Nervous Coordination

Question 1

What are neurones and what is their function? (2)

Answer 1

Specialised cells that carry electrical impulses from one part of the body to another

Question 2

Function of the myelin sheath (2)

Answer 2

Insulates the axon which increases the speed of electrical impulses along the axon

Question 3

What is a membrane potential difference? (1)

Answer 3

Difference in electrical potential across the membrane

Question 4

How is a resting potential established? (4)

Answer 4

Higher concentration of potassium ions inside and higher concentration of sodium ions outside (the neurone)
Membrane more permeable to potassium ions (leaving than sodium ions entering)
Sodium potassium pump actively transports 3 sodium ions out and 2 potassium ions in
Net result is that are more positive ions on the outside of the membrane than inside the neuron so the inside is slightly negative compared to the outside

Question 5

What is an action potential? (1)

Answer 5

High concentration of positive ions inside the cell

Question 6

Describe the process of depolarisation (5)

Answer 6

Stimulus causes the membrane to become more permeable to Na+ ions
Membrane potential reaches threshold (-50mV), all the voltage-gates Na+ channel proteins opens
Na+ ions rapidly diffuse into the cell (+40mV)
Higher concentration of positive Na+ ions inside the cell so the inside is more positive than the outside
K+ voltage-gates channel proteins remain closed

Question 7

Describe the process of repolarisation (3)

Answer 7

When the internal potential difference reaches +40mV, Na+ ion voltage-gated channel proteins close
K+ ion voltage-gated channel proteins open
More K+ ions on the inside than the outside so they diffuse out of the cell down a concentration gradient

Question 8

Describe hyperpolarisation (2)

Answer 8

K+ ion channel proteins remain open longer than needed to reach resting potential
So the inside of the cell becomes even more negative

Question 9

What does threshold mean? (1)

Answer 9

Minimum intensity of stimulus

Question 10

What is the all or nothing law? (1)

Answer 10

Full size action potential is given regardless of the increase in the size of the stimulus

Question 11

What is the refractory period? (4)

Answer 11

Time taken to restore the resting potential
Limits the number of impulses per second
Maximum frequency of impulse transmission
Produces discrete impulses

Question 12

What are the factors affecting the speed of conduction? (3)

Answer 12

Myelination and saltatory conduction
Axon diameter
Temperature

Question 13

How does myelination and saltatory conduction affect the speed of conduction of impulses? (3)

Answer 13

Myelin sheath provides electrical insulation along the axon
Electrical impulse depolarise the next node and the action potential jumps from node of Ranvier to the next node of Ranvier
Increases the rate of transmission as depolarisation only occurs at the nodes/less of the axon membrane needs to be depolarised

Question 14

How does temperature affect the speed of conduction of impulses? (3)

Answer 14

Higher temperature increases the kinetic energy
Increases rate of diffusion of ions
Increases rate of conduction

Question 15

How does axon diameter affect the speed of conduction of impulses? (3)

Answer 15

Longer the axon diameter, the longer the surface area
Increased number of channel proteins
Greater speed of conduction
Greater diameter means less resistance to flow of ions
Less ‘leakage’ of ions so easier to maintain membrane potential

Question 16

Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane (6)

Answer 16

Depolarisation of presynaptic membrane
Ca2+ channels open and calcium ions enter synaptic knob
Calcium ions cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine
Acetylcholine diffuse across the synaptic cleft
Acetylcholine binds to receptors on the post synaptic membrane
Sodium ions enter postsynaptic neuron leading to depolarisation

Question 17

What are neuromuscular junctions? (1)

Answer 17

Synapse between a motor neuron and a muscle cell

Question 18

How is a neuromuscular junction different to cholinergic synapse? (3)

Answer 18

Post synaptic membrane has lots of fold that form the cleft which increases surface area so more acetylcholinesterase enzymes
Post synaptic membrane has more receptors
When a motor neuron fires an action potential it always triggers a response in a muscle cell

Question 19

Function of acetylcholinesterase (2)

Answer 19

Hydrolyses acetylcholine into choline and ethanoic acid which diffuse back across the synaptic cleft in to presynaptic membrane
ATP is used to reform acetylcholine for storage in vesicles

Question 20

What is spatial summation? (2)

Answer 20

Different neurones converge at a single synapse so actional potential arrives from several different neurones at the synapse
Causes the release of enough neurotransmitters to reach threshold and causes an action potential in the post synaptic neurone

Question 21

What is temporal summation? (2)

Answer 21

Only one presynaptic neuron
Impulse arrives in rapid succession giving a cumulative effect which is sufficient to depolarise the post synaptic neurone

