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Muscular System
Nursing (RLE70)
Capitol University
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Muscular System
Graded responses
Graded responses are different degrees of skeletal muscle shortening
Muscle fiber contraction is “all-or-none,” meaning the muscle fiber (not the whole muscle) will contract to its fullest extent when stimulated adequately
Within a whole skeletal muscle, not all fibers may be stimulated during the same interval
Different combinations of muscle fiber contractions may give differing responses
Graded responses can be produced in two ways
By changing the frequency of muscle stimulation
By changing the number of muscle cells being stimulated a tone time Muscle response to increasingly rapid stimulation
Muscle twitch
Single, brief, jerky contraction
Not a normal muscle function
In most types of muscle activity, nerve impulses are delivered at a rapid rate
As a result, contractions are “summed” (added) together, and one contraction is immediately followed by another
When stimulations become more frequent, muscle contractions get stronger and smoother
The muscle now exhibits unfused (incomplete) tetanus
Fused (complete) tetanus is achieved when the muscle is stimulated so rapidly that no evidence of relaxation is seen
Contractions are smooth and sustained
Muscle response to stronger stimuli
- Muscle force depends upon the number of fibers stimulated
- Contraction of more fibers results in greater muscle tension
- When all motor units are active and stimulated, the muscle contraction is as strong as it can get
Providing Energy for Muscle Contraction
ATP
Only energy source that can be used to directly power muscle contraction
Stored in muscle fibers in small amounts that are quickly used up
After this initial time, other pathways must be utilized to produce ATP
Three pathways to regenerate ATP
- Direct phosphorylation of ADP by creatine phosphate
- Aerobic pathway
- Anaerobic glycolysis and lactic acid formation
Direct phosphorylation of ADP by creatine phosphate (CP) —fastest
- Muscle cells store CP, a high-energy molecule
- After ATP is depleted, ADP remains
- CP transfers a phosphate group to ADP to regenerate ATP
- CP supplies are exhausted in less than 15 seconds
- 1 ATP is produced per CP molecule
Aerobic respiration
Supplies ATP at rest and during light/moderate exercise
A series of metabolic pathways, called oxidative phosphorylation, use oxygen and occur in the mitochondria
Glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP)
Slower reaction; requires continuous delivery of oxygen and nutrients
Anaerobic glycolysis and lactic acid formation
•Reaction that breaks down glucose without oxygen
- Glucose is broken down to pyruvic acid to produce about 2 ATP
- Pyruvic acid is converted to lactic acid
Muscle Fatigue and Oxygen Deficit
- If muscle activity is strenuous and prolonged, muscle fatigue occurs
- Suspected factors that contribute to muscle fatigue include:
- Ion imbalances (Ca+2 and K+)
- Oxygen deficit and lactic acid accumulation
- Decrease in energy (ATP) supply
- After exercise, the oxygen deficit is repaid by rapid, deep breathing
Types of Muscle Contractions
Isotonic contractions
Myofilaments are able to slide past each other during contractions
The muscle shortens, and movement occurs
Example: bending the knee; lifting weights, smiling
Isometric contractions
Muscle filaments are trying to slide, but the muscle is pitted against an immovable object
Tension increases, but muscles do not shorten
Example: pushing your palms together in front of you
Muscle tone
State of continuous partial contractions
Result of different motor units being stimulated in a systematic way
Muscle remains firm, healthy, and constantly ready for action
Muscular System
Effect of Exercise on Muscles
Exercise increases muscle size, strength, and endurance
Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue
Makes body metabolism more efficient
Improves digestion, coordination
Resistance (isometric) exercise (weight lifting) increases muscle size and strength
Individual muscle fibers enlarge
Five Golden Rules for understanding skeletal muscle activity
- With a few exceptions, all skeletal muscles cross at least one joint.
- Typically, the bulk of a skeletal muscle lies proximal to the joint crossed.
- All skeletal muscles have at least two attachments: the origin and the insertion.
- Skeletal muscles can only pull; they never push.
- During contraction, a skeletal muscle insertion moves toward the origin. Types of Body Movements
Muscles are attached to no fewer than two points
- Origin: attachment to an immovable or less movable bone
- Insertion: attachment to a movable bone
When the muscle contracts, the insertion moves toward the origin
Body movement occurs when muscles contract across joints
Flexion
Decreases the angle of the joint
Brings two bones closer together
Typical of bending hinge joints (e., knee and elbow) or ball-and- socket joints (e., the hip)
Extension
Opposite of flexion
Increases the angle between two bones
Typical of straightening the elbow or knee
Extension beyond 180 degrees is hyperextension
Rotation
Movement of a bone around its longitudinal axis
Common in ball-and-socket joints
Example: moving the atlas around the dens of axis (i., shaking your head “no”)
Abduction
Movement of a limb away from the midline
Adduction
Opposite of abduction
Movement of a limb toward the midline
Circumduction
Combination of flexion, extension, abduction, and adduction
- Common in ball-and-socket joints
- Proximal end of bone is stationary, and distal end moves in a circle
Dorsiflexion
- Lifting the foot so that the superior surface approaches the shin (toward the dorsum)
Plantar flexion
- Pointing the toes away from the head
Inversion
- Turning sole of foot medially
Eversion
- Turning sole of foot laterally
Supination
- Forearm rotates laterally so palm faces anteriorly
- Radius and ulna are parallel
Pronation
- Forearm rotates medially so palm faces posteriorly
- Radius and ulna cross each other like an X
Opposition - Moving the thumb to touch the tips of other fingers on the same hand Interactions of Skeletal Muscles in the Body
Muscles can only pull as they contract—not push
In general, groups of muscles that produce opposite actions lie on opposite sides of a joint
Prime mover—muscle with the major responsibility for a certain movement
Antagonist—muscle that opposes or reverses a prime mover
Synergist—muscle that aids a prime mover in a movement or reduces undesirable movements
Fixator—specialized synergists that hold a bone still or stabilize the origin of a prime mover
Naming Skeletal Muscles
Muscles are named on the basis of several criteria
Direction of muscle fibers
Example: rectus (straight)
Relative size of the muscle
Example: maximus (largest)
Location of the muscle
Example: temporalis (temporal bone)
Number of origins
Example: triceps (three heads)
Location of the muscle’s origin and insertion
Example: sterno (on the sternum)
Shape of the muscle
Example: deltoid (triangular)
Action of the muscle
Example: flexor and extensor (flexes or extends a bone)
Common patterns of fascicle arrangement
Circular: fascicles are in concentric rings
Convergent: fascicles converge on a single insertion tendon
Parallel: length of fascicles run parallel to the long axis of the muscle
Fusiform: modified parallel arrangement resulting in a spindle-shaped muscle
Pennate: short fascicles attach obliquely to a central tendon
Muscular System
Course: Nursing (RLE70)
University: Capitol University
