Title: The Muscular System rev 12-12
1The Muscular System rev 12-12
- Muscle cells are involved in every movement that
our bodies perform. - They are found in every body organ and tissue
- Muscles can
- Shorten or contract to produce movement (prime
mover or agonist) - Relax or be pulled back to their original length
by gravity or by opposing muscle groups, called
antagonistic muscles - Work with other muscle groups, called synergistic
muscles, to produce movement - Resist movement to maintain our posture
- Generate heat to maintain our body temperature
- Shiver, sweat
2- Muscle tissue is made up of tightly packed cells
called muscle fibers. The muscle fiber cytoplasm
contains proteins which allow the cell to contract
3- There are 3 types of muscles
- Skeletal muscles
- Cardiac muscles
- Smooth muscles
- Skeletal muscles
- attach to the bones of our skeleton and provide
strength and mobility (movement) for our body - Cardiac muscle
- found in the heart pumps blood throughout the
body - Smooth muscles
- found in most internal organs generally they
work to push something (fluids or other body
substances) through a body part
4- Muscles may also be classified as
- voluntary (muscles over which we have conscious
control and requires peripheral nervous
stimulation to contract) - involuntary (muscles over which we have no
conscious control require autonomic nervous
stimulation to contract) - The term sarcolemma refers to the cell membrane
of a muscle cell
5- Skeletal Muscles
- are multinucleated
- cells are arranged in a parallel fashion
- are responsible for all locomotion and
manipulation - enable us to respond quickly to changes in the
external environment - compared to other muscle types, their speed of
contraction is fast
6Skeletal Muscle
- Is also called Striated or Voluntary muscle
- they have striations (or stripes) which are
caused by alternating dark and light bands - bands are composed of tightly packed contractile
proteins called myofilaments which are made up of
thicker myosin filaments and thinner actin
filaments
7Cardiac Muscle
- Cells are striated, short, fat, branched and
interconnected - Have specialized areas called intercalated disks
where the cells connect with each other - Intercalated disks contain gap junctions that
permit one cell to electrically stimulate the
next one. - because of these connections, cardiac muscle
works as a single, coordinated unit - usually contracts at a steady rate set by the
hearts pacemaker, but neural controls allow for
a faster beat for brief periods (i.e. when you
perform intense activities) - compared to other muscle types, their speed of
contraction is moderate
8Smooth Muscle
- Cells are shorter than skeletal and cardiac
muscle cells - Because the cells have fewer contractile proteins
they do not have striations (thus their name,
smooth muscle) - Cells are spindle shaped (thicker in the middle
and tapered at each end) each cell has a
centrally located nucleus - Are found in the walls of hollow visceral organs
(i.e. stomach, intestines, bladder, blood
vessels) - role is to force fluids and other substances
through body channels - compared to other muscle types, their speed of
contraction is slow and sustained
9Muscle Contraction
- Contractile proteins or myofilaments, called
actin and myosin, slide past each other using
energy from ATP molecules. - These myofilaments produce alternating light and
dark areas called striations - Dark areas are called A-bands
- Lighter areas are called I-bands
- The Z-line is a thin, dark line where sets of
actin myofilaments are woven together - The space between 2 Z-lines is called a
sarcomere - A sarcomere is the smallest functional
(contractile) unit of a muscle fiber
10Mechanism of Muscle Contraction Nerve
Activation of Individual Muscle Cells
- In order for a muscle to contract, its cells must
be stimulated by a nerve - The motor neuron secretes acetylcholine (ACh) at
the neuromuscular junction (the space where the
motor neuron and muscle cell meet). - ACh is a neurotransmitter--a chemical which can
either stimulate or inhibit another excitable
cell (either a nerve cell or a muscle cell) - The ACh diffuses across the space between the
neuron and the muscle cell (called the synaptic
cleft) and binds to receptor sites on the muscle
cell membrane.
11- The ACh binding causes the muscle cell membrane
to generate an electrical impulse which travels
along the cell membrane and along the T-tubules
(cylindrical extensions of the cell membrane or
sarcolemma which travel into the interior parts
of the cell and activate the sarcoplasmic
reticulum) - the function of the T-tubules is to allow the
electrical impulse to quickly travel to all cell
parts - The electrical impulse triggers the release of
calcium from the sarcoplasmic reticulum . - Muscles require calcium in order to contract.
