Autonomic Nervous System Flashcards
sympathetic
fight or flight
parasympathetic
rest and digest
examples of sympathetic effects
pupil dilation, saliva inhibit, heartbeat increase, airways relaxed, secrete epinephrine and norepinephrine, ejaculation, inhibits stomach
examples of parasympathetic effects
pupil constriction, decreased heartbeat, stimulates saliva, constricts airways, stimulates stomach, contracts bladder, erection
structure of the ANS
signal starts in brainstem, through preganglionic neuron, to autonomic ganglion
autonomic ganglion = junction of one to another, pre-ganglionic to post
ganglions contain synapse for signal transferring
post-ganglionic neuron continues to effector tissue e.g. smooth muscle, glands, adipose
what is a synapse?
specialized structure for transmitting signal from one neuron to another
neurotransmitters are synthesized in
first neuron and released into synaptic cleft
what is a neurotransmitter?
chemical messenger which binds to receptors on surface of second neuron and activates it
neurotransmitters are synthesized in
first neuron and released into synaptic cleft
how do synapses transmit signal?
neurotransmitter is synthesised in first neuron
electrical impulse releases neurotransmitter into synaptic cleft
neurotransmitter acts fast on target cell
neurotransmitters are short lived and broken down in the synaptic cleft by some enzyme and recycled
where is acetylcholine synthesised?
from Choline in the presynaptic terminal
Choline is recycled from the synaptic cleft
ACh is stored in vesicles in the presynaptic terminal ready for
release
Vesamicol inhibits uptake through
VAT
how is acetylcholine released from vesicles?
electrical impulse arrives through Axon
from neuron cell body.
depolarization opens voltage sensitive calcium channels.
calcium flows into the cell down its concentration gradient
calcium is needed to activate SNAP
proteins
SNAPs pull vesicle toward synaptic
cleft and allow vesicle fusion.
botox inhibits SNAPs – if injected
into somatic muscles this stops
movement but systemically inhibits
ANS so is toxic
what happens to acetylcholine in the synapse?
ACh in synaptic cleft binds to
cholinoreceptors on postsynaptic
neuron.
ACh is rapidly degraded to Choline
(recycled into cell).
Rapid inactivation is a very important
property of a synapse.
ACh also acts on presynaptic
modulatory receptors to fine tune
activation threshold off the nerve
(repeat stimulation will reduce
sensitivity).
Breakdown of ACh is by Acetylcholinesterase (inhibited by
neostigmine – myasthenia gravis).
what is Myasthenia gravis?
long-term neuromuscular disease that
leads to muscle weakness.
most affected muscles are those of
the eyes, face, and swallowing. It
can result in double vision, drooping eyelids, trouble talking, and trouble walking
what is the treatment of Myasthenia gravis and how does it work?
Nostigmine
* Blocks ACh breakdown in synapse (inhibits acetylcholinesterase) so stimulates ACh
receptors indirectly
* Neostigmine can induce generic ocular side effects including headache, brow pain, blurred vision, phacodonesis (lens tremor), pericorneal injection, congestive iritis,
various allergic reactions, and rarely, retinal detachment
what is Ach an agonist of?
ACh is an agonist of both muscarinic
and nicotinic acetylcholine receptors
Nicotinic are FAST ion channel
receptors - nerve transmission
Muscarinic are SLOW acting G
Protein Coupled Receptors (GPCRs) - parasympathetic
what is Muscarine?
natural product found in mushrooms Muscarine mimics the action of the neurotransmitter acetylcholine by binding muscarinic acetylcholine receptors. These receptors were named after muscarine.
