6.2 Nervous Coordination

Question 1

What is a neurone?

Answer 1

A single nerve cell

Question 2

What is a nerve?

Answer 2

A bundle of axons surrounded by connective tissue which binds them together

Question 3

What is the sensory neurone made up of? (In direction of nerve impulse)

Answer 3

Dendrites 
Dendron
Cell body (in the middle)
Axon
Branches of axon
Synaptic knob

Potentially with myelin sheath and nodes of Ranvier

Question 4

What is the intermediate (multipolar) neurone made up of?

Answer 4

Cell body in the middle

Axons and dendrites, with branches of axon and dendrites attached, all around the cell body

Question 5

What is the motor neurone made up of? (In direction of nerve impulse)

Answer 5

Cell body at the end (surrounded by dendrites)
One large axon
Branches of axon
Motor end plate (forms neuromuscular junction)

Potentially with myelin sheath and nodes of Ranvier

Question 6

How to remember the direction of the impulse?

Answer 6

Dendrites - dick in

Axon - away

Question 7

What do dendrites do?

Answer 7

Subdivisions of the dendron which transmits nerve impulses towards the cell body

Question 8

What does the cell body contain?

Answer 8

A nucleus

Large amounts of rough endoplasmic reticulum- for production of proteins and neurotransmitters

Question 9

What are the nodes of Ranvier?

Answer 9

Gaps between adjacent schwann cells where there is no myelin sheath

Question 10

What is the myelin sheath?

Answer 10

Forms a covering to the axon

Made up of membranes of Schwann cells

Question 11

What are the stages of an action potential?

Answer 11

Resting potential
Depolarisation
Repolarisation
Hyperpolarisation

Question 12

What are the numbers we need to learn from the action potential?

Answer 12

Resting potential: -65mV
Threshold: -55mV
Height of depolarisation: +40mV

Question 13

What is resting potential?

Answer 13

No impulse is being passed along
More positive ions outside the axon

-65mV

Question 14

What is the threshold for an action potential to take place?

Answer 14

-55mV

It needs to exceed the threshold

Question 15

Describe resting potential in terms of ions?

Answer 15

Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel is closed
K+ ion channel

-65mV

Question 16

Describe Depolarisation in terms of ions?

Answer 16

Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ion channel is open - Na+ facilitated diffuses into axon down electrochemical gradient
K+ ion channel is closed

-65mV to +40mV

Question 17

Describe Repolarisation in terms of ions?

Answer 17

Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel closes
K+ ion channel opens - K+ facilitated diffuses out of axon down conc gradient and electrochemical gradient

+40mV to -65mV

Question 18

Describe Hyperpolarisation in terms of ions?

Answer 18

Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel closed
K+ ion channel open - too many +ions have diffused out (temporary overshot of the electrochemical gradient)
The Na+/K+ pump, pumps K+ ions back into the axon to restore resting potential

Question 19

Which neurone is faster from a myelinated and unmyelinated neurone and why is it faster?

Answer 19

Myelinated is faster

As the fatty sheath of myelin around the axon acts as an electrical insulator preventing action potentials from forming
Action potentials only occur at the nodes of Ranvier where a localised current can form and the action potential ‘jumps’ from node to node

Called saltatory conduction

Question 20

Which neurone is slower from a myelinated and unmyelinated neurone and why is it slower?

Answer 20

Unmyelinated is slower

Depolarisation has to take place across the entire axon as oppose to just small sections

Question 21

What are the factors affecting nerve impulses?

Answer 21

Diameter of axon - increased = faster speed of conductance (due to less leakage of ions)

Myelin sheath - increases speed of conductance

Temperature - increased = speeds up the nerve impulse (due to enzymes being able to function faster and ATP formed faster for AT)

Question 22

What are the refractory periods?

Answer 22

Absolute - from start of depolarisation through to partway through hyperpolarisation NO action potential can be generated

Relative - from mid way through hyperpolarisation to resting potential an action potential is inhibited but not impossible

Question 23

What are the three purposes for the refractory period?

Answer 23

Ensures the action potentials only move in one direction

Produces discrete impulses

Limits the number of action potentials

Question 24

What is the principal to do with action potentials?

Answer 24

All or Nothing

There is an action potential or not at all
It needs to exceed threshold of -55mV
The strength of the stimulus is determined by the frequency

Question 25

What are the stages of synaptic transmission? P1

Answer 25

The action potential arrives at the synaptic knob
Ca+ ion channels open = Ca+ ions flow into the synaptic knob
Causing vesicles containing the transmitter to move to the presynaptic membrane
The vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft (exocytosis)
Acetylcholine diffuse down conc gradient across the gap and bind to specific receptor sites on postsynaptic membrane

Question 26

What are the stages of synaptic transmission? P2

Answer 26

Permeability of the postsynaptic membrane changes = Na+ ions flow inwards building up EPSP charge (e-excitatory)
If EPSP exceeds threshold = action potential some transmitters cause IPSP (i-inhibitory)
Acetylcholine is hydrolysed by acetylcholineresterase in the cleft
Choline and ethanoic acid are reabsorbed into the synaptic knob, which are resynthesised using energy from ATP
Na+ channels closed -absence of acetylcholine

Question 27

What is summation? Types?

Answer 27

The build up of neurotransmitter in the synapse

Spatial
Temporal

Question 28

What is spatial summation?

Answer 28

Where two or more action potentials arrive at the synapse at the same time down different neurones
So sufficient neurotransmitter is released to initiate the action potential in the postsynaptic neurone

Question 29

What is temporal summation?

Answer 29

Where two or more action potentials arrive at a synapse in quick succession down the same neurone
So sufficient neurotransmitter is released to initiate an action potential in the postsynaptic neurone

Question 30

How are some synapses inhibitory?

Answer 30

Neurotransmitter at synapses open K+ and Cl- channels rather than Na+
The resulting ion movement causes an IPSP which hyperpolarises the postsynaptic membrane

Question 31

Why is it beneficial to have inhibitory synapses?

Answer 31

Particular pathways can be selected

Makes it more difficult for an action potential to be generated

Question 32

How are synapses affected by morphine/codein?

Answer 32

It works agonistically

Has the same effect as endorphins

Question 33

How are synapses affected by prozac or ecstasy?

Answer 33

Blocks the reuptake of serotonin

So there is a high concentration of serotonin in the synapse = feeling happy

Question 34

How are synapses affected by valium?

Answer 34

It increases the efficiency of synaptic transmission

More Cl- channels are open to hyperpolarise the neurone = less excitable

Question 35

How are synapses affected by beta blockers?

Answer 35

Reduces the transmission of nerve impulses by binding to the receptor on the second neurone
Stops the heart speeding up