Nervous coordination

Question 1

Explain how a resting potential is maintained across the axon membrane in a neurone

Answer 1

1. Higher concentration of potassium ions inside
   and higher concentration of sodium ions outside
   the neurone. So potassium ions diffuse out and sodium ions diffuse in.
2. Membrane more permeable to potassium ions
   leaving than sodium ions entering
3. Sodium ions actively transported out and
   potassium ions in.

Question 1

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon.

Answer 1

1. Myelination provides electrical insulation
2. In myelinated saltatory conduction occurs
3. In non-myelinated depolarisation occurs along
   whole length of axon

Question 2

Describe the roles of calcium ions and ATP in the contraction of a myofibril.

Answer 2

1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
2. Calcium ions cause movement of tropomyosin on actin
3. Causing the exposure of the binding sites on the actin
4. Myosin heads attach to binding sites on actin
5. Hydrolysis of ATP on myosin heads causes myosin heads to bend
6. pulling actin molecules
7. Attachment of a new ATP molecule to each myosin head
   causes myosin heads to detach from actin sites

Question 3

Structure of skeletal muscle

Answer 3

…

Question 4

Fast twitch muscle fibres V slow twitch muscle fibres

Answer 4

Fast twitch:
- Contract more rapidly and produce more powerful contractions but only for a short period of time
- Adapted to intense activity (e.g. weight lifting)
- Adapted to anaerobic respiration
- Thicker/ more myosin filaments
- Increased conc. of glycogen
- Store of phosphocreatine
Slow twitch:
- Slower and less powerful contractions, but last for longer period of time
- Adapted for endurance work (e.g. a marathon)
- Adapted to aerobic respiration
- Large myoglobin store
- Rich supply of blood vessels
- Many mitochondria

Question 5

temporal v spatial summation

Answer 5

Temporal - Repeated impulses in short period of time from one presynaptic knob provide enough neurotransmitter to reach threshold to trigger action potential.
Spatial - A number of different presynaptic neurones together release enough transmitter to exceed threshold value of postsynaptic neurone to trigger action potential.