chapter 11 fundamentals of the nervous system and nervous tissue part 1
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Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Part 1. Angela Peterson-Ford, PhD E209 [email protected] Nervous System. The master controlling and communicating system of the body Functions

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nervous system
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
nervous system3
Nervous System

Figure 11.1

organization of the nervous system
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
peripheral nervous system pns two functional divisions
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
motor division two main parts
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
histology of nerve tissue
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
supporting cells neuroglia
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
  • 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

Figure 11.3a

microglia and ependymal cells
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
oligodendrocytes schwann cells and satellite cells
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
neurons nerve cells
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
nerve cell body perikaryon or soma
Nerve Cell Body (Perikaryon or Soma)
  • Contains the nucleus and a nucleolus
  • Is the major biosynthetic center
  • Is the focal point for the outgrowth of neuronal processes
  • Has no centrioles (hence its non-mitotic nature)
  • Has well-developed Nissl bodies (rough ER)
  • Contains an axon hillock – cone-shaped area from which axons arise (formation of action potential).
  • Armlike extensions from the soma
  • Called tracts in the CNS and nerves in the PNS
  • There are two types: axons and dendrites
dendrites of motor neurons
Dendrites of Motor Neurons
  • Short, tapering, and diffusely branched processes
  • They are the receptive, or input, regions of the neuron
  • Electrical signals are conveyed as graded potentials (not action potentials)
axons structure
Axons: Structure
  • Slender processes of uniform diameter arising from the hillock
  • Long axons are called nerve fibers
  • Usually there is only one unbranched axon per neuron
  • Rare branches, if present, are called axon collaterals
  • Axonal terminal – branched terminus of an axon
axons function
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
myelin sheath
Myelin Sheath
  • Whitish, fatty (protein-lipid), 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
myelin sheath and neurilemma formation
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
nodes of ranvier neurofibral nodes
Nodes of Ranvier (Neurofibral Nodes)
  • Gaps in the myelin sheath between adjacent Schwann cells
  • They are the sites where axon collaterals can emerge
unmyelinated axons
Unmyelinated Axons
  • A Schwann cell surrounds nerve fibers but coiling does not take place
  • Schwann cells partially enclose 15 or more axons
axons of the cns
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
regions of the brain and spinal cord
Regions of the Brain and Spinal Cord
  • White matter – dense collections of myelinated fibers
  • Gray matter – mostly soma and unmyelinated fibers
neuron classification
Neuron Classification
  • Structural:
    • Multipolar — three or more processes
      • Most of the neurons within the CNS and motor neurons are multipolar
    • Bipolar — two processes (axon and dendrite)
      • Bipolar neurons are located in some sensory organs, such as in the retina of the eye and in the nasal cavity.
    • Unipolar — single, short process
      • One branch extends to the CNS, and the other branch extends to the periphery and has dendrite-like sensory receptors.
      • Most sensory neurons are unipolar.
neuron classification31
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
  • Neurons are highly irritable (excitable)
  • 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