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Psychology Neurons
Neurons and Synaptic Transmission
| Term | Definition |
|---|---|
| Neurons are... | Specialised cells that move electrical impulses to and from the Central Nervous System/throughout the body |
| 3 types of Neuron | SENSORY neuron MOTOR neuron RELAY neuron |
| Basic structure of a neuron | CELL BODY (contains nucleus), DENDRITES and an AXON. |
| DENDRITES | Found at one end of a neuron, they receive signals from other neurons or from sensory receptors. They are connected to the cell body. |
| AXON | Carries the impulse from the cell body to the axon TERMINAL. Many neurons have an insulating layer around the AXON - the MYELIN sheath- which helps to speed up transmission of the nerve impulse. mm-m in length. |
| SENSORY NEURONS | Carry nerve impulses FROM sensory receptors (e.g. retina in eye) TO the CNS. They convert information from sensory receptors into nerve (electrical) impulses. Brain translates impulses into sensations e.g. visual input or pain so can react appropriately. |
| RELAY NEURONS | Allow sensory and motor neurons to communicate with each other. Also known as INTERNEURONS, situated in the brain and spinal cord. |
| MOTOR NEURONS | Form synapses with muscles and control their contraction. When stimulated they release neurotransmitters that bind to muscle receptors and trigger contraction. Muscle relaxation caused by inhibition of motor neuron. Lie in CNS but project axons outside. |
| ACTION POTENTIAL | Dendrites receive information, pass it to cell body and on to axon. Information travels down the length of the axon in the form of an electrical signal known as an action potential. |
| REFLEX ACTION | Some sensory information travels to the spinal cord and then to motor neurones. This allows reflex actions to happen quickly without the delay of sending impulses to the brain. |
| What is a synapse? | The end of the PRESYNAPTIC Neurone, the membrane of the POSTSYNAPTIC neurone and the GAP (known as the Synaptic gap or cleft) in between. |
| Where are synaptic vesicles found and what do they contain? | At the end of the axon of a neuron. They are sacs that contain neurotransmitters (chemical messengers). |
| How do nerve impulses travel between 2 neurones or between a neurone and muscle cell? (Synaptic transmission). | When action potential reaches synaptic vesicles, they release their contents into the synaptic gap (by EXOCYTOSIS). The neurotransmitter rapidly diffuses across the gap and binds to receptors on surface of post synaptic neurone and activates them. |
| What are the two effects that can happen on the post synaptic neuron once receptor molecules have been activated? | EXCITATORY or INHIBITORY effects. |
| Describe the "re-uptake" process | The neurotransmitter is taken up again by the presynaptic neurone. It is stored ready for release again. This process terminates the effects of synaptic transmission. How quickly the neurotransmitter is taken back decides how long the effects last. |
| How do SSRIs, used to treat depression, prolong the action of the neurotransmitter? | They inhibit the re-uptake process. |
| Name of 2 EXCITATORY neurotransmitters | ACETYLCHOLINE NORADRENALINE |
| Function of excitatory neurotransmitters | System's "ON switches". They increase the likelihood that an excitatory signal is sent to a postsynaptic cell, which is then more likely to FIRE. |
| Name 2 inhibitory neurotransmitters | SEROTONIN GABA |
| Function of Inhibitory neurotransmitters | System's "OFF switches". They decrease the likelihood of that neuron firing. Usually responsible for calming mind and body, inducing sleep and filtering out unnecessary excitatory signals. |
| What is an EPSP? | When an excitatory neurotransmitter binds with a postsynaptic receptor it causes an electrical change in the membrane of that cell. This results in an EXCITATORY POST SYNAPTIC POTENTIAL (EPSP). meaning that the postsynaptic cell is more likely to fire. |
| What is an IPSP? | When an inhibitory neurotransmitter binds with a postsynaptic receptor it causes an electrical change in the membrane of that cell. This results in an INHIBITORY POST SYNAPTIC POTENTIAL (IPSP). meaning that the postsynaptic cell is LESS likely to fire. |
| What determines the likelihood of a cell firing? | A neuron can receive both EPSPs and IPSPs at the same time. The likelihood of the cell firing is determined by adding up the excitatory and inhibitory synaptic input. The net result is known as SUMMATION and decides whether a cell fires or not. |
| 2 ways the strength of the EPSP can be increased. | |
| What decides the rate at which a particular cell fires? | A large number of EPSPs are generated at many DIFFERENT synapses on the same postsynaptic neuron at the same time. |
| What is TEMPORAL SUMMATION? | A large number of EPSPs are generated at the SAME synapse by a series of high-frequencyaction potentials on the presynaptic neuron. |
| What determines the rate at which a particular cell fires? | If excitatory synapses are more active, the cell fires at a higher rate. If inhibitory synapses are more active, the cell fires at a lower rate, if at all. |
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