Topic 15: Nervous systems Flashcards
What is the Node of Ranvier
- Gaps in between shwann cells
In the cells, what bit is more negative
Inside the cell is more negative
Why is it important to have a barrier betwen inside and outside of the cell
because of the differences in charge, and the fact that opposites attract, you need a physical barrier to make sure they dont attract
How is potential energy there
The separated charges have a difference in charge which creates a potential energy
What is the resting membrane potential (exact value)
-70mV
How is a negative resting membrane potential achieved
There are less positively charged ions (Na+ and K+) inside the cell compard to outside of it, making the inside more negative
What do you call a cell that has a negative membrane potential
A polarised cell
How does the sodium potassium pump create an electrochemical gradient
- By transporting 3 Na+ out and 2 K+ in
What type of transport is the sodium potassium pump
Co-transport
Why dont these ions even out (2 reasons)
- more K+ channels than Na+ channels
- K+ channels mostly stay open while sodium channels are voltage gated (increased permeability of the K+ than the Na+
What will happen with a large stimulus of sodium
- the voltage-gated sodium channels will open
- allowing the sodium to flood into the cell, creating the action potential
What threshold needs to be met for an action potential to be created
-55mV
What are the steps within an action potential
- Stimulus causes the Na+ ion channels to open, causing a high conc. of sodium, which diffuses into the axon, causing depolarisation
- If the threshold potential (-55mV) is met, the action potential will be generated, and more Na+ ion channels will open, causing more diffusion of Na+
- When the voltage reaches +40mV, the Na+ ion channels will close, and the K+ ion channels will open, causing sodium to stop diffusing in and for potassium to start diffusing out of the neurone. This is called repolarisation
- K+ ion channels are slow to close, so there is a light overshoot in polarisation, causing the potential to reach -80mV, hyperpolarisation
- The resting potential is restored by the Na+/K+ pump
Why is the refractory period important
3 reasons
- Ensures discrete impulses so no overlapping
- Ensures time between each impulse so no overstimulation
- Ensures the impulse travels in a single direction
Why is the All-or-Nothing principle important
- Ensures organisms are only responding to a large enough stimulus, rather than every little thing in their environment because it would overstimulate them
What is the myelin sheath
- made from Shwann cells
- the membrane of shwann cells have a high lipid content, allowing them to wrap around the axon and provide insulation
- Gaps between shwann cells are known as the nodes of ranvier
What type of neurone ahs transmission which acts as a Mexican wave
Unmyelinated neurones
Explain how an unmyelinated neurone moves the action potential down its axon
- Action potential is generated, causing voltage-gated sodium ion channels to open, and allowing an unflux of Na+ into the axon, generating an action potential
- The influx of Na+ will cause more ion channels to open further down the axon, causing an action potential there afterwards
- The action potential in one location of the axon because the stimulus for the action potential further down the axon
Is unmyelinated neurone transmission slow/fast and explain why
- Unmyelinated transmission is slow, because it takes time for each successive set of Na+ ion channels to be triggered and opened
State how myelinated neurones do transmit their impulses
Through saltatory conduction
Explain how saltatory conduction occurs
- The opening of Na+ ion channels in one location and the influx of Na+, acts as a stimulus for the action potnetial further down the axon.
