Coverings of the CNS

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Coverings of the CNS

• 1) Bone Cranium, Vertebrae
• 2) Meninges Three connective tissue membranes
  covering the brain and spinal cord
• a) Dura Mater outermost , composed of
  tough fibrous connective tissue. Vascular.
  Attached to cranium but not to the vertebrae.
  Epidural Space exists between the vertebra and
  Dura Mater. Composed of fat.
• b) Arachnoid Mater middle layer. Thin,
  web-like layer
• c) Pia Mater innermost layer. Very
  thin, vascular. Clings to the surface of the
  brain. Aids in nourishing underlying brain cells

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• Subarachnoid Space exists between the Arachnoid
  and Pia Mater. Filled with cerebrospinal fluid.

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The Brain

• Composed of 100 Billion Neurons Divided into 4
  major regions
• 1) Cerebrum largest region. Surface has
  elevated ridges called Gyri, separated by shallow
  grooves called Sulci and less numerous but deeper
  grooves called Fissures.
• Sulci and fissures divide the cerebrum into lobes
  named for the cranial bones above them.
• Divided into hemispheres by the Longitudinal
  Cerebral Fissure.
• Hemispheres connected by a bridge of nerve fibers
  called the Corpus Callosum

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• Impulses cross over to the other side of the body
  in the brainstem. Impulses from the right side
  of the brain control muscles on the left side of
  the body.
• Hemisphere Dominance both hemispheres
  participate in basic functions. In most people
  one side acts as a dominate hemisphere for other
  functions. 90 of people are left hemisphere
  dominant

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• Within cerebral hemispheres and brainstem are
  interconnected cavities called Ventricles
• The ventricles are continuous with the central
  canal of the spinal cord and are filled with
  Cerebrospinal Fluid
• Cerebrospinal fluid (CSF) completely surrounds
  the brain and functions to
• 1) support and protect
• 2) Maintain ion concentration of the CNS
• 3) Remove wastes

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Functions of the Cerebrum

• 1) Interpret sensory impulses
• 2) Initiate voluntary muscle movement
• 3) Store Information
• 4) Reasoning
• 5) Personality, Intelligence

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• 2) Diencephalon Sits atop the brainstem and
  consists of 3 regions
• Thalamus relay station for sensory
  impulses
• Hypothalamus Plays a role in the
  regulation of body temperature, water balance and
  metabolism. Also thirst, appetite, pain and
  pleasure centers are in the hypothalamus.
• Epithalamus tissues lining the epithalamus
  form cerebrospinal fluid

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• 3) Brain Stem Bundle of nerve tissue that
  connects the cerebrum to the spinal cord. It
  also has many areas of gray matter that controls
  vital activities. 3 Main
  Regions
• a) Midbrain Center for auditory and
  visual reflexes
• b) Pons Relay impulses from the medulla
  to the cerebrum
• c) Medulla Oblongata Regulates blood
  pressure, heart rate, breathing and certain
  reflexes

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• 4) Cerebellum Acts as a control center in the
  coordination of skeletal muscle movements

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Cranial Nerves

• 12 pairs of nerves arise from the underside of
  the brain that mostly serve the head and neck
• Numbered in order, front to back
• Most are mixed nerves, but three are sensory only
• Olfactory Sense of smell
• Optic Sense of Vision
• Vestibulocochlear Hearing and balance
• Vagus Sensations and movements of Visceral
  organs.

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Spinal Cord

• Extends from the foramen magnum to the disk
  between the 1st and 2nd Lumbar vertebrae
• It is surrounded and protected by the meninges
• The meninges extends below the end of the cord
  and provide for safe sampling of CSF below L3
  (spinal tap)
• Spinal cord gives rise to 31 pairs of spinal
  nerves that exit the vertebrae and serve the body
  close by.

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• Nerves exiting below the end of the cord travel
  through the vertebral canal and form the Cauda
  Equina (horses tail)
• Cross section of the cord reveals a core of gray
  matter surrounded by white matter. Pattern of
  gray matter resembles a butterfly
• Neurons of the gray matter are interneurons.
  Neurons in the white matter are nerve tracts
• Central canal filled with Cerebrospinal Fluid
• Divided into right and left halves much like the
  brain

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Spinal Cord Functions

• 1) Reflex Center (gray matter)
• 2) Conduct impulses to and from the brain (white
  matter)

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Peripheral Nervous System

• Nerves that branch out of the CNS to different
  parts of the body
• 2 Divisions Somatic and Autonomic
• Somatic Nerves Nerves that lead to the skin and
  skeletal muscles involved in conscious activities
• Autonomic Nerves Nerves that lead to the
  visceral organs involved in unconcious activities

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Autonomic Nervous System

• Further subdivided into the Sympathetic and
  Parasympathetic divisions
• Impulses from one set of nerves activate an
  organ. Impulses from the other nerves inhibit
  the organ
• Sympathetic division is concerned with preparing
  the body for energy expending, stressful or
  emergency situations

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• 31 pairs of spinal nerves originate from the
  spinal cord
• All are mixed nerves. Not named but numbered
• 8 pairs of Cervical nerves
• 12 pairs of Thoracic nerves
• 5 pairs of Lumbar nerves
• 5 pairs of Sacral nerves
• 1 pair of Coccygeal nerves

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• Each spinal nerve emerges from the spinal cord as
  two short branches or roots
• The dorsal root is composed of sensory fibers and
  the ventral root is composed of motor fibers
• The dorsal and ventral root unite to form a
  spinal nerve which passes outward from the
  vertebral canal through the intervertebral
  foramen
• After emerging from the vertebral canal, main
  portions of the spinal nerves combine to form
  complex networks called plexuses

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Plexuses

• 1) Cervical Plexus C1-C4 muscles of the neck,
  diaphragm
• 2) Brachial Plexus C5-T1 arm, forearm, hand
• 3) Lumbosacral Plexus T12-S5 Lower abdomen,
  legs