Chapter 8 (PART TWO)
Types of Contractions
Isotonic Contractions: Muscle contracts and changes length while generating equal force.
Concentric Contraction: Muscle shortens while contracting.
Eccentric Contraction: Muscle lengthens while contracting.
Isometric Contractions: Muscle contracts but does not change length; there is a change in force.
(a) Muscle contracts with a force greater than resistance, resulting in a shortening contraction (concentric contraction).
(b) Muscle contracts with a force less than resistance, leading to a lengthening contraction (eccentric contraction).
(c) Muscle contracts but does not change length, indicating an isometric contraction.
Smooth Muscle
Characteristics of Smooth Muscle Cells
Smooth muscle cells are elongated with tapered ends and lack striations, giving them a "smooth" appearance.
They possess a relatively undeveloped sarcoplasmic reticulum.
Contains thick and thin filaments arranged more randomly compared to skeletal muscle.
Types of Smooth Muscle
Multiunit Smooth Muscle:
Found in blood vessels and the iris of the eye.
Fibers occur separately rather than as sheets and are stimulated by neurons and certain hormones.
Visceral Smooth Muscle:
Found in sheets within the walls of hollow organs.
Fibers can stimulate one another and demonstrate rhythmicity, contributing to peristalsis in tubular organs.
Smooth Muscle Contraction
Similarities with Skeletal Muscle Contraction
Both contractions involve reactions between actin and myosin.
Both are stimulated by membrane impulses, require an increase in calcium ions in the cells, and utilize ATP energy.
Differences from Skeletal Muscle Contraction
Neurotransmitters: Both acetylcholine (ACh) and norepinephrine can stimulate or inhibit smooth muscle contraction; however, only ACh stimulates skeletal muscle contraction.
Hormonal Influence: Hormones can stimulate or inhibit smooth muscle contraction but do not have this effect on skeletal muscle.
Speed of Contraction and Relaxation: Smooth muscle is slower to contract and relax compared to skeletal muscle.
Duration of Contraction: Smooth muscle can maintain a contraction longer with the same amount of ATP.
Length Change without Tautness Change: Smooth muscle can change length without altering tautness.
Cardiac Muscle
Location: Cardiac muscle is exclusively found in the heart.
Structure: Consists of branching, striated cells that interconnect to form three-dimensional networks.
Mechanism of Contraction
Similar to that of skeletal and smooth muscle but with differences:
Sarcoplasmic reticulum is not well-developed and does not store much calcium.
Transverse tubules provide additional calcium from extracellular fluid, resulting in longer-lasting twitches in cardiac muscle cells.
Cardiac muscle is self-exciting and rhythmic, creating a regular pattern of contraction and relaxation.
Intercalated Discs: Complex membrane junctions that join cells and transmit the force of contraction from one cell to another.
Types of Muscle Tissue
Table 8.3: Summary of Muscle Types
Skeletal Muscle:
Major Location: Skeletal muscles.
Major Function: Movement of bones at joints, maintenance of posture.
Cellular Characteristics: Striations (present), multiple nuclei.
Special Features: Well-developed transverse tubule system.
Mode of Control: Voluntary.
Contraction Characteristics: Contracts and relaxes rapidly when stimulated by a motor neuron.
Smooth Muscle:
Major Location: Walls of hollow viscera and blood vessels.
Major Function: Movement of viscera, peristalsis, vasoconstriction.
Cellular Characteristics: Striations (absent), single nucleus.
Special Features: Lacks transverse tubules.
Mode of Control: Involuntary.
Contraction Characteristics: Contracts and relaxes slowly; single-unit type is self-exciting and rhythmic.
Cardiac Muscle:
Major Location: Wall of the heart.
Major Function: Pumping action of the heart.
Cellular Characteristics: Striations (present), single nucleus.
Special Features: Well-developed transverse tubule system; intercalated discs separating adjacent cells.
Mode of Control: Involuntary.
Contraction Characteristics: Network of cells contracts as a unit; self-exciting; rhythmic.
