Biopsychology

What is a neuron?

• Neurons are nerve cells that process and transmit messages through electrical and chemical signals 

Types of Neurons 

• Three types:
  • Motor neurons = connects the CNS to effectors such as muscles and glands = they have short dendrites and long axons
  • Sensory neurons = carry messages from the PNS to the CNS = they have long dendrites and short axons
  • Relay neurons = connect the sensory neurons to the motor neurons = they have short dendrites and long axons 

Structure of a neuron

• The cell body of a neuron contains a nucleus which has genetic material of the cell 
• Branch-like structures called dendrites extend beyond from the cell body = these carries nerve impulses from neighbouring neurons towards the cell body 
• Axons carries the impulses away from the cell body down the neuron = axons are covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse 
• Myelin sheath are seperated by gaps called nodes of Ranvier to speed up the electrical transmission 
• At the end of the axon are terminal buttons that communicate with the next nueron

Electric Transmission = the firing of a neuron 

• When a neuron is in a resting state the inside of the cell is negatively charged 
  • RESTING STATE + NEGATIVELY CHARGED
• The outside of the cell is positively charged 
• When a neuron is activated by a stimulus
• Inside the cell becomes positively charged for a split second causing an action potential 
• This creates electrical impulse that travels down the axon

What is synaptic transmission?

• when neighbouring neurons communiate with each other by sending chemical messages across the gap that seperates them 

Chemical transmission - synapses 

• Neurons are seperated from the next neuron by a synapse 
• Synapse includes the space between them which is called the synaptic cleft 
• It also includes the presynaptic terminal and a postsynaptic receptor site  
• Signals within a neuron are transmitted electrically 
• Signals between neurons, so through the synapse are transmitted chemically by synaptic transmission 
• When the electrical impulse reaches the end of the neuron which is called the presynaptic terminal, it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles

Neurotransmitter

What is a neurotransmitter?

• Neurotransmitters are chemicals that diffuse across the synapse to the next neuron
• Once the neurotransmitter crosses the synapse, it is taken up by the postsynaptic receptor sites (the dendrites of the next neuron) 
• At the postsynaptic receptor site, the chemical impulse is converted back to a electrical impulse 
• Each neurotransmitter has it own specific molecular structure that fits perfectly into the post-synaptic receptor site 

Excitation and Inhibition

• Neurotransmitters have either an excitatory or inhibition effect on the neighbouring neuron 

Inhibition

• What is it? = this is when neurotransmitter makes the charge of the postsynaptic neuron more negative = this decreases the likelihood that the neuron will fire and pass on the electrical impulse 
• Serotonin makes the neuron more negatively charged and therefore is less liekly to fire 

Excitation 

• What is it? = when neurotransmitters inceases the postive charge of the postsynaptic neuron = which increases the likelihood that the neuron will fire and pass on the electical impulse 
• A neurotransmitter called adrenaline increases the postive charge of the postsynaptic neuron and making it more likely to fire 

Summation

• Whether a postsynaptic neuron does fire is decided by the process of summation 
• If the net effect on the postsynaptic neuron is inhibitory then the postsynaptic neuron is less likely to fire 
• If the net effect on the postsynaptic neuron is excitatory, it is more likely to fire

Summary

1. Electrical impulse reaches the pre-synaptic nerve terminal 

2. The electical impulse triggers the release of a neurotransmitter from tiny sacs called synaptic vesicles 

3. The chemical message diffuses across the synaptic cleft and to the post-synaptic receptor sites (the dendrites) 

4. The chemical message is then converted back into a electrical impulse and then travels along the axon