Muscle Tissue and Joints

• This document contains lecture slides about muscle tissue and joints, presented by Li Yichen from the Department of Anatomy, with contact information: phone 2144-15 and email [email protected].

Introduction to Muscle Tissue

• There are three types of muscle tissue in the human body: skeletal muscle and cardiac muscle and smooth muscle
• The human body has over 700 skeletal muscles, which together form the muscular system.

Characteristics of Muscle Tissue

• Excitability (irritability): External stimuli can trigger electrical changes within muscle fibers (cells), leading to contraction.
• Contractility: Stimulation of muscle fibers can cause them to shorten.
• Elasticity: The ability of muscle fibers to return to their original length after being stretched and tension is released.
• Extensibility: The ability of muscle fibers to be stretched beyond their relaxed length.

Functions of Skeletal Muscle Tissue

• Body Movement (motion).
• Posture maintenance (posture).
• Temperature regulation (generates heat).
• Storage and Transport of substances (sphincter muscles regulate passage).
• Support (muscles support body weight).

Gross Anatomy of Skeletal Muscle

• Skeletal muscle is composed of fascicles, which are bundles of muscle fibers.
• Connective tissue layers (epimysium, perimysium, endomysium) surround and organize the muscle components.
• Tendons attach muscles to bones.
• Blood vessels and nerves supply the muscle with nutrients and signals.

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma: Muscle cell membrane.
• Sarcoplasm: Muscle cell cytoplasm.
• Myofibrils: Contractile units within muscle fibers.
• Myofilaments: Protein filaments (actin and myosin) within myofibrils.
• Sarcoplasmic Reticulum: Smooth ER network that stores calcium.
• Transverse Tubules: Inward extensions of the sarcolemma.
• Triad: A T tubule sandwiched between two terminal cisternae of the SR.

Organization of Skeletal Muscle

• Each muscle is composed of muscle fibers.
• Muscle fibers are organized into bundles called fascicles.
• Muscle fibers contain myofibrils.
• Myofibrils are composed of myofilaments (actin and myosin).
• Myofilaments are primarily composed of the proteins actin (thin filaments) and myosin (thick filaments).
• Muscle fibers exhibit striations (stripes) when viewed under a microscope.

Myofibrils

• Muscle fibers contain 100 to 1000 cylindrical structures called myofibrils that extend the entire length of the cell.
• Myofibrils possess the ability to shorten, leading to muscle contraction and movement.
• Myofibrils are composed of short bundles of myofilaments.

Myofilaments

• Myofilaments do not extend the entire length of the muscle fiber but are organized into repeating groups.
• Myofilaments are of two types: thin filaments (actin) and thick filaments (myosin).
• Thin filaments are composed of actin and associated proteins.
• Thick filaments are composed of myosin.

Organization of Thin and Thick Filaments

• The organization of thin and thick filaments is the basis for the striated appearance of skeletal muscle.

Sarcomere Organization

• The sarcomere is the functional contractile unit of skeletal muscle fibers.
• Sarcomeres are defined as the region between two adjacent Z discs.
• Myofibrils contain multiple repeating sarcomeres.
• Each sarcomere shortens during muscle fiber contraction.

Sliding Filament Model

• Muscle fibers shorten through the interaction of thin and thick filaments within each sarcomere.
• The mechanism of contraction is explained by the sliding filament theory.
• During contraction, the thin filaments slide past the thick filaments, shortening the sarcomere.

Muscle Fiber Terminology

• Sarcolemma: Muscle cell membrane.
• Sarcoplasm: Muscle cell cytoplasm.
• Sarcoplasmic reticulum: Smooth endoplasmic reticulum in muscle cells.
• Transverse tubules (T-tubules): Extensions of the sarcolemma that penetrate into the sarcoplasm.
• Terminal cisternae: Expanded regions of the sarcoplasmic reticulum located near the T-tubules.

Muscle Fiber Components

• Structure and function overview of the muscle fiber.
• Muscle Fiber: Single muscle cell.
• Sarcolemma: Plasma membrane of the muscle fiber; surrounds the muscle fiber and regulates entry/exit of materials.
• Sarcoplasm: Cytoplasm of the muscle fiber; site of metabolic processes for normal muscle fiber activities.
• Sarcoplasmic Reticulum: Stores calcium ions needed for muscle contraction.
• Terminal Cisternae: Site of calcium ion release to promote muscle contraction.
• Transverse Tubule: Quickly transports a muscle impulse from the sarcolemma throughout the entire muscle fiber.

