Conditions that cells require to work properly:

temperature
pH
humidity
water
concentration (of enzyme/substrate)
cofactors and prosthetic groups
inhibitors
aqueous environment - keeps the substrate and products in solution
freedom from toxins

Stimulus: is any change in the environment that causes a response
E.g.: External - temperature, pH, salinity. length of day, sunlight
         Internal - temperature, toxins in blood, blood glucose levels

Response: a change in behaviour or physiology as a result of a change in the environment
E.g. sweating, shivering
       Hibernating due to food shortage
       Horse loses its coat due to increase in temperature

Rapid change: bright light to dim light - pupil size

A good communication system is required to ensure that these different parts of the body work together effectively.
A good communication system will:

cover the whole organism
enable cells to communicate with each other
enable specific communication (target cells)
enable sufficiently rapid communication
enable both short term and long term responses

Cell Signalling
Two major systems of communication that work by cell signalling:

neuronal system - usually rapid
hormonal system - enables long term responses

Once cells have received an external signal (stimulus) there will be a sequence of changes inside the cell, involving enzymes, leading to a change (response).

Homeostasis
Conditions that need to be kept constant:

body temperature
blood glucose concentration
blood salt concentration
water potential of blood
blood pressure
carbon dioxide concentratin

Negative Feedback

Stimulus -> receptor -> communication pathway -> effector -> response

Receptors - temperature, pH, pressure
Effectors - muscle tissue or glands
Communication pathway - nervous tissue, endocrine tissue (glands) and circulatory system (coordination centres in CNS)

Coordination involves comparing the input from the receptor with a set value to determine whether or not a response is required.

Positive Feedback
Less common

Optimum condition -> change away from optimum -> receptor detects change -> communication system informs effector -> effector reacts to increase change -> change away from optimum (repeats)

E.g.
As the cervix begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to secrete the hormone oxytocin. Oxytocin increases the uterine contractions, which stretch the cervix more, which causes more secretion of oxytocin.

	Created by siobhan.quirk almost 11 years ago

Undergraduate A2 Biology (Communication) Note on Communication Systems, created by siobhan.quirk on 11/11/2013.