ANATOMY AND PHYSIOLOGY: MUSCULAR SYSTEM REPORT

Muscular System

THE SUMMARY

OVERVIEW OF MUSCLE TISSUES

A.     Terminologies

·          Mus Latin word means “little mouse” (because flexing muscles look like mice scurrying beneath the skin, some scientist long ago dubbed them muscles)

·          Myo and mys means muscle

·          Sarco means flesh

·          Epi means upon /over/ beside

B.     Definition of Muscular System

·          The muscular system is an organ system  consisting of skeletal, smooth and cardiac muscles. It permits movement of the body, maintains posture, and circulates blood throughout the body. The muscular system in vertebrates is controlled through the nervous system, although some muscles (such as the cardiac muscle) can be completely autonomous. Together with the skeletal system it forms the musculoskeletal system, which is responsible for movement of the human body. (Retrieved on Feb. 5, 2014 from  http://en.wikipedia.org/wiki/Muscular_system)

C.     Types of Muscle Tissue

1.     Skeletal Muscle/Fibers

o    Are packaged into the organs called skeletal muscles that attach to the body’s skeleton.

o    Are cigar-shaped , multinucleate cells, and the largest of the muscle fiber types—some ranging up to 30 cm (nearly 1 foot) in length.

o    They are often called muscle fibers

o    Also known as striated muscle (because its fibers appear to be striped) and as voluntary muscle (because it is the only muscle type subject to conscious control).

o    Skeletal muscle tissue can contract rapidly and with great force, but it tires easily and must rest after short periods of activity.

§   Soft and fragile

§   Can exert tremendous power

·          The force they generate is often much greater than that required to lift the weight. How so?

o    They are not ripped apart as they exert force is that thousands of their fibers are bundled together by connective tissue, which provides strength and support to the muscle as a whole

o    MUSCLE FIBER (cell)

§   Endomysium, a delicate connective tissue sheath, enclosing the muscle fibers.

§   Perimysium, a coarser fibrous membrane in which several sheathed muscle fibers is wrapped.

§   Fascicle, bundle of fibers formed, wrapped by Perimysium.

§   Epimysium/Epymisia, an even tougher “overcoat” of connective tissue, where fascicles are bounded together and cover the entire muscle.

§   Tendons, the strong cordlike part of the muscle fiber, where epimysia blends.

·          Mostly tough collagenic fibers, so they can cross rough bony projections, which would tear the more delicate muscle tissues.

Functions of Tendons:

o    Acting to anchor muscles

o    Providing durability (most important)

o    Conserving space (most important)

§   Aponeuroses, sheetlike in which attach muscles indirectly to bones, cartilages, or connective tissue coverings of each other.

2.     Smooth Muscle

o    has no striations and is involuntary, which means that we cannot consciously control it.

o    Found mainly in the walls of hollow visceral organs  (other than the heart) such as:

§   Stomach

§   Urinary bladder

§   Uterus

§   Blood vessels

§   Respiratory passages

o    Smooth muscle propels substances along a definite tract or pathway, within the body.

o    We can best describe smooth muscles using the terms:

§   Visceral

§   Nonstriated

§   Involuntary

o    Are spindled-shaped and have a single nucleus

o    They are arranged in sheets or layers.

o    Most often there are two layers: as the two layers alternately contract and relax, they change the size and shape of the organ.

§   Running circularly

§   Running longitudinally

o    Housekeeping Activities are normally handled by smooth muscles, in which it involves the movement of food through the digestive tract and emptying the bowels and bladder.

o    Peristalsis, a wavelike motion that keeps food moving through the small intestine, is typical of its activity.

o    Smooth muscle contraction is slow and sustained, is like a steady, heavy-duty engine that lumbers along tirelessly.

3.     Cardiac Muscle

o    Is found in only one place in the body—the heart.

o    Heart- serves as a pump, propelling blood into the blood vessels and to all tissues of the body.

§   When the heart contracts, its internal chambers become smaller, forcing the blood into the large arteries leaving the heart.

