Divisions of the Nervous System

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

  • Central Nervous System (CNS): the division of the nervous system located within the skull and spine

  • Peripheral Nervous System (PNS): the division located outside the skull and spine

• Brain vs Spinal Cord

  • Brain: the part of the CNS located in the skull

  • Spinal Cord: part located in the spine

• Somatic Nervous System vs Automatic Nervous System

  • Somatic Nervous System (SNS): part of the PNS that interacts with the external environment

  • Automatic Nervous System (ANS): part of the PNS that regulated the body’s internal environment

• Efferent Nerves vs Afferent Nerves

  • Efferent Nerves: nerves that receive motor impulses (external)

    • SNS: carry motor signals from the CNS to the skeletal muscles

    • ANS: carry motor signals from the CNS to internal organs

  • Afferent Nerves: nerves that receive sensory information

    • SNS: carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and so on

    • ANS: carry sensory signals from the internal organs to the CNS

• Sympathetic Nerves vs Parasympathetic Nerves

  • under PNS → ANS → Efferent

  • Sympathetic Nerves: fight or flight; activation

    • automatic 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: resets; puts nervous system into balance again; baseline

    • automatic motor nerves that project from the brain and sacral (lower back) region of the spinal cord

  • 3 Important Principles:

    • Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations, whereas parasympathetic nerves act to conserve energy

    • Each automatic target organ receives opposing sympathetic and parasympathetic input, and its activity is thus controlled by relative levels of sympathetic and parasympathetic activity

    • Sympathetic changes are indicative of psychological arousal, whereas parasympathetic changes are indicative of psychological relaxation

• Cranial Nerves

  • 12 pairs that are numbered in sequence from front to back

  • include purely sensory nerves such as the olfactory nerves (I) and the optic nerves (II), but most contain both 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 functions of various cranial nerves are commonly assessed by neurologists as a basic for diagnosis

    • Because the functions and locations of the cranial nerves are specific, disruptions of particular cranial nerves functions provide excellent clues about the location and extent of tumors and other kinds of brain pathology

Meninges/ Meninx (Singular)

• protects the brain

• 3 Layers

  • Pia Mater: innermost layer; closely adherent to the surface of the brain (gentle/pious mother)

  • Arachnoid Membrane: middle layer (spidery mother/spider-web-like membrane)

    • Subarachnoid Space: space which contains many large blood vessels and cerebrospinal fluid'; beneath the arachnoid membrane

  • Dura Mater: outermost layer; not sticking to the brain; like a thin callous (tough mother)

Ventricles and Cerebrospinal Fluid

• Ventricles

  • Cerebral Ventricles: 4 large internal chambers of the brain: 2 lateral ventricles, 3rd ventricle, and 4th ventricle

  • Central Canal: a small central channel that runs the length of the spinal cord

• Cerebrospinal Fluid (CSF)

  • supports and cushions the brain

  • fills the subarachnoid space, the central canal of the spinal cord, and the cerebral ventricles of the brain

  • Choroid Plexus: networks of capillaries or small blood vessels that protrude into the ventricles

    • produce CSF

  • excess CSF is continuously 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

  • Hydrocephalus: excess CSF; ventricles are dilated or enlarged; blockage somewhere so the CSF did not drain quickly (water head)

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

  • Flow of Cerebrospinal Fluid

choroid plexus → lateral (usually dilated) → 3rd ventricle → cerebral aqueduct (most common structure blocked, between 3rd and 4th) → 4th ventricle → central canal → subarachnoid space

• Spinal Tap

  • take our spinal fluid from subarachnoid space for check up like suspected meningitis

  • Ends of Spinal: coda equina (horse’s tail)

Blood-Brain Barrier

• a mechanism impedes the passage of many toxic substances from the blood into the brain

• a consequence of the special structure of cerebral blood vessels

• tightly packed cells → a lot of substances cannot pass through

• protects brain

• active transport for large molecules

• Glucose: most common substance transported