AQA Psychology for A Level Year 2 - Student Bk

The specification says… The structure and function of sensory, relay and motor neurons. The process of synaptic transmission including reference to neurotransmitters, excitation and inhibition. On the previous spread we considered the major biological structures and systems. Now we will delve a little deeper and, in so doing, get a good deal smaller! We will investigate how the nervous system transmits signals for communication via the billions of nerve cells (neurons) it houses. We will also consider how these nerve cells communicate with each other, through electrical and chemical messages, within the body and the brain. Key terms Neuron – The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals. Sensory neurons – These carry messages from the PNS (peripheral nervous system) to the CNS (central nervous system). They have long dendrites and short axons. Relay neurons – These connect the sensory neurons to the motor or other relay neurons. They have short dendrites and short axons. Motor neurons – These connect the CNS (central nervous system) to effectors such as muscles and glands. They have short dendrites and long axons. Neurons and synaptic transmission Concepts: Function of neurons B A @ookx hs @ookx hs Question Identify the type of neuron labelled A and B. The structure and function of neurons There are 100 billion neurons (nerve cells) in the human nervous system, 80% of which are located in the brain. By transmitting signals electrically and chemically , these neurons provide the nervous system with its primary means of communication. Types of neuron There are three types of neurons: motor neurons , sensory neurons and relay neurons . The features of each are summarised in the key terms on the left and illustrated in the diagram below. relay neuron motor neuron axon axon dendrites myelin sheath nodes of Ranvier cell body cell body sensory neuron direction of conduction The structure of a neuron Neurons vary in size from less than a millimetre to up to a metre long, but all share the same basic structure. The cell body (or soma) includes a nucleus , which contains the genetic material of the cell. Branch-like structures called dendrites protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body. The axon carries the impulses away from the cell body down the length of the neuron. The axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse. If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse. Thus, the myelin sheath is segmented by gaps called nodes of Ranvier . These speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon. Finally, at the end of the axon are terminal buttons that communicate with the next neuron in the chain across a gap known as the synapse (see facing page). Electric transmission – the firing of a neuron When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur. This creates an electrical impulse that travels down the axon towards the end of the neuron. spinal cord pain receptor muscle effector Chapter 2 Biopsychology 36 •