Muscular System Flashcards
Characteristics of Muscle
- Contractility
- Extensibility
- Elasticity
- Excitability
- Conductibility
Contractility
The ability to apply tension when stimulated
Extensibility
The ability to stretch
Elasticity
The ability to return to resting length after stretch is removed (somewhat limited)
Excitability
The ability to be excited by a stimulus
Conductibility
The ability to move or transmit an impulse
Muscle Types
- Smooth muscle
- Cardiac muscle
- Skeletal muscle
Skeletal Muscle
- Is innervated (stimulated) by the somatic nervous system (voluntary nervous system), an efferent division of the PNS.
- Comprises 40-50% of total body weight
- Over 600 individual muscles.
- Responsible for movement, maintenance of posture and heat production.
- Striated and multinucleated.
- Muscle fibers vary in their content of myoglobin, the red-colored protein that binds oxygen in muscle fibers.
- Muscle fibers high in myoglobin content are termed red muscle fibers those low are termed white muscle fibers.
Origin
The more stable end of the muscle attachment, usually proximal
Insertion
The less stable end of the muscle attachment, usually distal
Tendon
White glistening fibrous bands of connective tissue which attach the muscle to the bone
Fascia
Gross term indicating all fibrous connective tissue not otherwise specifically named. It varies in thickness and density
Aponeurosis
Fibrous or membranous, closely packed, parallel collagenous bundles which represent very much flattened tendons; provide strength and support to structures
Composition of Skeletal Muscles
- Individual muscle cells called fibers
- Fibers are held together by fascia, this layer is called endomysium
- Bundles of muscle fibers are called fasciculi
- Fascia surrounding fasciculi are called perimysium
- Fascia covering the entire muscle is called epimysium
Fusiform Muscle Shape
- Fibers run parallel to long axis of the muscle
- 100% of muscles contraction contributes to moving the attachments
- Has fewer fibers per unit area
- Has longer fibers and produces greater ROM but less force production
Pennate Muscle Shape
- Fibers run obliquely to the muscle tendon
- Produces less ROM for a given shortening distance, but greater force
- Has shorter fibers, but more per unit area
- As the angle of the muscle fiber increases, the effective shortening component shrinks
Muscle Shapes (named according to the arrangement of the fasciculi)
- Longitudinal (ex- sartorius)
- Unipennate (ex- EDL)
- Bipennate (ex- rectus femoris)
- Multipennate (ex- deltoid)
- Radiate (ex- pectoralis major)
How muscles are named
- Shape
- Action
- Location
- Attachments
- Number of parts
- Size
- Fiber orientation
What determines the action of a muscle?
- Where the muscle crosses the joint it is acting upon
- The relationship of the location of the joint crossing with the axis of rotation of the joint
What determines how well a muscle performs its function?
- Size of the muscle
- Angle of pull
Muscle Classification (due to articulations)
- Uniarticulate
- Bi/Multiarticulate
Uniarticulate
Single joint muscles
Bi/Multiarticulate
- 2+ joint muscles
- Tends to pull the bony attachments toward the center of the muscle.
Advantages of Bi/Multiarticulate Muscles
- Produces motion in all the articulations that it passes. -
Considered to be more efficient. - They provide for the synchronous movement of multiple joints
- Less complex innervation
- Less muscle mass than if all muscles were single joint; this allows greater ROM
- Pulley action of muscles - Involves antagonistic muscles: movement in one joint puts a muscle on stretch so it can be more efficient in contraction in the other joint it passes.
Disadvantages of Bi/Multiarticulate Muscles
- Active Insufficiency: inability of a muscle crossing two or more joints to shorten and produce enough force to cause full ROM in both joints at the same time. (hamstrings in knee flexion and hip extension)
- Passive Insufficiency: inability of muscle crossing two or more joints to be stretched enough to allow for full ROM in both joints at the same time (hamstrings in hip flexion and knee extension)
Functions of a Muscular Contraction
- To act as a motive force
- To act as a resistive force
- To stabilize or fixate a body part
What’s the opposite of contraction?
Relaxation
Agonist
The worker muscle (causes the desired action)
Antagonist
- Causes movement opposite to the agonist
- “True antagonist” has EXACTLY the opposite action(s) of the agonist
Stabilizer
A muscle that fixes or holds a bone so the agonist can do the intended movement - eliminates undesirable movement – static or dynamic
Synergist
A muscle that has at least one antagonistic action to the agonist and contracts to eliminate an undesirable movement, thus enabling the agonist to be more efficient. Sometimes called “true synergy”
Neutralizer
A muscle that has a common and an antagonistic action with the agonist. The antagonistic actions cancel each other out and the common action results
Co-contraction
The simultaneous contraction of antagonistic muscles