§   The heart can also be stimulated by the nervous system to shift into “high gear” for short periods, as when you race to catch a bus.

o    Is like skeletal muscle in that it is striated and like smooth muscle in that it is involuntary and cannot be consciously controlled by most of us.

o    Usually contracts at a fairly steady rate set by the heart’s “in-house” pacemaker.

o    Important keywords to jog your memory for this muscle type are:

§   Cardiac

§   Striated

§   Involuntary

o    CARDIAC FIBERS

§   Are cushioned by small amounts of soft connective tissue and arranged in spiral or bundles.

§   Are branching cells joined by special junctions called intercalated discs

§   Intercalated disks, contain gap junctions that allow ions to pass freely from cell to cell, resulting in rapid construction of the exciting electrical impulse across the heart.

D.     Muscle Functions

·          Produces movement

·          Maintaining posture

·          Stabilizing joints

·          Generating heat

MICROSCOPIC ANATOMY OF SKELETAL MUSCLE

·          Sarcolemma “muscle husk” in muscle cells.

·          Myofibrils, long ribbon-like organelles, in which nuclei are pushed aside and nearly, fill the cytoplasm. They are actually chains of sarcomere.

o    Consists of two bands:

§   Light (I) bands- has a midline interruption a darker area called Z disc.

§   Dark (A) bands- has a lighter central area called H zone.

·          Sarcomeres, tiny contractile units which are aligned end to end like boxcars in a train along the length of the myofibrils. (segment of myfibril)

·          Myofilaments, are segments of sarcomere. There are two types of threadlike protein myofilaments:

o    Think Filaments also called myosin filaments

§   Are made mostly of bundled molecules of the protein myosin.

§   Myosin, contain ATPase enzymes, which split ATP to generate the power for muscle contraction.

o    Thin Filaments also called actin filaments

§   are composed of the contractile protein called actin and some  regulatory proteins that play a role in allowing myosin head-binding to actin.

§   Are anchored to the Z disc.

o    Sarcoplasmic Reticulum (SR), a specialized smooth endoplasmic reticulum.

§   The interconnecting tubules and sacs of the SR surround each and every myofibril just as the sleeve of a loosely crocheted sweater surrounds your arm.

§   The major role of this elaborate system is to store calcium and release it on demand when the muscle fiber is stimulated to contract.

SKELETAL MUSCLE ACTIVITY

A.     Stimulation and contraction of Single Skeletal Muscle Cells

1.     Irritability, the ability to receive and respond stimulus.

2.     Contractility, the ability to shorten (forcibly) when an adequate stimulus is received.

B.     The Nerve Stimulus and the Action Potential

o    Skeletal muscle cells must be stimulated by nerve impulses to contract.

o    One motor neuron (nerve cell) may stimulate a few muscle cells or hundreds of them, depending on the particular muscle and the work it does.

o    Motor Unit, stimulates one neuron and all the skeletal muscle cells

o    Nerve fiber or axon, a long threadlike extension of the neuron, reaches the muscle, it branches into a number of axon terminals, each of which forms junctions with the sarcolemma of a different muscle cell.

o    Neuromuscular junctions (nerve-muscle), junctions with the sarcolemma of a different muscle cell.

o    Synaptic cleft, filled with tissue fluid and the gap between the nerve endings and the muscle cells’ membranes, even they are very close but they never touch.

o     When the nerve impulses reach the axon terminals, a chemical reffered to as a neurotransmitter is released.

o    Acetylcholine, the specific neurotransmitter that stimulates skeletal muscle.

o    Action potential, travels over the entire surface of the sarcolemma, conducting the electrical impulse from one end of the cell to the other.

C.     What causes the filaments to slide?

o    According to the Sliding Filament Theory, when muscle fibers are activated by the nervous system. The myosin heads attach to binding sites on the thin filaments, and the sliding begins.

D.     Types of Muscle Contractions

o    Tension the event that is common to all muscle contractions and it develops in the muscle as the actin and myosin myofilaments interact.

§   Isotonic contractions, (literally same “tone or tension”)

·          Are more familiar to most of us.

·          The myofilaments are successful in their sliding movements, the muscle shortens, and movement occurs.

§   Isometric contractions (literally, “same measurement”)

·          The myosin myofilaments are “skidding their wheels” and the tension in the muscle keeps increasing.

