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VAN 504, Lecture 03
Muscular tissue types and their
functional peculiarities, Neurons,
nerve fiber and ganglion
Overview of Muscle Tissue
• There are three types of muscle tissue
– Skeletal muscle
– Cardiac muscle
– Smooth muscle
• These muscle tissues differ in the structure of
their cells, their body location, their function, and
the means by which they are activated to
contract
• Without these muscles, nothing in the body would
move and no body movement would occur
• All skeletal and smooth muscle cells are
elongated and are referred to as muscle fibers
• Muscle contraction depends on two types of
myofilaments, actin and myosin
• All prefixes of myo or mys and sarco reference
muscle
• highly cellular
• well-vascularized
Similarities
(Skeletal & Smooth Muscle)
1. cells
– elongated
– called muscle fibers
2. muscle contraction
– dependent on two kinds of myofilaments
• actin
• myosin
3. muscle terms
– myo, mys, sarco
• sarcolemma - PM of muscle
• sarcoplasm - muscle fiber cytoplasm
Skeletal Muscle Tissue
• striated
• packed by connective tissue sheets into
skeletal muscles
• fibers are longest
– stripes (striations)
• location
– attached to and covers bony skeleton
• controlled voluntarily
Skeletal Muscle Tissue
Cardiac Muscle Tissue
• Cardiac muscle occur only in the heart
• The muscle is striated but involuntary
• Cardiac fibers are short, fat, branched and
interconnected
• Cardiac muscle cells are interlocked by intercalated
discs
• function as a single Cardiac Muscle Tissue unit
Smooth Muscle Tissue
• It is found in the walls of hollow organs such as
the stomach, urinary bladder, and intestines.
• It has no striations
• It is not subject to voluntary control
Differences in Contractions
• Skeletal muscle can contract rapidly but tire
easily and must be rested.
• Skeletal muscle contractions vary in force
depending on use.
• Cardiac muscle contracts at a steady rate but
can accelerate to cope with demand.
• Smooth muscle contracts in steady, sustained
contractions and continues on tirelessly.
Muscle Functions
• Muscle performs four important functions in
the body:
– Producing movement
– Maintaining posture
– Stabilizing joints
– Generating heat
Producing Movement
• Movement results from skeletal muscle
contraction.
• Skeletal muscle are responsible for all
locomotion and manipulation.
• Allows to interact or react with external
environment.
• It controls eye movement, facial expression
(skeletal); circulation (cardiac), and moves gas,
liquids, and solids through organs (smooth)
Maintaining Posture
• Skeletal muscles are utilized constantly to
maintain sitting, standing, and moving
postures.
• Curves of the spinal column are shaped by the
interplay of skeletal muscle and gravity
Stabilizing Joints
• Skeletal muscle provide the dynamic stability
of joints
• Many joints are poorly reinforced by ligaments
and connective tissue
• Many joints have non complementary surface
which do not contribute to stability
Generating Heat
• Muscles generate heat as they contract
• The heat generated is vitally important to
maintain normal body temperature
• Skeletal muscle generates most of the heat
because it represents 40% of body mass
• Excess heat must released to maintain body
temperature
Functional Characteristics
1. Excitability & Irritability
– ability to receive & respond to a stimulus
• stimulus
– environmental change that arises inside or outside the body
– usually a chemical
» NT, hormone, change in pH
• response
– generation of electrical impulse
» passes along the sarcolemma contraction of muscle cells
2. contractility
–
ability of a muscle to shorten forcibly when adequately stimulated
3. extensibility
–
ability of a muscle to be stretched or extended
•
even beyond its resting length when relaxed
4. elasticity
–
ability of a muscle fiber to recoil & resume its resting length
• after being stretched
Skeletal Muscle
Anatomy of a Skeletal Muscle
• Each skeletal
muscle is a
discrete organ
with thousands of
fibers
• Muscle fibers
predominate the
tissue
• it also, contains
blood vessels,
nerve fibers, and
connective tissue
Connective Tissue Wrappings
• Each muscle fiber is
wrapped by fine sheath
of areolar connnective
called endomysium
• Several fibers are
gathered side by side into
bundles called fascicles
•Each fascicle is bound by
collagen a fiber layer
called the perimysium
Connective Tissue Wrappings
• Fascicles are bound
by a dense fibrous
connective tissue
layer called the
epimysium
• The epimysium
surrounds the entire
muscle
• External to the
epimysium is the
deep fascia that
binds muscles into
functional groups
Connective Tissue Wrappings
• All the connective tissue
layers are continuous with
one another as well as with
the tendons that join
muscles to bone
• When muscle fibers
contract they pull these
connective tissue sheaths
which in turn transmit the
force to the bone to be
moved
• Connective tissues supports
each cell
Nerve and Blood Supply
• Normal activity of skeletal muscle is totally
dependent on its nerve and blood supply
• Each skeletal muscle fiber is controlled by a
nerve ending (neuromuscular junction)
• Contracting muscle fibers use huge amounts
of energy which requires a continuous supply
of oxygen and nutrients
• In general, each muscle is served by an artery
and one or more veins
Attachments
• Most muscles span joints and have at least two
attachments an origin and an insertion
• Origin
– Attachment of a muscle that remains relatively fixed
during muscular contraction
– Generally a more proximal or axial location
• Insertion
– Attachment of a muscle that moves during muscular
contraction
– Generally a more distal or appendicular attachment
Attachments
• Direct attachments have the epimysium
attaching directly to the periosteum of the
bone or perichondrium of a cartilage.
