Sensory receptors

Definition

A membrane that has a potential difference across it. This is a resting potential.

Definition

Loss of polarisation across a membrane. The period when sodium ions are entering the cell making the inside less negative with respect to the outside.

Specialised cells that can detect changes in our surroundings

• They are energy transducers - convert one form of energy to another
• They are adapted to detect changes in a particular form of energy
• Stimulus - change in energy levels in the environment
• Sensory receptors convert energy into a form of electrical energy - a nerve impulse

• Light sensitive cells - in retina, detect light intensity and range of wavelengths (colour)
• Olfactory cells - in the nasal cavity, detect presence of volatile chemicals
• Tastebuds - detect presence of soluble chemicals
• Pressure receptors - detect pressure on skin
• Sound receptors - in the cochlea, detect vibrations in the air
• Muscle spindles - detect length of muscle fibres

• Neurones have specialised channel proteins that are specific to sodium or potassium ions
• Possess a gate that can open or close the channel
• Contain carrier proteins that actively transport Sodium ions OUT of the cell or Potassium ions INTO the cell
• These are sodium/potassium pumps
• More sodium ions are actively transported out that potassium ions in
• Inside of cell is negatively charged with respect to the outside
• Cell membrane is POLARISED

• Receptor cells respond to changes in envrionment
• Gated sodium ion channels open
• Sodium ions diffuse across the membrane and INTO the cell
• Generator Potential - small change in potential cause by the opening of the channels
• The larger the stimulus, the more channels that open
• If enough sodium ions enter the cell, the potential difference is a significant change
• This causes an action potential