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MUSCLE PHYSIOLOGY
CHAPTER 11
I. MUSCLES
• 600+
• 40-50% of body weight
A. 3 Types of muscle
• 1. Skeletal
• 2. Cardiac
• 3. Smooth
• **majority of chapter will be focused on
skeletal muscle
II. Functions of Skeletal
Muscle
1.
2.
3.
4.
5.
Movement
Posture
Support
Guard entrances/exits
Body Temperatures
III. Anatomy of Skeletal
Muscle
a. Skeletal muscle contains bundles of
skeletal muscle fibers.
• The cells actually called fibers
b. Components of skeletal
muscle
i. Connective tissue
ii. Blood vessels
iii. nerves
c. Connective Tissue
A. Fascia - connective tissue found underskin
and surrounding deeper organs
B. Epimysium - covers entire muscle
•
Surounded by fascia
C. Perimysium - covers fasicles or groups of
skeletal muscle fibers
•
•
Within epimysium
Tough connective tissue
D. Endomysium - covers skeletal muscle fiber
Delicate connective tissue within perimysium
MUSCLE
IV. TENDON
• Epimysium, perimysium, and
endomysium continue beyond the
muscle to form the tendon of a muscle
• Connect muscle to bone
• Tough connective tissue
• Aponeuroses - merging of tendons to
create a flat strong connective tissue
TENDON
d. Blood vessels
• Innovate muscles to provide
nourishment muscle needs to function
and rid of wastes.
e. Nerves
• Innovate muscles to control movements
IV. Overview of Skeletal
Muscle/fiber
• Composed of bundles of skeletal
muscle fibers that run entire length
• Have same structural parts as cells just
different names
a. Structures found in skeletal
muscle
i.
ii.
iii.
iv.
v.
vi.
vii.
Multinucleated
Sacrolemma
Sarcoplasm
Sarcoplasmic reticulum
Mitochondria
Myofibrils
Sarcomere
Skeletal Muscle Cell
i. multinucleated
• Muscle have many nuclei
• Allows to make ribosomes which
important for protein synthesis
ii. Sarcolemma
• Plasma membrane of muscle fiber
iii. sarcoplasm
• Cytoplasm of muscle cell
iv. Sarcoplasmic reticulum
•
•
•
•
Network of tubules and sacs
Equates to ER
Contains Calcium ions
Plays a role in muscle contraction
v. mitochondria
• Many mitochondria
• To produce ATP
vi. myofibrils
• Bundles of very fine fibers
• Extend lengthwise along skeletal fibers
• Made of thick and thin myofilaments
vii. sarcomere
• Basic unit of the muscle
• Like an osteon is to bone
V. Structure of Sarcomere
Structure cont….
• A band
– Entire length of THICK filaments
– Within A band is
• M line - line down the middle of thick filament
• H zone - middle region of THICK filaments
ONLY
 Zone of overlap - where thick and thin fibers
overlap
Structure cont….
b. I band
a. Segment that includes the Z line and
ends of THIN filaments.
b. THIN filaments ONLY
c. Z lines
• Signif a sarcomere
• Z line to Z line = 1 sarcomere
• Many sarcomeres make up a myofibril
d. Transverse Tubules
• T-tubules
• Run transversely across sarcoplasm
and rt. angles to long axis of the cell
• Formed by inward extensions of
sarcolemma
• Function - allows electrical impulses
traveling along sarcolemma to move
deeper into the cell
e. Triad
• T-tubules sandwiched between 2
sarcolemma reticulum
• Important because impulse travels
through t-tubules and stimulates release
of Ca+ needed for contraction
Sarcomere
Sarcomere
Triad
f. Myofibrils
• Each muscle fiber contains thousands
of subunits called myofibrils
• Within myofibril are thick and thin
myofilaments
i. Thin myofilament
• Made from 3 proteins
1. Actin
2. Tropomyosin
3. troponin
1. Actin
• Globular
• Bead like strand of protein
• Twists around each other to form bulk of
thin filament
• Chemically attracted to myosin
2. Tropomyosin
• Strand of protein that twists around
actin
3. Troponin
• Spaced at intervals
• Blocks active sites (on actin) needed for
muscle contraction
Actin, troponin, tropomyosin
Thin filament
ii. Thick Filament
1. Myosin
– Shaped like golf clubs
2. Long flat shafts bundled together to
form their crossbridges (heads)
– Heads stick out and are chemically
attracted to actin active site of thin filament
Myosin
VI. Muscle Physiology
A. Sliding filament theory
i. As a result of contraction
H zone gets smaller
I band smaller
Zone overlap larger
Z lines closer together
A band - same
Fibers shorten by 30%
When I band completely gone, contraction ends.
