Neurons Flashcards
What is a neuron?
Basic building blocks of the nervous system, 80% of which are located in the brain.
By transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication
3 types of neuron
Sensory neuron
Relay neuron
Motor neuron
Sensory neuron (3)
Sensory neurons are found in receptors such as the eyes, ears, tongue and skin, and carry nerve impulses to the spinal cord and brain. When these nerve impulses reach the brain, they are translated into ‘sensations’, such as vision, hearing, taste and touch. However, not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.
Motor neuron (3)
Motor neurons are found in the central nervous system (CNS) and control muscle movements. When motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement.
Relay neuron (3)
Relay neurons are found between sensory input and motor output/response. Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.
Cell body (also known as soma)
Includes a nucleus which contains genetic material of the cell
Dendrites
Branchlike structures that protrude from the body. These carry nerve impulses from neighbouring neurons towards the cell body
Axon
Carries electrical impulses away from the cell body down the length of the neuron
It is covered by a fatty layer of myelin sheath that protects the axon
Gaps in the axon called nodes of ranvier speed up the transmission of the impulse
Terminal buttons
These are at the end of the axon which communicate with the next neuron in the chain across a gap called the synapse
Electrical transmission (firing of a neuron)
When a neuron is in a resting state the inside of the centre is negatively charged compared to the outside
When a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur
This creates an electrical impulse that travels down the axon towards the end of the neuron
What is a synapse?
Each neuron is separated from the next by an extremely tiny gap -> synapse
Neurotransmitters
They are chemicals that diffuse across the synapse to the next neuron in the chain
Each has its own specific molecular structure that fits perfectly into a postsynaptic receptor site, like a lock and key
Each has specific function e.g serotonin affects mood and social behaviour
Process of synaptic transmission (4 steps)
- include action potential
- An Action Potential causes an electrical impulse to travel down a neuron to the Pre synaptic nerve terminal.
- Triggers a release of neurotransmitters from the vesicles into the synaptic cleft.
- Neurotransmitters travel across the synaptic cleft and bind to their complementary postsynaptic receptor sites.
- This opens ion channels, allowing either positive or negatively charged ions to flow into the next neuron.
Action Potential
* Excitatory neurotransmitters (Adrenaline) cause the absorption of positively charged ions.
* Inhibitory neurotransmitters (GABA) cause the absorption of negatively charged ions.
* The Action Potential is set by the overall charge from the absorbed positive and negatively
charged ions.
* The higher the positive charge, the more likely it is to fire the next electrical impuls
Excitation and inhibitation
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
Summation
Excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential to be triggered
If the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire. It is more likely to fire if the net effect is excitatory
