Chapter 11-12: Muscular System

Types and Functions of Muscles

• Skeletal muscle

• Smooth muscle

• Cardiac muscle

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© 2012 Pearson Education, Inc.

Characteristics of Muscles

•Skeletal and smooth muscle cells are elongated (muscle cell = muscle fiber)

•Contraction and shortening of muscles is due to the movement of microfilaments

•All muscles share some terminology

•Prefixes myo and mys refer to “muscle”

•Prefix sarco refers to “flesh”

Whole Muscle Structure

• Fascia– Epimysium– Perimysium– Endomysium

• Fascicles (bundles)• Tendon

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Muscle Fiber: Cell

• Group of myofibrils– Series of sarcomeres– Sarcomere is inside a

myofibril

• Sarcoplasmic reticulum– Covering of each

sarcomere

• T-tubule system– Transmit electrical signal

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Sarcomeres: Inside the Myofibril

• From Z line to Z line• Thin filaments

– Protein called Actin – Troponin-tropomyosin

• Binding part of Actin

• Thick filaments– Protein called Myosin

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Two Aspects of Muscle Contraction

Electrical • Involves motor

neuron and NMJ• Results in calcium

release from SR• Happens first

Contractile • Involves actin and

myosin • Sliding filaments• Happens second

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Contractile Function: Sliding Filament Mechanism

• Myosin heads make contact with actin. • Myosin heads rotate.• Actin is pulled to the center of the sarcomere.• Sarcomere shortensmuscle contraction• Animation

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Contracting Muscles Need Calcium

• Calcium is stored away from thin and thick filaments in the sarcoplasmic reticulum (SR).

• When stimulated, the SR releases calcium.• Calcium allows actin, myosin, and ATP to

interact, causing muscle contraction.• Why does muscle relax?

– Calcium returns to the SR. Then Muscle relaxes

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Whole Muscle Contraction

• A single muscle fiber has an “all or nothing” response, but a whole muscle can vary its force of contraction.

• Two characteristics of a whole muscle allow this– Motor unit– Recruitment

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Motor Unit and Recruitment

• Motor unit: The nerve and innervated muscle fibers

• Recruitment: The more motor units activated, the greater the force of contraction.

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Two Aspects of Muscle Contraction

Electrical • Involves motor

neuron and NMJ• Results in calcium

release from SR• Happens first

Contractile • Involves actin and

myosin • Sliding filaments• Happens second

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Neuromuscular Junction (NMJ)

• Space between motor neuron and muscle

• Site of ACh action and activation of muscle membrane– Ach= Acetylcholine

• Neurotransmitter

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Electrical Events• Electrical signal travels to axon terminal,

releasing ACh.• ACh diffuses across NMJ and activates muscle

receptors.• Activated receptors send electrical signal along

muscle membranes and T tubules.• Electrical signal stimulates the SR to release

calcium, initiating the sliding filament.

• Electrical signal travels to axon terminal, releasing ACh.

• ACh diffuses across NMJ and activates muscle receptors.

• Activated receptors send electrical signal along muscle membranes and T tubules.

• Electrical signal stimulates the SR to release calcium, initiating the sliding filament.

Impairment at the NMJ• Myasthenia gravis:

– Autoimmune disease: atrophy and weakness

• Curare– Alkaline substance that can

paralyze (poison darts)

• Neurotoxins– Clostridium tetani (tetanus)– Clostridium botulinum

(botulism and Botox)

Muscles Part II

• Define twitch and tetanus.• Identify the sources of energy for muscle

contraction.• State the basis for naming muscles.• List the actions of the major muscles.

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Responses of a Whole Muscle

• Twitch: Single muscle response in which muscle contracts and then fully relaxes

• Tetanus: Sustained muscle contraction caused by repeated stimulation

• Tonus: Normal, continuous state of partial muscle contraction

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Sources of Energy (ATP)

• Aerobic metabolism: need oxygen– Breakdown of fat, and sugars into energy

• Anaerobic metabolism: no oxygen present– Causes lactic acid to build up (soreness)– D.O.M.S.: Delayed onset muscle

• Metabolism of creatine phosphate– Quick boost of ATP

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Muscle Terms• Origin: Nonmoving part

• Insertion: Movable part

• Prime mover– “Chief” muscle, most

responsible for movement

• Synergist– Helps prime mover

• Antagonist– Opposes prime move– Returns to “normal” position

Muscle Overuse and Underuse

• Hypertrophy: Growth in response to overuse• Atrophy: Wasting

– Disuse atrophy: cast for broken bone– Denervation atrophy: damage to nervous

system– Senile atrophy: wearing down of muscle

(age related)

• Contracture: Abnormal fibrous formation in muscle that “freezes” in flexed position

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How Skeletal Muscles Are Named• Size: vastus(huge); maximus(large); longus(long);

minimus(small); brevis(short) – Ex.:Gluteus maximus

• Shape: deltoid(triangular); latissimus(wide); trapezius (trapezoid); rhomboideus (rhomboid); teres(round)– Ex. Trapezius, Latissimus dorsi

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• Direction of fibers: Fibers are lined up; rectus(straight); oblique(diagonal); transverse(across); circularis(circular)– Ex. Rectus abdominis

• Location: reflect location on body; pectoralis (chest); gluteus (buttock); brachii (arm); supra(above); infra(below); Sub(underneath); lateralis(lateral)– Ex.: Pectoralis major, biceps brachii

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• Number of origins: where it’s anchored; Biceps(2), Triceps(3); Quadriceps(4)

• Origin and insertion: Both sites of attachment; Sterno-cleido-mastoid (sternum-clavicle-mastoid)

• Muscle action: type of action; aways from midline(abductor), toward midline(Adductor); levator(elevates); masseter(chews)

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Muscles from Head to Toe

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Facial Muscles• Frontalis: raises eyebrows and wrinkles

forehead

• Orbicularis oculi: closes eye, winking, blinking

• Levator palpebrae superioris: lifts eyelid

• Orbicularis oris: closes mouth, forms words

• Buccinator: flattens cheek, positions food

• Zygomaticus: smiling muscles

• Platysma: open your mouth wide, pout

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Facial Muscles: Chewing

• Masseter: chewing muscles

• Temporalis: temple

• Sternoclediomastoid: flexion and rotation of the head and rotation of the head.

• Trapezius: helps with the extension and hyperextension of the head at the neck

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Muscles of the Trunk: Breathing

• Intercostal muscles– Internal– External

• Diaphragm

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More Muscles of the Trunk• Abdominal wall

– Transversus abdominis– Internal oblique– Rectus abdominis– External oblique

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Muscles of the Shoulder and Arm

• Trapezius• Serratus anterior• Pectoralis major• Latissimus dorsi• Deltoid

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Muscles of the Forearm

• Biceps brachii• Triceps brachii• Brachialis• Brachioradialis• Supinators and

pronators

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Muscles of the Thigh• Extend thigh, climb stairs, and sitting:

– Gluteus maximus, medius, and minimus

• Iliopsoas: Flexes thigh, opposes gluteual group

• Adductor group: inner thigh, horseback riders muscle

• Quadriceps femoris: Extend Leg(kicking), anterior

• Sartorius: crosses over leg, allows you to sit in crossed leg position

• Hamstrings: posterior side of leg, flex leg opposes quadriceps

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Muscles: Leg and Foot, Posterior View

• Gastrocnemius: calf• Soleus: calf• Tibialis posterior:

flexes foot, shin splits• Calcaneal or Achilles

tendon: where muscles connect to work foot

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Muscles with Colorful Names

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Carpal Tunnel Syndrome

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