Neurons and synapses Flashcards
what is a neuron?
Neuron- the basic building blocks of the nervous system, they are nerve cells that process and transmit messages through electrical and chemical signals.
what is a sensory neuron?
Sensory neurons- carry messaged from the PNS to the CNS. They have long dendrites and short axons.
what is a relay neuron?
Relay neurons- these connect sensory neurons to motor or other relay neurons. They. Have short dendrites and short axons.
what is a motor neuron?
Motor neurons- these connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons.
what is the structure of a neuron?
- The cell body includes a nucleus, which contains the genetic material of the cell.
- Branch like structures which protrude from the cell body are called dendrites.
- The axon carries the impulse away from the cell body down the length of the neuron.
- Axon is covered in a fatty layer of myelin sheath, this protects the axon as well as speeding up the electrical transmission of the impulse.
- Myelin sheath is segmented by nodes of Ranvier, these speed up transmission by forcing the impulse to ‘jump’ across the gaps of the axon.
- At the end of the axon are terminal buttons that communicate with the next neuron in the chain across the gap, known as a synapse.
where are the neurones located?
- Cell bodies of motor neurons may be in the CNS but their long axons may form part of the PNS.
- Sensory neurons are located outside the PNS and CNS in the ganglia.
- Relay neurons make up 97% of neurons and are found in the brain.
what is the process of electrical transmission?
- When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside.
- When neuron is activated by a stimulus, inside of the cell becomes positively charged for a split second causing action potential to occur.
- This creates a electrical impulse that travels down the axon to the end of the neuron.
what is chemical transmission?
- Signals within neurons are transmitted electrically. Signals between neurons are transmitted chemically across the synapse
- When the electrical impulse reaches the end of the neuron it triggers the release of neurotransmitter from the synaptic vesicles.
what are neurotransmitters?
- Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.
- Once neurotransmitter crosses the gap, it is taken up by a post synaptic receptor site on the dendrites of the next neuron.
- Here the chemical messages is converted back into an electrical impulse.
- Direction of travel can only be one-way, this is because neurotransmitters are released from the presynaptic neuron terminal and received by the posy synaptic neuron.
- Each neurotransmitter has it own specific molecular structure that fits perfectly into a post synaptic receptor site, similar to a lock and key.
what is excitation and inhibiition?
- Neurotransmitters have a excitatory or inhibitory effect on neighbouring cells.
- Serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire.
- Adrenaline causes excitation of the post synaptic neuron by increasing its positive charge and making it more likely to fire.
what is summation?
- Whether a postsynaptic neuron fires is decided by the process of summation.
- Excitatory and inhibitory influences are summed: if effect o posy synaptic neuron is inhibitory then the post synaptic neuron is less likely to fire. If excitatory then it is more likely to fire.
- The action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals reaches a threshold.
