Download The Muscular System

Muscular System
Chapter 6
Muscle Tissue Functions
• Producing body movements
• Stabilizing body positions
• Regulating organ volumes
– Bands of smooth muscle called sphincters.
• Movement of substances within the body
– Blood, lymph, urine, air, food and fluids, sperm.
• Producing heat
– Voluntary and involuntary (shivering) contractions
of skeletal muscle.
Properties of Muscle Tissue
• Electrical Excitability
– Ability of skeletal muscles to respond to stimulus. Skeletal
muscle contracts as a result of stimulation by nerves.
• Contractility
– Ability to contract (shorten and generate force).
• Extensibility
– Ability to be stretched without damaging tissue.
• Elasticity
– Ability to return to original shape after being stretched.
Smooth Muscle Tissue
• Histology- spindle-shaped, nonstriated fibers with one centrally
located nucleus.
• Location- walls of hollow internal structures such as blood
vessels, airways to lungs, stomach, intestines, uterus.
• Speed of Contraction- slowest.
• Function- motion.
• Nervous Control- involuntary; autorhythmic.
Cardiac Muscle Tissue
• Histology- branched, striated fibers, with one or two centrally
located nuclei and intercalated discs.
• Location- heart wall.
• Speed of Contraction- moderate.
• Function- pumps blood.
• Nervous Control- involuntary; autorhythmic.
Anatomy of
Cardiac
Muscle
Skeletal Muscle Tissue
• Histology- long, cylindrical, striated fibers with many
peripherally located nuclei.
• Location- attached primarily to bones by tendons.
• Speed of Contraction- fastest.
• Function- motion, posture, heat production.
• Nervous Control- voluntary; no autorhythmicity.
• Fascicle- a bundle of skeletal muscle fibers.
Muscle Terminology
• Origin- stable attachment of muscle to
skeleton.
• Insertion- moveable attachment of muscle
to skeleton.
• Flexor- decreases joint angle.
• Extensor- increase joint angle.
• Adductor- moves bone closer to midline.
• Abductor- moves bone away from midline.
• Levator- raises a body part.
• Depressor- lowers a body part.
Anatomy of Skeletal Muscles- Fascia
Connective Tissue and Skeletal Muscles
• Fascia- a sheet or broad band of fibrous connective
tissue that supports and surrounds organs of the body.
– Superficial fascia- loose connective and adipose tissue that
separates muscle from skin.
– Deep fascia- dense, irregular connective tissue that lines the
body wall and limbs, it also holds muscles together.
Deep Fascia
• 3 Layers of deep fascia
– Epimysium- surrounds the whole
muscle.
– Perimysium- surrounds bundles
(fascicles) of 10-100 muscle fibers.
– Endomysium- surrounds individual
muscle fibers.
• Muscle Belly- the fleshy portion of
the muscle between the tendons.
• Tendon- cord of dense, regular
connective tissue that attaches a
muscle to the periosteum of a bone.
Tendon
Bone
Deep fascia
Skeletal muscle
Epimysium
Perimysium
Muscle fiber (cell)
Perimysium
Fascicle
Endomysium
Muscle fiber (cell)
Myofibril
Muscle Fiber- elongate shaped muscle cell.
• Myofibrils- contractile elements of skeletal muscle.
• Filaments- smaller structures inside the myofibrils.
– Thin (actin) filaments (8 nanometers in diameter).
– Thick (myosin) filaments (16 nanometers in diameter).
Thin filaments
Myofibril
Terminal cisterns
Sarcoplasmic reticulum
Thick filaments
Myofibril
Filaments and Sarcomeres
• Thick (myosin) and thin (actin) filaments overlap each
other in a pattern that creates striations.
• Sarcomeres
– Contractile units in skeletal and cardiac muscle fibers.
– Extend from one Z disc to another Z disc.
Sliding Filament Theory
Skeletal Muscle Fiber Contraction
• Motor Neurons
make contact
with about 150
muscle fibers.
• Motor unit- a
motor neuron,
and all of the
muscle fibers
that it
innervates.
Neuromuscular Junction
(NMJ) or Synapse
Rigor Mortis
• Rigor mortis is a state of muscular
rigidity that begins 3-4 hours after
death and lasts about 24 hours.
• After death, Ca2+ ions leak out of the
sarcoplasmic reticulum and allow
myosin heads to bind to actin.
• Since ATP synthesis has ceased,
crossbridges cannot detach from actin
until proteolytic enzymes begin to
digest the decomposing cells.
Energy for Muscle Contraction
• ATP (Adenosine Triphosphate)- energy.
– Phosphate breakdown (anaerobic).
– Glycolysis and fermentation (anaerobic).
– Cellular respiration (aerobic).
Creatine Phosphate
• Creatine phosphate is 3-6X
plentiful than
muscles.
• Its quick breakdown
provides the P for
creation of ATP.
• Sustains maximal contraction
sec (used for 100 meter sprint).
• Creatine supplementation
more
ATP within
– Gain muscle mass but shut down bodies own synthesis.
for 15
Anaerobic Cellular Respiration
• ATP produced from the
breakdown of glucose into
pyruvic acid during glycolysis.
– If still anaerobic, pyruvic acid
is converted to lactic acid.
• Glycolysis can continue
anaerobically to provide ATP
for 30 to 40 seconds of
maximal activity (200 meter
race).
Aerobic Cellular Respiration
• ATP for any activity lasting over 30 seconds.
– If sufficient oxygen is available, pyruvic acid enters the
mitochondria to generate ATP, water, and heat.
– Fatty acids and amino acids can also be used by the
mitochondria.
• Provides 90% of ATP energy if activity lasts more than
10 minutes.
Athletics and Muscle Contraction
• Hypertrophy- increase in muscle size.
– The result of forceful muscular activity over a prolonged
period of time.
– Results in an increase in the number of myofibrils within a
muscle fiber.
Atrophy
• Atrophy- decrease in muscle size.
– The result of muscles not being used or only being
used in weak contractions.
– Causes muscle fibers to progressively shorten,
leaving body parts contracted and in contorted
positions.
Classification of Muscle Fibers
• Slow-twitch fibers
–
–
–
–
–
Designed for endurance
Contract slowly
Strong, sustained contractions
Red in color (lots of mitochondria, myoglobin, & blood vessels)
Muscles of abdomen and back (posture)
• Fast-twitch fibers
–
–
–
–
–
Designed for rapid, powerful response
Contract rapidly
Short, powerful contractions
White in color (few mitochondria, myoglobin, & blood vessels)
Muscles of the arms of legs
Aging and Muscle Tissue
• Skeletal muscle starts to
be replaced by fibrous
connective tissue and fat
beginning at age 30.
• Slowing of reflexes, loss
of flexibility, and
decrease in strength.
• Change in fiber type
from fast to slow.
Muscle Disease
• Muscular dystrophy- a broad term applied to a
group of inherited muscular disorders
characterized by progressive muscle degeneration
and weakening.
• Frequency- 1 in 3,500 males.
• Genetics- males XY, females XX.
• Treatment- none.
Mutation in DMD gene. DMD codes
for dystrophin, a protein that
protects muscle fibers.
Abnormal Contractions
• Spasm- involuntary contraction of a single muscle.
– Cramp- a painful spasm.
– Seizure- multiple spasms of a skeletal muscle.
• Tic- involuntary twitching of muscles normally under
voluntary control.
• Tremor- rhythmic, involuntary contraction of opposing
muscle groups.
• Fasciculation- involuntary, brief twitch of a motor unit
visible under the skin.
• Fibrillation- spontaneous contraction of a single muscle
fiber that is not visible under the skin.