Chapter 7 The Chapter 7 The Muscular SystemMuscular System

Specialized tissue that enable Specialized tissue that enable the body and its parts to the body and its parts to

move.move.

Alireza Ashraf, M.D.Professor of Physical Medicine & Rehabilitation

Shiraz Medical school

SummarySummary Functions of skeletal muscleFunctions of skeletal muscle Structure of skeletal muscleStructure of skeletal muscle ContractionContraction MusclesMuscles

– Head and neckHead and neck– Upper extremityUpper extremity– TrunkTrunk– Lower extremitiesLower extremities

Types of movementsTypes of movements

Functions of Skeletal MuscleFunctions of Skeletal Muscle Movement – muscle move bones by Movement – muscle move bones by pullingpulling

not pushing.not pushing.– SynergistsSynergists – any movement is generally – any movement is generally

accomplished by more than one muscle. All of the accomplished by more than one muscle. All of the muscles responsible for a particular movement muscles responsible for a particular movement are synergists. The one that is most responsible are synergists. The one that is most responsible for the movement is the for the movement is the Prime MoverPrime Mover..

– AntagonistsAntagonists - muscles and muscle groups usually - muscles and muscle groups usually work in pairs – example the biceps flex your arm work in pairs – example the biceps flex your arm and its partner, the triceps, extend your arm. The and its partner, the triceps, extend your arm. The two muscles are two muscles are antagonistsantagonists, i.e. cause opposite , i.e. cause opposite actions. When one contracts the other relaxes.actions. When one contracts the other relaxes.

– LevatorsLevators – muscle that raise a body part. – muscle that raise a body part.

Functions of Skeletal MuscleFunctions of Skeletal Muscle Maintenance of posture or muscle Maintenance of posture or muscle

tonetone– We are able to maintain our body position because We are able to maintain our body position because

of tonic contractions in our skeletal muscles. These of tonic contractions in our skeletal muscles. These contractions don’t produce movement yet hold our contractions don’t produce movement yet hold our muscles in position.muscles in position.

Heat productionHeat production – contraction of – contraction of muscles produces most of the heat muscles produces most of the heat required to maintain body required to maintain body temperature.temperature.

Structure of Skeletal MuscleStructure of Skeletal Muscle Composed of striated muscle cells Composed of striated muscle cells

(=muscle fibers) and connective (=muscle fibers) and connective tissue.tissue.– TendonsTendons anchor muscle firmly to bones. anchor muscle firmly to bones.

– Most muscles attach to 2 bones that have a Most muscles attach to 2 bones that have a moveable joint between them. moveable joint between them.

Structure of Skeletal MuscleStructure of Skeletal Muscle BursaeBursae – small fluid – small fluid

filled sacs that lie filled sacs that lie between some between some tendons and the tendons and the bones beneath bones beneath them. They are them. They are made of connective made of connective tissue and are lined tissue and are lined with synovial with synovial membrane that membrane that secretes synovial secretes synovial fluid.fluid.

Figure 8.8a

Structure of Skeletal MuscleStructure of Skeletal Muscle Contribution of the nervous systemContribution of the nervous system

– Electrochemical impulses travel from Electrochemical impulses travel from the the frontal lobesfrontal lobes of the cerebrum via of the cerebrum via motor nervesmotor nerves to the muscle fibers and to the muscle fibers and cause them to contract.cause them to contract.

– SensationSensation is a function of the brain – is a function of the brain – impulses are integrated in the impulses are integrated in the parietalparietal lobes of the cerebrum (conscious lobes of the cerebrum (conscious muscle sense) and in the muscle sense) and in the cerebellumcerebellum (unconscious). These activities promote (unconscious). These activities promote coordinationcoordination..

Structure of Skeletal MuscleStructure of Skeletal Muscle Microscopic anatomyMicroscopic anatomy

– Muscle cells (fibers) are grouped in a highly Muscle cells (fibers) are grouped in a highly organized way in the muscle. The membrane that organized way in the muscle. The membrane that surrounds each muscle cell is called the surrounds each muscle cell is called the sarcolemmasarcolemma..

– Muscle cells are filled with 2 types of fine threadlike Muscle cells are filled with 2 types of fine threadlike proteins called myofilaments:proteins called myofilaments:

– The myofilaments are arranged in the cells in small The myofilaments are arranged in the cells in small units called units called sarcomeressarcomeres. .

