
integration center (may be a preganglionic neuron, dorsal horn interneuron, or in walls of GI tract)
motor output (autonomic pathway consisting of 2 neurons)
effector
Neurotransmitters and Receptors
Cholinergic Fibers
bind ACh
nicotinic receptors
receptors on muscle cells of neuromuscular junctions and present on ALL postganglionic fibers
always stimulatory/excitatory
muscarinic receptors
occur on all effector cells stimulated by postganglionic cholinergic fibers
associated with ion channels (depends on the target cell)
can be stimulatory or inhibitory
ACh has short effect due to presence of AChE at the synapse
Adrenergic fibers
bind norepinephrine and epinephrine
Alpha
a1
located in blood vessels serving the skin, mucosa, abdominal viscera, kidneys, salivary glands, virtually all sympathetic effectors except heart
generally excitatory
increase in intercellular calcium levels - muscle contraction, sphincter restriction
a2
located in some vascular smooth muscle, blood platelets, and on beta cells (secrete insulin), and acinar cells (digestive secretions) of the pancrease
effects generally inhibitory
Beta
B3
in adipose tissue
effect is to stimulate lipolysis
increase heat production in body --> release substrates into bloodstream - circulates to liver where it can be used for fuel production in long term excercise
B2
found in smooth muscle in walls of blood vessels, respiratory passages, digestive tract, the bladder and urinary passages
inhibitory
act by increasing intracellular cAMP levels
B1
located in cardiac muscle and various other sites
generally excitatory
Sympathetic (Thoracolumbar) Division
Anatomy of the Sympathetic Division
Ventral roots of spinal nerves T1-L2
Pathway of pre and postganglionic fibers
fibers leave the cord in the ventral roots
ventral ramus
white ramus communicans
paravertebral ganglion (aka sympathetic chain)
One of 3 things can happen to the preganglionic fiber in the paravertebral ganglion:
it can ascend/descend the chain and synapse in another chain ganglion at a higher/lower level
it can pass through the sympathetic trunk and synapse in a collateral ganglion anterior to the vertebral column
it can synapse with a postganglionic neuron in the paravertebral ganglion at the same level
the postganglionic fibers enter the ventral or dorsal ramus of adjoining spinal nerves via the gray rami communicantes
from there, they travel to effectors
Synaptic terminals
varicosities (NT release cavities)
cause NT to be released near the surface of an effector but not precisely at a synapse = diffuse effect
Sympathetic Responses
"fight or flight" response
constriction of cutaneous blood vessles, increased HR and force of contraction, arrector pili muslces
increased blood flow to skeletal muscles and away from viscera, increased lipolysis, dilation of pupils and respiratory passages