Muscular System 1 Prof. Abdulameer Al-Nuaimi E-mail: a.al-nuaimi@sheffield.ac.uk E. mail: abdulameerh@yahoo.com

Skeletal muscle tissue Is so named because the function of most skeletal muscles is to move bones of the skeleton. There are a few that attach to structures other than bone, such as the skin or even other skeletal muscles. Skeletal muscle tissue is referred to as striated because alternating light and dark protein bands (striations) are visible when the tissue is examined under a microscope. Skeletal muscle tissue works primarily in a voluntary manner; its activity can be consciously (voluntarily) controlled.

Functions of Muscular Tissue 1-Producing body movements. Total body movements such as walking and running, and localized movements such as grasping a pencil 2-Stabilizing body positions. Skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting. 3-Storing and moving substances within the body. Sustained contractions of ringlike bands of smooth muscles called sphincters may prevent outflow of the contents of a hollow organ (like holding urine in the bladder) 4- Producing heat. When muscular tissue contracts, it produces heat, a process called thermogenesis. Much of that heat used to maintain normal body temperature. Involuntary contractions of skeletal muscles, known as shivering, can dramatically increase the rate of heat production.

Structure of a Skeletal Muscle Skeletal muscle consists of a muscle belly connected by tendons attached to the skeleton. Muscle belly is the reddish or meatlike appearance, it can be an elongated, thick, rounded mass, a triangular shape, a thick rectangular mass, or a thin, flat sheet of muscular tissue. Tendons: are tough, glistening white dense regular connective tissue. Tendon attaches the muscle belly to the bones. They are minimally vascular, and consist parallel arrangements of collagen fibres. Their shapes could be 1- long, ropelike structures, 2- flat sheets called aponeuroses and 3- bands or extensions of connective tissue that are so short they make the muscle body appear as if it attaches directly to the bone.

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long, ropelike tendons flat sheets called aponeuroses bands or extensions of connective tissue that are so short

Structure of Skeletal Muscle If you take one whole muscle and cut through it, you would find the muscle is covered in a layer of connective muscle tissue known as the Epimysium. The Epimysium protects the muscle from friction against other muscles and bones. It also continues at the end of the muscle to form (along with other connective tissues) the muscles tendon. Looking at the cross section of the muscle you can see bundles of fibres, known as Fasciculi, which are surrounded by another connective tissue, called the Perimysium. Each Fascicule contains anywhere between 10 and 100 muscle fibres

Muscle cell ( )

Muscle fibre is covered in a fibrous connective tissue, known as Endomysium which insulates each muscle fibre. Muscle fibres can range from 10 to 80µ in diameter and may be up to 35cm long. Beneath the Endomysium and surrounding the muscle fibre is the Sarcolemma which is the fibres cell membrane and beneath this is the Sarcoplasm, which is the cells cytoplasm. This contains Glycogen and Fats for energy and also Mitochondria which are the cells powerhouses, inside which the cells energy is produced. Each muscle fibre itself contains cylindrical organelles known as Myofibrils. Each muscle fibre contains hundreds to thousands of Myofibrils. Myofibril contains bundles of Actin and Myosin proteins which run the length of the muscle fibre and are important in muscle contraction.

Surrounding the Myofibril there is a network of tubules and channels called the Sarcoplasmic Reticulum in which Calcium is stored which is important in muscle contraction. Transverse tubules pass inwards from the Sacrolemma throughout the Myofibril, through which nerve impulses travel. Each Myofibril can then be divided into functional repeating segments called Sarcomeres

Sarcoplasmic Reticulum Transverse tubule Sarcoplasmic Reticulum

Myocyte Skeletal Muscle

The sarcomeric subunits of one myofibril are in nearly perfect alignment with those of the myofibrils next to it. This alignment gives rise to certain optical properties which cause the cell to appear striped or striated. In smooth muscle cells, this alignment is absent, hence there are no apparent striations and the cells are called smooth Myofibril Myosin Actin Myocyte Striation of skeletal muscle

Muscle action Lever Systems A lever is a rigid structure that can move around a fixed point called a fulcrum, A lever is acted on at two different points by two different forces: the effort (E), which causes movement, and the load or resistance, which opposes movement. The effort is the force exerted by muscular contraction; the load is typically the weight of the body part that is moved or some resistance that the moving body part is trying to overcome (such as the weight of a book you might be picking up). Motion occurs when the effort applied to the bone at the insertion exceeds the load, an object is lifted.

