Chapter 6: The Muscular system 022508
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Another online book with chapter on muscles
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Objectives
Figures
6.2 Know the major
muscle groups
6.3 Know the
Muscle structure
6.6 and 7 Know the role of calcium in the Sliding Filament
Theory.
1. Muscular system
A. All types of muscle are capable of contracting (with force) in response to stimulation and return to the original resting position (passively) They also generate heat..
1)
Skeletal muscle responds to nervous
system signals and interacts with the skeleton to cause movement. This muscle attaches one bone to another.
2)
Cardiac(heart)
muscle contracts intrinsically(on it's own) Does not
attach to bone.
3)
Smooth muscle (intestine) responds to
stimulation by nerves, hormones, and can contract intrinsically. Can maintain at least some contractile force
indefinitely.
4) Cardiac and smooth muscle can contract spontaneously and they are both influence by the nerves of the autonomic nervous system.
B.
Muscle Facts you should know
1) The body has over 600 skeletal muscles
2) Muscles are
a) Excitable and respond to stimuli
b) Contractable and will shorten when responding to stimuli
c) Extensible and will stretch
d) Elastic,
can return to their original shape
C. How
skeletal muscles and bones interact. (each end of the muscle is attached to a
bone by a tendon)
1) The
human body’s skeletal muscles (more than 600 of them) are arranged in pairs or
groups.
a) Some
work together synergistically: others operate antagonistically.
(1) Antagonistic example biceps bend and triceps
straighten.
(2) Synergistic example, the finger flexor muscles
cross both the wrist and finger joints.
You can make a fist without bending your wrist because synergist muscles
stabilize the wrist joints.
b) The
origin end of the muscle is designated as being attached to the bone
that moves relatively little: whereas the insertion is attached to the
bone that moves the most
c)
Because most muscle attachments are located
close to joints, only a small contraction is needed to produce considerable
movement of some body part (leverage advantage).
2) Reciprocal
innervation dictates that only one muscle of an
antagonistic pair (e.g. biceps and triceps) can be stimulated at a time.
D. Major muscles that you should know.
1) Pectoralis major: draws arm forward and toward the body.
2) serratus anterior: helps raise
arm, contributes to pushes, draws shoulder blade forward.
3) Biceps
brachii: bends forearm at elbow.
4) Rectus
abdominis: compresses abdomen, bends backbone,
compresses chest cavity.
5) External
oblique: lateral rotation of trunk, compresses abdomen.
6) Adductor
longus: flexes thigh, rotates thigh laterally, draws
thigh towards body.
7) Sartorius:
bends thigh at hip, bends lower leg at knee, rotates thigh outward.
8) Quadriceps
group: flexes thigh at hips, extends leg at knee.
9) Tibialis anterior: flexes foot towards knee.
10)Achilles
tendon: connects gastrocnemius muscle to heel.
11)Gastrocnemius: bends lower leg at knee, Bends foot away
form knee.
12) Hamstring group: draws thigh backward, bends knee.
13) Gluteus maximus: extends thigh rotates thigh laterally.
14) Latissimus dorsi: rotates and draws arm backward and toward body.
15) Triceps brachii: straightens forearm at elbow.
16) Trapezius: lifts shoulder blade, braces shoulder, draws head back.
17) Deltoid: raises arm.
2. Muscle function,
Contraction and relaxation
A. Functional
Organization of a skeletal Muscle (striated
muscle)
1) Muscles
are composed of individual muscle cells (fibers), each of which
is composed of many myofibrils, divided into
contractile units called sarcomeres.
2) Myofibrils
are composed of thin (actin)filaments,
and thick (myosin) filaments.
a) Each
actin filament is actually two headed strands of protein twisted
together.
b) each myosin filament is a protein with a head (projecting
outward) and a long tail (which is bound together with others).
B. There
are four key steps to understanding how muscles contract and relax.
1) A
muscle cell is activated by the release of a neurotransmitter by a nerve.
2) The
neurotransmitter increases the concentration of calcium in the vicinity of the
contractile proteins (myofibrils).
3) The
presence of calcium permits contraction, the absence prevents contraction.
