nerves Flashcards
why are synapses unidirectional
Vesicles containing neurotransmitter are only found in presynaptic neurone
· Receptors for neurotransmitter are only found on post synaptic neurone
As a neurone transmits an impulse, its rate of oxygen consumption increases. Explain why. ·
ATP required for active transport; · Na+ (actively) moved out only at nodes in myelinated / Na+ (actively) moved out along whole length of axon in non-myelinated;
Describe how a resting potential is maintained in a neurone. ·
active transport/pumping of sodium (ions across membrane); · out of neurone/higher concentration outside; · differential permeability to K+ and Na+; · Membrane more permeable to K+ ions;
SYNAPSE:
Describe the sequence of events leading
to the release of acetylcholine and its
binding to the postsynaptic membrane.
·
Depolarisation of presynaptic membrane; · Ca2+ channels open and calcium ions enter (synaptic knob) through facilitated diffusion · (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter; ·using ATP Acetylcholine/neurotransmitter diffuses across (synaptic cleft); · (Acetylcholine attaches) binds to receptors on the postsynaptic membrane; · Sodium ions diffuse (postsynaptic neurone) reaches threshold (-55) leading to depolarisation; and action potential
The binding of GABA to receptors on
postsynaptic membranes causes
negatively charged chloride ions to enter
postsynaptic neurones.
Explain how this will inhibit transmission
of nerve impulses by postsynaptic
neurones. ·
(Inside of postsynaptic) neurone becomes more negative/hyperpolarised; · More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold); · For depolarisation/action potential;
When a nerve impulse arrives at a
synapse, it causes the release of neurotransmitter from vesicles in the
presynaptic knob. Describe how.
· (Nerve impulse/depolarisation of membrane) causes Ca2+ channel (proteins) to open; · Ca2+ enter by (facilitated) diffusion; · Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
The potential across the membrane is
reversed when an action potential is
produced. Describe how. ·
Sodium ion gates / channel (proteins) open; · Na+ (rapidly) diffuse in;
Describe how the inhibition of
acetylcholinesterase affects the action
of synapses. ·
Acetylcholine not broken down / stays bound to receptor; · Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
Myelination affects the rate of
conduction of a nerve impulse. Explain
how. ·
Impulse jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier; · Fewer jumps / depolarisations to travel length of axon;
Describe how the speed of the
conduction could be increased in a
neurone
. · Axon is myelinated; · So shows saltatory conduction/impulses jump from node of Ranvier to node of Ranvier; OR · Axon has a larger diameter; · So less resistance to flow of ions;
how is resting potential maintained 5
maintained by Na/K pump and involves active transport and ATP hydrolysis.
There is a higher concentration of Sodium on the outside of the neurone
· There is a higher concentration of Potassium on the inside of the neurone
· The difference is maintained by many Na+/ K+ pumps that actively transports 3Na+ out of the cell (this requires the energy released from ATP) and diffuse 2K+ in to the cell
There are also voltage gated channel proteins for both K+ ions and Na+ ions embedded within the axon membrane.
· In a resting neurone the Na+ ion “voltage-gated” channel proteins are closed.
· Na+ ions pumped out of the cell cannot therefore diffuse (facilitated) back in
· Some of the K+ ion channel proteins are open (membrane is more permeable to K+ ions)
· Some of the K+ ions can diffuse (leak back out)
· The net result is that there are more positive ions on the outside of the membrane than inside the neurone and so the inside is slightly negative compared to the outside.
Describe what is meant by the term
refractory period ·
(Refractory period) limits number of impulses per second/frequency of nerve impulses; · Maximum frequency of impulse transmission · Period of time between threshold and resting membrane potential. · When maximum frequency reached/exceeded, no further increase in information/ all (higher) stimuli seem the same
describe repolarisation
Once the internal potential difference reaches +40 mV (forming the action potential due to depolarisation), the Na+ ion voltage-gated channel proteins CLOSE and the K+ ion voltage-gated channel proteins OPEN.
· There are more K+ ions on the inside of the axon than the outside of the axon membrane and therefore the K+ ions diffuse OUT of the cell down a concentration gradient. This process is called REPOLARISATION
describe depolarisation
the stimulus causes the membrane to become more permeable to Na+ ions
· IF the membrane potential reaches threshold, all the voltage-gated Na+ channel proteins OPEN
· Because there is a higher concentration of Na+ ions outside the cell the Na+ ions rapidly diffuse INTO the cell (by
facilitated diffusion)
· The higher concentration of positive Na+ ions inside the cell now reverses the resting potential and causes the inside to become positive in relation to the outside. This process in called DEPOLARISATION
(K VGC remain closed)
· The K+ voltage gated channel proteins remain (mostly) CLOSED at this time
· The high concentration of positive ions inside the cell is the ACTION POTENTIAL
describe hyperpolarisation
The K+ ion channel proteins remain open longer than needed to reach resting potential, making the inside of the cell even more negative to about -90mV. This process is called hyperpolarisation.
· The sodium potassium pump restores the resting potential back to -70mV
A student wanted to investigate the resting blink rate in people 60 years of age and people 15 years of age.
Describe how the student could find out whether there was a significant difference in blink rates between the two age groups. 3
Reference to large group size;
- Reference to matching a specific, named variable;
- Applying a statistical test to the data;
- Accept ‘≥ 20 / many / lots’ but not ‘several / less than 20’
- Accept any named variable other than age.
- Accept ‘use SE / 95% confidence limits’
The blink reflex involves synapses. Channel proteins on presynaptic neurones are involved in reflex responses.
Explain how. 3
Allows calcium ions in; by FD
- At end of presynaptic neurone;
- Causing release of neurotransmitter;
- Accept Ca2+/Ca ions but not Ca/Ca+
- The idea of the end of the presynaptic neurone must be given e.g. presynaptic knob
The student did not draw a line of best fit.
Suggest two reasons why.
Not possible to predict intermediate values;
- Only one result for each time period / not mean values;
