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Aggregate Muscle Action
Muscles work in groups rather than independently to achieve a given joint motion.
Skeletal Muscles
two types: Parallel & Pennate
Parallel Muscles
Fibers arranged parallel to length of muscles will produce a greater range of movement than similar-size muscles with a pennate arrangement.
Five types: Flat, Fusciform, Strap, Radiate, Sphincter
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Flat Muscles
Usually thin & 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
Spindle-shaped with a central belly that tapers to tendons on each end; this allows them to focus their power on small, bony targets.
Ex. brachialis & brachioradialis
Strap Muscles
More uniform in diameter with essentially all fibers arranged in a long parallel manner. This also enables a focusing of power onto small, bony targets.
Ex. sartorius
Radiate Muscles
Also described sometimes as being triangular, fan-shaped or convergent
have combined arrangement of flat & fusiform muscles, in that they originate on broad aponeuroses & converge onto a tendon.
Ex. pectoralis major & trapezius
Sphincter (Circular) Muscles
Technically endless strap muscles that surround openings & function to close them upon contraction.
Ex. orbicularis oris (surrounding the mouth)
Pennate Muscles
Have shorter fibers
arranged obliquely to their tendons in a structure similar to a feather. This arrangement increases the cross-sectional area of the muscle, thereby increasing its force production capability.
three types: Unipennate, Bipennate, Multipennate
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Unipennate Muscle Fibers
Fibers run obliquely from a tendon on one side only.
Ex. biceps femoris, extensor digitorum longus, & tibialis posterior
Bipennate Muscle Fibers
Fibers run obliquely from a central tendon on both sides.
Ex. rectus femoris & flexor hallucis longus
Multipennate Muscles
Several tendons with fibers running diagonally between them.
Ex. deltoid
Skeletal Muscle Tissue
Its ability to produce force effecting movement about joints.
four types: Irritability or Excitability, Contractility, Extensibility, Elasticity
Irritability or Excitability
The muscle property of being sensitive or responsive to chemical, electrical, or mechanical stimuli.
Contractility
The ability of muscle to contract & develop tension or internal force against resistance when stimulated.
Extensibility
The ability of muscle to be passively stretched beyond its normal resting length.
Elasticity
The ability of muscle to return to its original length following stretching.
Muscle Terminology - Intrinsic
Pertaining usually to muscles within or belonging solely to the body part upon which they act.
Muscle Terminology - Extrinsic
Pertaining usually to muscles that arise or originate outside of (proximal to) the body part on which they act.
Muscle Terminology - Action
The specific movement of joint resulting from a concentric contraction of a muscle that crosses the joint.
Muscle Terminology - Innervation
Occurs in the segment of the nervous system responsible for providing a stimulus to muscle fibers within a specific muscle or portion of a muscle.
Muscle Terminology - Amplitude
The range of muscle fiber length between maximal & minimal lengthening.
Muscle Terminology - Gaster (Belly or Body)
The central, fleshy portion of the muscle. This contractile portion of the muscle generally increases in diameter as the muscle contracts.
Muscle Terminology - Tendon
Tough, yet flexible bands of fibrous connective tissue, often cordlike in appearance, that connect muscles to bones & other structures. By providing this connection, tendons transmit the force generated by the contracting muscle to the bone.
Muscle Terminology - Aponeurosis
A tendinous expansion of dense fibrous connective tissue that is sheet- or ribbon-like in appearance and resembles a flattened tendon.
Muscle Terminology - 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.
Muscle Terminology - Retinaculum
A connective tissue band that tendons from separate muscles pass under in facial tissue.
Muscle Terminology - Origin
The proximal attachment of a muscle or the part that attaches closest to the midline or center of the body.
Muscle Terminology - Insertion
The distal attachment, or the part that attaches farthest from the midline or center of the body.
Muscle Contractions (Action)
When tension is developed in a muscle as a result of a stimulus, it is known as a contraction. Can be used to cause, control, or prevent joint movement.
two types: Isometric Contractions & Isotonic Contractions
Isometric Contractions
occurs when tension is developed within the muscle but the joint angles remain constant.
Static Contractions
Isometric contractions (no movement)
Isotonic Contractions
Involve the muscle developing tension to either cause or control joint movement.
