Essentials of Human Anatomy Muscular System

Introduction There are more than 600 skeletal muscles in the body From 40% to 50% of body weight is skeletal muscle Muscles, along with the skeleton, determine the form and contour of the body

Functions of skeletal Muscles Body movements Maintaining Posture Stabilizing Joints Body positions Generating heat

Muscular System Three basic muscle types are found in the body Skeletal muscle Cardiac muscle Smooth muscle

Types Of Muscle

4 Unique Characteristics of Muscle Tissue Excitability is equated with responsiveness. Contractility causes the fiber to shorten resulting in either a pull on bones or the movement of specific body parts. Elasticity is the muscle’s ability to return to its original length when tension is released. Extensibility is capability of extending in length in response to the contraction of opposing muscle fibers.

Structure of a Skeletal Muscle Organ of the muscular system - skeletal muscle tissue - nervous tissue - blood - connective tissues Fascia Tendons Aponeuroses

Skeletal Muscle Tissue Skeletal muscles are organs Vary in shape and size A skeletal muscle is composed of cells Each cell is as long as the muscle Small muscle: 100 micrometers long; 10 micrometers in diameter Large muscle: 35 centimeters long; 100 micrometers in diameter

Skeletal Muscle Structure Connective tissue components Endomysium Delicate connective tissue membrane that covers specialized skeletal muscle fibers Perimysium Tough connective tissue binding together fascicles Epimysium Coarse sheath covering the muscle as a whole These three fibrous components may become a tendon or an aponeurosis

Skeletal Muscle Anatomy

Muscle Fiber Structure Multiple nuclei Sarcolemma T-tubules Sarcoplasmic reticulum Sarcoplasm Mitochondria Glycogen & ions Myofibrils

Muscle Fiber Structure

Sliding Filament Mechanism

Neuromuscular Junction Also known as myoneural junction Site where an axon and muscle fiber meet Motor neuron Motor end plate Synapse Synaptic cleft Synaptic vesicles Neurotransmitters

Motor Unit single motor neuron all muscle fibers controlled by motor neuron

Types of Contractions Eccentric – lengthening contraction Concentric – shortening contraction Eccentric – lengthening contraction Isometric – muscle contracts but does not change length Isotonic – muscle contracts and changes length

Muscle Atrophy Reduction in muscle size, tone, and power. Due to reduced stimulation, it loses both mass and tone. Muscle becomes flaccid, and its fibers decrease in size and become weaker. Even a temporary reduction in muscle use can lead to muscular atrophy.

Muscle Hypertrophy An increase in muscle fiber size. Muscle size may be improved by exercising. Repetitive, exhaustive stimulation of muscle fibers results in more mitochondria, larger glycogen reserves, and an increased ability to produce ATP. Ultimately, each muscle fiber develops more myofibrils, and each myofibril contains a larger number of myofilaments.

Posture Maintaining the posture of the body is one of the major roles muscles play “Good posture”—body alignment that most favors function and requires the least muscular work to maintain, keeping the body’s center of gravity over its base

Posture How posture is maintained Muscles exert a continual pull on bones in the opposite direction from gravity Structures and systems other than muscle and bones have a role in maintaining posture Nervous system—responsible for determining muscle tone and also regulation and coordination of the amount of pull exerted by individual muscles Respiratory, digestive, excretory, and endocrine systems all contribute to maintain posture

Axial Muscles Have both their origins and insertions on parts of the axial skeleton. Support and move the head and spinal column. Function in nonverbal communication by affecting facial features. Move the lower jaw during chewing. Assist in food processing and swallowing. Aid breathing. Support and protect the abdominal and pelvic organs. Are not responsible for stabilizing or moving the pectoral or pelvic girdles or their attached limbs.

Appendicular Muscles Control the movements of the upper and lower limbs. Stabilize and control the movements of the pectoral and pelvic girdles. Organized into groups based on their location in the body or the part of the skeleton they move. Work in groups that are either synergistic or antagonistic.

Appendicular Muscles Organized into specific groups. muscles that move the pectoral girdle muscles that move the glenohumeral joint/arm arm and forearm muscles that move the elbow joint/forearm forearm muscles that move the wrist joint, hand, and fingers intrinsic muscles of the hand

Intramuscular Injections The gluteus maximus is a large, thick muscle with coarse Fasciculi that can be easily separated without damage. The great thickness of this muscle makes it ideal for intramuscular Injections. To avoid injury to the underlying Sciatic nerve, the injection should be given well forward On the upper outer quadrant of the buttock.

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