• Indirect attachments have the epimysium
attaching to a tendon or an aponeurosis.
• Temporalis has both muscle attachments.
The Motor Unit
• Each muscle is served by at least one motor
nerve which contains hundreds of motor
neuron axons
• As a nerve enters a muscle it branches into a
number of axonal terminals, each of which
forms a neuromuscular junction with a single
nerve fiber
• A motor neuron and all the muscle fibers it
supplies is called a motor unit
The Motor Unit
• When a motor neuron
transmits an electrical
impulse, all the muscle
fibers that it innervates
respond by contracting
• The average number of
muscle fibers per unit is
150, but it ranges from
4 to several hundred
The Motor Unit
• Muscles that exert
very fine control
have small motor
units (eyes, fingers)
• Large muscles of
locomotion and
weight bearing
have large motor
units and as a
consequence have
less precise control
The Motor Unit
• The muscle fibers in a
unit are not clustered
together but rather are
spread throughout the
entire muscle
• Stimulation of a single
unit causes a weak
contraction of the
entire muscle
• This allows control of
the intensity of the
contraction
Skeletal Muscle Fiber
• Skeletal muscle fibers are
long and cylindrical
• These cells are of huge
Diameter of 10-100 m
up to 10 times average
cell size
• Length is phenomenal
for a cell - from several
centimeters to dozens of
centimeters in long
muscles
Microscopic Anatomy of a
Skeletal Muscle Fiber
• Muscle fiber
– Are long, cylindrical cell
– Have multiple oval nuclei
• multinucleate
– arranged just beneath sarcolemma
• Myofibril
– Rod like bundle of contractile filaments
– hundreds to thousands in a single muscle fiber
– make up 80% of cell volume
Microscopic Anatomy of a
Skeletal Muscle Fiber
• striations
– repeating series of dark A bands and light I bands
• nearly perfectly aligned
• give cells its striped (striated) appearance
– located along length of each myofibril
• sarcomere
– smallest contractile unit of a muscle fiber
– consists of thick (myosin) filaments & thin (actin) filaments
• arranged in a regular array
– region of myofibril between two successive Z discs (lines)
High microscope magnification of sarcomeres
within a myofibril
Microscopic Anatomy of a
Skeletal Muscle Fiber
• Z disc ~ Z line
– darker area of midline interruption in the I band
– coin-shaped sheet
• composed of proteins
– connectins
– anchors the thin filaments
– connects each myofibril to the next throughout
the width of muscle cell
Microscopic Anatomy of a
Skeletal Muscle Fiber
• Thick filaments
– composed primarily of protein myosin
• each molecule has a rod like tail terminates in two globular
heads
– head
- crossbridges
- serve as actin binding sites
- contain ATP binding sites & ATPase enzymes that split ATP to
generate energy for contraction
- link the thick & thin myofilaments together during contraction
– Myosin molecules are bundled together
• tails form central part of the filament
• heads face outward & in opposite directions at each end
Microscopic Anatomy of a
Skeletal Muscle Fiber
• Thin filaments
– composed chiefly of actin
• polypeptide subunits of actin
– globular actin or G actin
- contain active sites to which myosin crossbridges attach
during contraction
– also contains regulatory proteins
• help to control myosin-actin interactions involved in
contraction
– two strands of tropomyosin
– troponin
Tropomyosin
•
•
•
•
rod-shaped protein
spirals about actin core
helps stiffen it
successive molecules arranged end to end
along actin filaments
• relaxed muscle
– block actin’s active sites
• so myosin heads cannot bind to thin filaments
Troponin
• Three polypeptide complex
– one inhibitory subunit
• binds to actin
– one positioning subunit
• binds to tropomyosin
– helps position it onto actin
– one subunit binds to Ca
Microscopic Anatomy of a
Skeletal Muscle Fiber
Microscopic Anatomy of a
Skeletal Muscle Fiber
Microscopic Anatomy of a
Skeletal Muscle Fiber
Microscopic Anatomy of a
Skeletal Muscle Fiber
Actin & Myosin Filaments
Organization of
Skeletal Muscle Fibers
