Nervous system

• Homeostatis is the maintenance of a constant internal environment, some examples are blood glucose, temperature and blood water
• Cell signalling is when a cell releases a chemical which affects the target cell
• A stimulus is a change in the internal or external environment
• The role of neurones is to transmit electrical impulses rapidly so there organism can respond to changes in the internal and external environment
• Dendrons are short extensions from the cell body and divide into dendrites. They are responsible for transmitting impulses towards the cell body
• Axons are singular nerve fibres and transmit impulses away from their cell body
• The electical impulse pathway is: receptor - sensory neurone - relay neurone - motor neurone - effector cells 1. The receptor detects a stimulus and sends a signal to the sensory neurone 2. The sensory neurone sends a signal to the relay neurone 3. The relay neurone sends a signal to the motor neurone 4. The motor neurone sends a signal to the effector cells
• The sensory neurone transmits impulses from sensory receptors to a relay neurone, motor neurone or brain
• The sensory neurone has one dendron that carries an impulse to the cell body and one axon that carries impulses away from body
• Relay neurones transmit impulses between neurones
• A relay neurone has many short axons and dendrons
• The motor neurone transmits impulses from a relay neurone to an effector (muscle or gland)
• A motor neurone has one long axon and many short dendrites
• Myelin sheaths are produced by schwann cells by wrapping around the axon many times
• Myelin sheaths provide an insulating layer which allows them to transmit impulses 100x faster. It does this by eliciting salvatory conduction (electrical impulses and jump along the axon)
• The node of ranvier is found between each schwann cell and creates gaps in the myelin sheath and allows the impulse to jump making it faster
• Sensory receptors are specific to a single stimulus and act as a transducer
• Mechanoreceptors detect pressure and movement, for example pacinian corpuscle which is found in the skin
• Chemoreceptors detect chemicals, for example the olfactory receptor which is found in the nose
• Thermoreceptors ▪ detects changes in temperature ▪ responds to changes in temperature
• Photoreceptors detect light, for example the cone cell that is found in the eye
• A generator potential is when a sensory receptor detects a stimuli znd converts the stimulus into a nervous impulse
• Resting potential is when the neurone is not transmitting an impulse, outside is more positively charged than the inside of the axon and the membrane is polarised at -70mV