Skeletal Muscle Actions
Key Terminology
Origin: The less movable end of a skeletal muscle.
Insertion: The more movable end of a skeletal muscle.
Muscle contraction pulls the insertion towards the origin.
Example Muscle: Biceps Brachii
Originates from the scapula (coracoid process and tubercle above the glenoid cavity).
Inserts at the radial tuberosity of the radius.
Located on the anterior surface of the humerus.
Action includes the flexion of the forearm at the elbow.
Muscle Relationships
Common Movements Across Joints
Flexion: Decrease in the angle between bones at a joint; e.g., flexion of the arm at the elbow bends the arm.
Extension: Increase in the angle between bones at a joint; e.g., extension of the arm at the elbow straightens the arm.
Muscle Groups Involved
Agonist (Prime Mover): The muscle that causes the action and does the majority of the work; e.g., brachialis.
Synergists: Muscles that assist the prime mover; e.g., biceps brachii.
Antagonists: Muscles that oppose an action; e.g., triceps brachii.
Functional Dependency: The relationships between muscles can change based on the action; a muscle can be a synergist for one action and an antagonist for another.
Naming of Skeletal Muscles
Naming Criteria Include:
Size.
Shape.
Location.
Action.
Number of attachments.
Direction of fibers.
Combinations of the above.
Examples of Muscle Names
Pectoralis Major: Named for size and location; large size and located in the chest.
Deltoid: Named for shape; triangular in shape.
Extensor Digitorum: Named for action; extends digits (fingers/toes).
Biceps Brachii: Named for number of attachments and location; has 2 origins (heads) and is found in the arm (brachium).
Sternocleidomastoid: Named for attachments; attaches to the sternum, clavicle, and mastoid process.
External Oblique: Named for location and direction of fibers; located on the outside of the body with fibers running at a slant.
Muscles of Facial Expression
Overview
Muscles of facial expression attach to underlying bones and the overlying connective tissue of skin, enabling a wide range of facial expressions (e.g., anger, fear, pain, disgust, surprise, happiness).
Major Muscles of Facial Expression:
Epicranius:
Origin: Occipital bone.
Insertion: Skin around the eye.
Action: Elevates the eyebrow.
Orbicularis Oculi:
Origin: Maxilla and frontal bone.
Insertion: Skin around the eye.
Action: Closes the eye.
Orbicularis Oris:
Origin: Muscle near the mouth.
Insertion: Skin of lips.
Action: Closes and protrudes lips.
Buccinator:
Origin: Alveolar processes of maxilla and mandible.
Insertion: Orbicularis oris.
Action: Compresses cheeks.
Zygomaticus:
Origin: Zygomatic bone.
Insertion: Skin and muscle at the corner of the mouth.
Action: Elevates the corner of the mouth.
Platysma:
Origin: Fascia in the upper chest.
Insertion: Skin and muscles below the mouth.
Action: Depresses the lower lip and angle of the mouth.
Muscles of Mastication
Overview
Chewing movements are derived from muscles attached to the mandible.
Major Chewing Muscles:
Masseter:
Origin: Zygomatic arch.
Insertion: Posterior lateral surface of mandible.
Action: Elevates and protracts mandible.
Temporalis:
Origin: Temporal bone.
Insertion: Coronoid process of mandible.
Action: Elevates and retracts mandible.
Muscles that Move the Head
Overview
Paired muscles in the neck and upper back cause flexion, extension, and rotation of the head.
Major Muscles:
Sternocleidomastoid:
Origin: Manubrium of sternum and medial clavicle.
Insertion: Mastoid process of temporal bone.
Action: Individually - laterally flexes head and neck to the same side, rotates head to the opposite side. Together - pulls head forward and down; aids in forceful inhalation by elevating sternum and first ribs.
Splenius Capitis:
Origin: Ligamentum nuchae; spinous processes of 7th cervical and upper thoracic vertebrae.
Insertion: Occipital bone and mastoid process of temporal bone.
Action: Individually - rotates head to the same side; Together - brings head into an upright position.
