Warm-Up
• Outline pages 222-230
The Nervous System
Chapter 7
Functions
• Master controlling and communicating system
of the body
• Monitor changes (stimuli) both inside and
outside of the body
▫ Gathered information is called sensory input
• Processes and interprets the sensory input and
makes decisions about what should be done at
every moment
▫ This is called integration
• Effects a response by activating muscles or
glands (effectors) via motor output
• Does not work alone to regulate and maintain
body homeostasis
▫ Endocrine system is a second important
regulating system
Produces hormones
Typically brings about its effects in a more leisurely
way
Organization of the Nervous System
• Structural Classification
▫ Central nervous system (CNS)
Brain and spinal cord
Occupy the dorsal body cavity and act as the integrating
and command centers of the nervous system
Interpret incoming sensory information
Issue instructions
▫ Peripheral nervous system (PNS)
Parts of the nervous system that are outside of the
CNS
Consists mainly of the nerves that extend from the
brains and spinal cord
Spinal nerves carry impulses to and from the spinal
cord
Cranial nerves carry impulses to and from the brain
Serve as communication lines
Functional Classification
• Concerned only with PNS structures
• 2 subdivisions
▫ Sensory (afferent) division
Consists of nerve fibers that convey impulses to the
CNS from sensory receptors located through the
body
Somatic (afferent fibers) – impulses from the skin,
skeletal muscles and joints
Visceral fiber (visceral afferents) – impulses from the
visceral organs
▫ Motor (efferent) division
Carries impulses from the CNS to effector organs,
the muscles and glands
Effect a motor response
Two subdivisions
Somatic nervous system – voluntary nervous system
Autonomic nervous system (ANS) – involuntary
nervous system
▫ Sympathetic
▫ Parasympathetic
Background Information
• Two Principal Types of Nervous Cells
▫ Supporting cells
▫ Neurons
Supporting Cells
• Neuroglia – supporting cells in the CNS that are
“lumped together”
▫ Many types of cells that support, insulate and
protect the neurons
• Glia – different types of neuroglia that have a
special function
Types of Glial
• Astrocytes
▫ Star shaped
▫ Account for nearly half of the neural tissue
▫ Form a living barrier between capillaries and
neurons and play a role in making exchanges
between them
▫ Help control the chemical environment in the
brain
• Microglia
▫ Spiderlike phagocytes
▫ Dispose of debris
• Ependymal
▫ Line the cavities of the brain and the spinal cord
▫ Helps circulate the cerebrospinal fluid
• Oligodendrocytes
▫ Wrap their flat extensions tightly around the nerve
fibers
▫ Produce fatty insulating covering called the myelin
sheaths
• Glia do not transmit nerve impulses
• Never lose their ability to divide
• Most brain tumors are gliomas
• Supporting Cells in the PNS come in two major
varieties
▫ Schwann cells
Form the myelin sheaths around the nerve cells that
are found in the PNS
▫ Satellite cells
Act as protection, cushioning cells
Neurons
• Also called nerve cells
• Highly specialized to transmit messages
• Have a cell body containing the nucleus and is
the metabolic center of the cell
▫ No centrioles
▫ Very abundant are the
Nissl substances – specialized RER
Neurofibrils – intermediate filaments that are
important in maintaining cell shape
• Extending from the cell body there are one or
more slender processes (fibers)
▫ Vary in length
▫ Dendrites – convey incoming messages (electrical
signals) towards the cell body
May have hundreds of branching dendrites
▫ Axons – generate nerve impulses and typically
conduct them away from the cell body
Only has one
Arise from the axon hillock
Occasionally branch to give off a collateral branch
Branch profusely at their terminal end to form the
axon terminals
▫ Terminals contain the neurotransmitters in tiny
vesicles which are released when stimulated
▫ Synaptic cleft separates the one neuron for the
next
The functional gap is the synapse
▫ Myelin – whitish, fatty material with a waxy
appearance surrounds most nerve fibers
Protects and insulates the fibers along with
increasing the transmission rate
Outside the CNS, the myelination is done by
Schwann cells
A myelin sheath results from the myelination
Most of the Schwann cell cytoplasm ends up just
beneath the outermost part of its plasma membrane
and is called the neurilemma
▫ Remains intact (for the most part) when a peripheral nerve
fiber is damages, it plays an important role in fiber
regeneration
Nodes of Ranvier form where there are gaps between
the adjacent Schwann cells
• In the CNS, the oligodendrocytes form the
myelin sheaths.
▫ Coil around as many as 60 different nerve fibers at
a time
▫ Lack neurilemma
• Clusters of neuron cell body and collections of nerve
fibers
▫ In the CNS, the cell body clusters are called nuclei
Protected in the skull and vertebral column
Do not routinely undergo cell division
Carries out most of the metabolic functions
▫ In the PNS, small collections of cell bodies are called
ganglia
Found in few sites
▫ In the CNS, bundles of nerve fibers are called tracts
White matter – dense collections of myelinated tracts
Gray matter – mostly unmyelinated fibers and cell bodies
▫ In the PNS, bundles of nerve fibers are called nerves
Neuron Classification
• Functional
▫ Groups neurons according to the direction the
nerve impulse is traveling relative to the CNS
▫ Sensory (afferent) neurons – carry impulses from
sensory receptors to the CNS
Cell bodies are always found in a ganglion outside
the CNS
Keep use informed about what is happening both
inside and outside the body
Dendrite endings are usually associated with
specialized receptors that are activated by specific
changes occurring nearby.
Complex receptors may be discussed later; we will
focus on the simpler type of sensory receptors
found in the skin (cutaneous sense organs),
muscles and tendons (proprioceptors).
The pain receptors (which are bare dendrite
endings) are the least specialized cutaneous
receptors as well as the most numerous.
Proprioceptors detect the amount of stretch
(tension) skeletal muscles, their tendons and joints
These allow the body to make the proper adjustments
to maintain balance and normal posture.
▫ Motor (efferent) neurons carry impulses from the
CNS to the viscera and/or muscles and glands
The cell bodies of motor neurons are always located
in the CNS
▫ Association neurons (interneurons) connect the
motor and sensory neurons in neutral pathways
Their cell bodies are always located in the CNS
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