Week 2 Friday Flashcards
Muscles
Responsible for body movement and joint movement.
Provide protection, posture and support, produce major portion of body heat.
How many skeletal muscles?
Over 600. Comprise about 40 to 50% of body weight.
How many pairs of skeletal muslces?
- They usually work in cooperation with each other to perform opposite actions at the joints which they cross.
Aggregate muscle action
muscles work in groups rather than independently to achieve a given joint motion
Muscle nomenclature
muscles are usually named due to visual appearance, anatomical location, or function.
Shape and fiber arrangement affects
- Muscle’s ability to exert force
- Range through which it can effectively exert force onto the bones
Cross section diameter
factor in muscle’s ability to exert force
greater cross section diameter = greater force exertion
Muscle’s ability to shorten
Longer muscles can shorten through a greater range.
More effective in moving joints through large ranges of motion.
2 Major types of fiber arrangements
- Parallel and pennate
- Each is further subdivided according to shape
Parallel Fiber Arrangement
- Fibers arranged parallel to length of muscle
- Produce a greater range of movement than similar sized muscles with pennate arrangement.
Parallel muscles categorized into these shapes:
Flat Fusiform Strap Radiate Sphincter or circular
Flat muscles
- Parallel Fiber arrangement
- Usually thin and broad, originating from broad, fibrous, sheet-like aponeuroses
- Allows them to spread their forces over a broad area.
- Ex: rectus abdominus, external oblique
Fusiform Muscles
- parallel fiber arrangement
- spindle-shaped with a central belly that tapers to tendons on each end.
- allows them to focus their power onto small, bony targets.
- Ex: brachialis, biceps brachii
Strap Muscles
- Parallel fiber arrangement
- more uniform in diameter with essentially all fibers arranged in a long, parallel manner.
- enables focusing of power onto small, bony targets
- Ex: sartorius
Radiate Muscles
- Parallel fiber arrangement
- Also described sometimes as being triangular, fan-shaped, or convergent.
- Have combined arrangement of flat and fusiform
- Originate on broad aponeuroses and converge onto a tendon.
- Ex: pectoralis major, trapezius
Sphincter or circular muscles
- Parallel fiber arrangement
- technically endless strap muscles
- surround openings and function to close them upon contraction
- Ex: orbicularis oris surrounding the mouth
Pennate fiber arrangement
- Have shorter fibers
- Arranged obliquely to their tendons in a manner similar to a feather
- arrangement increases the cross-sectional area of the muscle, thereby increasing the power
Pennate muscles categorized based on…
The exact arrangement between fibers and tendon.
- Unipennate
- Bipennate
- Multipennate
Unipennate muscles
Fibers run obliquely from a tendon on one side only
-Ex: biceps femoris, extensor digitorum longus, tibialis posterior
Bipennate muscles
- Fibers run obliquely on both sides from a central tendon.
- Ex: rectus femoris, flexor hallucis longus
Multipennate muscles
- Have several tendons with fibers running diagonally between them
- Ex: deltoid
Which type of pennate muscles produce the strongest contractions?
Bipennate & Unipennate
4 properties of skeletal muscle tissue related to its ability to produce force & movement about joints:
- Irritability or excitability
- Contractility
- Extensibility
- Elasticity
Extensibility
ability of muscle to be passively stretched beyond its normal resting length
Elasticity
ability of muscle to return to its original length following stretching
Intrinsic
pertaining usually to muscles within or belonging solely to body part upon which they act
Ex: small intrinsic muscles found entirely within the hands or feet
Extrinsic
pertaining usually to muscles that arise or originate outside of (proximal to) body part upon which they act
Ex: forearm muscles that attach proximally on distal humerus and insert on fingers
Action
Specific movement of joint resulting from a concentric contraction of a muscle which crosses a joint.
Ex: biceps brachii has the action of flexion at elbow
Actions are usually caused by a group of muscles working together
Any of the muscles in the group can be said to cause the action, even though it is usually an effort of the entire group
A muscle may cause more than one action either at the same joint or a different joint depending upon the characteristics of the joints crossed by the muscle
Innervation
Segment of nervous system defined as being responsible for providing a stimulus to muscle fibers within a specific muscle or portion of a muscle
A muscle may be innervated by more than one nerve and a particular nerve may innervate more than one muscle or portion of a muscle
Amplitude
range of muscle fiber length between maximal and minimal lengthening
Gaster (belly or body)
Central, fleshy portion of the muscle that generally increases in diameter as the muscle contracts
The contractile portion of muscle
Tendon
Fibrous connective tissue, often cordlike in appearance, that connects muscles to bones and other structures.
