lesson 7

• Nervous System

  Coordinates the actions of complex organisms via the transmission of electrochemical signals
• Nervous System

  • Can be divided into two main parts: CNS (Central NS) and PNS (Peripheral NS)
• CNS (Central NS)

  Made up of the brain and spinal cord
• PNS (Peripheral NS)

  Links CNS to receptors & effectors
• Neurons

  Cells that make up the nervous system
• Neurons communicate via electrical impulses
• The nervous system is composed of cells called neurons
• Divisions of the Nervous System

  • Central Nervous System
  • Peripheral Nervous System
  • Autonomic Nervous System
• Central Nervous System

  Brain and spine (relay nerves)
• Motor (Efferent) Division

  Signals from CNS to effectors
• Somatic Nervous System

  Controls voluntary responses
• Sympathetic Division

  'Fight or flight' responses
• Parasympathetic Division

  'Rest and digest' responses
• Peripheral Nervous System

  Sensory and motor nerves
• Sensory (Afferent) Division

  Signals from receptors to CNS
• Autonomic Nervous System

  Controls involuntary responses
• Stimulus-Response Model

  The nervous system communicates information via a stimulus-response model
• Stimulus-Response Model

  1. Stimuli (internal or external) are converted into electrical signals by receptors

  2. Effectors (muscles or glands) convert the electrical signals into a response
• Neurons are specialised nerve cells that function to transmit electrical impulses
• Main types of neurons

  • Sensory neurons
  • Motor neurons
  • Relay neurons (or connector/interneurons)
• Sensory neurons

  Conduct impulses to the CNS (via afferent pathway of the PNS)
• Motor neurons

  Conduct impulses from the CNS (via efferent pathway of the PNS)
• Relay neurons (or connector/interneurons)

  Conduct impulses within the CNS
• Neurons

  • They all possess a cell body (i.e. soma), dendrites and an elongated axon
• While neurons may differ according to role, they all share some basic features
• Ion channels in the axon

  • They are voltage-gated
• Propagation of action potential

  1. Depolarisation at one axon segment triggers the opening of channels in the next segment

  2. Consequently, the action potential spreads along the axon as a 'wave' of depolarisation
• Refractory periods

  • They ensure the impulse moves in a single direction
• Stages of action potential

  • Resting
  • Depolarize
  • Repolarizing
• Synapses

  Junctions between two neurons or receptor/effector cells
• Synapses

  • Gaps allow signaling pathways to diverge, enabling complex decision making
  • Electrical signals are not able to be transferred across a synaptic cleft
• Synaptic transmission

  1. Chemicals called neurotransmitters are released into the synaptic junction

  2. Neurotransmitters diffuse across the gap and bind to post-synaptic receptors

  3. Binding to dendritic receptors will trigger the continuation of a nerve impulse

  4. Binding to receptors on effectors (muscles or glands) will initiate a response
• Synaptic Transfers

  1. Action potential arrives at axon terminal

  2. Voltage-gated calcium channels open

  3. Calcium enters the pre-synaptic neuron

  4. Ca2+ signals neurotransmitter vesicles

  5. Vesicles move to membrane and dock

  6. Neurotransmitter released (exocytosis)

  7. Neurotransmitter binds to receptor

  8. Signal initiated in post-synaptic cell
• Neurotransmitters

  Bind receptors (on dendrites) to open ligand-gated ion channels
• Graded potentials

  Small changes in membrane polarity triggered by neurotransmitters binding receptors
• Neurotransmitters

  • Can trigger excitatory or inhibitory post-synaptic potentials
• Excitatory neurotransmitters

  Promote depolarisation (may open Na* channels)
• Inhibitory neurotransmitters

  Promote hyperpolarisation (via K* or Cl channels)
• Determining whether a threshold potential is reached

  Combined action of all excitatory and inhibitory post-synaptic potentials (EPSPs and IPSPs)
• Types of Neurotransmitters

  • ADRENALINE
  • GABA
  • NORADRENALINE
  • DOPAMINE
  • SEROTONIN
  • ACETYLCHOLINE
  • GLUTAMATE
  • ENDORPHINS