A&P Exam 3

• Nervous system

  Master controlling and communicating system of body
• Nervous system


  • Cells communicate via electrical and chemical signals
  • Rapid and specific
  • Usually cause almost immediate responses
• Functions of Nervous System

  • Sensory input
  • Integration
  • Motor output
• Sensory input


  Information gathered by sensory receptors about internal and external changes
• Integration


  Processing and interpretation of sensory input
• Motor output


  Activation of effector organs (muscles and glands) produces a response
• Nervous system is divided into two principal parts

  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
• Central nervous system (CNS)


  • Brain and spinal cord of dorsal body cavity
  • Integration and control center
  • Interprets sensory input and dictates motor output
• Peripheral nervous system (PNS)


  • The portion of nervous system outside CNS
  • Consists mainly of nerves that extend from brain and spinal cord
• Components of PNS


  • Spinal nerves
  • Cranial nerves
• Functional divisions of PNS

  • Sensory (afferent) division
  • Motor (efferent) division
• Sensory (afferent) division


  • Somatic sensory fibers: convey impulses from skin, skeletal muscles, and joints to CNS
  • Visceral sensory fibers: convey impulses from visceral organs to CNS
• Motor (efferent) division


  Transmits impulses from CNS to effector organs (muscles and glands)
• Divisions of motor (efferent) division

  • Somatic nervous system
  • Autonomic nervous system
• Somatic nervous system


  • Nerve fibers conduct impulses from CNS to skeletal muscle
  • Voluntary nervous system - conscious control of skeletal muscles
• Autonomic nervous system


  • Consists of visceral motor nerve fibers from CNS to regulate smooth muscle, cardiac muscle, and glands
  • Involuntary nervous system
• Functional subdivisions of Autonomic Nervous System

  • Sympathetic
  • Parasympathetic
• Neurons


  • Structural units of nervous system
  • Large, highly specialized cells that conduct impulses
• Neurons


  • Extreme longevity (lasts a person's lifetime)
  • Amitotic, with very few exceptions
  • High metabolic rate; requires continuous supply of oxygen and glucose
• Components of a neuron

  • Cell body
  • Processes
• Cell body


  • Also called the soma
  • Biosynthetic center of neuron
  • Synthesizes proteins, membranes, chemicals
• Neuron processes


  • Armlike processes that extend from cell body
  • Two types: Dendrites and Axon
• Dendrites


  • Receptive (input) region of neuron
  • Convey incoming messages toward cell body as graded potentials (short distance signals)
  • Contain dendritic spines, appendages with bulbous or spiky ends
• Axon


  • Generates nerve impulses and transmits them along axolemma (neuron cell membrane) to axon terminal
  • Terminal region secretes neurotransmitters, which are released into extracellular space
  • Can excite or inhibit neurons it contacts
• Axon


  • Relies on cell bodies to renew proteins and membranes
  • Quickly decay if cut or damaged
• Anterograde transport


  Movement of molecules and organelles away from cell body
• Retrograde transport


  Movement of molecules and organelles toward cell body
• Neuroglia of the CNS

  • Astrocytes
  • Microglial cells
  • Ependymal cells
  • Oligodendrocytes
• Astrocytes


  • Most abundant, versatile, and highly branched
  • Cling to neurons, synaptic endings, and capillaries
  • Functions include support, chemical environment control, information processing
• Microglial cells


  • Small, ovoid cells with thorny processes that touch and monitor neurons
  • Migrate toward injured neurons
  • Can transform to phagocytize microorganisms and neuronal debris
• Ependymal cells


  • Line the central cavities of the brain and spinal column
  • Form permeable barrier between cerebrospinal fluid (CSF) in cavities and tissue fluid bathing CNS cells
• Oligodendrocytes


  • Branched cells
  • Processes wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers
• Neuroglia of PNS


  • Satellite cells
  • Schwann cells (neurolemmocytes)
• Satellite cells


  • Surround neuron cell bodies in PNS
  • Function similar to astrocytes of CNS
• Schwann cells


  • Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers
  • Similar function as oligodendrocytes
  • Vital to regeneration of damaged peripheral nerve fibers
• Myelin sheath


  • Composed of myelin, a whitish, protein-lipid substance
  • Protect and electrically insulate axon
  • Increase speed of nerve impulse transmission
• Types of nerve fibers

  • Myelinated fibers
  • Nonmyelinated fibers
• Myelination in the PNS

  • Formed by Schwann cells
  • Wraps around axon in jelly roll fashion
  • One cell forms one segment of myelin sheath
• Myelin sheath gaps

  • Gaps between adjacent Schwann cells
  • Sites where axon collaterals can emerge
• Myelination in the CNS

  • Formed by processes of oligodendrocytes, not whole cells
  • Each cell can wrap up to 60 axons at once