#86 Simple reflex arc
A reflex action is an automatic response to a stimulus.
A reflex arc describes the pathway of an electrical impulse in response to a stimulus.
A reflex arc describes the pathway of an electrical impulse in response to a stimulus.
Relay neurones are found in the spinal cord, connecting sensosy neurones to motor neurones.
On the picture below, the stimulus is a drawing-pin sticking in the finger. The response is the withdrawal of the arm due to contraction of the biceps.
The sequence of events is:
Reflex: automatically and rapidly integrating and coordinating stimuli with responses
Neurones do not connect directly with each other: there is a gap called a synapse. The impulse is 'transmitted' across the synapse by means of a chemical called acetylcholine.
Try this
Figure below shows a nerve cell.
Neurones do not connect directly with each other: there is a gap called a synapse. The impulse is 'transmitted' across the synapse by means of a chemical called acetylcholine.
Try this
Figure below shows a nerve cell.
a. i) Name the type of nerve cell shown in the figure [1 mark]
ii) State two features that distinguish it from other types of nerve cell [2 mark]
iii) Where, in the nervous system, is this cell located? [1 mark]
b. Nerve cells are specialised cells. Suggest how the following parts of the nerve cell, labelled in the figure, enable the nerve cell to function successfully:
cytoplasm; myelin sheath. [4 mark]
c. Reflex involve a response to a stimulus.
i) Copy and completes the flowchart by putting the following terms in the boxes to show the correct sequence in a reflex. [2 marks]
ii) State two features that distinguish it from other types of nerve cell [2 mark]
iii) Where, in the nervous system, is this cell located? [1 mark]
b. Nerve cells are specialised cells. Suggest how the following parts of the nerve cell, labelled in the figure, enable the nerve cell to function successfully:
cytoplasm; myelin sheath. [4 mark]
c. Reflex involve a response to a stimulus.
i) Copy and completes the flowchart by putting the following terms in the boxes to show the correct sequence in a reflex. [2 marks]
ii) For the pupil reflex , identify each of the parts of the sequence by copying and completing the table below. The first has been done for you. [ 4 marks]
Answer
a. i) Motor neurone
ii) Two features from:
- presence of motor end plates
- the cell body is at the beginning of the cell
- the cell body has dendrites on
- there is no dendron (only on axon).
iii) Peripheral nervous system.
b. Cytoplasm: two suggestions from:
- is elongated
- passes electrical signals along
- connects different parts of the body
- is modified to form dendrites.
Myelin sheath: two suggestions from:
- acts as insulating material
- so prevents leakage of electrical signal from axon
- allows faster transmission of impulses.
c. i) flowchart
a. i) Motor neurone
ii) Two features from:
- presence of motor end plates
- the cell body is at the beginning of the cell
- the cell body has dendrites on
- there is no dendron (only on axon).
iii) Peripheral nervous system.
b. Cytoplasm: two suggestions from:
- is elongated
- passes electrical signals along
- connects different parts of the body
- is modified to form dendrites.
Myelin sheath: two suggestions from:
- acts as insulating material
- so prevents leakage of electrical signal from axon
- allows faster transmission of impulses.
c. i) flowchart
ii)
Video: Reflex Arc