Anatomy & Physiology Unit 4: Muscular System -Notes
Ch. 7: Muscular System
I. Introduction
· ______is the most abundant tissue in the body
· It is always working:
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Anatomy & Physiology Unit 4: Muscular System -Notes
- Movement
- Locomotion
- Breathing
- Sitting/standing upright
- Beating heart
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Anatomy & Physiology Unit 4: Muscular System -Notes
II. Muscular System Functions
A. Body ______
· Via muscle ______; create overall body movements
B. ______maintenance
· Constant skeletal ______keeps us sitting or standing erect
C. ______
· Thoracic muscles are responsible for the movements necessary for breathing.
D. ______production
· Heat released as byproduct of skeletal muscles & is critical for maintenance of ______
E. ______
· Speaking, writing, typing, gesturing, & facial expression
F. ______& ______contraction
· Move/mix food & water in GI tract, excrete secretions, regulate blood flow
G. ______
· Cardiac muscle contraction; propels blood to body
III. Three Types of Muscle
A. ______muscle
B. ______muscle
C. ______muscle
IV. Comparison of Muscle Types
A. Know these major differences on Table 7.2 (p. 171)
V. Characteristics of Skeletal Muscles
· Approximately ______% of body weight (with associated connective tissues)
· Attached to ______
A. ______
· Muscles can ______with force causing movement of structures to which they’re attached; lengthen passively (due to gravity or the force of an opposing muscle)
B. ______
· Muscles respond to ______(usually nerves cause contraction of skeletal muscle)
C. ______
· Skeletal muscle can be ______to resting length and a little beyond
D. ______
· Ability of muscles to ______to original resting length after stretching
VI. Structure of Skeletal Muscle
A. Hierarchical organization:
1. Each muscle (organ) surrounded by ______(upon + muscle) /fascia (fillet) – connective tissue
a. ______(bundle) – bundles of muscle cells/fibers; surrounded by ______(around + muscle) – loose connective tissue
i. Several ______per fasciculus; surrounded by ______(within + muscle) – loose connective tissue
VII. Structure of Skeletal Muscle Cells (muscle ______= muscle ______)
A. Microscopic structure
1. Each fiber composed of ______– fine, longitudinal fibril within skeletal muscle fiber. Each muscle fiber has many myofibrils.
a. Myofibrils composed of ______(protein filaments) arranged in ______(flesh + part)
i. ______myofilaments (thin)
ii. ______ myofilaments (thick)
2. Each muscle fiber has:
a. ______(muscle cell membrane)
b. ______(cytoplasm) (flesh + formed)
c. ______(ER) – increased [Ca2+] produces muscle contractions
d. ______(T tubules) – network of tubes connecting sarcolemma to sarcoplasmic reticulum
Structure of Skeletal Muscle Cells
B. Banding Pattern (striations) (See 7.3 a)
1. ______(I-LIGHT): thin myofilaments only (actin); from Z-disk to myosin
2. ______(A-DARK): thick & thin myofilaments (myosin & actin); dark, central region of sarcomere; length of myosin myofilaments
3. ______: dark line in middle of I-band; site of actin attachment; make of protein fibers
4. ______: lighter, central region in middle of A-band; thick myofilaments only (myosin)
5. ______: dark line in middle of H-zone; site of myosin attachment
6. ______: smallest functional contractile unit of muscle cell; runs from Z-disk to Z-disk; highly ordered units
VIII. Membrane Potentials
1. ______of most cell membranes is positively charged relative to ______
2. A ______is created = charge difference across the membrane of a resting cell
3. Occurs because:
a. Higher [K+] ______inside than outside
b. Cell membrane more ______to K+ than other ions (K+ channels open)
4. ______= change in membrane potential in an excitable tissue that is propagated as an electrical signal
a. Made via ______.
Creating an action potential…
1. ______ membrane potential. Na+ channels & some K+ channels closed. A few K+ diffuse down c.g. through open K+ channels, making outside positive.
2. ______. Na+ channels open. A few Na+ diffuse down c.g. through open Na+ channels, making ______positive.
3. ______. Na+ channels closed; Na+ movement into cell stops. K+ channels open. K+ movement outside cell increases, making ______positive.
