Nervous system Flashcards
PNS
somatic nervous, autonomic, parasympathetic, sympathetic
Somatic
Conscious control, bicep curl
Autonomic
unconscious body activity; heart and breathing rate
parasympathetic
slows things down, acetycholine neurotransmitter, decreasing heart reate
sympathetic
speeds things up; noradrenaline neurotransmitter,increasing heart rate
nerve pathway
sitmulus, receptor, seconsry neurone, relay neurone, motor neurone, effector, response
sensory neurone
1) single long dendron
2) single short axon
relay neurone
1) within CNS
2) many short dendrites
3) many short axons
motor neurones
1) many short dendrites
2) single long axon
3) ends with neuromuscular junction
Resting potential
1) na+/K+ pump uses active transport (atp), 3 NA+ out and 2K+ in
2) voltage gated sodium ion channel: closed, membrane is not permeable to Na+ ions
3) K+ ion channels: open, some K+ diffuse down the electochemical gradient, doesnt reach eq due to the postiive charge outside the axon
7 stages of action potential
1) resting potential
2) generator potential
3) threshold
4) depolarisation
5) repolarisation
6) hyperpolarisation
7) Refractory period
Generator potential
1) weak stimulus
2) some Na+ voltage gated channels open
3) some Na+ diffuses in
4) does not reach threshold
5) Na+K+ pump restores resting potential
Threshold
1) Generator potential reaches threshold
2) many voltage gated Na+ channels open
3) Na+ diffused into axon
4) positive feedback; rapid change–> depolarisation
Depolarisation
1) Na+ channels are open
2) Na+ diffuses in
Repolarisation
1) K+ voltage gated channels are open
2) K + diffuses out
3) voltage gated Na+ close
Hyperpolarisation
1) when membrane potential is more neagitve than the resting potential
2) K+ channels are slow to close
Refractory period
1) another action potential cannot be started
2) ensures action potentials are discrete ( don’t overlap) and are unidirectional ( one way)
3) behind the depolarisation phase of an action potential
myelin sheath
1) schwann cells produce myelin
2) electrical insulator prevents depolarisation of membrane
3) prevents movement of ions in or out of neurone
Nodes of Ranvier
1) gaps in myelin sheath
2) lots of Na+K+ ion channels
3) depolarisation can only happen at the nodes
4) saltatory conduction
Saltatory conduction
1) when an action potential jumps between nodes of ranvier
2) speeds up transmission of nerve impulses
3) cytoplasm conducts enough charge to depolarise next node
temperature
higher temp causes faster speeds of action potentials (up to 40 degrees)
molecules diffuses faster at higher temps due to more KE
Diameter of axon
1) greater the diameter, the faster the speed of the action potential
2) less resistance
3) more surface area for ion movement
synapse
junction between neurones; chemical transmission by neurotransmitters, ACh
Cholinergic synapse stages
1) Action potential arrives at presynaptic knob
2) voltage gated Ca2+ channels open , Ca2+ diffuse in
3) vesicles full of ACh fuse with the presynaptic membrane by exocytosis
4) ACh diffuses across the synaptic cleft
5) ACh binds with receptor on post synaptic membrane ( complementary to ACh shape)
6) Some Na+ channels open, Na+ diffuses in, if threshold is reached…
7) change in potential difference across a mebrane: excitatory post synaptic potential set up as voltage gated Na+ channels are open
8) action potential triggered in the post synaptic membrane
9) enzyme acetylcholinesterase breaks down ACh and stops the response
10) Products are reabsorbed into the preysnaptic knob and recycled
inhibitory ion channel synapse
1) have neuroreceptors that are Cl- channels
2) when channels are open, negative cl- ions diffuse in causing a local hyperpolarisation called an inhibitory post synaptic potential (IPSP), therefore makes an action potential less likely
3) impulse in one neurone can inhibit an impulse in the next
4) neurotransmitters such as glycine or GABA
Synapses are uni directional
1) only receptors on post synaptic membrane
2) neurotransmittere are released from presynaptic knob
3) diffuses from hig to low conc across synaptic cleft
synaptic divergence
when one neurone joins many neurones: spreads the action potnetial to other parts of the body
synaptic convergence
many neurones join a single neurone which amplifies the signal
spatial summation
weak stimulus may only create a few action potentials, doesnt always trigger an action potnetial on post synaptic neurone
therefore, when neurotransmitters from multiple neurone combine to trigger an action potnetial in a post syantpic neurone
temporal summation
a single action potential doesn’t always trigger an action potential in the post synaptic membrane
therefore a strong stimulus will cause more frequent action potentials which will release more neurotransmitter and adds up to tirgger an action potential in post synaptic membrane
neuromuscular junctions
synapse between a motor neurone and a muscle fibre
difference between cholinerigc synapse and neuromusucular junction
1) more receptors on post synaptic membrane
2) an action potential is always generated in the post synaptic membrane
3) acetylcholineesterase is found in pits in the post synaptic membreane
4) receptors are called nicotinic cholinerigc receptors
agonist
drugs that sitmulate a synapse
antagonist
drugs that inhibit a synapse
nictotine
mimcs affect of ACh, agonist
1) binds to cholinergic receptors
2) triggers action potential in post synaptic neurone
3) receptor remains unrepsonsive to more stimulation for some time
4) affected neurorecpetors release other trnasmitters in CNS:
adrenaline: triggers fight or flight repsonse of sympathetic nervous system and heart rate and blood pressure increases
dopamine: stimualtes reward system in brain; feelings of pleasure
endorphins: cause feelings of well being; lead to withdrawal symptoms causing addiction
lidocaine
quick acting, short lasting local anesthetic
1) blocks voltage gated Na+ channels preventing production of action potnetials, therefore no pain felt
2) can also prevent heart arrhythmias; blocks sodium channels, rasing depolarisation thresholds, reduces prevents early action portential from pacemaker region that could lead to arrythmias
3) local anaesthetic; inhiboits sensory neurones
4) muscle relaxant; inhibiting motor neurones
cobra venom; alpha neurotoxin
1) binds tightly and irrevirsibly to acetylcholine receptors in neuromuscular junctions
2) stops the receptors from openign
3) therefore prvents transmission of impulses across synapses
4) skeletal muscles stop contracting leading to paralysis
5) fatal if the toxin reaches the breathing muscles
6) in very low conc, relaxes muscles of trachea and bronchi in severe asthma attacks, saves lives
