5.1.3 Neuronal communication

Question 1

What is the role of a sensory receptor?

Answer 1

respond to stimuli
by acting as a transducer

Question 1

What is a pacininan corpuscle?

Answer 1

sensory receptor found in the skin that detects pressure changes

Question 2

How does the Pacinian corpuscle detect changes?

Answer 2

when pressure is applied;
the membrane surrounding the neurone stretches and caused gaps between the phospholipids;
this opens sodium channels ;
sodium rushes in along electrochemical gradient generating an action potential;

Question 2

What is the structure and function of a sensory neurone?

Answer 2

dendron present and links to cell body;
cell body is in the middle of the neurone;
axon is shorter than a motor neurone;
neurone connects to a sensory receptor;
not found in the CNS

Question 2

What is the structure and function of a relay neurone?

Answer 2

short axon;
dendrites present;
found in the CNS;

Question 3

What is the structure and function of a motor neurone?

Answer 3

no dendrons;
cell body is at the end of the neurone;
dendrites are directly connected to cell body;
axon is longer than sensory neurone;
neurone ends at the motor end plate;

Question 3

What is a myelin sheath?

Answer 3

later of fatty material of schwann cells; create an insulating later = speeds up transmission of action potential

Question 4

What is saltatory conduction?

Answer 4

membrane is only depolarised at the nodes of Ranvier;
creates a long localised current;
increases rate of impulse transmission;

Question 5

How is the resting potential established?

Answer 5

• 3 sodium ions leave the neurone
• 2 potassium ions enter
• via active transport
• using a sodium potassium pump
  some potassium ions leak back out as the membrane is more permeable to potassium ions
• sodium voltage gated channels are closed

Question 6

How is a action potential generated?

Answer 6

1) Depolarisation:
- sodium ion voltage gated channels open to allow sodium ions to rush into the membrane along its electrochemical gradient increase its membrane potential (positive feedback)

2) Repolarisation:
- sodium ion voltage gated channels close
- postassium voltage gated channels open
-K+ rushes out of the membrane along its electrochemical gradient decreasing its membrane potential

3) Refractory period
- K+ voltage gated channels close by there is an overshoot of K+ = hyperpolarisation

Question 7

What is the function of the refractory period?

Answer 7

allows the nerve impulse to travel in one direction AP only occurs = resting potential

Question 8

What is the ‘all or nothing’ law?

Answer 8

not enough change in potential difference to reach threshold = no action potential generated

if above threshold high or just about = same action potential

Question 9

What is a rule of action potentials?

Answer 9

All action potentials have the same magnitude;
the stronger the stimuli the higher the frequency of the nerve impulses

Question 10

What is the function of a synapse?

Answer 10

• action potential incoming
• cause calcium channels to open
• calcium rushes in down it chemical gradient
• cause vesicles containing NT fuse with membrane using cytoskeleton
• vesicles release NT in synapse - exocytosis
• diffuse across synapse and bind to receptor/sodium voltage gated channel

Question 11

What is the enzyme that breaks down acetylcholine?

Answer 11

acetylcholinesterase into acetyl and choline - reabsorbed

Question 12

Outline the role of synapses?

Answer 12

allows neurones to communicate;
ensures transmission in one direction;
allows convergence and divergence
filters out background stimuli
prevent fatigue
allows low level stimuli to be amplified

Question 13

Why does the synapse allow transmission in one direction?

Answer 13

vesicles containing neurotransmitter found in presynaptic knob
receptors on the sodium voltage gated channels found on the post synaptic membrane
calcium channels can only be found on the pre-synaptic membrane

Question 14

What is summation?

Answer 14

rapid build up of NTs in the synapse to help generate the action potential

Question 15

What is spatial summation?

Answer 15

many different neurones collectively trigger a new action potential by combing the NTs they release to exceed the threshold value

Question 16

What is temporal summation?

Answer 16

one neurone releases NTs repeatedly over a short period of time to add up enough to exceed the threshold value