·          They are trying to slide but the muscle is pitted against some more or less immovable object.

o    HOMEOSTATIC IMBALANCE

§   If the nerve supply to a muscle is destroyed, the muscle is no longer stimulated in this manner and it losses tone and becomes paralyzed. Soon after it becomes a flaccid or soft and flabby and begins atrophy.

MUSCLE MOVEMENTS, TYPES AND NAMES

A.     Types of Body Movements

o    Flexion- a movement, generally in the sagittal plane, that decreases the angle of the joint and brings two bones closer together.

§    Is typical of hinge joints (bending the knee or elbow) but it is also common at ball-and-socket joints (bending forward at the hip).

o    Extension- is the opposite of flexion, so it is a movement that increases the angle, or the distance, between two bones or parts of the body (straightening the knee or elbow).

o    Rotation- is movement of a bone around its longitudinal axis.

§   Is a common movement of ball-and-socket joints and describes the movement of the atlas around the dens of the axis (as in shaking your head “no”)

o    Abduction- is moving a limb away from the midline, or median plane of the body.

§   The terminology also applies to the fanning movement of the fingers or toes when they are spread apart.

o    Adduction- is the opposite of abduction, so it is the movement of a limb toward the body midline

o    Circumduction- is a combination of flexion, extension, abduction and adduction commonly seen in ball-and-socket joints such as the shoulder.

§   The proximal end of the limb is stationary, and its distal end moves in a circle. The limb as a whole outlines a cone.

o    Dorsiflexion and plantar flexion- up and down movements of the foot at the ankle are given special names.

§   Lifting the foot so that its superior surface approaches the shin (standing on your heels), is called dorsiflexion.

§   Depressing the foot (pointing the toes) is called plantar flexion.

o    Inversion and eversion

§   To invert the foot turn the sole medially

§   To evert the foot turn the sole laterally

o    Supination and pronation

§   The terms supination (turning backward) and pronation (turning forward) refer to movements of the radius around the ulna.

§   Suppination occurs when the forearm rotates laterally so that the palm faces anteriorly, and the radius and ulna are parallel.

§   Pronation occurs when the forearm rotates medially so that the palm faces posteriorly.

o    Opposition – this is the action by which you move your thumb to touch the tips of the other fingers on the same hand.

§   It is this unique action that makes human hand such a fine tool for grasping and manipulating things.

GROSS ANATOMY OF SKELETAL MUSCLES

A.     Head and Neck Muscles

o    The head muscles are an interesting group. They have many specific functions but are usually grouped into two large categories:

·          FACIAL MUSCLES

o    Frontalis, covers the frontal bone as it runs from cranial aponeurosis to the skin of the eyebrows, where it inserts.

§   This muscles allows you to raise your eyebrows, as in surprise, and to the cranial aponeurosis is the small occipitalis muscle.

o    Orbicularis oculi, has fibers that run in circles around the eyes.

§   It allows you to close your eyes, squint, blink and wink.

o    Orbicularis Oris, is the circular muscle of the lips. Because it closes the mouth and protrudes the lips.

§   It is often called “THE KISSING MUSCLE”

o    Buccinator, the fleshly buccinators muscle runs horizontally across the cheek and inserts into the orbicularis oris.

§   It flattens the cheek (in whistling or blowing a trumpet)

§   It also listed as a CHEWING MUSCLE

o    Zygomaticus, extends from the corner of the mouth to the cheekbone.

§   It is often reffered to as the SMILING MUSCLE because it raises the corners of the mouth upward.

·          CHEWING MUSCLES

o    Masseter, covers the angle of the lower jaw as it runs from zygomatic process of the temporal bone to the mandible.

o    Temporalis, is fan-shaped muscle overlying the temporal bone. It inserts into the mandible and acts as a synergist of the masseter in closing the jaw.

·          NECK MUSCLES

o    The neck muscles, which move the head and shoulder girdle, are small and straplike. Only two muscles are considered here.

o    Platysma, is a single sheetlike muscle that covers the anterolateral neck.

§    It originates from the connective tissue covering of the chest muscles and inserts into the area around the mouth.

§   Its action is to pull the corners of the mouth inferiorly, producing downward sag of the mouth.

o    Sternocleidomastoid, muscles are two-headed muscles, one found on each side of the neck. Of the two heads of each muscle, one arises from the sternum and the other arises from the clavicle.

