neurones and neurotransmission

structure of neurones

all 3 neurones consist of similar parts. dendrites receive signals from other neurones or from sensory receptor cells. dendrites are connected to the cell body ('control centre' cuz contains nucleus).

the axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal known as AP, away from the cell body towards the axon terminals, where the neurone ends. most axons are surrounded by a myelin sheath (except for relay neurones) which insulates the axon so that the electrical impulses travel faster along the axon. the axon terminal connects the neurone to other neurones (or directly to organs), using a process called synaptic transmission.

sensory neurones

found in receptors such as eyes, ears, tongue and skin, and carry nerve impulses to the spinal cord and brain. when these nerve impulses reach the brain, they’re translated into 'sensations', such as vision, hearing, taste and touch.

but, not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.

relay neurones

found between sensory input and motor output. relay neurones are found in the brain and spinal cord and allow sensory and motor neurones to communicate.

motor neurones

found in the CNS and control muscle movements. when stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which leads to movement.

synaptic transmission

info is passed down the axon of the neurone as an electrical impulse known as AP. once the AP reaches the end of the axon it needs to be transferred to another neurone or tissue. it must cross the synaptic cleft (the gap between the pre- and post-synaptic neurones). at the end of the neuron (in the axon terminal) are the synaptic vesicles which contain neurotransmitters. When the AP reaches these synaptic vesicles, they release their contents of neurotransmitters.

Neurotransmitters then carry the signal across the synaptic gap. They bind to receptor sites on the post-synaptic cell that then become activated. Once the receptors have been activated, they either produce excitatory or inhibitory effects on the post-synaptic cell.

Some neurotransmitters are excitatory and some are inhibitory. Excitatory neurotransmitters (e.g. noradrenaline) make the post-synaptic cell more likely to fire, whereas inhibitory neurotransmitters (e.g. GABA) make them less likely to fire. e.g. if an excitatory neurotransmitter like noradrenaline binds to the post-synaptic receptors it will cause an electrical charge in the cell membrane which results in an excitatory post-synaptic potential (EPSP), which makes the post-synaptic cell more likely to fire. Whereas, if an inhibitory neurotransmitter like GABA binds to the post-synaptic receptors it will result in an inhibitory post-synaptic potential (IPSP), which makes the post-synaptic cell less likely to fire.