NERVOUS SYSTEM

• Nervous System


  Composed of specialized cells, function is to receive sensory stimuli and transmit them to effector organs
• Central Nervous System

  • Brain
  • Spinal cord
• Peripheral Nervous System

  • Cranial nerves, spinal nerves, associated ganglia
• Autonomic Nervous System


  • Parasympathetic
  • Sympathetic
• Central Nervous System


  1. Main centers where correlation and integration of nervous information occur

  2. Covered with MENINGES and suspended in CEREBROSPINAL FLUID
• Neurons

  Excitable cells
• Neuroglia


  Specialized tissue supporting neurons
• 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 of nerve fibers
• Peripheral Nervous System


  Conducts information to and from the central nervous system
• Cranial nerves

  • 12 pairs
• Spinal nerves

  • 31 pairs
• Automatic Nervous System

  Innervation of involuntary structures such as heart, smooth muscle, and glands
• Sympathetic

  • Prepares the body for an emergency
• Parasympathetic


  • For conservation and restoring energy
• Spinal Cord

  Cylindrical structure located within the vertebral canal, surrounded by 3 meninges, has 2 enlargements, inner core of gray matter surrounded by white matter
• Brain

  • Consists of four principal parts: Cerebrum, Brain stem, Cerebellum, Diencephalon
• Protective Coverings of the Brain

  Dura mater (outer), Arachnoid mater (middle), Pia mater (inner)
• Blood flows to the brain mainly via blood vessels branching from the Circle of Willis at the base of the brain
• 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, total deprivation of oxygen for 4 mins causes permanent injury
• Blood-brain barrier protects brain cells from harmful substances and pathogens by preventing the passage of many substances from the blood to brain tissue
• The brain is 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
• Total deprivation of oxygen for 4 mins causes permanent injury
• Blood brain barrier


  Protects brain cells from harmful substances and pathogens by preventing the 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
  • Continuously circulates between arachnoid and pia mater
  • Total volume (adult): 80-150 mL (3-5 oz)
  • CSF is reabsorbed into the blood through arachnoid villi at a rate of 20mL/hr
• CSF contributes to homeostasis in three main ways

  • Mechanical protection: serves as a 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 production of CSF is the choroid plexus (networks of capillaries in the walls of the ventricles)
• Circulation of CSF

  1. CSF flows from Choroid plexus in lateral ventricles

  2. Flows through 3rd ventricle through foramen of Monro: more CSF added

  3. Flows through aqueduct of Sylvius

  4. Passes the midbrain

  5. Fourth ventricle: more CSF added

  6. CSF enters the subarachnoid space through 3 openings in 4th ventricle: median aperture of Magendie and paired internal aperture of Luschka

  7. CSF circulates in the subarachnoid space of the brain and spinal cord
• The brain stem is part of the brain between the spinal cord and the diencephalon
• Components of the brain stem

  • Medulla oblongata
  • Pons
  • Midbrain
• Medulla oblongata

  • Continuation of the superior part of the spinal cord
  • Contains all ascending (sensory) and descending (motor) tracts
  • Contains nuclei that receive sensory input or provide motor output to five of the 12 cranial nerves
  • Contains cranial nerves: Glossopharyngeal Nerve (CN9), Vagus Nerve (CN10), Accessory Nerve (CN11), Hypoglossal Nerve (CN12)
• Pons


  • Lies directly superior to the medulla and anterior to the cerebellum
  • Consists of nuclei and tracts
  • Acts as a bridge that connects parts of the brain with one another
  • Contains important nuclei that help control breathing: Pneumotaxic Area and the Apneustic area
  • Contains associated with 4 pairs of cranial nerves: Trigeminal (CN5), Abducens (CN6), Facial nerve (CN7), Vestibulocochlear (CN8)
• Reticular formation


  • Also contained in brainstem
  • Net-like arrangement of small areas of gray matter interspersed among threads of white matter
  • Main sensory function: alerting the cerebral cortex to incoming sensory signals
  • Responsible for maintaining consciousness and for awakening from sleep
  • Incoming impulses from ears, eyes, skin are effective stimulators of RAS
• Cerebellum


  • Second largest part of the brain
  • Shaped like a butterfly
  • Has central constricted areas, "vermis"
  • 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
  • Main function: evaluate how well movements initiated by motor areas in the cerebrum are carried out
  • Has cerebellar hemispheres
  • 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: Thalamus, Hypothalamus, Epithalamus, Subthalamus
• Thalamus


  • Principal relay station for sensory impulses
  • Allows crude perception of sensation such as pain, temperature, and pressure
  • Plays a role in awareness and acquisition of knowledge termed as cognition
  • Medial geniculate nucleus: relays auditory impulses
  • Lateral geniculate nucleus: relays visual impulses
  • Ventral lateral nucleus: receives impulses form basal ganglia
  • Anterior nucleus: concerned with emotions and memory
• Hypothalamus


  • Controls body activities and a major regulator of homeostasis
  • Has four major regions: Mammillary region, Tuberal region, Pre optic region, Supraoptic region
• Epithalamus


  • Small region superior and posterior to the thalamus
  • Consists of pineal gland and habenular nuclei
  • Pineal gland: pea-sized gland, secretes melatonin (setting the body's biological clock)
  • Habenular nuclei: involved in olfaction, especially in emotional responses to odors