Neuromuscular Junction

• Muscle contraction begins when a motor neuron stimulates an impulse in the muscle fiber.
• The neuromuscular junction is the region where a motor neuron comes into close proximity to a muscle fiber.
• Steps listed which describes the neuromuscular junction involved in muscle contraction.

Muscle Contraction Summary

• Nerve impulse triggers release of acetylcholine (ACh) from synaptic knob.
• Ach binds to Ach receptors on motor end plate, initiating a muscle impulse.
• Muscle impulse spreads along T-tubules, causes release of calcium from terminal cisternae.
• Calcium binds to troponin, shifting tropomyosin to uncover active sites on actin.
• Myosin heads bind to actin, forming crossbridges.
• Myosin heads pivot, sliding thin filaments toward sarcomere center.
• ATP binds to myosin heads, causing detachment from actin.
• Cycle repeats as long as calcium is present.

The Skeletal Muscle Organization

• Table of the Skeletal Muscle Organization from Muscle to the Sarcomere.

Cardiac Muscle Fibers

• Found almost exclusively in the walls of the heart.
• Striated muscle with one or two nuclei per cell.
• Forms Y-shaped branches.
• Connected to adjacent cells by intercalated discs (containing gap junctions and desmosomes).
• Autorhythmic (can generate its own rhythmic contractions without nervous stimulation).
• Under involuntary control.

Smooth Muscle Fibers

• Located in the walls of internal organs and blood vessels.
• Spindle-shaped cells with one centrally located nucleus.
• Lacks striations (smooth appearance).
• Thin filaments are attached to dense bodies.
• Under involuntary control.

Muscle Tissue Types Comparison

• Comparison chart of skeletal, cardiac, and smooth muscle.
• Focus on the microscopic and and anatomical differences between the three types of muscle.

Introduction to Joints

• Joints are another word for articulations,
• Articulations occur where one bone meets another bone, cartilage, or teeth.
• These structures are said to be "articulated" to each other.
• Range of motion for joints can vary from flexible to inflexible.
• There is a tradeoff between flexibility and stability in the joint.

Types of Movements at Synovial Joints

• Gliding (sliding).
• Angular (changing the angle between bones).
• Rotational (movement around a longitudinal axis).
• Special Movements (unique to certain joints).

Gliding Movement

• Two opposing surfaces slide back and forth or side to side.
• Occurs mainly in plane joints, such as those between the carpals.

Angular Movements

• Increase or decrease the angle between two articulating bones.
• Types include:
  • Flexion vs. Extension
  • Abduction vs. Adduction
  • Lateral flexion
  • Circumduction

Types of Motion

• Rotation- Moving joints along long axis of bone.
• Special Movements- Movements only occurring within specific joints.

Special Joint Action

• List of special joint movements:
  • Depression vs. Elevation
  • Dorsiflexion vs. Plantar Flexion
  • Inversion vs. Eversion
  • Pronation vs. Supination
  • Protraction vs. Retraction
  • Opposition vs. Reposition

Joint Classification

• Joints are classified based on structure and function.
• Structural classification is based on the type of connective tissue that binds the bones together (fibrous, cartilaginous, or synovial).
• Functional classification is based on the amount of movement allowed (synarthrosis, amphiarthrosis, or diarthrosis).

Fibrous joints

• Bones are connected by dense connective tissue.
• There is no joint cavity.
• Most are immobile or have limited motion.
• Three types: sutures, syndesmoses, and gomphoses.
• Suture: connects bones of the skull
• Gomphosis: tooth with maxilla or mandible
• Syndesmosis: radius with ulna

Cartilaginous Joints

• Bones are connected by cartilage.
• There is no joint cavity.
• Two types: synchondroses (hyaline cartilage) and symphyses (fibrocartilage).
• Synchondrosis: sternum with first rib
• Symphyses: pubic symphysis

Synovial Joints

• Freely mobile joints that have a joint cavity filled with synovial fluid.
• Articular surfaces are covered with articular cartilage.
• Stabilized by ligaments.

Specific Joints

• Atlantoaxial joint allows the head to turn in rotation.
• The sternoclavicular joint: where the sternum meets the clavicle allowing the arm to articulate.
• Glenohumeral (Shoulder joint)
• Elbow joint.
• Hip Joint connects the leg to the hip allowing all movements of the lower extremity.
• Knee joint that allows the upper and lower joint to articulate.
• The Z joint. A Z shaped joint with connections in multiple bones, and cartilage.
• The vertebrae joints along the spinal column.