Communication and homeostasis

Communication basics

Animals and plants increase chances of survival by responding to stimuli. Receptors detect stimuli, they are specific and can be cells or proteins on membrane. Effectors bring a response to stimuli, they can be muscle or gland cells.

Homeostatis-maintenance of a constant internal environment within a small range.

negative feedback-when a system reacts to a change in a way that pushes it back towards a stable state

positive feedback-when a system reacts to a change in way that pushes it away from a stable state

Ectotherms cant control their internal temperature and so they have behavioural responses to control body temperature, eg lying in the sun. they also have variable metabolic rates and dont generate a lot of heat themselves.

Endotherms can control their internal temperature, they ahve a high constant metabolic rate and generate a lot of heat from these reactions. Body temperature is controlled by the hypothalamus, which recieves information from thermoreceptors in the skin and in the hypothalamus.

mechanisms to reduce temp: sweating, flat hairs, vasodilation

mechanisms to increase temp: shivering, hormones (adrenaline, thyroxine), hairs stand, vasoconstriction

The nervous System

sensory neurones-transmit nerve impulses from receptors to CNS

motor neurones-transmit nerve impulses from CNS to effectors

relay neurones-transmit nerve impluses between sensory and motor

structure; all neurones have a cell body with a nucleus, dendrites and dendrons (carry impulse towards cell body) and axons (carry impluse away from cell body)

, they convert

Sensory receptors are transducers, they convert different forms of energy into electrical impulses.

the resting potential; when the nervous system is at rest, the inside of the cell is negative and the outside is positive. this means there is a potential difference of about -70mv across the membrane called the resting potential. the resting potential is created by the movement of sodium and potassium ions.

• sodium-potassium pumps use active transportto move 3 Na out of the membrane for every 2 K moved in
• potassium ion channels are open at rest and allow facilitated diffusion of K down thier electrochemical gradient

the generator potential; when a stimulus is detected the cell membrane is excited and becomes more permeable to ions which alters the potential difference, this change is called the generator potential.

the action potential; if the generator potential is bigger to reach the threshld level of -55mv enough itll trigger an action potential.

• stimulus- this excites the membrane which causes sodium ion channels to open and Na diffuse down their electrochemical gradient, making the inside less negative
• depolarisation- if the potential difference reaches -55mv voltage gated sodium ion channels open and more Na diffuse
• repolarisation- at +30mv the sodium ion channels close and voltage gated potassium ion channels open. K diffuse down gradient out of neurone and membrane starts to get back to resting potential
• hyperpolarisation- potassium ion channels are slwo to close and the potentail difference becomes more negative than resting
• resting potential- the ion channels are reset and the membrane returns to resting potential.

the refractory period; after an action potentail the membrane cant be…