CNS & Neurotransmission

Specification

• The role of the central nervous system (CNS) and neurotransmitters in human behaviour, including the structure and role of the neuron, the function of neurotransmitters and synaptic transmission.

The Central Nervous SYstem

The CNS consists of the brain and the spinal cord. Messages from the body, e.g. arms, travel up the spinal cord to the brain where the information is processed. The brain then sends messages back down the spinal cord resulting in an action from the person.

The brain provides conscious awareness and is involved in all psychological processes. The brain consists of many regions, which are responsible for different functions.

For example, the brain consists of four main lobes:

• frontal lobe

• parietal lobe

• temporal lobe

• occipital lobe

The occipital lobe processes visual information; the temporal lobe processes auditory information; the parietal lobe integrates information from the different senses and therefore plays an important role in spatial navigation; the frontal lobe is associated with higher-order functions, including planning, abstract reasoning and logic.

The brain stem connects the brain and spinal cord and controls involuntary processes, including our heartbeat, breathing and consciousness.

The role of the spinal cord is to transfer messages to and from the brain, and the rest of the body. The spinal cord is also responsible for simple reflex actions that do not involve the brain, for example jumping out of your chair if you sit on a drawing pin.

The Neuron

The neuron has dendrites attached to the cell body to pick up messages from surrounding neurons. The messages from other neurons transform into an electrical impulse that passes down the axon. When the action potential gets to the terminal button it can release neurotransmitters that cross the synaptic gap, passing on the message.

Synaptic Transmission

Neurotransmitters are electrochemical messengers that transmit nerve impulses across the synaptic gap during the process of synaptic transmission. Some neurotransmitters are excitatory and some are inhibitory. Excitatory neurotransmitters (e.g. noradrenaline) make the post synaptic cell more likely to fire, whereas inhibitory neurotransmitters (e.g. GABA) make them less likely to fire. For example, if an excitatory neurotransmitter like noradrenaline binds to the postsynaptic receptors it will cause an electrical charge in the cell membrane which results in an excitatory post-synaptic potential (EPSP), which makes the post-synaptic cell more likely to fire. Whereas, if an inhibitory neurotransmitter like GABA binds to the post-synaptic receptors it will result in an inhibitory post-synaptic potential (IPSP), which makes the post-synaptic cell less likely to fire.

Watch this process in action in the 2-minute neuroscience videos below.

Evaluation

• Supporting evidence for the role of acetycholine and memory formation comes from Martinez & Kesner (1991) who found that human memory can be explained by neurotransmitters.

• Acetylcholine has been found to have links to REM (dream) sleep, in that if your acetycholine levels are not low enough during REM sleep you may act out your dreams or sleep walk.

• The mental illness schizophrenia has been shown to involve excessive amounts of dopamine in the frontal lobes so neurotransmitters do explain human behaviour.

• The function of neurotransmitters as an explanation of human behaviour is reductionist as it ignores the effect of the environment on our behaviour so it is not a complete explanation of human behaviour; social learning theory explains human behaviour through imitation and modelling.

Past Paper Questions

• State one neurotransmitter that affects human behaviour. (1) October 2018

• Describe the role of the neuron in human behaviour. (3) January 2018

• Describe the role of the central nervous system (CNS). (3) January 2020

• Synaptic transmission occurs throughout the body, including in the brain. Describe what is meant by ‘synaptic transmission’. (3) June 2018

• Charong picked up a hot pan and dropped it on the floor. Describe the role of the central nervous system when Charong dropped the hot pan. (3) October 2017

• Explain one weakness of using neurotransmitters to explain human behaviour. (2) October 2018

• Evaluate whether the role of neurotransmitters can fully explain human behaviour. (8) October 2016