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© 2007 McGraw-Hill Higher Education. All © 2007 McGraw-Hill Higher Education. All rights reserved.rights reserved. 2-2-11

TodayToday

• Finish Muscle Function OverviewFinish Muscle Function Overview

• General NeuroanatomyGeneral Neuroanatomy

• Neural ControlNeural Control– All or noneAll or none– ProprioceptionProprioception


Role of MusclesRole of Muscles

• Agonist Agonist musclesmuscles– cause joint motion through a specified cause joint motion through a specified

plane of motion when contracting plane of motion when contracting concentricallyconcentrically

– known as primary or prime movers, or known as primary or prime movers, or muscles most involvedmuscles most involved



• AntagonistAntagonist musclesmuscles– located on opposite side of joint from located on opposite side of joint from

agonistagonist– have the opposite concentric actionhave the opposite concentric action– known as contralateral musclesknown as contralateral muscles– work in cooperation with agonist muscles work in cooperation with agonist muscles

by relaxing & allowing movementby relaxing & allowing movement– when contracting concentrically perform when contracting concentrically perform

the opposite joint motion of agonistthe opposite joint motion of agonist



• StabilizersStabilizers– surround joint or body partsurround joint or body part– contract to fixate or stabilize the area to contract to fixate or stabilize the area to

enable another limb or body segment to enable another limb or body segment to exert force & moveexert force & move

– known as fixatorsknown as fixators– essential in establishing a relatively firm essential in establishing a relatively firm

base for the more distal joints to work from base for the more distal joints to work from when carrying out movementswhen carrying out movements



• SynergistSynergist– assist in action of agonistsassist in action of agonists– not necessarily prime movers for the actionnot necessarily prime movers for the action– known as guiding musclesknown as guiding muscles– assist in refined movement & rule out assist in refined movement & rule out

undesired motionsundesired motions



• NeutralizersNeutralizers– Counteract or neutralize the action of Counteract or neutralize the action of

another muscle to prevent undesirable another muscle to prevent undesirable movements such as inappropriate muscle movements such as inappropriate muscle substitutionssubstitutions

– referred to as neutralizingreferred to as neutralizing– contract to resist specific actions of other contract to resist specific actions of other

musclesmuscles


Neural control of voluntary Neural control of voluntary movementmovement

• Functionally, PNS is divided into Functionally, PNS is divided into sensory & motor divisionssensory & motor divisions– Sensory or afferent nerves bring impulses Sensory or afferent nerves bring impulses

from receptors in skin, joints, muscles, & from receptors in skin, joints, muscles, & other peripheral aspects of body to CNSother peripheral aspects of body to CNS

– Motor or efferent nerves carry impulses to Motor or efferent nerves carry impulses to outlying regions of body from the CNSoutlying regions of body from the CNS



• Efferent nerves further subdivided intoEfferent nerves further subdivided into– voluntary or somatic nerves which are voluntary or somatic nerves which are

under conscious control & carry impulses under conscious control & carry impulses to skeletal muscles to skeletal muscles

– involuntary or visceral nerves, referred to involuntary or visceral nerves, referred to as the autonomic nervous system (ANS) as the autonomic nervous system (ANS) which carry impulses to the heart, smooth which carry impulses to the heart, smooth muscles, and glandsmuscles, and glands



• PNS - 2 groups of PNS - 2 groups of nerves of primary nerves of primary importance importance – Cranial nervesCranial nerves– Spinal nervesSpinal nerves

Modified from Booker JM, Thibodeau GA: Athletic injury assessment, ed 4, Dubuque, IA, 2000, McGraw-Hill.



• Cranial nervesCranial nerves– 12 pair originating from undersurface of 12 pair originating from undersurface of

brain & exiting from the cranial cavity brain & exiting from the cranial cavity through skull openingsthrough skull openings

– numbered for the order in which they numbered for the order in which they emerge from anterior to posterioremerge from anterior to posterior

– named in relation to their function or named in relation to their function or distributiondistribution



• Cranial nervesCranial nerves– I, II, & VIII are sensoryI, II, & VIII are sensory– III, IV, VI, XI, & XII, except for some III, IV, VI, XI, & XII, except for some

proprioceptive function, are primarily motorproprioceptive function, are primarily motor– V, VII, IX, & X have mixed functions - both V, VII, IX, & X have mixed functions - both

motor & sensorymotor & sensory



I. Olfactory I. Olfactory – smell smell – identifying familiar odorsidentifying familiar odors

II. OpticII. Optic– sight or Visionsight or Vision– visual acuity visual acuity



III. OculomotorIII. Oculomotor– levator of eyelid; superior, medial, and levator of eyelid; superior, medial, and

inferior recti; inferior oblique muscles of inferior recti; inferior oblique muscles of eyeballeyeball

– upward, downward, & medial gaze, upward, downward, & medial gaze, reaction to lightreaction to light