Two muscles may share a common tendon.
Ex: achilles tendon of gastrocnemius and soleus muscles
A muscle may have multiple tendons connecting it to one or more bones
Ex: Three proximal attachments of triceps brachii
Aponeurosis
A tendinous expansion of dense fibrous connective tissue that is sheet or ribbonlike in appearance and resembles a flattened tendon
Aponeuroses serve as a fascia to bind muslces together or as a means of connecting muscle to bone
Fascia
A sheet or band of fibrous connective tissue that envelopes, separates, or binds together parts of the body such as muscles, organs, and other soft tissue structures of the body
In certain places throughout the body, such as around joints like the wrist and anke, fascial tissue forms a retinaculum to retain tendons close to the body
Origin
Structurally, the proximal attachment of a muscle or the part that attaches closest to the midline or center of the body
Functionally and historically, least movable part or attachment of the muscle
Insertion
Structurally, the distal attachment or the part that attaches furthest from the midline or center of the body
Functionally and historically, the most movable part is generally considered the insertion
When a particular muscle contracts
It tends to pull both ends toward the gaster
If neither of the bones to which a muscle is attached are stabilized then both bones move toward each other upon contraction
More commonly one bone is more stabilized by a variety of factors and the less stabilized bone usually moves toward the more stabilized bone upon contraction
contraction
when tension is developed in a muscle as a result of a stimulus.
In some contractions the muscle does not shorten in length. Because of this, contractions are sometimes called muscle actions instead
Muscle contractions can be used to…
- Cause, control, or prevent joint movement
- initiate or accelerate movement
- slow down or decelerate movement
- prevent movement by external forces
Two types of muscle contraction
Isometric and Isotonic
Isometric contraction
- Active tension is developed within muscle but joint angles remain constant
- Static contractions
- May be used to prevent a body segment from being moved by external forces
- PREVENTING MOTION
Isotonic contraction
-involves muscle developing active tension to either cause or control joint movement
2 types: concentric and eccentric
Passive joint movement
movement with no muscle contraction. Caused by an outside force
Concentric contractions
involve muscle developing active tension as it shortens, CAUSING MOTION
Eccentric contractions
involve the muscle lengthening under active tension, CONTROLLING MOTION
Characteristics of Concentric contraction
- Muscle develops active tension as it shortens
- Occurs when muscle develops enough force to overcome applied resistance
- Causes movement against gravity or resistance
- Described as being a positive contraction
- Accelerates movement
- force developed by the muscle is greater than that of the resistance
- results in joint angle changing in the direction of the applied muscle force
- causes body part to move against gravity or external forces
Characteristics of Eccentric contraction
- muscle lengthens under active tension
- occurs when muscle gradually lessens in tension to control the descent of resistance
- weight or resistance overcomes muscle contraction but not to the point that muscle cannot control descending movement
- decelerates movement
- controls movement with gravity or resistance
- described as a negative contraction
- force developed by the muscle is less than that of the resistance
- results in joint angle changing in the direction of the resistance or external force
- controls body part to allow movement with gravity or external forces (resistance)
- used to decelerate body segment movement
- some refer to it as a muscle action because the muscle is lengthening and not shortening
Isokinetics
A type of dynamic exercise using concentric and/or eccentric muscle contractions
- speed of movement is constant
- muscular contraction (ideally max) occurs througout movement
- not another type of contraction
- ex: biodex, cybex, lido
Sliding Filament Theory
- Action potential
- AP travels through T-tubules
- Release of calcium from sarcoplasmic reticulum
- calcium binds to troponin
- Conformational shift in actin to expose binding sites
- Myosin heads bind to actin
- Power stroke (contraction)
Agonist muscles
- cause joint motion through a specified plane of motion when contracting concentrically
- known as primary or prime movers, or muscles most involved
- some agonists contribute more to the movement than other agonists
Assisters or assistant movers
agonist muscles that contribute significantly less to the joint motion
Antagonist muscles
- located on the opposite side of joint from agonist
- have the opposite concentric action
- known as contralateral muscles
- work in cooperation with agonist muscles by relaxing and allowing movement
- when contracting concentrically perform the opposite joint motion of agonist.
