Human Anatomy

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Human Anatomy

• Nervous System Introduction

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Functions

• Communication and control between various organs
  of the body
• To detect changes in the environment and respond
  to them
• To maintain homeostasis
• Homeostasis is the condition by which internal
  physiological conditions remain constant despite
  changes in the environment.

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Overview of the Nervous System

• Two anatomical subdivisions
• Central nervous system (CNS)
• Brain
• Spinal cord
• Peripheral nervous system (PNS)
• 12 pair of cranial nerves
• 31 pair of spinal nerves
• Autonomic nervous system (ANS)
• Runs with the CNS and PNS

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A. The Neuron

• The nerve cell
• Basic functional unit of the nervous system
• Capable of generating and transmitting electrical
  activity

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The Neuron
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The Neuron
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Structure of the Neuron
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Structure of the Neuron

• Dendrites numerous and short, conveys
  electrical impulse to rest of neuron

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Structure of the Neuron

• 2. Cell Body contains typical organelles of
  most cells

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Structure of the Neuron

• 3. Axon single and long, conveys electrical
  impulses away from cell body

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Structure of the Neuron

• Synapse
• a communication
• junction between a
• neuron and another
• cell

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Chemical Synapse

• When electrical impulse reaches terminal part of
  axon, chemicals called neurotransmitters are
  released into synaptic cleft (space between the 2
  cells)
• Neurotransmitter causes second cell to become
  active i.e., muscle contraction, gland secretion,
  neuron activation

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Synapse
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Synapse
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Neuromuscular Junction (NMJ)
Muscle fiber
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B. Neuroglia

• Support cells of the nervous system

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Neuroglia -- CNS

• Microglia small, mobile, remove cell debris,
  wastes and pathogens
• Astrocytes maintain blood-brain barrier
• Oligodendrocytes myelinate CNS axons

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Microglia
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Astrocytes
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Astrocytes

• The astrocytes help to form the blood-brain
  barrier
• Prevents harmful
• materials in the blood
• from reaching the
• brain

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Oligodendrocytes
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Oligodendrocytes

• Associated with axons of neurons found in CNS
  (brain and spinal cord)
• Wrap themselves around axon in jellyroll
  fashion
• Produce myelin which is a lipid that serves as an
  insulator to electrical currents (see saltatory
  conduction)

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Oligodendrocyte
Node of Ranvier
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Development of Oligodendrocyte
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Development of Oligodendrocyte
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Saltatory Conduction

• Occurs only on myelinated axons
• Myelin is a fatty substance that insulates from
  electrical activity
• Electrical activity jumps from node to node
  rather than traveling the entire length of the
  axon
• Faster than non-myelinated axons
• 100m/sec vs 1m/sec

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Saltatory Conduction
Electrical current jumps from node to node
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Myelinated vs Non-myelinated
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Neuroglia -- PNS

• Schwann cell
• Same structure and function as oligodendrocyte
  except in PNS

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Schwann Cell
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Summary of Neuroglia

• CNS microglia, astrocytes and oligodendrocytes
• PNS Schwann cells (neurolemma cells)

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Nerve and Axon Regeneration

• Schwann cells and oligodendrocytes

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Nerve Regeneration
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Nerve Regeneration
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Nerve Regeneration
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Amyotrophic lateral sclerosis (ALS)Lou Gehrig
disease

• Affects neurons in CNS
• Causes weakened skeletal muscles
• Does not affect sensory abilities
• Fatal
• Steven Hawking

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Multiple Sclerosis (MS)

• Progressive demyelination of CNS neurons
• This causes scarring (sclerosis) of neurons
• Disrupts conduction of nerve impulses
• Affects both muscles and sensory
• Occurs mainly 18-40 yo
• Progression is slow
• Read entirety of p.435