3.3 Cells of the Nervous System and Neurotransmitters Flashcards
Function of neurons
Recieve and transmit electrical signals
Function of glial cells
Support and maintain the neurons
Composition of neurons
- Nerve cell body
* Nerve fibres
The three types of neurons
- Sensory
- Inter
- Motor
Function of dendrites
Nerve fibres that recieves nerve impulses
Function of the cell body
Contains the nucleus, containing DNA, coding for a neurotransmitter, or a receptor, or enzymes needed for the synthesis or degredation of neurotransmitters
Funtion of axons
Nerve fibre that carries inpulses away from the cell body
Order in which nerve impulses travel
Dendrite -> Cell Body -> Axon
Funtion of sensory neurons
Passes information from sense organs to neurons in the CNS
Function of Inter neurons
Link sensory neurons to motor neurons within the CNS
Function of motor neurons
Passes information from the CNS to an effector (a muscle or a gland)
Why axon terminals of a neuron contain many mitochondria
- Provide ATP for synthesis reactions
* Privide ATP for the creation of vesicles which are able to store, carry and release neurotransmitters
Definition of myelination
The development of myelin around the axon fibres if individual neurons
The two jobs of the myelin sheath
- Insulates the axon fibres of neurons
* Increases the soeed of impulse conduction
The two jobs of the glial cells
- Maintain a homeostatic environment around the neurons
* Remove debris by phagocytosis
Definition of synapse
The junction between an axon of one neuron and the dendrite of another
Definition of synaptic cleft
The narrow space between the plasma membranes of the two neurons at the synapse
Where neurotransmitters are stored in neurons
Vesicles
Where neurotransmitters are released from
Vesicles from the presynaptic membrane
What neurotransmitters do after diffusing across the synaptic cleft
Bind to receptors on the postsynaptic membrane
What a neurotransmitter is
Protein molecules produced by ribosomes
Jobs of receptors on the postsynaptic membrane
Determine whether the signal is excitory or inhibitory
Definition of neurotransmitter threshhold
Minimum quantity of neurotransmitter to allow activation/ muscle contraction
Hiw the continuous stimulation of the post synaptic neuron is prevented
- Neurotransmitters are removed from the synaptic cleft by enzymes
- Re-uptake occurs
Why many mitochondria are needed in nerve cells
Provide ATP for:
• release of neurotransmitters
• to allow vesicles to the cleft and fuse with the membrane
•for re-uptake to occur (active transport)
Enzyme involved in enzyme degredation
Acetylcholine
How enzyme degredation works
- The neurotransmitter is broken down by a degredative enzyme
- Non active products are reabsorbed by the presynaptic neuron
- It is then re-synthesised in to qctuve transmitters
How reuptake works
- The neurotransmitter is reabsobed directly into the presynaptic membrane
- It is then stored in a vesicle ready for reuse
Neurotransmitter involved in reuptake
Noradrenaline
Definition of Summation
When a series of weak stimuli trigger an inpulse or when a higher concentration of neurotransmitter is released to trigger an impulse
What controls the direction if nerve impulse?
Vesicles only occur in the axon on the terminal side of the synaptic cleft
What is a neural pathway?
The route a nerve impulse follows through the nervous system
Definition of converging pathway
Several neurons linked to one neuron, increasing the neurotransmitter concentration and therefore the chance of impulse generation
Definition of diverging pathway
One neuron linked to several neurons, so impulses are sent to several destinations at the same time
When diverging pathways are used
For fine motor control of the fingers or eyes (several muscles are activated at once when writing)
Definition of reverberating pathway
A pathways which has neurons later in the pathway which link back to form synapses with neurons earlier in the pathway
Definition of plasticity
The ability of brain cells to become altered as a result of new environmental experiences
Example of major plasticity
The undamaged cells to form new neural pathways following brain damage (eg stroke)
Example of minor plasticity
When the brain suppresses reflexes like blinking or supresses sensory impulses
Definition of endorphines
Neurotransmitters which stimulate neurons involving the intensity of pain
When endorphine prorduction increases
- severe injury
- continuous excersise
- stress
- certain foods
What increased levels of endorphines do
- euphoric feelings (intense happiness)
- appetite regulation (modulation)
- release of sex hormones
Definition of dopamine
The neurotransmitter that induces feelings of pleasure and reinforces certain behaviours in the reward pathway
When neurotransmitter related disorders occur
When there is an imbalance, overproduction or underproduction of neurotransmitters
Examples of neurotransmitter related disorders
- Alzheimer’s disease
- Parkinson’s disease
- anxiety disorders
- depression
- schizophrenia
What kinds of drugs are given to treat neurotransmitter disorders
Drugs that are similar to the neurotransmitters, act as agonists, antagonist and enzyme inhibitors
Action of Agonists
Bind to and stimulate the receptors mimicking the neurotransmitters
Action of Antagonists
Bind to specific receptors, blocking the action of the neurotransmitters
Action of Enzyme inhibitors
Inhibits the enzymes which degredate neurotransmitters or inhibit reuptake
Effects of recreational drugs
- Changes brains neurochemistry
- alters moods
- alters cognition
- alters perception
- alters behaviour
Action of recreational drugs acting as agonists
Mimics the action of natural neurotransmitters and can enhance the action of these
Eg. Nicotine mimics the action of acetylcholine
Action of recreational drugs acting as antagonists
Block the binding of natural neurotransmitters or bind to receptors, preventing the nerve impulses passing from the synapse
Eg. Nicotine blocks the reuptake of dopamine (continuing stimulation of the reward pathway and reinforcing smoking habits)
Definition of sensitisation
An increase in the number and sensitivity of neurotransmitter receptors
What sensitivity occurs with
The use of antagonistic drugs, blocking the receptors
Definition of desensitisation
A decreased number and sensitivity of receptors as the nervous system tries to compensate for the overstimulation of certain neurotransmitter receptors
What desensitisation occurs because of
An exposure to drugs that are agonists. This leads to a drug tolerance
Cocaine’s effect on dopamine
- Blocks the dopamine reuptake proteins
- It therefore acts as an antagonist
- Dopamine then stays in the synaptic cleft and continues to stimulate the receptors
