The Cells of the Nervous System and Neurotransmitters at Synapses Flashcards
What are the 3 types of neurons?
Sensory, Inter and Motor
What is the basic structure of a neuron?
Cells body, Axon and Dendrites
What does the cell body do?
It is the control centre as it contains a nucleus
What does the axon’s do?
Its a single nerve fibre that carry’s nerve impulses away from the cell body
What does dendrites do?
It passes impulses towards the cell body
What is the function of the myelin sheath?
It surrounds the axons with a layer of fatty material that insulates the axon, it greatly increases the speed of impulse conduction
What is myelination?
This is the development of myelin and continuous from birth to adolescence
*Responses to stimuli in the first 2 years of life are not as rapid or coordinated as those of an older child or adult
What do certain diseases do in relation to the myelin sheath?
They destroy it which causes a loss in coordination
What is the function of glial cells?
To produce myelin sheath and support neurons
What is the region of functional contraction?
This is between the axon ending of one neuron (pre-synaptic neuron) and a dendrite of another (postsynaptic neuron) is called a synapse with a tiny gap between them known as the synaptic cleft
How are messages relayed across the synaptic cleft?
This is done by neurotransmitters stored in vesicles on the presynaptic neuron only, such as acetylcholine and noradrenaline
What happens when an impulse passes through the presynaptic neuron?
It stimulates several vesicles to move to the synapse, fuse with the membrane and discharge the neurotransmitters which diffuse across the synaptic cleft and bind to receptors on the membrane of the synaptic neuron
To ensure precise control and prevent continuous stimulation, what has to happen?
The postsynaptic neuron must remain excited fir only a brief moment to pass on the impulse, so removal of neurotransmitters by enzyme degeneration (enzyme breaks down neurotransmitters which is then reabsorbed and synthesised into new neurotransmitter) or by reabsorption directly (to be stored in vesicles)
The receptors present on the postsynaptic neuron determine what?
Whether the signal is excitatory and inhibitory
In order for an impulse to be transmitted, what has to happen?
A certain threshold of neurotransmitter molecules must attach to receptors otherwise they are filtered out due to being weak
However, if a postsynaptic neuron were to receive information via several synapses (convergent pathway), this collective of weak stimuli could be enough to fire an impulse known as summation
What are endorphins?
They are neurotransmitters that stimulate neurons involved in reducing intensity of pain by combining with receptors synapses and blocking the transmission of the pain signal
Endorphins are produced by what?
The hypothalamus and increases levels are produced in the response to:
Severe injury
Prolonged and continuous exercise
Physical and emotional stress
Certain foods (e.g. chocolate)
Increased levels are linked with feelings of pleasure obtained from activities, such as:
Eating
Sex
Prolonged exercise
What is dopamine?
It is a neurotransmitter that induces feelings of pleasure by stimulating the reward pathway which reinforces certain behaviour to satisfy a need that is beneficial such as hunger or thirst
What is an Agonist?
It binds to and stimulates specific receptors on postsynaptic neuron mimicking action of naturally occurring neurotransmitters triggering normal cellular response
What is an Antagonist?
It binds to specific receptors om postsynaptic neuron and blocking the action of the neurotransmitter inhibiting normal cellular response
What do other drugs do (inhibitors)?
They act by preventing the removal of the neurotransmitter (by degrading the enzymes or preventing re-uptake) causing an enhanced effect
Recreational drugs act like what?
Agonists and Antagonists
What do recreational drugs do?
They affect transmission at synapses in the brain altering an individuals:
- Mood (feels happier, more confident, more aggressive)
- Cognition (cant carry out complex mental tasks such as problem solving and decision making)
- Perception (misinterpretation of stimuli)
- Behaviour (stay awake for longer, talk endlessly about themselves)
Many recreational drugs effect what?
The neurotransmitters in the reward circuit of the brain causing them to be overstimulated
What is drug addiction caused by?
Repeated use of drugs that act as antagonists. Antagonists block specific receptors causing the nervous system to compensate by increasing both the number and sensitivity of these receptors
This sensitisation leads to addiction where the individual craves more of the drug
What is drug tolerance caused by?
Repeated use of drugs that act as agonists. Agonists stimulate specific receptors causing the nervous system to compensate by decreasing both the number and sensitivity of these receptors
This desensitisation leads to drug tolerance where the individual must take more of the drug to get an effect
