Chapter 7

Chapter 7

The Muscular System Learning Objectives List the 3 types of muscles and describe the characteristics of each. Describe the structure and function of tendons, aponeuroses, and ligaments. Differentiate between prime mover, antagonist, synergist,

and fixator muscles. List the locations and actions of the muscles of the head and neck, abdomen, thoracic limb, pelvic limb, and the muscles of respiration. Muscle One of the four basic tissues of the body Made up of cells that can shorten or contract

Three different types of muscle skeletal muscle moves the bones of the skeleton Voluntary striated muscle cardiac muscle

smooth muscle eyes, air passageways in lungs, stomach, intestines, urinary bladder, blood vessels, reproductive tract Striated means stripes (light and dark colored bands) Skeletal Muscle Skeletal muscle- multiple nuclei

Smooth muscle cells Cardiac muscle cells (intercalated discs) Questions What is muscle?

What are the three types of muscle and some characteristics of each? Muscle Attachments : Are well defined groups of skeletal muscle cells

surrounded by a layer of fibrous (collagen)connective tissue called fascia Surrounds, binds together Sliding and gliding Are attached to bones by tendons (fibrous connective tissue)

Are attached to bones or other muscles by broad sheets of fibrous connective tissue called aponeuroses Linea Alba-abdominal muscles come together at the linea alba Common surgical incision site abdominally (ventral midline)

Aponeurosis (in human) Muscle fascia Muscle Attachment sites Origin: the more stable of a muscle's attachment sites

The bone does not move much when the muscle contracts Insertion: site that undergoes most of the movement when a muscle contracts Undergoes most movement when a muscle contracts

Belly of a muscle- the bulging central part of a muscle. (Pretty much between tendon and tendon) Important to know for intramuscular injections purpose of depositing drug Questions

What is the difference between a tendon, fascia and an aponeurosis? What is the origin of a muscle? What is the insertion of a muscle? Muscle Actions Muscles contract/ relaxthey do not push or stretch by their own

Prime mover (agonist): a muscle or muscle group that directly produces a desired movement Antagonist: a muscle or muscle group that directly opposes the action of a prime mover Muscle Actions

Synergist: a muscle that contracts at the same time as a prime mover and assists it in carrying out its action Fixator: muscles that stabilize joints to allow other movements to take place example

Bicep Curl movement Prime mover is the biceps Antagonist is triceps Fixator is deltoid Synergist is brachialis Muscle-Naming Conventions Action: flexor muscles; extensor muscles

levatator, depressor, rotator, supinator, pronator Shape: deltoid means triangular shaped Quadratus Rhomboideus Scalenus Serratus Teres

Location: Biceps brachii muscle is located in the brachial region Pectoral = chest Epaxial = above pelvic axis Intercostal=between ribs Infraspinatus=beneath spine of scapula

Supraspinatus=above spine of scapula Inferior=below, medius=middle, superior=above Externus=outer, internus=inner Orbicularis=surrounding another structure Direction of fibers: rectus means straight Oblique means slanted (outward away from

midline Transverse means crosswise (to midline) Muscle-Naming Conventions Number of heads or divisions: -cep means head; biceps brachii muscle has two heads

Attachment sites: origin of the sternocephalicus muscle is the sternum and insertion is the back of the head Cutaneous Muscles Thin, broad, superficial muscles

Found in the fascia just beneath the skin Little or no attachment to bones Serve to twitch the skin

Cutaneous Muscles Cutaneous Trunci Platysma Head and Neck Muscles Functions Control facial expressions Enable mastication

Move structures such as eyes and ears Support the head Allow the head and neck to flex, extend, and move laterally Head and Neck Muscles Masseter muscle - closes the jaw Splenius and Trapezius muscles extend the head and neck

Brachiocephalicus muscle - extends the head and neck; also pulls the front leg forward Sternocephalicus muscle - flexes (LOWER) the head and neck Head muscles Masseter

O=zygomatic arch I=mandible A= elevates mandible to close mouth Temporal O=temporal fossa I=coronoid process (of the mandible)

A=elevate mandible, moves lower jaw backward FYI: Digastric Muscle opens the mouth Muscles of the Head and Neck These muscles move the head and neck

Sternocephalicus Origin - manubrium (sternum) Insertion 2 points of insertion mastoid nuchal crest of occipital bone Action depresses the head and neck, draws the head and neck to side

Sternocephalicus head and neck The sternocephalicus, runs along side the braciocepalicus (thoracic

limb muscle) Forms the jugular groove Brachiocephalicus is a complex Dorsal part of Neck : muscle!

