Nerve impulse process action potential term 2

Question 1

Describe and explain what a nerve impulse is and it’s function

Answer 1

electrochemical change that travels along a nerve fibre
-transmitted quickly
-make it possible for body to respond rapidly to any change in the internal/external environment

Question 2

What is contained in intercellular vs extracellular fluid following dissolving in water

Answer 2

intracellular- low conc of sodium ions and chloride ions
main positive ions are K
extracellular- has high

Question 3

What occurs due to difference in concentration of ions in outer/inner cell fluid? What is this called?

Answer 3

There is a potential between the inside and outside of cell membrane =membrane potential

Question 4

Explain what the resting membrane potential is and it’s value? What does it mean?

Answer 4

-70mV
the charge difference across plasma membrane of an unstimulated nerve cell

-means the potential of the inside of the membrane is 70mV less than outside

Question 5

Describe differences between the concs of Na and K in relevance to neuron

Answer 5

Na
-conc is 10x higher outside neuron than in. the cell membrane is only slightly permeable to Na ions due to limited number of sodium leakage channels=limited facilitated diffusion of Na ions

K
-conc is 30x larger inside neuron than out. cell is highly permeable to K due to large number of K leakage channels=more K ions able to diffuse than sodium ions

Question 6

Define difference between leakage channel and voltage gated

Answer 6

leakage-protein channel that is always open
voltage-protein channel that is opened by an electrical stimulus to nerve

Question 7

Describe how sodium-potassium pump works following hyperpolarisation

Answer 7

Needed to maintain RMP. Pump moves 2xK into cell for every 3xNa removed=net reduction of positive ions inside cell

Question 8

How is net flow of positive ions out of cell established?

Answer 8

-the location of ions
-permeability of membrane (channels)
-sodium-potassium pump

and presence of negative organic ions

Question 9

Define polarised

Answer 9

the situation when the inside of the membrane of a nerve cell has a negative electrical charge compared with the outside

Question 10

Define action potential. How does it occur? (shorter summary)

Answer 10

rapid depolarisation and repolarisation of the membrane
=opening/closing of voltage-gated channels caused by sufficient stimulus, passing a signal along the neuron

Question 11

Describe the process of depolarisation

Answer 11

1. RMP is -70mV
2. ligand gated channels open when stimulus transmitted by neurotransmitter to neuron
3. membrane permeable to Na allowing entrance of some Na increases potential difference (inner more positive)
4. if increases to -55mV threshold, voltage gated channels open
5. influx of Na ions into cell that proceeds independently of stimulus =all or nothing
6. original polarity of membrane increases as inside more positive than outside=depolarised membrane

Question 12

Describe the process of repolarisation.
How does hyperpolarisation occur
Use diagram to display

Answer 12

1. Na voltage gated channels close simultaneously to K voltage channels open
   -increases diffusion of K out of cell
2. inside membrane become negatively charged in comparison to out, decreasing the membrane potential to RMP (-70mV)
3. channels open longer than needed=lower membrane potential due to too much k rushing out=hyperpolarised membrane
4. k gate will close

Question 13

Explain and give the significance of the refractory period

Answer 13

short period following stimulus to RMP
-nerve cell cannot be re-stimulated/action potential cannot occur
-once Na channels opened they quickly become inactive=unresponsive to stimulus

-prevent nerve impulse moving backwards due to inability of another action potential being generated at that point

Question 14

Describe transmission along unmyelinated fibres
(revise over diagram either book or worksheet)
How does this continue down an axon

Answer 14

-positive out and neg inside (-70mV RMP)
-stimulus causes open of ligand gated, and if higher than -55mV threshold, voltage gate open
-influx of Na into membrane=depolarised
-stimulates movement of Na+ into adjacent area
-movement stimulates opening of voltage gated channels in next part of membrane, initiating action potential
-mention repol and hyperpol
-slower response

Question 15

Describe transmission along myelinated fibres
(revise over diagram either book or worksheet)
Describe “saltatory conduction”

Answer 15

-positive out and neg inside (-70mV RMP)
-stimulus causes open of ligand gated, and if higher than -55mV threshold, voltage gate open
-influx of Na into membrane=depolarised node
-triggers open of next sodium gate in node of ranvier
-impulse moves bwn uninsulated gaps = nodes of Ranvier that exist between each Schwann cell.
-called saltatory conduction
-mention repolarisation and hyperpolarisation
-Sodium-Potassium pump restores the concentration of the sodium and potassium ions during this period.
-allows faster impulse

Question 16

How is the strength of a stimuli determined

Answer 16

-strong stimulus causes depol. of more nerve fibres than weak
-strong stimulus produces more nerve impulses in a given time than weak

Question 17

Draw, annotate and label a diagram to describe transmission across a synapse
including axon terminal, presynaptic and postsynaptic[tic terminal, synaptic vesicles, neurotransmitters, receptors, voltage gated calcium channels, synaptic cleft

Answer 17

1.When impulse reaches the axon pre-synaptic terminal of receptor, it activates voltage-gated Ca ion channels to open
-increasing Ca uptake into cell at the pre-synaptic terminal
2. Vesicles move toward axon surface. Release of neurotransmitters via exocytosis
3. Transmitter diffuses across synapse and binds to receptor on post-synaptic terminal on dendrite of other neuron
4. This stimulates ligand-gated protein channels to open, allowing original impulse through the next neuron

Question 18

How is a neurotransmitter removed from a synapse

Answer 18

-being reabsorbed by the presynaptic membrane
-degraded by enzymes
-moving away through diffusion

Question 19

Explain the all-or-none response

Answer 19

if potential increases to -55mV threshold, voltage-gated Na channels open
this produces movement of Na ions into cell that proceeds independently of stimulus i.e. size of response is not related to strength of stimulus

Question 20

Define and describe the role of a “neurotransmitter”

Answer 20

molecule that carries a nerve impulse across the small gap between branches of adjacent nerve cells

Question 21

Describe the structure and function of a synapse

Answer 21

junction between branches of adjacent neurons