2.4 Flashcards
3 basic parts of neurons
Dendrites
Cell body
Axons
Dendrites
Nerve fibres that can receive nervous signals from another neuron or sense organ. They then pass these signals to the cell body
Cell body
Cell body contains cytoplasm, nucleus, mitochondria and ribosomes for the neuron. The DNA is important as it contains genes for production neurotransmitters
Axon
Long cell structure that can carry nervous signals at speed. The ends of the axon terminate at the synapse between 2 neurons. Axon surrounded by myelin sheath
What is axon surrounded by
Myelin sheath
Myelin sheath purpose
Insulates axon and allows speed of impulses to be increased , allowing cells to transmit signals more quickly. This is why children have slower reaction speeds
When is myelin sheath formed
Myelin sheath formed during early development (conception) (myelination)
Problems with myelin sheath if damaged
People lose coordination and speed in their movement. Neurones experience problems with correct transmission of signals
Disease of myelin example
Multiple Sclerosis (MS)
Synapse
The gap between two neurones.
How do electrical signals cross synapses
First neuron releases chemicals called neurotransmitters to cross the gap and activate a signal in the second neurone.
Synaptic cleft
Tiny region between the axon ending of one neurone and the dendrite of another neurone.
Presynaptic neuron
Neuron carrying signal before the synapse
Postsynaptic neuron
Neuron that generates signal after synapse
Neurotransmitter
Protein that crosses the synapse and binds to receptor on postsynaptic membrane
Vesicles
Small membrane bound organelles which act as containers for neurotransmitters.
What do vesicles do when electrical signal arrives
Rise to the surface of presynaptic membrane and fuse with the membrane to allow the release of neurotransmitters into synaptic cleft
Two ways you can dispose of neurotransmitters are
Reuptake by presynaptic membrane
Enzyme degradation (breakdown)
How does reuptake work
Presynaptic membrane contains receptors that can collect and re absorb the neurotransmitter back into the Presynaptic knob.
The neurotransmitter can then be repackaged into vesicles or broken down
Example of neurotransmitter reuptake
Adrenaline
How does breakdown / enzyme degradation work
Certain enzymes act to break down specific neurotransmitters in the synaptic cleft, preventing them from further transmission
Neurotransmitter enzyme degradation example
Acetylcholine
Excitatory receptors
When a neurotransmitter binds to an excitatory receptor, the change of an impulse being created is increased
Inhibitory receptors
If a neurotransmitter binds to an inhibitory receptor on the postsynaptic membrane, it decreases the chances of an impulse being created
Threshold
In order for impulse transmission to be successful, there must be enough neurotransmitters bound to receptors on the postsynaptic membrane. This helps prevent constant stimulation of nervous pathways.
Summation
If enough weak stimuli release enough neurotransmitters across a synapse, this can be enough to generate a signal in the postsynaptic neuron. (Several weak signals combining to reach threshold)
Endorphins
Neurotransmitter released by brain. Stimulate neurones to reduce pain. Painkilling properties have been linked to improve mood and reduce depression.
How to increase endorphins
Pain, intense exercise, stress, eating chocolate
Dopamine
Neurotransmitter induces feelings of pressure and happiness . Involved in reward pathway
Reward pathway
When body engages in beneficial behaviour, brain releases dopamine. Dopamine activates neurons which emit positive feelings, making them more likely to do it again.
Behaviours that activate reward pathway
Eating when hungry
Drinking when thirsty
Having sex
Positive social interactions
Types of neurotransmitter treatments
Agonists
Antagonists
Drugs that inhibit reuptake
Drugs that inhibit breakdown enzymes
Agonists
Mimic the shape of a neurotransmitter. They can bind to receptors on the postsynaptic membrane and cause a similar action to the main neurotransmitter. They cause activation of those receptors in a similar way to the original neurotransmitter.
Example of agonists used
Parkinsons treated by giving dopamine agonists.
Antagonists
Antagonists bind to a receptor, but cause no action, blocking any neurotransmitters from stimulating the receptor. The normal action of the neurotransmitter, wether excitatory or inhibitory, is blocked.
Antagonists example
Beta blockers, block noradrenaline
Reuptake inhibitors
Allow the effects of some neurotransmitters to last longer as they prevent their reabsorptiom into the Presynaptic knob.
Reuptake inhibitors example
Depression by seratonin Reuptake inhibitors (SSRIS)
Neurotransmitter breakdown enzymes inhibitor
Prevent breakdown of neurotransmitters in the synaptic cleft, allowing for longer duration and more signalling of neurotransmitters.
Recreational drugs can affect
Mood , cognition, perception, behaviour, movement, digestion, reproduction
Addiction
Needing drug to feel normal
Tolerance
Requiring more of the drug to feel an effect
How is addiction caused
Addiction caused by repeated use of antagonists. Blockage of receptors causes the postsynaptic neuron to make more receptors and they become more sensitive. sensitisation !!
How is tolerance caused
Tolerance caused by repeated use of agonists. Repeated activation of receptors causes Presynaptic neuron to lower their number. This means larger amount of drug needed for same effect. Desensitisation
Tolerance example
Alcohol
Addiction example
Ketamine
Sensitisation
Number of receptors increase
Desentisisation
Number of receptors decrease
