F214 - Communication and Homeostasis

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  • Created by: Emma
  • Created on: 05-01-14 13:04
What is the resting potential of the neurone membrane inside the cell?
The state of readiness to produce a Action Potential is called resting potential; it is -40mV. This is more -ve than outside of the cell
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What happens at the Na+/K+ pumps?
In the plasma membrane - active transport - 3 x Na+ out - 2 x K+ in
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What happens when a receptor detects an energy change? (i.e. change in pressure/vibration)
Causes an influx of Na+ ions, causing the voltage inside the the cell to increase (depolarisation)
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How is this an example of positive feedback?
The more depolarised it is, the more channels that open and so more Ions move in
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What is the threshold potential/ all or nothing response?
If the depolarisation reaches the threshold potential of -40mV, an action potential will be generated. A small stimulus would not generate a response - all or nothing response.
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Describe depolarisation
Some Na+ channels open and Na+ moves down the conc grad causing more channels to open. There is an influx of Na+ making inside cell less -ve, causing more Na+ channels to open, making it more +ve until around +40mV where all of the Na channels close.
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Describe repolarisation
Voltage-gated potassium channels open, and K+ ions flow out of the neurone through facilitated diffusion, lowering the electronegativity back to -ve inside, and +ve outside moving further towards the resting potential.
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Describe hyperpolarisation
Outflow of K+ overcompensates change in charge and becomes even less -ve. It is the overshooting of the resting potential.
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What is the refractory period?
Returns to resting potential. It is the time delay between Action Potential when an Action Potential cannot be created.
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Why is it negative inside the neurone cell?
Proteins carry a -ve charge. Large no. of proteins carrying a -ve charge remain inside the axon, as they are too big too leave. (inside-outside is diff' of 70mV)
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Why are neurones described as 'excitable' and 'conductive'?
Excitable - can respond to a stimulus. Conductive - allows action potential to be carried.
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Pacinian corpuscles?
Type of receptor in the skin which detects pressure change+vibrations. Membranes surrounding pressure-gated Na+ channels are deformed and forced to open, increasing permeability to Na+; more ions move into cell (steeper depolaristion, chance of AP->)
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Sensory neurones vs Motor neurones
Sensory; long dendrites, short axon, sensory neurone -> CNS, cell body in middle. Motor; many short dendrites, long axon, CNS -> effector, cell body at end in CNS.
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Order of impulse travelling through the nervous system?
Receptor -> sensory neurone (DNS) -> relay neurone (CNS) -> motor neurone (PNS) -> effectors
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What is and how is a local current produced?
An action potential disrupts the concentrations of sodium and potassium conc's creating a local current which opens more sodium voltage-gates channels further down the neuroneLocal currents are movements of charged particles along a conc grad.
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What is saltatory conduction
Schwann cells make a fatty myelin sheath. Less membrane is exposed so the neurone is depolarised quicker. Local currents can only occur at the nodes of ranvier (longer + less area to depolarise). This is saltatory conduction.
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Describe the process at cholinergic synapse (pre-synaptic)
The AP arrives at synaptic knob causing voltage-gates Ca+ channels to open. Ca+ binds with vesicles containing acetylcholine, bringing them to the plasma membrane at the synaptic cleft. The vesicles fuse by exocytosis to membrane and release acetylc'
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Describe the process at cholinergic synapse (post-synaptic)
The neurotransmitter is released into the cleft. They diffuse across the gap and bind to Na channel proteins, causing Na channels to open and Na+ to move into the cell via facilitated diffusion. The influx of Na induces an AP.
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Describe the rold of acetylcholinesterase
Removes Acetylcholine from Na channels. Channels cose. breaks into choline + ethanoic acid. Diffuse down conc grad to pre-synaptic membrane where is is recombined and recycled.
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What is spatial summation?
Where 2+ presynaptic neurones synapse onto 1 post synaptic neurone. Enough acetylcholine is released from (combined) pre-syn' neurones to create generator potential.
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What is temporal summation?
A weak signal will build up over time , and it is the amount of signal over a set period of time causing enough acetylcholine to be released to create a large enough generator potential.
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What is summation?
A term that refers to the way that several small potential changes an combine to produce one larger change in PD across the membrane.
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Exicatatory and inhibitory post-synaptic potential?
EPSP - generator potential. IPSP - reduces strength of action potential so that generator potential is less likely to be reached.
