pressure receptors

• Action potential- a temporary reversal of the charges across the axon membrane which increases from -65mv to +40mv, depolarizing the membrane.
• All-or-nothing principle is where an action potential is exactly the same size , regardless of the size of the stimulus , providing it reaches the threshold value.
• Depolarized- this occurs because of a stimulus which causes some sodium voltage-gated channels in the axon membrane opening and sodium ions diffusing into the axon.
• Generator potential- a nerve impulse produced by a sensory receptor following a conversion of one form of energy into electrical energy.
• Nerve impulse- A self-propagating electrical signal that travels along a neuron.
• Neuron- a nerve cell that carries electrical impulses around the body
• Pacinian corpuscle: A sensory receptor that detects pressure and vibration.
• Receptors are cells or proteins which can detect a specific stimulus, some receptors proteins found in cell membrane and some are cells which are connected to the nervous system.
• Resting potential (stage one)- when a receptor is not being stimulated the inside of the cell is more negatively charged than the outside of the cell. This means there is a voltage across the membrane , usually measured in millivolts. This is known as the resting potential.
• Generator potential (stage two)- when a stimulus is detected the cell membrane becomes more permeable. This can cause a change in voltage thus we say the membrane is depolarized. this charge is known as the generator potential.
• Action potential (stage three)- when generator potential is large enough to reach the threshold level it will cause a wave of depolarisation along the neurone this is called an electrical impulse.
• Pacinian corpuscle- is an example of a nervous system receptor ,it responds to mechanical stimuli (pressure). It has a single sensory neurone and the neurone is wrapped in layers of connective tissue . the cell membrane has special stretch-mediated sodium channels.
• Initiating a generator potential:

  1. A pressure stimulus pushes on the lamellae which deforms the membrane of the sensory neurone.
  2. stretch-mediated sodium ion channels in the membrane of the neurone open.
  3. sodium ions diffuse into the neuron, depolarizing it and creating a generator potential.
  4. if enough sodium ions enter the cell to reach a threshold potential , then an action potential will be initiated.