Ch 3: Anatomy of the NS

• Divisions of the Nervous System

  central nervous system

  peripheral nervous system
• central nervous system (cns)


  division of the nervous system located within the skull and spine
• peripheral nervous system (pns) 


  division located outside the skull and spine
• The central nervous system is composed of two divisions: the brain and the spinal cord
• the brain is the part of the CNS located in the skull
• the spinal cord is part located in the spine
• The peripheral nervous system is also composed of two divisions: the somatic nervous system and the autonomic nervous system
• The somatic nervous system (SNS) is the part of the PNS that interacts with the external environment.
• the somatic nervous system is composed with afferent nerves that carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and etc., to the cns and efferent nerves that carry motor signals from the central nervous system to the skeletal muslces.
• autonomic nervous system


  • part of the peripheral nervous system that regulates the body's internal environment
  • composed of afferent nerves that carry sensory signals from internal organs to the CNS and efferent nerves that carry motor signals from the CNS to internal organs
• going toward the CNS- begin with an a (i.e., advance, approach, arrive)
• many words that involve going away start with an e (e.g., exit, embark, escape)
• A = Central Nervous System

  B = Peripheral Nervous System

  A) A

  B) B

  
• autonomic nervous system


  • has two kinds of efferent nerves: sympathetic and parasympathetic nerves
• Sympathetic nerves

  are autonomic motor nerves that project from the CNS in the lumbar (small of the back) and thoracic (chest area) regions of the spinal cord
• parasympathetic nerves

  are autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord
• All sympathetic and parasympathetic nerves are two-stage neural paths: The sympathetic and parasympathetic neurons project from the CNS and go only part of the way to the target organs before they synapse on other neurons (second-stage neurons) that carry the signals the rest of the way
• Sympathetic vs Paras

  • sympathetic neurons project from the CNS synapse on second-stage neurons at a substantial distance from their target organs
  • parasympathetic neurons project from the CNS synapse near their target organs on very short second-stage neurons
• The conventional view of the respective functions of the sympathetic and parasympathetic systems stresses three important principles:
• Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations
• Parasympathetic nerves act to conserve energy
• Each autonomic target organ receives opposing sympathetic and parasympathetic input
• The activity of each autonomic target organ is controlled by relative levels of sympathetic and parasympathetic activity
• Sympathetic changes are indicative of psychological arousal
• Parasympathetic changes are indicative of psychological relaxation
• Most of the nerves of the peripheral nervous system project from the spinal cord, but there are 12 pairs of exceptions: the 12 pairs of cranial nerves, which project from th ebrain
• 12 cranial nerves


  • numbered in sequence from front to back
  • include purely sensory nerves such as the olfactory nerves (I) and optic nerves(II), but mostly contain sensory and motor fibers
• the longest cranial nerves are the vagus nerves (X), which contain motor and sensory fibers traveling to and from the gut
• the autonomic motor fibers of the cranial nerves are parasympathetic
• Meninges 


  • three protective membranes that protect the brain and spinal cord (CNS)
  • the outer meninx is a tough membrane called the dura mater (tough mother)
  • arachnoid membrane (spider-web-like membrane)
  • subarachnoid space (contains many large blood vessels and cerebrospinal fluid)
  • pia mater (delicate; pious mother; adheres to the surface of the CNS)
• Major DIvisions of the Nervous System

  A) Nervous System

  B) Central Nervous System

  C) Brain

  D) Spinal cord

  E) Peripheral Nervous System

  F) Somatic Nervous System

  G) Autonomic Nervous System

  H) Afferent nerves

  I) Efferent nerves

  J) Afferent nerves

  K) Efferent Nerves

  L) Sympathetic Nervous System

  M) Parasympathetic nervous system

  
• Cerebrospinal fluid (CSF) 


  • protects the CNS
  • fills the subarachnoid space, the central canal of the spinal cord, and the cerebral ventricles of the brain
  • supports and cushions the brain
  • is produced by the choroid plexuses (networks of capillaries, or small blood vessels that protrude into the ventricles from the pia mater)
  • the excess CSP is absorbed from the subarachnoid space into large blood-filled spaces, or dural sinuses, which run through the dura mater and drain into the large jugular veins of the neck
• central canal


  small central channel that runs the length of the spinal cord
• cerebral ventricles

  are the four large internal chambers of the brain: the two lateral ventricles, the third ventricle, and the fourth ventricle
• The subarachnoid space, central canal, and cerebral ventricles are interconnected by a series of openings and form a single reservoir
• cerebral aqueduct 


  connects the third and fourth ventricles
• The flow of csf is blocked by a tumor near one of the narrow channels that link the ventricles. The resulting buildup of fluid in the ventricles causes the walls of the ventricles, and thus the entire brain, to expand, producing a condition called hydrocephalus (water head)
• hydrocephalus 


  treated by draining the excess fluid from the ventricles and trying to remove the obstruction
• Cerebral ventricles and central canal

  A) Lateral Ventricles

  B) third ventricle

  C) cerebral aqueduct

  D) fourth ventricle

  E) central canal

  F) third ventricle

  G) cerebral aqueduct

  H) fourth ventricle

  I) lateral ventricles

  
• The absorption of cerebrospinal fluid (CSF) from the subarachnoid space (blue) into a major sinus. Note the three meninges

  A) Scalp

  B) skull

  C) dura mater meninx

  D) arachnoid meninx

  E) subarachnoid space

  F) pia mater meninx

  G) cortex

  H) artery

  I) sinus