Semispinalis Capitis:
Origin: Below the articular facets of lower cervical vertebrae; transverse processes of upper thoracic vertebrae.
Insertion: Occipital bone.
Action: Individually - rotates head to the opposite side; Together - extend head and neck.
Scalenes:
Origin: Transverse processes of cervical vertebrae.
Insertion: Superior and lateral surface of first two ribs.
Action: Individually - laterally flexes head and neck to the same side; Together - elevate first two ribs during forceful inhalation.
Muscles That Move the Pectoral Girdle
Overview
Muscles that move the pectoral girdle are associated with those that move the arm and include chest and shoulder muscles affecting the scapula.
Major Muscles:
Trapezius:
Origin: Occipital bone, ligamentum nuchae, and spinous processes of 7th cervical and all thoracic vertebrae.
Insertion: Clavicle; spine and acromion process of scapula.
Action: Rotates and retracts scapula; superior portion elevates scapula, inferior portion depresses scapula.
Rhomboid Major:
Origin: Spinous processes of upper thoracic vertebrae.
Insertion: Medial border of scapula.
Action: Elevates and retracts scapula.
Levator Scapulae:
Origin: Transverse processes of cervical vertebrae.
Insertion: Superior angle and medial border of scapula.
Action: Elevates scapula.
Serratus Anterior:
Origin: Anterior surfaces of ribs 1 to 10.
Insertion: Medial border of scapula.
Action: Protracts and rotates scapula.
Pectoralis Minor:
Origin: Anterior surfaces of ribs 3 to 5.
Insertion: Coracoid process of scapula.
Action: Depresses and protracts scapula, elevates ribs during forceful inhalation.
Muscles that Move the Arm
Overview
Muscles connect the arm to the pectoral girdle, ribs, and vertebral column, allowing the arm to move freely.
Grouping by Action:
Flexors: Include coracobrachialis and pectoralis major.
Extensors: Include teres major and latissimus dorsi.
Abductors: Include supraspinatus and deltoid.
Rotators: Include subscapularis, infraspinatus, and teres minor.
Major Muscles:
Coracobrachialis:
Origin: Coracoid process of scapula.
Insertion: Medial midshaft of humerus.
Action: Flexes and adducts the arm at the shoulder.
Pectoralis Major:
Origin: Clavicle, sternum, and costal cartilages of upper ribs.
Insertion: Intertubercular sulcus of humerus.
Action: Flexes, adducts, and medially rotates the arm at the shoulder.
Teres Major:
Origin: Lateral border of scapula.
Insertion: Intertubercular sulcus of humerus.
Action: Extends, adducts, and medially rotates the arm at the shoulder.
Latissimus Dorsi:
Origin: Spinous processes of lower thoracic and lumbar vertebrae, iliac crest, and lower ribs.
Insertion: Intertubercular sulcus of humerus.
Action: Extends, adducts, and medially rotates the arm at the shoulder.
Supraspinatus:
Origin: Supraspinous fossa of scapula.
Insertion: Greater tubercle of humerus.
Action: Abducts the arm.
Deltoid:
Origin: Acromion process, spine of scapula, and clavicle.
Insertion: Deltoid tuberosity of humerus.
Action: Lateral portion abducts the arm; anterior portion flexes the arm at the shoulder; posterior portion extends the arm at the shoulder.
Subscapularis:
Origin: Anterior surface of scapula.
Insertion: Lesser tubercle of humerus.
Action: Medially rotates the arm.
Infraspinatus:
Origin: Infraspinous fossa of scapula.
Insertion: Greater tubercle of humerus.
Action: Laterally rotates the arm.
Teres Minor:
Origin: Lateral border of scapula.
Insertion: Greater tubercle of humerus.
Action: Laterally rotates the arm.
Muscles that Move the Forearm
Overview
Most forearm movements are accomplished by muscles arising from the humerus or pectoral girdle connecting to the ulna and radius.
Muscle Groupings:
Flexors: Biceps brachii, brachialis, brachioradialis.
Extensor: Triceps brachii muscle.
Rotators: Include supinator, pronator teres, and pronator quadratus.
