Week 3 - Excitable Tissues Flashcards
T/F: it is important that there is effective communication between spatially separated cells, tissues, and organs
Failure of these communication systems can have quite ________ _________
True
Dramatic consequences
What do some tissues synthesise and then secrete into the blood stream?
How do these get to their target tissue?
Hormones
Circulation via the blood stream
Communication mediated by hormones is relatively slow?
Yes
Which system does hormonal communication form the basis of?
Endocrine system
How is electrical communication faster than hormonal?
electrical signals travel along cells and can be readily transferred from cell to cell.
These electrical signals travel very quickly and consequently constitute a much more rapid form of communication
Tissues that utilise electrical signals for communication are know as __________ (reflecting their electrical excitability) and are the topic of this lesson.
excitable tissues
What are the major excitable tissues?
neurones and all three varieties of muscle (skeletal, cardiac and smooth).
T/F: a number of other cells types have been shown to exhibit electrically excitable properties that underpin their physiology
True
electrical activity in the nervous system determines things like…
T/F: Therefore, in many respects, excitable tissues really define what we, as humans, ‘are’.
consciousness, memory External link icon and personality.
True
The resting membrane potential is…
the membrane potential that you observe in any excitable cell that is simply sitting around, minding its own business and not being influenced in any way by other cells (i.e. it is at rest).
What is the usual magnitude of the membrane potential of cells?
Does it vary from cell to cell?
-80mV
Yes
Define polarised in terms of a cell
Cell at rest is -80mV, more negative than outside therefore is polarised
Graded potentials are observed wherever an…?
excitable tissue cell is subjected to an excitatory or inhibitory stimulus
T/F: Graded potential effect the entire cell/produce global effects?
False - only effect part of the cell and produce local effects
Two main types of graded potentials?
Depolarising graded potentials
Hyperpolarising graded potentials
What is the difference between a graded potential and an action potential?
An action potential is a graded potential which was large enough to reach a value referred to as threshold (varies from cell to cell but is around -65mV)
If a stimulus is too small to reach threshold what do we get?
A depolarising graded potential
If the stimulus is big enough so that the depolarising graded potential reaches threshold then we get….?
An action potential.
The speed of action potential propagation is fairly rapid and usually referred to as?
conduction velocity
Different cells have different conduction velocities but these are usually in the order of…?
0.5 - 130 m.sec-1
What is the secret to the very rapid form of communication that is enabled by excitable tissues?
The speed at which the electrical signals travel along cells
What are action potentials travelling along excitable tissues responsible for?
every sensation, thought and movement we make because these large, fast changes in the membrane potential encode all the information that is communicated in nervous and muscle tissue.
How do action potentials encode information?
The frequency of action potentials. (Frequency is usually expressed in Hertz (Hz) which means number of cycles per second. So when we talk about frequency in excitable tissues we are talking about the number of action potentials per second.)
How do we distinguish between a large deformation in the skin and a small one?
Frequency of action potentials (large deformation will yield a higher frequency of action potentials than a small one)