How is the nervous system organised, and how do neural pathways process information?
The organisation of the nervous system into the central and peripheral nervous systems, the somatic and autonomic (sympathetic and parasympathetic) divisions, and the converging, diverging and reverberating neural pathways.
An SQA Higher Human Biology answer on the divisions of the nervous system, covering the central and peripheral nervous systems, the somatic and autonomic divisions, the antagonistic sympathetic and parasympathetic systems, and converging, diverging and reverberating neural pathways.
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What this dot point is asking
The SQA wants you to describe how the nervous system is divided into the central and peripheral nervous systems, explain the somatic and autonomic divisions (including the antagonistic sympathetic and parasympathetic systems), and describe the converging, diverging and reverberating neural pathways.
The central and peripheral nervous systems
The CNS receives sensory information, processes it, and decides on a response, which is then carried out by the PNS. The PNS therefore acts as the communication link, carrying sensory impulses in to the CNS and motor impulses out to the muscles and glands.
The somatic and autonomic divisions
The PNS is divided according to what it controls:
- The somatic nervous system controls voluntary actions, carrying impulses to the skeletal muscles under conscious control (for example, deciding to move your arm).
- The autonomic nervous system controls involuntary actions of internal organs, such as the heartbeat, breathing rate and digestion, without conscious thought.
Neural pathways
Within the nervous system, neurons are linked into pathways that shape how signals are processed:
- Converging pathway. Impulses from several neurons travel to a single neuron. By summing the inputs, a converging pathway makes it more likely that the threshold to fire the next neuron is reached, increasing the sensitivity of a response.
- Diverging pathway. Impulses from one neuron travel to several neurons, spreading the signal so that one input affects several destinations at once.
- Reverberating pathway. Neurons later in the pathway re-stimulate neurons earlier in it, so the signal cycles back. This prolongs the response, which is useful for activities such as breathing that must continue without conscious thought.
Examples in context
Example 1. The fight or flight response. When you are frightened, the sympathetic division acts on many organs at once: the heart speeds up, breathing deepens and the pupils widen. This shows the autonomic system preparing the body for action through its sympathetic division.
Example 2. Keeping breathing going. Reverberating pathways in the brainstem re-stimulate themselves to maintain the steady, rhythmic nerve impulses that drive breathing, so it continues automatically even while you sleep, illustrating a prolonged response.
Try this
Q1. Name the two parts of the central nervous system. [1 mark]
- Cue. The brain and the spinal cord.
Q2. Explain why a converging neural pathway increases the sensitivity of a response. [1 mark]
- Cue. It sums the inputs from several neurons, making it more likely the threshold to fire the next neuron is reached.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20193 marksDescribe the difference between the somatic and autonomic divisions of the peripheral nervous system, and explain how the autonomic system controls the heart rate.Show worked answer →
A 3-mark answer needs the two divisions distinguished and the antagonistic control of the heart.
The somatic nervous system controls voluntary actions, carrying impulses to the skeletal muscles under conscious control. The autonomic nervous system controls involuntary actions of internal organs, such as the heartbeat and digestion, without conscious thought.
The autonomic system controls heart rate through two antagonistic divisions. The sympathetic division speeds the heart up, for example during exercise, while the parasympathetic division slows it down at rest. Balancing these two opposing inputs sets the heart rate.
Award (1) somatic controls voluntary skeletal muscle, (2) autonomic controls involuntary organs, and (3) sympathetic speeds the heart and parasympathetic slows it (antagonistic control).
SQA Higher 20213 marksDescribe what is meant by a converging and a diverging neural pathway, and state one advantage of a converging pathway.Show worked answer →
This is a 3-mark recall and application question.
In a converging neural pathway, impulses from several neurons travel to a single neuron, so the inputs are combined. In a diverging pathway, impulses from one neuron travel to several neurons, so the signal is spread to more than one destination at once.
An advantage of a converging pathway is that it increases the chance of a response, because the combined input from many neurons is more likely to reach the threshold needed to fire the next neuron. This increases the sensitivity of the response.
Award (1) converging means several neurons to one, (2) diverging means one neuron to several, and (3) a converging pathway increases sensitivity by summing inputs to reach threshold.
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