- Because the myelin sheath provides insulation, the impulse must ‘jump’ from one Node of Ranvier to the next
- This is known as saltatory conduction
Explain two reasons why damage to the myelin sheath slows responses and jerky movement
- Less / no saltatory conduction, so depolarisation must occur all down the axon, taking longer to reach the neuromuscular junction
- Ions / depolarisation may leak into other neurones, causing the wrong muscle fibres to contract
What is the one thing about action potentials that can change
Frequency
Bigger stimulus = higher frequency
What is multiple sclerosis
beyond spec
Autoimmune disease where the myelin sheath of braina nd spinal cord is damaged by the immune system, leading to no axon insulation
What three factors affect the speed of which an action potential is transmitted
- Mylenation / saltatory conduction
- Axon diameter
- Temperature
Explain how axon diameter affects speed of conductance
- Wider diameter, speed increases
- Less resistance for ions to moce, and increased SA for diffusion
Explain how temperature affects speed of conductance
- Higher temp, more kinetic energy of particles, faster rate of diffusion of Na+ and K+
- More frequent collisions between enzymes and substrates, more ATP produced for Na/K pump
- At too high temp the enzymes will denature
Explain how transmission occurs across a synapse
- At presynaptic neurone, the depolarisation reaches the synaptic knob, causes voltage-gated Ca+ channels to open, the Ca+ diffuses into the pre-synaptic knob
- The Ca+ will bind to a vesicle containing the neurotransmitter, and causes it to move towards the presynaptic membrane
- The neurotransmitter vesicle fuses with the membrane, and releases the neurotransmitter into the synapse by exocytosis
- The neurotransmitter diffuses across the synpase and binds to its receptors on the post-synaptic membrane
- This causes the Na+ ligand-gated channels to open, cuasing Na+ to move into the post-synaptic neurone and causing depolarisation, and generating an action potential whrn the threshold is met
What happens to the neurotransmitter once it has binded to the receptor
- The neurotransmitter is hydrolysed and its products are reabsorbed into the pre-synaptic neurone
Why is it important for the neurotransmitter to be hydrolysed?
- to prevent overstimulation
- to prevent constant stimulation
Explain the details of a cholinergenic synapse
- The neurotransmitter is acetylcholine
- The hydrolysing enzyme is acetylcholinesterase
- The products of hydrolysation are acetate and choline
What are two ways in which synapses are unidirectional
- There are only receptors on the post-synaptic neurone
- There are only neurotransmitters on the pre-synaptic neurone
State the two types of summation
- Spatial summation
- Temporal summation
Explain the two types of summation
- Temporal summation is where a single pre-synaptic neurone releases neurotransmitter to a single post-synaptic neurone many times
- Spatial summation is where many pre-synaptic neurones send neurotransmitter to a single post-synaptic neurone
Explain what happens at an inhibitory synapse
- At an inhibitory synapse, the neurotransmitter binds to its receptors and causes chloride ligand gated ion channels to open, causing the chloride to move into the post synaptic neurone and potassium to move out
- This makes the membrane potential more negative (hyperpolarisation), making it very hard for an action potential to be generated
Explain three differences between a normal synapse and a neuromuscular junction
- Receptors are on a muscle fibre instead of a post-synaptic neurone
- Neurotransmitters trigger muscle contraction instead of action potential
- Muscle fibres form clefts that are able to store the enzymes needed to hydrolyse the neurotransmitters
What does a neuromsucular junction connect
Muscle fibre to motor neurone
What does a cholinergenic synapse connect
Neurones / effectors
What are the two ways that drugs act on synapses
- By stimulating the nervous system to create more action potentials
- By inhibiting the nervous system to decrease the amount of action potentials
What are some ways a drug might help stimulate the nervous system to create more action potentials
- By mimicking a neurotransmitter
- By stimulating the release of nuerotransmitter
- By inhibiting the enzyme that hydrolyses the neurotransmitter
What are some ways a drug might help inhibit the nervous system to decrease the frequency of action potentials
- By inhibiting the release of neurotransmitter
- By blocking receptors of the Na+ ion channels on post-synaptic neurone
What are the three types of muscles
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Order the components of a msucle cell from outer to inner
- skeletal msucle
- muscle fibres / cells /myocytes
- sarcoplasm
- T-tubules
- myofibrils
- sarcomere
- thin / thick filaments
What do you call the cytoplasm of a muscle cell
Sarcoplasm
What do you call the cell membrane of the muscle cell
Sarcolemma
What are T-tubules
The inward folding of the sarcolemma, which surrounds the myofibrils.
What is the location of contraction in a myofibril
The sarcomere
