Download Intro to Nervous System

6/13/16
Collin County Community College
BIOL 2401
Week 5
Nervous System
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Nervous System
The process of homeostasis makes sure that the
activities that occur in the body are maintained within
normal physiological limits. In addition, our body
constantly reacts to a multitude of signals, be it
external or internal signals.
Two body systems are responsible for dealing with
these signals and controlling the state of
homeostasis
•  Endocrine system : releases hormones into the
blood stream, with a slow action response
•  Nervous system : communicates by means of electrical
signals, resulting in an immediate response
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Nervous System
The nervous system has 3 overlapping functions:
Sensory : uses sensory receptors to detect
internal and external changes (stimuli)
Integrative : analyzes the sensory information,
stores it and makes decision
Motor : responds to stimuli by initiating muscular
contractions or glandular secretions
The branch of Neurology is the study of the normal and
disordered nervous system
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Organization of the Nervous System
The Central Nervous system (CNS)
•  consists out of the Brain and Spinal Cord (integrating
and command center )
•  it is connected to the sensory receptors, muscles and
glands in the Peripheral Nervous system
The Peripheral Nervous system (PNS)
•  consists out of cranial ( arise from the brain) and spinal
( originate from the spinal cord) nerves
•  they carry impulses in and out of the CNS
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The Peripheral Nervous system
The Sensory division
•  the input component ( from sensory receptors to the CNS)
•  contain the afferent nerves
•  somatic afferent part : input from skin, skeletal muscle and joints
•  visceral afferent part: input from the organs and glands
The Motor division
•  the output component ( from CNS to the muscles, glands)
•  contain the efferent nerves
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The Motor division
The motor division of the PNS has an additional two functional
subdivisions
The Somatic (motor)Nervous system
•  also called the voluntary nervous system
•  composed of somatic motor nerve fibers that conduct
impulses from CNS to skeletal muscles
The Autonomic Nervous System
•  also called involuntary nervous system
•  consist of visceral motor nerve fibers that regulate the
activities of smooth muscles, cardiac muscles and glands
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The Autonomic Nervous System
The Autonomic Nervous System
•  Sympathetic :
•  usually involves expenditure of body energy, stimulates
•  fight or flight response
•  Parasympathetic :
•  restores and conserves body energy, slows down or inhibits
•  referred to as the rest and digest
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Nervous system
Sensory Division
Afferent or
Sensory Nerves
Motor Division
Central NS
Efferent or
Motor Nerves
Somatic Division
Somatic Division
Visceral Division
Autonomic Division
Peripheral NS = Sensory and Motor
Division and corresponding nerves
Sympathetic
Parasympathetic
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Nervous system
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Nervous system
Organization of the Nervous System
Central Nervous System (CNS)
(brain and spinal cord)
Peripheral Nervous
System (PNS)
(neural tissue
outside the CNS)
Integrate, process, and coordinate
sensory data and motor commands
Sensory information
within
afferent division
Motor commands
within
efferent division
includes
Somatic nervous
system (SNS)
Autonomic
nervous system (ANS)
Parasympathetic
division
Effectors
Receptors
Special sensory
receptors
monitor smell, taste, vision,
balance, and hearing
Visceral sensory
receptors
monitor internal organs
Somatic sensory
receptors
monitor skeletal
muscles, joints, and
skin surface
Skeletal
muscle
Sympathetic
division
•  Smooth
muscle
•  Cardiac
muscle
•  Glands
•  Adipose
tissue
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Histology of the Nervous System
Nervous tissue is made up of two principle types of
cells
•  Neurons : the excitable nerve cells that
conduct the electrical signals
•  Supporting cells: support, nurture and protect
the neurons (also called Neuroglial cells)
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Neurons
Neuron
Anatomy
Axons: undergo action potentials to deliver information,
typically neurotransmitters, from the axon terminals.
Dendrites: receive information (the neurotransmitters)
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Figure 12-2a The Anatomy of a Multipolar Neuron.
Neuron Anatomy
Dendrites
Perikaryon
Nucleus
Cell body
or
Soma
Telodendria
Axon
This color-coded figure shows the four
general regions of a neuron.
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Neuron Anatomy
An understanding of neuron function
requires knowing its structural components.
Nissl bodies (RER and
free ribosomes)
Dendritic branches
Mitochondrion
Axon hillock
Initial segment of
axon
Axolemma
Axon
Telodendria
Direction of action potential
Golgi apparatus
Neurofilament
Nucleolus
Axon
terminals
Nucleus
Dendrite
See Figure 12–3
Presynaptic cell
Postsynaptic cell
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Neuronal Synapse
Synapse: a special site where
two neurons communicate via
neurotransmitters (= chemical
messengers)
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NEURONAL COMMUNICATION
Presynaptic membranes “deliver
information” in the form of
neurotransmitters.
Postsynaptic membranes
“receive information” because
they have receptors for
neurotransmitters.
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Axonal Transport
Communication between cells and along an axon is in the form of
electrical signals.
