Nervous Coordination Flashcards
Sensory neurones
Carry nervous impulses from receptors into the central nervous systems
Motor neurones
Carry impulses from the CNS to effecter organs
Relay neurones
Intermediate neurones which receive impulses from a sensory neurone and relay them to motor neurones
Dendrites
Carries nervous impulses towards a cell body
Axons
Carries nervous impulses away from the cell body
Cell body
Where the nucleus is normally located
Myelinated motor neurones
Schwann cells are wrapped around the axon of the neurone which form the myelin sheath
Gaps between the adjacent Schwann cells are called nodes of ranvier
Resting potential
At resting state the inside of the neurone is more negatively charged than the outside because there are more positive ions outside the cell
About -70mV
How is the resting potential maintains
By sodium-potassium pumps in the neurone membrane : three Na+ ions are actively transported out of the neurone for every two K+ ions that are transported in which leads to a build up of positive ions outside the cell
Stimulation
Na+ ion channels in cell membrane open when a neurone is stimulated so sodium ions flood into the neurone which causes the potential difference across the membrane to become more positive inside the neurone
Depolarisation
If the potential difference increases above the threshold value (about -55mV) then the membrane will become depolarised so more sodium channels open and there is a sharp increase in the potential difference to about +30mV
All or nothing response
If the potential difference reaches the threshold, depolarisation will always take place and the change in potential difference will always be the same. If the stimulus is stronger, action potentials will be produced more frequently, but their size will not increase
Repolarisation
After the neurone membrane has depolarised to +30mV the sodium ion channels close and potassium ion channels open
Na+ ions are transported back out of the neurone and the potential difference becomes more negated
Hyper polarisation
Short period after depolarisation of a neurone where the potential difference becomes slightly more negative than the resting potential which prevents the neurone from being restimulated instantly = refractory periods
How do action potentials move along the neurone
When an action potential is generated , there are more Na+ ions inside the neurone than outside. Some of these Na+ ions diffuse sideways along the neurone axon which creates a change in the potential difference further along the neurone membrane and if this reaches the threshold value, sodium ions channels at this part of the membrane open which creates a wave of depolarisation
How does myelination speed up transmission of nerve impulses
Schwann cells wrap around the axon of neurones to create a myelin sheath which acts as an electrical insulator because it is impermeable to ions.
Depolarisation and action potentials cannot occur at the myelinated parts of the axon and can only occur in the gaps between. The nervous impulse jumps from one node to the next = saltatory conduction
How does temperature speed up transmission
Increase in temperature increase kinetic energy so ions move across the membrane more rapidly when they have more kinetic energy
Axon diameter
Greater surface area for the movement ions across the cell membrane
Synapse
Junction between two neurones or between a neurone and an effector
Synaptic cleft
At a synapse, there is a gap between the cells . When an action potential reaches a synapse, it. Must be transmitted across the synaptic cleft
Presynaptic neurone
Neurone before the synapse, when an action potential reaches the end of the neurone, it is transmitted across the presynaptic membrane to the postsynaptic membrane or to an effector cell
Synaptic knob
Swelling which contains synaptic vesicles where the nerve impulse is transmitted across the synaptic cleft
Lots of mitochondria needed to synthesise neurotransmitters
Synaptic vesicles
Located in the synaptic knob
Contain neurotransmitters and fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft
Neurotransmitters
Chemicals that allow an action potential to be transferred across a synapse.
When neurotransmitters are released from the synaptic vesicles into the synaptic cleft, they bind to specific receptors on the postsynaptic membrane
Post synaptic membrane
Membrane of the post synaptic neurone or effector cells.
Receptors on the post synaptic membrane have a complementary shape to the neurotransmitters released from the synaptic knob
When neurotransmitters bind to the receptors, the Action potential continues
Excitatory neurotransmitters
Generate an action potential in the postsynaptic cell.
When the neurotransmitters bind to receptors on the postsynaptic membrane, the ,membrane is depolarised
Inhibitory neurotransmitters
Prevent an action potential from being generated in the post synaptic cell. When the neurotransmitters bind to the receptors on the post synaptic membrane, the membrane is hyperpolarised
summation
Process where neurotransmitters from multiple neurones are summed together to produce a response
Spatial summation
Takes place when multiple presynaptic neurones form a junction with a single neurone
Each presynaptic neruone release neurotransmitters which means they can establish a generator potential that reaches the threshold value
Temporal summation
Takes place when multiple nerve impulses arrive at the same synaptic knob within a short period of time.
More neurotransmitter is released into the synaptic cleft, so more neurotransmitter is available to bind to receptors on the post synaptic membrane
Neuromuscular junction
A synapse between a motor neurone and a muscle cell. An action potential is transmitted across the synapse using the neurotransmitter acetylcholine
Process at the neuromuscular junction
