Receptors

• Sensory neurones are not directly sensitive to stimuli
• transducers convert stimulus into electrochemicals (charged particles/ions)
• receptors are transducers, converting a stimulus into a nerve impulse
• specific receptors respond to specific stimuli to produce a generator potential
• Pacinian corpuscles are receptors located in the skin, joints and internally and are sensitive to changes in mechanical pressure
• Pacinian corpuscles consists of layers of connective tissue around the unmyelinated (no lipid covering) tip of a myelinated neurone
• At rest the Pacinian corpsuscle is round in shape and the neurone is impermeable to the movement of Na+ (the sodium ion channels are too small to allow the movement of Na+ into the neurone)
• An increase in pressure compresses the Pacinian corpuscle and the stretch mediated sodium ion channels change shape (they are stretched and opened) and become more permeable to Na+
• Label the Pacinian corpuscle:

  A) Sensory neurone

  B) Layers of tissue

  
• Between the sensory neurone and the tissue layers of a Pacinian corpuscle are stretch mediated sodium ion channel
• Stretch mediated sodium ion channels open under mechanical pressure. The influx of sodium ions into the sensory neurone results in a depolarisation of the neurone, known as a generator potential
• When multiple generator potentials build up, the threshold is reached and an action potential is triggered