Neurons Flashcards
Neurons
Cells within the nervous system that transmit information.
What are the 3 main types of neurons?
1) Sensory
2) Relay
3) Motor
Sensory neurons
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.
Not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.
Relay neurons
Found between sensory input and motor output/response.
Allows sensory and motor neurons to communicate.
Motor neurons
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.
Similarities & Differences
Similarities
- All contain a cell body (sometimes called a ‘soma’).
- All contain an axon.
Differences
- Only the sensory neuron contains a receptor cell.
- Only the relay neuron is without a myelin sheath.
- Only motor neuron is attached to a muscle or effector cell.
Dendrites
Receive signals from other neurons or from sensory receptor cells. Dendrites are typically connected to the cell body, which is often referred to as the ‘control centre’ of the neuron, as it contains the nucleus.
Axon
Long slender fibre that carries nerve impulses, in the form of an electrical signal known as an action potential, away from the cell body towards the axon terminals, where the neuron ends.
Myelin Sheath
Insulates the axon so that the electrical impulses travel faster along the axon.
Pre-synaptic Terminal
connects the neuron to other neurons (or directly to organs), using a process called synaptic transmission.
Process of Synaptic Transmission
1) Information is passed down the axon of the neuron as an electrical impulse known as action potential.
2) Once the action potential reaches the end of the axon, it needs to be transferred to another neuron or tissue.
3) It must cross over a gap between the pre-synaptic neuron and the post-synaptic neuron - which is known as the synaptic gap.
4) At the end of the neuron, in the axon terminal, are the synaptic vesicles which contain chemical messengers, known as neurotransmitters.
5) When the action potential reaches these synaptic vesicles, they release their content of neurotransmitters.
6) Neurotransmitters then carry the signal across the synaptic gap and they bind to receptor sites on the post-synaptic cell that then become activated.
7) Once the receptors have been activated, they either produce excitatory or inhibitory effects on the post-synaptic cell.
Excitatory Neurotransmitters
Excitatory neurotransmitters (e.g. noradrenaline) make the post-synaptic cell more likely to fire. They bind to the post-synaptic receptors causing 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.
I.e. Excitation occurs when receptor stimulation results in an increase in the positive charge of the postsynaptic neuron which increases the likelihood of the neuron firing.
Inhibitory Neurotransmitters
Inhibitory neurotransmitters (e.g. GABA) make the post synaptic cell less likely to fire. 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.
I.e. Inhibition occurs when receptor stimulation results in an increase in the negative charge of the postsynaptic neuron and decreases the likelihood of the neuron firing.
Summation
The addition of positive and negative post-synaptic potentials.
A nerve cell can receive both positive and negative potentials simultaneously.
These potentials are summed and if the net effect on the postsynaptic neuron is inhibitory, the neuron will be less likely to fire, and if the net effect is excitatory, the neuron will be more likely to fire.
I.e. Summation is when the excitatory neurotransmitter binds to the receptor sites on the post-synaptic neuron, causing an increase in the positive charge of the neuron meaning it is more likely to fire. In the same way, when an inhibitory neurotransmitter binds to receptor sites, it causes an increase in the negative charge meaning it is less likely to fire.
If the sum charge of the postsynaptic neuron is positive then it will increase the likelihood of firing and vice versa for inhibitory.
