Chp - 12 Nervous System

• Stimulus


  Changes in daylight, wind speed, temperature, movement, availability of food that living organisms detect
• Receptors


  Cells that detect stimuli
• Effectors


  Organs, such as glands and muscles, that bring about responses
• Response


  The actions taken as a result of detecting a stimulus
• Nervous control in humans


  1. Stimulus

  2. Sensory neuron

  3. Central nervous system

  4. Motor neuron

  5. Effector
• Central nervous system (CNS)


  Made up of the brain and spinal cord
• Peripheral nervous system (PNS)


  Contains cranial nerves and spinal nerves
• Neurone


  Nerve cell that transmits information in the form of nerve impulses
• Types of neurones


  • Motor neurones
  • Sensory neurones
  • Relay neurones
• Neurones


  • Have a nucleus, cytoplasm, and cell membrane
  • Have long, thin fibres of cytoplasm stretching out from the cell body (axons and dendrites)
  • Axons can be more than a metre long
• Synapse


  Junction between two neurones where the nerve impulse is transferred
• How a nerve impulse transfers across a synapse


  1. Vesicles containing neurotransmitter move to presynaptic membrane

  2. Vesicles fuse with presynaptic membrane, neurotransmitter diffuses into synaptic gap

  3. Neurotransmitter binds to receptor in postsynaptic neurone, allowing passage of impulse
• Presynaptic neurone


  Neurone that carries the impulse to the synapse
• Postsynaptic neurone


  Neurone that carries the impulse away from the synapse
• Sense organs


  Groups of sensory cells responding to specific stimuli like light, sound, touch, temperature and chemicals
• Parts of the eye


  • Cornea
  • Iris
  • Lens
  • Retina
  • Optic nerve
• Cone cells


  • Sensitive to bright light, detect colour
• Rod cells


  • Sensitive to low light intensity, detect black and white
• Fovea


  Part of the retina containing only cone cells, responsible for detailed colour vision
• Accommodation


  1. Ciliary muscles contract to make lens more spherical for near objects

  2. Ciliary muscles relax to make lens more elliptical for distant objects
• Hormone


  Chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Examples of hormones


  • Glucagon
  • Insulin
• Hormones help lower sugar levels by helping move glucose to the cells
• Lens


  • Surrounded by elastic tissue which can be stretched and can recoil
• Lens shape control


  Controlled by the ciliary muscles
• Looking at a near object


  1. Ciliary muscles contract to counteract the pressure inside the eye

  2. Suspensory ligaments become slack so the lens becomes more spherical (fatter)

  3. This shape is better at bending the light rays from a close object
• Looking at a distant object


  1. Ciliary muscles relax

  2. Pressure inside the eye pulls the suspensory ligaments tight (or taut) so the lens is pulled into an elliptical (thin) shape

  3. The eye is now accommodated (i.e. focused) for distant objects
• Hormone


  A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Main endocrine glands of the body


  • Pituitary (at the base of the brain)
  • Thyroid
  • Ovary
  • Adrenal (above renal)
  • Pancreas (insulin, glucagon)
• Adrenaline


  • Secreted by the adrenal glands
  • Coordinates responses necessary to survive in 'fight or flight' situations by: increasing breathing rate, increasing heart rate, widening pupils, increasing blood glucose concentration, widening air passages, dilating arterioles in brain and muscles, constricting arterioles in gut and other organs
• Tropisms


  Growth responses of plants to stimuli such as light and gravity
• Gravitropism


  • Roots are positively gravitropic (grow downwards in the direction of gravity)
  • Shoots are negatively gravitropic (grow upwards against the direction of gravity)
• Gravitropism control


  1. Auxin plant hormone controls growth

  2. In shoots, auxin builds up on lower side and stimulates elongation, causing shoot to bend upwards

  3. In roots, auxin inhibits elongation, causing upper side to elongate more and root to bend downwards
• Phototropism


  • Shoots are positively phototropic (grow towards light)
  • Advantage is leaves can absorb light more efficiently for photosynthesis
  • Controlled by auxin made in shoot tip
• Roots are not sensitive to light
• Parts of the nervous system


  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
• Nerve impulse transmission


  Stimulus -> Receptor -> Sensory neurone -> CNS -> Motor neurone -> Effector (muscle)
• Synapse


  Where two neurones meet and electrical impulses are transferred
• Mitochondria


  Provide energy needed to transmit nerve impulses
• Neurotransmitter release


  1. Stored in vesicles near presynaptic membrane

  2. Fuse with membrane and diffuse across synaptic gap

  3. Bind to receptors on postsynaptic neurone