Chap 11 nervous system part 1

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Anatomy & Physiology 1
Fundamentals of nervous system tissue

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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

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Nervous System
Figure 11.1

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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

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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
Peripheral Nervous System (PNS): Two
Functional Divisions

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Somatic nervous system
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulates smooth muscle, cardiac muscle, and
glands
Divisions – sympathetic and parasympathetic
Motor Division: Two Main Parts

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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
Histology of Nerve Tissue

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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
Supporting Cells: Neuroglia

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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
Astrocytes

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Astrocytes
Figure 11.3a

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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
Microglia and Ependymal Cells

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Microglia and Ependymal Cells
Figure 11.3b, c

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Oligodendrocytes – branched cells that wrap CNS
nerve fibers
Schwann cells (neurolemmocytes) – surround fibers
of the PNS
Satellite cells surround neuron cell bodies with
ganglia
Oligodendrocytes, Schwann Cells, and Satellite
Cells

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Oligodendrocytes, Schwann Cells, and Satellite
Cells

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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
Neurons (Nerve Cells)

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Neurons (Nerve Cells)
Figure 11.4b

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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 amitotic nature)
Has well-developed Nissl bodies (rough ER)
Contains an axon hillock – cone-shaped area from
which axons arise
Nerve Cell Body (Perikaryon or Soma)

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Armlike extensions from the soma
Called tracts in the CNS and nerves in the PNS
There are two types: axons and dendrites
Processes

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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)
Dendrites of Motor Neurons

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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: Structure

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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
Axons: Function

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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
Myelin Sheath

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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
Myelin Sheath and Neurilemma: Formation

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Myelin Sheath and Neurilemma: Formation
Figure 11.5a-c

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Gaps in the myelin sheath between adjacent
Schwann cells
They are the sites where axon collaterals can emerge
Nodes of Ranvier (Neurofibral Nodes)
InterActive Physiology
®
: Nervous System I: Anatomy ReviewPLAY

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A Schwann cell surrounds nerve fibers but coiling
does not take place
Schwann cells partially enclose 15 or more axons
Unmyelinated Axons

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Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma
Axons of the CNS

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White matter – dense collections of myelinated
fibers
Gray matter – mostly soma and unmyelinated fibers
Regions of the Brain and Spinal Cord

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Structural:
Multipolar — three or more processes
Bipolar — two processes (axon and dendrite)
Unipolar — single, short process
Neuron Classification

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

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Comparison of Structural Classes of Neurons
Table 11.1.1

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Comparison of Structural Classes of Neurons
Table 11.1.2

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Comparison of Structural Classes of Neurons
Table 11.1.3

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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
Neurophysiology