Nerve supply
IX. Neuromuscular Communication
· Muscle fibers contract when stimulated by motor neurons
A. ______- nerve cells that innervate all muscle tissue
1. pass along action potentials as ______
2. axons form junctions with many muscle fibers called ______(NMJ’s) or synapses)
B. The “______” = 1 motor neuron + all muscle fibers it stimulates
1. From 2-3 fibers/unit (fine control) to 2000 fibers/unit (large power movements)
2. several motor units = 1 ______
C. Neuromuscular junction structures:
· Occur near ______of muscle fiber
· Tips of axons are enlarged (sticky) and rest in little pits on muscle fiber
1. ______ terminals – bulbous ends of motor neuron (ends of axons)
2. NMJ or ______– region of chemical communication between cells
a. ______contain neurotransmitter (______)
i. Neuron releases ACh to stimulate or inhibit a postsynaptic cell (muscle fiber)
b. ______– space between presynaptic terminals and postsynaptic ______(sarcolemma of muscle fiber)
D. Basic events of ______:
· Role of ACh in muscle contraction
- ACh inhibitors or stimulators (or molecules that affect acetylcholinesterase) affect muscle contractions – some poisons and insecticides do this (don’t allow muscles to contract/relax)
1. ______(nerve impulse) arrives at presynaptic terminals
2. Synaptic vesicles release ______(ACh) into synaptic cleft via ______
3. ACh binds to receptors sites on Na+ channels in ______membrane, causing them to open
4. Na+ moves into cell causing an ______which travels along sarcolemma & T-tubules
5. ACh triggers ______release from sarcoplasmic reticulum
6. Ca2+ inside muscle triggers ______& ______“sliding filament” action
7. ______is spent
8. ______degrades remaining ACh to limit contraction stimulus
E. ______
· Mechanism by which actin and myosin myofilaments ______over one another during muscle contraction
1. Actin & myosin myofilaments slide past one another causing ______to shorten
a. Sarcomere shortening (end to end) causes ______shortening
i. Myofibril shortening causes ______
ii. Sarcomeres lengthen during ______(due to opposing force of another muscle or gravity)
2. ______and ______shorten; A-bands maintain constant width (Fig 7.7)
3. ______binds to troponin
4. Tropomysin molecules slide into groove
5. Myosin attaches to exposed sites on ______myofilament
6. Energy from ______stored in myosin heads
7. Myosin heads bind to actin forming ______
8. Stored energy used to myosin heads causing actin myofilament to slide
9. ATP binds to myosin causing head to ______& ______to resting position
10. Cycle repeats if Ca2+ still bound to troponin & ______still available
· ______– (stiffness + death) – no more ATP, therefore myosin heads remain attached and crossbridges are left intact, causing stiff muscles
· ATP breakdown also releases ______, therefore, increase in body temperature when exercising and shivering (homeostatic mechanism)
X. Muscle Twitch, Summation, Tetanus, & Recruitment (see 7.9)
A. ______- contraction of a muscle fiber in response to a stimulus; three phases:
1. ______ phase – time between stimulus application and beginning of contraction
a. Action potential produced by at least 1 motor neuron and sent to a NMJ
b. ACh is released and binds to receptors on Na+ channels – creates another action potential
c. Action potential travels along ______& ______membranes
d. Ca2+ released from sarcoplasmic reticulum into myofibrils
e. Ca2+ binds to troponin, causing tropomysin to expose myosin to actin’s attachment sites
f. Crossbridges form
2. ______ phase – time of contraction
a. Crossbridge movement and cycling
b. Increased tension in muscle fibers
3. ______ phase – time of relaxation
a. Ca2+ actively transported back to sarcoplasmic reticulum
b. Troponin without Ca2+ causes tropomysin to slide back into groove, blocking attachment sites
B. Strength of Muscle Contraction (increased by:) (See Fig. 7.10)
1. ______– increasing force of contraction of muscle fibers in muscle
2. ______– increasing number of muscle fibers contracting within muscle
3. ______(convulsive tension) – sustained muscular contraction caused by a series of nerve stimuli repeated so rapidly that there is no ______, instead a sustain contraction results
a. Caused by Ca2+ buildup in myofibrils due to rapid action potential production (faster than transport back to sarcoplasmic reticulum)
XI. Energy Requirements for Muscle Contraction
A. ______produce ATP
1. Multiple mitochondria in sarcoplasm produce ATP needed for muscular contractions (lie between ______)
a. Must constantly produce ATP (just for cell maintenance)
b. ______be stored (in sufficient amounts)
B. Creatine phosphate is energy storage
1. Used to generate ATP; high energy molecule (see 7.11)
C. ______respiration (w/o O2)
1. Breakdown of glucose in absence of O2 to produce ______and ______
a. Glycolysis ® pyruvic acid ® lactic acid)
