Neurons and synaptic transmission

Sensory neuron:

Long dendrites and short axon

Located in the PNS in clusters called ganglia

Connects the receptor (e.g. pain) to the CNS

Relay neuron:

Short dendrites and short axon

Located in the brain and visual system

Connects CNS to CNS (sensory to relay/motor)

Motor neuron:

Short dendrites and long axon

Located in the CNS, and due to long axon, it forms part of the PNS

Connects CNS to effectors (muscles and glands)

Nucleus, dendrites + axons:

Nucleus - contains genetic material of the cell

Dendrites - carry nerve impulses from neighbouring neurons towards the cell body

Axon - carries the impulses AWAY from the cell body and down the neuron

Myelin sheath, nodes of ranvier + terminal buttons:

Myelin sheath - protects the axon and speeds up transmission

Nodes of ranvier - speeds up transmission by forcing the impulse to jump across the gaps in the axon

Terminal buttons - they communicate with the next neuron in the chain across the synapse (synaptic transmission)

Neurons firing:

When resting, the charge is negative, but when activated by a stimulus, the charge is positive, causing action potential to occur. This creates an electrical impulse to travel down the axon towards the end of the neuron.

Synaptic transmission:

Vesicles containing the neurotransmitter move to the presynaptic terminal where it is released. It then travels across the synapse to the receptor sites on the post-synaptic neuron where it is broken down.

Excitation:

When an excitatory neurotransmitter (e.g. adrenaline) increases the POSITIVE charge of the postsynaptic neuron. This will INCREASE the potential that the electrical impulse will be passed on.

Inhibition:

When an inhibitory neurotransmitter (e.g. serotonin) increases the NEGATIVE charge of the postsynaptic neuron. This will DECREASE the potential that the electrical impulse will be passed on.

Summation:

The excitatory and inhibitory potentials are summed together which determines whether the neuron will fire. E.g. if the net effect on the postsynaptic neuron is inhibitory, it is less likely to fire.