A&P unit 4 - Autonomic Nervous System

autonomic NS

-part of Efferent NS

-involuntary/unconscious

-control heart, smooth muscle, glands

where in the spinal cord are the autonomic neurons?

in the lateral horn (shown in blue)

autonomic NS pathway

2-neuron pathway

-starts at spinal cord, ends at effector

-preganglionic neurons and postganglionic neuron

preganglionic neuron

-body is within spinal cord (lateral horn)

-thin, myelinated axon projects to autonomic ganglion in PNS

-releases Ach from syn. knob to excite 2nd neuron

postganglionic neuron

-body is within autonomic ganglion

-very thin, unmyelinated axon projects to effectors

-releases Ach or norepinephrine from syn. knob to excite or inhibit effector depending on effector type

Why does the autonomic pathway involve a ganglion? Why not just have nerve go from spinal cord straight to effectors?

allows for neuronal convergence and divergence

-more control of response

-more areas of response

neuronal convergence

multiple preganglionic synapse onto one postganglionic neuron

-integration of signals

-fine tune response

-allow for one targeted, controlled response

neuronal divergence

one preganglionic synapse with many postganglionic neurons

-increase effect by targeting many areas

-disperse areas that effectors are activated

Where are the control centers for the ANS?

hypothalamus = regulate many autonomic processes, sleep, involved in emotions

brain stem = major reflex centers, digestion, cardiovascular, respiratory

spinal cord = reflex centers for defecation and urination → these reflexes become controlled as we get older

sympathetic NS

-fight or flight

-needed for exercise, excitement, emergency

thoracolumbar outflow

in sympathetic, nerve fibers originate in chest and abdominal regions of the spinal cord

-lateral horns of T1-L2

-preganglionic fibers are short and branched (allow for divergence), postganglionic are long

parasympathetic NS

-rest and digest

-maintain homeostasis when resting

craniosacral outflow

in parasymp, nerve fibers originate in brain and lower spinal cord

-brainstem nuclei, and S2-S4

-preganglionic fibers are long, postganglionic are short

terminal ganglion vs intramural ganglion

terminal = if ganglion lies close to the effector

intramural = if ganglion lies within the effector

parasympathetic activation vs sympathetic activation

sympathetic = mass activation → branched preganglionic allow many effectors to be activated at once

parasymp = localized reponse → ganglion close to effectors allow for only one or a few structures activated at a time

adrenal medulla role in sympathetic mass activation

-adrenal glands are on top of kidneys

-when stimulated, releases epinephrine (E) and norepinephrine (NE) into blood

-now the hormones flow thru blood and reach many targets

Adrenal medulla

-modified autonomic ganglion, NO postganglionic fibers

-medulla release NE and E into blood, reinforces sympathetic response

cholinergenic vs adrenergenic fibers

cholinergenic = release Ach. more common in parasymp

-includes nicotinic and muscarinic

adrenergenic = release NE. more common in sympathetic

-includes alpha and beta receptors

nicotinic receptors

-type of cholinergenic receptor (binds Ach) in parasymp

-found on all postganglionic cell bodies in ANS (parasym and sym)

-found on neuron, not effector organ

-when Ach binds, it opens cation channel. more Na in than K out leads to cell depolarization, AP

agonist vs antagonist

both refer to a foreign molecule

agonist = binds to a receptor and has same response as NT would

antagonist = binds, but in doing so prevents NT binding/response

muscarinic receptors

-type of cholinergenic receptor (binds Ach) in parasymp

-found in all target organs of parasymp, AND sweat glands and blood vessels of symp

-found on effector organ, not neuron

-when Ach binds, activates GPCR, that leads to kinase activating a protein in the effector cell

alpha and beta receptors

-type of adrenogenic receptor (binds E and NE) in sympathetic

-most commonly found on effector organ

-all have GPCR pathway, but pathway is diff based on subtype

-A1, A2, B1, B2

-in general, A/B1 is excitatory and A/B2 is inhibitory

alpha 1 receptors (A1)

-most common adrenogenic

-greater affinity for NE than E

-activation excites effector organ

alpha 2 receptors (A2)

-on mainly digestive organs

-greater affinity for NE than E

-activation inhibits effector (stop digestion for fight or flight)

beta 1 receptors (B1)

-in heart

-equal affinity for E and NE

-excitatory response (heart pump faster)

beta 2 receptors (B2)

-in small blood/airway vessels

-affinity for E

-activation is mostly inhibitory (relax smooth muscle walls, BV dilate)

dual innervation

when organ can receive input from both parasymp and symp

-ability to produce opposite effects in the organ

-allows for precise control of organ, functions can change depending on situation needed

Nicotinic mnemonic

nicotinic = all post-ganglionic

No Alligators Prowl Gracefully

muscarinic mnemonic

muscarinic = parasympathetic targets

Mice Prefer Treats

adrenergic mnemonic

adrenergic = sympathetic targets

A Swift Tiger