7 - Biopsychology: Neurons & Synaptic Transmission

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How many neurons do we have?

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100 billion neurons

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Where are 80% of neurons located?

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in the brain

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42 Terms

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How many neurons do we have?

100 billion neurons

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Where are 80% of neurons located?

in the brain

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How does the nervous system communicate?

through electrical and chemical signals

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What are the 3 types of neurons?

  • sensory

  • relay

  • motor

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What is the purpose of the sensory neurons?

carry messages from PNS (peripheral) → CNS (central)

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What type of dendrites and axons do sensory neurons have?

  • long dendrites

  • short axons

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What is the purpose of the motor neurons?

connects the CNS(central) to the effectors

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What type of dendrites and axons do motor neurons have?

  • short dendrites

  • long axons

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What is the purpose of the relay neurons?

connect sensory to motor/other relay neurons

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What type of dendrites and axons do motor neurons have?

  • short dendrite

  • short axon

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What is the cell body?

includes the nucleus ( stores genetic material of the cell)

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What are dendrites?

branch-like structures that carry nerve impulses from neighbouring neurons towards the cell body

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What are axons?

carries the impulse away from the cell body down the length of the neuron

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What is the myelin sheath?

fatty layer that protects the axon + speeds up electrical transmission of the impulse

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What are the nodes of ranvier?

gaps between the myelin sheath that speed up electrical transmission by forcing the impulse to “jump“

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What are terminal buttons?

at the end of axons - communicate with the next neuron in the chain across synapse

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Where are the cell bodies of motor neurons located?

  • in CNS (central)

  • have long axons forming part of PNS

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Where are sensory neurons located?

  • outside of CNS (central)

  • in PNS in ganglia (clusters)

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Where are relay neurons located?

  • in brain + the visual system

    (make up 97% of all neurons )

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What is the charge of the inside of the cell when the neuron is in its resting state?

negatively charged

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What happens when a neuron is activated by a stimulus?

  • the inside of cell becomes positively charged for a split second

  • causes an action potential to occur

  • creates an electrical impulse that travels down the axon towards the end of the neuron

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What is action potential?

an explosion of electrical activity

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Reflex Arc (Example: Knee Jerk)

  • stimulus (hammer) hits knee

  • detected by sense organs in PNS - convey message via sensory neuron

  • message reaches CNS where it connects w/ relay neuron

  • transfers message to motor neuron

  • carries message to effector (knee)

    (muscle contracts, knee jerks)

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What are the groups that neurons communicate with each other within called?

neural networks

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How are signals within neurons transmitted?

electrically

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How are signals between neurons transmitted

chemically (across synapse)

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What happens when the electrical impulse reaches the end of the neuron (presynaptic neuron)?

triggers the release of neurotransmitters (from synaptic vesicles)

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What are neurotransmitters?

chemicals that diffuse across the synapse + are released from synaptic vesicles

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What happens to a neurotransmitter when it cross the gap?

  • taken up by postsynaptic receptor site on dendrite of next neuron

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What happens at the postsynaptic receptor sites?

chemical message is converted back into electrical impulse

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What happens to neurotransmitters that do not get to a postsynaptic receptor site?

  • they are “taken back up“ into terminal buttons via reuptake

  • broken down by enzymes

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What does each neurotransmitter have?

it’s own molecular structure that fits perfectly with the postsynaptic receptor site

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What two types of effects can neurotransmitters have on a neighboring neuron?

  • excitatory

  • inhibitory

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Excitation

  • when neurotransmitter increases the positive charge of the postsynaptic neuron

  • increases likelihood to fire

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Inhibition

  • when neurotransmitter increases the negative charge of the postsynaptic neuron

  • decreases likelihood to fire

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examples of excitatory neurons

adrenaline

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examples of inhibitory neurons

serotonin

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What does normal brain function depend on?

regulated balance between excitatory and inhibitory influences

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What is summation?

the sum of inhibitory + excitatory influences (both coming through)

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What happens if the net effect on the postsynaptic neuron is inhibitory?

it’s less likely to fire

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What happens if the net effect on the postsynaptic neuron is excitatory?

it’s more likely to fire

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What is the process of synaptic transmission?

  1. Nerve impulse travels down axon

  2. Nerve impulse reaches synaptic terminal

  3. Triggers release of neurotransmitters

  4. Neurotransmitters fired into synaptic gap

  5. Neurotransmitters bind w/ receptors of dendrite adjacent neuron

  6. if successfully transmitted - neurotransmitter is taken up by postsynaptic neuron

  7. message will continue to be passed in this way via electrical impulses