Chapter 11: The Musculoskeletal System Flashcards
Skeletal muscle
Responsible for voluntary movement and is therefore innervated by the somatic nervous system; sacromeres - repeating units of actin and myosin; striated
Red fibers
Slow-twitch fibers; high myoglobin content and primarily derive their energy aerobically
White fibers
Fast-twitch fibers; contain much less myoglobin; less iron and the color is lighter; both red and white fibers can be mixed in muscles
Smooth muscle
Involuntary action; controlled by the ANS; found in the respiratory tree, digestive tract, bladder, uterus, blood vessel walls, and many other locations; each muscle cell has a single nucleus; no striations; involved in tonus; can contract without nervous system input known as myogenic activity
Cardiac muscle
Characteristics of both smooth and skeletal muscle types; primarily uninucleated but cells may contain two nuclei; involuntary and innervated by the ANS; striated; connected by intercalated discs which contain many gap junctions
Z-lines
Define the boundaries of each sarcomere
M-line
Runs down the center of the sarcomere, through the middle of the myosin filaments
I-band
Region containing exclusively thin filaments
H-zone
Contains only thick filaments
A-band
Contains the thick filaments in their entirety, including any overlap with thin filaments
Myofibrils
Sarcomeres are attached end-to-end to form myofibrils
Sarcolemma
Cell membrane of a myocyte; capable of propagating an action potential and can distribute the action potential to all sarcomeres in a muscle using a system of transverse tubules (T-tubules)
Myocyte
Contains many myofibrils arranged in parallel and can also be called a muscle fiber; many myocytes in parallel form a muscle
Initiation of muscle contraction
Neuromuscular junction; nervous system communicates with muscles via the motor (efferent) neurons; signal travels down the neuron until it reaches the nerve terminal (synaptic bouton) where acetylcholine is released into the synapse; each nerve terminal controls a group of myocytes; depolarization triggers an AP which spreads via T-tubules; release of Ca2+ from SR; Ca2+ binds to troponin and triggers a conformational change in tropomyosin; exposes the myosin-binding sites on the actin thin filament
Actin-myosin cross-bridge cycle
1) ATP is hydrolyzed
2) Ca2+ binds to troponin; myosin binds to actin
3) Powerstroke occurs; the sarcomere contracts; ADP and Pi dissociate from myosin
4) New ATP binds to myosin, causing detachment of myosin from actin; hydrolysis of ATP to ADP and Pi causes recocking of the myosin head
Relaxation
Acetylcholinesterase degrades acetylcholine, resulting in termination of the signal
Simple twitch
Response of a single muscle fiber to a brief stimulus at or above threshold; consists of a latent period, contraction period and relaxation period
Frequency summation
Contractions will combine, become stronger, and more prolonged
Tetanus
If the contractions become so frequent that the muscle is unable to relax at all
Creatine phosphate
Created by transferring a phosphate group from ATP to creatine during times of rest
Oxygen debt
After the cessation of strenuous exercise, the body must metabolize all of the lactic acid it has produced; most lactic acid is converted back to pyruvate which can enter the CAC; difference between the amount of oxygen needed by the muscles and the actual amount present
Axial skeleton
Consists of skull, vertebral column, ribcage, and hyoid bone (a small bone in the anterior neck used for swallowing)
Appendicular skeleton
Consists of the bones of the limbs (humerus, radius, ulna, carpals, metacarpals, and phalanges in the upper limb; and femur, tibia and fibula, tarsals, metatarsals, and phalanges in the lower limb), the pectoral girdle (scapula and clavicle) and pelvis
Compact bone
Where bone’s characteristic strength comes from
Spongy or cancellous bone
Consists of bony spicules (points) known as trabecular and bone marrow
Red marrow
Filled with hematopoietic stem cells; responsible for generation of all the cells in our blood
Yellow marrow
Composed primarily of fat and is relatively inactive
Long bones
Characterized by cylindrical shafts called diaphyses that swell at each end to form metaphyses and that terminate in epiphyses
Bone composition
The outermost part of bone is composed of compact bone while the internal core is made of spongy bone
Epiphyseal plate
Catilaginous structure and the site of longitudinal growth; filled with mitotic cells prior to puberty
Periosteum
Surrounds the long bone to protect it as well as serve for muscle attachment
Tendons
Attach muscle to bone
Ligaments
Hold bones together at joints
Organic components of the bone matrix
Collagen, glycoproteins, and other peptides
Inorganic components of the bone matrix
Calcium, phosphate, and hydroxide ions, which harden to form hydroxyapatite; minerals such as sodium, magnesium, and potassium are also stored in bone
Osteons or Haversian systems
Structural units of the bony matrix
Lamellae
Concentric circles of bony matrix surrounding a central microscopic channel
Haversian canals
Longitudinal channels
Volkmann’s canals
Transverse channels
What do the canals contain?
Blood vessels, nerve fibers, and lymph vessels that maintain the health of the bone
Lacunae
Between the lamellar rings; house mature bone cells known as osteocytes
Canaliculi
Tiny channels that allow for the exchange of nutrients and wastes between osteocytes and the Haversian and Volkmann’s canals
Osteoblasts
Build bone
Osteoclasts
Polynucleated resident macrophages of bone, resorb it
Cartilage
Softer and more flexible than bone; consists of a firm but elastic matrix called chondrin that is secreted by cells called chondrocytes; not innervated and relatively avascular
Endochondral ossification
Hardening of cartilage into bone; responsible for most of the long bones of the body
Intramembranous ossification
Undifferentiated embryonic connective tissue (mesenchymal tissue) is transformed into and replaced by bone; occurs in the bones of the skull
Immovable joints
Consist of bones that are fused together to form sutures or similar fibrous joints; primarily in the head
Movable joints
Structures include joints like the elbow and knee, ball-and-socket joints (like the shoulder or hip) and others; permit bones to shift relative to one another; strengthened by ligaments and consist of a synovial capsule which encloses the actual joint cavity (articular cavity)
Synovium
Secretes synovial fluid which lubricates the movement of structures in the joint space
Articular cartilage
Contributes to the joint by coating the articular surfaces of the bones so that impact is restricted to the lubricated joint cartilage
Origin
The end with the larger attachment to bone (proximal connection)
Insertion
The end with the smaller attachment to bone (usually the distal connection)
Flexor
Decreases the angle across a joint (biceps_
Extensor
Increases or straightens this angle (triceps)
Abductor
Move a part of the body away from the midline (deltoid)
Adductor
moves a part of the body toward the midline (pectoralis major)
Medial and lateral rotation
Describe motions that occur in limbs, rotating their axis toward or away from the midline, respectively