- Sliding Filament Mechanism muscle contracts when
the sarcomeres shorten. This occurs when the
thick and thin filaments form cross bridges and
slide past each other resulting in shortening of
the sarcomere.
12- Calcium binds to troponin, a protein molecule,
and causes the - Troponintropomyosin protein complex to shift
position - this exposes the actin-myosin binding sites and
allow the myosin heads and actin filaments to
make contact, forming cross-bridges. - The actin filaments are pulled toward the center
of the sarcomere and the muscle contracts. - In order to stop the contraction, nerve cell
stimulation stops - calcium is no longer secreted and the
troponintropomyosin protein complex shifts
position so the myosin heads are no longer
exposed. They can no longer make contact with the
actin filaments and - the muscle will be unable to contract
13- http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter10/animation__action_potential
s_and_muscle_contraction.html -
- http//www.brookscole.com/chemistry_d/templates/st
udent_resources/shared_resources/animations/muscle
s/muscles.html - http//www.dnatube.com/video/1310/Action-potential
- GOOD ONE
- http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter10/animation__breakdown_of_atp
_and_cross-bridge_movement_during_muscle_contracti
on.html - http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter10/animation__sarcomere_contra
ction.html
14Muscle Relaxation
- Nerve activation ends, contraction ends
- Calcium pumped back into sarcoplasmic reticulum
(requires ATP) - Calcium removed from actin filaments
- Myosin-binding site covered
- No calcium no cross-bridges
15Energy Use by Muscle Cells
- Muscle contraction requires energy
- In the presence of calcium, myosin acts as an
enzyme to split ATP?ADP inorganic phosphate to
release energy. - So, ATP is the muscles energy source
- Typically muscle cells store enough ATP for
approximately 10 seconds of heavy activity - After this, ATP can be replenished by
- Creatine phosphate which makes enough ATP for
20-30 seconds - After this short amount of time, energy must be
obtained from stored glycogen
16- For long term energy, ATP can also be obtained
via aerobic metabolism of glucose, fatty acids,
and other high-energy molecules which are
constantly supplied by the blood - Glycogen is broken down by a process called
glycolysis. (The end products of glycolysis begin
the Krebs Cycle Citric Acid Cycle and the
electron transport chain to generate energy for
the organism.)
17- Glucose molecules are removed from the glycogen
and the cell uses the glucose to synthesize more
ATP. - Part of the glucose breakdown process can be done
anaerobically (without oxygen). This is a fast
process but only yields 2 ATP molecules per
glucose molecule. - Or glucose? 2 ATP lactic acid
- It also produces lactic acid as a waste product
which can make muscles sore.
18- ---The most efficient, but much slower, process
for energy production is aerobic metabolism.
This yields 36 ATP molecules from 1 molecule of
glucose. Carbon dioxide is produced as a waste
product. - or glucose O2 ? 36 ATP CO2 H2O
- When you perform strenuous activity, it usually
takes a few minutes to start breathing heavily.
The increase in respirations indicates that
aerobic metabolism is now occuring. - During strenuous exercise, typically the blood is
unable to carry enough oxygen for complete
oxidation of glucose in our muscles. So, the
muscles will also contract anaerobically and
produce lactic acid.
19- The lack of oxygen and subsequent production of
lactic acid is called oxygen debt or oxygen
deficit. - So, oxygen debt occurs when the muscles have
consumed oxygen at a faster rate than it can be
replaced. The body must take in an extra amount
of oxygen to replace the oxygen in the muscles
and return the muscles to their resting state. - Therefore, the reason we breathe heavily after
exercise is to erase or pay back the oxygen debt.
20Gross Anatomy of Skeletal Muscle
- Individual muscle fibers are wrapped and held
together by several different layers of
connective tissue - The individual muscle fibers are surrounded by a
fine sheath of connective tissue called the
endomysium. - The fibers within the muscle are grouped into
fascicles, bundles of muscle fibers with a
connective tissue covering and look like a bunch
of sticks with an outer wrapping - The perimysium layer is fibrous connective tissue
that surrounds the fascicles. - The outermost connective tissue layer is called
the epimysium and surrounds the whole muscle. - Portions of the epimysium project inward and
divide the muscle into compartments
21- Skeletal muscles can be made up of hundreds or
thousands of muscle fibers bundled together - Myofibrils are contractile units made up of long
protein molecules called myofilaments
22- Fascia, connective tissue outside the epimysium,
surrounds the entire muscle - At the ends of the muscle, all of the connective
tissues come together and form the tendon that
attaches the muscle to bone.
