Nervous coordination Flashcards
Explain how the resting potential of a neurone is maintained
- The sodium potassium pump actively transports sodium ions out of the neurone and potassium ions into the neurone
- The membrane is more permeable to potassium ions than sodium ions
- There is a higher concentration of sodium ions outside and higher concentration of potassium ions inside the neurone
- The membrane is polarised, there is more positive charge outside the cell than inside creating a resting potential
Give the step by step for how an action potential is produced
- When the neurone is stimulated the voltage gated sodium ion channels open
- Na+ diffuse into the axon down their electrochemical gradient causing depolarization
- More voltage gated sodium ion channels open (positive feedback) and if threshold is reached, the neurone depolarizes to about +40mv
- The sodium ion channels then close preventing Na+ entering the axon and potassium ion channels open
- K+ diffuse out down their electrochemical gradient. The neurone becomes more negative (repolarisation)
- Too many K+ diffuse out causing the neurone to become too negative. This is called hyperpolarization
- Potassium ion channels close and the sodium potassium pump returns the neurone back to resting potential
Explain what a refractory period is
the time during which no new action potentials can be generated
Explain the 3 functions of the refractory period
- so action potentials move in one direction
- produces discrete impulses
- limits the maximum frequency of action potentials
Explain what is meant by the ‘all or nothing’ principle
All- only if threshold is reached will an action potential be generated which is always the same size (same neurone)
Nothing- if threshold isn’t reached there will be no action potential
Describe how action potential spreads along a non-myelinated axon
- An action potential occurs at a section of axon membrane
- The membrane adjacently in front of the action potential detects the depolarization and adjacent voltage gated sodium ion channels open, also forming an action potential
- The action potential moved forward. The refractory period behind the action potential prevents the impulse being conducted backwards
Describe how an action potential spreads along a myelinated axon by saltatory conduction
- The myelin insulates the axon
- Depolarizations only occur at the nodes of Ranvier so the action potentials ‘jump’ from node to node. This is known as saltatory conduction
- Therefore there are less depolarizations along the whole length of the axon membrane
Why is nerve transmission quicker in a myelinated axon?
- The myelin insulates the axon
- Depolarizations only occur at the nodes of Ranvier so the action potentials ‘jump’ from node to node. This is known as saltatory conduction
- Therefore there are less depolarizations along the whole length of the axon membrane
Describe the 3 methods of increasing the speed of conductance of an action potential in a neurone
- Myelination allows saltatory conduction
- A higher temperature increases the kinetic energy of ions so they diffuse faster through the membrane
- A greater axon diameter reduced resistance to ion flow
Give the sequence of events in transmission of a cholinergic synapse
- An action potential depolarizes the pre-synaptic membrane, voltage gated Ca2+ channels open and calcium ions diffuse in
- Calcium ions cause synaptic vesicles to fuse with the pre synaptic membrane and release ACh into the synaptic cleft
- ACh diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane
- Sodium ion channels open and sodium ions diffuse into the post synaptic neurone, depolarizing the post synaptic membrane causing an action potential
- Acetylcholinesterase hydrolyses the ACh. The sodium ion channel closes and no more action potentials are generated
Explain why synaptic transmission is unidirectional
- Neurotransmitters only released from/stored in pre-synaptic neurone
- Receptors only on post-synaptic membrane
Explain how a synapses can be inhibitory
Some neurones have chloride ion channels as well as sodium ion channels on the post-synaptic membrane.
- Chloride ions diffuse in and make the post-synaptic membrane potential more negative (hyperpolarized)
- More sodium ions need to diffuse in to reach threshold for an action potential
Define temporal summation
repeated action potentials arrive in short time from one presynaptic neurone and provide enough neurotransmitters to reach threshold in post-synaptic
Define spatial summation
action potentials arrive from more than one pre-synaptic neurone connected to one post-synaptic neurone and provide enough neurotransmitter to reach threshold in post-synaptic neurone
Give the differences between a cholinergic synapse and neuromuscular junction
- Cholinergic synapses have less ACh receptors on post-synaptic membrane whereas neuromuscular junction has more ACh receptors on muscle fiber
- Cholinergic synapses are neurone to neurone whereas neuromuscular junctions are neurone to muscle fiber
- Cholinergic synapses can be excitatory or inhibitory whereas neuromuscularjunctions are only excitatory
- Cholinergic synapses have no clefts in post-synaptic neurone whereas neuromuscular junction contains clefts in muscle fiber membrane which store acetylcholinesterase