Thin filaments sliding toward center of sarcomere
along side of the thick filaments
b. Nervous Stimulation of
contraction
i. Motor neuron - nerve that sends signal
ii. Action potential - the actual signal
iii. Motor end plate-where motor neuron
meets sarcolemma(forms
neuromuscular junction)
iv. Neuromuscular junction- contact point
between nerve and muscle
CONTRACTION
• Muscle contraction has 3 phases
– Latent
– Contraction
– relaxation
i. Latent stage of contraction
a. Action potential (nerve impulse) of
motor neuron reachs motor end plate,
neurotransmitters (acetylcholine)
released into synaptic cleft -goes
across sarcolemma to excite cell
b. The Ach diffuses across synaptic cleft
and binds to receptors which changes
the sacrolemma
i. Latent Stage cont….
c. Impulse travels over sarcolemma
inward along T-Tubules which release
Ca+ from Sarcoplasmic Reticulum
(adjacent to T-tubules)
ii. Contraction
• The Ca+ combine with troponin
molecules of the thin filaments which
causes tropomyosin to shift and expose
active sites of actin
b. Once active sites exposed, the myosin
heads (containing lots of ATP) of thick
filament bind to actin and bend. This
pulls thin filaments past thick filaments
ii. Contraction cont…
c. Each head then releases itself and
binds to the next active site and pulls
again (until ATP ends or I band
disappears).
d. Thin filaments slide toward center of
sarcomere to shorten each myofibril
which shortens the muscle
iii. Relaxation
a. Sarcoplasmic reticulum pumps Ca+
back into sacs (within millisec. Most
Ca+ are recovered).
b. Ca+ ions stripped off troponin which
hides active site and myosin can’t
attach, so filaments not being pulled
and the relax.
videos
• http://video.google.com/videosearch?gbv=2&
hl=en&q=%20latent%20phase%20of%20cont
raction&ie=UTF8&sa=N&tab=iv#q=sarcomere+contraction&hl
=en&emb=0
• http://video.google.com/videosearch?gbv=2&
hl=en&q=%20latent%20phase%20of%20cont
raction&ie=UTF8&sa=N&tab=iv#q=sarcomere+contraction&hl
=en&emb=0
• http://www.youtube.com/watch?v=EdHzKYDx
rKc&NR=1
d. Energy source
• ATP
– Provides nrg to pull thin myofilaments
during contraction
– Muscles must continually make ATP
because can only store small amounts of it.
– When run out of ATP contraction stops and
relaxation begins
e. Length-tension relationship
• Amount of tension is proportional to
number of cross bridges interacting with
the thin filament
• The number of cross bridges interacting
is determined by degree of overlap
between thick and thin filaments
• When muscle fiber stimulated to
contract, only myosin heads with in
zone of overlap can bind to active sites
to produce tension.
f. Rigor Mortis
• When die, circulation stops and skeletal
muscles deprived of nutrients and
oxygen.
• Within few minutes skeletal fibers run
out of ATP and SR can’t pump Ca+
back into SR so cross bridges stay
attached and stay contracted or stiff
Motor Unit
Motor unit - nerve and muscle cell
a single motor neuron divides into branches
1 neuron can control a few muscle fibers
1 neuron can control hundreds of muscle
fibers
**The fewer the # of fibers controlled by
neuron, the more precise the movement
VII. Muscle Tone
• Tone of muscle due to continual, partial contraction
• Small # of fibers contracted causing a taut (tight)
muscle
• This is tonic contraction
– Important for posture
– Ex. Loss of consciousness - unable to maintain posture
• Muscle with more than normal tone - spastic
• Muscles with less tone = flaccid
• Muscle tone maintained by negative
feedback
– Sensors - stretch sensors in muscle/tendon
– Integrator - spinal cord/brain
– Effectors - somatic motor neurons
– Ex. Stretching - if stretch beyond limits, sensors
in muscle tendon detect this and send signal to
spinal cord/brain and tell somatic neuron to pull
back
– This is called a spinal reflex
VIII. Classification of Muscle
Contraction
• Skeletal muscles contract with varying
degrees of strength
• 5 factors contribute to this principle:
– 1. Amt ATP in muscle fiber
– 2. # fibers contracting simultaneously (more
fibers-stronger contraction
– 3. Intensity and freq. of motor neuron stimul.
• More motor units recruited, stronger contraction
• 4. Length-tension relshp
– Muscle can’t contract strongly if initial length is
shortened (can’t slide much more)
– Muscles can’t contract strongly when
overstretched b/c myosin heads can’t interact
with actin
– Best contraction occurs when muscle is optimal
length
– Ex. Biceps, slightly bent is greatest contraction
• 5. Amount of load imposed on muscle
– Heavier load, harder contraction
– Ex. Hold a book on hand, then hold a pencil on
hand. --- body uses negative feedback to
control this.
Types of contractions
1.
2.
3.
4.
Isotonic - “same tension”
Isometric - “same length”
Tetnus
Treppe
Isotonic
• Tension of muscle remains the same as
length of muscle changes
• 2 types of isotonic contraction
– 1. Concentric - shortening of muscle
– Ex. Pick up a book - same tension throughout the
movement, but muscle shortens
- 2. Eccentric - lengthening of muscle
- Ex. When lower a book, same muscles but you are actually
lengthening them.
Ex. Walking - Flex knee then extend it, flex hip
then extend it
Isometric
• Muscle length remains same while muscle
tension increases.
