slu nervous lab

• Nervous System


  • Central Nervous System
  • Peripheral Nervous System
• Central Nervous System (CNS)

  • Consists of the brain and spinal cord, which occupy the dorsal body cavity
  • The integrating and control center of the nervous system
  • Interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience
• Peripheral Nervous System (PNS)

  • Part of the nervous system outside the CNS
  • Consists mainly of nerves that extend from the brain and spinal cord, and ganglia
  • Spinal nerves carry impulses to and from the spinal cord, and cranial nerves carry impulses to and from the brain
  • Serve as communication lines that link all parts of the body to the CNS
• Functions of the Nervous System

  • Sensory input
  • Integration
  • Motor output
• Parasympathetic division


  • Promotes maintenance functions and conserves body energy
  • "Rest and digest" system, keeps body energy use as low as possible, even as it directs vital "housekeeping" activities like digesting food and eliminating feces and urine
• Sympathetic division


  • Mobilizes the body during activity
  • "Fight-or-flight" system
• Parasympathetic division and Sympathetic division have structural and functional differences
• Differences between Parasympathetic and Sympathetic divisions

  • Sites of origin
  • Relative lengths of their fibers
  • Location of their ganglia
  • Functional role

  
• Cerebrospinal Fluid (CSF)


  • A clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries
  • Prevents the delicate brain from crushing under its own weight
  • Protects the brain and spinal cord from blows and other trauma
  • Has a rich blood supply
  • Helps nourish the brain
  • There is some evidence that it carries chemical signals (such as hormones and sleep-and-appetite-inducing molecules) from one part of the brain to another
• In adults, the total CSF volume of about 150 ml is replaced every 8 hours or so; about 500 ml of CSF is formed daily in choroid plexuses which helps cleanse the CSF by removing waste products and unnecessary solutes
• Hydrocephalus


  • A condition wherein something (such as a tumor) obstructs CSF circulation or drainage, CSF accumulates and exerts pressure on the brain
  • The head enlarges because the skull bones have not yet fused
  • This causes damage to the brain because accumulating fluid compresses blood vessels and crushes the soft nervous tissue
  • Can be treated by inserting a shunt into the ventricles to drain excess fluid into the abdominal cavity
• Location and Circulatory Pattern of Cerebrospinal Fluid (CSF)

  1. The choroid plexus of each ventricle produces CSF

  2. CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures

  3. CSF flows through the subarachnoid space

  4. CSF is absorbed into the dural venous sinuses via the arachnoid granulations

  
• Choroid Plexus


  • Each choroid plexus consists of a knot of porous capillaries surrounded by a single layer of ependymal cells joined by tight junctions and bearing long cilia
  • Fluid leaking from porous capillaries is processed by the ependymal cells to form the CSF in the ventricles
• Choroid plexus


  • Consists of a knot of porous capillaries surrounded by a single layer of ependymal cells joined by tight junctions and bearing long cilia
  • Fluid leaking from porous capillaries is processed by the ependymal cells to form the CSF in the ventricles

  
• Brain stem


  Midbrain, pons, and medulla oblongata
• Brain stem regions are each roughly an inch long, collectively they account for only 2.5% of total brain mass
• Brain stem


  • Produces the rigidly programmed, automatic behaviors necessary for survival
  • Provides a pathway for fiber tracts running between higher and lower neural centers
  • Brain stem nuclei are associated with 10 of the 12 pairs of cranial nerves, so it is heavily involved with innervating the head
• Midbrain


  • Located between the diencephalon and pons
  • Contains visual (superior colliculi) and auditory (inferior colliculi) reflex centers
  • Contains subcortical motor centers (substantia nigra and red nuclei)
  • Contains nuclei for cranial nerves III and IV

  
• Cranial nerve III


  Nuclei in the midbrain provide motor impulses that control movements of the eyeball, while accessory oculomotor nuclei provide motor control to the smooth muscles that regulate constriction of the pupil and changes in shape of the lens via the oculomotor nerves

  
• Cranial nerve IV


  Nuclei in the midbrain provide motor impulses that control movements of the eyeball via the trochlear nerves
• Pons


