Divisions of the nervous system

• Nervous System

  Contains 2 parts: CNS - central nervous system, PNS - peripheral nervous system
• Central Nervous System


  • Brain
  • Spinal Cord
• Central Nervous System


  • Carries messages to and from the Peripheral Nervous System (PNS)
  • Brain is the body's main information-processing and decision-making organ
  • Spinal cord is a bundle of complex nerve fibers that carry message between Brain and PNS
  • Receives sensory information from various sensory neurons coming from receptors, and then interpret and process that sensory information
• Peripheral Nervous System


  PNS made up of all parts of the nervous system other than brain and spinal cord
• Functions of Peripheral Nervous System


  • Carry information from receptors in body to the CNS (sensory function)
  • Convey information from CNS to the effector muscles, organs and glands (motor function)
• Sub-divisions of Peripheral Nervous System


  • Autonomic nervous system - responses which happen automatically, no thought required e.g. breathing, heartbeat
  • Somatic sensory nervous system - collects information through sensory organs (eyes, ears) and coordinates body movement
• Neurons


  Specialised cells that transmit and receive messages as electrical impulses
• Sensory (afferent) neurons


  Detect stimuli, convert to electrical impulse and carry sensory information from sense receptors (eyes, ears, skin) TOWARDS the CNS
• Motor (efferent) neurons


  Send information AWAY from the central nervous system to effector muscles or glands
• Interneurons


  Send information BETWEEN sensory neurons and motor neurons. Most interneurons are located in the central nervous system.
• Dendrite


  • Small threads around cell body
  • Makes contact with other cells to receive info
  • Highly branched which creates a large surface area to receive information
• Soma (cell body)


  • Processes input from the dendrites and determines whether the neuron will transmit (send) messages to other neurons
  • If the input received is large enough, the cell body relays it to the axon, where an impulse is initiated
  • The nucleus is located in the soma which maintains the neuron's functioning
• Axon


  • A long, thin structure that transmits messages away from the soma (cell body)
• Myelin


  • A white, fatty substance that encases (surrounds) the axon and insulates it (called a myelin sheath)
  • Helps messages to be transmitted quickly
• Axon terminals


  • Branches at the end of each axon
  • Each axon terminal has a small knob-like swelling at its tip called a terminal button
  • A terminal button is a small sac that stores chemicals called neurotransmitters which assist in the transmitting information from one neuron to the next neuron
• Synapses


  The small gaps between neurons
• Transmission of information across synapses


  1. When the neural impulse reaches the end of each axon, the terminal buttons releases chemicals called neurotransmitters

  2. Neurotransmitters are stored in and released from sacs called vesicles

  3. Sometimes the neurotransmitter triggers or activates a neural impulse on the connecting neuron (excitatory)

  4. At other times, the neurotransmitter inhibits or prevents the connecting neuron from firing (inhibitory)

  5. When the neurotransmitter has done its job it is either taken back by the terminal buttons or disposed of
• Stimulus


  A change that happens in or out of our body that makes us respond
• Stimulus


  • Balloon bursts - makes us jump
• Receptors


  Ending of our nerve cells that pick up info from the stimulus
• Receptors


  • Nerves in our fingers - so we know when we touch things
  • Rods and cones in our eyes - so we see colour and light
• Effector


  Muscles or glands in our body to make us do something
• Effector


  • Muscle in our arm to move our arm
• Response


  The action we take because of the change
• Response


  • Move our arm out of the way when hurt
• Stimulus response model


  1. Stimulus

  2. Receptors

  3. Effector

  4. Response
• Types of nerve cells (Neurons)


  • Sensory neuron
  • Interneuron (relay neuron)
  • Motor neuron
• Sensory neuron


  Pick up info and send it to our brain
• Interneuron (relay neuron)


  Nerve cells in our brain or spine (central nervous system)
• Motor neuron


  Carry message from brain to muscles
• Reflexes


  Quick action to protect us from danger, our brain is not involved
• Reflexes


  • Quick
  • Protects us from danger
  • Don't have to learn how to do it
  • Don't need to think and make decisions
• Dendrite


  Pick up info from another nerve cell
• Soma


  Cell body - contains nucleus - instructions to make the cell work
• Axon


  Long fibre to carry message away from soma
• Myelin


  Insulates axon fibre so message goes faster
• Axon terminal bud


  Passes message on to the next nerve cell
• Synapse


  The tiny space between one nerve cell and the next