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
Describe the structure of a myelinated motor neuron (6)
Cell body - contains organelles and high proportion of rough endoplasmic reticulum
Dendrons - branch into dendrites which carry impulses towards cell body
Axon - long, unbranched fibre that carries nerve impulses away from cell body
Schwann cells - wrap around axon many times
Myelin sheath
Nodes of Ranvier
What is resting potential? (1)
Potential difference across neuron membrane when not stimulated, usually about -70mV
Explain the importance of the refractory period (3)
Ensures unidirectional impulse
Ensures discrete impulses
Limits frequency of impulse transmission
How can an organism detect the strength of a stimulus (2)
Larger stimulus raises membrane to threshold potential more quickly after hyperpolarisation
Greater frequency of impulses
Why is synaptic transmission unidirectional (3)
Only presynaptic neuron contains vesicles of neurotransmitter
Only post synaptic membrane has complementary receptors
So impulse always travels from presynaptic neuron to post synaptic neuron
Explain the importance of acetylcholinesterase (2)
Prevents overstimulation of skeletal muscles
Enables acetyl and choline to be recycled
Describes what happens in inhibitory synapses (5)
Neurotransmitter binds to and opens Cl- channels on postsynaptic membrane and triggers K+ channel proteins to open
Cl- moves in and K+ moves out by facilitated diffusion
Potential difference becomes more negative = hyperpolarisation
More sodium ions required (to reach threshold)
OR
Not enough sodium ions enter (to reach threshold)
For depolarisation/action potential
Describe the effect of inhibiting acetylcholinesterase (5)
Acetylcholine not hydrolysed
Remains attached to receptors
Sodium ion channels remain open
Continued stimulus to muscles
Fatigue/continuous contraction/no relaxation
Draw a simple reflex arc (3)
https://www.toppr.com/ask/question/draw-a-labelled-diagram-of-reflex-arc-and-explain-reflex/
Sensory neuron going to the grey matter from the receptor
Relay neuron in the grey matter synapses with sensory and motor neuron
Motor neuron going from the grey matter to effectors
Explain the features of a reflex arc which result in the response being rapid and automatic (6)
Rapid:
Only involves three neurones
Myelination / saltatory conduction
and two / a few synapses;
Synaptic transmission is slow OR electrical/ nervous transmission is fast
Automatic:
Does not necessarily involve passage to brain / only spinal cord;
Same pathway used each time
higher brain centres not involved / no thinking
Explain the role of the Na+ and K+ channels in producing the membrane resting potential (3)
More permeable to K+
More potassium (leaks) out
Therefore more positive on outside
The rate of oxygen consumption of a neurone increases when it conducts a high frequency of impulses. Explain why (4)
Oxygen used in aerobic respiration
To produce ATP
For energy used by Na/K pump to actively transport Na+ and K+
Higher frequency of impulses –> more sodium ion entry and potassium ion lost
Suggest two functions of the energy released by the mitochondria in the synaptic knob (2)
Active transport of ions/ ionic pump
Synthesis of acetylcholine
Reabsorption of acetylcholine, or acetyl + choline (from cleft)
Movement of vesicles (to membrane)
Synthesis of relevant enzyme, e.g. acetylcholinesterase
Give two differences between a cholinergic synapse and a neuromuscular junction (2)
Neurone to neurone and neurone to muscle
Action potential in neurone and no action potential in muscle
Sarcolemma
No summation in muscle
Muscle response always excitatory
Some neuromuscular junctions have different neurotransmitters
