Unit 2: Skeletal and Muscular Systems

Comprehensive question and answer practice flashcards covering Unit 2: Skeletal and Muscular Systems.

How many bones make up the adult human body, and what proportion of body weight do they represent?

The adult human body has 206 bones, making up almost 1/5th of a healthy person's body weight.

Which four types of tissues compose bone as a living organ?

Connective tissue (osseous tissue, cartilage, dense connective tissue), nervous tissue (nerves), epithelial tissue (blood vessels), and muscle tissue (skeletal muscle).

How frequently does the human skeleton replace itself through rebuilding?

Every 7 to 10 years.

What hormone is produced by bones to help maintain homeostasis by regulating insulin secretion, glucose regulation, and energy usage?

Osteocalcin.

What are the four main types of bones classified by shape?

Long bones, short bones, flat bones, and irregular bones.

What are the key structural characteristics and functional role of long bones?

They are longer than they are wide, having a long shaft with wider ends; located mostly in the limbs, they act as levers to aid in movement.

What are sesamoid bones, and what is a primary example?

Sesamoid bones are a special type of short bone shaped like a sesame seed that are embedded within tendons, such as the kneecap (patella).

What are the structural features and main functions of flat bones?

Flat bones are thin, flat, and often slightly curved; they provide a large surface area for attaching to muscles.

What are two examples of irregular bones?

Hip bones and vertebrae.

What is the general internal structural layout of most bones?

A dense and smooth outer layer of compact (cortical) bone tissue surrounding a porous inner layer of spongy bone tissue.

What is an osteon?

The basic structural unit of compact bone, consisting of long cylinders that act as tiny weight-bearing pillars.

What structural component of osteons helps bone resist torsion stress?

Lamellae, which are hollow tubes filled with tiny salts and collagen fibers.

What structures run through the Haversian (central) canal in compact bone?

Small blood vessels for nourishment and nerve fibers for signaling.

What are trabeculae in spongy bone?

Tiny bone struts that help the bone resist stress and house bone marrow.

What are the primary functions of red bone marrow and yellow bone marrow?

Red bone marrow forms blood cells (hematopoiesis), while yellow bone marrow stores energy in the form of fat.

What are osteocytes, and where are they located?

Osteocytes maintain healthy bone structure and are housed in lacunae (gaps between lamellae).

Contrast the functions of osteoblasts and osteoclasts.

Osteoblasts build and construct bones by calcifying bone tissue as it forms, whereas osteoclasts absorb bone tissue during bone remodeling.

What is the difference between intramembranous ossification and endochondral ossification?

Intramembranous ossification develops bone from a fibrous membrane (e.g., clavicle and skull bones), while endochondral ossification develops bone by replacing cartilage (e.g., all other bones).

Where does cartilage remain in bones following endochondral ossification?

In two places: the articular cartilage on the ends of bones and the epiphyseal plates.

What is bone resorption?

The process where osteoclasts release enzymes to digest calcium phosphate, returning calcium and phosphate into the blood.

What are reduction and immobilization in the context of fracture treatment?

Reduction is the realignment of broken bone ends, and immobilization is keeping the bone stable so it has time to heal.

What are the four steps of fracture repair?

1) Hematoma formation due to blood clots, 2) Fibrocartilaginous callus formation, 3) Spongy bone formation by osteoblasts replacing the callus, 4) Bone remodeling.

How do ligaments and tendons differ in what they connect?

Ligaments attach bones to bones, whereas tendons attach muscles to bones.

What are the three functional classifications of joints?

Synarthroses (non-moving joints), Amphiarthroses (slightly-moving joints), and Diarthroses (freely moving joints).

What are the three structural classifications of joints?

Fibrous joints (connected by collagen fibers), Cartilaginous joints (connected by cartilage), and Synovial joints (connected by dense connective tissue with a fluid-filled joint cavity).

What are three types of fibrous joints?

Sutures (in the skull), syndesmoses (fibula and tibia held by ligaments), and gomphoses (teeth embedded in sockets).

Distinguish between synchondrosis and symphysis cartilaginous joints.

Synchondrosis is an immovable joint connected by hyaline cartilage (e.g., between sternum and first rib); symphysis is a slightly movable joint made of fibrocartilaginous discs (e.g., intervertebral discs).

What six special features characterize synovial joints?

Articular cartilage, joint cavity, fibrous joint capsule, synovial fluid (lubricant), bandlike reinforcing ligaments, and sensory nerve fibers and blood vessels.

Define abduction and adduction.

Abduction is moving a limb away from the median plane along the frontal plane; adduction is moving a limb toward the median plane.

What is the difference between isotonic and isometric muscle contractions?

Isotonic contractions cause a change in muscle length (e.g., lifting a box), while isometric contractions cause no change in muscle length (e.g., doing a plank).

Define the insertion and origin points of a muscle.

Insertion is where the muscle attaches to the movable bone; origin is where it attaches to the immovable or less movable bone.

How are muscles functionally classified into prime movers, antagonists, and synergists?

Prime movers (agonists) produce a specific movement; antagonists oppose or reverse that movement; synergists assist prime movers and stabilize joints.

What are fixators in the muscular system?

Synergist muscles that specifically immobilize a muscle's origin bone to increase the prime mover's effectiveness and help maintain upright posture.

What are the three types of muscle tissue and their primary characteristics?

Cardiac (striated, involuntary, heart), Smooth (non-striated, involuntary, visceral organ walls), and Skeletal (striated, voluntary, attached to bones).

What is a sarcomere?

The contractile unit of a muscle, bounded by Z discs within a myofibril.

What connective tissue layers wrap around the muscle organ, fascicles, and muscle fibers?

Epimysium wraps the outside of the muscle, perimysium surrounds each fascicle, and endomysium surrounds each muscle fiber.

Explain the Sliding Filament Model of muscle contraction.

Sarcomeres contract when thick myosin filament heads grab thin actin filaments and pull them, sliding the thin filaments past the thick filaments and shortening the sarcomere.

What role do $\text{Ca}^{2+}$, troponin, and tropomyosin play in enabling muscle contraction?

$\text{Ca}^{2+}$ binds to troponin, which shifts tropomyosin away from actin's binding sites, granting myosin access to touch actin.

What neurotransmitter is used by somatic motor neurons at the neuromuscular junction?

Acetylcholine (ACh).

What typical resting membrane potential range do neurons and muscle cells maintain?

Between $-50\text{ to }-90\,\text{mV}$.

What three methods can muscles use to increase the force of their contraction?

1) Increasing the frequency of motor neuron stimulation, 2) Increasing the number of motor units stimulated, 3) Increasing the size of muscle fibers.

In the lever systems formed by muscles and bones, what serve as the lever, fulcrum, effort, and load?

Bones act as levers, joints act as fulcrums, muscle contractions produce the effort, and the bone being moved (with any weight) is the load.

Compare first-class, second-class, and third-class levers in the body.

First-class has the fulcrum in the middle (e.g., raising head off chest); second-class has the load in the middle (e.g., standing on toes); third-class has the effort in the middle (e.g., bicep curl).