Nervous Coordination

Question 1

What are the two main forms of coordination in animals?

Answer 1

Nervous + Hormonal System

Question 2

Describe the Nervous System

Answer 2

Uses nerve cells to pass electrical impulses along them.

Stimulate target cells by secreting neurotransmitters.

Question 3

Describe the Hormonal System

Answer 3

Produces hormones that are transported via blood to target cells.
Target cells have specific receptors on the CSM

Question 4

Differences between Hormonal and Nervous System

Answer 4

Communication: Hormones - Nerve Impulses
Transmission: Blood - Neurones
Speed: Slow - Fast
Travel: everywhere but only target cells respond — Specific parts of the body

Question 5

What is the Structure of a Myelinated Motor neuron?

Answer 5

Cell body
Dendrons - dendrites
Axon
Schwann Cells - Myelin sheath - Nodes of Ranvier

Question 6

Neuron - Cell body features

Answer 6

Large amounts of rough ER.

Production of proteins and neurotransmitters

Question 7

Dendron features

Answer 7

Extentions , subdivide into smaller branched dendrites.

Carry nerve impulses to cell body

Question 8

Axon features

Answer 8

single long fibre that carries nerve impulses away from the cell body

Question 9

Schwann Cell features

Answer 9

Wrap around Axon many times
Protects and provides insulation.
Carry out phagocytosis to remove cell devbris.

Question 10

What is a myelin sheath?

Answer 10

Schwann cell membrane rich in the lipid myelin that covers the axon.
Myelin sheath neurons = myelinated neurons.

Question 11

What are the Nodes of Ranvier?

+

Answer 11

Gaps between Schwann cells with no myelin sheath

Question 12

What is the resting potential?

Answer 12

The negative state of the inside of the axon compared to the outside, making the axon polarised. (60mV)

1) This happens as 3Na+ ions move out of the axon into the tissue fluid but 2K+ions move into the axon via sodium-potassium pumps on the axon CSM.
2) Since there are more positive ions in the tissue fluid than inside of the axon, this electrochemical gradient is formed.
3) Na+ ions begin to diffuse back into the axon and K+ ions back out the axon naturally.
4) But, most K+ gates are open whereas most Na+ gates are closed.

Question 13

What is the action potential?

Answer 13

(Axon is transmitting a nerve impulse)
1)Stimulus detected by receptors causes the voltage-gated Na+ channels to open and Na+ ions enter. They enter rapidly since as more Na+ ions move in, more Na+ channels open.
2)The positive charge causes a reversal in the potential difference across the membrane.
3)When an action potential is reached (40mV) the voltage-gated Na+ channels close and some voltage-gated K+ ions open.
4)Repolarisation starts - as more K+ ions diffuse out, more VG K+ channels open.
5)Hyperpolarization occurs as the outward diffusion of K+ ions causes the electrical gradient to temporarily overshoot, reaching less than -65mV, as the outside is more negative to the inside of the axon than usual.
Closable VG K+ channels close, Na+K+ pump now function as before (Na+ out K+ in).
Repolarisation occurs, -65mV to -60mV.

Question 14

What is the passage of an action potential along an unmyelinated axon?

Answer 14

1)RP - Na+ concentration = outside > Inside axon. K+ concentration = inside > outside axon. Axon membrane is polarised. Overall concnetration is greater on the outside so more positive outside than inside.
2)Stimulus causes a a sudden influx of Na+ ions = reversal of charge on the axon membrane.
The action potential is formed and the membrane is depolarised.
3)This causes VG Na+ channels to open further along the axon, allowing an influx of Na+ ions to flow in, causing depolarisation here. In this region the VG NA+ sadium channels close and the K+ ones open which allows K+ ions to move out the axon.
This causes depolarisation to occur along the membrane. (AP moves along).
4)Axon membrane which started the AP returns to its original shape.
5)Repolarisation of the axon allows Na+ ions to be AT out, returning the axon to the RP ready for a new stimulus.

Question 15

What is the passage of an action potential along a myelinated axon?

Answer 15

Myelin sheath prevents action potentials from forming as they act as electrical insulators.
Although they can occur at the nodes of Ranvier (break of myelin sheath) which causes localized circuits to form between adjacent NoR and via saltatory conduction the AP jumps from node to node.

Question 16

Why is a myelinated axon faster than an unmyelinated axon?

Answer 16

In an unmyelinated axon, depolarisation does not need to occur all the way along an axon which takes longer.

Question 17

How does the diameter of an axon affect the speed at which an AP travels?

Answer 17

Greater the diameter of an axon = faster the speed.

Less leakage of ions - meaning the membarne potential is easier to maintain.

Question 18

How does temperature affect the speed at which an AP travels?

Answer 18

• Affects the rate of ion diffusion so therefore a faster nerve impulse.
• Na+K+ pump is controlled by enzymes so the enzymes used will function more rapidly at higher temperatures. Although if the temperature is too high the enzymes and plasma membrane proteins will denature so an impulse will fail to conduct completely.

Question 19

What is the all-or-nothing principle?

Answer 19

A stimulus must be a certain level to pass the threshold value, which triggers an action potential.
Although all APs are all around the same size so the strength of the stimulus cannot be detected by the AP.

Question 20

How is the strength of a stimulus detected?

Answer 20

• The number of impulses passing in a given time.
• By having different neurones with different threshold values. The brain interprets the number and type of neurones that pass impulses, given by a stimulus and therefore determines it’s size.

Question 21

What is the refractory period?

Answer 21

After an AP has been create, there is a period afterwards when the inward movement of Na+ ions is prevented as the VG Na+ channels are closed.

Question 22

What are the purposes of a refractory period?

Answer 22

• Allows the AP to be propagated in one direction only. AP can only be passed from an active region to a resting region so if there was not a refractory period then the AP would move in both directions.
• It produces discrete impulses. A new AP cannot be formed immediately, this ensures that AP are separated from one another.
• Limits the number of action potentials and therefore limits the strength of stimulus that can be detected.

Question 23

Why are neurons unidirectional?

Answer 23

AP can only be passed from an active region to a resting region so if there was not a refractory period then the AP would move in both directions.

Question 23

Why are neurons unidirectional?

Answer 23

AP can only be passed from an active region to a resting region so if there was not a refractory period then the AP would move in both directions.

Question 24

Why are synapses unidirectional?

Answer 24

Receptors are only on the post synaptic membrane.

Question 25

What is the purpose of summation?

Answer 25

• Low frequency APs lead to an insufficient concentrations of neurotransmitters so a new AP cannot be formed.
• Through summation, neurotransmitters can rapidly build up.

Question 26

What are the two types of summation?

Answer 26

Spatial

Temporal