nervous control

• General pattern of homeostasis

  1. Stimulus

  2. Receptor

  3. Control centre

  4. Effector

  5. Response
• Stimulus


  • A change in the environment that causes the organism to react
• Receptor

  • Detects the stimulus and sends nerve impulses down the sensory neuron and the relay neuron which reach the control centre

  
• Control centre


  • In the nervous system, known as the CNS which consists of the brain, spinal cord, which process the information and nerve impulses via the relay neuron and the motor neuron down the effector which allows us to react

  
• Effector

  • Brings about a response and is usually a muscle (for the nervous system)
• Response


  • Organism's reaction to the stimulus and the muscles contract
• Sensitivity


  • Ability to respond to a stimulus
• Overview of the nervous system


  • CNS (brain, spinal cord)
  • PNS (cranial nerves, spinal nerves, sense organs)

  
• How the nervous system works

  1. Sense organs receive stimuli through receptors in the form of nerve impulses

  2. Nerve impulses transported to the CNS through the various nerves

  3. Information processed and transmitted to the effectors to produce a response

  
• Neuron


  Specialised cell adapted to rapidly carry nerve impulses from one part of a body to another

  
• Structure of a sensory neuron


  • Circular cell body (contains all organelles)
  • Long nerve fibre (dendron) and short nerve fibre (axon) extending from the cytoplasm
  • Myelin sheath that acts as an insulating layer around the cells/nerves
  • Gaps in the myelin sheath called the nodes of Ranvier which speed up transmission
  • Axon transmits nerve impulses away from the cell body, dendron transmits nerve impulses towards the cell body
  • Dendrite receives input from cells, axite/axon terminal transmits messages to cells via neurotransmitters at synapses

  
• Structure of a relay neuron

  • Lie within the CNS (grey matter of the spinal cord)
  • Transmit nerve impulses from the sensory neuron or from the CNS to the motor neuron
  • Can also transmit nerve impulses from the CNS to the effector to produce a response
  • Form synapses with the sensory and motor neurons

  
• Structure of a motor neuron


  • Short dendron and long axon
  • Dendrites receive nerve impulses from other neurons, axites/axon terminals transmit nerve impulses to the effector
  • Cell body is irregular in shape
  • Motor end plate is the junction between the dendrite and the muscle fibre

  
• Synapse


  • Tiny space between 2 neurons where nerve impulses are not able to cross from one neuron to another directly
  • When it reaches the end, it stimulates a chemical release
  • The chemicals then diffuse across the tiny space to reach the adjacent neuron which triggers the formation of a new nerve impulse and continues the transmission of information within the nervous system

  
• Grey matter

  Cell bodies of neurons, outer layers of the brain and central parts of the spinal cord
• White matter


  Mainly made up of nerve fibers of neurons, central parts of the brain and outer layers of the spinal cord
• Structure of the spinal cord


  • Each spinal nerve divides into 2 roots - the dorsal root (sensory neurons) and the ventral root (motor neurons) before it joins the spinal cord
  • Dorsal root ganglions - cell bodies of sensory neurons

  
• Pathways of nerve impulses

  1. A. Sensory pathway: receptor -> sensory neuron -> relay neuron in spinal cord -> brain

  2. B. Voluntary action pathway: stimulus -> receptor -> sensory neuron -> relay neuron in spinal cord and brain -> motor neuron -> effector/response

  3. C. Reflex action pathway: receptor -> sensory neuron -> relay neuron -> motor neuron -> effector/response

  
• Voluntary action


  Conscious actions which occur according to the will of an individual, response to a stimulus with conscious control

  
• Reflex action

  A fast, automatic and immediate response to a stimulus without conscious control, cranial reflexes (controlled by the brain) and spinal reflexes (controlled by the spinal cord and consists of reflex arcs)

  
• Reflex arc

  Fast, automatic, immediate response without conscious control, shortest pathway of nerve impulses from the receptor to the effector

  
• Answering technique for nervous system questions

  • Stimulus + receptor
  • Signal
  • Pathway
  • Pathway
  • Pathway
  • Effector + response