23Movememt
- If the muscle spans a joint, one bone moves while
the other one remains stationary - the muscles origin is on the bone which does not
move - the muscles origin is generally closer to the
midline of the body than its insertion - the insertion is on the bone which moves
- All muscle cells in a muscle have the same origin
and insertion
24Muscle Contractions
- Isotonic contractions occur when the muscle
shortens and movement occurs - Isometric contractions occur when muscle tension
develops but the muscle doesnt shorten and no
bony movement occurs. These contractions help
stabilize the skeleton. - Degree of nerve activation influences force
generated by the muscle - A single muscle consists of many individual
muscle cells typically organized into groups of
cells that work together cooperatively. - Each group of cells is controlled by a single
nerve cell called a motor neuron.
25- Terms to know
- Motor unit the motor neuron and all the muscle
fibers it supplies. Is the smallest functional
unit of muscle contraction. - Muscle tension force generated by a contracting
muscle upon an object - How much tension is generated by a muscle depends
on - The number of muscle cells in each motor unit
- The number of motor units active at the time
- The frequency of stimulation of individual motor
units - All-or-none principle muscle cells are
completely under the control of their motor
neuron. Muscle fibers always respond with a
complete cycle of contraction and relaxation
every time they are stimulated. - Muscle tone low level of contractile activity
in a relaxed muscle.
26Muscle Activity
- Muscle twitch a complete cycle of contraction
and relaxation - Humans have 2 types of skeletal muscle fibers
slow-twitch and fast-twitch fibers. The
difference is based on how quickly the fibers can
produce a contraction and whether the muscle
contracts aerobically or anaerobically. - Most muscles contain a mixture of both types of
fibers - Ratio of fibers depends on the function of the
muscle - Abnormal muscle twitches occur when almost all
muscle spindles are excited simultaneously
27- Slow twitch fibers break down ATP slowly and
contract slowly - Tend to make ATP aerobically, as they need it
- endurance, long duration contraction, contain
myoglobin to store oxygen - Jogging, swimming, biking
- Fast twitch break down ATP quickly, contract
more quickly - Store large amounts of glycogen and tend to rely
on anaerobic metabolism for quick bursts of high
energy - Rapid, powerful contractions but cant be
sustained - strength, short duration contraction
- Sprinting, weight lifting, tennis
28Exercise Training
- Strength training
- Resistance training
- Short, intense
- Builds more fast-twitch myofibrils
- Aerobic training
- Builds endurance
- Increases blood supply to muscle cells
- Target heart rate at least 20 minutes, three
times a week
29Muscle Contraction Myogram
- Latent period-the time
- between stimulation and the
- start of a contraction
- Contraction-time when the muscle actually
shortens - Relaxation-muscle returns to its original length
- Summation vs. tetanus
- Summation an increase in the frequency with
which a muscle is stimulated so that the muscle
doesnt relax completely. This causes a
summation of the contractile force so total
force produced is greater than the force produced
by one twitch. - Tetanus If muscle stimulation is so rapid that
the muscle cant relax at all, it will remain in
a state of maximal contraction.
Figure 6.10
30Diseases and Disorders of the Muscular System
- Muscular dystrophy group of inherited muscle
diseases in which muscle fibers are unusually
susceptible to damage. - Muscles, primarily voluntary muscles, become
progressively weaker. In the late stages of
muscular dystrophy, fat and connective tissue
often replace muscle fibers OR - loss of muscle fibers due to muscles inability
to create some proteins it needs to function
normally OR - Leak of calcium into the muscle cell which
damages muscle proteins and may kill the cell - results in muscle wasting and paralysis death
usually from heart failure or respiratory failure
31 Tetanus or lock jaw bacterial infection
resulting in overstimulation of nerves and
therefore muscles resulting in tetanic
contractions death from exhaustion or
respiratory failure Muscle cramps painful,
uncontrollable muscle contractions caused by
dehydration and ion imbalances caused by heavy
exercise Pulled muscles caused by stretching a
muscle too far causing some fibers to tear
apart Fasciitis inflammation of the connective
tissue fascia that surrounds a muscle