Co-ordination A Level

What is the name of the cells that produce myelin sheaths?

Match the following.

• presynaptic knob

• Where neurotransmitter receptor proteins can be found

• mitochondria

• Entry of calcium ions into presynaptic knob

• exocytosis

• Where neurotransmitter molecules are stored

• facilitated diffusion

• Secretion of neurotransmitter

• postsynaptic membrane

• Where ATP is synthesised

Reorder the following events that lead to muscle contraction.

• Neurotransmitters bind to their receptors on the sarcolemma.

• Neurotransmitters are secreted.

• Action potential runs along T-tubule.

• Action potential is generated in the sarcolemma.

• Sarcoplasmic reticulum releases Ca⁺⁺ ions

Which part of the graph shows the event when sodium ion channels close and potassium ion channels begin to open?

By which process is resting membrane potential maintained?

• facilitated diffusion

• exocytosis

• endocytosis

• active transport

What do you call a gap between two myelin sheaths?

What do you call an increase of membrane potential in a receptor that is too weak to start an action potential?

Which action potential comes from an ear which senses a whispering sound?

Ouabain is a poison that stops the activity of sodium–potassium pumps. If ouabain is added to part of an axon at a specific place along an axon, action potentials can continue to pass that region for about 1000 impulses. Which one explains why the transmission of impulses does not stop immediately?

• There is still concentration gradient of ions built-up by sodium-potassium pumps before the poison is given.

• The concentration gradient of sodium and potassium ions is maintained by sodium and potassium ion channels which are not affected by the poison.

• Mitochondria can still produce ATP which can power the active transport of Na⁺ and K⁺ ions.

• Impulse transmission does not depend on the activity of sodium-potassium pumps much.

Label the structure correctly.

f

e

d

a

b

c

I band

Thin filament

Thick filament

H band

A band

Z line