Chapter 10 - Muscles Flashcards
Three Types of Muscles
- Skeletal
- Cardio
- Smooth
Muscular System
only skeletal muscles
Myology
study of the skeletal muscles
Skeletal Muscle
- Voluntary
- Striated
- Attached to bone
- Muscle cell = “muscle fiber” or “myofiber”
- Mutinucleated
Cardiac Muscle
- Involuntary
- Striated
- Cell = “cardiocyte” or “myocyte”
- Short, branched cells
- Intercalated discs w/ gap junctions
- Typically mononucleated
Smooth Muscle
- Involuntary
- Non-striated
- Fusiform cell shape
- Mononucleated
Functions of Muscle
- Movement (body parts, communication)
- Stability
- Heat production
- Control of body openings & passages
- Store nutrients (amino acids, glycogen)
Properties of Skeletal Muscle
- Excitability (responsiveness)
- Conductivity (electrical impulse)
- Contractility (shorten)
- Extensibility (stretch)
- Elasticity (recoil)
Fascia
wraps muscle group
Epimysium
wraps muscle
Perimysium
wraps fascicle
Endomysium
wraps muscle cell
Skeletal Muscle Shapes
- Fusiform - tapered ends
- Parallel - uniform width
- Triangular (convergent) - tapered at one end
- Pennate - feather-shaped
- Circular - forms rings around body openings
Muscle Attachments
- Indirect - tendon, connects into periosteum and matrix
- Aponeurosis - broad sheet of tendon (e.g. scalp, wrist, abdomen)
- Direct - muscle to bone, w/ collagen fiber
- Other tissues, i.e. dermis
Origin
muscle attachment at relatively stationary end
Insertion
muscle attachment at more mobile end
Belly
muscle area between origin and insertion
Functional Groups of Muscles
- Prime Mover - produce main force of action
- Synergist - aids prime mover, may stabilize joint
- Antagonist - opposes prime mover (antagonistic pair act on opposite sides of joint)
- Fixator - prevents bone movement
Lever Model for Muscles
Lever = bone
Fulcrum = joint
Effort of Force = muscle
Resistance = object moved
First Class Lever
- “Seesaw”
- E.g. extension of neck
- Fulcrum in middle (atlanto-occipital joint)
- Resistance is weight of head
- Effort by neck muscle to hold head erect
Second Class Lever
- “Wheelbarrow”
- E.g. bouncing child on thight
- Fulcrum = hip
- Resistance is weight of child in middle
- Effort from quads
Third Class Lever
- “Paddling Canoe”
- Most common
- E.g. Paddling
- Fulcrum = elbow
- Resistance is weight in hand
- Effort from biceps & brachialis
Sarcolemma
muscle fiber plasma membrane
Transverse (T) Tubules
conduct impulses from the sarcolemma down into the cell
Sarcoplasm
cytoplasm of skeletal muscle cell (fiber)
- Myofibrils (contain myofilaments)
- Glycogen (carbohydrate)
- Myoglobin (red pigment)
Sarcoplasmic Reticulum
endoplasmic reticulum of skeletal muscle cell (fiber)
- terminal cisternae (enlarged areas of sarcoplasmic reticulum surrounding the T tubules)
- Ca++ reservoir
Types of Myofilaments
- Myosin
2. Actin
Myosin
- Myofilament
- Thick, contractile
- Heads project from bundled tails of hundreds of molecules
Actin
- Myofilament
- Thin, contractile
- Fibrous (F) Actin = resembles necklace
- Globular (G) Actin = resemble one head of necklace
- Active site = myosin binding site area on G actin
Skeletal Muscle Regulatory Proteins
- Tropomyosin (“gate”) - blocks active sites when muscle is relaxed
- Troponin (“lock”) - attaches to tropomyosin, binds calcium (“key”) when excited
Muscle Striations
narrow stripes (light and dark) that run perpendicular to the length of the cell
A Band
area of myosin and actin overlap
H Band
central region of A band that is lighter due to lack of actin
M Line
midline of A band (and H band) that anchors myosin filaments together
I Band
area of actin filaments
Z Disc
midline of I Band, protein that anchors actin filaments together, define boundaries of a sarcomere
Sarcomere
basic unit of striated muscle tissue
Motor neuron’s synaptic knob contains vesicles with _____________.
Acetylcholine (ACh)
Junctional folds of muscle cell’s membrane contain _________ _________.
Acetylcholine (ACh) Receptors
Motor Unit
- Consists of one motor neuron and multiple muscle fibers
- Behaves as a single, functional unit
- Fibers from one unit are dispersed in muscle
Phases of Contraction and Relaxation
- Excitation
- Excitation-Contraction Coupling
- Relaxation
Excitation of a Muscle
- nerve signal arrives at knob
- knob releases ACh, which binds to muscle’s receptors, opening ion gates and exciting muscle
- excitation spreads down and through muscle cell
Excitation-Contraction Coupling
- electrical impulse triggers calcium release from SR
- calcium binds troponin, which moves tropomyosin to expose actin
- myosin breaks down ATP and extends head
- myosin form cross-bridge with actin
- myosin pulls actin in power stroke, then detaches, reattaches, pulls again, etc.
Relaxation of a Muscle
- nerve signal stops
2. SR reabsorbs calcium, tropomyosin blockade resumes, and tension subsides
At rest, muscle receives about ___________ of heart’s output.
one-quarter
During heavy exercise, muscular system receives more than _______________ of heart’s output.
three-quarters
Muscle Growth and Atrophy
- resistance exercise stimulates production of more myofilaments, thus more myofibrils
- growth by hypertrophy
- exercise also stimulates production of mitochondria, myoglobin, glycogen, and blood vessels
- unused muscles atrophy
Two Classes of Muscle Fibers
Type I = Slow Oxidative (SO)
Type II = Fast Glycolytic (FG)
Slow Oxidative Muscle Fibers
- slow-twitch, red, Type I
- small diameter
- aerobic ATP production
- abundant: mitochondria, myoglobin, capillaries
- resistant to fatigue
- predominate in postural muscles (e.g. soleus, back muscles)
Fast Glycolytic Muscle Fibers
- fast-twitch, white, Type II
- large diameter
- anaerobic ATP production
- abundant glycogen
- fatigue quickly
- predominate in quick response muscles (e.g. gastrocnemius, bicep)
Myopathies
diseases of the muscle
Muscular Dystrophy
- several types of skeletal muscle degeneration
- most common
- Duchenne
- Hereditary (sex-linked)
Myasthenia gravis (MG)
- autoimmune disease
- affects women age 20-40
- destruction of ACh receptors
How Muscles are Named
- Size (e.g. brevis = short)
- Shape (e.g. teres = round)
- Location (e.g. brachii = of the arm)
- Number of heads (e.g. biceps = two heads)
- Orientation of the fibers (e.g. rectus = straight)
- Action (e.g. flexor = muscle that flexes joint)
