Muscle Terminology

Key Terms and Definitions

• Myology: The scientific study of muscle.

• Muscle fibers: Another term for muscle cells, reflecting their elongated shape.

• Word roots: mys and sarco are roots commonly used in muscle terminology (e.g., sarcolemma, myofibril).

Three Types of Muscle Tissue

Overview and Differences

Muscle tissue in the human body is classified into three main types, each with distinct microscopic anatomy, location, and regulatory mechanisms.

• Skeletal Muscle: Attached primarily to bones; under voluntary (conscious) control; contracts quickly and tires easily; allows for a wide range of forces to be generated.

• Cardiac Muscle: Found in the heart wall (myocardium); involuntary (unconscious) control; rhythmic contractions without external stimuli; non-fatigable; contraction can be modified by neural and hormonal input.

• Smooth Muscle: Located in the walls of hollow internal structures (digestive, respiratory, reproductive tracts, blood vessels, etc.); involuntary control; slow, sustained contractions; non-fatigable.

Characteristics of Skeletal Muscle

Structure and Function

• Attachment: Primarily attached to bones via tendons.

• Control: Voluntary (conscious) control, usually via the somatic nervous system.

• Contraction: Contracts quickly, but is easily fatigued.

• Force Generation: Capable of generating a wide range of forces.

Skeletal Muscle Cells

• Shape: Long, cylindrical cells.

• Striations: Display a banded (striated) appearance under the microscope due to the arrangement of contractile proteins.

• Nuclei: Multinucleate (contain multiple nuclei per cell).

Example: Histological images of skeletal muscle show striations and multinucleate cells, with fibers cut both longitudinally and transversely.

Characteristics of Cardiac Muscle

Structure and Function

• Location: Makes up most of the heart wall (myocardium).

• Control: Involuntary (unconscious); contracts rhythmically without external stimuli (autorhythmicity).

• Fatigue Resistance: Non-fatigable; contracts at a constant rhythm, modifiable by neural and hormonal signals.

• Cell Structure: Branched, striated cells; usually uninucleate (occasionally binucleate); connected by intercalated discs containing gap junctions and desmosomes.

Characteristics of Smooth Muscle

Structure and Function

• Location: Found in the walls of hollow organs (digestive, respiratory, reproductive tracts, blood vessels, arrector pili muscles, pupil of the eye, etc.).

• Control: Involuntary (unconscious); contracts slowly and is non-fatigable.

• Cell Structure: Spindle-shaped, non-striated (smooth) cells; uninucleate.

Functions of Muscle Tissue

Major Roles

• Movement: Produces external (walking, running, talking) and internal (heartbeat, blood pressure, digestion) body movements.

• Posture: Maintains body posture.

• Stabilization: Stabilizes joints by maintaining muscle tone.

• Thermogenesis: Generates heat through normal contractions and shivering.

Functional Characteristics of Muscle Tissue

• Excitability (Irritability): Ability to receive and respond to stimuli (usually chemical signals).

• Contractility: Ability to shorten forcibly when stimulated.

• Extensibility: Ability to be stretched without damage.

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

• Conductivity: Ability to conduct excitation (action potentials) along the cell membrane.

Additional info:

• Further sections in the original document (not shown in the images) likely cover microscopic anatomy, muscle contraction mechanisms, and clinical correlations.