essentials of human anatomy essentials of human anatomy anatomy of the muscular system chapter 6 dr...
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Essentials of Human Anatomy Essentials of Human Anatomy Anatomy of the Muscular System
Chapter 6
Dr Fadel NaimAss. Prof. Faculty of Medicine
IUG
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
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
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
• Multiple nuclei• Sarcolemma• T-tubules• Sarcoplasmic reticulum• Sarcoplasm
– Mitochondria– Glycogen & ions– Myofibrils
Muscle Fiber Structure
Skeletal Muscle Has Striations
• Appearance is due to size and density differences between thick filaments and thin filaments.
• Under the light microscope, two differently shaded bands are present.
• The dark bands, called A bands, contain the entire thick filament.
• At either end of a thick filament is a region where thin filaments extend into the A band between the stacked thick filaments.
• Light bands, called I bands, contain thin filaments only.• I band is lighter shaded than an A band because only
the thin filaments occupy this region.
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
skeletal muscles Classification
• By the way fascicles are organized
• By relationships of fascicles to tendons
– 4 patterns of fascicle organization:• parallel• convergent• pennate• circular
Parallel Muscles
• Fibers parallel to the long axis of muscle
• e.g., biceps brachii
• The center or body of the muscle thickens when parallel muscle contracts
• Parallel muscles contract about 30%
Convergent Muscles
• A broad area converges on attachment site (tendon, aponeurosis, or raphe)
• Muscle fibers pull in different directions, depending on stimulation
• e.g., pectoralis muscles
Pennate Muscles
• Unipennate:
– fibers on 1 side of tendon e.g., extensor digitorum
• Bipennate:
– fibers on both sides of tendon e.g., rectus femoris
• Multipennate:
– tendon branches within muscle e.g., deltoid
Circular Muscles
• Also called sphincters
• Open and close to guard entrances of body
• e.g., obicularis oris
Types of Contractions
• isotonic – muscle contracts and changes length
• concentric – shortening contraction
• eccentric – lengthening contraction
• isometric – muscle contracts but does not change length
Descriptive Names or Skeletal Muscles
1. Location in the body-identifies body regions:– e.g., temporalis muscle
2. Origin and insertion-First part of name indicates origin, second part of name indicates insertion: e.g., genioglossus muscle
3. Fascicle organization-Describes fascicle orientation within muscle: i.e., rectus (straight), transversus, oblique
4. Relative position- • Externus (superficialis):visible at body surface• Internus (profundus):deep muscles• Extrinsic:muscles outside an organ• Intrinsic:muscles inside an organ
5. Structural characteristics • Number of tendons: bi = 2, tri = 3• Shape: trapezius, deltoid, rhomboid• Size
6. Action
Names for Muscle Size
• Longus = long
• Longissimus = longest
• Teres = long and round
• Brevis = short
• Magnus = large
• Major = larger
• Maximus = largest
• Minor = small
• Minimus = smallest
• Action – Movements:
• e.g., flexor, extensor, retractor
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.
Three Types of Skeletal Muscle Fibers
• Fast– are large in diameter – contain large glycogen reserves– densely packed myofibrils– relatively few mitochondria – called white fibers due to lack of myoglobin– majority of skeletal muscle fibers in the body
• Intermediate– resemble fast fibers; however– have a greater resistance to fatigue
• Slow– smaller and they – contract more slowly– called red fibers because due to myoglobin
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
Cycle of Life: Muscular System
• Life cycle changes—manifested in other components of functional unit– Infancy and childhood—coordination and controlling
of muscle contraction permits sequential development steps
• Degenerative changes of advancing age result in replacement of muscle cells with nonfunctional connective tissue– Diminished strength
Cycle of Life: Muscular System
• Muscle cells—increase or decrease in number, size, and ability to shorten at different periods
• Pathological conditions at different periods may affect the muscular system
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.