Human

• organisms can respond to stimuli for survival
• nervous system allows body to respond to stimuli and is coordinated by the brain
• organisms have reflexes

  fast, involuntary actions that protect the body from damage
• Stimuli

  change in enviroment (internal/external)
• Receptor

  specialised cells that detect stimuli
• Effector

  part of the body that produced the response
• Homeostasis is the maintenance of a constant internal enviroment
• Homeostasis

  regulations of conditions inside the body
• Homeostasis includes osmoregulation and thermoregulation
• Osmoregulation

  control of water levels in the body
• Thermoregulation

  keeping the body at optimum body temperature (37 degrees C)
• Nervous systems and hormones both coordinate responses within the body
• Nervous system does this via electrical impulses so it is very fast
• Hormones do this with chemicals which is slower
• Nervous Communications

  • stimulation of receptors in sense organs sends electrical impulses
  • messages carried by electrical impulses along nerves and neurons
  • fast impulses
  • short lived
• Hormonal Communications

  • endocrine glands produce hormones
  • hormones are carried by plasma to target organs to stimulate change
  • slow as it is carried by plasma
  • long lived
• Similarities in hormonal and nervous communications

  • chemicals involved
  • requires stimuli receptor, effector
• Differences in hormonal and nervous communications

  • Nervous is faster, Hormonal slower
  • Nervous is electrical, Hormonal is chemical
  • Nervous is short lived, Hormonal is long lived
• CNS

  • centre of nervous system
  • receptors in sense organs (eyes ,skin etc) send electrical impulses through nerves to CNS
  • decides a response for stimulus
  • response is created for effectors to carry out response
• Detailed Process

  • CNS decides the response for a stimulus, which is detected by the receptor
  • Sensory Neurons will carry electrical impulses to CNS to be passed into effector by motor neurons
  • Effector carries out the response
• Receptors send electrical impulses through nerves when stimulated by a stimulus - the electrical impulse goes to the CNS where a response is decided and then is sent straight back out in electrical impulses through nerves to effector
• Detailed Process

  • Stimuli is detected by receptors and will stimulate Sensory neurons to send electrical impulses to CNS
  • CNS will pass on impulses to relay neurons across synapse by chemicals
  • Relay Neurons will pass on impulses to Motor neurons which will be carried to the effector
  • Effector will carry out response quickly, allowing for the rapid response
• Sensory Neurones

  afferent neurones, take nerve impulses from receptors to CNS. → receptors on one end → cell body perpendicular to the axon/dendron → surrounded by myelin sheath
• Relay Neurones

  found within CNS, link sensory neurones to motor neurones.
• Motor Neurones

  efferent neurones, take nerve impulses from the CNS to muscle or gland. → cell body at one end of cell → structures that carry a nerve impulse towards the cell body are called dendrites → axon is long thin projection of the cell that takes the nerve impulse away from cell body → surrounded by myelin sheath
• Synapse

  gap between 2 neurons, where transmission of impulse is chemical rather than electrical → nerve cells are linked together by synapses
• Neurotransmitter

  chemical substance released at the end
• Detailed process:

  • electrical impulse is carried along an axon and triggers the nerve ending of a neuron to release neurotransmitters
  • neurotransmitters will diffuse across synapse and bind with receptor molecules on the membrane of the second neuron.
  • receptor molecules on second neuron bind only to specific neurotransmitters released from the first neuron
  • this stimulates the second neuron to transmit an electrical response.
• Reflex

  fast involuntary action that protects the body from damage
• Sequence of events when touching hot object:

  • touch hot object (pain receptors stimulated in skin)
  • move your arm away (reflex arc)
  • feel the pain (brain receives the nerve impulses and a conscious sensation of pain is felt)
• Detailed Process of heat

  • heat(stimulus) is detected by the finger (receptor) and will stimulate sensory neurones to carry electrical impulses to CNS
  • electrical impulses will be carried from CNS to relay neurons which will carry it through the CNS (where response is decided) and carried to motor neurons
  • motor neuron will carry electrical impulses to muscles in the arm (effector)
  • muscles (effector) will contract and will withdraw finger away from hot object (response)
• Cornea


  transparent convex lens, refracts light
• Iris


  contains pigment and controls how much light enters pupil
• Lens


  transparent disc, focuses light on retina
• Retina


  inner most layer of the wall of the eye, contains rods that detect black and white and cones that detect light
• Optic Nerve


  connects the eye to the brain, because of sensory neurons that sends impulses between eye and brain
• Pupil


  hole that allows light to enter the eye to be focused on retina
• Ciliary muscles


  change the shape of the lens in the eye to help with focusing
• Eye diagram

  
• object is near


  
  

  ciliary muscles contracts

  suspensory ligaments slack

  muscle tension on lens low

  lens shaped thicker and more curved