The Central Nervous System

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The Central Nervous System
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The Central Nervous System

• There are two main structures that make up the
  central nervous system (CNS)
• Brain
• Spinal Cord

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Coverings of the Brain and Spinal Cord

• The brain and spinal cord are both delicate and
  vital, nature has provided them with two
  protective coverings
• Bone (cranium and vertebrae)
• Meninges (3 layers of connective tissues)

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The Meninges

• Dura mater made of strong white fibrous tissue
• Arachnoid membrane delicate cob-web like layer
• Pia mater transparent innermost layer of the
  meninges that covers the brain and spinal cord
  and contains blood vessels

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Spaces Between Around the Meninges
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Epidural Space

• Outside the dura and inside the bony coverings
  of the brain and spinal cord. Contains
  supporting cushion of fat and other connective
  tissues.

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Subdural Space

• Between the dura mater and the arachnoid membrane
• Contains a small amount of lubricating fluid

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Subdural Hematoma
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Subarachnoid Space

• Under the archnoid space and outside of the pia
  mater
• Contains a significant amount of cerebrospinal
  fluid

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Menenges and Spaces
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Histology of the Meninges
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Meningitis

• An infection or inflammation of the meninges
• Most commonly caused by bacteria, however, it may
  also be caused by viral or fungal infections or
  tumors
• Usually complain of fever and severe headaches
• Can be fatal

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Cerebrospinal Fluid (CSF)

• Acts as additional cushion
• Reservoir of circulating fluid that, along with
  blood, the brain monitors for changes in the
  internal environment.
• If CO2 content in the CSF goes up, a homeostatic
  response is triggered in the respiratory control
  centers of the brainstem

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Fluid Spaces

• Found in the subarachnoid space
• Within cavities and canals of the brain and
  spinal cord
• The large, fluid-filled cavities of the brain are
  called ventricles.

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Ventricles of the Brain
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Formation and Circulation of CSF
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The Spinal Cord

• About 45 cm long
• Extends from the foramen magnum to the border of
  the first lumbar vertebrae
• Two nerve roots project from each side of the
  spinal cord
• Dorsal carries sensory information
• Ventral carries motor information out

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Structure of the Spinal Cord
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Spinal Cord Function

• Two main functions
• Provides conduction routes to and from the brain
• Serves as an integrator for all spinal reflexes
• Tracts provide conduction paths to and from the
  brain (composed of axon bundles)
• Ascending tracts conduct sensory impulses up the
  cord to the brain
• Descending tracts conduct motor impulses down the
  cord from the brain

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Spinal Tracts
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The Brain

• Weighs about three pounds in adults
• Neurons can grown in size, but not increase in
  number
• Grows rapidly during the first nine years and
  matures at about 18 years
• 6 Major divisions

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Medulla Oblongata

• Attaches to the spinal cord
• Contains control centersfor example, the
  cardiac, respiratory, and vasomotor control
  centers

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Pons

• Lies just above the medulla
• Passes information from the brain to the body and
  vice versa, controls facial expression.

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Midbrain

• Also called the mesencephalon
• Forms the midsection of the brain
• Involved in auditory and visual function as well
  as some muscular control functions

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Functions of the Brainstem

• Sensory, motor and reflex functions
• Reflexes such as those for vomiting, coughing,
  sneezing, hiccupping and swallowing are located
  in the brain stem

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Cerebellum

• 2nd largest part of the brain
• Gray matter makes up the outer portion, or cortex
  and white matter makes up the interior portions
• Has numerous grooves (sulci) and raised areas
  (gyri)

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Functions of the Cerebellum

• Acts with cerebral cortex to produce skilled
  movements by coordinating activities of groups of
  muscles
• Helps control posture
• Controls movements so they are not jerky
• Controls skeletal muscles to maintain balance

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Diencephalon

• Located between the cerebrum and midbrain
• The main structures of the diencephalon are the
• Thalamus sensations, relay info to cerebrum,
  emotions, complex reflex movements
• Hypothalamus link between mind and body and
  links the nervous system and endocrine system
• Optic chiasma optic nerves cross
• Pineal body seems to be important in regulating
  the bodys biological clock

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Cerebrum

• Largest division of the brian
• Consists of two hemispheres
• Surface (cerebral cortex) is made up of gray
  matter only 2 4 mm thick
• Each hemisphere is divided into 5 lobes

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Functional Areas of the Cerebral Cortex
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Primary Somatic Sensory and Motor Areas of the
Cortex