Download Central Nervous System

Neurology
NERVOUS SYSTEM
INTRODUCTION TO NERVOUS SYSTEM
Histology of Nervous Tissue
• 2 types of cells
• Neurons
− Structural & functional part of nervous system
− Specialized functions
• Neuroglia (glial cells)
− Support & protection of nervous system
Neurons
• Function
• Conduct electrical impulses
• Structure
• Cell body
− Nucleus with nucleolus
− Cytoplasm
• Cytoplasmic processes
− Dendrites
− Axon
 Basic functional unit of N.S.
 Specialized cell
 All cells have same basic properties
 information processing
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Transmits
Integrates
Stores
 Regulation of behavior ~
Nervous Tissue: Neurons
Neurons = nerve cells
 Cells specialized to transmit messages
 Major regions of neurons
 Cell body – nucleus and metabolic center of the cell
 Processes – fibers that extend from the cell body
(dendrites and axons)
Neuron Cell Body Location
 Most are found in the central nervous system
 Gray matter – cell bodies and unmylenated fibers
 Nuclei – clusters of cell bodies within the white matter of the
central nervous system
 Ganglia – collections of cell bodies outside the central nervous
system
Neuron Anatomy
 Cell body
 Nucleus
 Large nucleolus
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 Extensions outside the cell body
 Dendrites – conduct impulses toward the cell body
 Axons – conduct impulses away from the cell body
(only 1!)
Axons and Nerve Impulses
 Axons end in axonal terminals
 Axonal terminals contain vesicles with neurotransmitters
 Axonal terminals are separated from the next neuron by a
gap
 Synaptic cleft – gap between adjacent neurons
 Synapse – junction between nerves
Chemical Synapses
Why are neurons connected?
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Are all neurons equal in size?
 Brain vs spinal cord vs peripheral nerves?
About how many neurons are in the human brain? 100 billions
About how many neurons are in the spinal cord? 1 billion
How long do you think the longest axon in the world is? around 15
feet
Nerve Fiber Coverings
 Schwann cells – produce myelin
sheaths in jelly-roll like fashion
 Nodes of Ranvier – gaps in myelin
sheath along the axon
Functional Classification of
Neurons
 Sensory (afferent) neurons
 Carry impulses from the sensory receptors
 Cutaneous sense organs
 Proprioceptors – detect stretch or tension
 Motor (efferent) neurons
 Carry impulses from the central nervous system
Neuroglia
Neuroglia of CNS
○ Astrocytes
Form the blood-brain barrier
Form a structural framework for the CNS
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Repair damaged neural tissue
Control the interstitial environment of the CNS
○ Oligodendrocytes
CNS
Form myelin sheaths
○ Microglia
Phagocytose foreign microbes, etc.
○ Ependymal
Line ventricles of the brain, secrete cerebrospinal fluid
Neuroglia of PNS
○ Schwann cells
Form myelin sheaths of PNS
○ Satellite cells
Nerve Fibers of the PNS
◦ An axon and its sheaths
Myelinated axon
Axon is surrounded by a myelin
sheath
Unmyelinated axon
Axon has no myelin sheath
Structural Classification Neurons
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Nervous Tissue: Support Cells (Neuroglia or Glia)
 Astrocytes
 Abundant, star-shaped cells
 Brace neurons
 Form barrier
between capillaries
and neurons
 Control the chemical
environment of
the brain (CNS)
 Nutrition.
 Microglia (CNS)
 Spider-like phagocytes
 Dispose of debris
 Ependymal cells (CNS)
 Line cavities of the
brain and spinal cord
 Circulate
cerebrospinal
fluid
 Oligodendrocytes(CNS)
 Produce myelin sheath around nerve fibers in the
central nervous system
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Blood Brain Barrier : Function
 Maintains stable brain environment large fluctuations in
periphery
 Barrier to poisons
 Retains neurotransmtters
& other chemicals
 Regulates nutrient supplies
glucose levels
active transport ~
Structural Classification of the Nervous System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerve outside the brain and spinal cord
Central Nervous System:
Consists of Brain Located in cranial vault of skull
And Spinal cord Located in vertebral canal . Brain and spinal cord
Continuous with each other at foramen magnum
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Peripheral Nervous System: comprises peripheral nerves
(cranial & spinal ) & ganglia
Two subcategories
Sensory or afferent (input)
Motor or efferent (output)
• Divisions
– Somatic nervous
system
– Autonomic nervous system (ANS)
» Sympathetic
» Parasympathetic
» Enteric
PNS (Cranial
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Functions of the Nervous System
1. Sensory input – gathering information
 To monitor changes occurring inside and outside the
body (changes = stimuli)
2. Integration –
 to process and interpret sensory input and decide if
action is needed.
3. Motor output
 A response to integrated stimuli
 The response activates muscles or glands
Functional Classification of the Peripheral Nervous System
 Sensory (afferent) division
 Nerve fibers that carry information to the central
nervous system
 Motor (efferent) division
 Nerve fibers that carry impulses away from the central
nervous system
 Motor (efferent) division
 Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
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Anatomical classification
• Cerebral hemispheres
• Diencephalon
• Thalamus
• Hypothalamus
• Brain stem
• Midbrain
• Pons
• Medulla
• Cerebellum
• Spinal cord
Parts of Brain
Cerebrum
Diencephalon
Brainstem
Cerebellum
Usual pattern of gray/white in CNS
• White exterior to gray
• Gray surrounds hollow central cavity
• Two regions with additional gray called
“cortex”
• Cerebrum: “cerebral cortex”
• Cerebellum: “cerebellar cortex”
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Spinal cord anatomy
 Gray commissure with central canal
 Columns of gray running the length of the spinal cord
 Posterior (dorsal) horns (cell bodies of interneurons)
 Anterior (ventral) horns (cell bodies of motor neurons)
 Lateral horns in thoracic and superior lumbar cord
White matter of the spinal cord (myelinated and unmyelinated axons)
 Ascending fibers: sensory information from sensory
neurons of body up to brain
 Descending fibers: motor instructions from brain to spinal
cord
 Stimulates contraction of body’s muscles
 Stimumulates secretion from body’s glands
 Commissural fibers: white-matter fibers crossing from one
side of cord to the other
 Most pathways cross (or decussate) at some point
 Most synapse two or three times along the way, e.g. in brain
stem, thalamus or other
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Anatomical Tracts
1- Motor system
2- Somatic –sensory system
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younis alomary
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