§   When both sternocleidomastoid muscles contract together, they flex your neck.

§   It is the action of bowing the head that has led some people to call these muscles the PRAYER MUSCLES

B.     Trunk Muscles

o     The trunk muscles include:

§   Those that move the vertebral column

§   Anterior thorax muscles, which move the ribs, head, and arms

§   Muscles of the abdominal wall, which help to move the vertebral column and most importantly, form the muscular “natural gridle” of the abdominal body wall.

·          ANTERIOR MUSCLES

o    Pectoralis Major, is a large fan-shaped muscle covering the upper part of the chest.

§   Its origin is from the sternum, shoulder girdle, and the first six ribs.

§   It inserts in the proximal end of the humerus.

§   Froms the anterior wall of the axilla and acts to adduct and flex the arm.

·          Intercostal Muscles, are deep muscles found between the ribs.

§   Important in breathing because they help to raise the rib cage for breathing air in

§   the internal intercostals, which lie deep to the external intercostals, depress the rib cage, which helps to move air out of the lungs when you exhale forcibly.

·          Muscles of the Abdominal Girdle, the anterior abdominal muscles form a natural “girdle” that reinforces the body trunk.

o    Rectus abdominis, the paired straplike rectus abdominis muscles are the most superficial muscles of the abdomen.

§   They run from pubis to the rib cage, enclosed in an aponeurosis.

§   Main function is to flex the vertebral column.

§   Also compress the abdominal contents during defecation and childbirth

§   Are involved in forced breathing

o    External oblique, are paired superficial muscles that make up the lateral walls of the abdomen.

§   Their fibers run downward and medially from the last eight ribs and insert into the ilium

§   They flex the vertebral column

§   But they also rotate the trunk and bend it laterally

o    Internal oblique, are paired muscles deep to the external oblique

§   Their fibers run at right angles to those of the external obliques

§   Arise from the iliac crest and insert into the last three ribs.

§   Their functions are the same as those  of the external obliques

o    Transverses abdominis, is the deepest muscle of the abdominal wall

§   Has fibers that run horizontally across the abdomen

§   It arises from the lower ribs and iliac crest and inserts into the pubis

§   Compresses the abdominal contents

·          Posterior Muscles

o    Trapezius, muscles are the most superficial muscles of the posterior neck and upper trunk.

§   When seen together, they form diamond- or kite- shaped muscle mass.

§    Their origin is very broad. Each muscle runs from the occipital bone of the skull down the vertebral column to the end of the thoracic vertebrae.

§   Extend the head, they are antagonists of the sternocleidomastoid.

§   Can also elevate, depress, adduct, and stabilize the scapula

o    Latissimus dorsi, is the large, flat muscle pair that covers the lower back.

§   it originates on the lower spine and ilium and then sweeps superiorly to insert into the proximal end of the humerus

§   it extends and adducts the humerus

§   are very important muscles when the arm must be brought down in a power stroke

o    Erector Spinae, is a prime mover of back extension.

§   These paired muscles are deep muscles of the back

§   Each is a composite muscle consisting of three muscle columns that collectively span the entire length of the vertebral column:

·          Longisimus, iliocostalis and spinalis

§   These muscles not only act as powerful back extensors (erectors)

§   Also provide resistance that helps control the action of bending over at the waist

§   Following injury to back structures, these muscles go into spasms, a common source of lower back pain.

o    Deltoid, are fleshly, triangle-shaped muscles that form the rounded shape of your shoulders.

§   They are so bulky, that they are a favorite injection site when relatively small amounts of medication must be given intramuscularly.

§   The origin of each deltoid winds across the shoulder girdle from the spine of the scapula to the clavicle.

·          Muscles of the Humerus that Act on the Forearm

o    Biceps Brachii, is the most familiar muscle of the forearm because it bulges when the elbow is flexed

§   It originates by two heads from the shoulder girdle and inserts into the radial tuberosity

§   Is the powerful prime mover for flexion of the forearm

§   Acts to supinate the forearm

o    Brachialis, lies deep to the biceps muscle and is as important as the biceps in elbow flexion.

o    Brachioradialis, is a fairly weak muscle that arises on the humerus and inserts into the distal forearm

§   Resides mainly in the forearm

o    Triceps Brachii, is the only muscle fleshing out the posterior humerus

§   Its three heads arise from the shoulder girdle and proximal humerus and it inserts into the olecranon process of the ulna

§   The powerful prime mover of elbow extension, the antagonist of the biceps brachii.