Level 1: Skeletal Muscle
Level 2: Muscle Fascicle
Level 3: Muscle Fiber
Level 4: Myofibril
Level 5: Sarcomere
Types of Skeletal Muscle Fiber
• Red slow twitch fibers contract slowly, are
resistant to fatigue as long as oxygen is
present
• Deliver prolonged contractions
• Used in many of the postural muscles of the
axial skeleton
• Because their fibers are thin, slow twitch
fibers do not generate much power
Types of Skeletal Muscle Fiber
• White fast twitch fibers are pale because they contain
little myoglobin
• The fibers are about twice the diameter of red slow
twitch fibers, they contain more myofibrils and
generate more power
• The fibers depend on anaerobic pathways (no oxygen
used) to make ATP
• They contain few mitrochondria or capillaries but have
many glycosomes containing glycogen as a fuel source
• White fast twitch fibers contract rapidly and tire quickly
Types of Skeletal Muscle Fiber
• Intermediate fast twitch are sized between the
other two fiber types
• Like white fibers they contract quickly; like slow
twitch they are oxygen dependent and have a
high myoglobin content and a rich supply of
capillaries
• They are more powerful than red fibers, but not
as strong as white
• Used to move the body for long periods of time in
activities.
Smooth Muscle Tissue
• Nonstriated, involuntary
• location
– walls of hollow visceral organs
• stomach, urinary bladder, respiratory passages
• function
– force fluids & other substances through internal
body channels
• controlled involuntarily
• contractions are slow & sustained
Smooth Muscles
• Smooth muscle
lacks the courser
connective tissue
seen in skeletal
muscle
• Small amounts of
endomysium is
found between
smooth muscle
fibers
Smooth Muscles
• Smooth muscles are
organized into sheets of
closely apposed fibers
• These sheets occur in the
walls of all but the
smallest blood vessels
and in the walls of hollow
organs of the respiratory,
urinary digestive and
reproductive tracts
Smooth Muscles
• In most cases two sheets
of muscles are present
with their fibers aligned
at right angle to each
other
• These forms the
longitudinal (long axis)
and circular (encircling)
layer
• These two layers squeeze
the contents of the organ
Smooth Muscle Cell
Smooth Muscle
Cardiac Muscle Tissue
• Striated, involuntary
• location
– found only in heart
• constitutes the bulk of the heart wall
• controlled involuntarily
– neural control allows a shift into high gear for short
periods
• cells
– uninucleate
• branch & fit tightly together at junctions (intercalated discs)
• contracts at a steady rate
– pacemaker of heart (SA node)
Muscle cells are not fused they connect by cell junctions called
intercalated discs and have a branching pattern. Each cell
has one to
two nuclei in the center. The cells have
sarcomeres which makes the tissue look striated.
This tissue has an abundance of mitochondria to prevent fatigue.
Contractions are also triggered by calcium ions. Not all cells are
innervated, cells can independently have rhythmic contractions.
The length of the cells is proportionally related to the force it
produces when it contracts
Cardiac Muscle
Cardiac Muscle
Neuron Classification Schemes
• Neurons can be classified according to
– Number of axon processes:
• Unipolar: one stalk that splits into two branches
• Bipolar: one axon, one dendritic tree
• Multipolar: one axon, many dendritic branches
– Function
• Sensory neurons carry messages toward brain
• Motor neurons carry messages to muscles
• Interneurons connect cells
– Neurotransmitter (NT) used by neuron
– Effects of NT (excitatory vs. inhibitory)
Functional Variations in Neurons
• Sensory (afferent) neurons transmit
information about the environment to the
central nervous system.
• Motor (efferent) neurons transmit commands
from the central nervous system to muscles
and glands.
• Interneurons act as bridges between sensory
and motor neurons.
Neuron Internal Structure
The Soma
Nervous Tissue
Axon
•
•
•
•
One axon three parts:
hillock,
axon,
terminal ending
Dendrites
Afferent part of the neuron that is specialized
for receiving information