IV. TrochlearIV. Trochlear– superior oblique muscle of eyeballsuperior oblique muscle of eyeball– downward and lateral gazedownward and lateral gaze



V. TrigeminalV. Trigeminal– touch, paintouch, pain– skin of face, scalp behind the ears, mucous skin of face, scalp behind the ears, mucous

membranes of nose, sinuses, mouth, membranes of nose, sinuses, mouth, anterior tongueanterior tongue

– muscles of masticationmuscles of mastication– corneal reflex, facial sensation, teeth corneal reflex, facial sensation, teeth

clenching; chewingclenching; chewing



VI. AbducensVI. Abducens– lateral rectus muscle of eyeballlateral rectus muscle of eyeball– lateral gazelateral gaze

VII. FacialVII. Facial– tastetaste– touch, paintouch, pain– facial musclesfacial muscles– lateral gaze, facial expressions, identifying lateral gaze, facial expressions, identifying

familiar tastes with front of tonguefamiliar tastes with front of tongue



VIII. Vestibulocochlear (Acoustic Nerve)VIII. Vestibulocochlear (Acoustic Nerve)– hearing, balance/equilibriumhearing, balance/equilibrium– detecting presence of sounds, balance & detecting presence of sounds, balance &

coordinationcoordination

IX. GlossopharyngealIX. Glossopharyngeal– touch, paintouch, pain– tastetaste– muscles of pharynxmuscles of pharynx– gag reflex, swallowinggag reflex, swallowing



X. VagusX. Vagus– touch, paintouch, pain– muscles of palate, pharynx, & larynxmuscles of palate, pharynx, & larynx– gag reflex, swallowing, speechgag reflex, swallowing, speech

XI. AccessoryXI. Accessory– sternocleidomastoid & trapezius musclesternocleidomastoid & trapezius muscle– shoulder shrugging, head movementshoulder shrugging, head movement



XII. HypoglossalXII. Hypoglossal– muscles of tonguemuscles of tongue– tongue movementstongue movements



• Spinal nervesSpinal nerves– 31 pairs originate from the spinal cord 31 pairs originate from the spinal cord – pass through openings between the pass through openings between the

vertebrae on each side vertebrae on each side – from here certain spinal nerves form from here certain spinal nerves form

different plexusesdifferent plexuses– eventually become peripheral nerve eventually become peripheral nerve

braches supplying specific anatomical braches supplying specific anatomical locations while others run directly to locations while others run directly to specific anatomical locationsspecific anatomical locations



• Spinal nervesSpinal nerves– provide both motor & sensory function for provide both motor & sensory function for

their respective portions of bodytheir respective portions of body– named for the location from which they exit named for the location from which they exit

vertebral columnvertebral column– from each of side of spinal column from each of side of spinal column

• 8 cervical nerves8 cervical nerves• 12 thoracic nerves12 thoracic nerves• 5 lumbar nerves5 lumbar nerves• 5 sacral5 sacral• 1 coccygeal nerve1 coccygeal nerve



• Cervical nerves 1 through 4Cervical nerves 1 through 4

– form the cervical plexus form the cervical plexus – generally responsible for sensation from generally responsible for sensation from

upper part of shoulders to back of head upper part of shoulders to back of head and front of neckand front of neck

– supplies motor innervation to several supplies motor innervation to several muscles of the neckmuscles of the neck



• Cervical nerves 5 - 8 & thoracic nerve 1Cervical nerves 5 - 8 & thoracic nerve 1– form the brachial plexusform the brachial plexus– supplies motor & sensory function to the supplies motor & sensory function to the

upper extremity and most of the scapulaupper extremity and most of the scapula



• Thoracic nerves 2-12 run directly to Thoracic nerves 2-12 run directly to specific anatomical locations in thoraxspecific anatomical locations in thorax

• All lumbar, sacral, & coccygeal nerves All lumbar, sacral, & coccygeal nerves form the lumbosacral plexus which form the lumbosacral plexus which supplies sensation & motor function to supplies sensation & motor function to lower trunk, entire lower extremity & lower trunk, entire lower extremity & perineumperineum



• Sensory function of spinal nerves is to Sensory function of spinal nerves is to provide feedback to CNS regarding skin provide feedback to CNS regarding skin sensationsensation

• DermatomeDermatome - defined area of skin - defined area of skin supplied by a specific spinal nervesupplied by a specific spinal nerve

• MyotomeMyotome - muscle or group of muscles - muscle or group of muscles supplied by a specific spinal nervesupplied by a specific spinal nerve

• Certain spinal nerves are also Certain spinal nerves are also responsible for reflexesresponsible for reflexes



