Unit 3.5.2 - Coordination may be chemical or electrical in nature Flashcards
During depolariation is the membrane more permeable to sodium or potassium ions?
Sodium
Draw a graph that represents the potential differnce when an action potential is triggered.
Why isn’t an action potential always fired in the post synaptic knob?
If the stimulus is too weak then only a small amount of neurotransmitter will be released
Draw a diagram of a synapse.
What is salutatory conduction?
When the impulse jumps between the nodes of ranvier
Name two classification for neurotransmitters.
Excitatory or inhibitory
Is the membrane of a neurone permeable or impermeable to sodium ions when at rest?
Impermeable
Do larger or small diameters of the axon increase the speed of conduction? And why?
Larger- there is less resistance to the flow of ions than in a cytoplasm of a small axon
Name an important auxin produced in the root and shoots of flowering plants.
IAA - Indoleacetic acid
What is summation?
Where the effect of the neurotransmitter released from many neurones is added together
Where is histamine stored? And when is is released?
Stored in mast cells, in response to the body being injured or infected
What do excitatory neurotransmitters do?
They depolarise the postsynaptic knob making it fire go an action potential
What is a gland?
A group of cells that are specialised to secrete a useful substance such as a hormone
Do neurotransmitters have a localised or widespread effect? And why?
Localised - they are secrete directly onto cells so only have a localised effect
Do hormones provide a fast or slow response compared to the nervous system?
Slow - the hormones aren’t released straight onto the target cells like neurotransmitter and must travel around the body first making the response slower than nerves
What is the general name for the chemical that takes the nerve impulse across a synapse?
Neurotransmitter
Give two purposes of the refractory period.
1.) Makes sure the potentials don’t overlap and so pass as discrete impulses 2.) Makes sure impulses can only pass in one direction
What is meant by resting potential?
The electrical potential across the neurone when it is not conducting an impulse
Describe how the resting potential is maintained, in two steps.
1.) 3 Na⁺are actively transported out of the axon and 2K⁺ are actively transported inside the axon by the sodium potassium pump 2.) They creates an electrochemical gradient as outside the neurone is more positively charged and so the membrane is polarised
What does the all-or-nothing principle prevent?
The brain from getting over stimulated by not responding to very small stimuli
During the resting potential what are the relative charges instead and outside of the neurone? And why?
The outside of the membrane is relatively positively charged because there are more positive ions outside than inside
What two ways can a gland be stimulated?
1.) Change in concentration of a specific substance 2.) By an electrical impulse
What is the refractory period?
The time delay between the conduction of one action potential and the next
Why does increasing the temperature increased the speed of conduction but only up to a point?
Any higher than 40ºC proteins start to become denatured
What is hyperpolarisation and what is it caused by?
When the potential difference becomes less than the resting potential - potassium ion channels are slow to close so there is a slight dip when too many potassium ions diffuse out of the neurone
Draw a myelinated motor neurone.
What is spatial summation?
Where two or more presynaptic knobs release neurotransmitter at the same time onto the postsynaptic knob
What is a chemical mediator?
A chemical messenger that acts locally
What breaks down acetylcholine when it is binded to receptors?
Acetylcholinesterase
What is the exact voltage across the membrane of a neurone during the resting state?
-70mV
What is a neuromuscular junction?
A specialised cholinergic synapse between a motor neurone and a muscle cell
What causes the waves of depolarisation?
During an action potential some of the sodium ions that enter the neurone diffuse sideways, is its creates a potential difference past the threshold in the next part of the cell then more sodium ion channels open and more sodium diffuses into that part of the cell This process is repeated and causes a wave of depolarisation to travel along the neurone
Why does myelination increase the speed of conduction?
Depolarisation only happens are the nodes of ranvier as the neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impulse can jump from one node to the next, this means the whole axon doesn’t have to be depolarised and so the impulse travels faster
Why do spatial and temporal summation increase the chance of an action potential being fired in the post synaptic knob?
There is more neurotransmitter being released so there is a higher chance the threshold level is reached
Is the effect of hormones long lasting or short lived and why?
Long lasting - they aren’t broken down very easily so the effect lasts longer
What happens when a neurone is stimulated for it to become depolarised during an action potential?
Sodium channels open and sodium ions diffuse into the axon down the sodium ion electrochemical gradient, when the membrane reaches a potential difference of -55mV then more sodium ions rapidly changing the potential difference until it is depolarised
What effect does histamine have?
