The nervous system function

• The brain is the control center of the body, responsible for processing information from sensory organs.
• Nerves carry messages between different parts of the body and the central nervous system (CNS).
• The spinal cord transmits signals between the brain and other parts of the body.
• Sensory neurons

  Afferent, receive signals from receptors
• Sensory neuron function in PNS

  Carry messages from receptors in the sense organs to the CNS
• Motor neurons


  Carry messages from the CNS to the effectors (e.g. muscles or glands)
• Motor neuron function in PNS

  Carry messages from the CNS to the effectors in order to bring about a response to the environment
• Interneurons

  Association neurons, located in the CNS, link sensory and motor neurons
• Some interneurons have long extensions to carry messages over long distances to the CNS, while many connect neighbouring neurons forming dense neural networks
• Nerve fibres

  The axons and dendrites of nerve cells
• Nerve fibre organisation

  1. Grouped together to form nerves

  2. Nerves are surrounded by connective tissue

  3. Multiple bundles of nerve fibres form a nerve
• Nerve impulses

  Electrochemical change that travels along a nerve
• Nerve impulses are described as electrochemical because they involve a change in electrical voltage, which is brought about by changes in chemicals
• stimulus response model

  1. Stimulus

  2. Receptor

  3. Central control

  4. Effector

  5. Response
• Receptor


  A structure that is able to detect change in the body's internal and external environment
• Receptors

  • Cells of a particular type can be grouped together in a sense organ (e.g. light receptors in the eye)
  • Receptors can be simple nerve endings spread through the whole body or parts (e.g. pain or temperature receptors)
• When a receptor is stimulated

  The body is able to respond to the change via an automatic reflex or more complex response
• Photoreceptors


  Light receptors
• Receptor types

  • Mechanoreceptors (pressure/vibrations)
  • Chemoreceptors (concentration of devices)
  • Thermoreceptors (temperature)
  • Nociceptors (pain)
  • Osmoceptors (changes in concentration)
• Receptor types are based on stimulus location
• Reflexes are automatic and rapid responses to stimuli
• Reflexes are designed to minimize any conditions that could potentially harm essential organs for the survival of the organism
• Patellar (deep tendon) reflex

  1. Tendon is stretched

  2. Message sent to spinal cord

  3. Spinal cord sends message to quadriceps muscle to contract
• Reflexes

  • They do not use the brain
  • They are a nerve impulse pathway from a receptor to an effector
• Protective reflexes include blinking, coughing, and sneezing
• Reflexes

  Most are in the spinal cord, some are in the motor centers & centers of the brain
• Reflexes

  • Work to protect the body from injury
  • Form the basis for more complicated physical activities e.g. standing, walking, riding a bike
• When you trip and fall

  Reflexes automatically command your hands/arms to reach out and break your fall
• Reflexes

  Cause muscles to contract throughout the body to minimize injury
• Conscious motor control from the brain would take longer to react to a fall and decide whether to break what you're holding
• Modifying reaction time

  1. Practice

  2. Repeat the same movements

  3. Make them almost automatic
• Motor skills


  Can become almost reflexive through practice and repetition, e.g. learning to ride a bike
• Reflexes

  Involuntary responses to stimuli
• Reflexes

  Change with age
• Changes in reflexes with age

  • Physical changes in nerve fibres - lower speed of conduction
  • Parts of the brain involved in motor control lose cells
• Effect of age on reflexes varies from person to person
• Staying active


  Can slow or reverse effects of aging on reflexes