5.1.3 Neuronal Communication

Question 1

What are communication systems needed for?

Answer 1

• detect stimuli
• coordinate information
• respond in order to survive

Question 2

what are the three key features of neurones?

Answer 2

• Cell body- Contains large amounts of smooth ER for synthesising neurotransmitters
• Dendrons- Extensions which transmit impulses towards cell body
• Axons- Transmit impulses away from cell body contain a small amount of cytoplasm

Question 3

What are pacinian capsucules and where are they found?

Answer 3

Pressure sensors found in skin

Question 4

How do pacinium capsucules detect pressure?

Answer 4

• Have a capsule which deforms under pressure
• Causes Na+ and K+ ion channels to open
• This causes it to reach threshold potential

Question 5

What are the features of a sensory neurone?

Answer 5

• 1 dendron 1 axon
• Transmit impulses from receptors to relay

Question 6

What are the features of a motor neurone?

Answer 6

Many short dendrites with only one dendron
Transmit impulses from relay/sensory to effector

Question 7

What are the features of a relay neurone?

Answer 7

Many short axons and dendrons
Transmit impulses between neurones

Question 8

What are the features of an axolemma membrane at rest?

Answer 8

Na channels are closed
Membrane is leaky to K+ ions
At resting potential

Question 9

What voltage is resting potential?

Answer 9

-70 mV

Question 10

What is a generator potential?

Answer 10

• Small change in potential difference
• Caused by Na+ channels opening
• Higher strength of stimuli means more channels open

Question 11

What is threshold potential?

Answer 11

50 mv
The minimum potential needed for an action potential to take place

Question 12

What is a refractory period and what does it prevent?

Answer 12

Short period of time where it is impossible for another action potential to be formed
Stops actionpotentials from travelling in different directions

Question 13

What happens at the membrane when threshold potential is reached?

Answer 13

-More voltage gated Na+ channels opendepolarising membrane to +40mv

Question 14

What happens at a membrane after 40mv are reached?

Answer 14

Na channels close and K+ channels open causing K+ to diffuse out

Question 15

What is hyperpolarisation?

Answer 15

Where Potential difference has overhsot slightly and needs to be fixed by the Na+/K pump

Question 16

What the three steps in the transmission of an action potential?

Answer 16

1.Voltage gated Na channels open and Na+ diffuse in
2.Na+ in a igh concentration where they diffuse in so move to an area of low concentraton via diffusion in a local circuit
3. P.D altered across membrane where Na + have moved to therefore more Na channels open and action potential has moved

Question 17

What are the features of myelination?

Answer 17

• Insulating layer of Schwann cells meaning action potential cannot occur within it
• Nodes of ranvier - Places of no myelination

Question 18

What are the advantages of myelination?

Answer 18

Speeds up transmission of action potentials as elongates local circuits and means saltatory conduction can occur

Question 19

Why is the width of an axon important?

Answer 19

Larger diameter = faster conduction
Greater area of membrane which ionic exchange can occur

Question 20

What is acclimatisation?

Answer 20

• Repeated stimulation will cause synapse to run out of neurotransmitter vesicles meaning no more action potentials can be transferred

Question 21

What are the roles of synapses?

Answer 21

• Ensures all action potentials are unidirectional
• Several stimuli warning us of danger
• One signal can be transmitted all over the body
• Filters out low level signals

Question 22

What is summation?

Answer 22

Where low levels of stimulation can cause a reaction if persistent

Question 23

What is spacial summation?

Answer 23

Where two or more synaptic knobs act simultaneously

Question 24

What is temporal summation?

Answer 24

Where several action potentials arrive in great succession

Question 25

What are the steps involved in the transmission across a synapse?

Answer 25

1. Action potential arrives at end of presynaptic neurone
2. Voltage gated Ca 2+ channels open
3. Synaptic vesicles fuse with presynaptic membrane
4. Acetylcholine released by exocytosis and diffuses across cleft
5. Acetylcholine bind to receptors on Na channels
6. Na channels open and Na+ diffuses into post synaptic membrane
7. Generator potential created
8. Membrane reaches threshold potential