intro to autonomic nervous system Flashcards
What does the autonomic nervous system control?
Exists to control the things you don’t want to think about including smooth muscle in:
Blood vessels
Airways
Bladder
The eye
Gut
Sex organs
Cardiac muscle
Glands
What are the three branches of the autonomic nervous system?
sympathetic NS
parasympathetic NS
enteric NS
Differences between somatic and autonomic NS?
SOMATIC
cell bodies of motor neurons are in CNS and in ventral horn of spinal cord.
Send axons out through ventral root and to periphery, where meet skeletal muscle (target)
AUTONOMIC
not one fibre that is able to get out all the way to its target.
Pre ganglionic fibre (small myelinated) synapses onto ganglion (collection of cell bodies) then post ganglionic fibres( unmyelinated) and onto targets such as Smooth muscle, cardiac muscle, glands,
GI neurons
Differences in somatic vs autonomic synapses?
SOMATIC
Specialised NMJ (composed of pre synaptic terminal of motor neuron, synaptic cleft and end plate of muscle cell)
Ionotropic receptors (nicotinic cholinergic receptors, ionotropic and have integral ion channel)
Non specific mono-valent ion channels that allow sodium to flow into cell and evoke very large graded potential( end plate potential)
End plate p- always excitatory can always get muscle cell to threshold and evoke action potentials
Always excites target
AUTONOMIC
Less specialised junction
instead of pre-synaptic terminals have bumps called varcosities along post ganglionic fibre and these release neurotransmitter.
Neurotransmitter released into interstitial fluid and bump around till finds receptors on cells. One post ganglionic fibre in ANS can innervate a large area of tissue.
Metabotropic receptors
G protein couples and depending on second messengers- can excite or inhibit contractors
May excite or inhibit target
Differences between sympathetic and parasympathetic?
sympathetic- fight or flight
parasympathetic- rest and digest
Anatomical differences between somatic and parasympathetic NS?
SYMPATHETIC- outflow of sympathetic division is from thoracic region of spinal cord and from first two lumbar levels
(thoracolumbar outflow)
very short pre ganglionic fibres- ganglia close to spinal cord- most of these are in paravertebral ganglia and some in pre vertebral ganglia. After synapse have very long post-ganglionic fibres that go all way out to targets
PARASYMPATHETIC
outflow is from brain and sacral region of spinal cord (cranialsacral)
Cranial nerves supply structures around head (eye and salivary glands)
Vagus nerve- goes basically everywhere in body
very long pre gnaglionic fibres and very short post gnaglionic fibres and these lie within targets
Describe parasympathetic NS division?
Parasympathetic outflow is from cranial (III, VII, IX, X) and sacral (S2-4) regions
Parasympathetic ganglia lie close to or within the target
Describe sympathetic division?
Sympathetic outflow is from thoracic (T1-12) and lumbar (L1-2) regions
Sympathetic ganglia lie close to spinal cord in the sympathetic chain (paravertebral ganglia), or in collateral (prevertebral) ganglia
Describe acetylcholine neurotransmitters?
Acts on cholinergic receptors
can be Nicotinic receptors
or Muscarinic receptors
Describe noradrenaline neurotransmitters?
Acts on adrenergic receptors
α receptors
β receptors
Sympathetic vs parasympathetic chain of events?
Sympathetic and parasympathetic preganglionic fibres release acetylcholine which acts on nicotinic cholinergic receptors
Parasympathetic postganglionic fibres release acetylcholine which acts on muscarinic cholinergic receptors in target
Sympathetic postganglionic fibres release noradrenaline which acts on α or β adrenergic receptors in target
Why are noradrenaline and adrenaline described as hormones as well as neurotransmitters?
pre ganglionic fibre comes out of spinal cord and goes all the way to adrenal medulla before it synapses onto post ganglionic cell. This post ganglionic cell then releases its neurotransmitter and this is adrenaline and noradrenaline. Circulate around body and find targets in diff organs.
What is different about sympathetic cholinergic fibres (innervate sweat glands)?
thoracolumbar outflow
short preganglionic fibre that synapses onto a long post ganglionic fibre
would expect post ganglionic fibre to release noradrenaline as neuotransmitter but instead releases acetylcholine
What postganglionic fibres use non-adrenergic non-cholinergic transmitters?
Some postganglionic fibres use non-adrenergic non-cholinergic (NANC) transmitters e.g. peptides
Sometimes co-released with the orthodox transmitter
