Neurons Flashcards
Neurons
Neurons are specialised cells in the nervous system that transmit electrical impulses. They carry messages between the brain, spinal cord, and other parts of the body, allowing for communication within the nervous system.
What are the 3 main types of neurons?
1) Sensory
2) Relay
3) Motor
(see image of them)
Sensory neurons
Sensory neurons are responsible for carrying information from sensory receptors, e.g., in the skin, eyes and ears, to the Central Nervous System (brain and spinal cord). They transmit sensory input like touch, pain, temperature and visual stimuli, where they become ‘sensations’.
Sensory neurons have long dendrites that receive information from sensory receptors and an axon that transmits the signal to the Central Nervous System. The cell body is located in a sensory ganglion outside the Central Nervous System.
Sensory neurons play a key role in reflex actions by quickly sending sensory information to the spinal cord for an immediate response, bypassing the brain for faster reactions.
Relay neurons
Relay neurons act as connectors or bridges between sensory neurons and motor neurons. They transmit signals within the Central Nervous System, such as from the spinal cord to the brain or between different regions of the brain.
Relay neurons typically have short axons and dendrites, as they connect sensory neurons to motor neurons or other relay neurons within the Central Nervous System.
They play a key role in processing information and integrating sensory input before sending it to the appropriate motor neurons for a response.
Motor neurons
Motor neurons transmit signals from the Central Nervous System to muscles and glands, triggering movement or secretion. They are responsible for voluntary movements like walking or talking and involuntary actions, like reflexes.
Motor neurons have long axons that carry impulses from the Central Nervous System to muscles or glands. Their cell bodies are located in the Central Nervous System, and they extend to various muscles throughout the body.
Motor neurons play a crucial role in reflex actions, allowing quick, automatic responses by transmitting signals from the spinal cord to muscles.
Dendrites
Dendrites receive electrical signals from other neurons or from sensory receptor cells and transmit them towards the cell body. Dendrites are branch-like structures, extending from the neuron’s cell body, increasing the surface area for connections with other neurons. They play a crucial role in allowing communication between neurons by receiving neurotransmitter signals across synapses and initiating an electrical impulse within the neuron.
Axon
Axons are a long, slender fibre that carries the action potential along its length. They transmit electrical impulses away from the neuron’s cell body towards the axon terminal, where the neuron ends. At the axon terminal, neurotransmitters are released to pass the signal to the next neuron across the synapse.
Myelin Sheath
The myelin sheath insulates the axon and speeds up signal transmission so that it can travel faster along the axon.
Cell Body
The cell body (also known as the soma) is the central part of a neuron that contains the nucleus and other organelles essential for the neuron’s function. It is responsible for maintaining the cell’s metabolic activities, such as energy production and protein synthesis. The cell body integrates incoming electrical signals from the dendrites and, if the signal is strong enough, generates an action potential that travels down the axon.
Similarities & Differences
Similarities
- All contain a cell body.
- 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.
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), making 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), making 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 which decreases the likelihood of the neuron firing.
Summation
- Summation is the addition of the positive and negative post-synaptic potentials.
- A nerve cell can receive both positive and negative potentials simultaneously.
- These potentials are summed if the net effect on the post-synaptic neuron is excitatory, it will be more likely to fire. If the net effect on the post-synaptic neuron is excitatory, it will be less likely to fire.
- If the sum charge of the post-synaptic neuron is positive then it will increase the likelihood of firing yet if the sum charge of the post-synaptic neuron is negative then it will decrease the likelihood of firing.