It increases the permeability of the capillaries nearby to allow more immune system cells to move out of the blood to the injected or injured area
What is the neurotransmitter called in a neuromuscular junction?
Acetylcholine
What are the two types of summation?
Spatial and temporal summation
What is temporal summation?
Where two or more nerve impulses arrive in quick succession from the same presynaptic knob
During repolarisation is the membrane more permeable to sodium or potassium ions?
Potassium
What maintains the resting potential?
The sodium-potassium pump
Name four things that prostaglandin is involved in.
Inflammation, fever, blood pressure regulation and blood clotting
What is meant by some neurones are myelinated?
Some parts are covered in myelin sheath
What three factors affect the speed of conduction of an action potential
Myelination, axon diameter and temperature
Do hormones have a localised or widespread effect and why?
Widespread - they aren’t realised directly onto target cells so have to be transported around the body making the effect widespread
Give three differences between chemical mediators and hormones?
1.) Secreted from cells all over the body not just from glands 2.) The target cells are right next to where they are produced so they have a localised response instead of widespread 3.) They only have to travel a short distance to their target cells so they have a quicker response than hormones
What are the ten steps for how an action potential/impulse travels across a synaptic cleft?
1.) The action potential arrives at the presynaptic knob 2.) This causes calcium channels open 3.) Calcium ions diffuse into the knob 4.) This causes vesicles containing the neurotransmitter to move to the membrane 5.) The vesicles release the neurotransmitter into the synaptic cleft by exocytosis 6.) The neurotransmitter diffuses across the synapse 7.) It binds to receptors on the postsynaptic knob 8.) This causes sodium channels to open 9.) Sodium ions diffuse into the postsynaptic knob 10.) This sets up a new action potential
What are synapses that use acetylcholine called?
Cholinergic synapses
What is a hormone?
A chemical messenger that travel in the blood which are secreted once a gland is stimulated
What is acetylcholine broken down into and where does it go after it is broken down?
Into acetyl and choline, it diffuses back across the synaptic cleft and is reabsorbed and formed back into acetylcholine inside a vesicle
What happens if the potential difference across a neurone doesn’t reach the threshold level?
No action potential is generated
What is meant by waves of depolarisation?
When the action potential/impulse moves down the neurone
What do hormones diffuse into? And what carries that around the body?
They diffuse directly into the blood and are carried around by the circulatory system
Name five ways drugs can affect synaptic transmission?
1.) Mimiking neurotransmitters in receptors 2.) Blocking receptors 3.) Inhibit the enzyme that breaks down the neurotransmitter 4.) Stimulate the release of neurotransmitter 5.) Inhibit the release of neurotransmitter
Why does an increase in temperature increase the speed of conduction?
The ions move faster and so diffuse faster increases the speed of the depolarisation
What do inhibitory neurotransmitters do?
They hyper polarise the postsynaptic knob preventing it from firing an action potential
Are chemical mediators similar to hormones? And why?
Similar - the cells release chemicals that bind to receptors on target cells to cause a response
Where is prostaglandin produced?
By most cells in the body
What two systems do receptors communicate with effectors through?
The nervous system or the hormonal system
What is the all-or-nothing principle?
Once the threshold is reached the action potential generated is always the same size no matter how big the stimuli
What two things is the hormonal system made up of?
Glands and hormones
After an action potential why can’t the neurone be stimulated straight away?
Time is needed for it to return to the resting potential - repolarisation and hyperpolarisation
Why does myelin sheath act as?
An electrical insulator
Name two examples of chemical mediators.
Histamine and prostaglandins
What happens to a neurone after depolarisation during an action potential?
At around +30mV the sodium channels close and potassium channels open causing potassium ions to diffuse into the son down the potassium ion electrochemical gradient decreasing the potential difference and re polarising the membrane
What about synapses ensures the impulse only travels in one direction?
The neurotransmitter is only released from the presynaptic knob and there are only receptors for it on the postsynaptic knob
Name three difference between normal synapses and neuromuscular junctions?
1.) Has folds in the postsynaptic membrane which forms clefts, the clefts store acetylcholinesterase 2.) There are more receptor sites than usual 3.) When a motor neurone fires an action potential it will always trigger a response in muscle cells
How does IAA move short and long distances?
Short - diffusion or active transport Long - through the phloem
What are nodes of ranvier?
Gaps in the myelin sheath
Why is the membrane of a neurone said to be polarised?
As there is a difference in charge between the outside and inside
Is the effect of neurotransmitters long lasting or short lived and why?
Short lived - neurotransmitters are easily removed
