Structure and Function of Neurons
All neurones have a Cell Body containing a Nucleus with genetic material, Dendrites that carry impulses from other neurons to the cell body and the Axon that carries impulses away from the cell body. The axons have Myelin Sheaths to speed up transmission (the gaps are Nodes of Ranvier). The ends of axons have Terminal Buttons to communicate with other neurons.
Sensory - Located in the PNS. Carry signals from PNS to CNS, and are myelinated with long dendrites and short axons.
Motor - Located mostly in the CNS, and are myelinated with short dendrites and long axons form part of PNS
Relay - Make up 97% of neurons, located in the brain and visual system. Connect sensory and motor neurons, unmyelinated with short dendrites and axons
Electrical Transmission
A neuron is negatively charged in resting state. When activated, it becomes positive causing action potential, sending the impulse down the axon
Synaptic Transmission
Neurons are separated by the synapse, where signals are transmitted chemically. An electrical signal reaching the presynaptic terminal triggers the release of neurotransmitters from vesicles
After a neurotransmitter crosses the synapse, its taken up by the postsynaptic receptor sites, where its converted back to electrical impulses. They all travel one-way. Each neurotransmitter has a different function, acetylcholine (ACh) causes muscle contraction
Neurotransmitters have an excitatory or inhibitory effect. Serotonin causes inhibition in the receiving neuron, making it more negative (less likely to fire). Adrenaline causes excitation of postsynaptic neuron, making it more positive (more likely to fire).
The firing of a neuron is decided through summation. If the net effect of neuron is inhibitory, its less likely to fire and vice versa.