How many neurons do we have?
100 billion neurons
Where are 80% of neurons located?
in the brain
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How many neurons do we have?
100 billion neurons
Where are 80% of neurons located?
in the brain
How does the nervous system communicate?
through electrical and chemical signals
What are the 3 types of neurons?
sensory
relay
motor
What is the purpose of the sensory neurons?
carry messages from PNS (peripheral) → CNS (central)
What type of dendrites and axons do sensory neurons have?
long dendrites
short axons
What is the purpose of the motor neurons?
connects the CNS(central) to the effectors
What type of dendrites and axons do motor neurons have?
short dendrites
long axons
What is the purpose of the relay neurons?
connect sensory to motor/other relay neurons
What type of dendrites and axons do motor neurons have?
short dendrite
short axon
What is the cell body?
includes the nucleus ( stores genetic material of the cell)
What are dendrites?
branch-like structures that carry nerve impulses from neighbouring neurons towards the cell body
What are axons?
carries the impulse away from the cell body down the length of the neuron
What is the myelin sheath?
fatty layer that protects the axon + speeds up electrical transmission of the impulse
What are the nodes of ranvier?
gaps between the myelin sheath that speed up electrical transmission by forcing the impulse to “jump“
What are terminal buttons?
at the end of axons - communicate with the next neuron in the chain across synapse
Where are the cell bodies of motor neurons located?
in CNS (central)
have long axons forming part of PNS
Where are sensory neurons located?
outside of CNS (central)
in PNS in ganglia (clusters)
Where are relay neurons located?
in brain + the visual system
(make up 97% of all neurons )
What is the charge of the inside of the cell when the neuron is in its resting state?
negatively charged
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
What is action potential?
an explosion of electrical activity
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)
What are the groups that neurons communicate with each other within called?
neural networks
How are signals within neurons transmitted?
electrically
How are signals between neurons transmitted
chemically (across synapse)
What happens when the electrical impulse reaches the end of the neuron (presynaptic neuron)?
triggers the release of neurotransmitters (from synaptic vesicles)
What are neurotransmitters?
chemicals that diffuse across the synapse + are released from synaptic vesicles
What happens to a neurotransmitter when it cross the gap?
taken up by postsynaptic receptor site on dendrite of next neuron
What happens at the postsynaptic receptor sites?
chemical message is converted back into electrical impulse
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
What does each neurotransmitter have?
it’s own molecular structure that fits perfectly with the postsynaptic receptor site
What two types of effects can neurotransmitters have on a neighboring neuron?
excitatory
inhibitory
Excitation
when neurotransmitter increases the positive charge of the postsynaptic neuron
increases likelihood to fire
Inhibition
when neurotransmitter increases the negative charge of the postsynaptic neuron
decreases likelihood to fire
examples of excitatory neurons
adrenaline
examples of inhibitory neurons
serotonin
What does normal brain function depend on?
regulated balance between excitatory and inhibitory influences
What is summation?
the sum of inhibitory + excitatory influences (both coming through)
What happens if the net effect on the postsynaptic neuron is inhibitory?
it’s less likely to fire
What happens if the net effect on the postsynaptic neuron is excitatory?
it’s more likely to fire
What is the process of synaptic transmission?
Nerve impulse travels down axon
Nerve impulse reaches synaptic terminal
Triggers release of neurotransmitters
Neurotransmitters fired into synaptic gap
Neurotransmitters bind w/ receptors of dendrite adjacent neuron
if successfully transmitted - neurotransmitter is taken up by postsynaptic neuron
message will continue to be passed in this way via electrical impulses