introduction to muscle anatomy. types of muscle 1. skeletal –elongated cells –multi nucleated...
TRANSCRIPT
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Introduction to Muscle Anatomy
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Types of Muscle1. Skeletal
– Elongated Cells– Multi nucleated– Striated – striped
appearance– Voluntary – Produces powerful
contractions– Tires easily, needs
rest (fatigue).– Covers bony skeleton
(motility)Cross Section
Notice nuclei around outside of cell.
Longitudinal View
Notice striations and nuclei around outside of cell.
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Skeletal Muscle Composite Sketch
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2. Smooth– Spindle-shaped Cell– Single nucleus in
each cell– No Striations– Involuntary– Slow, sustained
contractions– In hollow visceral
organs (stomach, bladder, respiratory passages)
Cross SectionNucleus is in center of cell. Cells much smaller.
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Smooth Muscle Composite Sketch
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3. Cardiac (Heart)– Branched cell– Contain intercalated
discs– Single nucleus in
each cell– Striations– Involuntary– Steady, constant
contractions– Never tires
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Cardiac Muscle Composite Sketch
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Muscle Functions• Produce movement
– locomotion & manipulation– Help blood move through veins &
food thru small intestines
• Maintain posture• Stabilize joints• Body temp homeostasis
– Shivering: movement produces heat energy
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Muscle Requirements
• Demands continuous oxygen/nutrient supply.– Lots of arteries/capillaries to muscle.
• Each muscle cell w/ its own nerve ending controlling its activity.
• Produce much metabolic waste due to constant activity.
Motor end plate (terminus)
Axon of neuron
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Muscle Attachments• Most muscles span joints• Attaches to bone in two places: (video)
1. Insertion: the moveable bone• Bicep insertion is the radius
2. Origin: the stationary bone• bicep originates in two different places in scapula
• Attachment types1. Direct: attaches right onto bone
- ex. intercostal muscles of ribs
2. Indirect: via tendon or aponeurosis (sheet-like tendon) to connect to bone
- leaves bone markings such as tubercle
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Muscle Organization
Muscles are complex bundled structures: fibers within fibers
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Muscle organization
Muscle (organ)Fascicle
Muscle fiber (cell)
Myofibril
Sarcomere
Myofilaments:
Actin & Myosin
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Muscle Fibers• A Muscle Fiber = Muscle Cell• HUGE cell:
– 10 - 100m in diameter– can be hundreds of centimeters long (created by
cytoplasmic fusion of multiple embryonic cells)
– extends the length of the muscle• Main content: bundles of proteins
(actin and myosin)• Multinucleated
– to maintain high rate of protein synthesis.
– Muscle fiber nucleus = myonucleus
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Insulation of Muscles
•Muscle cells must be insulated from one another by specialized membranes
•Muscle cells work electrically– if not insulated, nerves cannot control individual muscles.
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• Epimysium surrounds entire muscle– Dense CT that merges
with tendon– Epi = outer– Mys = muscle
• Perimysium surrounds muscle fascicles– Peri = around – Within a muscle fascicle
are many muscle fibers• Endomysium surrounds
muscle fiber– Endo = within
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Structural Terminology Associated with Muscle Fibers
Prefixes: myo, mys, and sarco all refer to muscle• Sacroplasmic Reticulum = Smooth ER of
muscle (regulates calcium levels for muscle contraction)
• Sarcoplasm = Cytoplasm– To maintain ATP production during cellular
respiration, contains high amounts of:• mitochondria• glycosomes that store sugar • oxygen binding protein called myoglobin
• Sarcolemma = Plasma Membrane• T tubules - The sarcolemma of muscle cells
are not just on the outside, rather forms tubes that dive into the muscle cells
• Myosin and Actin= muscle proteins that create muscle cytoskeletal filaments for contraction
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myofibril
sarcolemma
T-tubule
Sarcoplasmic Reticulum
Myosin (red) and Actin (blue)
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Microstructures
• Each muscle fiber (muscle cell), is composed of many myofibrils.– Organized system of cytoskeleton
filaments of actin and myosin proteins that do the actual contracting
– Myofibrils are NOT CELLS– A sarcomere is one segment of a
myofibril (muscle segments).– The series of sarcomeres produce the
striated appearance of muscles
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Muscle Fiber
Sarcomere
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Sarcomere organization
• Myofibril composed of repeating series of sarcomeres with dark A and light I bands.
• I bands intersected by Z discs mark the outer edges of each sarcomere.
• Contraction happens within one sarcomere.
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Sarcomere Banding Pattern
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Let’s sketch the sarcomere together and discuss the sliding filament model of
muscle contraction
How do muscle contract?