• Neurons (nerve cells) - basic functional Neurons (nerve cells) - basic functional units of nervous system responsible for units of nervous system responsible for generating & transmitting impulses and generating & transmitting impulses and consist of consist of – a neuron cell bodya neuron cell body– one or more branching projections known as one or more branching projections known as

dendrites which transmit impulses dendrites which transmit impulses toto neuron neuron & cell body& cell body

– axon - an elongated projection that transmits axon - an elongated projection that transmits impulses impulses awayaway from neuron cell bodies from neuron cell bodies



• Neurons are classified as one of three Neurons are classified as one of three types according to the direction in which types according to the direction in which they transmit impulsesthey transmit impulses– Sensory neurons Sensory neurons – Motor neuronsMotor neurons– InterneuronsInterneurons



• Sensory neurons transmit impulses to Sensory neurons transmit impulses to spinal cord & brain from all parts of spinal cord & brain from all parts of bodybody

• Motor neurons transmit impulses away Motor neurons transmit impulses away from the brain & spinal cord to muscle & from the brain & spinal cord to muscle & glandular tissueglandular tissue

• Interneurons are central or connecting Interneurons are central or connecting neurons that conduct impulses from neurons that conduct impulses from sensory neurons to motor neurons sensory neurons to motor neurons


Motor UnitMotor Unit*All-or-None-Principle If the stimulus is of sufficient magnitude all of the fibers will be activated.


Neuron and Motor UnitNeuron and Motor Unit• Neuron is a single nerve Neuron is a single nerve

cellcell• 101014 14 neurons in brainneurons in brain• Synapses convey Synapses convey

information via information via chemicalschemicals

• Afferent-from periphery Afferent-from periphery to CNSto CNS

• Efferent-from CNS to Efferent-from CNS to peripheryperiphery

• Neuron body, dendrites Neuron body, dendrites and axon (myelin and axon (myelin sheath)sheath)


Action PotentialAction Potential• Alteration in Alteration in

permeabilitypermeability• Sodium influx and Sodium influx and

potassium outflowpotassium outflow• Negative to positiveNegative to positive• Nerve conduction Nerve conduction

velocityvelocity– 120 m/s or 120 m/s or 270mph270mph for for

myelinatedmyelinated• 400 f/s400 f/s

– 5 m/s or 5 m/s or 2mph2mph for for unmyelinatedunmyelinated

• 16 f/s16 f/s


Fiber Type CharacteristicsFiber Type Characteristics


Characteristics of Muscle Fiber Characteristics of Muscle Fiber TypesTypes


Size Principle of Size Principle of Muscle RecruitmentMuscle Recruitment

TYPE I

TYPE IIa

TYPE IIb

% FIBERS USED

MUSCULAR FORCE


ReflexesReflexes

• Sensory receptors send a signal to a Sensory receptors send a signal to a motor neuronmotor neuron

• Motor neuron sends signal to the Motor neuron sends signal to the effectoreffector

• Stretch shortening cycle (SSC)?Stretch shortening cycle (SSC)?


Moritani and deVries Moritani and deVries Hypertrophy vs. LearningHypertrophy vs. Learning

Trained

0

20

40

60

80

100

2 4 6 8

Weeks%

Con

trib

utio

n

Neural

Hypertrophy

Untrained

0

20

40

60

80

100

120

2 4 6 8

Weeks

% C

ontr

ibut

ion

Neural

Hypertrophy


Proprioception & KinesthesisProprioception & Kinesthesis

• Activity performance is significantly Activity performance is significantly dependent upon neurological feedback dependent upon neurological feedback from the bodyfrom the body

• We use various senses to determine a We use various senses to determine a response to our environmentresponse to our environment– Seeing when to lift our hand to catch a fly Seeing when to lift our hand to catch a fly

ballball



• Taken for granted are sensations Taken for granted are sensations associated with neuromuscular activity associated with neuromuscular activity through proprioceptionthrough proprioception

• Proprioceptors - internal receptors Proprioceptors - internal receptors located in skin, joints, muscles, & located in skin, joints, muscles, & tendons which provide feedback relative tendons which provide feedback relative to tension, length, & contraction state of to tension, length, & contraction state of muscle, position of body & limbs, and muscle, position of body & limbs, and movements of jointsmovements of joints



• Proprioceptors work in combination with Proprioceptors work in combination with other sense organs to accomplish other sense organs to accomplish kinesthesiskinesthesis

• Kinesthesis – conscious awareness of Kinesthesis – conscious awareness of position & movement of the body in position & movement of the body in spacespace

• Proprioceptors specific to musclesProprioceptors specific to muscles– Muscles spindlesMuscles spindles– Golgi tendon organs (GTO)Golgi tendon organs (GTO)



• Proprioceptors specific to joints & skinProprioceptors specific to joints & skin– Meissner’s corpusclesMeissner’s corpuscles– Ruffini’s corpusclesRuffini’s corpuscles– Pacinian corpusclesPacinian corpuscles– Krause’s end-bulbsKrause’s end-bulbs



