��Essentials of Human Anatomy �Anatomy of the Muscular System ����

Introduction

• There are more than 600 skeletal muscles in the body.
• Half of the body’s weight is muscle tissue.
• Skeletal muscle ~ 40% in males, 32% in females
• Muscles, along with the skeleton, determine the form and contour of the body.

(b) Cardiac muscle

(c) Visceral smooth muscle

(a) Skeletal muscle

Three Types of Muscular Tissue

Three Types of Muscular Tissue

Functions of skeletal Muscles

1. Body movements
2. Maintaining Posture
3. Stabilizing Joints
4. Generating heat

Functions of skeletal Muscles

Movement:

• muscle move bones by pulling (not pushing).
• Synergists:
• Most movements are generally accomplished by more than one muscle.
• The muscles responsible for the same movement are called synergists.
• Prime Mover (agonist):
• The muscle that is most responsible for the movement.

Functions of skeletal Muscles

• Muscles and muscle groups usually work in pairs causing opposite actions.
• Antagonists:
• A muscle that opposes the agonist.
• The biceps flex the arm, and its partner the triceps extends the arm.
• The two muscles are antagonists.
• When one contracts, the other relaxes.
• Levators:
• muscles that raise a body part.
• Fixator:
• A muscle that stabilizes the origin of another muscle.
• Note: a single muscle can be any of the above at one time or another.

Functions of skeletal Muscles

Maintenance of posture:

• The body position is maintained because of tonic contractions in skeletal muscles.
• These contractions don’t produce movement yet hold the muscles in position.

Heat production:

• Contraction of muscles produces most of the heat required to maintain body temperature.

4 Unique Characteristics of Muscle Tissue

1. Excitability: equated with responsiveness.
2. Contractility: causes the fiber to shorten resulting in a pull on bones and movement of the body part.
3. Elasticity: is the muscle’s ability to return to its original length when tension is released.
4. Extensibility: is capability of extending in length in response to the contraction of opposing muscle fibers.

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Structure of a Skeletal Muscle

Skeletal muscles:

• Organs of the muscular system, composed of:
• 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:
• 1 mm 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 fascicles together
• Epimysium
• Coarse sheath covering the muscle as a whole
• These three fibrous components may become �a tendon or an aponeurosis

A muscle, a fasciculus, and a fiber all visualized

Organization of Muscle Tissue

Organization of a muscle fiber

Organization of Muscle Tissue

Connective Tissue Coverings

• Fascia
• Surrounds an individual skeletal muscle, separating it from other muscles
• Fascia may extend beyond the ends of the muscle to contribute to tendons
• Fascia may connect muscle to muscle and is called an aponeurosis

Fascia

Muscle Fiber Structure

• 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.
• Light bands, called I bands, contain thin filaments only.
• At either end of a thick filament is a region where thin filaments extend into the A band between the stacked thick filaments.

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Sliding Filament Mechanism

Neuromuscular Junction

• Myoneural Junction
• The spot where the axon of a motor nerve nears the muscle fiber.
• The axon terminal does not touch the muscle but comes close.
• The space between the axon and the muscle cell is called the synapse.
• Within the terminal end of the axon are small sacs filled with a neurotransmitter called acetylcholine.

Motor Unit

• Consists of a motor neuron and all the myofibers it innervates.
• Units for fine control have fewer fibers.
• Units for gross control have many fibers.

Three Types of Skeletal Muscle Fibers

• Fast (type IIb)
• 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 (type IIa)
• resemble fast fibers.
• a hybrid of type I and II fibres. These fibres contain a large number of mitochondria and Myoglobin
• have a greater resistance to fatigue.
• Slow (type I)
• Smaller.
• They contract more slowly.
• called red fibers due to abundant myoglobin.

Skeletal Muscles Classification

• According to:
1. Fascicles organization.
2. Relationships of fascicles to tendons.

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• 4 patterns of fascicle organization:
2. Parallel
3. Convergent
4. Pennate
5. Circular

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Parallel Muscles

• Fibers are 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 by about 30%.

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Convergent Muscles

• A broad area converges on attachment site (tendon, aponeurosis).
• Muscle fibers can 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

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Circular Muscles

• Also called sphincters.
• Open and close to guard entrances of body.
• e.g., obicularis oris.

Types of Contractions

1. Isometric (iso=same, metric=length)– muscle contracts but does not change length.
2. Isotonic – muscle contracts and changes length.
1. Concentric – shortening contraction.
2. Eccentric – lengthening contraction.

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Anatomy of Skeletal Muscles

• Origin—
• stationary end of a muscle when contracts
• Belly--
• thicker, middle region of muscle
• Insertion—
• mobile end of muscle

Biceps brachii

Descriptive Names of 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, brachioradialis 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
• Movements: e.g., flexor, extensor, retractor.

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Names for Muscle Size

• Longus = long.
• Longissimus = longest.
• Teres = long and rounded.
• Brevis = short.

• Magnus = large
• Major = larger
• Minor = smaller
• Maximus = largest
• Minimus = smallest

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Muscles Named by Location

• Epicranius
• (around cranium)
• Tibialis anterior
• (front of tibia)

Naming Skeletal Muscles: Shape

• Deltoid (triangle)
• Trapezius (trapezoid)
• Serratus (saw-toothed)
• Rhomboideus (Rhomboid)
• Orbicularis and Sphincters (circular)

Muscles Named by�Direction of Fibers

• Rectus (straight)
• parallel to the long axis
• Transverse
• Oblique

Muscles Named for�Number of Origins

• Biceps (2)
• Triceps (3)
• Quadriceps (4)

Muscles Named for Origin and�Insertion

• Sternocleidomastoid
• originates from sternum and clavicle and inserts on mastoid process of temporal bone

Muscles Named for Action

• Flexor carpi radialis
• flexes wrist in the radial direction
• Abductor pollicis brevis
• flexes thumb
• Adductor magnus
• adducts thigh
• Extensor digitorum
• extends fingers

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.

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• 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 exercise.
• 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.

Muscle Trivia

• How many muscles are there in the human body?
• Answer: 640 Muscles
• The muscles make up about 40 % of the body mass.
• What is the longest muscle in the body?
• Answer: The Sartorius
• The Sartorius runs from the outside of the hip, down and across to the inside of the knee. It twists and pulls the thigh outwards.
• What is the smallest muscle in the body?
• Answer: The Stapedius
• The Stapedius is located deep in the ear. It is only 5mm long and thinner than a cotton thread. It is involved in hearing.
• What is the biggest muscle in the body?
• Answer: The Gluteus Maximus
• The Gluteus Maximus is located in the buttock. It pulls the leg backwards powerfully for walking and running.

• There are about 60 muscles in the face.
• Smiling is easier than frowning.

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• It takes 20 muscles to smile and over 40 to frown.

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• Smile and make someone happy.

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.

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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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