T3.3 nervous system

• Nervous system


  • Allows human beings to collect information about external and internal environment and make decisions about how to maintain homeostasis
• Nervous system functions

  1. Collect information

  2. Transmit information

  3. Process and evaluate information

  4. Initiate a response
• Collect information

  This is achieved via the senses using specialised monitoring structures called receptors
• Transmit information

  Information is relayed via sensory neurons as electrical signals along specialised nerve cells to the brain and spinal cord
• Process and evaluate information


  The brain and spinal cord determine the action, if any, required in response to the information
• Initiate a response

  A response to information is sent along specialised nerve cells to effectors (muscles and glands) which contract, relax or secrete
• Nervous system

  • Divided structurally into central (brain and spinal cord) and peripheral nervous system (neural tissue outside of CNS)
  • Divided functionally into two main pathways: input and output
• Cells of the nervous system

  • Neurons
  • Glial cells
• Neurons


  • Transfer information from senses to brain and spinal cord, brain and spinal cord to effector muscles and glands
  • Initiate and transmit information in form of electrical signals, known as action potentials
  • Electrical signals generated as a result of ion concentration changes across neuron's plasma membrane
  • Electrical signals transferred from neuron to neuron - process called neurotransmission until desired destination is reached
• Glial cells


  • Smaller than neurons, outnumber them in nervous system
  • Incapable of transmitting electrical signal
  • Nourish, guide and organise activity of neurons
• Types of glial cells in CNS

  • Astrocytes
  • Ependymal cell
  • Microglia
  • Oligodendrocytes
• Astrocyte


  Forms blood-brain barrier
• Ependymal cell

  Produces cerebrospinal fluid
• Microglia

  Phagocytic cells of CNS
• Oligodendrocyte

  Myelination in CNS
• Schwaan cell

  Myelination in PNS
• Resting membrane


  Neuron at 'rest' not initiating or transmitting electrical signals
• Graded potentials


  Small, short lived changes in resting membrane potential caused by movement of small amounts of ion across cell membrane
• Action potential


  • Large charges in resting membrane potential, cause positive then negative change n voltage
  • Initiate initial segment of neuron and propagate along axon of neuron
  • Only generated when electrical voltage difference exceeds threshold value, causing voltage-gated channels to open
• Synaptic transmission


  Once nerve signal reaches end of neuron, needs to send signal to next neuron
• Neurotransmitters


  Chemical messenger molecules released from one neuron, float (diffuse) across synaptic cleft (space between neurons) and bind to receptors on another neuron - causing opening of ion channels in neuronal membrane