16: Coordination in Humans - Problems

Question 1

The electron micrographs below show the cross sections nerve fibres X and Y.

Name layer P and state its functions. (1+2)

Answer 1

Myelin sheath
It insulates the nerve fibres, thus preventing the transmission of nerve impulses to the surroundings. It speeds up the transmission of nerve impulses.

Question 2

Suggest and explain the difference in speed of nerve impulse transmission in nerve fibres X and Y. (2)

Answer 2

The speed of nerve impulse transmission of nerve fibre X is higher than that of nerve fibre Y.
This is because nerve fibre X is myelinated but nerve fibre Y is not.

Question 3

AL 2009 I Q1

With reference to one observable feature in the electron micrograph, deduce the direction of signal transmission between the two neurones. (3)

Answer 3

Signal transmits from neurone A to neurone B.
There is a large number of vesicles in the synaptic knob of neurone A,
which shows that A is the presynaptic neurone which releases neurotransmitter to depolarise the membrane of B.

Question 4

The electron micrograph below shows a synapse between two neurones. Identify and explain the direction of nerve impulse transmission. (3)

Answer 4

From neurone P to neurone Q.
Synaptic vesicles containing neurotransmitters are present in the ending of neurone P only.
Neurotransmitters released from neurone P diffuse across the synaptic cleft to neurone Q and bind with the receptors in the membrane of neurone Q to stimulate neurone Q to generate a nerve impulse.

Question 5

Explain the significance of the abundance of mitochondria in the neurone ending. (1)

Answer 5

To provide sufficient energy by aerobic respiration for the production of neurotransmitters.

Question 6

Suggest the significance of involving a few neurones in a reflex arc. (1)

Answer 6

It helps producing fast responses to protect the body from further damage.

Question 7

Describe how nerve impulses are transmitted across gap X. (4)

Answer 7

At first, when a nerve impulse arrives at the synaptic knob at the axon terminal of the neurone Z, the synaptic vesicles move to and fuse with the neurone Z membrane, releasing the neurotransmitters contained in the synaptic vesicles into the synaptic cleft.
Then, the neurotransmitter diffuses across gap X, which is the synaptic cleft,
and binds to the specific receptors on the membrane of the postsynaptic neurone, which is an interneurone.
Finally, this binding stimulates the dendron or cell body of the interneurone to generate a nerve impulse.

Question 8

State the differences in the structure and functions of neurones Y and Z. (2)

Answer 8

Structure:
Y (motor neurone) has very short dendrons while Z (sensory neurone) has a long dendron. / Y has a long axon while Z has a short axon.
Function:
Y transmits nerve impulses from the spinal cord of the central nervous system to the effectors while Z transmits nerve impulses from the receptors to the spinal cord of the central nervous system.

Question 9

Explain why pain is only felt after the hand is withdrawn. (2)

Answer 9

The nerve impulses are transmitted to the brain via another nervous pathway.
As this pathway is longer than the reflex arc and involves more synapses, pain is felt after withdrawing the hand.