  • Bulging brain stem region wedged between the midbrain and the medulla oblongata
  • Composed of conduction tracts
  • Contains nuclei of cranial nerves V–VIII

  
• Cranial nerve V


  Nuclei in the pons receive sensory impulses for somatic sensations from the head and face and provide motor impulses that govern chewing via the trigeminal nerves
• Cranial nerve VI


  Nuclei in the pons provide motor impulses that control eyeball movement via the abducens nerves
• Cranial nerve VII


  Nuclei in the pons receive sensory impulses for taste and provide motor impulses to regulate secretion of saliva and tears and contraction of muscles of facial expression via the facial nerves
• Cranial nerve VIII


  Nuclei in the pons receive sensory impulses from and provide motor impulses to the vestibular apparatus via the vestibulocochlear nerves
• Pons


  • Contains projection fibers
  • Deep projection fibers run longitudinally as part of the pathway between higher brain centers and the spinal cord
  • Superficial ventral fibers (oriented transversely and dorsally) form the middle cerebellar peduncles and connect the pons bilaterally with the two sides of the cerebellum dorsally fibers
  • Issue from numerous pontine nuclei, which relay "conversations" between the motor cortex and cerebellum

  
• Pons function


  Relays information from the cerebrum to the cerebellum - cooperates with the medullary respiratory centers to control respiratory rate and depth

  
• Medulla oblongata


  • Most inferior part of the brain stem that blends imperceptibly into the spinal cord at the level of the foramen magnum of the skull
  • Contains nuclei of cranial nerves VIII–X and XII
  • Contains projection fibers
  • Site of decussation of pyramids

  
• Medulla oblongata functions


  • Relays ascending sensory pathway impulses from skin and proprioceptors through nuclei cuneatus and gracilis
  • Contains visceral nuclei controlling heart rate, blood vessel diameter, respiratory rate, vomiting, coughing, etc.
  • Relays sensory information to the cerebellum through inferior olivary nuclei

  
• Cranial nerve VIII


  Several nuclei in the medulla receive sensory input from and provide motor output to the cochlea of the internal ear via the vestibulocochlear nerves

  
• Cranial nerve IX


  Nuclei in the medulla relay sensory and motor impulses related to taste, swallowing, and salivation via the glossopharyngeal nerves
• Cranial nerve X


  Nuclei in the medulla receive sensory impulses from and provide motor impulses to the pharynx and larynx and many thoracic and abdominal viscera via the vagus nerves

  
• Cranial nerve XI


  These fibers are actually part of the vagus (X) nerves, nuclei in the medulla are the origin for nerve impulses that control swallowing via the vagus nerves (cranial portion of the accessory nerves)

  
• Cranial nerve XII


  Nuclei in the medulla are the origin for nerve impulses that control tongue movements during speech and swallowing via the hypoglossal nerves
• Medulla oblongata


  • An autonomic reflex center involved in maintaining homeostasis
• Cerebellum


  • Located dorsal to the pons and medulla
  • Accounts for about 11% of total brain mass
  • Second only to the cerebrum in size, occupies the inferior and posterior aspects of the cranial cavity
  • Protrudes under the occipital lobes of the cerebral hemispheres, from which it is separated by the transverse cerebral fissure

  
• Cerebellum functions


  • Processes information from cerebral motor cortex, proprioceptors, and visual and equilibrium pathways
  • Provides "instructions" to cerebral motor cortex and subcortical motor centers, resulting in smooth, coordinated skeletal muscle movements
  • Responsible for balance and posture
• Diencephalon


  • Superior to the brain stem
  • Forms the central core of the forebrain and surrounded by the cerebral hemispheres
• Thalamus


  • Consists of bilateral egg-shaped nuclei, which form the superolateral walls of the third ventricle
  • Deep, well-hidden brain region that makes up 80% of the diencephalon

  
• Thalamus functions


  • Relays sensory impulses to cerebral cortex for interpretation
  • Relays impulses between cerebral motor cortex and lower (subcortical) motor centers, including cerebellum
  • Involved in memory processing