Coordination

Question 1

Differences between synapse and neuromuscular

Answer 1

• neurone to neurone but neurone to muscle;
• no summation in neuromuscular synapse;
• some chlolinergic synapse can have different neurotransmitters e.g noradrenaline;

Question 2

Describe the events that occur at the synapse during the delay between AP in the pre/postsynaptic neurone

Answer 2

• Voltage-gated Ca ion channels open
• Calcium ion enter
• vesicles fuse with preS memb
• exocytosis (release of neurotransmitter)
• these diffuse across cleft ;
• attach to receptors on postS memb
• this causes Na channels to open, allowing Na to diffuse in

Question 3

Why is the impulse on transmitted in one direction

Answer 3

• Neurotransmitter only produced in pre-synaptic neurone;
• Receptor proteins for neurotransmitter only in post-synaptic membrane;
• Neurotransmitter diffuses from high conc to low
• Acetylcholinesterase is in the post-synaptic neurone

Question 4

How is the resting potential re-established?

Answer 4

• Na-K pump
• 3 sodium actively transported out as 2 potassium in;
• ATP needed

Question 5

Why does an increase in the length of myelination between nodes lead to an increase in the speed of conductance

Answer 5

• Impulse jumps from node to node
• Fewer jumps needed

Question 6

what is a reflex?

Answer 6

Rapid** reactiom to stimulus which produces an **automatic** response. It is **innate

Question 7

Why can’t another AP be created straight after?

Answer 7

• During refractory period
• Sodium ion channels closed;
• So Sodium ions cannot enter axon;
• Membrane potential becomes more negative than resting potential
• so threshold less likely to be exceeded

Question 8

How is a new AP made? (2 M)

Answer 8

• Sodium ion channels open;
• Allowing rapid influx of sodium ions;

Question 9

Why does a myelinated axon use less ATP to transmit a nerve impulse than an unmyelinated axon of the same diameter

Answer 9

• 3 Na+ actively moved out and 2 K+ in
• ATP required for active transport;
• Only at nodes in myelinated
• This occurs over whole length of axon in non-myelinated;

Question 10

Criteria for a response to be a simple reflex action?

Answer 10

• Not involve conscious thought (brain isn’t used)
• Reaction is innate and not learned;
• Reaction is protective (prevent damage);

Question 11

Function of energy released by the presynaptic mitochondria

Answer 11

• Synthesis of acetylcholine from acetyl + choline ;
• Movement of vesicles to membrane;
• Synthesis of enzyme acetylcholinesterase.

Question 12

Why do people without mylein sheath have slower reflexes

Answer 12

• No saltatory conduction
• Depolarisation occurs over whole length of neurone
• This leads to slower transmission of AP
• Hence slowing down the arrival of impulses to muscle;
• So delay in muscle contraction

Question 13

Explain why nervous transmission is delayed at synapses.

Answer 13

• Neurotransmitters need to diffuse across cleft
• Process of diffusion takes time

Question 14

Why does a lower temp lead to a slower transmission?

Answer 14

1. Slower diffusion;
2. Of Na+ and K+ as less kinetic energy

Question 15

Why do fewer AP pass along a myelinated neurone?

Answer 15

• Myelin insulates axon so ions can only pass through at gaps in myelin sheath;
• Gaps in sheath are called nodes of Ranvier;

Question 16

How is the membrane repolarised?

Answer 16

• Sodium ion channels close and potassium ion channels open;
• Allowing efflux of potassium ions;

Question 17

Define summation and lists the benefits

Answer 17

• addition** of many impulses which is directed onto a **single post synaptic neurone;
• spatial summation: allows integration** of stimuli from a **variety of sources
• temporal summation allows weak** background stimuli to be **filtered out before reaching the brain

Question 18

How is the resting potential maintained at -65 mV

Answer 18

• Membrane more permeable to potassium ions than to sodium ions;
• So Potassium ions diffuse out faster than sodium ions diffuse in;
• Sodium-potassium pump uses ATP;
• 3 Na pumped out for every 2 K in
• Higher conc of +ve ions outside cell

Question 19

All-or-nothing definition

Answer 19

• All action potentials are the same size;
• There’s a threshold value for action potential to occur
• Below it, no AP formed

Question 20

After a reflex has occured, how do we know it has?

Answer 20

• impulses sent to brain
• sensory areas in brain interpretes and processes the impulse

Question 21

Describe the formation of an AP

Answer 21

1. Stimulus excites membrane, causing Na channels to open so Na+ enter;
2. Down electrochemical gradient;
3. If threshold met more Na+ channels open via +ve feedback
4. At 40mV, Repolarisation occurs as Na channels close K channels open so K+ leave
5. Down electrochemical gradient
6. Hyperpolarisation occurs as K close slowly
7. Sodium-potassium pump restores resting potential;

Question 22

If acetylcholinesterase is inhibited how can this lead to death by affecting breathing?

Answer 22

• acetylcholine not broken down;
• it remains attached to receptor
• Na channels remain open, so Na depolarises axon
• would lead to continuous impulses, causing muscle spasms;
• no relaxation of intercostal muscle leads to fatigue
• stops breathing

Question 23

Explain why the rate of oxygen consumption of a neurone increases when it conducts a high frequency of impulses.

Answer 23

• Oxygen used in respiration,
• Increase in respiration so more ATP made
• ATP used in sodium-potassium pump
• More Na+ actively moved out and more K+ actively moved in
• This is to maintain resting potential

Question 24

Due to the refractory period, after a certain concentration of acid the brain can’t obtain information about the concentrations. Why

Answer 24

• Refractory period leads to discrete nerve impulses
• Refractory period limits the frequency of nerve impulses;
• When maximum frequency reached/exceeded, all higher concentrations of acid seem the same;

Question 25

Give one similarity and one difference between a taxis and a tropism.

Answer 25

1. Similarity – directional response to a stimulus (movement towards/away)
2. Difference – taxis whole organism moves but tropism a growth response;