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what does the somatic nervous system innervate?
skeletal muscle
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what is the difference between the somatic and the autonomic nervous system in terms of their neurons?
- the somatic system has one long motor neuron that begins at the upper motor neuron, runs through the corticospinal tract along the ventral horn and ends at the lower motor neuron at neuroskeletal junctions.
- the autonomic nervous system has two neurons arranged in series the innerveate organs (depending on whether its sympathetic or parasympathetic pathway).
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describe the nervous system
It is firstly divided into CNS and Peripheral NS. the PNS is made of sensory (afferent) and motor (efferent) neurons. motor nerves can be either part of the somatic or the autonomic systems. the autonomic system is divided into the sympathetic and parasympathetic
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which neurotransmitter is used in the somatic system?
acetylcholine, and is received by nicotinic-acetylcholine receptors
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what can be used for muscle relaxation?
spalmolitycs (diazepam), neuromuscular blockers (anaesthetics), myotropic muscle relaxants (dantrolen).
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explain the pathway to muscle contraction
the acetylcholine is released from the lower motor neurons into the synaptic cleft and is uptaken by the N-AchR. This opens Na+ ion gated channels causing depolarization and an action potential that can be sensed by L-type voltage gated Ca channels. the inflow of Ca causes the activation of ryanodine which releases Ca from the sarcoplasmic reticulum and thus we can have muscle contraction.
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How does Ach bind the N-AchR?
- Ach binds the two alpha subunits of the receptor thus opening the pore and allowing for Na ions influx and K ions efflux.
- (neuromuscular N-AchR are made of alpha,1beta and 1 delta e subunits)
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what is α bungarotoxin?
an irreversible, competitive antagonist for N-AchRs that leads to paralysis and respiratory failure
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what is myesthenia gravis?
an autoimmune disease characterized by the decrease of N-AchRs. it causes fatigue, eye muscle weakness, head droopines, facial paralysis, eating difficulties, breathing difficulties. can be treated with neostigmine
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how do cholinesterase inhibitors work, and what are some examples?
they work by blocking acetylcholinesterases thus allowing for a longer Ach presence in the synaptic cleft. examples are neostigmine and endrophonium (used for diagnosis only)
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what are some non depolarizing N-AchR drugs?
these are competitive antagonists such as α bungarotoxin, tubocurarine, pancuronium and mivacurium.
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what are some depolarizing N-AchR blockers?
these are agonists that keep the receptor open but blocked such as succynylcholine.
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what is tubocurarine?
this is a naturally ocurring mono-quaternary alkaloid that causes total paralysis of the body in high doses.
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what is malignant hyperthermia?
this is an autosominal dominant disease that mutates the ryanodine receptor. in this disease the threschold for the release of Ca ions is lower than normal, and when succynilcholine is added the threshold is drastically lowered leading to a high efflux of Ca ions from the sarcoplasmic reticulum leading to high muscle contractions, ATP depletion and excessive heat generation from increased metabolism.
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how does dantrolene work?
it works by inhibiting the release of ca ions form the sarcoplasmic reticulum
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