Download Slide 1

Muscular System Functions
 Body movement (Locomotion)
 Maintenance of posture
 Respiration
*Diaphragm and intercostals contractions
 Communication (Verbal and Facial)
 Constriction of organs and vessels
 Heart beat
 Production of body heat (Thermogenesis)
Typical cells
Muscle cell=fiber
Plasma membrane
Sarcolemma
Cytoplasm
Sarcoplasm
Endoplasmic
reticulum
Sarcoplasmic
reticulum (SR)
Many mitochondria
Multiple nuclei
Muscle cell structures not found in other
cells
 Myofibrils: bundles of very fine fibers
 Thick and thin myofilaments: very fine fibers that make
up myofibrils
 Sarcomere: segment of myofibril between two Z lines;
contractile unit
 T tubules: transmit electrical impulses through cell
Myofilaments
4 protein molecules that make up
myofilaments: Myosin, actin, tropomyosin,
troponin
Thin filaments: actin, tropomyosin, troponin
Thick filaments: mostly myosin
Properties of Muscle
Excitability: Capacity of muscle to respond to a
stimulus
Contractility: Ability of a muscle to shorten and
generate pulling force
Extensibility: Ability stretches when pulled
Elasticity: Ability to return to original shape and
length after contraction or extension
Muscle structure
Connective Tissue Sheaths
Connective Tissue (CT) of a Muscle
Epimysium: Dense regular CT surrounding entire muscle
*Separates muscle from surrounding tissues and organs
Perimysium: Collagen and elastic fibers surrounding a group of
muscle fibers called a fascicle
*Contains blood vessels and nerves
Endomysium: Loose CT that surrounds individual muscle fibers
*Also contains blood vessels and nerves
*Collagen fibers of all 3 layers come together at each end of muscle
to form a tendon or aponeurosis.
Motor neurons
*Stimulate muscle fibers to contract
*Neuron axons branch so that each
muscle fiber
(muscle cell) is innervated
*Form a neuromuscular junction
Capillary beds surround muscle fibers
*Muscles require large amount of energy
*Extensive vascular network delivers
necessary
oxygen and nutrients and carries away metabolic
waste produced by muscle fibers
Energy for Muscle Contractions
*ATP: adenosine triphosphate
*CP: creatine phosphate
Glucose & Oxygen
*Glucose stored in form of glycogen in muscle
*Excess oxygen molecules in sarcoplasm bound
to myoglobin
Anaerobic respiration
Allows body to avoid use of oxygen
in short term
Produces lactic acid
Accumulation of
lactic acid in
muscles causes burning sensation
Types of Muscle
Skeletal
* Attached to bones
* Makes up 40% of body weight (Women’s skeletal muscle makes up
36% of their body mass, Men’s skeletal muscle makes up 42% of their
body mass)
* Responsible for locomotion, facial expressions, posture, respiratory
movements, other types of body movement
* Voluntary in action; controlled by somatic motor neurons
Smooth
* In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
* Functions: propel urine, mix food in digestive tract, regulating blood
flow
* Controlled involuntarily by endocrine and autonomic nervous
systems
Cardiac
* Heart: major source of movement of blood
Basic Features of a Skeletal Muscle
Muscle attachments
* Most skeletal muscles run from one bone to another
* One bone will move – other bone remains fixed
* Origin – less movable attachment
* Insertion – more movable attachment
* Muscles attach to origins and insertions by connective tissue
Fleshy attachments – connective tissue fibers are short
Indirect attachments – connective tissue forms a tendon
Skeletal Muscle Structure
*Composed
of muscle cells
(fibers), connective tissue,
blood vessels, nerves
*Fibers
are long, cylindrical,
and multinucleated
*Tend to be smaller diameter in
small muscles and larger in
large muscles. 1 mm - 4 cm in
length
*Striated appearance
*Nuclei are peripherally located
Muscle Fiber Anatomy
Sarcolemma - cell membrane
* Surrounds the Sarcoplasm (cytoplasm of fiber)
* Punctuated by openings called the transverse
tubules (T-tubules)
Myofibrils -cylindrical structures within muscle fiber
* Are bundles of protein filaments (=myofilaments)
* Two types of myofilaments
1. Actin filaments (thin filaments)
2.Myosin filaments (thick filaments)
– When myofibril shortens, muscle shortens
(contracts)
Sarcoplasmic Reticulum (SR)
SR
is an elaborate, smooth endoplasmic
reticulum
 Runs longitudinally and surrounds each
myofibril
SR stores Ca++ when muscle not contracting
When stimulated, calcium released into
sarcoplasm
SR membrane has Ca++ pumps that function to
pump Ca++ out of the sarcoplasm back into the
SR after contraction
Smooth Muscle
*Cells are not striated
*Fibers smaller than those in
skeletal muscle
*Spindle-shaped;
single,
central nucleus
*More actin than myosin
*No sarcomeres
*Not
arranged
as
symmetrically
as
in
skeletal muscle, thus no
striations.
Smooth Muscle
• Grouped into sheets in walls of hollow organs
• Longitudinal layer: muscle fibers run parallel to organ’s long
axis
• Circular layer: muscle fibers run around circumference of the
organ
• Both layers participate in peristalsis
Cardiac Muscle
 Found
only in heart where it forms a thick layer called the
myocardium
 Striated fibers that branch
 Each cell usually has one centrally-located nucleus
 Fibers joined by intercalated disks
Disorders of Muscle Tissue
*Muscle Fatigue
*Lack of oxygen causes ATP deficit
*Lactic acid builds up from anaerobic
respiration
*Muscle Atrophy
*a decrease in the mass of the muscle
*Weakening and shrinking of a muscle
*May be caused
*Immobilization
*Loss of neural stimulation
Disorders of Muscle Tissue
* Muscle Hypertrophy
*Enlargement of a muscle
*More capillaries
*More mitochondria
*Caused by
* Strenuous exercise
* Steroid hormones
* Muscle Tonus
* Tightness of a muscle
* Some fibers always contracted