Study Guide: Bone Tissue, Skeletal System, Joints, Muscular System, and Muscle Tissue (Chapters 7–11)

Chapter 7: Bone Tissue

Types of Bone Tissue

Bone tissue is a specialized connective tissue that forms the rigid part of bones. It is composed of cells, fibers, and ground substance.

• Compact bone: Dense outer layer providing strength and protection.

• Spongy bone (cancellous bone): Porous inner layer containing trabeculae and red marrow.

Bone Structure: Diaphysis, Epiphysis, Metaphysis, and Marrow Cavity

• Diaphysis: The shaft of a long bone, mainly compact bone.

• Epiphysis: The expanded ends of a long bone, mostly spongy bone.

• Metaphysis: The region between diaphysis and epiphysis; contains the growth plate (epiphyseal plate) in children.

• Marrow cavity (medullary cavity): Located in the diaphysis; contains yellow marrow in adults.

Classification of Bones by Shape

• Long bones: Longer than wide (e.g., femur, humerus).

• Short bones: Nearly equal in length and width (e.g., carpals, tarsals).

• Flat bones: Thin, often curved (e.g., sternum, ribs, skull bones).

• Irregular bones: Complex shapes (e.g., vertebrae, sphenoid).

• Sesamoid bones: Develop within tendons (e.g., patella).

Periosteum vs Endosteum

• Periosteum: Tough, fibrous membrane covering the outer surface of bones; contains osteoblasts for bone growth and repair.

• Endosteum: Thin membrane lining the internal surfaces of bones, including the medullary cavity; contains bone-forming cells.

Bone Cells and Their Functions

• Osteogenic cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; synthesize bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-dissolving cells; break down bone matrix (resorption).

Mineralization vs Resorption

• Mineralization (ossification): Deposition of minerals (mainly calcium and phosphate) into bone matrix by osteoblasts.

• Resorption: Removal of bone matrix by osteoclasts, releasing minerals into the blood.

• Hormonal regulation:

  • Parathyroid hormone (PTH): Increases bone resorption.

  • Calcitonin: Inhibits bone resorption, promotes mineralization.

  • Calcitriol (active vitamin D): Promotes bone resorption and increases calcium absorption from the gut.

• Positive feedback: Bone resorption can involve positive feedback in certain pathological conditions (e.g., osteoporosis).

Calcium Homeostasis Hormones

• Parathyroid hormone (PTH): Secreted by parathyroid glands; increases blood calcium by stimulating osteoclasts.

• Calcitonin: Secreted by thyroid gland; lowers blood calcium by inhibiting osteoclasts.

• Calcitriol: Synthesized from vitamin D; increases calcium absorption in intestines.

Most Common Bone Disease

• Osteoporosis: Characterized by decreased bone mass and increased fracture risk.

Chapter 8: The Skeletal System

Axial vs Appendicular Skeleton

• Axial skeleton: Skull, vertebral column, ribs, sternum (central axis of body).

• Appendicular skeleton: Limbs and girdles (pectoral and pelvic girdles).

Major Bones and Their Locations

• Skull: Cranial bones (protect brain) vs facial bones (form face structure).

• Sella turcica (sphenoid bone): Houses the pituitary gland.

• Vertebrae: 33 total; cervical (7), thoracic (12), lumbar (5), sacrum (5 fused), coccyx (4 fused).

• Ribs: 12 pairs; true ribs (1–7), false ribs (8–12), floating ribs (11–12).

Chapter 9: Joints

Definition and Classification of Joints

• Joint (articulation): Site where two or more bones meet.

• Structural classification:

  • Fibrous joints: Bones joined by dense connective tissue (e.g., sutures of skull).

  • Cartilaginous joints: Bones joined by cartilage (e.g., intervertebral discs).

  • Synovial joints: Bones separated by a fluid-filled cavity; most movable type.

Movements at Joints

• Flexion vs Extension: Decreasing vs increasing the angle between bones.

• Abduction vs Adduction: Movement away from vs toward the midline.

• Elevation vs Depression: Lifting a body part superiorly vs moving it inferiorly.

• Supination vs Pronation: Rotating forearm so palm faces up vs down.

Synovial Joint Types and Examples

Type	Example	Movement
Ball-and-socket	Shoulder (glenohumeral), hip (coxal)	Multiaxial (most movable)
Hinge	Elbow, knee	Flexion/extension
Pivot	Atlantoaxial joint	Rotation
Condyloid	Wrist	Biaxial
Saddle	Thumb (carpometacarpal)	Biaxial
Plane	Intercarpal joints	Gliding

• Most movable joint: Shoulder (glenohumeral joint).

• Most movable synovial joint: Ball-and-socket joints.

Chapter 10: The Muscular System

Muscle Groups and Locations

• Head and neck: Facial expression, mastication, neck movement.