• ProprioceptionProprioception– Subconscious mechanism by which body is Subconscious mechanism by which body is

able posture & movement by responding to able posture & movement by responding to stimuli originating in proprioceptors of the stimuli originating in proprioceptors of the joints, tendons, muscles, & inner earjoints, tendons, muscles, & inner ear


Proprioception & KinesthesisProprioception & Kinesthesis• Muscle spindlesMuscle spindles

– concentrated primarily in muscle belly concentrated primarily in muscle belly between the fibersbetween the fibers

– sensitive to stretch & rate of stretchsensitive to stretch & rate of stretch– Insert into connective tissue within muscle & Insert into connective tissue within muscle &

run parallel with muscle fibersrun parallel with muscle fibers– Spindle number varies depending upon level Spindle number varies depending upon level

of control neededof control needed• Ex. Greater concentration in hands than thighEx. Greater concentration in hands than thigh



• Muscle spindles & myotatic Muscle spindles & myotatic or stretch reflexor stretch reflex1.1. Rapid muscle stretch occursRapid muscle stretch occurs

2.2. Impulse is sent to the CNSImpulse is sent to the CNS

3.3. CNS activates motor neurons CNS activates motor neurons of muscle and causes it to of muscle and causes it to contractcontract

Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill.



• Ex. Knee jerk or patella tendon reflexEx. Knee jerk or patella tendon reflex– Reflex hammer strikes patella tendonReflex hammer strikes patella tendon– Causes a quick stretch to musculotendinis Causes a quick stretch to musculotendinis

unit of quadricepsunit of quadriceps– In response quadriceps fires & the knee In response quadriceps fires & the knee

extendsextends

• More sudden the tap, the more significant More sudden the tap, the more significant the reflexive contractionthe reflexive contraction



• Stretch reflex may be utilized to facilitate Stretch reflex may be utilized to facilitate a greater responsea greater response– Ex. Quick short squat before attempting a Ex. Quick short squat before attempting a

jumpjump– Quick stretch placed on muscles in the squat Quick stretch placed on muscles in the squat

enables the same muscles to generate more enables the same muscles to generate more force in subsequently jumping off the floorforce in subsequently jumping off the floor



• Golgi tendon organGolgi tendon organ– found serially in the tendon found serially in the tendon

close to muscle tendon close to muscle tendon junctionjunction

– sensitive to both muscle sensitive to both muscle tension & active contractiontension & active contraction

– much less sensitive to stretch much less sensitive to stretch than muscles spindlesthan muscles spindles

– require a greater stretch to be require a greater stretch to be activatedactivated

Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill.



• Tension in tendons & GTO increases as Tension in tendons & GTO increases as muscle contract, which activates GTOmuscle contract, which activates GTO1.1. GTO stretch threshold is reachedGTO stretch threshold is reached2.2. Impulse is sent to CNS Impulse is sent to CNS 3.3. CNS causes muscle to relaxCNS causes muscle to relax4.4. facilitates activation of antagonists as a facilitates activation of antagonists as a

protective mechanismprotective mechanism

• GTO protects us from an excessive GTO protects us from an excessive contraction by causing its muscle to contraction by causing its muscle to relaxrelax


Proprioception & KinesthesisProprioception & Kinesthesis• Pacinian corpusclesPacinian corpuscles

– concentrated around joint capsules, concentrated around joint capsules, ligaments, tendon sheaths & beneath skinligaments, tendon sheaths & beneath skin

– activated by rapid changes in joint angle & by activated by rapid changes in joint angle & by pressure changes affecting the capsulepressure changes affecting the capsule

– activation only last briefly & is not effective in activation only last briefly & is not effective in detecting constant pressuredetecting constant pressure

– helpful in providing feedback regarding the helpful in providing feedback regarding the location of a body part in space following location of a body part in space following quick movements such as running or jumpingquick movements such as running or jumping


Proprioception & Proprioception & KinesthesisKinesthesis

• Ruffini’s corpusclesRuffini’s corpuscles– located in deep layers of the skin and the located in deep layers of the skin and the

joint capsulejoint capsule– activated by strong & sudden joint activated by strong & sudden joint

movements as well as pressure changesmovements as well as pressure changes– reaction to pressure changes are slower to reaction to pressure changes are slower to

developdevelop


Proprioception & Proprioception & KinesthesisKinesthesis

• Ruffini’s corpusclesRuffini’s corpuscles– activation is continued as long as pressure activation is continued as long as pressure

is maintainedis maintained– essential in detecting even minute joint essential in detecting even minute joint

position changes & providing information position changes & providing information as to exact joint angleas to exact joint angle



