Question

Fig. 2.1 shows a reflex arc involving a finger and a muscle in the arm.

(a) State two stimuli that can be detected by receptors in the finger.
1.
2.

(b) Using labels from Fig. 2.1, state the site of the cell body of
1. a sensory neuron
2. a relay neuron [2]

(c) (i) In what form are impulses transmitted in the nervous system?
[1]

(d) State the structure, present in many mammalian neurones, which reduces leakage
of the impulse.
[1]

(e) The impulse takes 0.02 seconds to pass from the finger to the spinal cord, a
distance of 1.5 metres. Calculate the speed of the impulse. Show your working.
Speed [2]

(f) Although the total distance the impulse travels in the reflex arc is less than 3
metres, the time taken is more than 0.04 seconds. Suggest why the time taken is
more than expected.

Answer 1

Answer:

a) The sharp pin (as suggested in the fig.)

An object with high temperature.

b) 1. The muscle V is in contact with sensory neurons.

2. The spinal cord has relay neurons.

c) Impulses are transported in electrical and chemical forms.

d) Myelin sheath is present on the axon that serves as insulation.

e) speed = distance / time = 1.5/0.02

= 75m/s.

f) That.... I don't know..

P.S. - for the e) one the speed can change if you consider the distance of whole arc (3m).

*Mic drop*

Hope it helps..

✌