b. Occurs in cytoplasm
2. Generates ______ATP; short-lived, but faster than aerobic – this is important when O2 is limited.
3. ______as waste product (irritant to muscle fibers)
4. Sprinting: first uses ______respiration, uses up creatine phosphate, then switches to ______respiration
D. ______respiration (w/ O2)
1. Breakdown of glucose in the presence of O2 to produce CO2, H2O, & ~38 ATP
a. Glycolysis ® Krebs ® ETC
b. Occurs in ______
2. Generates up to ______ATP; long-term
a. More efficient (up to 18x more ATP than anaerobic respiration)
3. Uses other nutrient molecules (F.A., a.a.)
a. ______– must be repaid after labor
i. Amount of oxygen needed in chemical reactions to:
· Convert lactic acid to ______
· Replenish ATP and creatine phosphate in muscle fibers
· Replenish O2 stores in lungs, blood, and muscles
ii. Explains high heart rate & breathing rate for extended period of time after exercise
4. Long-distance/endurance uses ______respiration (fatty acids important)
XII. Fatigue
A. ______ fatigue – CNS causes the perception that continued muscle contraction is impossible
1. can be overcome – last sprint at end of race
B. ______ fatigue – force of muscle contractions become increasingly weak when ATP is used faster than can be produced and lactic acid builds up faster than it can be removed
1. ______contracture – muscles cannot contract or relax (not enough ATP to bind to myosin for crossbridging or to release the myosin heads)
a. Occurs with extreme muscle fatigue
XIII. Types of Muscle Contractions
A. ______ contractions (equal distance) – muscle contraction in which the length of the muscle does not change, but the amount of tension increases
B. ______ contractions (equal tension) – muscle contraction in which the amount of tension is constant and the muscle shortens
1. Movement of arms and fingers
2. Most muscle contractions are a combination of isometric & isotonic
3. ______– isotonic contraction in which muscle tension increases while muscle shortens
4. ______– isotonic contraction in which muscle tension is maintained (constant) while muscle lengthens
a. Ex. – letting a weight down slowly
· ______– constant tone produced by muscles over long periods of time
- Ex – back & leg muscles tight; heat up right; abdomen in
XIV. Smooth & Cardiac Muscle
Smooth Muscle / Cardiac MuscleSmall, spindle-shaped / Long, striated, branching
1 nucleus/cell / Usually 1 nucleus/cell
<actin & myosin / Irregular distribution of actin & myosin
No sarcomeres (striations) / Less distinct striations
Slower contraction / Intermediate rate of contractions
Autorhythmicity – periodic spontaneous contraction of smooth muscle (peristalsis) / Autorhythmicity
Involuntary motor control / Involuntary motor control
Aerobic (no O2 debt) / Aerobic (limited anaerobic capacity)
Layers of smooth muscle tissue act together as one unit to produce simultaneous contractions / Intercalated disks – communication between cells
XV. Disorders & Other Conditions of Muscle Tissue
A. ______– painful, spastic contractions of muscle
1. Caused by muscle irritation
a. Lactic acid buildup or inflammation of connective tissue
B. Hypertrophy and Atrophy
1. ______– enlargement of muscle from an increase in number of myofibrils within muscle fibers
a. From exercise
b. Greater in males (more testosterone)
2. ______– decrease in muscle size from a decrease in myofilaments within muscle fibers
a. Severe atrophy = permanent loss of skeletal muscle and subsequent replacement with connective tissue
i. Can be caused by long-term immobility or nervous system damage
C. ______(bad + nourishment) – group of inherited muscle disorders in which the skeletal muscle degenerates accompanied by progressive weakness in the person. Progressive degeneration of muscle fibers with atrophy and eventual tissue replacement with fat or other connective tissue.
1. ______ muscular dystrophy – slow motor development, progressive weakness & muscle wasting beginning in the pelvic girdle. First identified in children ~3 years of age. Leads to replacement of muscle tissue with connective tissue, muscular atrophy, and skeletal deformity.
2. ______ muscular dystrophy – failure of muscles to relax after a forceful contraction and muscular weakness. Dominant trait in both sexes. 1 in 20,000 births. Slow progression first affecting face and neck muscles, then the hands.
D. ______(muscle + weakness) – muscular weakness that is not accompanied by atrophy. Chronic, progressive disease caused by destruction of acetylcholine receptors in NMJ. Neuronal stimulation is hindered, thus, weaker muscles.
E. ______– inflammation of the tendon or its attachment point. Usually from overtraining in athletes.
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