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STRUCTURE/FUNCTION OF SENSORY, RELAY + MOTOR NEURONS - Coggle Diagram
STRUCTURE/FUNCTION OF SENSORY, RELAY + MOTOR NEURONS
Neurones
- The nerve cells are called neurones
- The average human brain has about 100 billion neurons
Sensory Neurons
- Carry signals from sensory receptors (sight/smell) to the spinal cord + brain
- They carry signals from the PNS to the CNS
- Length of fibres = long dendrites + short axons
Relay Neurons
- Allow sensory + motor neurones to communicate
- Transfers messages from sensory neurons to other interconnecting neurons/motor neurons
- Length of fibres = short dendrites + short or long axons
Motor Neurons
- Carry signals from the CNS to muscles/glands + control contractions
- Length of fibres = short dendtrites + long axons
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Neurotransmitters
- Chemicals that are released from a synaptic vesicle into the synapse by neurons
- They affect the transfer of an impulse to another nerve or muscle
- There neurotransmitters are 'taken back up' into the terminal buttons of neurons through the process of reuptake
Synaptic Transmission
1 - An electrical impulse travels along the axon of the transmitting neuron
2 - This triggers the nerve-ending of the pre-synaptic neuron to release chemical messengers called neurotransmitters from the synaptic vesicles
3 - These chemicals diffuse across the synapse (the gap) which bind with receptor molecules on the membrane of the next neuron (postsynaptic neuron)
4 - The receptor molecules on the post-synaptic neuron bind only the the specific chemicals releases from the first neuron. This stimulates the post-synaptic neuron to transmit the electrical impulse
5 - Re-uptake: the neurotransmitter is reabsorbed in the vesicles of the pre-synaptic neuron after it has performed its function of transmitting a neural impulse and stored for later release
Excitatory Effects
- The creation of a positive charge on the pre-synaptic cell
- E.g. dopamine/adrenaline
- This neurotransmitter then lands on the receptor to end up on the post synaptic cell + make it more likely to fire
- 'On switch' for the nervous system
Inhibitory Effects
- The creation of a negative charge on the pre-synaptic cell
- E.g. serotonin
- This makes it less likely for an impulse to continue down to the postsynaptic cell
- Calming effect on the mind, induces sleep
The Knee-jerk reflex
- In a reflex, like the knee-jerk reflex, a stimulus, such as hammer hitting the knee, is detected by sense organs in the peripheral nervous system (PNS), which conveys a message along a sensory neuron
- The message reaches the central nervous system (CNS) where it connects with a relay neuron
- This then transfers the message to a motor neuron
- This then carries the message to an effector such as a muscle, which causes the muscle to contract + the knee to move/jerk