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Fundamentals of the Nervous System and Nervous Tissue. Lab 8. Nervous System. The master controlling and communicating system of the body Functions Sensory input – monitoring stimuli occurring inside and outside the body Integration – interpretation of sensory input

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slide2

Nervous System

  • The master controlling and communicating system of the body
  • Functions
    • Sensory input – monitoring stimuli occurring inside and outside the body
    • Integration – interpretation of sensory input
    • Motor output – response to stimuli by activating effector organs
slide3

Nervous System

Figure 11.1

slide4

Organization of the Nervous System

  • Central nervous system (CNS)
    • Brain and spinal cord
    • Integration and command center
  • Peripheral nervous system (PNS)
    • Paired spinal and cranial nerves
    • Carries messages to and from the spinal cord and brain
slide5

Peripheral Nervous System (PNS): Two Functional Divisions

  • Sensory (afferent) division
    • Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain
    • Visceral afferent fibers – transmit impulses from visceral organs to the brain
  • Motor (efferent) division
    • Transmits impulses from the CNS to effector organs
slide6

Motor Division: Two Main Parts

  • Somatic nervous system
    • Conscious control of skeletal muscles
  • Autonomic nervous system (ANS)
    • Regulates smooth muscle, cardiac muscle, and glands
    • Divisions – sympathetic and parasympathetic
slide7

Histology of Nerve Tissue

  • The two principal cell types of the nervous system are:
    • Neurons – excitable cells that transmit electrical signals
    • Supporting cells – cells that surround and wrap neurons
slide8

Supporting Cells: Neuroglia

  • The supporting cells (neuroglia or glial cells):
    • Provide a supportive scaffolding for neurons
    • Segregate and insulate neurons
    • Guide young neurons to the proper connections
    • Promote health and growth
slide9

Astrocytes

  • Most abundant, versatile, and highly branched glial cells
  • They cling to neurons and their synaptic endings, and cover capillaries
  • Functionally, they:
    • Support and brace neurons
    • Anchor neurons to their nutrient supplies
    • Guide migration of young neurons
    • Control the chemical environment
slide10

Microglia and Ependymal Cells

  • Microglia – small, ovoid cells with spiny processes
    • Phagocytes that monitor the health of neurons
  • Ependymal cells – range in shape from squamous to columnar
    • They line the central cavities of the brain and spinal column
slide11

Oligodendrocytes, Schwann Cells, and Satellite Cells

  • Oligodendrocytes – branched cells that wrap CNS nerve fibers
  • Schwann cells (neurolemmocytes) – surround fibers of the PNS
  • Satellite cells surround neuron cell bodies with ganglia
slide13

Neurons (Nerve Cells)

  • Structural units of the nervous system
    • Composed of a body, axon, and dendrites
    • Long-lived, amitotic, and have a high metabolic rate
  • Their plasma membrane functions in:
    • Electrical signaling
    • Cell-to-cell signaling during development
slide15

Axons: Function

  • Generate and transmit action potentials
  • Secrete neurotransmitters from the axonal terminals
  • Movement along axons occurs in two ways
    • Anterograde — toward axonal terminal
    • Retrograde — away from axonal terminal
slide16

Myelin Sheath

  • Whitish, fatty (protein-lipoid), segmented sheath around most long axons
  • It functions to:
    • Protect the axon
    • Electrically insulate fibers from one another
    • Increase the speed of nerve impulse transmission
slide17

Myelin Sheath and Neurilemma: Formation

  • Formed by Schwann cells in the PNS
  • A Schwann cell:
    • Envelopes an axon in a trough
    • Encloses the axon with its plasma membrane
    • Has concentric layers of membrane that make up the myelin sheath
  • Neurilemma – remaining nucleus and cytoplasm of a Schwann cell
slide18

Axons of the CNS

  • Both myelinated and unmyelinated fibers are present
  • Myelin sheaths are formed by oligodendrocytes
  • Nodes of Ranvier are widely spaced
  • There is no neurilemma
slide19

Regions of the Brain and Spinal Cord

  • White matter – dense collections of myelinated fibers
  • Gray matter – mostly soma and unmyelinated fibers
slide20

Neuron Classification

  • Functional:
    • Sensory (afferent) — transmit impulses toward the CNS
    • Motor (efferent) — carry impulses away from the CNS
    • Interneurons (association neurons) — shuttle signals through CNS pathways
slide24

Neurophysiology

  • Neurons are highly irritable
  • Action potentials, or nerve impulses, are:
    • Electrical impulses carried along the length of axons
    • Always the same regardless of stimulus
    • The underlying functional feature of the nervous system