• Ex. Push against a wall - not moving object
b/c load is too heavy, tighten muscles but not
lengthening or shortening
Tetnus
• Smooth sustained contraction
• Series stimuli come so fast that muscle
never has time to completely relax
• This caused by coordinated contractions by
different motor units within the muscle
• Contraction in muscle fibers overlap causing
a sustained contraction
• Ex. Posture, movement of most muscles
• Our nervous system “smooths” out these
movements so we don’t hurt ourselves
Treppe
• “staircase phenomenon”
• Gradual increase in strength of contraction
• This accounts for the fact a muscle contracts
more forcefully after it contracts a few times
(after it is warmed up)
• This is why warm up is important
IX. Types of Skeletal Muscle
Fibers
• 3 types of muscle fibers
• 1. Fast - “white”
• 2. Slow - “red”
• 3. Intermediate -
Fast
• Not a lot of myoglobin (white)
• Fire faster b/c have faster type of myosin
And more efficient SR and t-tubules
• Deplete ATP faster
• Less mitochondria
• Can’t contract long prds.
• Generates tremendous force when contract
Slow
• Contain high amts myoglobin (red)
• Myosin heads react slower
• Can keep up with ATP demand so don’t
fatigue as easily
• Large amts mitochondria and oxygen
• Can sustain contractions longer
• Ex. Posture muscles
Intermediate
• Combo slow and fast
• More fatigue resistant then fast, less then
slow
• Ex. Calf muscles, quads,
X. Exercise and muscle
• Improves muscle tone, strength and posture
• More efficient heart and lungs – Decreases resting heart rate, less fatigue
• Less fatigue
– More endurance
– Do things more efficiently
• Hypertrophy
– Increase in muscle size
– Increase in # myofilaments in each fiber
NRG use and level of muscle
activity
A. Muscle fatigue depend on
–
–
–
–
Glucose, oxygen supplied
Muscles store glucose in form called glycogen
Myoglobin attracts oxygen
More of each, less fatigue
B. Lactic Acid removal
– Anaerobic resp. results in formation of lactic acid
– Lactic acid accumulates in muscle causing burning
sensation
– Some lactic acid goes to liver- converted back to glucose
d. Muscle atrophy
– When don’t use muscles they get smaller
e. Physical conditioning
aerobic - endurance training
doesn’t create hypertrophy
anaerobic heavy weight training
produces hypertrophy
XII. Cardiac Muscle
• Aka striated involuntary muscle
• Found only in heart
• Made of cardiocytes
Function:
Pumps blood rhythmically and continuously
Structure:
•Cardiocytes
•Striated
•Intercalated discs- allows cells to “pump” as
one unit
•Self excited cells
– Contractions are longer b/c calcium remains in
SR longer
•Diads
– T-tubules are larger and forms a diad with SR
•Pacemaker cells – stimulate electrical
impulses
Smooth Muscle
•
•
•
•
Small tapered cells with single nuclei
Does not have t-tubules
Lack striations
Filaments arranged differently
– Thin criss-crossed fibers
– When myosin pulls the thin filaments, the muscle
“balls up”.
• Most flexible of all types of muscle
2 types of smooth muscle
1. Visceral
– Single unit
– Units join together to form continuous large
sheet of muscle
Ex. Digestive, urinary, reproductive
– Self excited that spreads across entire tissue,
like a wave of contraction (peristalsis)
Peristalsis- moves food along digestive tract,
urine to bladder and birth contractions
2. Multi unit
– Not act as a single unit
– Each individual unit – fiber does not generate its
own impulse
– Responds to nerve input
ex. Walls of blood vessels, arector pili
Aging and Muscular System
• Loss of muscle mass
(by age of 80 loss of 50%)
• Most muscle fibers develop into intermediate
fibers (muscles slower)
• Muscle fibers contain less ATP, glycogen,
and myoglobin
• Skeletal muscles become less flexible
• Tolerance of exercise less
• Ability to recover from musclular injuries
decreases
Muscle Disorders
1. Myopathies – muscle disorders
2. Strain – overexertion or trauma to muscle,
overstretch or tear muscle fibers
3. Myositis – muscle inflammation
4. Fibromyositis- tendon inflames along with
muscle inflammation.
ex. Charlie horse
5. Cramps – muscle spasms
can result from myositis or
fibromyositis
also caused by irritation
ion and water imbalance
6. Contusion – muscle bruise, internal bleeding
and inflammation
7. Muscle Infections –
virus, bacteria, parasites
causing myositis
trichinosis (parasite)
ex. muscle pain when get pain
8.
•
•
•
•
Muscular Dystrophy –
atrophy of skeletal muscle
muscle replaced by fat and fibrous tissue
begins with leg weakness and spreads
lack of DNA code for protein dystrophin
which forms strands in skeletal muscle
fiber and helps hold cytoskeleton to
sarcolemma. Helps keep muscle fiber
from breaking during a contraction.
• 9. Myasthenia Gravis
– Muscle weakness especially in face and throat
– Autoimmune disorder where body attacks muscle
cell at neuromuscular junction.
10.Hernia –
– Weakness in abdominal muscles
– Abdominal organ protrudes through muscles
(usually small intestines or fat)