4) When
the muscle cell is no longer stimulated by the neurotransmitter, the calcium
concentration goes down and the muscle stops actively contracting.
C.
Sliding filament Mechanism of Muscle contraction (after calcium
is released) see your CD
1) Within
each sarcomere, there are two sets of actin filaments, which are
attached on opposite sides of the sarcomere: myosin filaments lie suspended
between the actin filaments.
2) During
contraction , the myosin filaments physically slide
along and pull the two sets of actin filaments toward each other at the center
of the sarcomere: this is called the sliding filament mechanism of
contraction.
a) Cross
bridges form between the heads of myosin molecules and actin filaments.
b) When
a myosin head is energized, it attaches to an adjacent actin filament and tilts
in a power stroke toward the sarcomeres center.
c)
Energy from ATP derived the power stroke as the
heads pull the actin filaments along.
d) After the power stroke, the myosin heads
detach and prepare for another attachment (power stoke).
e) ATP
supplies the energy for both attachment and detachment.
f) A single contraction involves multiple power
strokes.
g) At
death, when their is no ATP to cause the heads to
detach, and the body enters rigor mortis.
3.
Control of
Contraction nerves stimulate this contraction
A. Skeletal
muscles constrict in response to signals form the nervous system that trigger
action potentials along the plasma membrane and into the interior of the muscle
cell.
1) Eventually
the signal reaches the sarcoplasmic reticulum (internal tubes), which responds
by releasing stored calcium ions that will bind to troponin, which is
associated with another protein, tropomyosin, both of which are parts of
the actin filaments.
2) When
calcium binds to troponin, the conformation of actin changes allowing myosin
cross bridges to form.
3) When
nervous stimulation stops, calcium ions are actively taken up the by the
sarcoplasmic reticulum and the changes in filament conformation are reversed:
the muscle relaxes.
B. Control
at Neuromuscular Junctions.
1) At
neuromuscular junctions impulses from the branched endings of motor
neurons pass to the muscle cell membranes by acetylcholine.
2) When
the neuron is stimulated, calcium channels open allow
calcium ions to flow inward, causing a release of acetylcholine into the
synapse.
C. ATP
formation and levels of exercise (note a single muscle
cell may use 600trillion ATP molecules per second)
1) During
periods (few seconds) of intense muscle activity, ATP stored in small amounts
in the muscle will give about 6-10 seconds of activity.
2) After
the ATP is depleted (converted to ATP) creatine
phosphate can be used as a source of high-energy phosphate to remake
ATP. The body stores enough CP for about
30 seconds of activity.
3) During
intense and prolonged muscle action (roughly another 40
seconds) ,
anaerobic lactate fermentation produces low amounts of ATP and leads to a
buildup of lactate.
4) When
muscle action is
moderate, most of the ATP is provided by aerobic electron transport phosphorolation, which is dependent on oxygen supply and
number of mitochondria present.
5) Muscle
stores some glycogen, enough for about 3-5 minutes of activity.
6) Aerobic
pathways produce roughly 90% of the energy during intense activity lasting more
than 10 minutes. However an oxygen debt
will be incurred.
7) Extended
periods require Aerobic metabolism with both glucose and oxygen being supplied
to the muscles from the circulatory system.
8) Glucose
is stored in muscle in the form of Glycogen up to 1.5% of muscle mass.
D. How
much tension is generated by a muscle depends on three factors
1) The
number of muscle cells in each motor unit (motor unit size)
2) The
number of motor units active at any one time
3) The
frequency of stimulation of individual motor units.
4.
Muscle tension,
Strength, and fatigue
A. Muscle Tension
1) The
cross-bridges that form during contraction exert muscle tension-- a mechanical
force that can perform work.
2) A
motor neuron and the muscle cells under its control at a motor unit.
1) A
single, brief stimulus to a motor unit causes a brief contraction called a
muscle twitch
a) A
second stimulus that quickly follows the first results in temporal summation. This twitch is stronger than the first. Because the
stimuli arrive at the muscle befoe the muscle has a
chance to transport calcium back to the sarcoplasmic reticulum.
b) repeated stimulation without sufficient interval causes a
constant sustained contraction called tetanus.