Dynamic Contractions
Isotonic contractions (movement)
Muscle Contractions - Concentric Contraction
Involve the muscle developing active tension as it shortens & occur when the muscle develops enough force to overcome the applied resistance.
Muscle Contractions - Eccentric Contraction (Muscle Action)
Involve the muscle lengthening under active tension and occur when the muscle gradually lessens in tension to control the descent of the resistance.
Muscle Contractions - Movement Differentiation
Joint movement may occur with muscle groups on either or both sides of the joint actively contracting or even without any muscles contracting.
Isokinetics
Development of exercise machines has resulted in another type of muscle exercise.
Role of Muscles - Agonist
When contracting concentrically, they cause joint motion through a specified plane of motion.
Primary Movers
Muscles most involved
Role of Muscles - Antagonist (Contralateral Muscles)
They work in cooperation with agonist muscles by relaxing & allowing movement; but when contracting concentrically, they preform the joint motion opposite to that of the agonist.
Role of Muscles - Stabilizers (Fixators)
They surround the joint or body part & contract to fixate or stabilize the area to enable another limb or body segment to exert force & move.
Role of Muscles - Synergist (Gliding Muscles)
Muscles that assist in the action of an agonist, but are not necessarily prime movers for the action, assist in refined movement & rule out undesired motion.
two types: Helping Synergists & True Synergists
Helping Synergists
They help another muscle move the joint in the desired manner and simultaneously prevent undesired actions.
True Synergists
They contract to prevent an undesired joint action of the agonist and have no direct effect on the agonist action.
Role of Muscles - Neutralizers
They counteract or neutralize the action of other muscles to prevent undesirable movements such as inappropriate muscle substitutions. They contract to resist specific actions of other muscles.
Role of Muscles - Force Couples
They occur when two or more forces are pulling in different directions on an object, causing the object to rotate about its axis.
Reversal of Muscle Function
A muscle group described to perform a given function can contract to control the exact opposite motion.
Determination of Muscle Action
Consideration of anatomical lines of pull, anatomical dissection, palpation, models, electromyography, & electrical stimulation.
Muscle Action - Anatomical Lines of Pull
Description of force exerted by a muscle.
Muscle Action - Anatomical Dissection
Looking at the muscle structures: determining their structural influence.
Muscle Action - Palpation
A very useful way to determine muscle action; it is done through using the sense of touch to feel or examine a muscle as it contracts.
Muscle Action - Models
Used to facilitate understanding of lines of pull & to stimulate muscle lengthening or shortening as joints move through various ranges of motion.
Muscle Action - Electromyography (EMG)
Utilizes either surface electrodes that are placed over muscle or fine wire/needle electrodes placed into the muscle.
Muscle Action - Electrical Stimulation
A reverse approach of electromyography; instead of electricity being used to detect muscle action, it is used to cause muscle activity.
Lines of Pull
Combining the knowledge of a particular joint's functional design & diarthrodial classification with an understanding of the specific location of a musculotendinous unit as it crosses a joint is extremely helpful in understanding its action on the joint.
Neural Control of Voluntary Movement
A result of the muscular & nervous systems working together.
Central Nervous System (CNS)
Consists of the brain and spinal cord; may be divided into five levels of control.
five levels: the Cerebral Cortex, the Basal Ganglia, the Cerebellum, the Brain Stem, & the Spinal Cord
CNS - The Cerebral Cortex
The highest level of control, provides for the creation of voluntary movement as aggregate muscle action but not as specific muscle activity.
CNS - Basal Ganglia
Controls the maintenance of postures & equilibrium & learned movements; sensory integration for balance & rhythmic activities is controlled here.
CNS - Cerebellum
A major integrator of sensory impulses & provides feedback relative to motion. It controls the timing & intensity of muscle activity to assist in the refinement of movements.
CNS - Brain Stem
Integrates all CNS activity through excitation & inhibition of desired neuromuscular actions & funstions in arousal or maintaining a wakeful state.
CNS - Spinal Cord
The common pathway between the CNS & the PNS. It has the most specific control & integrates various simple & complex spinal reflexes, as well as cortical & basal ganglia activity.
