Neuronal communication

• Role of neurones


  To transmit electrical impulses rapidly around the body to allow the organism to respond to changes in internal and external environment
• Parts of a general neurone


  Cell body, Dendron, axon,
• Role of the cell body


  To produce neurotransmitters
• Structure of cell body


  Nucleus, cytoplasm, lots of endoplasmic reticulum, mitochondria
• Function of dendrons


  To transmit electrical impulses towards the cell body
• Function of axons


  To transmit electrical impulses away from the cell body
• Structure of axons


  Cylindrical, narrow region of cytoplasm surrounded by plasma membrane
• Types of neurone


  Sensory, relay, motor
• Structure of sensory neurones


  One Dendron, one axon
• Structure of relay neurones


  Many short axons and dendrons
• Structure of motor neurones


  One axon, many short dendrites
• Function of sensory neurones


  To transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain
• Function of relay neurones


  To transmit impulses between neurones
• Function of motor neurones


  To transmit impulses from a relay or sensory neurone to an effector
• Myelinated neurones


  Neurones that have axons covered in myelin sheaths
• What makes the myelin sheath in myelinated neurones?


  Schwann cells grow around the axon multiple times, surrounding the axon with layers of membrane
• Name for gap between Schwann cells

  Node of Ranvier
• Why nodes of Ranvier are useful?


  Cause signal to jump which allows faster rate of transmission
• Why is the rate of transmission slower in non-myelinated neurones?


  No nodes of Ranvier so no jumping, continuous transmission is much slower
• Types of sensory receptors


  Mechano, chemo, thermo, photo
• Stimulus mechanoreceptors respond to


  Pressure, movment
• Example of mechanoreceptor


  Pacinian corpuscle
• Example of sense organ with mechanoreceptors


  Skin
• Example of chemoreceptor


  Olfactory receptor
• Example of thermoreceptor


  End bulbs of Krause
• Where do you find end bulbs of Krause?


  Tongue
• Shared features of sensory receptors


  Specific to a single type of stimulus, transducers
• Role of sensory receptors as transducers


  Sensory receptors convert stimulus into a nerve impulse (Generator potential)
• Structure of Pacinian Corpuscle


  End of neurone surrounded by layers of connective tissue separated by layers of gel, sodium ion channels in membranes, stretch-mediated sodium channels
• How Pacinian Corpuscles do transducing


  Sodium ion channels too narrow in a normal state, resting potential present, corpuscle changes shape when pressure applied to the corpuscle, membranes stretch, channels widen, sodium ions diffuse in, membrane depolarises, generates generator potential, generator potential creates action potential
• Resting potential


  The potential difference across a neurone's membrane when it isn't transmitting an impulse
• When there is a resting potential, where is there a more positive charge?


  Outside the membrane
• How resting potential develops


  Sodium ions actively transported out of the axon and potassium ions actively transported in by sodium potassium pump, more sodium ions outside the membrane and more potassium ions inside the cytoplasm, sodium ions try to diffuse in and potassium ions try to diffuse out, gated sodium ion channels closed so sodium ions can't diffuse, potassium ions can move freely, more positive ions outside than inside
• General value for resting potential


  -70mV
• Depolarisation


  Change in potential difference across a membrane from negative to positive
• How generator potential develops


  Receptor cells respond to stimuli, gated sodium ion channels open, larger stimuli will open more channels, sodium ions diffuse into the axon, inside of neurone is less negative, change in potential difference across the membrane is a generator potential
• How action potential develops


  Generator potential reaches threshold, voltage gated Na+ channels open, lots of Na+ diffuse into the axon (Positive feedback), membrane depolarised, voltage gated Na+ channels close, voltage gated K+ channels open, K+ diffuse out of membrane and become depolarised, potential difference overshoots, membrane becomes hyper polarised, resting potential restored by sodium potassium pump, refractory period
• Where is there positive feedback in action potentials?


  The diffusion of sodium ions into the axon when doing a generator potential will open voltage-gated sodium ion channels so more sodium ions diffuse in
• Threshold voltage value


  -50mV
• Potential difference across membrane when depolarised


  +40mV