Mastoid Process: Cleidomastoidus from clavicle remnant to mastoid process Cleidocervicalis from clavicle remnant to dorsal part of neck

Brachiocephalicus Cleidocervicalis from clavicle remnant to dorsal part of neck From clavicle remnant to distal

end of humerus: Cleidobrachialis Human Clavicle Brachiocephalicus Origin Cleidocervicalis clavicle remnant

Cleidomastoid clavicle remnant Cleidobrachialis-clavicle remnant Insertion Cleidocervicalis dorsal neck Cleidomastoid mastoid process (behind external acoustic meatus) Cleidobrachialis-humerus Action Pulls leg forward, neck and head down, neck

and head side to side. Brachiocephalicus Trapezius Origin Dorsal aspect of neck Insertion scapula spine

Action elevates and abducts forelimb (Holds shoulder against body) Trapezius Rhomboideus This muscle lies beneath the Trapezius and has

three parts Origin Nuchal Crest of Occipital bone Dorsal neck T1- T7 Insertion dorsal border of the scapula Action - pulls top of shoulder up forwards and towards the body. Elevates forelimb

When shoulder is still it can lift the neck. Rhomboideus Thoracic Limb Muscles Superficial muscles of the shoulder region Latissimus dorsi muscle - flexes the

shoulder Pectoral muscles - one superficial and one deep; adduct the front leg Deltoid muscle - abducts and flexes the shoulder joint Thoracic Limb Muscles Brachial muscles

Biceps brachii muscle - flexes the elbow joint Triceps brachii muscle - extends the elbow joint Carpal and digital muscles Extensor carpi radialis muscle extends the carpus Deep digital flexor muscle - flexes the

digit Supraspinatus Origin supraspinatus fossa Insertion - greater tubericle of humerus Action - Extends and stabilizes shoulder joint

Supraspinatus Infraspinatus Origin infraspinous fossa. Insertion - greater tubericle of the humerus. Action flexes the shoulder joint, abducts the limb at the shoulder

stabilize the shoulder joint. Infraspinatus Serratus Ventralis Origin 2 points of origin Neck transverse process of C3-C7 Chest Ribs 1 - 7

Insertion scapula Action supports the trunk, depresses the scapula Serratus Ventralis Latissimus Dorsi Origin - On the top of the spines, muscles starting at the top of the shoulder to the tips of the lumbar

vertebrae as well as from the last two or three ribs. Spinous process of the lumbar and thoracic vertebrae (T7 / T8) including ribs Insertion tuberosity of the humerus Action - pulls leg backwards, flexes shoulder joint Latissimus Dorsi

Deltoid Origin Acromial- Acromion at the bottom end of the spine of the scapula Spinal spine of the scapula Insertion - humerus Action flexes shoulder joint, pulls the foreleg away from the dogs body

Deltoid Biceps Brachii Origin supraglenoid tubercle (distal scapula) Insertion proximal medial radius/ ulna Action - Flexes elbow joint and extends

shoulder joint Bicep Tricep Origin caudal border scapula, proximal humerus Insetion olecranon tubercle

Action Long head Flexes the shoulder joint and extends the elbow joint Lateral Head only extends the elbow joint Tricep

Extensor Muscles of the radius, ulna, carpus, metacarpus, digits Origin-lateral epicondyle of humerus Insertion- carpals, metacarpals, digits Action- extend carpus, digits

Flexor muscles of radius, ulna, carpus, metacarpus, digits Origin- medial epicondyle of humerus Insertion-palmer and medial aspects of the carpus, metacarpus, digits Action- flexes carpus, and/ or digits, abducts digits

Flexor and Extensor muscles of the thoracic limb Abdominal Muscles Functions Support the abdominal organs Help flex the back

Participate in various functions that involve straining Defacation, urination, parturition, vomiting,regurgitation Play a role in respiration Abdominal Muscles

Arranged in layers External abdominal oblique muscle Internal abdominal oblique muscle Rectus abdominis muscle Transversus abdominis muscle Left and right parts of each muscle come together on the ventral midline

at the linea alba External Abdominal Oblique O=last rib I=Linea Alba Action= flexes vertebral column, compresses abdominal cavity

Pelvic Limb Muscles Gluteal muscles - extensor muscles of the hip Hamstring" muscle group - extend the hip joint; main flexors of the stifle joint Biceps femoris muscle

