AQA A2 (Module 6) Human Biology

ANSWERS TO IN-CHAPTER QUESTIONS

Unit 11: Nervous system

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Q1.	They synapse with the effector (a gland or muscle) i.e. they transmit the impulse to the effector, which effects a response. [4HBB & 4BIB]
Q2.	Axons, dendrites or dendrons, the cell body and nucleus are also present in relay and sensory neurones. [4HBB & 4BIB] Schwann cells wrap the axon in the sensory and motor cell only; consequently the gaps called the nodes of Ranvier are also present. [4HBB & 4BIB]
Q3.	In its normal state, the membrane of a neurone is –vely charged internally with respect to the outside. The p.d. is usually around –70mV. This is known as the resting potential, i.e. the membrane is said to be polarized. [4HBB & 4BIB]
Q4.	a) –70mV. b) +40mV. c) 3 msec. [4HBB & 4BIB]
Q5.	The colour of the Na^+/K^+ pumps is blue
Q6.	The membrane behind the action potential is in the refractory period for a short time. The Na^+ gates cannot be re-opened, i.e. this membrane cannot be depolarised and so cannot set up a new action potential of its own. An action potential can only depolarise the membrane “in front” as the membrane “behind” is in its refractory period and cannot be depolarised, so the impulse travels in one direction only.
Q7.	In smaller neurones, at any one point there is more axoplasm “in touch” with the pumps in the membrane therefore there would be more “leakage” of ions through pumps. Smaller axons have a greater SA, which assists “leakage”.
Q8.	Exocytosis.
Q9.	It is an automatic response; cannot be controlled by conscious thought. It is a very rapid response. These responses are not learned but in-born. A fixed response to a stimulus. Responses involve the spinal cord not the brain.
Q10.	Simple reflex actions can be modified through learning from previous experiences. In this example the impulse from the sensory neurone is passed along to additional relay neurones carrying the impulse up ascending tracts from the grey matter in the spinal cord to the brain. In the brain new pathways of relay neurones which will pass new “processed” impulse down the descending tract to the motor neurones. These impulses will “instruct” muscles in the hands to stay contracted gripping the hot dish despite the burning sensation, until the dish can be safely placed on a surface so preventing the meal being dropped onto the kitchen floor.
Q11.	Acetylcholine., released from the parasympathetic nervous system.