• Meissner’s corpuscles & Krause’s end-Meissner’s corpuscles & Krause’s end-bulbsbulbs– located in the skin & other subcutaneous located in the skin & other subcutaneous

tissuestissues– important in receiving stimuli from touchimportant in receiving stimuli from touch– not as relevant to kinesthesisnot as relevant to kinesthesis



• Quality of movement & reaction to Quality of movement & reaction to position change is dependent upon position change is dependent upon proprioceptive feedback from muscles & proprioceptive feedback from muscles & jointsjoints

• Proprioception may be enhanced Proprioception may be enhanced through specific trainingthrough specific training


All or None PrincipleAll or None Principle

• When muscle contracts, contraction When muscle contracts, contraction occurs at the muscle fiber level within a occurs at the muscle fiber level within a particular motor unitparticular motor unit

• Motor unitMotor unit– Single motor neuron & all muscle fibers it Single motor neuron & all muscle fibers it

innervatesinnervates– Function as a single unitFunction as a single unit



• Typical muscle contractionTypical muscle contraction– The number of motor units responding (and The number of motor units responding (and

number of muscle fibers contracting) within number of muscle fibers contracting) within the muscle may vary significantly from the muscle may vary significantly from relatively few to virtually allrelatively few to virtually all

– depending on the number of muscle fibers depending on the number of muscle fibers within each activated motor unit & the within each activated motor unit & the number of motor units activatednumber of motor units activated



• All or None PrincipleAll or None Principle - regardless of - regardless of number, individual muscle fibers within number, individual muscle fibers within a given motor unit will either fire & a given motor unit will either fire & contract maximally or not at allcontract maximally or not at all


Factors affecting muscle tension Factors affecting muscle tension developmentdevelopment

• Difference between lifting a minimal vs. Difference between lifting a minimal vs. maximal resistance is the number of muscle maximal resistance is the number of muscle fibers recruitedfibers recruited

• The number of muscle fibers recruited may The number of muscle fibers recruited may be increased bybe increased by– activating those motor units containing a greater activating those motor units containing a greater

number of muscle fibersnumber of muscle fibers– activating more motor unitsactivating more motor units– increasing the frequency of motor unit activationincreasing the frequency of motor unit activation



• Number of muscle fibers per motor unit Number of muscle fibers per motor unit varies significantlyvaries significantly– From less than 10 in muscles requiring From less than 10 in muscles requiring

precise and detailed such as muscles of precise and detailed such as muscles of the eyethe eye

– To as many as a few thousand in large To as many as a few thousand in large muscles that perform less complex muscles that perform less complex activities such as the quadriceps activities such as the quadriceps



• Motor unit must first receive a stimulus Motor unit must first receive a stimulus via electrical signal known as an via electrical signal known as an action action potentialpotential for the muscle fibers in the unit for the muscle fibers in the unit to contractto contract

• Subthreshold stimulusSubthreshold stimulus– not strong enough to cause an action not strong enough to cause an action

potentialpotential– does not result in a contraction does not result in a contraction



• Threshold stimulusThreshold stimulus– stimulus becomes strong enough to stimulus becomes strong enough to

produce an action potential in a single produce an action potential in a single motor unit axonmotor unit axon

– all of the muscle fibers in the motor unit all of the muscle fibers in the motor unit contractcontract



• Submaximal stimuliSubmaximal stimuli– Stimuli that are strong enough to produce Stimuli that are strong enough to produce

action potentials in additional motor unitsaction potentials in additional motor units

• Maximal stimuliMaximal stimuli– Stimuli that are strong enough to produce Stimuli that are strong enough to produce

action potentials in all motor units of a action potentials in all motor units of a particular muscleparticular muscle



• As stimulus strength increases from threshold As stimulus strength increases from threshold up to maximal more motor units are recruited up to maximal more motor units are recruited & overall muscle contraction force increases & overall muscle contraction force increases in a graded fashionin a graded fashion

From Seeley RR, Stephens TD, Tate P: Anatomy & physiology, ed 7, New York, 2006, McGraw-Hill.



• Greater contraction forces may also be Greater contraction forces may also be achieved by increasing the frequency or achieved by increasing the frequency or motor unit activationmotor unit activation

• Phases of a single muscle fiber Phases of a single muscle fiber contraction or twitchcontraction or twitch– StimulusStimulus– Latent periodLatent period– Contraction phaseContraction phase– Relaxation phaseRelaxation phase



• Latent periodLatent period– Brief period of a few Brief period of a few

milliseconds following stimulusmilliseconds following stimulus

• Contraction phaseContraction phase– Muscle fiber begins shorteningMuscle fiber begins shortening– Lasts about 40 millisecondsLasts about 40 milliseconds

• Relaxation phaseRelaxation phase– Follows contraction phaseFollows contraction phase– Last about 50 millisecondsLast about 50 milliseconds

From Powers SK, Howley ET: Exercise physiology: theory and application to fitness and performance, ed 4, New York, 2001 , McGraw-Hill.