Semimembranosus muscle Semitendinosus muscle Pelvic Limb Muscles Quadriceps femoris muscle - main extensor muscle of the stifle joint

Gastrocnemius muscle - extensor muscle of the hock Superficial Gluteal Muscle Origin-sacrum/ coccygeal vertebrae Insertion-greater trochanter of femur Action-abducts the limb/ extends the hip

Superficial Gluteal Muscle Gluteus Medius Origin-lateral ilium Insertion-greater trochanter of femur Action-abducts the limb/ extends the hip Gluteus Medius Muscle (Deep)

Quadriceps Femoris Muscle: Vastus Lateralis, Vastus Medius, Deep Vastus Intermedius, Rectus Femoris Quadriceps Femoris

Origin Vastus medialis Proximal femur (inside) Vastus lateralis Proximal femur (outside) Deep vastus intermedius Proximal femur (inside) Rectus Femoris ilium Insertion - All of the vastus muscles insert into their own areas of the rectus femoris then they all insert together into the patella and so also the tibial tuberosity.

Action - extend stifle and flex hip Quadriceps Rectus Femoris and Vastus Lateralis Patella (remember the patella is embedded in a tendon that

passes through the trochlea of the distal end of the femur) Biceps femoris This muscle spans 3 joints: The hip (coxofemoral joint), stifle, and tarsus Origin- ischiatic tuberosity of pelvis Insertion-patella, proximal tibia

Action: extends hip joint, flexes stifle, extends tarsal joints Biceps Femoris (Hamstring) Semitendinosus

(part of the hamstring group) Origin- ischiatic tuberosity Insertion- tibia and tuber calcanei Action-extends the hip, flexes the stifle Semitendinosus (Hamstring)

Semimembranosus (part of the hamstring group) Origin ischiatic tuberosity of pelvis Insertion femur and tibia

Action - Pulls the limb towards the middle of the body, extends hip joint Semimembranous Sartorius O=Crest of ilium I=Patella (cranial portion)

Tibia (caudal portion) Action= flexes hip, cranial portion of muscle extends stifle, caudal portion flexes stifle Sartorius Gastrocnemius and Achilles

tendon Origin- medial and lateral supracondylar tuberosities of femur (distal end of femur) Insertion-proximal calcaneal tuber Action- extends the tarsus, flexes the stifle

Muscles of respiration Function Increase and decrease the size of the thoracic cavity Inspiratory muscles Diaphragm External intercostal muscles

Expiratory muscles Internal intercostal muscles Abdominal muscles Subcutaneous Intramuscular, SQ, Intradermal

Intramuscular injections UU Locations of Injection sites Cat and Dog Pelvic limb Gluteal Muscles Quadriceps Femoris

Gastrocnemius semimembranosus, semitendinosus Thoracic Limb Triceps Brachii Epaxial muscles-why? IM injection sites

Semitendinosis Quadriceps Skeletal Muscle Cells Very large Multinucleate

Numerous myofibrils composed of actin and myosin Network of sarcoplasmic reticulum T tubules Skeletal Muscle Cells

A bands: thick myosin filaments I bands: thin actin filaments Dark line in the center of the I band is the Z line Disk that is the attachment site for the actin filaments

Skeletal Muscle Cells Sarcomere - basic contracting unit of skeletal muscle Area from one Z line to the next Z line Each myofibril is

made up of many sarcomeres lined up end to end. Neuromuscular Junction Nerves and muscles separated by the synaptic space

Synaptic vesicles sacs at the end of a nerve fiber; contain acetylcholine Acetylcholinesterase enzyme in the synaptic space that removes acetylcholine Motor Unit

One nerve fiber and all the muscle fibers it innervates Muscles that make small, delicate movements have only a few muscle fibers per nerve fiber in each motor unit Large, powerful muscles may have a hundred or more muscle fibers per

motor unit Connective Tissue Layers Hold components of the muscle together Contain the blood vessels and nerve fibers that supply the muscle fibers Continuous with tendons or

aponeuroses that connect muscle to bones or other muscles Connective Tissue Layers Endomysium - composed of fine, reticular fibers; surrounds each muscle fiber Fascicles - groups of skeletal muscle

fibers Perimysium - composed of reticular fibers and thick collagen fibers; surrounds fascicles Epimysium - fibrous layer composed of tough collagen fibers; surrounds groups of muscle fascicles

