MUSCLE TISSUE - Lancaster High School
MUSCLE TISSUE
I. Myology – the scientific study of muscles
II. Characteristics of muscle Tissue
A. Excitability – the ability to respond to a stimulus
B. Contractility – the ability to shorten when stimulated
C. Extensibility – the ability to be stretched
D. Elasticity – the ability to return to the original size
III. Functions of Muscle Tissue
A. Motion – movement
B. Posture – standing and sitting without falling
C. Heat Production – muscular contraction produces 85% of the body’s heat
IV. Types of Muscle
A. Skeletal
1. Location – attached to bones
2. Appearance – striated
3. Nervous Control – voluntary
B. Cardiac
1. Location – the heart
2. Appearance – striated
3. Nervous Control – involuntary
C. Smooth
1. Location – internal organs and blood vessels
2. Appearance – non-striated
3. Nervous Control – involuntary
V. Skeletal Muscle
A. Connective Tissue Associated with Skeletal Muscle – Covers muscles and holds muscle fibers in bundles
1.Fascia – sheets or bundles of fibrous connective tissue
a. Superficial Fascia – just beneath the skin
b. Deep Fascia – Holds muscles together
i. Epimysium – covers entire muscle
ii. Perimysium – covers bundles of fibers
iii.Endomysium – covers individual muscle fibers
c. Tendon – cord-like extension of deep fascia that connects muscle to bone.
d. Aponeurosis – a sheet of connective tissue, similar to a tendon that attaches muscles
B. Nerve and Blood Supply – Skeletal muscles are highly innervated and highly vascular
C. Histology of Muscle Tissue
1. Myofibers – Muscle Fibers (muscle cell)
a. Sarcolemma – plasma membrane of a muscle cell
b. Sarcoplasm – the cytoplasm of a muscle cell
c. Sarcoplasmic Reticulum – The ER of a muscle cell
d. Transverse Tubules (T-Tubules) – tubes that extend across the myofiber and open to the outside
2. Myofibril – structures that make up fibers
3. Myofilaments – structures that make up the fibrils
4. Sarcomeres – The basic functional unit of skeletal muscle
a. Z-lines – ends of the sarcomere
b. A-band – dark area made of both thick and thin filaments
c. I-band – area made of only thin filaments
d. H-zone – area made of only thick filaments
5. Actin and Myosin – proteins that make the filaments
D. Contraction of Skeletal Muscle
1. Sliding Filament Theory – the thin filaments slide over the thick filaments causing the sarcomere to shorten. This process uses ATP
E. Neuromuscular Junction – where a muscle is innervated
1. Neuron – nerve cell
a. Motor Neuron – the nerve that stimulates a muscle
b. Motor end plate – axon of a motor neuron that attaches to the sarcolemma of the muscle fiber
c. Acetylcholine (Ach) – the neurotransmitter released into the Neuromuscular Junction
2. Motor Unit – the combination of the motor neuron and the muscle fibers it innervates
F. Physiology of Contraction – an action potential causes the release of Ca+2 ions stimulating the myosin to move the actin filament
G. Energy for a Contraction – can come from one of three systems:
1. Phosphagen System – ADP + P + Energy ( ATP
2. Anaerobic System – 1C6H12O6 ( 2 C3H6O3 + ATP
3. Aerobic System – 1C3H6O3 + O2 ( CO2 + H2O + ATP
H. All or None Principle – When a muscle fiber is stimulated it either completely contracts or does not contract – it cannot partially contract.
1. Threshold Stimulus – the weakest stimulus that can cause a muscle contraction
2. Sub-Threshold Stimulus – Stimulus that is too weak to cause a muscle contraction
I. Myogram – a record of the electrical activity of a muscle to determine they type of contraction
1. Twitch – a rapid jerky response to a single stimulus
a. Latent Period – time between the application of the stimulus and the muscle contraction
b. Contraction Period – time when filaments are sliding over each other, causing a contraction
c. Relaxation Period – Time during which filaments slide back into place
d. Refractory Period - Time following a contraction during which a muscle is unable to respond to a stimulus
2. Tetanus – a sustained contraction
3. Treppe – a muscle contracts more forcefully after contracting several times
4. Isotonic – the tension remains constant but the muscle shortens
5. Isometric – the tension increases but the muscle does not shorten
L. Muscular Atrophy – Wasting away of muscle
M. Muscular Hypertrophy – Increase in the size of muscle fibers
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