2) Individual
muscle cells contract according to the all-or none principal.
a)
The number of motor units that are activated
determines the strength of the contraction: Small number of units = weak contractions: large number at greater frequency =
stronger contraction.
b) Muscle
tone is the continued steady, low level of contraction that stabilized joints
and maintains general health.
C. “fast” and “slow” twitch muscle. ( are distributed unequally throughout the
human body)
1) Humans
have two general types of skeletal muscle cells:
a) “Slow”
muscle is redder in color due to myoglobin and blood
capillaries: its contractions are slower but more sustained.
b) ‘fast’ or white muscle cells contain fewer mitochondria and
less myoglobin but can contract rapidly and
powerfully for short periods .
2) When
athletes train, one goal is to increase the relative size and contractile
strength of fast (sprinters) and slow(distance
swimmers) muscle fibers.
3) Sadly
the relative proportions of these types of cells are probably determined genetically.
5.
Cardiac and smooth muscles have special features.
A. Activation: Normally we do not have voluntary control
over these muscles.
1) A
set of cardiac pacemaker cells have the fastest rhythm and make the pace for
the rest of the cells. The ends are also
connected by intercalated disks containing gap junctions, so that cells
adjacent to one another can stimulate one another.
2) Smooth
muscles are also connected by gap juncations, so that
the whole tissue contracts together in a coordinated fashion. Smooth Muscle does not use troponin, but a
calcium activated Kinase and dephosphorolase. The contractions can be held for a long time
because the myosin heads are not released from the actin.
6. Diseases and disorders of the
muscular system
A. Muscular
dystrophy (refers to several different hereditary diseases) Dystrophy=
abnormal growth.
1) May
be due to the lack of a gene for a particular muscle cell protein (dystrophin) that is part of the muscle cell membrane. Which causes calcium to
leak into the cell, which is ultimately killed.
a) results in loss of muscle fibers and muscle wasting.
b) Death usually occurs by 30 due to loss of muscles for heartbeat of breathing.
B. Tetanus (caused by bacterial infection of a wound to a muscle).
1) bacteria produce a toxin resulting in tetanic contractions (uncontrolled constant maximal contractions).
2) usually affects the muscles of the neck and jaw (lockjaw).
3) death is usually to exhaustion or respiratory failure.
C. Muscle cramps; when a muscle contracts uncontrollably.
1) caused by ATP depletion, dehydration and ion imbalance or buildup of lactic acid.
2) can be solved by increasing circulation (stretching , heat and massage).
D. Pulled Muscles also called torn muscles.
1) result when the muscle is stretched too fare and causes the fibrils to tear apart. This tissue must be rebuild.
E. Muscle soreness: Whenever you start a new type of activity, you may experience muscle soreness. This occurs when the sarcomeres are overstretched and permanently damaged. The damaged sarcomere are destroyed and replaced. this takes time and it hurts.
Possible assignments:
things to think about
1. If
a muscle can only pull, then why can you push a door open?
2. What muscles are collectively called the
hamstrings, in which sports are these injured
3.
Describe specifically how a muscle contracts
4. What
are the signals that cause muscle to contract?
A table
listing all of the muscles in the body and different ways to get their http://www.ptcentral.com/muscles/
A better
listing of all muscles that gives pictures http://www.meddean.luc.edu/lumen/meded/grossanatomy/dissector/muscles/muscles.html
Scoliosis http://srs.org/
Youtube showing how the ligaments stabalise the knee http://www.youtube.com/watch?v=RTV5Yo3E7VQ
Another youtube video http://www.youtube.com/watch?v=_StElDL5A64&feature=related
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QP301 D29 |
deVries |
Laboratory experiments in Physiology of Exercise |
Very old reference, but it contains a lot of low tech experiments to do and how to figure things out. May be a good start for an at home lab component. |
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QP301.M375 1996 |
Katch, Datch and McArdle |
Exercise Physiology 4th ed. Study Guide |
Good source of questions and some study materials. Self Assesment tests are worth looking into. Again, will be good to do an athome for a online class |
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