• SummationSummation– When successive stimuli are provided before When successive stimuli are provided before

relaxation phase of first twitch has completed, relaxation phase of first twitch has completed, subsequent twitches combine with the first to subsequent twitches combine with the first to produce a sustained contraction produce a sustained contraction

– Generates a greater amount of tension than Generates a greater amount of tension than single contraction would produce individually single contraction would produce individually

– As frequency of stimuli increase, the resultant As frequency of stimuli increase, the resultant summation increases accordingly producing summation increases accordingly producing increasingly greater total muscle tensionincreasingly greater total muscle tension



• TetanusTetanus – results if the stimuli are provided at a results if the stimuli are provided at a

frequency high enough that no relaxation frequency high enough that no relaxation can occur between contractionscan occur between contractions

From Powers SK, Howley ET: Exercise physiology: theory and application to fitness and performance, ed 4, New York, 2001 , McGraw-Hill.



• TreppeTreppe– Occurs when multiple Occurs when multiple

maximal stimuli are provided maximal stimuli are provided at a low enough frequency to at a low enough frequency to allow complete relaxation allow complete relaxation between contractions to between contractions to rested musclerested muscle

– Slightly greater tension is Slightly greater tension is produced by the 2produced by the 2ndnd stimulus stimulus than with 1than with 1stst

From Seeley RR, Stephens TD, Tate P: Anatomy & physiology, ed 7, New York, 2006, McGraw-Hill..



• TreppeTreppe– 33rdrd stimulus produces even stimulus produces even

greater tension than the 2greater tension than the 2ndnd – Staircase effect occurs only Staircase effect occurs only

with the 1with the 1stst few stimuli few stimuli– Resultant contractions after Resultant contractions after

the initial ones result in equal the initial ones result in equal tension being producedtension being produced


Muscle Length - Tension Muscle Length - Tension RelationshipRelationship

• Maximal ability of a muscle to develop Maximal ability of a muscle to develop tension & exert force varies depending tension & exert force varies depending upon the length of the muscle during upon the length of the muscle during contractioncontraction



• Generally, depending upon muscle Generally, depending upon muscle involvedinvolved– Greatest amount of tension can be Greatest amount of tension can be

developed when a muscle is stretched developed when a muscle is stretched between 100% to 130% of its resting lengthbetween 100% to 130% of its resting length

– Stretch beyond 100% to 130% of resting Stretch beyond 100% to 130% of resting length significantly decreases the amount length significantly decreases the amount of force muscle can exertof force muscle can exert



• Generally, depending upon muscle Generally, depending upon muscle involvedinvolved– A proportional decrease in ability to A proportional decrease in ability to

develop tension occurs as a muscle is develop tension occurs as a muscle is shortenedshortened

– When shortened to around 50% to 60% of When shortened to around 50% to 60% of resting length ability to develop contractile resting length ability to develop contractile tension is essentially reduced to zerotension is essentially reduced to zero



• Ex. 1 Increasing ability to exert Ex. 1 Increasing ability to exert forceforce– squat slightly to stretch the calf, squat slightly to stretch the calf,

hamstrings, & quadriceps before hamstrings, & quadriceps before contracting same muscles contracting same muscles concentrically to jumpconcentrically to jump

• Ex. 2. Reducing ability to exert Ex. 2. Reducing ability to exert forceforce– isolate the gluteus maximus by isolate the gluteus maximus by

maximally shortening the hamstrings maximally shortening the hamstrings with knee flexionwith knee flexion


Muscle Force – Velocity Muscle Force – Velocity RelationshipRelationship

• When muscle is contracting (concentrically or When muscle is contracting (concentrically or eccentrically) the rate of length change is eccentrically) the rate of length change is significantly related to the amount of force significantly related to the amount of force potentialpotential

• When contracting concentrically against a When contracting concentrically against a light resistance muscle is able to contract at a light resistance muscle is able to contract at a high velocityhigh velocity



• As resistance increases, the maximal velocity As resistance increases, the maximal velocity at which muscle is able to contract decreasesat which muscle is able to contract decreases

• Eventually, as load increases, the velocity Eventually, as load increases, the velocity decreases to zero resulting in an isometric decreases to zero resulting in an isometric contractioncontraction

• As load increases beyond muscle’s ability to As load increases beyond muscle’s ability to maintain an isometric contraction, the muscle maintain an isometric contraction, the muscle begins to lengthen resulting in an eccentric begins to lengthen resulting in an eccentric contractioncontraction



• Slight increases in load results in relatively Slight increases in load results in relatively low velocity of lengtheninglow velocity of lengthening

• As load increases further the velocity of As load increases further the velocity of lengthening will increase as welllengthening will increase as well

• Eventually, load may increase to point where Eventually, load may increase to point where muscle can no longer resist, resulting in muscle can no longer resist, resulting in uncontrollable lengthening or dropping of loaduncontrollable lengthening or dropping of load