Initiation of Muscle Contraction & Relaxation Nerve impulse reaches the end bulb of the motor nerve fiber Acetylcholine is released into the synaptic space Acetylcholine molecules bind to receptors on the surface of the

sarcolemma Impulse travels along the sarcolemma and through the T tubules to the interior of the cell Initiation of Muscle Contraction & Relaxation Impulse reaches the sarcoplasmic

reticulum Calcium ions (Ca++) are released into the sarcoplasm Ca++ diffuses into the myofibrils and starts the contraction process Initiation of Muscle Contraction & Relaxation

Sarcoplasmic reticulum begins pumping Ca++ back in again Ca++ is pulled out of the myofibrils Contraction stops, muscle returns to its original length Mechanics of Muscle Contraction

Relaxed muscle fibers have actin and myosin filaments that slightly overlap When stimulated to contract, crossbridges on myosin filaments slide back and forth Mechanics of Muscle

Contraction Actin filaments on both sides are pulled toward the center of the myosin filaments. This shortens the sarcomere. Shortening of all the end-to-end sarcomeres in a muscle fiber results in a muscle contraction.

Characteristics of Muscle Contraction All-or-nothing principle When stimulated, an individual muscle fiber either contracts completely or not at all. Nervous system controls the number of muscle fibers it stimulates for a particular

movement Small, fine movements require only a few muscle fibers to contract. Larger, more powerful movements require contraction of many muscle fibers. Muscle Contraction Three phases:

1. Latent phase - time between nerve stimulus and beginning of contraction (about 10 ms) 2. Contracting phase - lasts about 40 ms 3. Relaxation phase - lasts about 50 ms Muscle Contraction

Maximum contraction efficiency occurs if nerve impulses arrive about 0.1 second apart. Results in a series of complete muscle fiber twitches Careful timing of the nerve impulses to motor units of the muscle is needed to make muscle contract

smoothly. Chemistry of Muscle Contraction ATP provides energy to allow the sliding of the actin and myosin filaments Creatine phosphate converts ADP

back to ATP Glucose and Oxygen - help produce ATP & CP Glucose stored in muscle as glycogen Oxygen stored as myoglobin Chemistry of Muscle Contraction

Anaerobic metabolism - used if oxygen need exceeds oxygen supply Results in lactic acid formation Lactic acid accumulation causes discomfort Heat Production Muscle activity generates heat

Panting or sweating - mechanisms to eliminate excess heat Shivering - spasmodic muscle contractions that increase heat production Cardiac Muscle Small cells with single nucleus

Intercalated disks: attachments between cardiac muscle cells Allow transmission of impulses from cell to cell for coordinated contraction of large groups of cells Physiology of Cardiac Muscle

Cardiac cells contract without any external stimulation Groups of cardiac muscle cells contract at the rate of the most rapid cell in the group Contractions are rapid and wavelike Physiology of Cardiac

Muscle Cardiac Conduction System Sinoatrial (SA) node Generates the impulse that starts each heartbeat Located in the wall of the right atrium Impulse follows a controlled path

through the conduction system of the heart Structures in the system transmit, delay, and redirect Nerve Supply Heart is innervated by nerves from both the sympathetic and

parasympathetic systems Sympathetic fibers stimulate the heart to beat harder and faster as part of the "fight or flight response Parasympathetic fibers inhibit cardiac function, causing the heart to beat more slowly and with less force

Smooth Muscle Gross Anatomy Two main forms Visceral smooth muscle Large sheets of cells in the walls of some hollow organs Multiunit smooth muscle

Small, discrete groups of cells Smooth Muscle Cells Small, spindle-shaped; single nucleus Actin and myosin filaments arranged as small contractile

units that crisscross the cell Attached at both ends to "dense bodies" that correspond to the Z lines of skeletal muscle

Visceral Muscle Found in the walls of many internal organs (e.g., stomach, intestines, uterus, urinary bladder) Contracts in large, rhythmic waves Contracts without external stimulation Reacts to stretching by contracting more strongly

Innervated by nerves from both the sympathetic and parasympathetic systems Sympathetic stimulation decreases activity; parasympathetic stimulation increases activity Multi-Unit Smooth Muscle Individual smooth muscle cells or

small groups of cells Found where small, delicate contractions are needed (e.g., iris, walls of small blood vessels) Contraction requires autonomic nervous system impulse Splenius

Origin - Nuchal ligament and spinous process of C3, C4, C5 Insertion - 5 points 1. Back of the skull (middle and top to mastoid process) 2. C1 3. C3 4. C4 5. C5

Action - move neck up and head forward One muscle moves neck to one side.

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