Biopsychology 2 AQA A Specification:The structure and function of sensory, relay and motor neurons. The process of synaptic transmission, including reference to neurotransmitters, excitation and inhibition.

Neuron The basic building blocks of the nervous system. Neurons are nerve cells that process and transmit messages through electrical and chemical signals.

The structure of a neuron Vary in size but have same structure. Cell body (soma) includes a nucleus which contains the genetic material of the cell. Dendrites (branch-like structures) protrude from the cell body. Axon carries the impulse away from the cell body down the length of the neuron. Axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse. 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. Terminal buttons (end of axon) – communicate with next neuron in the chain across a gap known as the synapse.

Electrical transmission 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.

A.k.a. Relay neuron

Types of neuron Sensory neurons These carry sensory information from the environment and peripheral nervous system to the central nervous system. They have long dendrites and short axons. Relay neurons A.k.a. interneurons Carry messages from one part of the CNS to another. These connect the sensory neurons to the motor neurons. They have short dendrites and short axons.

Types of neuron continued… Motor neurons These connect the central nervous system to effectors such as muscles and glands. They have short dendrites and long axons.

Label the diagram below with the correct type of neuron.

Independent task Complete the table of 10 key terms in your booklets. Class Q&A.

Independent task Explain the difference between sensory and motor neurons. (4 marks) Read through your answer and highlight key terms. Following discussion (and notes on whiteboard) give your answer a mark out of 4.

Synaptic transmission While the flow of a signal along (within) a neuron is electrical, the signal between neurons is chemical. This transmission happens at a synapse. A synapse is a specialised ‘gap’ between neurons through which the electrical impulse from the neuron is transmitted chemically to another neuron. When the electrical impulse reaches the end of the neuron (the pre- synaptic terminal) it triggers the release of a neurotransmitter from tiny sacs called synaptic vesicles.

Neurotransmitter (NT) Brain chemicals released from the synaptic vesicles that relay signals across the synapse from one neuron to another. Can be divided into those that perform an excitatory function and those that perform an inhibitory function. Can you think of any examples from the biological approach?

What happens? Each neurotransmitter has its own specific molecular structure that fits perfectly into a post-synaptic receptor site, similar to a lock and a key. When the right key (i.e. neurotransmitter) meets the right lock (i.e. receptor) a specific ion channel in the membrane is opened. Ions then flow through the membrane into the neuron along their specific pathways. This flooding of ions can cause an ‘action potential’ in the dendrites. The neurotransmitters can be excitatory or inhibitory

Excitation/Inhibition Excitatory – When a NT increases the positive charge of the postsynaptic neuron. This increases the likelihood that the neuron will fire and pass on the electrical impulse. E.g. noradrenaline. Inhibitory – When a NT increases the negative charge of the postsynaptic neuron. This decreases the likelihood that the neuron will fire and pass on the electrical impulse. E.g. serotonin.

Independent task Use your knowledge and understanding to draw the process of synaptic transmission into pictures in your booklet. Alternatively you can draw a diagram/flowchart or list in bullet points.

TASK 2: draw these as a flow diagram onto your booklet Task 1: Number these into the correct order of steps for synaptic transmission (hint: start with B) A Flooding of ions (+/-) B Electrical impulse arrives at pre-synaptic terminal C Travels across synapse D Ion channel opened E Action potential becomes more/less likely known as excitation/inhibition F Release of neurotransmitter from synaptic vesicles (excitatory/inhibitory) G Fits into post-synaptic receptor site TASK 2: draw these as a flow diagram onto your booklet

Independent task Label the diagram of the neuron in your booklets.