Coordination and response

• Organisms require proper coordination between various organs and systems to work together to keep them alive
• Organisms have to be able to sense changes in their environment and respond to them appropriately
• Nervous system


  Plays a key role in the coordination and regulation of body functions
• Nervous system function


  1. Receiving and processing information from the environment and from within the body

  2. Generating appropriate responses to maintain homeostasis
• Nerve


  Bundle of neurons
• Components of the mammalian nervous system

  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves outside brain and spinal cord)
• Types of neurons


  • Sensory neurons
  • Relay neurons
  • Motor neurons
• Sensory neurons


  • Carry impulses from sense organs to central nervous system
• Relay neurons


  • Found in central nervous system, connect sensory and motor neurons
• Motor neurons


  • Carry impulses from central nervous system to effectors (muscles or glands)
• Stimulus

  Any change in the environment that can be detected by sensory neurons
• Receptor


  Structure that can detect a stimulus and generate an electrical impulse
• Effector

  Structure, often a muscle or gland, that responds to a signal from the nervous system
• Voluntary response


  Conscious action, something you do on purpose
• Involuntary response


  Quick, automatic reaction to a stimulus that happens without thinking
• Reflex arc


  1. Stimulus detected by receptor

  2. Sensory neuron sends impulse to spinal cord

  3. Relay neuron connects to motor neuron

  4. Motor neuron carries impulse to effector

  5. Effector carries out response
• Synapse


  Junction between two neurons where messages are transmitted chemically
• Synaptic transmission


  1. Impulse travels along first neuron

  2. Neurotransmitters released into synaptic gap

  3. Neurotransmitters bind to receptors on next neuron

  4. Impulse stimulated in next neuron
• Synapses ensure impulses travel in one direction only
• A stimulus is any change in the environment that can be detected by structures called receptors
• Sense organs and the stimuli they respond to

  • Skin - touch and temperature
  • Tongue - chemicals in food and drink
  • Nose - chemicals in the air
  • Ear - sound
  • Eye - light
• Eye structures


  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina
  • Fovea
  • Optic nerve
  • Blind spot
  • Suspensary ligaments
  • Ciliary muscles
• Cornea


  Refracts or bends light when it enters the eye
• Iris


  Controls how much light enters the pupil
• Lens


  Focuses light onto the retina
• Retina


  Contains light receptors some sensitive to different colors
• Optic nerve


  Carries impulses to the brain
• Pupil reflex


  1. Pupil diameter gets smaller/constricts in bright light

  2. Pupil diameter gets larger/dilates in dim light
• Antagonistic muscles in the iris

  Circular muscles and radial muscles
• Accommodation


  1. Ciliary muscles contract, suspensory ligaments relax, lens thickens for near objects

  2. Ciliary muscles relax, suspensory ligaments stretch, lens thins for distant objects
• Retinal receptors


  • Rods - used for night vision
  • Cones - used for color vision
• Rods are found all over the retina except at the blind spot and fovea, cones are concentrated at the fovea
• The blind spot is the area where the optic nerve leaves the eye and has no photoreceptor cells
• The fovea is a small part of the retina with a high concentration of tightly packed cone cells for sharp, detailed vision
• Cones


  Photoreceptor cells in the retina responsible for color vision and concentrated in the fovea for sharp, detailed vision
• Rods


  Photoreceptor cells in the retina responsible for low light and peripheral vision
• Hormone


  A chemical substance produced by a gland and carried by the blood which alters the activity of one or more specific target organs
• Endocrine system


  The hormone system that produces and releases chemical messengers called hormones that regulate various functions in the body
• Endocrine glands


  • Adrenal glands
  • Pancreas
  • Testes
  • Ovaries
• Adrenaline


  A hormone produced by the adrenal glands in response to stress or danger, acts as a fight or flight hormone preparing the body for a rapid response to a perceived threat