Question 22

What is fatigue? (2)

Answer 22

Rate of transmitter release is higher than the rate at which it is reformed
So the presynaptic neuron cannot release enough neurotransmitter to generate an action potential in the post synaptic neuron until the transmitter is regenerated

Question 23

What are excitatory neurotransmitters? (2)

Answer 23

Cause action potential in post synaptic neurone by making the resting potential less negative
So less sodium ions required to reach threshold

Question 24

What are inhibitory neurotransmitters? (2)

Answer 24

Resting potential becomes hyperpolarised
So post synaptic membrane is less likely to reach the threshold value and generate an action potential

Question 25

Describe the structure of a myelinated motor neuron (6)

Answer 25

Cell body - contains organelles and high proportion of rough endoplasmic reticulum
Dendrons - branch into dendrites which carry impulses towards cell body
Axon - long, unbranched fibre that carries nerve impulses away from cell body
Schwann cells - wrap around axon many times
Myelin sheath
Nodes of Ranvier

Question 26

What is resting potential? (1)

Answer 26

Potential difference across neuron membrane when not stimulated, usually about -70mV

Question 27

Explain the importance of the refractory period (3)

Answer 27

Ensures unidirectional impulse
Ensures discrete impulses
Limits frequency of impulse transmission

Question 28

How can an organism detect the strength of a stimulus (2)

Answer 28

Larger stimulus raises membrane to threshold potential more quickly after hyperpolarisation
Greater frequency of impulses

Question 29

Why is synaptic transmission unidirectional (3)

Answer 29

Only presynaptic neuron contains vesicles of neurotransmitter
Only post synaptic membrane has complementary receptors
So impulse always travels from presynaptic neuron to post synaptic neuron

Question 30

Explain the importance of acetylcholinesterase (2)

Answer 30

Prevents overstimulation of skeletal muscles
Enables acetyl and choline to be recycled

Question 31

Describes what happens in inhibitory synapses (5)

Answer 31

Neurotransmitter binds to and opens Cl- channels on postsynaptic membrane and triggers K+ channel proteins to open
Cl- moves in and K+ moves out by facilitated diffusion
Potential difference becomes more negative = hyperpolarisation
More sodium ions required (to reach threshold)
OR
Not enough sodium ions enter (to reach threshold)
For depolarisation/action potential

Question 32

Describe the effect of inhibiting acetylcholinesterase (5)

Answer 32

Acetylcholine not hydrolysed
Remains attached to receptors
Sodium ion channels remain open
Continued stimulus to muscles
Fatigue/continuous contraction/no relaxation

Question 33

Draw a simple reflex arc (3)

Answer 33

https://www.toppr.com/ask/question/draw-a-labelled-diagram-of-reflex-arc-and-explain-reflex/
Sensory neuron going to the grey matter from the receptor
Relay neuron in the grey matter synapses with sensory and motor neuron
Motor neuron going from the grey matter to effectors

Question 34

Explain the features of a reflex arc which result in the response being rapid and automatic (6)

Answer 34

Rapid:
Only involves three neurones
Myelination / saltatory conduction
and two / a few synapses;
Synaptic transmission is slow OR electrical/ nervous transmission is fast
Automatic:
Does not necessarily involve passage to brain / only spinal cord;
Same pathway used each time
higher brain centres not involved / no thinking

Question 35

Explain the role of the Na+ and K+ channels in producing the membrane resting potential (3)

Answer 35

More permeable to K+
More potassium (leaks) out
Therefore more positive on outside

Question 36

The rate of oxygen consumption of a neurone increases when it conducts a high frequency of impulses. Explain why (4)

Answer 36

Oxygen used in aerobic respiration
To produce ATP
For energy used by Na/K pump to actively transport Na+ and K+
Higher frequency of impulses –> more sodium ion entry and potassium ion lost

Question 37

Suggest two functions of the energy released by the mitochondria in the synaptic knob (2)

Answer 37

Active transport of ions/ ionic pump
Synthesis of acetylcholine
Reabsorption of acetylcholine, or acetyl + choline (from cleft)
Movement of vesicles (to membrane)
Synthesis of relevant enzyme, e.g. acetylcholinesterase

Question 38

Give two differences between a cholinergic synapse and a neuromuscular junction (2)

Answer 38

Neurone to neurone and neurone to muscle
Action potential in neurone and no action potential in muscle
Sarcolemma
No summation in muscle
Muscle response always excitatory
Some neuromuscular junctions have different neurotransmitters