Unit 6 Nervous Coordination Flashcards
Describe the structure of a myelinated neurone
Outline the etablishment of a resting potential
- Resting potential maintained by sodium potassium pump, sodium ions actively transported out and potassium ions in using ATP
- Creating electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
- Membrane more permeable to K+ leaving than Na+ entering so more K+ are moved out resulting in -70mV
Outline the establishment of an action potential
- Pressure causes membrane to become stretched( if pacinian corpuscle)
- A stimulus causes a temporary reversal of charge and inside of axon becomes morer positive
- If reaches threshold (-55mV), energy of stimulus causes some sodium channels to open
so sodium diffuses into axon - Once an action potential of +40mV(Depolarisation) has been established, sodium channels close
- Potassium channels open and potassium ions diffuse out, causing repolarisation of axon
- Axon becomes more negative than usual(Hyperpolariation), so potassium gates close
Outline the all or nothing principle
ALL OR NOTHING PRINCIPLE
- If depolarisation does not exceed -55mV, an action potential not produced
- Any stimulus which triggers depolarisation to -55mV wil always peak at same max volatage but bigger stimuli increase frequency of action potentials
- Important so animals only respond to large enough stimuli
Outline the passage of an action potential along non-myelinated and
myelinated axons,
Myelinated Axon -
Saltatory conduction where
- Depolarisation cannot occur where myelin sheath is present so impulse does not occur the whole axon length
- Depolarisation occurs at the nodes of ranvia
Non Myelinated Axon
- Depolariation occurs along whole length of axon
- Stimulus leads to influx of Na+ ions so first action potential occurs
Outline the nature of the refractaory period and its importance
Refractry period - period where an action potential where the axon can’t be depolarised to initiate a new action potential
- Discrete impulses are produced mean that each action potential produced is separate.
- It ensures that action potentials travel in one direction
- It limits the number of impulse transmissions which prevent overreaction to a
stimulus
Outline the factors affecting the speed of conductance
- Myelination and saltatory conduction
- Action potential jumps from node to node, does not occur over whole length of axon, which means action potential travels along axon faster - Axon diameter
- Wider diamter increases speed of conductance as less leakage of ions and action potential generated faster - Temperature
- Higher temperature means ions diffuse faster as more kinetic energy and enzymes involved in respiration work faster so more ATP for active transport
Outline the structure of a synanpse
Outline the processes which occur at a synapse
- Depolariastion of presynaptic membrans so Ca 2+ channels open and Ca 2+ ions enter synaptic knob by facilitated diffusion
- Calcium ions cause synaptic vesicles to move and fuse with presynaptic membrane and release acetylcholine/neurotransmitter into synaptic cleft
- Acetylcholine/neurotransmitter diffuses across synaptic cleft cleft down conc gradient and attach to complementary receptors on postsynaptic membrane
- Na+ ion channels open, so sodium ions enter postsynaptic neurone leading to depolarisation; if threshold is reached, action potential occurs
Outline the importance of unidirectionality and inhibition
unidirectionality = Nerve impulse travels in one direction presynaptic neurone has
the neurotransmitter, postsynaptic cell has the receptors
Inhibitory synaspse = Chloride ions to move into the postsynaptic neurone and potassium ions to move out makes the membrane potential increase to -80mV (hyperpolarisation) and therefore an action potential is highly unlikely.
Outline the importance of summation
Summation is the rapid build-up of neurotransmitters in the synapse to help generate an action potential
Spatial summation - many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value.
Temporal summation - One neurone releases neurotransmitters repeatedly over a short period of time in order to exceed the threshold value.
Outline the structure of a neuromuscular junction
- Synapse which occurs between motor neurone and muscle
Compare a neuromuscular junction to chollorgenic synapse
Exaplain events in chollorgenic synapse
- At a cholinergic synapse, the neurotransmitter is acetylcholine.
- The enzyme that degrades the neurotransmitter down is acetylcholinesterase.
- This breaks the acetylcholine into choline and acetate to be recycled in the pre-synaptic neurone.
things to remember
-less saltotary conduction so depolariastion does occurs whole length of axon slowing nnervous transmission to chollorgenic synapse
-attaches to receptors on postsynaptic membrane stimulating entry of na+ ions for depolariastion
