B10 - The Human nervous system

• Function of the nervous system


  • Enables humans to react to their surroundings and to coordinate their behaviour
  • Includes both voluntary and involuntary actions
• Structure of the nervous system

  • Made up of the central nervous system (CNS) and a network of nerves
  • The CNS comprises the brain and the spinal cord
• Nervous system responses

  • Stimulus
  • a change in the environment (a stiumulus) is detected by receptors
  • Receptor
  • information from receptors passes along neurones to the CNS as electrical impulses
  • Coordinator
  • the CNS coordinates the body's response to the stimulus
  • Effector
  • effectors bring about a response
  • e.g. glands secreting hormones or muscles contracting
  • Response
  • the body responds to the stimulus
• Reflex actions


  • Do not involve the conscious part of the brain
  • Automatic and rapid
  • Important for survival as they help prevent damage to the body
• Neurones


  • Carry electrical impulses around the body
  • Relay neurones connect sensory neurones to motor neurones
• Nerve cells


  • Branched endings (dendrites) make connections with other neurones or effectors
  • Myelin sheath insulates the axon, increasing the speed of electrical impulses
  • Axon terminals are on effectors, such as muscles or glands
• Synapses


  • Gaps between neurones
  • Allow electrical impulses in the nervous system to cross between neurones
• Synapes

  • Impulse arrives in neurone
  • Chemicals are released into the gap between neurones
  • Chemicals attach to the surface of the next neurone and set up a new electrical impulse
• Reflex arc


  • Stimulus
  • Receptor
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • the coordinator in either the spinal cord or the brain
  • Effector
  • Response
• The brain


  • Controls complex behaviour
  • Made of billions of interconnected neurones
  • Has different regions to carry out certain functions
• Areas of the brain

  • Cerebral cortex
  • Hypothalamus
  • Cerebellum
  • Medulla
  • Pituatary gland
• Cerebral cortex

  • Outer layer of the brain
  • Important for consciousness, intelligence, memory and language
• Cerebellum


  • At the back of the brain
  • Coordinates muscle activity
• Medulla


  • Above the spinal cord
  • Controls unconscious activities such as breathing and the heart beating
• Hypothalamus


  • Involved with regulating body temperature
• Pituitary gland


  • Produces hormones
• The eye

  • A sense organ
  • Contains receptors sensitive to light intensity and colour
• The iris


  • Uncoloured part of the eye
  • Contains muscles that contract and relax to change the size of the pupil and allow more or less light in
• The cornea


  • Transparent and curved
  • Lets light in and changes its direction so the light is focused on the retina
• Lens


  • Sits behind the pupil
  • Focuses light on the retina
• Suspensory ligament


  • Tightens and slackens to change the shape of the lens
• Optic nerve

  • Nerve that connects the eye to the brain
• Blind spot


  Where the optic nerve leaves the eye
• Sclera


  • White tough layer that protects the eye
• Retina


  • Layer of receptors at the back of the eye
  • Contains light-sensitive cells (rods and cones)
• Ciliary muscle


  • Contracts and relaxes to change the shape of the lens
• Accomodation

  The process of changing the shape of the lens to focus on near or distant objects
• Accomodation for a close object

  • Ciliary muscles contract
  • Suspensory ligaments are slack
  • The lens is thicker and more curved, and refracts light rays more strongly
• Accomodation for a distant object

  • Ciliary muscles relax
  • Suspensory ligaments are pulled tight
  • The lens is thinner and flatter, and only refracts light rays slightly
• Myopia


  • Short sightedness
  • Distant objects look blurred because rays of light focus in front of the retina
  • Corrected using concave lenses
• Hyperopia


  • Long sightedness
  • Close objects look blurry because rays of light focus behind the retina
  • Corrected using con lenses
• Treating eye defects

  • Glasses
  • Refract light rays to focus on the retina
  • Contact lenses
  • Like glasses, but on the surface of the eye
  • Laser eye surgery
  • Changes the shape of the cornea
  • Replacement lenses
  • Adds another lens inside the eye to correct defects permanently
• Homeostasis


  • The regulation of internal conditions in response to internal or external changes to constantly maintain optimum conditions for function
  • Maintains optimal conditions for all cell functions and enzyme action
  • Internal conditions can be for a single cell or a whole organism
• Homeostasis in the human body includes:


  • Blood glucose concentration
  • Body temperature
  • Water levels
• Control systems include:

  • Receptor cells
  • detect stimuli (changes in the environment)
  • Coordination centres
  • include the brain, spinal cord and pancreas
  • recieve and process information from receptors
  • Effectors
  • muscles or glands
  • produce responses to restore optimum conditions