Cells of nervous system, neurotransmitters at synapses Flashcards
Nerve cells
Neurons - adapted to carry electrical impulses from one place to another
Parts of neurons
Axon - single fibre that carries nerve impulses away from cell body which is insulated by a fatty (myelin) sheath
Dendrites - branched nerve fibres which receive nerve impulses and pass them towards cell body
Axon - fatty myelin sheath function
Insulated by fatty (myelin) sheath which increases speed of nerve impulses along neuron
Myelination
process of developing myelin around axon fibres, it continues from birth to adolecense
Multiple sclerosis and poliomyeltis
Cause myelin sheath to be destroyed - damage to motor neurons which means muscles no longer receive signals from brain or spinal cord. Results in loss of strength and co-ordination in the limbs.
Myelin sheath is produced by what kind of cells?
Glial cells
Glial Cells
DO NOT transmit nerve impulses. Instead they maintain homeostasis, form myelin and provide support and protection for neurons. Glial cells also remove any debris by phagocytosis
Synapse
Where 2 neurons meet - small gap called synapse
The plasma membranes of each neuron are in very close contact and are seperated by a narrow space called synaptic cleft.
Mechanism for electrical impulse to cross gap
- electrical nerve travels along axon of 1st neuron (presynaptic neuron)
- when nerve impulse reaches dendrites at end of axon, chemical messenger called neurotransmitters are released
- these chemicals diffuse across synaptic cleft. Chemicals bind with receptors molecules on membrane of second neuron (postsynaptic neuron)
- receptor molecules on second neuron can only bind to specific neurotransmitters released from first neuron.
- binding of neurotransmitter to receptors stimulates 2nd neuron to transmit an electrical impulse along its axon. Signal is therefore been carried from one neuron to the next.
neurotransmitters are stored where?
inside vesicles which are found in presynaptic neuron
between impulses transmitter molecules are rapidly removed from synaptic cleft to prevent continuous stimulation of postsynaptic neurons - what are 2 types of removal?
Re-uptake - the neurotransmitter is reabsorbed back into presynaptic neuron and restored inside vesicle ready to be used again - e.g. noradrenaline
Enzyme degradation - neurotransmitters broken down by an enzyme into smaller inactive product which are then reabsorbed by presynaptic neuron and resynthesied into active neurotransmitter.
Receptors on the postsynaptic membrane determines whether the signal received is?
Excitatory - increases contraction of muscle fibres
Inhibitory - decreases contraction of muscle fibres
A critical number of neurotransmitter molecules is needed for what?
In order to affect enough receptors on the postsynaptic membrane
A nerve impulse is only transmitted across synapse if enough neurotransmitters is released.
Weak stimuli
Doesn’t reach critical number of neurotransmitter molecules to generate an impulse. This filters out weak stimuli.
Summation
A series of weak stimuli combine, increasing amount of neurotransmitters released. This means enough being diffused across the synaptic cleft to trigger the impulse in the postsynaptic neuron.
Endorphins
Neurotransmitters that stimulate neurons involved in reducing intensity of pain.
Connected to feeling of pleasure
Endorphins arise from activities such as
prolonged exercise, eating and sex
endorphin production increases in response to…
severe injury
prolonged and continuous exercise
stress
certain foods
increased endorphines can in turn stimulate the release of…
dopamine
Dopamine can bring around other responses such as…
Euphoria
Apetite regulation
Release of sex hormones
Dopamine
Neurotransmitter that indices feeling of pleasure and is involved in reinforcing particular behaviour as part of reward pathway (neurons which secrete or respond in increased levels of dopamine)
reward pathway = eating when hungry
Alzheimer’s disease
Linked to low levels of neurotransmitters acetylcholine which results in decline in signals between brain and cells
Parkinson’s disease
Low levels of dopamine affect part of brain controlling movement causing it to not work properly.
Drug treatments for neurotransmitter linked diseases?
Either agonists or antagonists
Agonists
Chemicals that mimic the neurotransmitter effect. Agonists bind to and stimulate receptors, triggering the same response as the neurotransmitter
Example of agonists
Morphine
Antagonsists
Block neurotransmitters from binding to and stimulating receptors.
Example of antagonsits
Antihistamines - blocking or inhibiting histamine receptors that the allergy triggered.
Antagonists other treatments available may affect uptake of neurotransmitters by either…
Inhibiting enzymes which degrade them or inhibiting the reabsorption.
Recreational drugs
Affect neurotransmitters in reward pathway. Act as either agonists or antagonists. Can also stimulate release of neurotransmitters or inhibit their uptake.
Recreational drugs cause changes in…
mood
awareness
perception
behaviour
Agonist recreational drugs
Repeated use results in tolerance
Stimulate specific receptors which decreases number and sensitivity of receptors. As sensitivity decreases the individual must take more drugs to trigger receptors and therefore feel effect.
Antagonist recreational drugs
Repeated use leads to addiction
Block specific receptors which increases both number and sensitivity of receptors. As result sensitisation leads to individual craving more of the drug.
