3.1.1 - central nervous system Flashcards
what is the nervous system?
a network of specialised cells which can transmit information around the body, coordinating the behaviour of the organism
what is the CNS?
the brain and spinal cord
what are neurons?
the cells that make up the nervous system
related - CNS
what are key structural features of a neuron?
dendrites, nucleus, cell body, myelin sheath, Node of Ranvier, axon, Schwann’s cells, axon terminals, terminal buttons
what is the role of the nucleus?
contains the genetic material for that neuron
related - neuron, cell body
what is the role of the mitochondria?
provides the neuron with energy
related - neuron, cell body
what is the cell body?
the main part of the neuron where the nucleus and mitochondria are found
related - dendrites, neuron, nucleus, mitochondria
what are dendrites?
branches attached to the cell body of a neuron which receive messages from other neurons to trigger an action potential in the cell
related - neuron, cell body, nucleus, mitochondria
what is the axon?
a long branch from the cell body which passes electrical impulses down to the axon terminals at the end of the neuron so it can communicate with others
related - cell body, neuron, axon hillock, myelin sheath, nodes of Ranvier
what is the axon hillock?
the area that connects the axon to the cell body where the nerve impulse is triggered from
related - axon, cell body, neuron
what is the myelin sheath?
layers of fatty deposits surrounding the axon which increase the speed of action potentials travelling down the axon
related - neuron, axon, nodes of Ranvier
what are nodes of Ranvier?
breaks between the cells along the myelin sheath
related - myelin sheath, axon, neuron
what are axon terminals?
the end of the axon which leads to the terminal buttons
related - axon, neuron, terminal buttons
what are terminal buttons?
the ends of a neuron where the nerve impulse becomes a chemical message which can pass to the dendrite of another neuron
related - axon terminal, neuron
what is the structure of a terminal button?
they are bulb-shaped structures containing tiny sacs called vesicles, which store neurotransmitters
what are neurotransmitters?
chemicals which pass messages between neurons
related - neuron, terminal button
what is an action potential?
the electrical trigger which passes along the axon and stimulates the neuron to activate and release neurotransmitters as a result of synaptic transmission
related - resting membrane potential, excitatory postsynaptic potential, inhibitory postsynaptic potential
what is resting membrane potential?
the difference in electrical potential on each side of a cell membrane while the cell is at rest
related - action potential, excitatory postsynaptic potential, inhibitory postsynaptic potential
why does resting membrane potential occur?
there are different concentrations of ions on either side of the cell membrane, and the outside has a higher concentration of positive ions than the inside
what is excitatory postsynaptic potential?
the temporary depolarisation of a neuron due to positive ions flowing into the cell which make it more likely to fire an action potential
related - action potential, resting membrane potential, inhibitory postsynaptic potential
what is inhibitory postsynaptic potential?
the change in polarisation of a neuron that makes it less likely to fire an action potential
related - action potential, resting membrane potential, excitatory postsynaptic potential
what is the resting membrane potential of a neuron?
about -70mV (so the inside has a slight negative charge in relation to the outside)
what happens when a neuron receives a message from another neuron?
the chemical message stimulates an excitatory postsynaptic potential which will slightly depolarise the neuron and reduce its charge, or an inhibitory postsynaptic potential which will hyper polarise the neon and increase its charge
when is an action potential triggered?
when the neuron receives more excitatory messages than inhibitory messages that are sufficiently strong to reach the neuron’s threshold
what happens during the process of an action potential?
- the neuron opens tiny ion channels in its membrane and positive ions diffuse into the cell
- this means the difference in charge across the cell membrane is reversed (depolarised) but only in that specific region
- when an action potential occurs in one area of the membrane, the adjacent membrane is disturbed and the process repeats
- this means the action potential propagates along the cell membrane in a chain reaction
what is the refractory period?
the brief period immediately after an action potential occurs in part of a cell membrane where the ion channels close and tiny pumps move the ions back to where they started - the membrane is repolarised and returns to its resting potential
what is saltatory conduction?
when action potentials ‘jump’ quickly between nodes of Ranvier which speeds up the propagation and explains why myelinated neurons can send messages faster
what is the charge on a neuron when an action potential is triggered?
usually about -55mV
what does the action potential do?
send an impulse along the axon towards the axon terminals at the end to stimulate the release of neurotransmitters
what is the synaptic gap/cleft?
the tiny space between the dendrite of one neuron and the terminal button of another where chemical messages can be passed
related - presynaptic neuron, postsynaptic neuron
what is the presynaptic neuron?
the neuron where the chemical message starts from
related - postsynaptic neuron
what is the postsynaptic neuron?
the neuron where the chemical message travels to
related - presynaptic neuron
what is an excitatory synapse?
when the firing rate of neurons varies in the same direction (upstream neuron increases firing rate so downstream does as well)
what is an inhibitory synapse?
when the firing rate of neurons varies in opposite directions
what happens to the electrical impulse within a neuron?
it starts as a small electrical impulse created at the axon hillock, and eventually reaches the terminal button and becomes a chemical message which can be passed to more neuron across the synaptic gap
what are individual neurons responsible for?
producing a certain neurotransmitter
what happens when the action potential reaches the axon terminal?
calcium channels open, flooding the terminal button with calcium ions
this causes vesicles containing the neurotransmitter to be released and travel to the outer membrane of the terminal button - the casing of the vesicle fuses with the membrane and the neurotransmitter is released into the synaptic gap (and the action potential finishes)
what is the role of the receptors on the postsynaptic neuron?
they are designed to bind to a specific neurotransmitter as their shape is specific to it, so if they detect it the neurotransmitter will be absorbed by the postsynaptic neuron
what happens when a receptor has bound to a neurotransmitter molecule?
there are ion channels attached to the receptor which open - positive charges flow out of them which causes an action potential
how does the firing rate of the upstream neuron influence the downstream neuron?
as the firing rate of the upstream neuron increases, more neurotransmitter is released, so there is an increased concentration in the synaptic gap
this increased concentration increases the number of receptors which are activated, so more positive charges flow and there is a greater probability of an action potential occurring
what happens to neurotransmitter molecules which aren’t absorbed?
they are destroyed by enzymes in the synaptic gap or absorbed again by the presynaptic neuron in the reuptake process, and then destroyed by enzymes in the neuron
why is it important for neurotransmitter molecules to be removed from the synaptic gap?
if the upstream neuron decreases its firing rate then the downstream neuron also needs to - if there are still neurotransmitters in the synaptic gap, these will still bind to receptors and possibly cause action potentials, so they must be removed for the firing rate of the downstream neuron to decrease too
what are four of the most common neurotransmitters?
dopamine, serotonin, noradrenaline, acetylcholine
what is the function of acetylcholine?
motor control and movement eg. stimulating muscle contraction
cognitive functions like memory, attention and alertness
involved in expressing certain emotions like anger and sexuality
what is the function of noradrenaline?
associated with emotion (mood control)
key functions like sleeping, dreaming, learning
what is the function of dopamine?
similar to noradrenaline
emotional and cognitive functions
posture/control of movement
reinforcement in learning
dependency in addictions
used in hormonal regulation eg. menstrual cycle
what is the function of serotonin?
commonly associated with mood control especially in limbic system
involved in other functions like feeling pain, sleep, regulating body temperature and hunger
what is firing rate?
the number of action potentials generated per second
how do neurons encode messages?
by changing the frequency of their firing rate
how does firing rate influence neurons?
neurons respond to signals from other neurons by varying their firing rate to be faster or slower, so the firing rate of the neuron which receives the message can influence the firing rate of the neuron it is connected to