Major Muscles:
Biceps Brachii:
Origin: Coracoid process (short head); tubercle above glenoid cavity of scapula (long head).
Insertion: Radial tuberosity.
Action: Flexes forearm at elbow and supinates forearm and hand.
Brachialis:
Origin: Anterior surface of humerus.
Insertion: Coronoid process of ulna.
Action: Flexes forearm at elbow.
Brachioradialis:
Origin: Distal lateral end of humerus.
Insertion: Lateral surface of radius above styloid process.
Action: Flexes forearm at elbow.
Triceps Brachii:
Origin: Tubercle below glenoid cavity of scapula (long head); lateral surface of humerus (lateral head); posterior surface of humerus (medial head).
Insertion: Olecranon process of ulna.
Action: Extends forearm at elbow.
Supinator:
Origin: Lateral epicondyle of humerus and proximal ulna.
Insertion: Anterior and lateral surface of radius.
Action: Supinates forearm and hand.
Pronator Teres:
Origin: Medial epicondyle of humerus and coronoid process of ulna.
Insertion: Lateral surface of radius.
Action: Pronates forearm and hand.
Pronator Quadratus:
Origin: Anterior distal end of ulna.
Insertion: Anterior distal end of radius.
Action: Pronates forearm and hand.
Muscles that Move the Hand
Overview
Hand movements are caused by various muscles originating from the distal humerus, radius, and ulna.
Muscle Groupings:
Flexors: Include flexor carpi radialis, flexor carpi ulnaris, palmaris longus, and flexor digitorum profundus.
Extensors: Include extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digitorum.
Major Muscles:
Flexor Carpi Radialis:
Origin: Medial epicondyle of humerus.
Insertion: Base of second and third metacarpals.
Action: Flexes wrist and abducts hand.
Flexor Carpi Ulnaris:
Origin: Medial epicondyle of humerus and olecranon process of ulna.
Insertion: Carpal bones and fifth metacarpal bone.
Action: Flexes wrist and adducts hand.
Palmaris Longus:
Origin: Medial epicondyle of humerus.
Insertion: Fascia of palm.
Action: Flexes wrist.
Flexor Digitorum Profundus:
Origin: Anterior and medial surface of ulna.
Insertion: Distal phalanges of fingers 2 to 5.
Action: Flexes wrist and joints of fingers.
Extensor Carpi Radialis Longus:
Origin: Lateral distal end of humerus.
Insertion: Base of second metacarpal.
Action: Extends wrist, abducts hand.
Extensor Carpi Radialis Brevis:
Origin: Lateral epicondyle of humerus.
Insertion: Base of third metacarpal.
Action: Extends wrist and abducts hand.
Extensor Carpi Ulnaris:
Origin: Lateral epicondyle of humerus and proximal, posterior ulna.
Insertion: Base of fifth metacarpal.
Action: Extends wrist, adducts hand.
Extensor Digitorum:
Origin: Lateral epicondyle of humerus.
Insertion: Posterior surfaces of phalanges in fingers 2 to 5.
Action: Extends wrist and joints of fingers.
Muscles of the Abdominal Wall
Overview
Abdominal wall does not have bony support, unlike the chest and pelvic regions. Instead, it is supported by broad, flattened muscles.
The abdominal muscles connect the rib cage and vertebral column to the pelvic girdle, and they increase abdominal pressure while decreasing the size of the abdominal cavity.
Major Muscles:
External Oblique:
Origin: Outer surfaces of lower 8 ribs.
Insertion: Outer lip of iliac crest and linea alba.
Action: Compresses abdomen, flexes and rotates vertebral column.
Internal Oblique:
Origin: Iliac crest and inguinal ligament.
Insertion: Lower 3 to 4 ribs, linea alba, and crest of pubis.
Action: Compresses abdomen, flexes and rotates vertebral column.
Transverse Abdominis:
Origin: Costal cartilages of lower 6 ribs, processes of lumbar vertebrae, lip of iliac crest, and inguinal ligament.
Insertion: Linea alba and crest of pubis.
