nervous system

• Cell body


  Contains a nucleus and cell organelles
• Cell body


  • Particular cell bodies contain mitochondria, providing energy for the movement of nerve impulses
  • Each cell body forms dendrites + axons that may emerge from it as well as neurotransmitter chemicals
• Sensory neurons


  Cell bodies located outside the (N)
• Motor neurons


  Cell bodies located within (NS)
• Axon terminals


  • Branches formed by splitting of an axon
  • Each small branch carries an impulse to a neurotransmitter swelling
  • The neurotransmitter swelling releases chemicals that carry the impulse from one nerve cell to another
• Neurotransmitters


  • Chemicals that carry the impulse from one nerve cell to another
  • Stored in vesicles in the swellings
• Transmission of nerve impulses

  1. When a neuron isn't carrying an impulse, ions are pumped in and out of the axon, inside the axon is negative and outside is positive

  2. The threshold is the minimum stimulus needed to cause an impulse to be carried

  3. If the threshold is reached, an impulse is carried, if not, no impulse is carried

  4. No matter how strong the stimulus is, once it's above the threshold level the impulse is carried

  5. Sensitivity to different degrees of stimulation depends on the number of neurons stimulated and the frequency with which they send their impulses

  6. Once the threshold is reached, the axon/dendrite changes its permeability to ions

  7. At the site of stimulation, inside the axon becomes positive and outside negative

  8. A chain reaction is set up and a movement of positive charge runs along the inside once the impulse has moved along, the area behind is restored to its resting state
• Nervous system


  Divided into 2 systems: Central nervous system (CNS) and peripheral nervous system (PNS)
• Central nervous system (CNS)

  • Consists of brain and spinal cord
• Peripheral nervous system (PNS)

  Rest of body
• Correct response to a stimulus

  1. Reception

  2. Transmission

  3. Integration

  4. Response
• Reception


  Stimulus must be detected by receptors, neurons and sensory organs
• Transmission


  Message passes along the neurons. Neurons carry messages from receptors to the CNS, and from the CNS to effectors, e.g. muscles
• Integration


  Incoming messages are sorted and processed, and a response is selected. Occurs in CNS, e.g. brain
• Response


  Carried out by effectors (muscles/glands) when they're stimulated by neurons
• Neurons


  • 3 types: Sensory, motor and interneurons. Vary in type and size, some in brain are tiny, others connecting spine and feet can be over 1 meter long
• Structure of neurons

  • Sensory ending
  • Axon
  • Terminus
  • Myelin sheath
  • Cell body
  • Dendrites
• Receptor cell or group of cells


  Detects a stimulus
• Nerve endings


  Connect sensory neurons to receptor sense organs
• Dendrites


  Fibres that carry impulses TOWARDS the cell body
• Axons


  Carry impulses AWAY from the cell body
• Schwann cells


  Produce the myelin sheath
• Myelin sheath


  A fat-rich layer that insulates the electrical impulses
• Hormones are chemical messengers that regulate various bodily functions such as growth, metabolism, reproduction, and homeostasis.