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Flashcards in Coordination Deck (25)
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1

Differences between synapse and neuromuscular 

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

2

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

  • 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

3

Why is the impulse on transmitted in one direction

  • 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

4

How is the resting potential re-established?

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

5

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

  • Impulse jumps from node to node
  • Fewer jumps needed

6

what is a reflex?

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

7

Why can't another AP be created straight after?

  • 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

8

How is a new AP made? (2 M)

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

9

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

  • 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;

10

Criteria for a response to be a simple reflex action?

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

11

Function of energy released by the presynaptic mitochondria

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

12

Why do people without mylein sheath have slower reflexes

  • 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

13

Explain why nervous transmission is delayed at synapses.

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

14

Why does a lower temp lead to a slower transmission?

1. Slower diffusion;

2. Of  Na+  and K+ as less kinetic energy

15

Why do fewer AP pass along a myelinated neurone?

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

16

How is the membrane repolarised?

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

17

Define summation and lists the benefits

  • 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 

18

How is the resting potential maintained at -65 mV

  • 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

19

All-or-nothing definition

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

20

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

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

21

Describe the formation of an AP

  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;

22

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

  • 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

23

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

  • 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

24

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

  • 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;

25

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

1. Similarity – directional response to a stimulus (movement towards/away)

 2. Difference – taxis whole organism moves but tropism a growth response;