neurones

• enzymes:

  all chemical reactions in your body are controlled by enzymes, but they require certain conditions to work, including; temperature, pH, presence of aqueous environment and presence of toxins or inhibitors
• stimulus - any change in environment that causes a response
• response - a change in behaviour or physiology as a result of a chaneg in environment
• external stimuli and their receptors:

  gravity - hair cells in the vestibule

  light - photoreceptor cells

  sound/vibration - hair cells in the cochlea

  airborne chemicals - olfactory receptors in the nose

  dissolved chemicals - taste buds

  external pressures - dermal pressure receptors

  pain - nerve endings in the skin

  temperature - nerve endings in the skin
• homeostasis - the maintenance of the internal environment in a constant state despite external changes
• internal and their receptors:

  blood pH/CO2 level - chemoreceptors

  blood pressure - baroreceptors
• coordination

  • multi-cellular organisms have groups of specialised cells that form tissues and organs
  • the cells that monitor the change, coordinate the change and respond to it, may be in very different place so good communication is needed
• a good communication will need:

  • cover the whole body
  • enable cells to communicate with each other (cell signalling)
  • enable specific communication
  • enable rapid communication
  • enable short and long term responses
• systems for communication:

  neuronal (nervous) system

  endocrine system (hormones)
• cell body - nucleus and large amounts of RER associated with production of proteins and neurotransmitter
• dendrons (dendrites) - carry nerve impulses away from the cell body
• axon - single long fibre that carries nerve impulses away from the cell body
• schwann cells - surround axon by wrapping around many times, protecting it and providing electrical insulation
• myelin sheath - forms covering of axon and made of membrane of the schwann cells. rich in lipids known as myelin. neurons can be myelinated or unmyelinated. Myelinated transmit nerve impulses faster.
• nodes of ranvier - gaps between adjacent schwann cells where there is no myelin sheath. Allows salutatory conduction to occur to speed up impulse
• passing on the message:

  1. stimulus detected
  2. energy converted to depolarisation of cell membrane
  3. impulse generated
  4. impulse needs to be passed on to other parts of the body
  5. impulse is transmitted along other neurones in the body
• sensory neurones - carry action potential from sensoy receptors to the CNS
• motor neurone - carry action potential from CNS to effector
• relay neurones - connect sensory and motor neurones
• sensory neurone

  • afferent neurone - moving away from central organ or point
  • relays messages from receptors to the brain or spinal cord
• motor neurone

  • efferent neurone
  • relays messages from the brain or spinal cord to the muscles and organs
• relay neurone

  • relays message from sensory neurone to motor neurone
  • make up brain and spinal cord
• sensory neurone

  • cell body on the side of the neurone
  • there is one dendron and one axon
  • direction of impulse from dendrites to the axon terminal
• motor neurone

  • one long axon away from the cell body
  • cell body is at the end
• relay neurone

  • short axons and short dendrons