Neurons and synaptic transmission

Sensory neuron:

Carries messages from the PNS to the CNS. They have long dendrites and short axons. They are located in the PNS in clusters called ganglia.

Relay neuron:

They connect the sensory neurons to the motor or other relay neurons. They have short dendrites and short axons. Found in the brain and visual system.

Motor neuron:

They connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons. They are in the CNS and part of the PNS.

Nucleus, dendrites + axons:

Nucleus - contains genetic material of the cell

Dendrites - branch-like structures that carry nerve impulses from neighbouring neurons towards the cell body

Axons - carries the impulses AWAY from the cell body and down the length of the neuron

Myelin sheath, nodes of ranvier + terminal buttons:

Myelin sheath - protects the axon and speeds up electrical transmission

Nodes of ranvier - speed up impulse by forcing it to jump across the gaps in the axon

Terminal buttons - they communicate with the next neuron in the chain across a gap called synapse

Neurons firing:

When its at resting the charge is negative but when it is activated it is positively charged 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 a neurotransmitter (adrenaline) increases the POSITIVE charge of the postsynaptic neuron. This will INCREASE that the electrical impulse will be passed on.

Inhibition:

When a neurotransmitter (serotonin) increases the NEGATIVE charge of the postsynaptic neuron. This will DECREASE 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.