Sensory receptors

A set of revision cards outlining sensory receptors and the generation of nerve impulses.

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A polarised membrane

Definition

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

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Depolarisation

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.

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Sensory receptors

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


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Roles of sensory receptors in mammals

  • 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
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Generating nerve impulses

  • 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
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Sequence of events

  • 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
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