Organisms Response to Change - Nervous Coordination Flashcards
what is a potential difference?
difference in electrical potential between 2 points
define a polarised cell
a cell with an electrical difference across its membrane
what is a leakage channel protein?
an ion channel in plasma membranes, where the permeability is constant
what is a voltage gated channel protein?
an ion channel in plasma membranes that open and close as a cell’s polarisation changes
what is a protein pump?
proteins involved in the active transport of substances across a membrane
why can’t ions pass directly through a membrane?
the charges can’t pass through the hydrophobic tails
how are neurons polarised in a resting state?
inside is negative, outside is positive
what is the potential difference of a neuron in the resting state?
-65mv
why is a neuron polarised at resting state?
there are more positive ions outside the cell than inside
which ions are present and where in a neuron at resting potential?
sodium ions - outside
potassium ions - inside
what maintains the resting potential of a neuron?
sodium-potassium pump
leakage channel proteins
how does the sodium-potassium pump help maintain the resting potential in a neuron?
actively transports sodium ions out of the cell and potassium ions into the cell
this is done in the ratio of 3 sodium ions out for 2 potassium ions in
how do leakage channels help to maintain the resting potential of a neuron?
sodium leakage channels closed - prevents sodium ions diffusing into the cell
potassium leakage channels open - potassium ions can diffuse out of the cell
what is an impulse?
wave of excitation caused by an action potential
what causes an action potential?
a stimulus reaching a neuron
what are the stages of an action potential?
stimulus
depolarisation
repolarisation
hyperpolarisation
what happens in the stimulus stage of an action potential?
stimulus causes voltage gated sodium channels to open
sodium ions diffuse into neuron, making inside less negative
what happens in depolarisation?
if there is a large enough stimulus the threshold is reached
more voltage gated sodium channels open until the cell is +40mv and an action potential occurs
what voltage is the threshold in action potential?
-55mv
what happens in repolarisation?
voltage gated sodium channels close, voltage gated potassium channels open
allows potassium to diffuse out of the cell
cell becomes more negative
what happens in hyperpolarisation?
neuron now too negative
voltage gated potassium ions shut
sodium-potassium pump restores resting potential
what is the refractory period?
period of time after an action potential when it is impossible for another action potential to occur
what happens during the refractory period?
voltage gated sodium channels are closed and cannot be opened
what is the importance of the refractory period?
ensures action potential only happens in 1 direction
produces discrete impulses
limits number of action potentials
why is it important that the no. action potentials fired is limited?
too many can cause siezures
why is it important that the impulses are discreet?
so 2 different action potentials can be distinguished
what is the all or nothing principle?
the principle where:
action potential will only occur once threshold is reached
once threshold reached, all action potentials that occur are the same, no matter size of stimulus
what factors can affect rate of impulse transmission?
myelin sheath
diameter of axon
temperature
how does the myelin sheath affect the rate of impulse transmission?
myelinated neurons transmit impulses faster
how does the diameter of an axon affect rate of impulse transmission?
larger diameter = faster impulse due to less leakage of ions
how does temperature affect the rate of impulse transmission?
higher temperature = faster impulse as ions can diffuse quicker
what is the myelin sheath made up of?
schwann cells and myelin membranes wrapped around neurons
what is the node of ranvier?
breaks in the myelin sheath
how are voltages propagated through non-mylenated neurons?
stimulus causes voltage gated sodium channels to open, reaching threshold so an action potential occurs
localised electric currents established by influx of sodium ions causes voltage gated sodium channels to open further along the axon, so AP passed down
how are action potentials propogated in myelinated neurons?
voltage gated Na and K channels only found at nodes of ranvier so AP only occurs here
AP jumps from one node to the next
label this diagram of a synapse
describe how impulses travel along a cholinergic synapse
Action potential arrives at presynaptic membrane
gated Ca channels open and Ca ions enter synaptic knob, causing synaptic vesicles to fuse with presynaptic membrane
Acetylcholine diffuses across and binds to Na ion channels
Na ions diffuse into postsynaptic neuron
Action potential generated in postsynaptic neuron
acetylcholine hydrolysed and diffuses back across the cleft to presynaptic membrane
ATP used to reform acetylcholine.
what hydrolyses acetylcholine?
acetylcholinerase
what is acetylcholine hydrolysed into?
acetyl / ethanoic acid
choline
what are the types of summation?
spatial
temporal
how do inhibitory synapses transmit impulses?
neurotransmitters bind to chloride ion channels on post synaptic membrane
causes chloride channels to open and chloride ions diffuse into cell
also causes potassium channels to open and potassium ions leave the cell
what is spatial summation?
lots of neurons releasing signals to one neuron
what is temporal summation?
repeated stimuli from one neuron in quick succession
what is the role of a transducer?
converting one form of energy to another
eg converting energy of stimulus into electrical impulse
what are 3 different types of receptors?
pacinian corpusle
rods
cones
what is the stimulus for a pacinian corpusle?
pressure on skin
where are pacinian corpusle receptors located?
skin, joints, ligaments, tendons
how is an action potential caused in a pacinian corpusle?
pressure causes pacinian corpusle to be stretched and stretch mediated sodium channels to widen
sodium ions diffuse into neuron
neuron becomes depolarised creating a generated potential, leading to an action potential
what are the layers in the structure of the retina?
optic nerve fibre
ganglion cells
bipolar neurons
rod/cone cells
pigment epithelium
what is the stimulus for rods?
low intensity light
where are rod cells found?
retina
where are cone cells found?
retina
how is an action potential propogated in rod cells?
light strikes cell
rhodopsin breaks down to form retinal and opsin
causes rod cell to depolarise
generator potential occurs, leading to action potential
what is the stimulus for cone cells?
bright light
how is an action potential propogated in a cone cell?
light strikes cell
iodopsin breaks down
cone cell depolarises
generated potential occurs, leading to action potential
what are the properties of rod cells?
temporal summation
low visual activity
sensitive to low levels of light due to rhodopsin’s sensitivity
black and white vision
what are the properties of cone cells?
spatial summation
high visual activity
respond to high light only
different cones for different wavelengths of light - so coloured vision
