Muscle Tissue and Function

Overview of Muscle Tissue

Muscle tissue is specialized for contraction, enabling movement and force generation in the body. There are three main types: skeletal, cardiac, and smooth muscle.

• Contractile Force: Muscles produce movement through contractile force, which is generated by the interaction of actin and myosin filaments.

• Oxygen-Binding Protein: Myoglobin is the oxygen-binding protein found in muscle cells, allowing for oxygen storage and release during muscle activity.

• Muscle Involvement in Breathing: The latissimus dorsi is NOT primarily involved in the breathing process; main muscles include the diaphragm and intercostals.

• Muscle Cell Structure: Striated muscle cells (skeletal muscle fibers) are long, cylindrical, and multinucleated.

• Contractility: The ability of muscle to shorten forcibly when stimulated is known as contractility.

• Motor Unit Recruitment: As contractile strength increases, motor units with larger, less excitable neurons are recruited later.

Muscle Contraction and Regulation

• Acetylcholine (ACh) Regulation: After nervous stimulation stops, acetylcholinesterase breaks apart ACh in the synaptic cleft, preventing continued stimulation.

• Sarcolemma and Receptors: The motor end plate of the sarcolemma contains acetylcholine receptors.

• Calcium Storage: The sarcoplasmic reticulum in skeletal muscle cells stores calcium ions, essential for contraction.

• Contractile Units: The contractile units of skeletal muscles are myofibrils, composed of repeating sarcomeres.

• Sliding Filament Model: Muscle contraction involves actin and myosin filaments sliding past each other and partially overlapping.

• Role of Tropomyosin: Tropomyosin acts as a contraction inhibitor by blocking myosin binding sites on actin molecules.

• Curare Poisoning: Curare blocks ACh receptors, paralyzing muscles with these receptors.

Muscle and Bone Interactions

• Muscle Origins: Terms like biceps, triceps, and quadriceps indicate two, three, or four origins, respectively.

• Muscle Involved in Facial Expression: The frontal belly of the epicranius produces horizontal wrinkles in the forehead.

• Orbicularis Oris: This muscle closes, purses, and protrudes the lips.

• Hamstrings: The gracilis is NOT a member of the hamstrings.

• Transversus Abdominis: A key muscle of the abdominal wall.

Skeletal System Structure and Function

Bone Types and Structure

The skeletal system provides support, protection, and movement, and is composed of various bone types and structures.

• Spongy Bone: Contains trabeculae, which are lattice-like structures providing strength and flexibility.

• True Wrist (Carpus): Consists of a group of eight short bones united by ligaments.

• Pelvic Girdle: Does NOT include the femur; it consists of the ilium, ischium, and pubis.

• Diaphysis: The shaft of a long bone; a fracture here is called a diaphyseal fracture.

• Diploë: Refers to the internal layer of spongy bone in flat bones.

• Central (Haversian) Canal: Site of blood vessels and nerve fibers in each osteon.

• Axial Skeleton: Provides central support and protects internal organs.

Bone Cells and Bone Formation

• Osteoclasts: Cells responsible for bone resorption (breaking down bone tissue).

• Osteoblasts: Cells responsible for secreting the bone matrix.

• Ossification (Osteogenesis): The process of bone formation.

• Endochondral Ossification: Cartilage forms the model for this type of bone development.

• Cranial Bone Development: Cranial bones develop within fibrous membranes (intramembranous ossification).

Bone Marrow and Mineral Storage

• Yellow Bone Marrow: Contains a large percentage of fat.

• Types of Marrow: Most bones contain two types of marrow: red (hematopoietic) and yellow (fat storage).

• Calcium Storage: The skeletal system serves as a reservoir for calcium and other minerals.

• Hormonal Regulation: Parathyroid hormone increases osteoclast activity to release calcium ions into the bloodstream.

Bone Disorders and Healing

• Osteoporosis Prevention: Adequate intake of calcium and vitamin D is essential.

• Paget's Disease: Characterized by excessive and haphazard bone deposit and resorption.

• Bone Healing: The thigh bone of an elderly individual would likely take the longest to heal due to decreased regenerative capacity.

Joints and Movement

Joint Structure and Function

• Rotational Motion: The proximal end of the radius and the capitulum form a joint allowing rotational motion of the forearm.

• Fibrocartilage: The pubic symphysis is composed of fibrocartilage, providing flexibility and strength during childbirth.

• Lateral Malleolus: The portion of the fibula that articulates with the talus.

Metabolic Pathways in Muscle

Energy Production

• Glycolysis: An anaerobic metabolic pathway producing two net ATPs per glucose and two pyruvic acid molecules. Equation:

• Lactic Acid Formation: During vigorous exercise, insufficient oxygen leads to conversion of pyruvic acid to lactic acid.

Additional Key Concepts

• Paranasal Sinuses: Found in the maxillae and other facial bones.

• Anterior Cranium: Formed by the frontal bone.

• Lumbar Region: Bears most of the weight of the body in the vertebral column.

• Sarcomeres: Functional units of skeletal muscle; responsible for muscle contraction.

• Actin Filaments: Essential components of the contractile apparatus in muscle cells.

• Muscle Tension: If thick and thin filaments no longer overlap, no muscle tension can be generated.