§   This muscle is often called the boxer’s muscle because it can deliver a straight-arm knockout punch

·          Muscles Causing Movement at the Hip Joint

o    Gluteus Maximus, is a superficial muscle of the hip that forms most of the flesh of the buttock

§   It is a powerful hip extensor that acts to bring the thigh in a straight line with the pelvis

§   Originates from the sacrum and iliac bones and inserts on the gluteal tuberosity of the femur

§   Needed in climbing stairs and jumping

o    Gluteus Medius, runs from the ilium to the femur, beneath the gluteus maximus for most of its length.

§   Is a hip abductor and is important in steadying the pelvis during walking.

§   Is important sit for giving intramuscular injections, particularly when more than 5 ml is administered

§   The medial part of each buttock overlies the large sciatic nerve (this area must be carefully avoided)

o    Iliopsoas, is a fused muscle composed of two muscles:

§   Iliacus

§   Psoas major

§   It is a prime mover of hip flexion

§   It also acts to keep the upper body from falling backwards when we are standing erect.

o    Adductor Muscles, form the muscle mass at the medial side of each thigh.

§   As indicates, they adduct or press the thighs together. But since there is gravity they tend to become flabby (sag/floppy/loose) very easily

§   Originate on the pelvis and insert on the proximal aspect of the femur

·          Muscles causing Movement at the Knee Joint

o    HAMSTRING GROUP- the muscles forming the muscle mass of the posterior thigh is the hamstrings. The group consists of 3 muscles:

·          Biceps femoris

·          Semimembranosus

·          Semitendinosus

§   it all originated on the ischial tuberosity and run down to the thigh to insert on both sides of the proximal tibia

o    Sartorius, it is not too important however, it is the most superficial muscle of the thigh so it is rather hard to miss

§   Runs obliquely across the thigh from the anterior iliac crest to the medial side of tibia

§   It is a weak thigh flexor

o    Quadriceps Group, consists of four muscles:

·          Rectus femoris, originates on the pelvis

·          Three (3) vastus muscles, originate from the femur

o     Help to flex the hip and sometimes used as an intramuscular injection sites particularly on infants who have poorly developed gluteus muscles.

·          Muscles causing movement at the ankle and foot

o    Tibialis Anterior, is a superficial muscle on the anterior leg.

§   Arises from upper tibia and then parallels the anterior crest as it runs to the tarsal bones, where it inserts by a long tendon.

§   It acts dorsiflex and invert the foot

o    Extensor Digitorum Longus, lateral to the tibialis anterior

§   This muscle arises from the lateral tibial condyle and proximal radius

o    Fibularis Muscles, there are three kinds:

·          Longus,

·          Brevis

·          Tertius

§   Are all found on the lateral part of the leg

§   They arise from fibula and insert into the metatarsal bones of the foot.

o    Gastrocnemius, is a two-bellied muscle that forms the curved calf of the posterior leg.

§   Arises by two (2) heads, one from each side of the distal femur and inserts through the large calcaneal (Achilles) tendons into the heel of the foot

§   Prime mover for plantar flexion of the foot; often called the “toe dancer’s” muscle

§   The foot drags because the heel cannot be lifted

o    Soleus, deep to the gastrocnemius is the fleshy soleus muscle.

§   Arises on tibia and fibula (rather than the femur) it does not affect the knee movement

Homeostatic imbalance

·          One rare disease that can affect muscles during adulthood is Myasthenia gravis

o    A disease characterized by drooping of the upper eyelids, difficulty in swallowing and talking and generalized weakness and fatigability.

·          Muscular dystrophy

o    A group of inherited muscles-destroying diseases that affect specific muscle groups. The muscles enlarge due to fat and connective tissue deposit, but the muscle fibers degenerate and atrophy.

Prepared and summarized by:             April G. Datahan

                                                                BSED-III

Date:                                                       Feb. 6, 2014