Skeletal Muscle

Functions• 1. Movement - contract (get shorter) bones

function as levers

• 2. Heat production through catabolism ( homeostasis)

• 3. Posture - muscle tone (constant, slight flexing of muscles)

• 4. Joint stabilization

Macroscopic Structure• 1. Belly = main part of

the muscle

• 2. Origin = attachment to the nonmoving bone

• 3. Insertion = attachment to the moving bone

Skeletal Muscle Organs• 1. Components - Study drawings

(pp. 282, 283, 285) know for quiz!!!– a. Epimysium (deep fascia) -

fibrous connective tissue sheath around each muscle.Extends past muscle as:• 1) Tendon - connects muscle

to bone• 2) Aponeurosis - connects

muscle to muscle as a flattened connective tissue sheet

Skeletal Muscle Organs (continued)

• b. Perimysium - connective tissue around bundles of deep fascia fibers (cells)

1) Fasicle = bundle of muscle cells

2) Myofiber = muscle cell

Skeletal Muscle Organs (continued)

• c. Endomysium - around each muscle fiber (cell)

1. Myofibril - bundle of muscle proteins

2. Myofilament - muscle protein (actin (thin) or myosin (thick))

3. Sarcomere the unit of contraction, from Z disc to Z disc

Skeletal Muscle Organs (continued)

• 2. Nerve Supply– a. Somatic motor neuron

= nerve cell that tells a skeletal muscle to contract.

– b. Motor unit = one neuron and all of the muscle cells it goes to.

Skeletal Muscle Organs (continued)

• c. Motor end-plate or neuromuscular junction = where neuron and myofiber meet at synaptic cleft (which is the space between them)

• d. Acetylcholine (Ach) = neurotransmitter (chemical) that initiates contraction. Broken down by acetylcholinesterase (Ach-ase) enzyme.

Muscle• 1. Contracts only when stimulated

by a motor neuron.• 2. Types of contraction:

– a. Tonic contraction = continual partial contraction muscle tone and posture.

– b. Isotonic contraction = tone stays the same, but muscle shortens movement.

– c. Isometric = length stays the same, but tone increases.

– d. Twitch = quick, jerky contraction in response to a single stimulus (done in lab with electricity.)

Types of contraction (continued):• e. Summation - 2nd contraction is stronger if 2nd

stimulus is applied before relaxation of the first

contraction. • f. Treppe (unfused tetanus) (staircase phenomenon) -

muscle contracts more forcefully after a few contractions (warm up exercise ex.) to a maximum.

• g. Tetanic contraction (tetanus) - from series of stimulation with no relaxation period between. (Normal movements are by complete tetanus.)

• h. Convulsions = abnormal, uncoordinated tetanic contractions.

• 3. Skeletal muscle organs contract on graded strength principle.

• 4. Skeletal muscle cells contract on the all-or-none principle (once threshold has been reached.)

• 5. Strength of contraction depends on:– a. Initial fiber length (Starling’s law of heart muscle)

= a stretched muscle contracts with more force.

– b. Metabolic condition (O2 and food supply)

– c. Number of fibers contracting (depends on frequency and intensity of stimulation.)

• d. Previous contraction (warm up)• e. Load (recruitment) - lifting a pencil compared to

lifting a book.• f. Muscle fatigue - build up of lactic acid until muscle

can no longer contract O2 debt.

Muscle Movement• 1. Skeletal Muscles move by pulling on

bones.• 2. Muscles are proximal to the part they

move.• 3. Muscles act in groups

– a. Prime movers - produce Work inthe movement

opposition to– b. Antagonists - relax when each

other the prime movers contract– c. Synergists contract at same time as

prime movers; help stabilize the movement

4. Muscle movements• a. Flexion / extension =

decrease / increase angle between bones

• b. Adduction / abduction = lower to / raise from midline

• c. Rotation

• d. Pronation / supination = inward / outward turning of palm

Naming of Muscles (pp 325-26)

• 1. Location - temporalis

• 2. Shape - deltoid• 3. Size - ____ maximus• 4. Direction of muscle

fibers - _____ oblique

• 5. Number of origins - triceps

• 6. Location of origin and/or insertion - sternocleidomastoid

• 7. Action of muscle - adductor _______