The Nervous System

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4 marks

Nerve impulses travel along axons as action potentials.

The graph shows an oscilloscope trace for an action potential in an axon.

q1a-unit-5-january-2021-edexcel-ial-biology

(i)

Which is the resting potential for this axon?

(1)

☐	A	–70mV
☐	B	–78mV
☐	C	38mV
☐	D	108mV

(ii)

Both voltage-gated sodium and voltage-gated potassium ion channels are involved in generating an action potential.

Which of these voltage-gated channels are open at Y?

(1)

☐	A	No voltage-gated ion channels are open
☐	B	Voltage-gated sodium ion channels only
☐	C	Voltage-gated potassium ion channels only
☐	D	Both sodium and potassium voltage-gated ion channels

(iii)

Which is the state of polarisation of the membrane at Z?

(1)

☐	A	Depolarised
☐	B	Hyperpolarised
☐	C	Hypopolarised
☐	D	Unpolarised

(iv)

How many of the following statements are correct?

The magnitude of the action potential is proportional to the strength of stimulus that generates the action potential
Action potentials spread out in both directions along the axon
Following an action potential, there is a refractory period during which it is not possible to generate a new action potential

(1)

☐	A	None
☐	B	One
☐	C	Two
☐	D	Three

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3 marks

Explain why maintaining a resting potential requires ATP.

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8a2 marks

The nervous system of an organism enables it to respond to a stimulus.

A reflex action is a rapid involuntary movement in response to a stimulus.

The response to a pinprick in a finger is an example of a reflex action.

(i)

Which component of the nervous system continues a reflex arc immediately after the receptor has been stimulated by the stimulus?

(1)

☐	A	motor neurone
☐	B	relay neurone
☐	C	Schwann cell
☐	D	sensory neurone

(ii)

Which pathway shows a reflex arc?

(1)

☐	A	muscle ⟶ receptor ⟶ brain
☐	B	muscle ⟶ spinal cord ⟶ brain
☐	C	receptor ⟶ spinal cord ⟶ muscle
☐	D	spinal cord ⟶ brain ⟶ muscle

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8b9 marks

Pacinian corpuscles are pressure receptors found in the skin of the fingertip.

The effect of different pressures applied to the finger tip, on electrode potentials across the axon membrane of the neurone of a Pacinian corpuscle was investigated.

The diagram shows the structure of a Pacinian corpuscle and the location of electrodes, X and Y, used to measure axon membrane potentials.

screenshot-2022-12-06-09-39-56

The table shows the results of the investigation.

Pressure applied to the fingertip	Membrane potential at electrode X / mV	Membrane potential at electrode Y / mV
None	−70	−70
Low	−60	−70
Medium	+20	+40
High	+40	+40

(i)

Describe how the resting potential of −70 mV is maintained in the axon when no pressure is applied.

(3)

(ii)

Suggest how a change in pressure at the Pacinian corpuscle causes an action potential in the axon.

(3)

(iii)

Explain why the membrane potential at electrode Y was the same when medium or high pressure was applied to the fingertip.

(3)

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Light intensity / a.u. per m²	Mean pupil diameter / mm
Light intensity / a.u. per m²	Incandescent light	LED light
0	25.5	25.5
75	24.0	22.0
150	24.0	18.5
200	23.0	17.5
300	21.5	16.0
650	17.5	12.0
1400	16.0	9.5

		Compared with a non-myelinated neurone the speed of conduction in a myelinated neurone is	Because membrane depolarisation only takes place in the axon membrane
☐	A	faster	at nodes of Ranvier
☐	B	faster	in between nodes of Ranvier
☐	C	slower	at nodes of Ranvier
☐	D	slower	in between nodes of Ranvier

Group	Mean quantity of myelin in a brain tissue sample / a.u.	Standard deviation
Control (no dementia)	52	± 3.2
Patients with vascular dementia	25	± 5.9
Patients with Alzheimer’s dementia	32	± 4.1
Patients with Lewy Body dementia	42	± 5.0

		Rod cell	Bipolar neurone
☐	A	hyperpolarised	hyperpolarised
☐	B	hyperpolarised	depolarised
☐	C	depolarised	hyperpolarised
☐	D	depolarised	depolarised

Light intensity /a.u.	Mean potential difference /mV
2	11
4	17
8	19
12	20
16	20
20	20

Edexcel International A Level Biology

Topic Questions

The Nervous System

☐	A	L-DOPA acts on a different post-synaptic receptor to dopamine
☐	B	L-DOPA crosses the blood-brain barrier and is then converted to dopamine in the brain
☐	C	L-DOPA is converted to dopamine in the blood and then crosses the blood-brain barrier
☐	D	L-DOPA is identical to dopamine

☐	A	cis‐retinal
☐	B	phytochrome
☐	C	rhodopsin
☐	D	trans‐retinal

☐	A	circular and radial muscles contract
☐	B	circular and radial muscles relax
☐	C	circular muscles contract and radial muscles relax
☐	D	circular muscles relax and radial muscles contract

☐	A	it filters out what is important and what is not important to react to
☐	B	it enables the animal to react more quickly to the stimulus
☐	C	it keeps the habitat of the animal protected
☐	D	it helps the animal find food more easily

☐	A	correlation coefficient
☐	B	Hardy-Weinberg
☐	C	index of diversity
☐	D	Student’s t-test

		Location of relay neurone	Location of cell body on the sensory neurone
☐	A	grey matter of spinal cord	at the end of the axon
☐	B	grey matter of spinal cord	in the middle of the axon
☐	C	white matter of spinal cord	at the end of the axon
☐	D	white matter of spinal cord	in the middle of the axon

☐	A	absorption
☐	B	adaptation
☐	C	habituation
☐	D	sensitivity

☐	A	Acetylcholine
☐	B	ADP
☐	C	Cholesterol
☐	D	NADP