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