Nervous system

Question 1

Two coordination systems

Answer 1

Hormonal and nervous

Question 2

Differences between them

Answer 2

Hormonal: slow, controlled by hormones in blood, long-lasting, permanent and irreversible, travel all body.
Nervous: fast, neurones, specific cells, localised, short lived

Question 3

Neurone structure

Answer 3

Cell body with usual organelles, a lot of RER to produce proteins and neurotransmitter.
Dendron, carry impulse toward cell body
Axon, away from
Schwann cell. surround axon, providing insulation and carry out phagocytosis of cell debris.
Myelin sheath to insulate cell and speed up impulse.
nodes of ranvier - constructions between schwann cells.

Question 4

Sensory neurone

Answer 4

Connect receptor to intermediate or motor neurone

Question 5

motor neurone

Answer 5

From relay to effector (gland or muscle)

Question 6

Relay neurone

Answer 6

Between neurones

Question 7

Resting potential voltage

Answer 7

-65mV

Question 8

How is resting potential maintained

Answer 8

Sodium ions actively transported out of axon by Na-K pump.
K pumped into axon by pump.
3 Na out for every 2 K in.
More sodium ions in tissue fluid than axon and more potassium ions in the cytoplasm, so electrochemical gradient.
Na diffuses back into axon and K into tissue fluid but more K moving as more K gates open.

Question 9

How is action potential

Answer 9

1) Some voltage gated K channels are open but Na closed.
2) energy from stimulus causes some V gated Na channels to open in axon which triggers reversal in potential difference across membrane.
3) More Na in by diffusion, increasing voltage, stimulating more gates to open.
4) When +40mV, Na ion channels close and K ion channels open.
5) Stimulates K to move out, repolarisation.
6) repolarise more than usual as overshoot of outward dif of K, so K gates close and pump brings back to -65mV.

Question 10

Passage of action potential along unmyelinated

Answer 10

Starts as -ve inside and +ve outside.
Stimulus causes Na+ influx and depolarisation.
Creates localised electrical currents that cause opening of sodium voltage-gated channels further along axon and further back, membrane is repolarising and sodium-potassium pump can return sodium back to tissue fluid to prepare for next action potential.

Question 11

Passage of action potential along myelinated

Answer 11

Myelin sheath acts as an insulator preventing action potentials from forming. At intervals of 1mm to 3mm, there are nodes of Ranvier where action potentials occur. Localised currents arise between nodes (saltatory conduction) making it faster.

Question 12

Factors affecting speed of action potential

Answer 12

Myelin sheath through saltatory conduction.
Diameter of neurone, higher = less leakage = faster, also less resistance to flow of ions
Temp affects rate of diffusion (also enzymes)

Question 13

All or nothing principle

Answer 13

When there is certain level of stimulus (threshold value), there is an action potential triggered.
All action potential same size.

Question 14

Purposes of refractory period

Answer 14

Ensures that action potential propagated in one direction only as cannot sodium gates are closed during repolarisation.
Discrete impulses.
Limits number of action potentials.

Question 15

How does Pacinian corpuscle work

Answer 15

Stretch mediated sodium channels are too narrow in normal state for Na ions to pass along. Neurone of Pacinian corpuscle has resting potential.
When pressure applied, membrane around corpuscle deformed and membrane around neurone is stretched. Widens sodium channels so they diffuse into membrane, depolarising, creating generator potential.

Question 16

What do rod and cone cells act as

Answer 16

s

Question 17

Sequence of events that control heart rate

Answer 17

Wave of electrical excitation spreads from SAN across both atria, creating contraction.
Atrioventricular septum prevent wave going to ventricles.
AVN (between both atria) receives electrical stimulus and after short delay conveys wave of electrical excitation along Purkyne tissue that forms bundle of His.
Bundle of HIs conducts wave through atrioventricular septum to base of ventricle. Then wave of excitation is released from the Purkyne tissue all at once so ventricle contracts at the same time.

Question 18

Action potential voltage

Answer 18

+40mV

Question 19

Synapse structure

Answer 19

Presynaptic knob and postsynaptic neurone separated by synaptic cleft.
Synaptic knob possess many REM and mitochondria to produce neurotransmitters stored in synaptic vesicles. Also has calcium ion protein channels.
Post synaptic neurone contains receptor sites and sodium ion protein channels.

Question 20

Function of synapses

Answer 20

Unidirectionality

Temporal and spatial summation

Question 21

Temporal summation

Answer 21

A single presynaptic neurone releases many neurotransmitter many times over short period. If conc of neurotransmitter exceed threshold value of the postsynaptic neurone, action potential is triggered.

Question 22

Spatial summation

Answer 22

Different presynaptic neurones release enough neurotransmitter to exceed threshold value of postsynaptic neurone and trigger action potential.

Question 23

Inhibitory synapse function

Answer 23

Presynaptic neurone releases neurotransmitter that binds to Cl- ion protein channels causing them to open on postsynaptic neurone.
Cl- move in postsynaptic neurone by facilitated diffusion.
Neurotransmitter also opens nearby K+ protein channels so K+ move out of postsynaptic neurone into synapse.
Therefore, inside of postsynaptic neurone even more negative and synapse even more positive (hyperpolarisation), less likely that action potential created because larger influx of sodium ions needed.