Biology (Divisions of the Nervous System)

• The major divisions of the nervous system are the central nervous system and the peripheral nervous system.
• Central Nervous System (CNS)


  composed of the brain and the spinal cord.
• The brain comprises approximately 100 billion neurons which do not regenerate once destroyed.
• • Skull protects the brain.
  • Vertebral column protects the spinal cord.
• Meninges


  Three layers of membranes covering the brain and spinal cord.
• Cerebrospinal Fluid (CSF)

  • Bathes the central nervous system (CNS).
  • Acts as a cushion, protecting from bumps and thuds.
• Major parts of the Brain

  • Hindbrain (medulla oblongata, cerebellum, pons)
  • Midbrain (reticular formation)
  • Forebrain (cerebrum/cerebral cortex, thalamus, hypothalamus)
• medulla oblongata

  • maintains upright position
  • regulates most involuntary functions
• cerebellum

  • coordinates fine muscle movement
  • regulates balance
• pons

  • Acts as a bridge to the midbrain.
  • Responsible for sleep regulation.
• reticular formation

  • Relays signals from eyes and ears to the cerebellum.
  • Regulates general levels of lethargy or liveliness.
• cerebrum/cerebral cortex

  • Seat of intelligence
  • responsible for: thinking, learning, emotions, consciousness, voluntary movements
• thalamus

  • Sorts and relays incoming and outgoing information.
  • Distributes information to different parts of the brain.
• hypothalamus

  • Monitors pleasurable activities (eating, drinking).
  • Influences the endocrine system.
  • Regulates hormone secretion.
• Spinal Cord

  • Large, ropelike segment of nerve tissue.
  • Connector mechanism for spinal reflexes.
  • Passage for sensory and motor information between the brain and other body parts.
• Spinal cord injuries demand immediate treatment to minimize long-term damage, often involving braces, surgery, and rehabilitation, with recovery outcomes ranging from full restoration to paralysis.
• Peripheral Nervous System (PNS)

  • Links brain and spinal cord to the body.
  • 12 pairs of cranial nerves.
  • 31 pairs of spinal nerves radiating from the spinal cord.
• Divisions of PNS

  • Somatic Nervous System
  • Autonomic Nervous System
• Somatic Nervous System

  • Includes cranial and spinal nerves.
  • Influences skeletal muscles, skin, and internal organs.
• Autonomic Nervous System


  controls involuntary activities
• Homeostatic Mechanisms


  sympathetic and parasympathetic mechanisms
• Sympathetic Mechanism

  • Dominates during stress.
  • Initiates fight-or-flight reaction.
  • Increases blood flow to emergency-use areas.
  • Decreases blood flow to kidneys and digestive tract.
• Parasympathetic Mechanism

  • Counteracts sympathetic response.
  • Promotes return to normal state.
  • Stimulates digestion and elimination.
  • Helps restore balance after stress.
• Nature of disease determines effects on patients.
• Functional Disorders


  e.g. headache, dizziness, epilepsy
• Vascular Disorders

  • Associated with circulatory system.
  • e.g. stroke, brain hemorrhage
• Infections

  • cause inflammation in various nervous system parts
  • brain (encephalitis), spinal cord (myelitis), meninges (meningitis)
• Structural Disorders

  • Result from physical damage.
  • e.g. brain or spinal cord injuries, Bell's palsy, carpal tunnel syndrome
  • increasing among children, attributed to prolonged computer game use
• Degenerative Disorders

  • More prevalent in elderly
  • e.g. Parkinson's disease, Huntington's disease, Alzheimer's disease
• olfactory cortex


  sense of smell
• 2 hemispheres of the brain


  left and right
• Cerebrum (Cerebral Cortex)


  the largest part of your brain and handles conscious thoughts and actions
• Thalamus


  major source of sensory information except sense of smell
• Medulla Oblongata


  associated with vital functions like breathing and circulation
• Cerebellum


  second largest part of the brain
• Pons


  links your brain to your spinal cord
• Peripheral Nervous System (PNS)


  all the nerves that lie outside of the central nervous system (CNS)
• Somatic Nervous System


  stimulates skeletal muscles under conscious control
• Parasympathetic Division


  most active under normal conditions