Neurons and synaptic transmission



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Neurons and synaptic transmission

  • Biopsychology
  • Specification details
  • The structure and function of sensory, relay and motor neurons.
  • The process of synaptic transmission, including reference to neurotransmitters, excitation and inhibition.
  • Pages 114-115

Key assumptions of biopsychologists

  • Biopsychologists assume that behaviour and experiences are caused by activity in the nervous system
  • The nervous system transmits signals for communication via the billions of nerve cells (neurons) it houses
  • These nerve cells communicate with each other, through electrical and chemical messages, within the body and the brain.

Neurons

  • Cells that conduct nerve impulses are called neurons
  • The things that people think and feel, say and do are caused, one way or another, by electrochemical events occurring within and between the neurons that make up the nervous system, particularly those in the brain (80%)
  • Relay Neuron

Write one sentence about what the following features do

  • Nucleus
  • the control centre of a cell, which contains the cell's chromosomal DNA
  • Dendrite
  • Receives the nerve impulse or signal from adjacent neurons
  • Axon
  • Where the electrical signals pass along.
  • Myelin sheath
  • Insulates /protects the axon from external influences that might effect the transmission of the nerve impulse down the axon.
  • Nodes of ranvier
  • These speed up the transmission of the impulse by forcing it to ‘jump’
  • Terminal buttons
  • Terminal buttons send signals to an adjacent cell.

Different types of neurons

  • 2. Relay (Interconnecting) neuron
  • 3. Sensory neuron
  • Function
  • Transfers messages from sensory neurons to other interconnecting neurons or motor neurons
  • Carries messages from the PNS to the brain and spinal cord
  • Length of fibres
  • Short dendrites and long axons
  • Short dendrites and short or long axons
  • Structural and functional differences
  • The cellular structure of all neurons is the same. There are anatomical differences in size, depending on their function
  • MOTOR RELAY SENSORY
  • Relay neuron

The knee-jerk reflex

  • In a reflex arc, like the knee-jerk reflex, a stimulus, such as a hammer hitting the knee, is detected by sense organs in the peripheral nervous system, which conveys a message along a sensory neuron. The message reaches the central nervous system where it connects with a relay neuron. This then transfers the message to a motor neuron. This then carries the message to an effector such as a muscle, which causes the muscle to contract and, hence, the knee to move or jerk.

Synapse between two neurons.

  • Synaptic tramsmission

Neurotransmitters…

  • …are chemicals that are released from a synaptic vesicle into the synapse by neurons.
  • They affect the transfer of an impulse to another nerve or muscle
  • These neurotransmitters are “taken back up” into the terminal buttons of neurons through the process of reuptake
  • Or they are broken down by an enzyme

How a synapse works

  • A synapse

Action Potential

  • An action potential occurs when a neuron sends information down an axon, away from the cell body.
  • The action potential is an explosion of electrical activity - this means that some event (a stimulus) causes the resting potential to move forward

Excitation and inhibition

  • Synaptic connections can be excitatory or inhibitory – the difference lies in the action of the neurotransmitter at the postsynaptic receptor
  • Excitatory - they make it more likely the next neuron will fire (such as acetylcholine)
  • Inhibitory - they make it less likely the next neuron will fire (such as GABA)
  • Normal brain function depends upon a regulated balance between excitatory and inhibitory influences
  • Synaptic transmission
  • Sort the cards into the correct order and then write the details up on the flow diagram to show the process of synaptic transmission

Synaptic transmission - answers

  • nerve impulse travels down an axon
  • nerve impulse reaches synaptic terminal
  • this triggers the release of neurotransmitters
  • the neurotransmitters are fired into the synaptic gap
  • neurotransmitter binds with receptors on the dendrite of the adjacent neuron
  • if successfully transmitted the neurotransmitter is taken up by the post-synaptic neuron
  • the message will continue to be passed in this way via electrical impulses

Synapse: The gap between the end of one neuron and the dendrites of the next neuron.

  • What you need to label:
  • Direction of impulse.
  • Axon terminal
  • Synaptic vesicles containing neurotransmitter
  • Synaptic gap
  • Dendrite
  • Receptor site

Can you?

  • Explain what is meant by sensory, relay and motor neurons (2 marks each)
  • With reference to neurotransmitters, explain what is meant by both excitation and inhibition (4 marks)
  • With reference to sensory, relay and motor neurons, explain the knee-jerk reflex (4 marks)
  • Explain the difference between excitatory or inhibitory synaptic connections (4 marks)
  • Answer the ‘Check it’ questions on page 117

Essay

  • Outline and evaluate the role of biological structures in explaining human behaviours
  • (12 marks)

Homework

  • Ensure you have written up your class notes to include the following:
  • The structure and function of sensory, relay and motor neurons.
  • The process of synaptic transmission, including reference to neurotransmitters, excitation and inhibition.


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