coordination & response

• The eye is the sense organ that detects the stimulus of light
• Eyes have receptor cells inside the retina, which include rods and cones
• In dim light:

  • Photoreceptors detect the change in the environment
  • Radial muscles contract and circular muscles relax
  • A wider pupil allows more light to enter
• In bright light:

  • Photoreceptors detect the change in the environment
  • Radial muscles relax and circular muscles contract
  • A narrow pupil allows less light to enter
• Rods:

  • Approximately 12 million in the eye
  • Located at the periphery
  • More sensitive in dim light
  • Low color sensitivity
  • Low detail sensitivity
• Cones:

  • Approximately 6 million in the eye
  • center of the retina
  • More sensitive in bright light
  • High color sensitivity
  • High detail sensitivity
• Focusing of the image:

  • When the object is far away, the ciliary muscle is relaxed, and the suspensory ligaments are pulled tight, making the lens thinner
  • When the object is close by, the ciliary muscle is contracted, and the suspensory ligaments are slack, making the lens fatter
• Parts of the eye include:

  • Suspensory ligament
  • Cornea
  • Pupil
  • Iris
  • Lens
  • Ciliary muscle
  • Retina
  • Fovea
  • Optic nerve
• The body detects and responds to the environment outside by:

  • Stimulus being detected by a receptor
  • Receptor sending electrical impulses to a sensory neuron
  • Sensory neuron transmitting the impulses to the Central Nervous System (CNS)
  • CNS relaying the impulses to a motor neuron
  • Motor neuron transmitting the impulses to an effector
  • Effector producing a response
• The nervous system has two parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

  • The CNS includes the brain and spinal cord
  • The PNS includes nerves and neurons
• Reflex action is an automatic action that serves the purpose of protecting oneself

  • Examples include shivering and eyes blinking
• A synapse is the gap between neurons
• Electrical impulses travel through a synapse by:

  1. Impulses traveling across the first neuron

  2. Reaching the presynaptic membrane

  3. Neurotransmitter diffusing across the synapse to the post-synaptic membrane

  4. Impulses traveling as electrical impulses once they reach the post-synaptic membrane
• Hormone is a chemical message that travels through the bloodstream
• Adrenaline:

  • Made from the adrenal gland
  • Increases heart rate
  • Causes pupil dilation
  • Sends more blood to muscles
  • Converts glycogen to glucose