topic 2: lesson 4

Question 1

define synapse

Answer 1

the junction between the branches of adjacent neurons. usually occurs between axon terminal of one neuron and dendrite or cell body of another

Question 2

define neuromuscular junction

Answer 2

the special synapse where an axon meets a skeletal muscle cell

Question 3

define nerve impulse

Answer 3

the message that travels along a nerve fibre

they are transmitted very quickly so that our body can carry out rapid responses to ant change in our intenal or external environment.

Question 4

nerve impulse is actually…

Answer 4

an electrochemical change because it involves:

a change in electrical voltage
brought about by a change in the concentration of positive and negative ions inside and outside the cell membrane of a neuron

Question 5

what causes the difference in speed of nerve impulses between neurons?

Answer 5

all travel quickly, but it depends on whether the fibre is myelinated or not and also the fibres diameter.

large diameter= faster conduction

Question 6

the speed of nerve impulse in unmyelinated fibres:

Answer 6

the impulse must travel steadily along the entire length.

Question 7

the speed of nerve impulses in myelinated fibres:

Answer 7

the myelin sheath is not continuous, the impulse jumps from one node of ranvier to the next. the jumping conduction is called Saltatory conduction. allows for faster transmission.

Question 8

define saltatory conduction:

Answer 8

the skipping conduction of nerve impulses from one node of ranvier to another.

Question 9

like charges =

Answer 9

repel eachother

Question 10

opposite charges=

Answer 10

attract one another

Question 11

the electrical force between opposite charges gets stronger when…

Answer 11

an electrical force tends to pull opposite charges together, it gets stronger when they are closer together

and when they come together energy is released

Question 12

explain Potential (potential difference):

Answer 12

if + and - charges are separated, they have the potential to come together to release energy.

the potential difference between 2 places can be measured in voltage

Question 13

hows voltage measured

Answer 13

volts (V) or millivolts (mV)

Question 14

define membrane potential

Answer 14

cells having a difference in ion concentration between inside and outside of their cell

Question 15

membrane potential is particularly large in nerve and muscle cells. membrane potential of unstimulated nerve cells is known as

Answer 15

resting membrane potential

STEP 1

Question 16

STEP 1
what is the measure of the resting membrane potential?

Answer 16

-70 (mV)
negative 70

Question 17

STEP 1
extracellular fluid (outside the cell) has:

Answer 17

a high concentration of sodium chlorides

Question 18

STEP 1
intracellular fluid (inside the cell) has:

Answer 18

positive ions, potassium (K+)

its main negative ions come from a variety of large organic substances

Question 19

STEP 1

the resting membrane potential is largely due to differences of …
(3 points)

Answer 19

Na+ and K+ ions on either side of the membrane

sodium conc. is 10x higher outside the cell, compared to inside

potassium conc. is about 30x higher inside the cell, compared to outside

Question 20

why is the inside of the cell negatively charged?
(3 points)

Answer 20

no enough potassium inside the cell to counteract all the large negative organic ions

potassium diffuses out easily and sodium struggles to get inside

the large negative organic ions remain trapped inside the cell, too big to get through

Question 21

STEP 1
3 properties of the resting membrane potential:
(3 points)

Answer 21

• highly permeable to potassium and calcium ions (they can easily cross)
  -slightly permeable to sodium ions
  -impermeable to the large negative organic ions

Question 22

STEP 1

the cell membrane maintains it’s potential difference in 2 ways, what are they?

(first point = 3 explanations)
(second point= 1 explanation)

Answer 22

1. actively moves ions across the membrane using the sodium potassium pump.
   -transports sodium out of the cell, and transports potassium into the cell
   -more sodium is pushed out then potassium coming in- this ensures there are more positive ions on the outside
   -active process- requires ATP
2. large negative organic ions remain trapped inside the cell, as the membrane is impermeable to them

Question 23

action potential occurs when the membrane becomes rapidly:

Answer 23

depolarised or repolarised

Question 24

define depolarised

Answer 24

the inside of the cell becomes positive

Question 25

define repolarised

Answer 25

returns to being negative

Question 26

what are the two main channels that allow different ions in and out of the cell to change the membrane potential?

Answer 26

stimulus gated channels voltage gated channels

Question 27

define stimulus gated channels: (explain and give 2 points)

Answer 27

open due to the amount of stimulus -when there is not much stimulus there is not much opening of the channel - when there is a lot of stimulus the channel opens a lot

Question 28

define voltaged gated channels: (explain and give 3 points)

Answer 28

opens and closes according to the voltage of the membrane -if correct threshold voltage is reached the channels open -the channel closes when the membrane voltage reaches the right level -sodium and potassium gated channels are this type

Question 29

STEP 2 stimulus occurs

Answer 29

-if strong enough stimulus is applied to a nerve fibre to change the membrane potential from -70 to -55, -the stimulus gated sodium channels open and some sodium floods into the cell -inside of cell becomes less negative

Question 30

the movement of the action potential occurs as a wave along the nerve fibre, this is what we call ...

Answer 30

nerve impulse

Question 31

after depolarisation, the membrane is restored to it's original condition...

Answer 31

Repolarisation

Question 32

STEP 5 Repolarisation

Answer 32

potassium leaves the cell beginning to return the cell to normal (less positive, more negative)

Question 33

STEP 8 Refractory period

Answer 33

brief period during and after an action potential when that part of the nerve fibre cannot be stimulated to respond again. the period ends when the resting potential is regained (all sodium and potassium have returned to their usual places)

Question 34

why is it harder to trigger a cell during the hyperpolarisation part of action potential?

Answer 34

because the 'threshold' level is further away. during this period the cell is returning to equilibrium

Question 35

when does depolarisation occur

Answer 35

only occurs if the initial stimulus exceeds the threshold level, had to be strong enough to cause the sodium voltage channels gated channels to open (occurs at -55mV)

Question 36

explain the all or none response

Answer 36

means that a cell either responds fully or not at all, depending on weather the stimulus is strong enough

Question 37

explain the conduction of unmyelinated fibres

Answer 37

-when one area depolarises, it creates a current that triggers nearby areas to reach their threshold and depolarise as well -this process repeats itself like a wave along the nerve fibre

Question 38

refractory periods role in conduction along unmyelinated fibres

Answer 38

prevents action potential from travelling backwards

Question 39

STEP 6 hyperpolarisation

Answer 39

potassium channels close for the cell to respond to another stimulus, the NA and K have to swap places cell is more negative than normal

Question 40

STEP 3 threshold reached

Answer 40

voltage gated sodium channels open because of the movement of sodium ions into the cell, the original polarity deceases to 0, and the inside actually becomes positive relative to outside. neuron is depolarised.

Question 41

STEP 4 peak depolarisation

Answer 41

the sodium voltage gated channels close, leaving a high concentration of sodium inside the cell lets potassium go out so channels can switch it back the potassium voltage channels open

Question 42

STEP 7 restoring resting membrane potential

Answer 42

sodium potassium pumps take over - returning the sodium to the outside and brining the potassium back inside cell gets back to -70mV