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
  • Responsible for receiving and processing information from the environment and from within the body
  • Generates appropriate responses to maintain homeostasis or the stable internal environment of the body
• Nervous system


  • Consists of millions of neurons or nerve cells
  • Information is sent through the nervous system as electrical impulses that travel along neurons for quick communication
  • A bundle of neurons is known as a nerve
• 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 the sense organs to the central nervous system
• Relay neurons


  Found inside the central nervous system and connect sensory and motor neurons
• Motor neurons


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


  Any change in the environment that can be detected by sensory neurons (e.g. light, sound, touch, temperature, chemicals)
• Receptor


  Structure that can detect a stimulus and generate an electrical impulse which is then sent to the central nervous system
• Effector


  Structure, often a muscle or gland, that responds to a signal from the nervous system resulting in a specific action or behavior
• Voluntary response


  Conscious action, something done on purpose because you choose to
• Involuntary response


  Quick and automatic reaction to a stimulus that happens without thinking about it
• Reflex arc


  Pathway that a nerve impulse follows in an involuntary or reflex response
• Reflex arc


  1. Stimulus detected by receptor

  2. Receptor converts stimulus into electrical impulse

  3. Impulse travels along sensory neuron

  4. Impulse passes to relay neuron

  5. Relay neuron connects to motor neuron

  6. Motor neuron carries impulse to effector

  7. Effector carries out response
• Synapse


  Junction between two neurons where neurons do not touch each other, but have a gap called the synaptic gap
• Synapse


  • Contains vesicles with neurotransmitter molecules
  • Neurotransmitters are chemical messengers that diffuse across the synaptic gap and bind to receptor proteins on the next neuron
  • Ensures 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 responds to touch and temperature
  • Tongue responds to chemicals in food and drink
  • Nose responds to chemicals in the air
  • Ear responds to sound
  • Eye responds to 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 light of different colors
• Optic nerve


  Carries impulses to the brain
• Pupil reflex


  1. Pupil diameter gets smaller or narrows in bright light

  2. Pupil diameter gets larger or widens in dim light
• Pupil reflex


  Involuntary response of the eye to changes in light intensity
• Accommodation


  1. Ciliary muscles contract in near vision

  2. Ciliary muscles relax in distant vision

  3. Lens shape changes to focus light
• 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 has a high concentration of tightly packed cone cells for sharp, color vision
• Hormone system


  Also called the endocrine system, produces and releases chemical messengers called hormones that regulate various functions in the body
• 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 glands


  • Adrenal glands
  • Pancreas
  • Testes
  • Ovaries
• Adrenaline


  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
• Fight or flight response

  1. Fight (using physical combat to overcome danger)

  2. Flight (running away quickly from a dangerous situation)
• Effects of adrenaline


  • Increased breathing rate
  • Increased heart rate
  • Increased pupil diameter