Action: Compresses abdomen.
Rectus Abdominis:
Origin: Crest of pubis and pubic symphysis.
Insertion: Xiphoid process of sternum and costal cartilages of ribs 5 to 7.
Action: Compresses abdomen, flexes vertebral column.
Muscles of the Pelvic Floor
Overview
The pelvic floor is composed of two muscular sheets that close off the inferior outlet of the pelvis and form the floor of the pelvis:
The deeper pelvic diaphragm, which includes the levator ani and coccygeus.
The superficial urogenital diaphragm, which includes the superficial transverse perineal, bulbospongiosus, and ischiocavernosus.
Major Muscles:
Levator Ani:
Origin: Pubis and ischial spine.
Insertion: Coccyx.
Action: Supports pelvic viscera, compresses the anal canal.
Coccygeus:
Origin: Ischial spine.
Insertion: Sacrum and coccyx.
Action: Supports pelvic viscera, compresses the anal canal.
Superficial Transversus Perinei:
Origin: Ischial tuberosity.
Insertion: Central tendon.
Action: Supports pelvic viscera.
Bulbospongiosus:
Origin: Central tendon.
Insertion:
Males: Corpus cavernosa of penis; Assists emptying of urethra, assists erection of penis.
Females: Corpus cavernosa of clitoris; Constricts vagina, assists erection of clitoris.
Ischiocavernosus:
Origin: Ischial tuberosity.
Insertion:
Males: Corpus cavernosa of penis; Contributes to erection of the penis.
Females: Corpus cavernosa of clitoris; Contributes to erection of the clitoris.
Muscles that Move the Thigh
Overview
The muscles that move the thigh attach to the femur and the pelvic girdle and are classified into anterior, medial, and posterior groups.
Major Muscle Groups:
Anterior Group:
Function: Flex the thigh.
Muscles Include: Psoas major and iliacus.
Medial Group:
Function: Adduct the thigh.
Muscles Include: Adductor magnus, adductor longus, gracilis.
Posterior Group:
Function: Extend, abduct, or rotate the thigh.
Muscles Include: Gluteus maximus, gluteus medius, gluteus minimus, and tensor fasciae latae.
Major Muscles:
Psoas Major:
Origin: Bodies and transverse processes of lumbar vertebrae.
Insertion: Lesser trochanter of femur.
Action: Flexes thigh at the hip.
Iliacus:
Origin: Iliac fossa of ilium.
Insertion: Lesser trochanter of femur.
Action: Flexes thigh at the hip.
Gluteus Maximus:
Origin: Sacrum, coccyx, and posterior surface of ilium.
Insertion: Posterior surface of femur and fascia of thigh.
Action: Extends thigh at hip, laterally rotates thigh.
Gluteus Medius:
Origin: Lateral surface of ilium.
Insertion: Greater trochanter of femur.
Action: Abducts and medially rotates thigh.
Gluteus Minimus:
Origin: Lateral surface of ilium.
Insertion: Greater trochanter of femur.
Action: Abducts and medially rotates thigh.
Tensor Fasciae Latae:
Origin: Anterior iliac crest.
Insertion: Fascia of thigh.
Action: Abducts and medially rotates thigh.
Adductor Longus:
Origin: Pubic bone near the pubic symphysis.
Insertion: Posterior surface of femur.
Action: Adducts thigh and flexes thigh at the hip.
Adductor Magnus:
Origin: Pubis and ischial tuberosity.
Insertion: Posterior surface of femur.
Action: Adducts and extends thigh at the hip.
Gracilis:
Origin: Lower edge of pubis.
Insertion: Proximal medial surface of tibia.
Action: Adducts thigh, flexes thigh at hip, medially rotates thigh and leg.
Muscles that Move the Leg
Overview
The muscle group of the leg connects the tibia or fibula to the femur or pelvic girdle.
Two major groups are identified: flexors and extensors of the knee.
Major Muscle Groups:
Flexors: Hamstring group includes biceps femoris, semitendinosus, semimembranosus, and sartorius.