Muscle Function = Lever + Fulcrum + Load L = Load F F = Fulcrum E E = Effort L E L E L F F E E E L L L F F F Muscle Function = Lever + Fulcrum + Load

Muscle Attachments And Actions There are over 600 muscles in the human body Muscles Attach to Bones At Locations Called Origins and Insertions They are attached to the membrane covering the bone called periosteum Origin: The attachment of a muscle to a bone is called an origin If that bone remains immobile during contraction of the muscle. Insertion: If the muscle attachment is on a bone that moves during the action, the attachment is called an insertion Flexion: decreasing the angle between two bones (bending) Extension: increasing the angle between two bones (straightening a bend)

Abduction: moving away from the body’s midline. Adduction: moving toward the body’s midline. Pronation: rotating the forearm so the palm is facing backward or down. Supination: rotating the forearm so the palm is facing forward or up. Elevation: moving a body part up. Depression: moving a body part down. Protraction: moving a bone forward without changing the angle. Retraction: moving a bone backward without changing the angle. Inversion: turning the sole of the foot inward. Eversion: turning the sole of the foot outward. Dorsiflexion: bringing your foot upward toward your tibia. Plantar flexion: depressing your foot.

How Skeletal Muscles are Named Knowing the names of a muscle will give you clues about its features. The following features are used in naming the muscles the pattern of the muscle’s fascicles; the size, shape, action, number of origins, location of the muscle; the sites of origin and insertion of the muscle and Orientation of muscle fascicles relative to the body’s midline NAME MEANING EXAMPLES Rectus Parallel to midline: Rectus abdominis Transverse Perpendicular to midline: Transversus abdominis Oblique Diagonal to midline :External oblique SIZE: Relative size of the muscle. Maximus Largest : Gluteus maximus Minimus Smallest : Gluteus minimus Longus Long : Adductor longus

Brevis Short :Adductor brevis Latissimus Widest : Latissimus dorsi Longissimus Longest : Longissimus capitis Magnus Large : Adductor magnus Major Larger : Pectoralis major Minor Smaller : Pectoralis minor Vastus Huge : Vastus lateralis SHAPE: Relative shape of the muscle. Deltoid Triangular : Deltoid Trapezius Trapezoid : Trapezius Serratus Saw-toothed : Serratus anterior Rhomboid Diamond-shaped : Rhomboid major Orbicularis Circular : Orbicularis oculi Pectinate Comblike : Pectineus Piriformis Pear-shaped : Piriformis Platys Flat : Platysma

Quadratus Square, four-sided : Quadratus femoris Gracilis Slender : Gracilis ACTION: Principal action of the muscle. Flexor Decreases a joint angle : Flexor carpi radialis Extensor Increases a joint angle : Extensor carpi ulnaris Abductor Moves a bone away from the midline : Abductor pollicis longus Adductor Moves a bone closer to the midline : Adductor longus Levator Raises or elevates a body part : Levator scapulae Depressor Lowers or depresses a body part : Depressor labii inferioris Supinator Turns palm anteriorly :Supinator Pronator Turns palm posteriorly : Pronator teres Sphincter Decreases the size of an opening : External anal sphincter

Tensor Makes a body part rigid : Tensor fasciae latae Rotator Rotates a bone around its longitudinal axis :Rotatore NUMBER OF ORIGINS: Number of tendons of origin. Biceps Two origins : Biceps brachii Triceps Three origins : Triceps brachii Quadriceps Four origins :Quadriceps femoris LOCATION: Structure near which a muscle is found. Example: Temporalis, a muscle near the temporal bone. ORIGIN AND INSERTION: Sites where muscle originates and inserts. Example: Sternocleidomastoid, originating on the sternum and clavicle and Inserting on mastoid process of temporal bone

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