• Inverse relationship between concentric Inverse relationship between concentric velocity & force productionvelocity & force production



• As force needed to cause movement of an As force needed to cause movement of an object increases the velocity of concentric object increases the velocity of concentric contraction decreasescontraction decreases

• Somewhat proportional relationship between Somewhat proportional relationship between eccentric velocity & force productioneccentric velocity & force production

• As force needed to control an object’s As force needed to control an object’s movement increases, the velocity of eccentric movement increases, the velocity of eccentric lengthening increases, at least until when lengthening increases, at least until when control is lostcontrol is lost


Angle of pullAngle of pull

• Angle between the line of pull of the muscle & Angle between the line of pull of the muscle & the bone on which it inserts (angle toward the the bone on which it inserts (angle toward the joint)joint)

• With every degree of joint motion, the angle With every degree of joint motion, the angle of pull changesof pull changes

• Joint movements & insertion angles involve Joint movements & insertion angles involve mostly small angles of pullmostly small angles of pull



• Angle of pull decreases as bone moves away Angle of pull decreases as bone moves away from its anatomical position through local from its anatomical position through local muscle group’s contractionmuscle group’s contraction

• Range of movement depends on type of joint Range of movement depends on type of joint & bony structure& bony structure

• Most muscles work at angles of pull less than Most muscles work at angles of pull less than 50 degrees50 degrees

• Amount of muscular force needed to cause Amount of muscular force needed to cause joint movement is affected by angle of pulljoint movement is affected by angle of pull



• Rotary component (Rotary component (vertical component) - vertical component) - component of muscular force that acts component of muscular force that acts perpendicular to long axis of bone (lever)perpendicular to long axis of bone (lever)– When the line of muscular force is at 90 When the line of muscular force is at 90

degrees to bone on which it attaches, all of degrees to bone on which it attaches, all of the muscular force is rotary force (100% of the muscular force is rotary force (100% of force is contributing to movement) force is contributing to movement)

– All of force is being used to rotate the lever All of force is being used to rotate the lever about its axisabout its axis

– The closer the angle of pull to 90 degrees, The closer the angle of pull to 90 degrees, the greater the rotary componentthe greater the rotary component

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.



• At all other degrees of the angle of pull, one At all other degrees of the angle of pull, one of the other two components of force are of the other two components of force are operating in addition to rotary componentoperating in addition to rotary component– Rotary component continues with less force, to Rotary component continues with less force, to

rotate the lever about its axisrotate the lever about its axis– Second force component is the horizontal, or Second force component is the horizontal, or

nonrotary componentnonrotary component and is either a and is either a stabilizing stabilizing componentcomponent or a or a dislocating componentdislocating component, depending , depending on whether the angle of pull is less than or greater on whether the angle of pull is less than or greater than 90 degreesthan 90 degrees



• If angle is less than 90 If angle is less than 90 degrees, the force is a degrees, the force is a stabilizingstabilizing force because its force because its pull directs the bone toward the pull directs the bone toward the joint axisjoint axis

• If angle is greater than 90 If angle is greater than 90 degrees, the force is degrees, the force is dislocatingdislocating due to its pull due to its pull directing the bone away from directing the bone away from the joint axisthe joint axis

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.



• Sometimes desirable to begin with the Sometimes desirable to begin with the angle of pull is at 90 degreesangle of pull is at 90 degrees– chin-up (pull-up)chin-up (pull-up)– angle makes the chin-up easier because of angle makes the chin-up easier because of

more advantageous angle of pullmore advantageous angle of pull– compensate for lack of sufficient strengthcompensate for lack of sufficient strength


Uniarticular, biarticular, and Uniarticular, biarticular, and multiarticular musclesmultiarticular muscles

• Uniarticular musclesUniarticular muscles– Cross & act directly only on the joint that Cross & act directly only on the joint that

they crossthey cross– Ex. BrachialisEx. Brachialis

• Can only pull humerus & ulna closer Can only pull humerus & ulna closer togethertogether



• Biarticular muscles – cross & act on two Biarticular muscles – cross & act on two different jointsdifferent joints– Depending, biarticular muscles may Depending, biarticular muscles may

contract & cause motion at either one or contract & cause motion at either one or both of its jointsboth of its joints

– Two advantages over uniarticular musclesTwo advantages over uniarticular muscles• can cause and/or control motion at more than can cause and/or control motion at more than

one jointone joint• are able to maintain a relatively constant length are able to maintain a relatively constant length

due to "shortening" at one joint and due to "shortening" at one joint and "lengthening" at another joint"lengthening" at another joint



• Muscle does not actually shorten at one Muscle does not actually shorten at one joint & lengthen at otherjoint & lengthen at other– The concentric shortening of the muscle to The concentric shortening of the muscle to

move one joint is offset by motion of the move one joint is offset by motion of the other joint which moves its attachment of other joint which moves its attachment of muscle farther awaymuscle farther away

