1Describe the role of proteins in the passage of a nerve impulse along a neuron (7 possible marks)
Change in voltage causes Na+ channel proteins to open
Na+ enters making inside more +ive
Allows more Na+ to enter, further changing p.d.
Delay in opening K+ channel proteins, allowing K+ to leave so p.d. is lower
Active transport involves pumping out Na+ and pumping in K+
Involves different membrane proteins (Na+/K+ pump)
Enzymes involved in respiration/production of ATP
2As a neurone transmits an impulse, its rate of oxygen consumption increases. Explain why (3 marks)
Active transport of Na+ in Na+/K+ pump
Requires ATP
So more respiration (aerobic)
3Myelination affects the rate of conduction of a nerve impulse. Explain how (2 marks)
Myelin insulates
Saltatory conduction
4Describe how a resting potential is maintained in a neurone (2 marks)
Na+ actively transported out
Membrane higher permeability to K+ than Na+
5The potential across the membrane is reversed when an action potential is produced. Describe how (2 marks)
Na+ channels open
Na+ diffuse in
6Myelinated axon uses less ATP to transmit a nerve impulse than an unmyelinated axon of the same diameter. Explain why (2 marks)
ATP required for active transport
Na+ actively moved out only at nodes in myelinated
7Describe how a resting potential is maintained in an axon (3 marks)
Active transport of Na+
Out of neurone
Different permeability to K+ and Na+
8Explain how movement of Na+ and K+ are involved in producing the action potnetial (3 marks)
Na+ diffuse in
Causes depolarisation
K+ then diffuse out to start recovery
9Describe how the resting potential is established in an axon by the movement of ions across the membrane (2 marks)
Active transport of Na+ out of axon
Little diffusion of Na+ into axon
10Describe the sequence of events leading to the release of Ach and its binding to the postSM (5 marks)
Depolarisation occurs
Ca2+ enter synaptic knob
Vesicles fuse with membrane
Ach diffuses
Binds to receptors
11Explain how the binding of GABA to receptors on postSM causing Cl- to enter postSM inhibits the transmission of nerve impulses by postSM (3 marks)
Inside becomes more negatively charged / hyperpolarised
Stimulation doesn't reach threshold / no AP produced
No depolarisation occurs
12Explain how a resting potential is maintained in a neurone (5 marks)
Na+ channels closed
Na+ actively transported out
By Na+ carrier
Higher Na+ conc outside of neurone
3Na+ out for 2K+ in
13What is a reflex (2 marks)
Automatic
Response to stimulus
14Nervous transmission is delayed at a synapse. Explain why (2 marks)
Chemical, not electrical
Process of transmission takes time (diffusion across synapse)
15Describe the sequence of events which allows info to pass from one neurone to the next neurone across a cholinergic synapse (8 marks)
Ca2+ enter axon
Vesicles fuse with preSM
Acetylcholine
Diffuses across synaptic cleft
Binds with receptors on postSM
Na+ enter neurone
Depolarisation of membrane
If above threshold, AP produced
16Explain what causes transmission ata synapse to occur only in 1 direction (3 marks)
Vesicles containing neurotransmitters found in preSM
Receptors for neurotransmitters only on postSM
So neurotransmitters diffuse down conc. gradient
17Explain how a resting potential is maintained across the axon membrane in a neurone (3 marks)
K+ diffuses out/higher K+ conc inside and higher Na+ conc outside
More permeable to K+
Na+ At out and K+ in
18Explain how Cl- entering postSM inhibits postSM (3 marks)
Neurone becomes more negative
More Na+ required / not enough Na+ enter (to reach threshold)
For depolarisation / AP
19Describe how when a nerve impulse arrives at a synapse and causes the release of neurotransmitters from vesicles in the preSM (3 marks)
Causes Ca2+ channels to open
Ca2+ enter by FD
Causes vesicles to fuse with preSM
20Explain how channel proteins on preSM are involved in reflex responses (3 marks)
Allows Ca2+ in
At end of preSM
Causing release of NET