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Introduction to Muscle Anatomy

Types of Muscle 1. 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

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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 Section Nucleus 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

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Cardiac Muscle Composite Sketch

Muscle Functions •  Produce movement

– Taking chemical energy and turning it into mechanical energy

–  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.

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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

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

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Muscle Attachments •  Attachment types

1.  Direct: attaches right onto bone - ex. intercostal muscles of ribs

Muscle Attachments •  Attachment types

1.  2.  Indirect: via tendon or aponeurosis (sheet-like

tendon) to connect to bone -  leaves bone markings such as tubercle

Agonist vs. Antagonist

•  If you do a bicep curl, how do you re-straighten your arm?

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Muscle Tissue

•  Four Behavioral Properties 1.  Extensibility – The ability to be stretched 2.  Elasticity – Returns to length after being

stretched 3.  Irritability – Responding to a stimulus 4.  Contractility - The ability to produce tension

(Muscle generates force by contraction)

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Change In Muscle Length Resting Length

Stretched

(extensibility)

Passive Elastic Recoil

(elasticity)

Concentric Contraction

(contractility)

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Movements

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Muscles of the human body

•  We are going to study the major ones

Surgery http://www.scivee.tv/node/2413

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Muscle Organization

Muscles are complex bundled structures: fibers within fibers

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 - 100µm 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

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Muscle Fiber

Sarcomere

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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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

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

muscle contraction http://highered.mheducation.com/sites/0072437316/

student_view0/chapter42/animations.html#

How do muscle contract?

Muscle Contraction

•  But First we need to learn about a few structures that allow for the contraction to actually happen

Sarcomere Banding Pattern

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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)

Muscle Contraction

•  Nerve Signal needs to be sent first •  Nerve signal travels down T-Tubules •  Signal affects Sarcoplasmic Reticulum •  Sarcoplasmic Reticulum releases calcium •  Calcium opens up troponin-tropomyosin

complex •  The Myosin and Actin can contract