Extensors: Quadriceps femoris group, consisting of 4 muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
Major Muscles:
Sartorius:
Origin: Anterior superior iliac spine.
Insertion: Proximal medial surface of tibia.
Action: Flexes leg at knee, flexes thigh at hip, abducts thigh, laterally rotates thigh, medially rotates leg.
Hamstring Group:
Biceps Femoris:
Origin: Ischial tuberosity and posterior surface of femur.
Insertion: Head of fibula.
Action: Flexes leg at knee, extends thigh at hip.
Semitendinosus:
Origin: Ischial tuberosity.
Insertion: Proximal medial surface of tibia.
Action: Flexes leg at knee, extends thigh at hip.
Semimembranosus:
Origin: Ischial tuberosity.
Insertion: Medial condyle of tibia.
Action: Flexes leg at knee, extends thigh at hip.
Quadriceps Femoris Group:
Rectus Femoris:
Origin: Anterior inferior iliac spine and margin of acetabulum.
Insertion: Patella (via tendon, continuing as patellar ligament to tibial tuberosity).
Action: Extends leg at knee, flexes thigh at hip.
Vastus Lateralis:
Origin: Greater trochanter and posterior surface of femur.
Insertion: Patella (via tendon, continuing as patellar ligament to tibial tuberosity).
Action: Extends leg at knee.
Vastus Medialis:
Origin: Medial surface of femur.
Insertion: Patella (via tendon, continuing as patellar ligament to tibial tuberosity).
Action: Extends leg at knee.
Vastus Intermedius:
Origin: Anterior and lateral surfaces of femur.
Insertion: Patella (via tendon, continuing as patellar ligament to tibial tuberosity).
Action: Extends leg at knee.
Muscles that Move the Foot
Overview
Many muscles that move the foot are located in the leg, attached from the femur, fibula, or tibia to the bones of the foot.
Directions of Movement:
Upward (Dorsiflexion): Muscles include tibialis anterior, fibularis (peroneus) tertius, and extensor digitorum longus.
Downward (Plantar Flexion): Muscles include gastrocnemius, soleus, and flexor digitorum longus.
Invert: Muscles include tibialis posterior.
Evert: Muscles include fibularis (peroneus) longus, and fibularis (peroneus) brevis.
Major Muscles:
Tibialis Anterior:
Origin: Lateral condyle and lateral surface of tibia.
Insertion: Tarsal bone (medial cuneiform) and first metatarsal.
Action: Dorsiflexion and inversion of foot.
Fibularis Tertius:
Origin: Anterior surface of fibula.
Insertion: Dorsal surface of fifth metatarsal.
Action: Dorsiflexion and eversion of foot.
Extensor Digitorum Longus:
Origin: Lateral condyle of tibia and anterior surface of fibula.
Insertion: Dorsal surfaces of middle and distal phalanges of the four lateral toes.
Action: Dorsiflexion of foot, extension of four lateral toes.
Gastrocnemius:
Origin: Lateral and medial condyles of femur.
Insertion: Posterior surface of calcaneus.
Action: Plantar flexion of foot, flexion of leg at knee.
Soleus:
Origin: Head and shaft of fibula and posterior surface of tibia.
Insertion: Posterior surface of calcaneus.
Action: Plantar flexion of foot.
Flexor Digitorum Longus:
Origin: Posterior surface of tibia.
Insertion: Distal phalanges of the four lateral toes.
Action: Flexion of the four lateral toes.
Tibialis Posterior:
Origin: Lateral condyle and posterior surface of tibia, and posterior surface of fibula.
Insertion: Tarsal and metatarsal bones.
Action: Inversion and plantar flexion of foot.
Fibularis Longus:
Origin: Lateral condyle of tibia and head and shaft of fibula.
Insertion: Tarsal bone (medial cuneiform) and first metatarsal.
Action: Eversion and plantar flexion of foot; supports the arch.
Fibularis Brevis:
Origin: Lower lateral surface of fibula.
Insertion: Base of fifth metatarsal.
Action: Eversion and plantar flexion of foot.