- Ex: quadriceps muscles are antagonists to hamstrings in knee flexion
Stabilizers
- Surround joint or body part
- contract to fixate or stabilize the area to enable another limb or body segment to exert force and move
- essential in establishing a relatively firm base for the more distal joints to work from when carrying out movements.
- Ex: biceps curl. Muscles of scapula and glenohumeral joint must contract in order to maintain shoulder complex and humerus in a relatively static position so that the biceps brachii can more effectively perform curls.
Synergist
- Assist in action of agonists
- not necessarily prime movers for the action
- known as guiding muscles
- assist in refined movement and rule out undesired motions
- Helping synergists and true synergists
Helping Synergists
- have an action in common but also have actions antagonistic to each other
- Help another muscle move the joint in the desired manner and simultaneously prevent undesired actions
- Ex: anterior and posterior deltoid
- Anterior deltoid acts as an agonist in glenohumeral flexion, while posterior deltoid acts as an extensor
- helping each other, they work in synergy with middle deltoid to accomplish abduction
True Synergists
- contract to prevent an undesired joint action of agonist and have no direct effect on agonist action
- Ex: Finger flexors are provided true synergy by wrist extensors when grasping an object
- Finger flexors originating on forearm and humerus are agonists in both wrist flexion and finger flexion
- Wrist extensors contract to prevent wrist flexion by finger flexors
- This allows finger flexors to utilize more of their force in flexing the fingers
Neutralizers
Counteract or neutralize the action of another muscle to prevent undesirable movements such as inappropriate muscle substitutions.
- contract to resist specific actions of other muscles
- Ex: when only supination action of biceps brachii is desired, the triceps brachii contracts to neutralize the flexion action of the biceps brachii
Force couples
- force couples occur when two or more forces are pulling in different directions on an object, causing the object to rotate about its axis
- coupling of muscular forces together in the body can result in a more efficient movement
Muscles with multiple agonist actions
- attempt to perform all of their actions when contracting
- cannot determine which actions are appropriate for the task at hand
- Actions actually performed depend on the motor units activated, joint position, muscle length, relative contraction or relaxation of other muscles acting on the joint
Example of muscle roles in kicking a ball
- muscles primarily responsible for hip flexion and knee extension are agonists
- hamstrings are antagonistic and relax to allow the kick to occur
- preciseness of the kick depends on the involvement of many other muscles
- Lowe extremity route and subsequent angle at the point of contact (during forward swing) depend on a certain amount of relative contraction or relaxation in the hip abductors, adductors, internal rotators and external rotators (acting synergistically to guide lower extremity precisely)
- these synergistic muscles are not primarily responsible for knee extension and hip flexion but contribute to accuracy of the total movement
- They assist in refining the kick and preventing extraneous motions
- These synergistic muscles in contralateral hip and pelvic area must be under relative tension to help fixate or stabilize the pelvis on that side to provide a relatively stable base for the hip flexors on the involved side to contract against
- Pectineus and tensor fascia latae are adductors and abductors, respectively, in addition to flexors
- abduction and adduction actions are neutralized by each other
- common action of the two muscles results in hip flexion
Antagonistic muscles produce actions opposite those of the agonist
- ex: elbow extensors are antagonistic to eblow flexors
- elbow movement in returning to hanging position after chinning is extension, but triceps and anconeus are not being strengthened
- elbow joint flexors contract concentrically followed by eccentric contraction of same muscles
- specific exercises are needed for each antagonistic muscle group
Methods of determination of muscle action
- consideration of anatomical lines of pull
- anatomical dissection
- palpation
- models
- electromyography
- electrical stimulation
palpation
-helpful in furthering one’s understanding of joint mechanics
electromyography (EMG)
- uses either surface electrodes which are placed over muscle or fine wire/needle electrodes placed into muscle
- as subject moves joint and contracts muscles, EMG unit detects action potentials of muscles and provides an electronic readout of contraction intensity and duration
- most accurate way of detecting presence and extent of muscle activity.
