Nervous Coordination Flashcards
What are neurones and what is their function? (2)
Specialised cells that carry electrical impulses from one part of the body to another
Function of the myelin sheath (2)
Insulates the axon which increases the speed of electrical impulses along the axon
What is a membrane potential difference? (1)
Difference in electrical potential across the membrane
How is a resting potential established? (4)
Higher concentration of potassium ions inside and higher concentration of sodium ions outside (the neurone)
Membrane more permeable to potassium ions (leaving than sodium ions entering)
Sodium potassium pump actively transports 3 sodium ions out and 2 potassium ions in
Net result is that are more positive ions on the outside of the membrane than inside the neuron so the inside is slightly negative compared to the outside
What is an action potential? (1)
High concentration of positive ions inside the cell
Describe the process of depolarisation (5)
Stimulus causes the membrane to become more permeable to Na+ ions
Membrane potential reaches threshold (-50mV), all the voltage-gates Na+ channel proteins opens
Na+ ions rapidly diffuse into the cell (+40mV)
Higher concentration of positive Na+ ions inside the cell so the inside is more positive than the outside
K+ voltage-gates channel proteins remain closed
Describe the process of repolarisation (3)
When the internal potential difference reaches +40mV, Na+ ion voltage-gated channel proteins close
K+ ion voltage-gated channel proteins open
More K+ ions on the inside than the outside so they diffuse out of the cell down a concentration gradient
Describe hyperpolarisation (2)
K+ ion channel proteins remain open longer than needed to reach resting potential
So the inside of the cell becomes even more negative
What does threshold mean? (1)
Minimum intensity of stimulus
What is the all or nothing law? (1)
Full size action potential is given regardless of the increase in the size of the stimulus
What is the refractory period? (4)
Time taken to restore the resting potential
Limits the number of impulses per second
Maximum frequency of impulse transmission
Produces discrete impulses
What are the factors affecting the speed of conduction? (3)
Myelination and saltatory conduction
Axon diameter
Temperature
How does myelination and saltatory conduction affect the speed of conduction of impulses? (3)
Myelin sheath provides electrical insulation along the axon
Electrical impulse depolarise the next node and the action potential jumps from node of Ranvier to the next node of Ranvier
Increases the rate of transmission as depolarisation only occurs at the nodes/less of the axon membrane needs to be depolarised
How does temperature affect the speed of conduction of impulses? (3)
Higher temperature increases the kinetic energy
Increases rate of diffusion of ions
Increases rate of conduction
How does axon diameter affect the speed of conduction of impulses? (3)
Longer the axon diameter, the longer the surface area
Increased number of channel proteins
Greater speed of conduction
Greater diameter means less resistance to flow of ions
Less ‘leakage’ of ions so easier to maintain membrane potential
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane (6)
Depolarisation of presynaptic membrane
Ca2+ channels open and calcium ions enter synaptic knob
Calcium ions cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine
Acetylcholine diffuse across the synaptic cleft
Acetylcholine binds to receptors on the post synaptic membrane
Sodium ions enter postsynaptic neuron leading to depolarisation
What are neuromuscular junctions? (1)
Synapse between a motor neuron and a muscle cell
How is a neuromuscular junction different to cholinergic synapse? (3)
Post synaptic membrane has lots of fold that form the cleft which increases surface area so more acetylcholinesterase enzymes
Post synaptic membrane has more receptors
When a motor neuron fires an action potential it always triggers a response in a muscle cell
Function of acetylcholinesterase (2)
Hydrolyses acetylcholine into choline and ethanoic acid which diffuse back across the synaptic cleft in to presynaptic membrane
ATP is used to reform acetylcholine for storage in vesicles
What is spatial summation? (2)
Different neurones converge at a single synapse so actional potential arrives from several different neurones at the synapse
Causes the release of enough neurotransmitters to reach threshold and causes an action potential in the post synaptic neurone
What is temporal summation? (2)
Only one presynaptic neuron
Impulse arrives in rapid succession giving a cumulative effect which is sufficient to depolarise the post synaptic neurone
What is fatigue? (2)
Rate of transmitter release is higher than the rate at which it is reformed
So the presynaptic neuron cannot release enough neurotransmitter to generate an action potential in the post synaptic neuron until the transmitter is regenerated
What are excitatory neurotransmitters? (2)
Cause action potential in post synaptic neurone by making the resting potential less negative
So less sodium ions required to reach threshold
What are inhibitory neurotransmitters? (2)
Resting potential becomes hyperpolarised
So post synaptic membrane is less likely to reach the threshold value and generate an action potential