Structure of Skeletal MuscleStructure of Skeletal Muscle Neuromuscular junctionNeuromuscular junction

– Spot where the axon of a Spot where the axon of a motor nervemotor nerve nears the muscle fiber.nears the muscle fiber.

– The axon terminal does not touch the The axon terminal does not touch the muscle but comes close. The space muscle but comes close. The space between the axon and the muscle cell is between the axon and the muscle cell is called the called the synapsesynapse..

– Within the terminal end of the axon are Within the terminal end of the axon are small sacs filled with a small sacs filled with a neurotransmitterneurotransmitter called called acetylcholineacetylcholine..

Muscle ContractionMuscle Contraction SequenceSequence

– Electrical impulse travels down a motor neuron. Electrical impulse travels down a motor neuron. When it reaches the end, acetylcholine (chemical) When it reaches the end, acetylcholine (chemical) is released into the synapse.is released into the synapse.

– Acetylcholine binds to special receptors on the Acetylcholine binds to special receptors on the muscle cell and causes an electrical impulse to muscle cell and causes an electrical impulse to spread over the cell.spread over the cell.

– The sarcomeres shorten and the muscle cell The sarcomeres shorten and the muscle cell contracts.contracts.

– Excess acetylcholine is destroyed by Excess acetylcholine is destroyed by acetylcholinesterase. *Myesthenia gravisacetylcholinesterase. *Myesthenia gravis

Muscle ContractionMuscle Contraction Muscles contract only when the Muscles contract only when the

stimulus from the motor neuron is stimulus from the motor neuron is strong enough = strong enough = Threshold stimulus Threshold stimulus is the minimum level of stimulation is the minimum level of stimulation necessary to cause a contraction.necessary to cause a contraction.

Additional stimuli arriving rapidly Additional stimuli arriving rapidly cause an increase in the force of the cause an increase in the force of the muscle contraction.muscle contraction.

BotoxBotox

Types of Skeletal Muscle ContractionTypes of Skeletal Muscle Contraction Twitch Twitch – – TetanicTetanic – –

*Tetanus*Tetanus Isotonic contractionIsotonic contraction – – Isometric contractionIsometric contraction – –

Energy for ContractionEnergy for Contraction Muscles require energy in the form of Muscles require energy in the form of

ATP to contract. ATP is produced by ATP to contract. ATP is produced by aerobic respiration.aerobic respiration.

Secondary sourcesSecondary sources– Creatine phosphateCreatine phosphate stored in the muscle stored in the muscle

is broken down to produce more ATP.is broken down to produce more ATP.– GlycogenGlycogen stored in the muscle and liver stored in the muscle and liver

is broken down into glucose which is is broken down into glucose which is broken down to produce ATP. This broken down to produce ATP. This process requires Oprocess requires O22..

Energy for ContractionEnergy for Contraction OO22 is transported to the muscle by is transported to the muscle by

the circulatory system (hemoglobin the circulatory system (hemoglobin in RBCs). Some Oin RBCs). Some O22 is stored in the is stored in the muscle by muscle by myoglobinmyoglobin..

Strenuous exercise can cause the Strenuous exercise can cause the muscles to “run out” of Omuscles to “run out” of O22 resulting resulting in in oxygen debtoxygen debt. Glucose is only . Glucose is only partially broken down to partially broken down to lactic acidlactic acid which causes muscle fatigue.which causes muscle fatigue.

Movements Produced by Muscle Movements Produced by Muscle ContractionsContractions

FlexionFlexion – movement reduces the angle – movement reduces the angle between two bones at their joint.between two bones at their joint.

ExtensionExtension – opposite of flexion – – opposite of flexion – increases the angle at a joint.increases the angle at a joint.

AbductionAbduction – moving a body part away – moving a body part away from the midline of the body.from the midline of the body.

AdductionAdduction – moving a body part – moving a body part toward the midline of the body.toward the midline of the body.

RotationRotation – movement of a body part – movement of a body part around an axis.around an axis.

Movements Produced by Muscle Movements Produced by Muscle ContractionsContractions

SupinationSupination – refers to hand position – – refers to hand position – movement turns palm up to the movement turns palm up to the anterior position (anatomical position).anterior position (anatomical position).