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How are hormones secreted?
Endrocrine glands secrete them straight into the bloodstream. Exocrine glands secrete directly into target tissue along a duct.
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Explain how a hormonal receptor works?
Target cells have complementary receptors. Each has an enzyme, adenyl cyclase (primary messanger) associated with it. When the hormone binds, this enzyme coverts ATP to cAMP (secondary messenger) causing the appropriate reaction
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What is negative feedback?
Reversing back to optimum conditions in relation to external changes. Homeostasis is controlled by negative feedback.
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What is positive feedback? Give an example.
Continues to increase away from optimum conditions i.e exercise and CO2 - start running -> CO2 increases -> deeper breaths (more CO2) --> continues in loop.
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What is an ectotherm?
It relies on external sources of heat to regulate it's body temp'. They cannot effectively manage their own body temp'
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Advantages of ectotherms...?
- Don't require food for heat, so save energy - slower metabolism so get more energy from food, so more growth, less energy for respiration, need to eat less so less time have to be vulnerable - last long time with no food - don't spend winter outsid
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Disadvantages of ectotherms...?
Vulnerability (when they are cold, can't move quickly - risk of predation) movement is temp' dependent. Many do not move in winter at all.
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Ectotherm physiological adaptations...?
- presense of antifreeze - +ve of slow metabolism - special features i.e. horned lizards or frills to increase SA - increase breathing movements which evaporate more water
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Ectothem behavioral adaptations...?
- reproduce at relatively easy time - hibernate in groups - live in hottest part of earth - move into Sun in mornings (orientate bodies and movement according to environment)
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What is an endotherm?
An organism that uses internal sources of heat e.g. metabolism to maintain its body temperature.
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Advantages of endotherm...?
- can live in more extreme conditions - no temperature dependent (move away from predators) - don't need to store as much energy i.e. during the winter
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Disadvantages of endotherm...?
Have to eat more, have to go and get more food, making them more vulnerable. Less energy can be used for growth.
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Endotherm behavioral adaptations...?
Move in sun/shade. Group together. Body shape. Increase/decrease activity. Eat more food.
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Endotherm physical adaptations...?
- Sweat glands (latent heat of vapourisation) - Lungs expelling water, panting - Hairs on skin - vasodilation/constriction (controlled by capillary sphincters) - skeletal muscles shivering
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How are liver cells involved in adapting ectotherm temperature?
- storage of energy - rate of metabolism decreased - fewer exergonic reactions (many chem' reactions in the body are exergonic, release energy in form of heat)
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How is heart rate controlled?
The heart is myogenic but it can be affected by signals from the medulla oblongta and hormones. The accelarator nerve increases rate of SAN signals, whereas the vegas nerve reduces rate of contractions.
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Is the pancreas exocrine or endocrine?
It is both. Mainly exocrine, as it secretes digestive enzymes along the pancreatic duct. However it also has the Islets of Langerhans, which are well supplied with blood capillaries where hormones are directly secreted.
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Diseases caused by lack of blood glucose regulation?
Diabetes mellitus occurs when the body can no longer maintain blood glucose conc. Hyperglycaemia (very high levels) and hypocglycaemia (very low levels).
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The difference between Type 1 and Type 2 diabetes?
Type 1 is caused by an auto-immune disease where the body kills its own insulin-secreting beta cells (insulin). Type 2 is where the receptors for insulin and glucagon in hepatocytes don't function usually from unhealthy living (diet)
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What happens when blood sugar levels are too high?
- detected by beta cells in Islets of Langerhans - B cells secrete insluin into blood - decetected by receptors on liver/muscle cells - glucose removed and converted to glycogen - blood sugar levels drop
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What happens when blood sugar levels are too low?
- detected by alpha cells in Islets of Langerhans - A cells screte glucagon into blood - detected by receptors on liver cells - liver converts glycogen to glucose which is realesed into blood raising blood sugar conc again
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Other cards in this set

Card 2


What happens at the Na+/K+ pumps?


In the plasma membrane - active transport - 3 x Na+ out - 2 x K+ in

Card 3


What happens when a receptor detects an energy change? (i.e. change in pressure/vibration)


Preview of the front of card 3

Card 4


How is this an example of positive feedback?


Preview of the front of card 4

Card 5


What is the threshold potential/ all or nothing response?


Preview of the front of card 5
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