Neuronal Communication

• Pacinian corpuscle: a pressure sensor found in the skin
• Sensory receptors: cells/sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials
• Transducer: a cell that converts one form of energy into another - in this case, to an electrical impulse
• Motor neurones: neurones that carry an action potential from the CNS to the effector
• Myelinated neurone: has an individual layer of myelin around it
• Non-myelinated neurone: has no individual layer of myelin
• Relay neurones: join sensory neurones to motor neurones
• Sensory neurones: neurones that carry an action potential from the sensory receptor to the CNS
• Action Potential: a brief reversal of the potential across the membrane of a neurone causing a peak of +40 mV compared to the resting potential of - 60 mV
• Positive feedback: a mechanism that increases a change taking the system further away from the optimum
• Resting potential: the potential difference across the membrane while the neurone is at rest
• Cholinergic Synapse: a synapse that uses acetylcholine as its neurotransmitter
• Neurotransmitter: a chemical used as a signalling molecule between two neurones in a synapse
• Summation: occurs when the effects of several excitatory post-synaptic potentials (EPSPs) are added together
• Threshold: the minimum value required for an action potential to be generated
• Nervous system sends information as nerve impulses
• Nervous system made up of complex network called neurones, of which there are three main types:

  • Sensory: transmit nerve impulses from receptors to the central nervous system (CNS)
  • Motor: transmit nerve impulses from the CNS to effectors
  • Relay: transmit nerve impulses between sensory neurones and motor neurones
• Central nervous system (CNS) consists of the brain and spinal cord
• A stimulus detected by receptor cells and nerve impulses is sent along a sensory neurone. When a nerve impulses reaches the end of this neurone, chemicals (neurotransmitters) take the information across to the next neurone, which then sends its own nerve impulse.
• The CNS processes any information on nerve impulses, decides what to do about it and sends impulses along motor neurones to an effector
• Stimulus -> receptor ->CNS via sensory neurones -> effectors via motor neurone > response
• Sensory receptors convert stimulus energy into nerve impulses
• 1. Different stimuli have different forms of energy e.g light or chemical energy but the nervous system only sends information in the form of nerve/electrical impulses
  2. Sensory receptors convert the energy of a stimulus into electrical energy
  3. Sensory receptors convert energy of a stimulus into electrical energy hence such receptors act as tranducers
• Tranducers are something that converts one form of energy into another
• When nervous system receptor is in its resting state, a difference in charge between the inside and outside of the cell generated by ion pumps and ion channels means there’s a voltage across the membrane.
• Voltage is also known as potential different
• Potential difference when a cell is at rest is called a resting potential. When a stimulus is detected, cell membrane is excited and becomes more permeable which allows for more ions to move in and out of the cell thus altering the potential difference.
• Generator potential: change in the potential difference due to a stimulus
• A bigger membrane = more excited membrane = bigger movement of ions = bigger change in potential difference = bigger generator potential produced
• If generator potential is big enough, an action potential is triggered along a neurone. This is only triggered if the generator potential reaches the threshold value.
• Stimulus too weak = generator won’t read threshold = action potential not generated
• Pacinian corpuscles = mechanoreceptors (detect mechanical stimuli e.g pressure and receptors) and are found in your skin. Contain the end of a sensory neurone (sensory nerve ending) which is wrapped in lots of layers of connective tissue (lamellae).
• When pacinian corpuscle is stimulated (e.g by tap on arm), the lamellae are deformed and pressed on the sensory nerve ending. Such deformation of stretch-mediated sodium channels in sensory neurone‘s cell membrane causes sodium ion channels to open and sodium ions to diffuse into the cell, thus creating a generator potential, which if it reaches the threshold, will generate an action potential.
• All neurones have cell body with a nucleus, cytoplasm and all other organelles you usually get in a cell. The cell body has extensions connecting to other neurones. Dendrites and dendrons carry nerve impulses towards the cell body and axons carry the nerve impulses away from the cell body.
• Sensory neurones: short dendrites, one long dendron to carry nerve impulses from receptor cells to the cell body and one short axon carries impulses from cell body to CNS.

  
• Motor neurones: many short dendrites which carry nerve impulses from CNS -> cell body; one long axon carrying nerve impulses from cell body -> effector cells

  
• Relay neurone: many short dendrites carrying nerve impulses from sensory neurones —>cell body; one axon carrying nerve impulses from cell body —>motor neurones

  Relay neurones transmit action potentials through the CNS.

  
• What is the charge of the outside of a neurone's membrane when it is at rest?

  Positively charged
• Why is the outside of the neurone's membrane positively charged compared to the inside?

  There are more positive ions outside the cell than inside
• What is the voltage across the neurone's membrane at resting potential?

  About -70 mV