Anatomy - Musculatory System
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Three Basic Muscle Types
- Skeletal: Cylindrical, Voluntary, multi-nucleic, striations
- Cardiac: Striations, single nucleus, joined to another muscle cell at an intercalated disc, Involuntary, only in heart, no nucleus
- Smooth: No striations, spindle shaped cells, single nucleus, Involuntary, found mainly in the walls of hollow organs, contracts slower
Characteristics of Muscles
- Muscle cells are elongated (muscle cell=muscle fiber)
- Contraction of muscles is due to the movement of micro-filaments
- All muscles share some terminology
- Prefix myo refers to muscle
- Prefix mys refers to muscle
- Prefix sarce refers to flesh
- Muscles are attached by tendons to bones
- Cells are multinucleic
- Striated: have visible bonding (stripes)
- Voluntary: subject to conscious control
- Cells are surrounded and bundled by connective tissue
Connective Tissue Wrappings of Skeletal Muscle
- Endomysium: encloses muscle fiber in a delicate connective tissue sheath (around single fiber)
- Perimysium: coarser fibrous membrane that wraps several sheathed muscle fibers called a fascicle (around bundle of fibers)
- Epimysium: overcoat of fascicles and bounds them together (covers entire skeletal muscle)
- Fascia: on the outside of the Epimysium
Skeletal Muscle Attachments
- Epimysium: blends into a connective tissue attachment
- Tendon: cord like structure
- Aponeuroses: sheet like structure
- Sites of muscle attachment: bone, cartilage, connective tissue coverings
Smooth Muscle Characteristics
- No striations
- Spindle shaped cells
- Single nucleus
- Found mainly in the walls of hollow organs
Cardiac Muscle Characteristics
- Usually has a single nucleus
- Joined to another muscle cell at an intercalated disc
- Only in heart
- Produce movement
- Maintain Posture
- Stabilize joints
- Generate heart
Microscopic anatomy of Skeletal muscle
- Cells are multinucleic
- Nuclei are just beneath the sarcolemma
- Sarcolemma: specialized plasma membrane
- Sarcoplasmic reticulum: Specialized smooth endoplasmic reticulum
Muscle Fatigue and Oxygen Debt
- Muscle Fatigue: happens in muscles are exercised strenuously for a long period of time. Its is when a muscle is unable to contract even though it is still being stimulated. Without rest and an active muscle contracts more weakly until it ceases to.
- Oxygen Debt: A person is not able to take in oxygen fast enough to keep the muscles supplied with all the oxygen they need when they are working vigorously.
- The work and muscle can do and how long it can go for depends on how good its blood supply.
- When muscle lack oxygen, lactic acid begins to accumulate in the muscle via the anaerobic mechanism.
- Also the muscle ATP supply beings to run low
- Both these factors above put together (increasing acidity and ATP supply starts to run low) cause the muscle to contract less and less effectively and finally to stop contracting altogether.
Types of Muscle Contractions-Isotonic and Isometric
- Muscles do not always shorten when they contract
- The event that is common to all muscle contractions is that tension develops in the muscles as the actin and myosin myofilaments interact and the myosin cross bridges attempt to slide within the muscle fibers.
- Isotonic contractions: "same tone" the myofiliments are successfull in there sliding movements, the muscle shortens and movement occurs. EX: Bending the knee, twisting the arm.
- Isometric Contractions: muscles do not shorten, myosin myofilaments are "skidding thier wheels" and the tension in the muscle keeps increasing.
- One aspect of skeletal muscle activity cannot be controlled, even when a muscle is voluntarily relaxed, some of its fibers are contracting , one group then the other.
- There contraction is not visible but as a result of it the muscle remains firm, healthy, and constantly ready for action.
- This state of continuous partial contraction is called muscle tone.
- Muscle tone: result of different motor units, which scattered through the muscle, being stimulated by the nervous system in systematic way.
Muscle tone: Homeostatic imbalance
- If the nerves supply to the muscle is destroyed (as in an accident) the muscle is no longer stimulated in this manner and it loses tone and becomes paralyzed.
- Soon after that it becomes flaccid or soft and flabby then being to atrophy or waste away.
Effect of exercise on muscles
- Aerobic or endurance types of exercises such as jogging or biking result in stronger more flexible muscles with greater resistance to fatigue.
- These changed come about, at least partly, because the blood supply to the muscles increases, and the individual muscle cells form more mitochondria and store more oxygen.
- Benefits more than just skeletal muscles, over all metabolism better, digestion, enhances neuromuscular coordination, and makes the skeleton stronger.
- Heart enlarges (hypertrophies) so that more blood is pumped out with each beat, fat deposits are cleared from the blood vessel walls, and the lungs become more efficient in gas exchanged
- These benefits may be permanent or temporary.
- Aerobic exercise does not cause the muscles to increase much in size.
- Bulging muscles of a body building come mainly from resistance.
- Require very little time, and no special equiptment
5 Golden Rules of Muscle Activity
- All muscles cross at at least one point
- Typically, the bulk of the muscle lie proximal to the joint crossed.
- All muscles have at least two attachments: the origin and the insertion.
- Muscles can only pull, they never push.
- During contraction, the muscles insertion moves toward the origin.
Types of body movements
- Flexion, Extension, Rotation, and Abduction
- Orgin: attached to the immovable or less movable joint
- Insertion: Attached to the movable bone
- A movement, generally in the saggital plane, that decreases the angle of the joint and brings two bones closer together.