However, an axon also transports molecules up and down the long
pathway in order to deliver material to and from the axon terminals
( from cell body towards axon terminals = anterograde transport
the other way around = retrograde transport)
Axon terminal has for example
no Nissl bodies ; thus no
means to produce proteins !
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Nervous
system
Axonal Transport
This axonal transport up and down
the axon is referred to as
axoplasmic transport .
Both Anterograde and Retrograde
transport is quite fast and uses
ATP fueled motor molecules such
as Kinesin and Dynein, motor
proteins that “carry” cargo via
microtubules that run along the
axon.
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Structural Classification of Neurons
Neurons come in different forms
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Structural Classification of Neurons
Typical Sensory
neuron
Anaxonic neuron
Typical motor
neuron
Multipolar neuron
Unipolar neuron
Bipolar neuron
Dendritic
branches
Dendrites
Dendrites
Initial
segment
Cell body
Axon
Dendrite
Cell body
Cell body
Axon
Axon
Cell
body
Axon
Axon
terminals
Axon
terminals
Axon
terminals
a Anaxonic neurons have more
than two processes, and they
are all dendrites.
b
Bipolar neurons have
two processes separated
by the
cell body.
c
Unipolar neurons have a
single elongated process, with
the cell body located off to
the side.
d
Multipolar neurons have
more than two processes;
there is a single axon and
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multiple dendrites.
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Functional Classification of Neurons
•  Sensory neurons (afferent neurons)
•  deliver information from exteroceptors, interoceptors, or
proprioceptors to wards the CNS
•  Somatic sensory neurons bring information in from skin, muscle and
joint receptors
•  Visceral sensory neurons are connected to interoceptors (receptors
inside organs)
•  Motor neurons (efferent neurons)
•  Form the efferent division of the PNS
•  Somatic motor neurons deliver impulses to skeletal muscles
•  Visceral motor neurons deliver impulses to effectors of the autonomic
nervous system
•  Interneurons (association neurons)
•  Located entirely within the CNS, involved in higher functions
•  Distribute sensory input and coordinate motor output
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Functional Classification of Neurons
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NeuroGlial Cells in CNS
There are Four types of neuroglia in the CNS
Ependymal Cells
Cross Section of
Spinal Cord
•  These are specialized epithelial cells that line the ventricles of the brain and
the central canal within the spinal cord.
•  They are instrumental in the production of the cerebrospinal fluid and in
circulating this fluid around.
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NeuroGlial Cells in CNS
Astrocytes
•  Only found in CNS and perform a variety of functions
•  Stabilize brain capillaries and blood brain barrier
•  Repair / prevent injury
•  Control Interstitial area by mopping up and recycling
neurotransmitters, regulate Na+ and K+ ions, release
chemicals that enhances communications
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NeuroGlial Cells in CNS
Oligodendrocytes
•  Only found in CNS
•  Are instrumental in forming the insulating coating
around axons = myelin sheaths
•  This speeds up electrical transmission
Microglia
•  Only found in CNS
•  Very small and migrate through neural tissues
•  Function like macrophages and remove debris, waste
products and pathogens
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NeuroGlial Cells in CNS
Gray matter
White matter
CENTRAL CANAL
Ependymal
cells
Gray
matter
Neurons
Microglial
cell
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NeuroGlial Cells in CNS
Gray matter
White matter
Myelinated
axons
Internode
Myelin
(cut)
White
matter
Axon
Oligodendrocyte
Astrocyte
Axolemma
Node
Unmyelinated axon
Basement
membrane
Capillary
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NeuroGlial Cells in PNS
Schwann cells or Neurilemmocytes
•  Only found in PNS
•  Have similar function as oligodendrocytes and
form the myelin sheaths (neurilemma) around
axons.
Satellite cells or Amphicytes
•  Only found in the ganglia of the PNS
•  Function is similar to that of astrocytes
•  Regulate environment around neuron cell bodies
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NeuroGlial Cells in PNS
node
Many Schwann cells are needed to cover one axon.
The space between the Schwann cells are called the
Nodes (exposed axon membrane is called axolemma).
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Figure 12-7c Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath.
NeuroGlial Cells in PNS
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A Schwann cell first surrounds a
portion of the axon within a groove of
its cytoplasm.
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The Schwann cell then begins to
rotate around the axon.
As the Schwann cell rotates, myelin is
wound around the axon in
multiple layers, forming
a tightly packed
membrane
Schwann cell
Myelin
Axon
Schwann cell cytoplasm
Stages in the formation of a myelin sheath by a single Schwann cell along a portion of
a single axon.
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Important Additional Definitions
!  White matter refers to the aggregation of myelinated processes
in the brain
!  Gray matter is the combination of nerve cell bodies, dendrites,
axonal terminals or bundles of un-myelinated axons and
neuroglia in the brain
•  A nerve fiber is the terminology for a single axon.
•  A nerve is a bundle of nerve fibers , surrounded by connective tissue, and
running within the PNS.
•  Tracts are bundles of nerve fibers within the CNS .
•  Ganglia are Nerve cell bodies clustered together in the PNS
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•  A nucleus (nuclei) is (are) a collection of nerve cell bodies within the CNS
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