Stimulus and responses

• Receptors are specialised cells that detect changes in the environment, they convert physical energy into electrical signals which travel along nerves to the brain where it is interpreted as information about the environment
• Neurons have three main parts - dendrites, cell body and axon
• A Stimulus is a change in the internal and external environment.
• Tactic response is the directional movement in response to a stimulus.
• Kinesis Response is a non-directional movement in response to a stimulus.
• Receptors detect stimuli - they can be cells or protein on cell surface membrane.
• Effectors bring about a response to a stimulus.
• Motor neurones carry impulses from CNS to effector organs.
• Sensory receptor cells detect changes in the internal and external environments.
• Sensory neurone transmit electrical signals from receptors to CNS
• Relay neurone transmit electrical signals from sensory neurones to motor neurones
• In a kinesis response the rate of movement and turning changes.
• The simple reflex is a rapid, involuntary response to a stimulus.
• Tropism is the directional response in plant to a stimulus.
• Phototropism is the growth of plant in response to light. Shoots are positive phototropic, so grow towards light and roots are negative phototropic , so grow away from light.
• What is Tropism

  the directional response in plant to a stimulus.
• Gravitropism is the growth of plants in response to gravity. Shoots are negative phototropic so grow upwards and Roots are positive gravitropic so grow downwards.
• IAA is an auxin produced in the shoots and it's diffused into roots of plants
• IAA diffuses on the shaded side of the shoot. There's a higher concentration of IAA in the shaded side of shoot, this causes cells on the shaded side of shoot to elongate, causing shoot to bend towards the light.
• IAA diffuses on the lower side of the root , this inhibits the growth of the cells on the lower side, while stimulating the elongation of cells on the upper side. This causing roots to bend downwards.
• The resting potential is when there's a difference in the charge inside and outside of the cell - more negative inside and more positive outside.
• The Action potential is the electrical signal that travels along the axon of a neuron. It is generated when threshold potential is reached.
• The Pacinian corpuscles are sensory receptors that detect pressure and vibration. They contain the end of a sensory neurone, wrapped around layers of tissues called lamallae.
• Pressure from the stimulus causes, lamellae to deform, causing stretch-mediated sodium channels to open. This allows Na ions to diffuse into axon, if enough Na diffuses into axon, an action potential is generated.