- Flexion is typical of hinge joints
- Also typical of ball and socket joints
- Opposite of flexion
- A movement that increases the angle or the distance between bones
- If it is more then 180 degrees its hyper extension.
- A movement of a bone around its longitudinal axis
- Rotation is a common movement of ball and socket joints
- Limb moving away from the mid line or median plane
- Terminology also applies to the fanning movement of the finger or toes when they are spread apart.
- Opposite of abduction
- Moving toward the midline
- Combination of flexion, extension, abduction and adduction commonly seen in ball and socket joints
- The proximal end of the limb is stationary and its distal end moves in a circle.
- Dorsiflexion and plantar flextion
- Inversion and eversion
- Supination and pronation
Dorsiflexion and plantar flexion
- Up and down movement of the foot at the ankle
- Dorsi: Up
- Plantar: Down
- These also correspond with the hand
Inversion and eversion
- Winging and sycling
- In: Medial
- E: Lateral
Supination and pronation
- Refers to movements of the radius and ulna
- Supi: occurs when the forearm rotates latterly so that the palm faces anterior and the radius and the ulna are parralel
- Pro: brings radius across the ulna creating an X
In the palm of the hand the saddle joint between metacarpal 1 and he carpals allows opposition of the thumb.
Types of Muscles
- Can only pull as they contract, so usually it is two or more muscles working together.
- Muscles are arranged in such a way that whatever one muscle can do another can o the opposite.
- Prime mover: major responsibility for causeing a partiular movement
- Antagonist: muscles that oppose or reverse the movement
- When a prime mover is active the antagonist is stretched and relaxed.
- Synergists: help prime movers by producing same movement or by reducing undesirable movements.
- Antagonist can be prime movers and vice versa. EX: bicep (elbow flexion) tricep (elbow extention)
- Fixators: specialized synergists, hold a bone still or stabilize the organ of a prime mover so all the tension can be used to move the insertion bone
Naming Skeletal Muscles
- Direction of the muscle fibers: Some are labeled by an imaginary line such as the midline of the body or the long axis of a limb bone. When muscle term include rectus (straight), its fibers run parallel to that imaginary line. If the term included is oblique it tells you that they run slanted to the imaginary line. EX: Rectus femoris, straight muscle of the thigh.
- Relative size of the muscle: Terms like maximus, minimus, and longus would be the largest or smallest muscle of that muscle group. EX: gluteus maximus
- Location of the muscle: Muscles are named after the bone they are associated with. EX: temoralis and frontalis, muscle overlie the temporal and frontal bones of the skull
- Number of origins: when the muscle has biceps, triceps, quadriceps it mean that the muscle as two three or even four origins. EX: Biceps have two heads or origins and the tricep as three.
- Location of the muscle origin and insertion: Some times names after there attachment sites. EX: Sternocliedomastiod muscles origin is on the sternum (sterno) and clavicle (cleido) and inserts on the mastoid process.
- Shape of the muscle: Distinctive shape help identify them. EX: Deltoid muscle is tringular (deltoid means triangle)
- Action of the muscle: when named after action terms such as flexor, or extensor come about. EX: Adductor muscles of the thigh, or the extensor muscles of the wrist.
Developmental aspects of Muscular System
- In the developing embryo, the muscular system is laid down in segments and then each segment is invaded by nerves.
- The muscles of the thoracic and lumbar become very extensive because they must cover and move the bones of the limbs.
- Development of muscles and their control by the nervous system, occur rather early in pregnancy.
- Without nerve supply muscles are inable to be stimulated and will atrophy.
- Expectant mother is usually astonished by the first movements (quickening) of the fetus which usually occur by the 16th week.
- Muscular dystrophy: a group of inherited muscle destroying diseases that affect specific muscle groups. The muscles enlarge due to fat and connective tissue deposit but the muscle fibers degenerate and atrophy.
- Duchenne muscular dystrophy: Most common, almost exclusively in males. Usually diagnosed between the ages of 2 and 6. Active, normal appearing children become clumsy and begin to fall frequently s their muscles weaken. Most victims are in a wheel chair by 12 and generally don't live past young adult hood. Cause: the diseased muscle fibers lack a protien that helps maintain sarcolemma. Cure: Elusive
- After birth baby's movements are are all gross reflex type of movements, this is because the nervous system must mature before the baby can control muscles. This development proceeds cephalic/caudial direction and gross muscular movements precede fine ones. Raising your head comes before sitting, sitting comes before walking. Muscle control also precedes in a proximal/ direction. They can wave bye before picking up a small pin.
- Because of rich blood supply very little damage comes to skeletal muscle.
- Muscles will atrophy even with normal tone if not used continually.
- Myasthenia gravis: Rare, can affect muscles during adulthood. Charcterized by, droopy eyelids, dificulty in swallowing and talking, and generalized muscle weakness. Involves a shortage of acetylcholine receptors at the neuromuscular junction. The blood of many of these patients contains antibodies to acetylcholine receptors which suggests that myasthenia gravis is an autoimmune disease. MUscle cells are not stimulated properly and progressively get weaker. Death is usuall because of the inability of the respiratory muscles to function.
- As we age the amount of connective tissues in muscle increases and the amount of muscle tissue decreases. The muscles become stringier. Because skeletal muscle represent so much of the body weight, that begins to decline in an elderly person.
- Strength decreases by 50 percent by the age of 80 but staying activating and lifting weights can offset the effects and even begin to build muscle mass again.
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