Introduction to Muscle Anatomy

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.

Skeletal Muscle Composite Sketch

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.

Smooth Muscle Composite Sketch

3. Cardiac (Heart)– Branched cell– Contain intercalated

discs– Single nucleus in

each cell– Striations– Involuntary– Steady, constant

contractions– Never tires

Cardiac Muscle Composite Sketch

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

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

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

Muscle Organization

Muscles are complex bundled structures: fibers within fibers

Muscle organization

Muscle (organ)Fascicle

Muscle fiber (cell)

Myofibril

Sarcomere

Myofilaments:

Actin & Myosin

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

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.

• 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

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

myofibril

sarcolemma

T-tubule

Sarcoplasmic Reticulum

Myosin (red) and Actin (blue)

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

Muscle Fiber

Sarcomere

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.

Sarcomere Banding Pattern

Let’s sketch the sarcomere together and discuss the sliding filament model of

muscle contraction

How do muscle contract?