Muscle General Information PDF

## Types of Muscle | Type of Muscle | Location | Appearance of Cells | Type of Activity | Stimulation | |---|---|---|---|---| | **Skeletal Muscle (Striated)** | Forms the majority of the muscles (e.g., biceps brachii) attached to the skeleton or to the fascia of the limbs, body wall, and head/nec...

## Types of Muscle | Type of Muscle | Location | Appearance of Cells | Type of Activity | Stimulation | |---|---|---|---|---| | **Skeletal Muscle (Striated)** | Forms the majority of the muscles (e.g., biceps brachii) attached to the skeleton or to the fascia of the limbs, body wall, and head/neck | Large, long, unbranched, cylindrical fibers with transverse striations (bands) running parallel; multiple nuclei located peripherally | Intermittent (phasic) contraction above a baseline tone; acts primarily to produce movement (isotonic contraction) by shortening (concentric contraction) or controlled lengthening (eccentric contraction), or to maintain position against gravity or other force without producing movement (isometric contraction) | Voluntary (or reflex) through the somatic nervous system | | **Cardiac Muscle (Striated)** | Muscle of the heart (myocardium) and portions adjacent to large vessels (aorta, vena cava) | Short fibers that branch and anastomose with transverse striations (bands) running parallel and connected at their ends by complex junctions (intercalated disks); single, central nucleus | Rhythmic, strong, and continuous contraction; acts by pumping blood from the heart | Involuntary; stimulated and propagated intrinsically (myogencially); frequency and strength of contraction modified by the autonomic nervous system or the enteric nervous system | | **Smooth Muscle (Non-Striated)** | Walls of hollow viscera and blood vessels, iris and ciliary body of the eye; attaches to the hair follicles of the skin (arrector pili muscle) | Small, spindle-shaped fibers; independent or aggregated, without striations, single, central nucleus | Weak, slow, rhythmic or sustained-tone contraction; acts primarily to propel substances (peristalsis, vascular pulse) and restrict flow (vasoconstriction and sphincter activity) | Involuntary through the autonomic nervous system or the enteric nervous system | ## Muscle Classifications **General Classifications** - Muscles are named according to their general features. - **Muscular Location:** Medial, lateral, anterior, posterior - **Muscular Length:** Short, long - **Muscular Position:** Superficial, deep ** Classifications by Shape and Fiber Arrangement** - **Flat Muscles:** Have parallel fibers and are often broad. An example is the **oblique external muscle of the abdomen**. - **Penniform Muscles:** Resemble a feather in the arrangement of their fasciculi. Can be: - **Unipenniform:** Fibers are arranged on one side of the tendon, an example is the **extensor digitorum longus**. - **Bipenniform:** Fibers are arranged on both sides of a central tendon, an example is the **rectus femoris**. - **Multipenniform:** Fibers are attached to multiple tendons, an example is the **deltoid muscle**. - **Fusiform Muscles:** Spindle-shaped muscles with a thick central belly and tapered ends. An example is the **biceps brachii**. - **Convergent Muscles:** Converge from a broad origin to a single tendon. An example is the **pectoralis major**. - **Circular Muscles or Sphincters:** Encircle an opening. An example is the **orbicularis oculi muscle** (which closes the eyelids). - **Quadrate Muscles:** Have four sides. An example is the **rectus abdominis muscle**. **Each skeletal muscle:** - An independent organ - Composed of hundreds or thousands of cells called muscle fibers (myocytes) - Also includes connective tissue, blood vessels, and nerves ## Components of Connective Tissue - **Subcutaneous Layer (Hypodermis)** - Separates muscle from the skin - Composed of loose areolar and adipose tissue - Allows passage of blood vessels, nerves, and lymphatic vessels - Stores fat - Provides insulation and protects muscles from trauma - **Fascia:** - Dense connective tissue sheet that surrounds muscles and other organs - Helps organize muscles - Allows for movement of muscles - Contains blood vessels, nerves, and lymphatic vessels - There are three layers of connective tissue that surround skeletal muscle: - **Epimysium:** - Outermost layer surrounding the entire muscle - Dense irregular connective tissue - **Perimysium:** - Surrounds fascicles (bundles of muscle fibers) - Dense irregular connective tissue - **Endomysium:** - Surrounds individual muscle fibers - Reticular connective tissue <start_of_image> - **Tendons:** - Rope-like extensions of connective tissue that attach muscle to bone - **Aponeurosis:** - Broad, sheet-like tendons that attach muscle to bone or other muscles **Fig. 10.1:** - Shows the organization of skeletal muscle and its connective tissue coverings - Connective tissue coverings provide support and protection for muscles - Connective tissue coverings allow for the transmission of forces from muscle to bone - **Epimysium** surrounds the whole muscle. - **Perimysium** surrounds **fascicles**, which are bundles of muscle fibers. - **Endomysium** surrounds individual muscle fibers - **Tendons** are cord-like structures that attach muscle to bone. - **Aponeurosis** are thin, sheet-like tendons that attach muscle to bone or other muscles. ## Sarcolema, Transverse Tubules, and Sarcoplasm - **Sarcolema:** - The plasma membrane of a muscle fiber - Surrounds the sarcoplasm - **Transverse Tubules (T-Tubules):** - Invaginations of the sarcolema that extend deep into the muscle fiber - Allow for the rapid transmission of nerve impulses to the interior of the muscle fiber - **Sarcoplasm:** - The cytoplasm of a muscle fiber - Contains many organelles, including mitochondria, glycogen granules, and myofibrils - Contains myoglobin, a protein that binds to oxygen ## Muscle Myofibrils and Sarcoplasmic Reticulum - **Myofibrils:** - Long, cylindrical structures that run the length of the muscle fiber - Composed of thin and thick filaments (actin and myosin) - **Sarcoplasmic Reticulum (SR):** - Network of membranous sacs that surround the myofibrils - Stores calcium ions, which are released during muscle contraction - Also contains proteins that help transport calcium ions ## Summary of Muscle Structure - Muscles are made up of bundles of muscle fibers, enclosed in connective tissue. - Muscle fibers are made up of myofibrils. - Myofibrils are made up of thin and thick filaments that slide past each other during muscle contraction. - The sarcoplasmic reticulum helps regulate calcium ions during muscle contraction. - The sarcolema is the plasma membrane of a muscle fiber. - **All of these structures work together to produce muscle contraction and movement.**