nervous coordination

Question 1

describe how an action potential is maintained across the axon membrane in a neurone (3)

Answer 1

• Higher concentration of sodium ions outside the neurone and higher concentration of potassium ions inside the neurone
• membrane is more permeable to potassium ions
• 3Na+ actively transported out and 2K+ actively transported into the membrane

Question 2

why is speed of transmission faster along a myelinated axon then along a non-myelinated axon (3)

Answer 2

• myelination provides electrical insulation
• in a myelinated neurone depolarisation occurs at the nodes of ranvier
• in a non-myelinated neurone depolarisation occurs along the whole length of the axon

Question 3

describe the events involved in transmission along a cholinergic synapse (6)

Answer 3

• depolarisation (nerve impulse) of the presynaptic membrane
• calcium ion channels open and calcium ions enter the synaptic knob
• calcium ions cause the synaptic vesicles to fuse with the pre-synaptic membrane and release acetylcholine (neurotransmitters)
• acetylcholine diffuses across the synaptic cleft
• acetylcholine attaches to receptors on the post-synaptic membrane
• sodium ions enter the post synaptic neurone leading to depolarisation

Question 4

explain the role of inhibitory substances (GABA) (6)

Answer 4

• GABA receptors found on the post-synaptic membrane
• GABA binds to its receptors increasing membrane permeability to Cl- ions
  -Cl- ions diffuse through Cl- ion channels
• causes inside of post-synaptic neurone to become more negative
• more Na+ ions required to reach threshold for action potential
• so less likely to generate an action potential when stimulated