Human Muscular System

Transcription

1 Human Muscular System Common Characteristics Excitability - receives & responds to nerve impulses Contractility - can shorten, thicken & generate force Extensibility - can be stretched Elasticity - returns to original shape after contraction or stretch

2 Skeletal Muscle Composition Basic unit - Muscle cell (fiber); can be up to 70 cm long» bound together to form a fascicle» fascicles bound together to form entire muscle» layer of tough connective tissue surrounds each level» this tough tissue extends beyond the muscle as a tendon

3 Terminology of Muscle Action Prime mover - contributes the most to the movement Synergist - assists the prime mover Agonist - same as prime mover Antagonist - opposes the agonist Agonist/Antagonist Patterns» flexors / extensors» adductors / abductors» medial / lateral rotators» etc...

4 Terminology of Muscle Contraction 3 Types of skeletal muscle contraction» Isometric - no movement equal opposition of agonist/antagonist OR immovable weight» Concentric - shortening contraction of muscle with expected osteokinematic motion» Eccentric - lengthening contraction of muscle for controlling the opposite osteokinematic motion; such as controlled lowering of forearm against gravity (brachialis) Muscle Contraction related to Exercise Isometric exercise» no movement (immovable weight or end of AROM)» isometric contraction Isotonic exercise» same weight, ex. Free weights» muscle contraction force varies as direction of object movement changes relative to the gravity line» speed of movement can vary» concentric or eccentric contractions

5 Isokinetic Exercise» accommodating/variable resistance muscle force production can stay at max because the machine will accommodate to the force output» same speed of movement» concentric or eccentric contractions» why does muscle force production vary at different parts of the AROM? Physical Factors Impacting Muscle Force Production Age Gender Speed of Contraction Type of Contraction Length - Tension Relationship

6 AGE Strength peaks between age 20 & 40 years of age» with aging comes a decrease in the number of muscle fibers (results in decreased mass & strength) Loss of muscle fibers & ms mass by 6 th decade of life Fiber type changes: less Type II

7 GENDER males have greater strength than females after onset of puberty greatest difference in muscle strength between genders is ages Differences due primarily to greater muscle mass» males can have up to 50% more muscle mass than females. Male and female muscle produce the same amount of force per cross-sectional area.

8 SPEED OF CONTRACTION With concentric contractions, maximal force production decreases with increasing speed of contraction (ie. force production decreases with faster movement)

9 TYPE OF CONTRACTION Maximal contraction force can be produced with eccentric contraction, followed by isometric and then concentric. Theoretic forcevelocity curve of an activated muscle is shown. Concentric activation is shown on the right and eccentric activation on the left. Isometric activation occurs at the zero velocity point on the graph.

10 LENGTH TENSION RELATIONSHIP The force that a muscle can generate is dependent on the number of cross bridges that can be formed during contraction. This is dependent on the amount of overlap of actin & myosin in a muscle fiber. The amount of overlap is dependent on muscle length (ie. the position of the muscle as related to it's range of excursion). Length-Tension... Example: the maximally lengthened position for the brachialis is full extension of the elbow & the maximally shortened position is full elbow flexion. The length at which a muscle can produce it maximal force or tension is called the optimal length. This is the length at which the actin & myosin can form the most cross bridge links. At lengths shorter or longer than the optimal length, a muscle cannot develop its maximal force when stimulated to contract.

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12 Active Insufficiency is the decreased force production of a muscle when the muscle attachments are either too close OR too far apart (puts the sarcomeres in the ascending or descending parts of the length-tension curve). Most common in two-joint muscles Examples.... Passive Insufficiency When the ANTAGONIST MUSCLE is being STRETCHED by contraction of the AGONIST, the PASSIVE STRETCH may become too great and limit joint motion Occurs primarily in two-joint muscles May cause movement at some joints crossed by the muscles» Examples...

13 Why max eccentric contraction is the greatest of all? A generalized passive length-tension curve is shown. As a muscle is progressively stretched, the tissue is slack during its initial shortened lengths until it reaches a critical length where it begins to generate tension. Beyond this critical length, the tension builds as an exponential function.