PronationPronation – palm of hand turned – palm of hand turned posteriorly.posteriorly.

DorsiflexionDorsiflexion – top of foot is elevated – top of foot is elevated with toes pointing upward.with toes pointing upward.

Plantar flexionPlantar flexion – foot directed – foot directed downward (standing on your toes).downward (standing on your toes).

MusclesMuscles Head and NeckHead and Neck

– Frontal (frontalis)Frontal (frontalis) – over the frontal skull – over the frontal skull bone raise your eyebrows.bone raise your eyebrows.

– Orbicularis oculiOrbicularis oculi – closes the eye. – closes the eye.– Orbicularis orisOrbicularis oris – around the mouth; – around the mouth;

kissing muscle.kissing muscle.– MasseterMasseter – elevates mandible allowing – elevates mandible allowing

use to close our mouth and chew food.use to close our mouth and chew food.– Temporal (temporalis) Temporal (temporalis) – assists the – assists the

masseter in closing the jaw.masseter in closing the jaw.

MusclesMuscles Head and neckHead and neck

– SternocleidomastoidSternocleidomastoid – flexes the head – flexes the head toward the chest.toward the chest.

– TrapeziusTrapezius – helps elevate, lower, and – helps elevate, lower, and adducts the shoulders (scapula) and adducts the shoulders (scapula) and extend the head backwards.extend the head backwards.

MusclesMuscles Upper extremitiesUpper extremities

– Pectoralis majorPectoralis major – upper anterior chest; flexor of – upper anterior chest; flexor of the upper armthe upper arm

– Latissimus dorsiLatissimus dorsi – extensor of the upper arm. – extensor of the upper arm.– DeltoidDeltoid – powerful abductor of the upper arm. – powerful abductor of the upper arm.– Biceps BrachiiBiceps Brachii – 2-headed muscle that serves as the – 2-headed muscle that serves as the

primary flexor of the forearm.primary flexor of the forearm.– Triceps brachiiTriceps brachii – 3 headed muscle on the posterior – 3 headed muscle on the posterior

surface of the upper arm; extensor of the surface of the upper arm; extensor of the elbow/forearm.elbow/forearm.

MusclesMuscles TrunkTrunk

– Anterior abdomen – 3 layers of muscles whose Anterior abdomen – 3 layers of muscles whose fibers run in different directions – girdle effect.fibers run in different directions – girdle effect. External obliqueExternal oblique – outermost layer – outermost layer Internal obliqueInternal oblique – middle layer – middle layer Transversus abdominisTransversus abdominis – innermost layer – innermost layer

– Rectus abdominusRectus abdominus runs down the midline of the runs down the midline of the abdomen from the thorax to the pubis. (6-pack)abdomen from the thorax to the pubis. (6-pack)

– Respiratory musclesRespiratory muscles IntercostalIntercostal muscles – between the ribs muscles – between the ribs DiaphragmDiaphragm – separates the thoracic and abdominal – separates the thoracic and abdominal

cavities.cavities.

MusclesMuscles Lower ExtremitiesLower Extremities

– Gluteus maximusGluteus maximus – forms the buttock; – forms the buttock; extensor of the thigh, supports the extensor of the thigh, supports the torso.torso.

– Gluteus mediusGluteus medius – abducts the femur; – abducts the femur; injection site.injection site.

– Hamstring musclesHamstring muscles – flexors of the lower – flexors of the lower legleg SemimembranosusSemimembranosus SemitendinosusSemitendinosus Biceps femorisBiceps femoris

MusclesMuscles Lower extremitiesLower extremities

– Quadriceps femorisQuadriceps femoris – covers the upper – covers the upper thigh, extends the leg.thigh, extends the leg. Rectus femoris Rectus femoris Vastus lateralisVastus lateralis – injection site – injection site Vastus medialisVastus medialis (Vastus intermedius)(Vastus intermedius)

– Tibialis anteriorTibialis anterior – dorsiflexes the foot – dorsiflexes the foot– GastocnemiusGastocnemius – primary calf muscle, – primary calf muscle,

plantar flexion of the foot.plantar flexion of the foot.

Intramusclular Injection Intramusclular Injection SitesSites DeltoidDeltoid

Gluteus mediusGluteus medius Vastus lateralisVastus lateralis