– This maintenance of a relatively constant This maintenance of a relatively constant length results in the muscle being able to length results in the muscle being able to continue its exertion of forcecontinue its exertion of force



• Ex.1 Hip & knee biarticular muscles Ex.1 Hip & knee biarticular muscles – ConcurrentConcurrent movement pattern occurs when movement pattern occurs when

both the knee & hip extend at the same both the knee & hip extend at the same timetime

– If only knee extension occurs, rectus If only knee extension occurs, rectus femoris shortens & loses tension as do femoris shortens & loses tension as do other quadriceps muscles, but its relative other quadriceps muscles, but its relative length & subsequent tension may be length & subsequent tension may be maintained due to its relative lengthening maintained due to its relative lengthening at the hip joint during extensionat the hip joint during extension



• Ex. 2 Hip & knee biarticular musclesEx. 2 Hip & knee biarticular muscles– CountercurrentCountercurrent movement pattern occurs movement pattern occurs

in kickingin kicking– During the lower extremity forward During the lower extremity forward

movement phase the rectus femoris movement phase the rectus femoris concentrically contracts to flex the hip & concentrically contracts to flex the hip & extend the kneeextend the knee

– These two movements, when combined, These two movements, when combined, increase the tension or stretch on the increase the tension or stretch on the hamstring muscles both at the knee & hiphamstring muscles both at the knee & hip



• Multiarticular muscles act on three or Multiarticular muscles act on three or more joints due to the line of pull more joints due to the line of pull between their origin & insertion crossing between their origin & insertion crossing multiple jointsmultiple joints

• Principles relative to biarticular muscles Principles relative to biarticular muscles apply similarly to multiarticular musclesapply similarly to multiarticular muscles


Reciprocal Inhibition or Reciprocal Inhibition or InnervationInnervation

• Antagonist muscles groups must relax & Antagonist muscles groups must relax & lengthen when the agonist muscle group lengthen when the agonist muscle group contractscontracts– This reciprocal innervation effect occurs through This reciprocal innervation effect occurs through

reciprocal inhibition of the antagonistsreciprocal inhibition of the antagonists– Activation of the motor units of the agonists Activation of the motor units of the agonists

causes a reciprocal neural inhibition of the motor causes a reciprocal neural inhibition of the motor units of the antagonistsunits of the antagonists

– This reduction in neural activity of the antagonists This reduction in neural activity of the antagonists allows them to subsequently lengthen under less allows them to subsequently lengthen under less tensiontension


Reciprocal Inhibition or Reciprocal Inhibition or InnervationInnervation

• Ex. Compare the ease ofEx. Compare the ease of– stretching hamstrings when simultaneously stretching hamstrings when simultaneously

contracting the quadriceps contracting the quadriceps

vs.vs.– stretching hamstrings without contracting stretching hamstrings without contracting

quadricepsquadriceps


Active & Passive Active & Passive InsufficiencyInsufficiency

• As muscle shortens its ability to exert As muscle shortens its ability to exert force diminishesforce diminishes– Active insufficiencyActive insufficiency is reached when the is reached when the

muscle becomes shortened to the point muscle becomes shortened to the point that it can not generate or maintain active that it can not generate or maintain active tensiontension

– Passively insufficiencyPassively insufficiency is reached when is reached when the opposing muscle becomes stretched to the opposing muscle becomes stretched to the point where it can no longer lengthen & the point where it can no longer lengthen & allow movementallow movement



• Easily observed in either biarticular Easily observed in either biarticular or multiarticular muscles when full or multiarticular muscles when full range of motion is attempted in all range of motion is attempted in all joints crossed by the musclejoints crossed by the muscle– Ex. Rectus femoris contracts Ex. Rectus femoris contracts

concentrically to both flex the hip & concentrically to both flex the hip & extend the kneeextend the knee

– Can completely perform either action Can completely perform either action one at a time but actively insufficient to one at a time but actively insufficient to obtain full range at both joints obtain full range at both joints simultaneouslysimultaneously



– Similarly, hamstrings can not usually Similarly, hamstrings can not usually stretch enough to allow both maximal hip stretch enough to allow both maximal hip flexion & maximal knee extension due flexion & maximal knee extension due passive insufficiencypassive insufficiency

• As a result, it is virtually impossible to As a result, it is virtually impossible to actively extend the knee fully when actively extend the knee fully when beginning with the hip fully flexed or beginning with the hip fully flexed or vice versavice versa

© 2007 mcgraw-hill higher education. all rights reserved. 2-1 today finish muscle function...

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somatic nerves

groups of nerves

afferent nerves

visceral nerves

smooth muscles

skeletal muscles involuntary

regions of body

body segment