Central nervous system (anatomical structure)

IN this article we will discuss the neuroanatomy as following

 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

Structural Classification of the Nervous System

Central nervous system (CNS)

• Brain
• Spinal cord

Peripheral nervous system (PNS)

• Nerve outside the brain and spinal cord

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
• Somatic nervous system = voluntary
• Autonomic nervous system = involuntary

Organization of the Nervous System

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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)

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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Neuroglia vs. Neurons

Neuroglia divide.

Neurons do not.

Most brain tumors are “gliomas.”

Most brain tumors involve the neuroglia cells, not the neurons.

Consider the role of cell division in cancer!

Support Cells  of the PNS

Satellite cells

• Protect neuron cell bodies

Schwann cells

• Form myelin sheath in the peripheral nervous system

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 Anatomy

Cell body

• Nucleus
• Large nucleolus

Extensions outside the cell body

• Dendrites – conduct impulses toward the cell body
• Axons – conduct impulses away from the cell body (only 1!)
  

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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

Nerve Fiber Coverings

• Schwann cells – produce myelin sheaths in jelly-roll like fashion
• Nodes of Ranvier – gaps in myelin sheath along the axon
  

Applications

In Multiple Scleroses the myelin sheath is destroyed.

The myelin sheath hardens to a tissue called the scleroses.

This is considered an autoimmune disease.

Why does MS appear to affect the muscles?

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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

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

Interneurons (association neurons)

Found in neural pathways in the central nervous system

• Connect sensory and motor neurons

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Structural Classification of Neurons

Multipolar neurons – many extensions from the cell body

Bipolar neurons – one axon and one dendrite

Unipolar neurons – have a short single process leaving the cell body

How Neurons Function (Physiology)

Irritability – ability to respond to stimuli

Conductivity – ability to transmit an impulse

The plasma membrane at rest is polarized

• Fewer positive ions are inside the cell than outside the cell

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Starting a Nerve Impulse

1. Depolarization – a stimulus depolarizes the neuron’s membrane
2. A deploarized membrane allows sodium (Na+) to flow inside the membrane
3. The exchange of ions initiates an action potential in the neuron
   
   
   

The Action Potential

1. If the action potential (nerve impulse) starts, it is propagated over the entire axon
2. Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
3. The sodium-potassium pump restores the original configuration (This action requires ATP).

Nerve Impulse Propagation

• The impulse continues to move toward the cell body
• Impulses travel faster when fibers have a myelin sheath
  

Continuation of the Nerve Impulse between Neurons

Impulses are able to cross the synapse to another nerve

• Neurotransmitter is released from a nerve’s axon terminal
• The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
• An action potential is started in the dendrite

How Neurons Communicate at Synapses

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COMING SOON ALL OF NEUROANATOMY ... 

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