The Nervous System and Neuron Structure

The same wiring, a different question

If you take Biology you have probably met the neuron already, drawn on a diagram with a reflex arc running through it. This module covers much of the same anatomy, and it is worth knowing straight away why you are meeting it twice, because the reason is the whole point of the topic. Biology asks how the body coordinates itself: how a signal gets from a hot surface to a muscle fast enough to matter. Psychology asks a different question of the same wiring: how does a physical system produce behaviour and thought? That is what your specification means when it says brain structure and function relate to behaviour and cognition, and it changes what you should notice. You will still learn the divisions of the nervous system and the parts of a neuron, but you are learning them as the physical basis of things people do: reacting to threat, learning a skill, forming a habit. The module runs from the largest scale to the smallest, starting with the whole system, narrowing to the three kinds of neuron, and finishing at a single junction between two cells. And it ends somewhere worth arriving at. Hebb argued that when connections are used repeatedly they become stronger, which means that learning is not only something that happens in the mind. It is a physical change in the connections themselves, and that is the idea this whole module is built to reach.

Words for the system and the cell

Six terms. The four divisions nest inside one another, so read them in order rather than as a list.

Match each division to its job

Which part is doing this

Someone is startled by a loud noise. Their heart rate rises sharply without them deciding anything. Which division is responsible?

• The autonomic nervous system, because it controls automatic bodily functions without conscious effort
• The somatic nervous system, because the person moved
• The central nervous system alone, since the brain noticed the noise
• None: this is a hormonal response rather than a nervous one

The body preparing itself

The fight-or-flight response is the clearest example of the autonomic nervous system doing its job, and your specification names it here rather than in the hormones topic, so learn it as a nervous-system function. When a threat is detected, the autonomic system produces a set of changes that prepare the body to act, and none of them is decided on. Heart rate and breathing speed up, so more oxygen reaches the muscles. Blood is directed towards the muscles and away from processes that can wait, such as digestion. The pupils widen, letting in more light. The body may sweat more, which helps it cope with the effort ahead. Taken together these changes prepare a person either to confront the threat or to get away from it, which is where the name comes from. Three things are worth noticing for an exam. First, the response is automatic, which is precisely why it belongs to the autonomic system: it happens before any decision is made, and it can be difficult to stop by deciding to. Second, it does not distinguish between kinds of threat. The same set of changes occurs whether the danger is physical or whether somebody is about to speak in front of an audience, which is why the response can appear in situations where fighting and fleeing are both useless. Third, it is a good illustration of the module's point: something that feels like an emotion has a describable physical basis, which is the connection between body and behaviour that psychology is interested in.

Which two describe fight-or-flight

Select the TWO accurate statements about the fight-or-flight response.

• It is produced automatically by the autonomic nervous system, before any conscious decision is made
• The same set of bodily changes occurs whether the threat is physical or social
• It is a voluntary response that a person chooses to produce when they judge a situation to be dangerous
• It slows the heart and directs blood away from the muscles to conserve energy

The divisions in words

The brain and spinal cord together form the _____ nervous system, while the nerves carrying information to and from it form the _____ nervous system. Within that, the _____ nervous system controls voluntary movement and carries sensory information, and the _____ nervous system controls automatic functions such as heart rate. The fight-or-flight response is produced by the latter, which is why it happens without being _____.

Three neurons, three jobs

The three kinds your specification names. The easiest way to keep them apart is to ask which way the information is travelling.

Across the gap, in order

Put the stages of synaptic transmission into order.

• An electrical impulse travels along the neuron and reaches its end
• The impulse cannot cross the gap directly, so chemicals called neurotransmitters are released into it
• The neurotransmitters cross the gap and bind to receptors on the next neuron
• Depending on the neurotransmitter, the next neuron is made either more likely or less likely to fire
• If the effect is strong enough, a new electrical impulse begins in the next neuron
• Remaining neurotransmitter is taken back up into the first neuron, clearing the gap

Why experience changes the brain

Two ideas finish this module, and together they are what makes it psychology rather than anatomy. The first is that synapses do not only pass signals on; they influence them. Some neurotransmitters have an excitatory effect, making the next neuron more likely to fire. Others have an inhibitory effect, making it less likely. That matters more than it sounds. A nervous system that could only excite would have no way of stopping anything, so inhibition is what allows a response to be held back rather than made. Being able to say that inhibition is as important as excitation is worth a mark, because most students describe only the excitatory half. The second idea is Hebb's, and it is the destination of the whole module. Hebb argued that when two connected neurons are repeatedly active at the same time, the connection between them becomes stronger, so that activity in one comes more readily to produce activity in the other. The consequence is the striking part. If that is right, then learning something is not only a mental event: repeatedly doing or thinking something physically alters the connections in the brain, making the same pattern easier to produce next time. That is why practice works, why habits become hard to break, and why psychologists are interested in this anatomy at all. ⚠️ Write it as Hebb's argument rather than as an established fact, in the same way you would report any theorist: "Hebb argued that...", which is both accurate and the register this specification expects.

Nervous system drill

Answer from memory. The divisions, the neuron types and the sequence are all examinable.

The claim that states it as fact

Four sentences about this topic. Select the ONE that states a theorist's account as established fact instead of attributing it.

• Hebb argued that connections used repeatedly become stronger, so learning has a physical basis.
• Learning works by strengthening connections in the brain every time something is practised.
• The autonomic nervous system produces the fight-or-flight response without conscious decision.
• Inhibitory neurotransmitters make the next neuron less likely to fire.

From signal to behaviour

Work through what happens in the nervous system in each situation, and how to write about it.

• Someone touches a surface and feels that it is warm. Which neuron carries that information first?
• They decide to move their hand away deliberately. Which division is now involved?
• A learner practises a skill every day and finds it becomes easier. How would you explain it?
• You are asked why psychologists study the nervous system at all. What is the strongest answer?

Explain the nervous system and neurons

Explain how the nervous system is organised and how neurons carry and pass on information, and explain why this matters to psychologists.

• Name and describe the central and peripheral nervous systems
• Explain the difference between the somatic and autonomic divisions
• Describe the fight-or-flight response and say why it counts as automatic
• Name the three types of neuron and say which way information travels in each
• Describe what happens at a synapse, including release and reuptake
• Explain the difference between excitation and inhibition, and why inhibition matters
• Explain what Hebb argued, attributing it to him
• Finish by explaining why a psychologist studies this rather than leaving it to biology