Nerve Tissue & The Nervous System

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Nerve Tissue The Nervous System

• Part Due

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Terminology

• a) Nerve - collection of neurons in PNS.
• b) Ganglion - collection of neuron nerve cell
  bodies in PNS.
• c) Tract - collection of neurons in CNS.
• d) Nuclei - collection of neuron nerve cell
  bodies in CNS.

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Nerves

• Cranial Nerves
• 12 pairs of cranial nerves (I to XII).
• Spinal Nerves
• 31 pairs of spinal nerves.

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Ganglia

• Ganglia Neuron cell bodies, glia, reticular
  fibers
• Sensory Ganglia
• Cranial Ganglia- cranials 5,7,8,9,10
• Dorsal Root Ganglia - in dorsal root of all
  spinal nerves
• pseudounipolar neurons
• Histology - nerve cell bodies clumped to one
  side with prominent fiber bundles between.
• Autonomic Ganglia
• Series of ganglia connected together parallel
  to spinal cord (Sympathetic chain), Multipolar
  Neurons
• Ganglia deep in body cavity (coeliac superior
• and inferior mesenteric) sympathetic motor.
• Parasympathetic - on surface of or in target
  organs

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Spinal Cord
CNS Spinal Cord - organized into gray matter in
center and white matter on surface. Hollow
central canal is filled with cerebrospinal
fluid. Nuclei - layers or columns of nerve cell
bodies in gray matter of CNS. Tracts - axons
and oligodendrocytes fascicles
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Gray Matter glial cell nucleus
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White Matter Gray Matter
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CNS

• Neuroglia (nerve glue) - cells that bind and
  support neurons and shape CNS - occur only in
  CNS.
• Blood vessel do not come into contact with
  neurons in CNS only neuroglia. Capillaries are
  adjacent to neurons only in the Hypothalamus.
• a) macroglia - astrocytes
• oligodendrocyte
• b) ependyma
• c) microglia

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Astrocytes

• Astrocytes stellate (star shape) cells with
  many cytoplasmic processes. Most numerous glial
  cell
• 1) Protoplasmic Astrocytes (mossy cells) many
  short, branched processes in gray matter of brain
  and spinal cord surround NCB's serve as a
  satellite cell.
• Fibrous Astrocyte - long, cytoplasmic processes
  in CNS white matter processes attach to blood
  vessels and separate neural elements from CT
  especially under Pia mater and ependyma.
• Repair and scarring cells of sclerosis.
• Regulate Interstitial Fluid Environment
• Maintain Blood Brain Barrier

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Oligodendrocytes
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Oligodendrocyte

• Oligodendrocytes - few cytoplasmic processes in
  white matter, in rows enveloping myelinated
  neurons
• In gray matter around NCB's as satellite cells
• 1 cell produces myelin for several neurons.

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Neuroglia

• Ependyma - tall, columnar shaped lining cells of
  CNS central canal ciliated when youthful, brush
  border in adult.
• Microglia - only nerve cell of mesodermal origin
  similar to fibroblasts derived from Pia Mater or
  CNS CT found along blood vessels and around
  NCB's in gray as satellite cells.
• Least numerous neuroglial cell phagocytic.

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CNS Membranes

• Meninges -
• Dura Mater
• Arachnoid
• Pia Mater

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Dura Mater

• Dura Mater (tough mother) - two layers around the
  brain
• 1) outer periosteal layer of DICT next to skull
  bones
• 2) less vascular fibrous layer next to the
  arachnoid (missing along the spinal cord).
• layer of flat mesothelial cells between inner
  Dura and arachnoid (on all surfaces).

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Arachnoid

• Non-vascular, cavitated layer lining the Dura.
  Fine white and yellow fibers (loose CT) form
  columns elevating Arachnoid from brain surface.
• Covered throughout with simp. sq. epith.
  (mesothelium)
• Filled with cerebrospinal fluid.

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Pia Mater

• Pia mater (intimate mother) - delicate CT layer
  over brain and spinal cord surface -
• Follows contours of the brain delicate loose CT
  with many blood vessels.

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Cerebrospinal Fluid

• CSF - almost pure water in and around CNS
  secreted by Anterior and Posterior Choroid
  Plexuses - of Ependyma and Pia Mater.
• 700 ml/day
• Anterior Choroid Plexus - roof of third brain
  ventricle and walls of numbers 1 and 2.
• Posterior Choroid Plexus - roof of fourth brain
  ventricle.
• Average brain weights 1500 g weighs only 50 g in
  CSF.

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CNS Brain

• Gray matter is on outside, white matter on
  inside.
• Cerebrum multiple layers of Pyramidal Neurons
  in gray matter
• sensory functions, thought, consciousness, memory
  and gross motor control.

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Cerebrum Silver stain
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Cerebellum

• Gray Matter of three layers
• a) outer molecular layer - small multipolar
  neurons with small NCB's and having many
  non-myelinated neurons.
• b) Purkinje Neuron Layer - middle layer of large
  multipolar Purkinje Cells.
• Granular Neuron Layer - inner layer of many small
  NCB granulated multipolar neurons.
• Functions in fine motor control of skeletal
  muscle Controls in regulating posture and
  coordination. Error control system for the
  cerebral motor cortex.

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