Peripheral Nervous System (PNS)
Connects the brain and spinal cord to the muscles, organs, and senses in the periphery of the body; can be divided into two levels.
two levels: Sensory & Motor Divisions
PNS - Sensory or __Afferent__Nerves
Bring impulses from receptors in the skin, joints, muscles, & other peripheral aspects of the body to the CNS.
PNS - Motor or Efferent Nerves
Carry impulses to the outlying regions of the body.
Spinal Nerves
Also provide both motor & sensory function for their respective portions of the body & are named for the locations from which they exit the vertebral column.
Dermatome
A defined area of skin supplied by a specific spinal nerve.
Myotome
Muscle or group of muscles supplied by a specific spinal nerve.
Neurons
The basic units of the nervous system responsible for generating & transmitting impulses are nerve cells.
Neuron Cell Body
Neurons consist of one or more branching projections.
Dendrites
Transmit impulses to the neuron & cell body.
Axon
An elongated projection that transmits impulses away form neuron cell bodies.
Sensory (Afferent) Neurons
Transmit impulses to the spinal cord & brain from all parts of the body.
Motor (Efferent) Neurons
Transmit impulses away from the brain and spinal cord to muscle and glandular tissue.
Interneurons (Association Neurons)
Central or connecting neurons that conduct impulses from sensory neurons to motor neurons.
Cervical Plexus
(Skull)-C1-C2-C3-C4-(C5)
Brachial Plexus
(C4)-C5-C6-C7-C8-T1-(T2)
Thoracic Plexus
(T1)-T2-T3-T12
Lumbosacral Plexus
L1-L2-L3-L4-L5-S1-S2-S3-S4-(S5)
Coccygeal Plexus
(S4)-S5-Co
Proprioreceptors
Internal receptors located in the skin, joints, muscles, & tendons that provide feedback relative to the tension, length & contraction state of muscle, the position of the body & limbs, & movement of joints.
Kinesthesis
The conscious awareness of the position & movement of the body in space.
Proprioception
The subconscious mechanism by which body is able to regulate posture & movement by responding to stimuli originating in the proprioceptors embedded in the joints, tendons, muscles, & inner ear.
Muscle Spindles
Sensitive to stretch & rate of stretch. Concentrated primarily in the muscle belly between the fibers.
Myotatic or Stretch Reflex
When rapid muscle stretch occurs, an impulse is sent to the CNS & then the CNS activates motor neurons of muscle & causes it to contract.
The Golgi Tendon Organs (GTO)
Continuously sensitive to muscle tension & active contraction. Located in the tendon close to the muscle-tendon junction.
Pacinian Corpuscles
Ligaments & tendon sheaths & beneath the skin, are activated by rapid changes in the joint angle & by pressure changes affecting the capsule. Concentrated around joint capsules.
Ruffini's Corpuscles
Activated by strong & sudden joint movements as well as pressure changes. Located in deep layers of the skin & the joint capsule.
Meissner's Corpuscles & Krause's End-Bulbs
Receives stimuli from touch. Located in the skin & in subcutaneous tissues.
Proprioceptive Feedback
The quality of movement & how we react to position change are significantly dependent upon this from the muscles & joints.
Neuromuscular Junction (NMJ)
Synapse between the axon terminal of a motor neuron & the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal.
Motor Unit
Consists of a single motor neuron & all the muscle fibers it innervates.
All-or-None Principle
The individual muscle fibers within a given motor unit will fire & contract either maximally or not at all.
Muscle Fiber Types
two catagories: Fast Fibers & Slow Fibers
three types: Type IIa & Type IIb, which are fast fibers, & Type I, which is a slow fiber
Fast Fibers
Can produce greater forces due to a greater shortening velocity but fatigue more quickly.
two types: Type IIa & Type IIb
Slow Fibers
Has a greater resistance to fatigue, but generally produce less tension.
one type: Type I
Action Potential (AP)
For the muscle fibers in a particular motor unit to contract, the motor unit must first receive a stimulus via an electrical signal.
Subthreshold Stimulus
If the stimulus is not strong enough to cause an action potential.
Threshold Stimulus
When the stimulus becomes strong enough to produce an action potential in a single motor unit axon.
Note
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