6b nervous coordination Flashcards
describe neurones resting state
outside of membrane positicely charged
more positive ions on outside of membranes than inside
its polarised
what is the voltage across a memebrane at resting state
-70mv
what creates and maintains resting potentials
sodium potassium pumps
and potassium ion channels
describe how resting potential is made
- sodium potassium pump pumps sodium ions out of neurone and as membrane isnt permeable to sodium ions they cannot diffuse back in
- electrochemical gradient created
- sodium potassium pump moves potassium ions into the neurone but membrane is permeable to potassium ions so they diffuse out of the neurone via potassium channels
- creates positive charge outside of cell
how does sodium potassium pumps work
active transport to move 3 sodium ions out of neurone for every two potassium ions moved in
ATP required
describe stages of action potential
STIMULUS- excites nuerone membrane causing sodium channels to open
-membrane becomes more permeable to sodium so sodium ions diffuse into neurone down gradient making inside of neurone less negative
DEPOLARISATION- if the potential difference reaches threshold near -55mv more sodium ions open so more sodium ions diffuse into neurone
REPOLARISATION- at potnetial difference of +30 sodium ion channels close
- potassium ion channels open
- membrane more permeable to potassium so they diffuse out of neurone getting membrane back to resting potential
HYPERPOLARISATION-potassium ion channels slow to close so slight overshoot so potential difference becomes more negative than resting potential
RESTING POTENTIAL-ion channels reset -sodium potassium pump returns membrane to resting potential
what is the refractory period
after action potential neurone membrane cannot be excited again straight away as channels closed
explain wave of depolarisation
during action potential some sodium ions diffuse sideways causing sodium channels to open in next region of neurone causing wave of depolarisation
what happens due to refractory period
- action potentials dont overlap they pass on discrete impulses
- limit to frequency at which impulses can be transmitted
- action potentials are unidirectional
describe all or nothing principle
bigger stimulus doesnt mean bigger action potential it means more frequent action potentials
if threshold isnt reached action potential will not fire
what three factors affect the speed of conduction of action potentials
myelination
axon diameter
temperature
what is a myelin sheath
electrical insulator
what cells make up myelinated sheath
schwann cells
what are between schwann cells
nodes of ranvier where sodium ions are concentrated
why does myelinated sheath increase speed of conduction to action potential
in myelinated neurone depolarisation only happens at the nodes of ranvier
cytoplasm conducts enough electrical charge to depolarise next node so impulse jumps from node to node
this is saltatory conduction
why is speed of conduction slower in non myelinated sheath
as impulses have to travel along the whole length of axon membrane
how does the diameter of axon effect speed of conduction
bigger axon means action potential conducted quicker as less resistance to flow of ions so depolarisation reaches other parts of neurone cell membrane quicker
how does temperature effect speed of conduction of action potential
speeds up diffuseion but after 40 degrees proteins begin to denature
what is a synapse
junction between two neurones 12
how does synapse work
- presynaptic neurone has synaptic knob which contains synaptic vesicles filled with neurotransmittors
- when action potential reaches end of neurone ig causes neurotransmitters to be releases to synaptic cleft and diffuse across tpo the postsynaptic membrane and bind to specific receptors
- when they bind with receptors they can trigger action potential
explain how synapses are unidirection
as receptors are only on postsynaptic membrane
how are neurotransmitters removed
removed from cleft to stop response from happening
taken back into presynaptic neurone and broken down by enzymes
describe nerve impulse across a cholingeric synapse
1-action potential arrives at synaptic knob of presynaptic neurone
2-action potential causes stimulates calcium ion channels to open
3- calcium ions diffuse into the synaptic knob
4-influx of calcium causes synaptic vesicle to move to presynaptic membrane
5-vesicle releases acetylcholine into synaptic cleft |(exocytosis)
6-ACH diffuses across cleft and binds to spefic cholinergic receptor on post synaptic membrane
7-causes sodium ion channels to open in postsynaptic neurone
8-influx of sodium ions causes depolarisation
9- action potenital generated if threshold reached
10-acetylecholineesterase breaks down ACH and products go to presynaptic neurone
what do excitatory neurotransmitters do
depolarise postsynaptic membrane making it fire action potential if threshold
what do inhinbitory neurotransmitters do
hyperpolarise the postsynaptic membrane preventing from firing action potential
what is summation
when effects of neurotransmitters from multiple neurones are added together - weak stimulius
what are the two types of summation
spatial and temporal
describe spatial summation
1- many neurones conected to one neurone
2-small amounts of neurotransmitters from each neurone are added together to reach threshoold in postsynaptic neurone
3- if some are inhibitory neurones then action potential may not be reached
what is temporal summation
two or more nerve impulses arrive in quick succesion from same presynaptic neurone - action potential more likely as more neurotransmitters in synaptic cleft
what is a neuromuscular junction
synapse between motor neurone and muscle cell
in neuromuscular junctions what does acetylcholine bind to
receptrors called nicotinic cholinergic receptors
what are the difference of neuromuscular junction and cholinergic synapse
post synaptic membrane has lots of folds forming clefts where enzyme acetylcholineesterase is stored
postsynaptic membrane has more receptors than pother synapses
acetylecholine is always excitatory
describe agonist drugs effect on synapse
same shape as neurotransmitters
mimic there action at receptors
so more receptors activated
describe antagonist drugs effect on synapse
block receptors
so cannot be activated by neurotransmitters
how do drugs that inhibit enzymes effect synapse
more neurotransmitters
as less enzymes to break them down
how do drugs work that effect presynaptic enurone
stimulate release of neurotransmitters or inhibit them
what are skeletal muscles
use to move
how is skeletal muscle attached to bones
tendons
how are bones attached to other bones
ligaments
how do muscles work together to move arm
work in antagonistic pairs
one contracts one relaxes
uses bone as lever as its incompressible- ridgid
what are skeletal muscles made up of
large bundles of long cells called muscle fibres
what is the cell membrane of muscle fibres called
sarcolemma
describe structure of sarcolemma in muscle fibres in skeletal muscle
bits fold inwards and stick into sarcoplasm
these fold called transverse tubules which help spread electrical impulses evenly throughout muscle fibres
what is the sarcoplasmic recticulum and how does it help muscle contraction
network of internal membranes which run through sarcoplasm
stores and releases calcium ions for muscle contraction
why do muscle fibres have a lot of mitochondira
to provide atp for muscle contraction
why are muscle fibres said to be multinucleate
contain multiple nuclei
describe microfibrils in muscle fibres
long cylindrical
made of proteins highly specialised for contraction
what does myofibrils contain which help muscles contract
thick myosin filaments and thin actic filaments
what are thick myofilaments made from
protein myosin
what are thin myofilaments made from
protein actin
what are a bands
what are a bands
