Mod.1-Communication and Homeostasis Flashcards
Define the term stimulus.
A stimulus is any change in the environment that causes a response.
Define a response.
A response is a change in behaviour or physiology as a result of a change in environment.
State three examples of a stimulus and coordinating response.
Insect Bite- to move away (a nervous coordination)
Large barking dog running towards you- Run away (nervous and hormonal)
Smell of appetising food- salivate (nervous)
What are the requirements of a good communication system?
Must be able to send and receive messages and signals and effectively distinguish between them. It must extend over the whole body.
Define Negative feedback.
Process that brings about reversal of any change in conditions. Ensures optimum can be maintained, as internal enviro. is returned to original conditions.
Define Positive feedback.
Process that increases any change detected by receptors it tends to be harmful and doesn’t lead to homeostasis
Explain the difference between positive and negative feedback.
Negative feedback monitors a change and initiates a process to reverse the change whereas positive feedback will increase the change.
Define an ectotherm.
An ectotherm is an organism that relies on external sources of heat to regulate body temperature.
Why is it important to maintain a constant body temperature?
If body temp is too low, enzyme activity falls and the rate of metabolism drops. High temp. denatures proteins such as channel proteins in the membranes.
Explain how basking can help regulate body temperature.
If an ectotherm is too cool it can absorb heat from the rock and direct from the sun. This will warm up the skin and the blood flowing near the surface which will warm muscles.
Define an endotherm.
An organism that use internal sources of heat such as heat generated from the metabolism in the liver to maintain body temp.
Explain how vasoconstriction helps reduce heat loss.
It reduces blood flow through the skin, blood flows through vessels deeper in the body. Heat is less easily radiated out from the body.
What is a polarised membrane?
One that has a potential difference across it known as the resting potential.
What is depolarisation?
Loss of polaris. across membrane. Refers to when Na+ ions are entering the cell making it less negative then the outside.
What is a generator potential
Small depolarisation caused by Na ions entering the cell.
How is an action potential achieved?
Membrane is depolarised to value +40mV. All or nothing response- membrane depolarises and lots of sodium enter the axon as the action potential is reached.
Suggest why neurone have to carry a large number of mitochondria.
Mitochondria produce ATP by aerobic respiration to maintain the resting potential and for exocytosis of neurotransmitter chemicals at synapses
Define resting potential.
The potential difference across the neurone cell membrane while the neurone is at rest- it is about -60mV compared with the outside.
What is Voltage-gated channels
Channels in membrane that allow passage of ions. Gates open and close the channel responding to potential difference across membrane.
What is Threshold potential.
P.D across the membrane -50mV. Depolarisation must reach the threshold potential in order for action potential to be created.
Define Action potential.
Depolarisation of membrane so inside is more positive (+40mV) -> Transmitted along axon/ dendron plasma membrane.
Explain why a neurone is active while it is said to be resting.
While the neurone is resting the membrane its actively transporting sodium ions out and potassium in.
What is the organic role of anions inside a neurone?
Organic anions help ensure that the inside of the cell remains negative compared to the outside.
Define Local currents
The movements of ions along the neurone. The flow of ions is caused by an increase in conc. at one point which causes diffusion
Define saltatory conduction.
This means ‘jumping conduction’. It refers to the way that action potential appears to jump from one node of Ranvier to the next.
How are sodium ion channels opened?
Each channel has a voltage-sensitive gate. A change in the potential around the gate causes it to move or change shape. This opens the channel.
Explain how the myelin sheath causes saltatory conduction.
Myelin sheath is a layer of fatty material tightly bound to the neurone K/Na ions cannot move through sheath neurone membrane is exposed is at Ranvier nodes.
