nervous system @notes sang classmate

• Nervous System


  Composed of specialized cells whose function is to receive sensory stimuli and to transmit them to effector organs, whether muscular or glandular
• Components of the Nervous System


  • Central Nervous System
  • Peripheral Nervous System
  • Autonomic Nervous System
• Central Nervous System


  Brain and spinal cord, main centers where correlation and integration of nervous information occur

  
• Central Nervous System


  • Covered with meninges and suspended in cerebrospinal fluid
  • Composed of excitable cells (neurons) and specialized tissue (neuroglia)
  • Gray matter consists of nerve cells embedded in neuroglia
  • White matter consists of nerve fibers embedded in neuroglia, white color due to lipid material in myelin sheath

  
• Peripheral Nervous System


  Cranial and spinal nerves that conduct information to and from the central nervous system

  
• Components of the Peripheral Nervous System


  • Cranial nerves (12 pairs)
  • Spinal nerves (31 pairs)

  
• Autonomic Nervous System


  Concerned with the innervation of involuntary structures such as the heart, smooth muscle and glands
• Components of the Autonomic Nervous System


  • Sympathetic
  • Parasympathetic
• Sympathetic


  Its activities prepare the body for an emergency
• Parasympathetic


  For conservation and restoring energy
• Spinal Cord


  Cylindrical structure located within the vertebral canal, begins at the foramen magnum of the skull and terminates inferiorly in the lumbar region, tapers off into conus medullaris and has prolongations of the pia mater: filum terminale

  
• Meninges surrounding the spinal cord


  • Dura mater
  • Arachnoid mater
  • Pia mater
• Spinal Cord


  • Has two enlargements: cervical enlargement to accommodate the brachial plexus, and lumbar enlargement to accommodate the lumbar plexus
  • Has an inner core of gray matter surrounded by an outer covering of white matter
• Principal parts of the brain


  • Brain stem
  • Cerebellum
  • Diencephalon
  • Cerebrum

  
• Brain stem


  Continuous with the spinal cord and consists of the medulla oblongata, pons and midbrain

  
• Cerebellum


  The "little brain", located posterior to the brain stem

  
• Diencephalon


  Located superior to the brain stem, consists of the thalamus and hypothalamus

  
• Cerebrum


  Spreads over the diencephalon like a mushroom cap and occupies most of the cranium
• Protective coverings of the brain


  • Dura mater
  • Arachnoid mater
  • Pia mater
• Dura mater


  • Outer layer, has 3 extensions that separate the brain: falx cerebri, falx cerebelli, and tentorium cerebelli

  
• Blood flows to the brain mainly via blood vessels that branch from the circle of willis, at the base of the brain
• Adult brain represents only 2% of total body weight but consumes about 20% of oxygen and glucose used at rest
• Interruption of blood flow for 1-2 mins impairs neuronal function, and total deprivation of O2 for 4 mins causes permanent injury
• Blood-brain barrier


  Protects brain cells from harmful substances and pathogens by preventing passage of many substances from the blood to brain tissue
• Cerebrospinal fluid


  A clear colorless liquid that protects the brain and spinal cord against chemical and physical injuries, carries oxygen, glucose and other chemicals needed, and continuously circulates between the arachnoid and pia mater
• Total volume of cerebrospinal fluid in an adult is 80-150 mL (3-5 oz)
• Cerebrospinal fluid is reabsorbed into the blood through arachnoid villi at a rate of 20mL/hr
• Functions of cerebrospinal fluid


  • Mechanical protection: serves as shock absorbing medium
  • Chemical protection: provides an optimal chemical environment for accurate neuronal signaling
  • Circulation: medium of exchange of nutrients and waste products
• Site of cerebrospinal fluid production


  Choroid plexus (networks of capillaries in the walls of the ventricles)
• Brain stem


  Part of the brain between the spinal cord and the diencephalon, consists of the medulla oblongata, pons and midbrain

  
• Medulla oblongata


  Continuation of the superior part of the spinal cord, behind the foramen magnum and extends to the inferior pons, contains all ascending (sensory) and descending (motor) tracts, and contains nuclei that receive sensory input from or provide motor output to five of the 12 cranial nerves

  
• Cranial nerves in the medulla oblongata


  • Glossopharyngeal nerve (CN9)
  • Vagus nerve (CN10)
  • Accessory Nerve (CN11)
  • Hypoglossal Nerve (CN12)

  
• Pons

  Lies directly superior to the medulla and anterior to the cerebellum, 2.5cm in length, consists of nuclei and tracts, acts as a bridge that connects parts of the brain with one another, has longitudinal axons that are part of ascending sensory tracts and descending motor tracts, and has transverse axons within paired tracts that connect the right and left sides of the cerebellum

  
• Cranial nerves associated with the pons


  • Trigeminal (CN5)
  • Abducens (CN6)
  • Facial Nerve (CN7)
  • Vestibulocochlear (CN8)

  
• Midbrain


  Extends from the pons to the diencephalon, about 2.5 cm long, contains both tracts and nuclei
• Cranial nerves in the midbrain


  • Occulomotor (CN3)
  • Trochlear (CN4)

  
• Reticular formation


  Net-like arrangement of small areas of gray matter interspersed among threads of white matter in the brainstem, main sensory function is alerting the cerebral cortex to incoming sensory signals, responsible for maintaining consciousness and for awakening from sleep

  
• Cerebellum


  Second largest part of the brain, shaped like a butterfly, occupies the inferior and posterior aspect of the cranial cavity, posterior to the medulla and pons and inferior to the posterior part of the cerebrum, separated from the cerebrum by the transverse fissure and tentorium cerebelli

  
• Lobes of the cerebellum


  • Anterior lobe: for conscious movement of skeletal muscle
  • Posterior lobe: for conscious movement of skeletal muscle
  • Flocculonodular lobe: for sense of equilibrium

  
• Diencephalon


  Extends from the brain stem to the cerebrum and surrounds the 3rd ventricle, includes the thalamus, hypothalamus, epithalamus and subthalamus