Chapter 2 Neuromuscular Fundamentals PPT Series 2A EXSC 314 Chapter 2 Neuromuscular Fundamentals PPT Series 2A

Skeletal Muscles Skeletal muscle contraction produces the force that causes joint movement. Skeletal Muscles also: Provide protection Provide dynamic stability of joints Contribute to posture and support Produce a major portion of total body heat (How?)

Skeletal Muscles FYI - Over 600 skeletal muscles comprise approximately 40% to 50% of body weight. There are 215 pairs of skeletal muscles that usually work in cooperation with each other to perform opposite actions at the joints they cross Aggregate muscle action - Muscles work in groups rather than independently to achieve a given joint motion.

Muscle Nomenclature Muscles are usually named by: Shape Action and Shape Size Action and Size Number of divisions Shape and location Direction of fibers Location and attachment Location Location and number of divisions Points of attachment Action

Muscle Nomenclature Shape: Deltoid Rhomboid

Muscle Nomenclature Size: Teres Minor Gluteus Maximus

Muscle Nomenclature Number of Divisions: Triceps brachii Direction of Fibers: External abdominal oblique Triceps brachii

Muscle Nomenclature Location: Rectus femoris Palmaris longus

Muscle Nomenclature Points of Attachment: Extensor hallucis longus Flexor digitorum longus Coracobrachialis

Muscle Nomenclature Action: Supinator Extensor digiti minimi Erector spinae

Muscle Nomenclature Action and shape: Adductor magnus Action and size: Pronator quadratus Adductor magnus

Muscle Nomenclature Shape and location : Serratus anterior Location and attachment : Serratus anterior Brachioradialis

Muscle Nomenclature Location and Number of Divisions: Biceps femoris

Muscle Grouping and Naming Muscles are often grouped together for appearance and shared function (action). Examples: Shape – Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus) Number of divisions – Quadriceps (Medius, Lateralis, Intermedius) Location – Abdominal (Oblique: external, internal, Transverse, Rectus) Action - Rotator Cuff

Shape of Muscles and Fiber Arrangement Cross-section diameter A factor in muscle’s ability to exert force Keeping all other factors constant, a muscle with a greater cross-section diameter will be able to exert a greater force Muscle’s ability to shorten Longer muscles can shorten through a greater range More effective in moving joints through large ranges of motion

Shape of Muscles and Fiber Arrangement Muscles have different shapes and fiber arrangements. Shape and fiber arrangement determine: Muscle’s ability to exert force ROM the muscle can effectively exert force onto the bones Major types of fiber arrangements Parallel and Pennate Each is further subdivided according to shape

Shape of Muscles and Fiber Arrangement Parallel muscles Fibers arranged parallel to the length of the muscle Produce a greater range of movement than similar-sized muscles with a pennate arrangement Categorized into the following shapes: Flat Fusiform Strap Radiate Sphincter or circular

Fiber Arrangement - Parallel Flat muscles Example - Rectus abdomins Usually thin and broad, originating from broad, fibrous, sheet-like aponeuroses (Link) Allows muscles to exert forces over a broad area

Fiber Arrangement - Parallel Fusiform muscles Example – Biceps brachii Spindle-shaped with a central belly that tapers to tendons on each end Muscle exerts power on small, bony targets

Fiber Arrangement - Parallel Strap muscles Example - Sartorius More uniform in diameter with essentially all fibers arranged in a long parallel manner Muscles can exert power on small, bony targets

Fiber Arrangement - Parallel Radiate muscles Example - Pectoralis major Also described sometimes as being triangular, fan- shaped, or convergent Have combined arrangement of flat and fusiform Originate on broad aponeuroses and converge onto a tendon

Fiber Arrangement - Parallel Sphincter or circular muscles Technically, endless strap muscles Surround openings and function to close them upon contraction Example - orbicularis oculi muscle surrounding the eye

Fiber Arrangement - Pennate Pennate muscles Have shorter fibers Fibers are arranged obliquely to tendons in a manner similar to a feather Arrangement increases the cross-sectional area of the muscle, thereby increasing the power Categorized based on the exact arrangement between fibers and tendon Unipennate Bipennate Multipennate

Fiber Arrangement - Pennate Unipennate muscles Example - Biceps femoris Fibers run obliquely from a tendon on one side only

Fiber Arrangement - Pennate Bipennate muscle Example - Rectus femoris Fibers run obliquely on both sides from a central tendon.

Fiber Arrangement - Pennate Multipennate muscles Example - Deltoid Have multiple tendons with fibers running diagonally between the tendons Bipennate and unipennate produce the strongest contractions

Muscle Tissue Properties Skeletal muscle tissue has four properties related to force production and movement: Irritability or excitability, contractility, extensibility, and elasticity. Irritability or excitability - Muscle property of being sensitive or responsive to chemical, electrical, or mechanical stimuli Contractility - Ability of muscle to contract and develop tension or internal force against resistance when stimulated Extensibility - Ability of muscle to be passively stretched beyond its normal resting length Elasticity - Ability of muscle to return to its original length following stretching.

Muscle Terminology Intrinsic - Pertaining usually to muscles within or belonging solely to the body part on which the muscle exerts force. Extrinsic - Pertaining usually to muscles that arise or originate outside of (proximal to) the body part on which the muscle exerts force.

Muscle Terminology Action - Specific movement of a joint resulting from a concentric contraction of a muscle that crosses the joint. Actions are usually caused by a group of muscles working together. Any of the muscles in the group can be said to cause an action, even though it is usually an effort of the entire group A muscle may cause more than one action either at the same joint or a different joint depending upon the characteristics of the joint crossed by the muscle

Muscle Terminology Innervation - Segment of the nervous system responsible for providing a stimulus to muscle fibers within a specific muscle or section of the muscle A muscle may be innervated by more than one nerve, and a particular nerve may innervate more than one muscle or section of a muscle

Muscle Terminology Amplitude - Range of muscle fiber length between maximal and minimal lengthening Gaster (belly or body) - Central, contractile portion of the muscle that generally increases in diameter as the muscle contracts Tendon - Fibrous connective tissue, often cordlike in appearance, that connects muscles to bones and other structures Two muscles may share a common tendon A muscle may have multiple connecting tendons

Muscle Terminology Aponeurosis - A tendinous expansion of dense fibrous connective tissue that is sheet- or ribbon-like in appearance and resembles a flattened tendon. Aponeuroses serve as a fascia to bind muscles together or as a means of connecting muscle to bone. Palmar aponeurosis

Muscle Terminology Fascia - A sheet or band of fibrous connective tissue that envelopes, separates, or binds together parts of the body such as muscles, organs, and other soft-tissue structures of the body. In some regions, (wrist and ankle), fascial tissue forms a retinaculum to retain tendons close to the body

Muscle Terminology Origin - Structurally, the proximal attachment of a muscle or the part that attaches closest to the midline or center of the body. Functionally and historically, the origin is the least movable part or attachment of the muscle. Insertion - Structurally, the distal attachment or the part that attaches farthest from the midline or center of the body. Functionally and historically, the most movable part is generally considered the insertion

Muscle Terminology In some movements the “fixed” or “stable” end may be reversed. Example - Biceps curl exercise Biceps brachii origin (least movable bone) is on the scapula and its insertion (most movable bone) on the radius HOWEVER, The movable end may be reversed… Example - Pull-up Radius is relatively stable and the scapula moves up End of PPT Series 2A