Synapses

Question 1

Synapses

Answer 1

Adjacent neurons do not touch each other. There is a small gap separating them. This gap or synaptic cleft plus the adjacent neurons forms a synapses.

A synapses is therefore the junction across which a nerve impulse passes from an axon terminal to a neuron, a muscle cell or a gland.

Question 2

How impulses travel across synapses

Answer 2

• when a nerve impulses reach the terminal branches of axons, they cause vesicles in the pre-synaptic knob to burst, releasing neurotransmitters which diffuse across the synaptic gap
• the neurotransmitters carry impulses across the gap - a chemical process which stimulates receptors in the post- synaptic membrane to initiate nerve impulses.

Question 3

Why are synapses important

Answer 3

• they make sure that the flow of impulses is in one direction only
• they allow the dispersal of impulses to many other neurons as neurotransmitters
• they allow the “filtering out” of continual unnecessary stimuli

Question 4

A reflex arc

Answer 4

It is the functional unit of the nervous system. It is the pathway followed by impulses from a receptor to an effector to bring about a reflex action

Question 5

Reflex action

Answer 5

Is a fast, automatic response by an effector organ, a muscle or a gland, to a stimulus received by a receptor organ.
Reflexes may be:
- somatic which activate skeletal muscles
- autonomic which activate muscle and glands

Question 6

Reflex centres

Answer 6

Brain- controlling reflexes such as sneezing, breathing, blinking
Spinal cord - controlling primitive reflexes such as the knee jerk

Question 7

What is the significance of reflex arc

Answer 7

Reflex arcs bring about reflex actions that:

• enable the body to respond quickly to stimulus
• provide inborn safety mechanisms which serve mainly to protect the body from danger

Question 8

Structure of a reflex arc

Answer 8

1. Receptor eg skin - responds to stimuli and generates impulses
2. Sensory neuron - carries impulse to CNS
3. Connector neuron - acts as reflex centre
4. Motor neuron - carries impulses to an effector organ
5. Effector - brings about change

Question 9

How does a simple reflex arc function

Answer 9

• The receptors that respond to pain generate impulses in sensory neurons
• the impulses are conducted along sensory neurons to the grey matter in the spinal cord
• here the impulses make synaptic contact with the connector neurons which act as reflex centres
• from connector neurons impulses make synaptic contact with motor neurons which conduct them to the effector
• the effector, brings about a response by contracting very quickly to pull the finger away from the pin