• Trunk: Abdominal wall, back, diaphragm.

• Shoulder and upper limb: Deltoid, biceps brachii, triceps brachii, rotator cuff (SITS: supraspinatus, infraspinatus, teres minor, subscapularis).

• Hip and lower limb: Gluteals, quadriceps, hamstrings, gastrocnemius.

Superficial vs Deep Muscles

• Superficial muscles: Located near the surface (e.g., external oblique).

• Deep muscles: Located beneath superficial muscles (e.g., transversus abdominis is the deepest abdominal muscle).

Muscle Function by Group

• Head/neck: Chewing, facial expression, head movement.

• Trunk: Breathing, posture, trunk movement.

• Upper limb: Arm, forearm, hand movement.

• Lower limb: Walking, running, balance.

Prime Mover for Inhalation

• Diaphragm: Main muscle for inhalation; innervated by the phrenic nerve.

Muscle Attachments

• Direct attachment: Muscle fibers attach directly to bone.

• Indirect attachment: Muscle connects to bone via tendon.

• Aponeurosis: Broad, flat tendon (e.g., abdominal muscles).

• Retinaculum: Band of connective tissue holding tendons in place.

Prime Mover, Synergist, Antagonist

• Prime mover (agonist): Main muscle responsible for movement (e.g., biceps brachii for elbow flexion).

• Synergist: Assists the prime mover (e.g., brachialis).

• Antagonist: Opposes the prime mover (e.g., triceps brachii for elbow extension).

Chapter 11: Muscle Tissue

Muscle Arrangement and Connective Tissue

• Muscle fiber: Single muscle cell.

• Muscle fascicle: Bundle of muscle fibers.

• Muscle: Bundle of fascicles.

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds fascicles.

• Epimysium: Surrounds entire muscle.

• Fascia: Separates muscles from each other.

Universal Characteristics of Muscle

• Excitability: Ability to respond to stimuli.

• Conductivity: Ability to conduct electrical signals.

• Contractility: Ability to shorten and generate force.

• Extensibility: Ability to stretch without damage.

• Elasticity: Ability to return to original length after stretching.

Acetylcholine (ACh) in Muscle Contraction

• Function: Neurotransmitter that stimulates muscle contraction.

• Release site: Neuromuscular junction (NMJ).

• Enzyme: Acetylcholinesterase breaks down ACh.

• Disease: Myasthenia gravis involves antibodies against ACh receptors.

Isometric vs Isotonic Contraction

• Isometric: Muscle tension increases, but length does not change (e.g., holding a weight steady).

• Isotonic: Muscle changes length (concentric: shortens; eccentric: lengthens) while tension remains constant.

Sarcomere Structure and Function

• Sarcomere: Functional unit of muscle contraction; extends from Z line to Z line.

• Elements: Thick filaments (myosin), thin filaments (actin), regulatory proteins (tropomyosin, troponin).

Myosin vs Actin; Thick vs Thin Filaments

• Myosin: Motor protein in thick filaments; binds to actin during contraction.

• Actin: Main protein in thin filaments; binding site for myosin.

• Tropomyosin: Blocks myosin-binding sites on actin.

• Troponin: Binds calcium, moves tropomyosin to expose binding sites.

Threshold in Skeletal Muscle Physiology

• Threshold: Minimum stimulus required to trigger a muscle contraction.

Smooth and Cardiac Muscle

• Smooth muscle: Involuntary, non-striated; found in walls of hollow organs (e.g., intestines, blood vessels).

• Cardiac muscle: Involuntary, striated; found only in the heart.

Skeletal Muscle Atrophy vs Hypertrophy

• Atrophy: Decrease in muscle size due to disuse or disease.

• Hypertrophy: Increase in muscle size due to exercise.

Effects of Calcium and ATP Availability

• No calcium: Muscle cannot contract because troponin does not move tropomyosin off actin's binding sites.

• No ATP: Myosin heads cannot detach from actin, leading to rigor mortis.

Process of Skeletal Muscle Contraction and Relaxation (Bonus)

1. Nerve impulse releases ACh at NMJ.

2. ACh binds to receptors, triggering action potential in muscle fiber.

3. Action potential travels along sarcolemma and T-tubules.

4. Calcium released from sarcoplasmic reticulum.

5. Calcium binds to troponin, moving tropomyosin and exposing actin sites.

6. Myosin binds to actin, performing power stroke (contraction).

7. ATP binds to myosin, causing detachment and resetting the cycle.

8. Relaxation occurs when calcium is pumped back into SR and ACh is broken down.

Example: During running, the quadriceps contract concentrically to extend the knee, while the hamstrings act as antagonists.

Additional info: This guide expands on brief points with academic context, definitions, and examples for comprehensive review.