Lecture 3 Flashcards
What is the resting membrane potential and how is it caused?
The resting membrane potential refers to how the inside of the cell membrane is negatively charged relative to the outside, it typically has a value of -70 mV relative to the outside of the cell and is a result of the seperation of a small number of oppositely charged ions across the lipid bilayer (primarily Na+ and K+).
What is the Goldman hodgkin-Katz equation?
An equation used to calculate the membrane potential of the cell or the relative ion concentrations (if we need to use it we will be given it).
When is the resting membrane potential reached?
When the amount of K+ leaving the cell down its concentration gradient is balanced by amound moving back in due to the electrical gradient.
What occurs with excitable tissues in relation to membrane potential? What occurs if ECF K+ concentrations are not controlled properly?
The membrane potential will not always be at resting membrane potential for cells like nerves and muscles as in order for them to function the membrane potential must change. Excitable tissues won’t function normally if ECF K+ levels are not kept constant, excitable tissues will experience problems, leading to cardiac arrhythmias and muscle weakness.
What do these mean?
regulated variable, set point, reference range, variation
Regulated variable: The variable the system senses and attempts to keep stable.
Set point: the target value for the regulated variable
Reference range: Values of the regulated variable which are within acceptable limits.
Variation: The different in the regulated variable values either within an individual (intra) or between individuals (inter).
How are reference values gotten for physiological variables?
Measurements are obtained from healthy people and values within two standard deviations (95% of the people) are considered normal values.
What factors may cause intra or inter-individual variation?
Genetic factors are the predominant affect for inter-individual variation, normal day to day rhythms or biological cycles can lead to intra-individual variation (e.g sleep).
What two feedback control systems are there and what do they act to do?
Negative feedback: opposes the change in regulated variable and moves it back towards the set-point.
Positive feedback: pushes the regulated variable with the change, pushing it further from the set point.
What key components are there in feedback systems? What order do they tend to go via?
- regulated variable changes.
- Sensor monitors the actual value of the variable.
- The integrator compares the actual and set point values and will determine and control the response.
- The effector produces the response to cause the needed change to the variable (either pushing it away, or toward the set point).
All of these steps are connected via communication pathways.
What are the physiological communication pathways? What are their key features?
There are two communication pathways used in the body:
Neuronal: A very fast (up to 100ms-1) and specific communication system which works by sending action potentials down neurons and releasing neurotransmitter at synapses. Good for rapidly changing conditions and where immediate responses are required to prevent tissue damage or loss of homeostatic control, also good for brief responses.
Hormonal: A system which targets any cell carrying a receptor for the hormone, allowing it to potentially affect several tissues or organs, works by releasing hormones into the blood stream and is good for widespread sustained responses.
What effector actions do we have for gaining or losing heat? with what methods can we lose or gain heat from the external environment?
Gaining heat: vasoconstriction to reduce heat loss by radiation, shivering to produce heat via metabolism in the muscles, formation of goose bumps by piloerector muscles to create a small insulating layer..
Losing heat: Sweating to cause heat loss by evaporation, vasodilation to increase heat loss by radiation. We can lose or gain heat from the environment via radiation, conduction, convection and evaporation.
What is a feed forward system? What types are there?
Feed forward systems anticipate or detect external conditions which could alter a regulated variable or disrupt homeostasis and take preemptive action. The integration center will establish a predicted value for the regulated variable and compares it with the set point.
Feed forward systems can be behavioural: e.g putting on more cloths, or physiological e.g shivering when entering a cold environment before core body temperature has changed.
Why are positive feed back systems dangerous? When can they be good?
They are dangerous because they push the regulated variable away from the set point, possibly destabilizing homeostasis and leading to death. In some cases though like childbirth, where there is a clear end point it can be helpful for ensuring the set point isn’t strayed from for too long.
