Autonomic Nervous System Flashcards
Structural features of the SOMATIC Nervous System
sensory input comes in synapse of MYELINATED motor neuron extends out to the dorsal root to striated muscle (effector) where Ach is released, causing contraction of the muscle
- innervation of target DIRECTLY
Structural features of the AUTONOMIC Nervous System
sensory input comes in through dorsal horn and descending innervation from higher brain centers; MYELINATED preganglionic neuron transmits signal to efferent neuron in an intermediate zone (not the target) and instead synapses onto a ganglion–> from ganglion UNMYELINATED postganglionic neuron sends its axon out to target where Ach (parasympathetic) or NorE (sympathetic) is then released
- innervation of target thru pre and postganglionic fibers and intermediate ganglion
What neurotransmitter is released in the Sympathetic NS?
Norepinephrine
What neurotransmitter is released in the Parasympathetic NS?
Acetylcholine for smooth muscle movements (“rest and digest”)
Adrenal Medulla
serves as intermediate ganglion in the ANS; contains cells that release norepinephrine into the blood in response to an action potential where it then can act on targets
Why are different neurotransmitters used in the sympathetic and parasympathetic nervous systems?
Both act on the same targets so different NT are needed to communicate the appropriate messages
Pre and postganglionic fibers of the Sympathetic NS
preganglionic fibers: SHORT (ganglia are right next to the spinal cord T-L spine)
postganglionic fibers: LONG (have to extend the rest of the way to reach the target)
Pre and postganglionic fibers of the Parasympathetic NS
preganglionic fibers: LONG (ganglia are closer to the TARGET)
postganglionic fibers: SHORT
why can sweat glands utilize both ACH and NE to send signals?
Sweat glands are ONLY innervated by the sympathetic NS so either NT will communicate that message (dual innervation)
Fibers of the Sympathetic trunk
- preganglionic fibers can synapse onto each other and add onto each other in same direction, or axon can split and some go up or down the trunk and then some at that level
= more DIVERGENCE - one preganglionic fiber can split and synapse onto on avg 20 postganglionic fibers
Fibers of the Parasympathetic trunk
preganglionic neurons often synapse with just ONE other postganglionic neuron in 1:1 fashion,
= LITTLE TO NO DIVERGENCE
- 1preganglionic fiber:3 postganglionic fibers ON AVG
Agonist
binds to receptor and activates it
Inverse Agonist
substance that when bound to receptor decreases its basal activity of receptor
- in the absence of its ligand it typically binds to the receptor which usually has SOME activity, so the inverse agonist REDUCES that
Antagonist
substance that when bound does not do anything BY ITSELF, BUT in the presence of an agonist it will decrease activity of the agonist or inverse agonist (may actually be antagonist or really an inverse agonist just incorrectly named)
hexamethonium
NICOTINIC receptor antagonist at the ganglia in the AUTONOMIC NS but no effect on the muscle in the NMJ (somatic NS) so we know they can respond to the same substance (nicotine) but have diff receptors
curare
NICOTINIC antagonist at the ganglia in the SOMATIC NS, has no effect on AUTONOMIC NS unless added in very large concentrations
Atropine
MUSCARINIC receptor antagonist at the POSTganglion of the PARASYMPATHETIC NS, has no effect on nicotinic receptors
- used to dilate pupils
Preganglionic Receptors in the Sympathetic and Parasympathetic NS
NICOTINIC ONLY
Postganglionic Receptors in the Sympathetic NS
NICOTINIC and MUSCARINIC
- beta1 receptors: increase heart rate and contractility
- beta2 receptors reduce gut motility
Postganglionic Receptors in the Parasympathetic NS
ONLY Muscarinic
Dopamine
precursor to norepinephrine so will be some present in any synapse that releases NE even from the adrenal medulla
- also serotonin, histamine, GABA
Other molecules with signaling abilities
NO (nitric oxide) and purines (i.e ATP)
En Passant Synapse
axon may not stop at target in ANS –> just has swellings (varicosities) along the way as it goes to its true target
–> = EN PASSANT synapses
alpha 2 receptor
receptor on the postganglionic decrease norepinephrine if too much NE (negative feedback mechanism)
what other substances have receptors that can release NE?
Angiotensin II and
Negative feedback between parasympathetic and sympathetic NS
when parasympathetic activity is high, sympathetic NS will signal by releasing norepinephrine to signal to stop producing ACH; when sympathetic activity is high, parasympathetic NS sends over some ACH and that binding to muscarinic receptor DECREASES norepinephrine release and slows sympathetic ns activity
–> PARASYMP and SYMP work TOGETHER to maintain homeostasis
Pattern of Neuronal Activity: Somatic NS
- initiates activity in muscle that is otherwise inactive (muscle will not contract unless stimulated)
- motoneurons are inactive until stimulated
Pattern of Neuronal Activity: Autonomic NS
- modulates targets with autogenic activity (most targets don’t need any neural stimulation to work)
- efferent neurons maintain tonic discharge (always active at a slow rate; will just increase or decrease the firing rate of pre/postganglionic neurons)
- can affect targets individually (more typical of parasympathetic since typically only synapse to 1-3 other postganglionic fibers)
- can affect targets in concert (more typical of sympathetic since synapse to ~20 postganglionic fibers- basis of polygraph testing)
consensual pupillary response
By shining light into one eye, retinal preganglion stimulate both eyes (negative feedback reflex)
Regulating orthostatic hypotension
baroreceptors combat orthostatic hypotension bc ACH production on the heart needs to slow and NE production to the heart must INCREASE to pump the heart and restore blood circulation
Horner’s Syndrome
Condition in which lesion/defect in SYMPATHETIC system leads to one- eye droop (miosis), decreased sweating on one side of the face, increased blushing/heat on one side of the face
- sweat glands ONLY receive sympathetic innervation so must be where lesion is
