p2: nervous coordination Flashcards
two divisions of nervous system
- CNS: brain and spinal cord
- Peripheral nervous system: nerves from and to the brain and spinal cord
and
- voluntary NS: voluntary conscious control
- autonomic NS: involuntary or subconscious
describe how the structure of dendrites enable it to serve its function
- thin extensions on post synaptic membrane
- receives chemical signals
- carries impulses to nerve endings
describe how the structure of the myelin sheaths enable it to serve its function
- electrical insulation
- speeds up transmission
- formed from schwann cells
describe how the structure of terminal end branches enable it to serve its function
forms a synapse
releases neurotransmitters
explain the advantages of simple reflex arcs
- rapid
- protect against damage to body tissues
- dont have to be learnt
- help escape predators
as a neurone transmits an impulse, its rate of oxygen consumption increases. explain why.
- ATP required for active transport
- Na+ moved out along the whole length of axon in non myelinated
describe how a resting potential is maintained in a neuron
- active transport of sodium ions across membrane
- membrane more permeable to K+ ions
- differential permeability to K+ and Na+ ions
- out of neurone, Na+ concentration higher and K+ conc higher inside neurone
- 3Na+ out and 2K+ in
the potential across the membrane is reversed when an action potential is produced
- sodium ion channels protein
- Na+ ions diffuse in
how is an action potential generated?
- membrane reaches threshold and becomes depolarised
- reversal of resting potential
depolarisation
- stimulus causes membrane to be more permeable to Na+ ions
- if reaches threshold, Na+ ion channel proteins open and inside becomes more positive
- K+ ion channel proteins mainly closed
- high conc of positive ions inside cell = action potential
repolarisation
- when reached 40 mV the Na+ channel proteins close
- K+ CHANNEL PROTEINS OPEN
- K+ ions diffuse out down a conc gradient = repolarisation
hyperpolarisation
- K+ ion channel proteins remain open longer than needed, so cell more negative (-90mV)
- sodium potassium pump restores back to (-70mV)
all or nothing response
- action potential only occurs if all Na+ voltage-gated ion channel proteins opemn
- threshold reached
- subthreshold = no action potential
- action potential size is always the same
- full size action potential always given regardless of size of stimulus
define threshold
minimum intensity of stimulus
refractory period
- time taken to restore the resting potential
- period of inactivation following transmission of an impulse
- limits number of impulses per second
- maximum frequency of impulse transmission
impulse transmission
action potentials act as stimulus to adjacent polarised areas of membrane
- is passed along
describe how the speed of conduction could vbe increased ina neurone
- axon is myelinated which provides insulation
- action potential jumps from node of ranvier to node of ranvier (saltatory conduction)
- axon has a large diameter
- so less resistance to flow of ions
saltatory conduction
imoulses travel from node of ranvier to node
- depolarisation occurs only at nodes
- less axon needs to be depolarised so increases rate of transmission
factor affecting rate of impulse conduction
- myelin sheaths
- temperature, higher KE so increased diffusion of ions
- larger axon diameter greater speed of conuctance and increases number of channel proteins
give two reasons why transmission across a cholinergic synapse is unidirectional?
- impulses are unidirectional from pre to post SN
- vesicles containing neurotransmiters only in presynaptic neurone a
- receptor proteins only in post SN
where is acetyl choline found?
parasympathetic branch of NS
describe the sequence of events leading to the release of acetylcholine and its binding to the post synaptic membrane
- depolarisation of presynaptic membrane
- Ca 2+ ions open and calcium ions enter synaptic knob
- vesicles fuse with presynaptic membrane and release acetyl choline
- acetylcholine diffuses across synaptic cleft
- acetylcholine binds to receptors on the post SN
- sodium ions enter post SN leading to depolarisation
when a nerve impulse arrives at a synapse, it causes the release of a neurotransmitter from vesicles in the presynaptic knob. describe how.
- depolarisation causes calcium ion channel proteins to open
- calcium ions enter by faciliated diffusion
- vesicles fuse with preSN
neuromuscular junction
- synapse between motor neurone and muscle cell
- uses acetylcholine which binds to nicotinic cholinergic receptors
what are the major differences between the cholinergic synapse and the neuromuscular synapse
- in neuro, postSN has lots of folds that form clefts, increase SA so more acetyl enzymes hydrolyse acetyl at a faster rate
- postSN has more receptors
- action potential always triggers a response in muscle cell
the binding of GABA to receptors on postSN membranes causes negatively charged chlorine ions to enter postSN
explain how this will inhibit transmission of nerve impulses by postSN neurones
- inside neurone is more negative
- not enough Na+ ions to reach threshold
- for action potential/depolarisartion
myelination affects the rate of conduction of a nerve impulse. explain how.
- myelination provides electrical insulation
- action potential jumps between nodes of ranvier
- fewer jumps to travel length of axon
describe how the inhibition of acetylcholinesterases affects the action of synapses
- acetyl choline not broke down
- Na+ ions continue to depolarise/create action potentials
summation
build up of neurotransmitters within the synapse
spatial summation
- causes release of enough neurotransmitters to reach threshold
- causes an axtion potential in postSN
- different neurones converge at a single synapse
temporal summation
- one presynaptic neuroe but impulses arrive at rapid succession
- cumulative effect sufficient to depolarise postSN
fatigue
if rate of transmission higher than rate reformed, then fatigued
- cant generate an action potential is postSN until transmitter is regenerated
excitatory neurotransmitters
- cause an action potential in postSN makes resting potential LESS negative, so less Na+ ions required to reach threshold
inhibitory neurotransmitters
- resting potential becomes hyperpolarised
- less likely to reach threshold
- less likely to generate an action potential
effects of drugs on synapses:
- stimulate NS by creating more action potentials
- similar shapes to neurotransmitter so bind on postSN and mimic effect
- or reduce action potentials so inhibitoty effect
- ior ncrease release of neurotransmitters
- inhibit enzymes hydrolysing neurotransmitters
ao2 examples of drugs
cocaine: prevents hydrolysis of neurotransmitters
- codeine: binds to receptors for endorphins
- heroin: binds to receptors for endorphins in pain pathways
- valium: increases effect of GABA
caffeine: reduces threshold for excitation of neurones
- botox inhibits release of acetylcholine
