MUSCULAR SYSTEM

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MUSCULAR SYSTEM

• CHAPTER 6

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Introduction

• Muscle comes from the Latin word mus meaning
  little mouse
• Makes up nearly half of the bodys mass
• Muscles can only CONTRACT or shorten
• Responsible for all body movement, interior as
  well as exterior.

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3 TYPES of MUSCLE

1. SKELETAL- long, multinucleate cells with
   striations. Voluntary muscle that can contract
   slow or fast
2. CARDIAC- uni-nucleate cells with striations and
   intercalated discs. Involuntary muscle that has
   slow contractions.
3. SMOOTH-(VISCERAL)- single strands uni-nucleate
   with no striations. Involuntary muscle with slow
   contractions.

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MUSCLE CELLS

• All MUSCLE CELLS are extremely elongated and
  called a MUSCLE FIBER.
• The prefixes myo , mys , and sarco will
  all refer to muscle.
• All muscle cells contract the same way by
  overlapping microfilaments in the cell called
  myofilaments.

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FUNCTIONS of MUSCLE

1. MOVEMENT- internal (blood, digestive system) and
   external
2. MAINTAIN POSTURE- pull against gravity
3. STABILIZE JOINTS- (good example is shoulder
   joint)
4. GENERATE BODY HEAT- if body temp drops too low we
   shiver

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Parts of SKELETAL MUSCLE (pg 164)

• Layers of connective tissue surround parts of
  muscle- MYSIUM
• Follow the prefixes.
• Muscle is bundled into groups

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• Outermost layer ?
• EPIMYSIUM- dense connective tissue that surrounds
  the muscle
• Collects connective tissue from each muscle
  fibers to form tendon or aponeurosis
• TENDON- strong cordlike tissue that connects
  muscle to the periosteum of bone
• APONEUROSIS- flat sheet of connective tissue
  that attached muscle to bone, cartilage, skin

9.2 / 9.2
9.23 / 9.22
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• FASCICLES- bundles of muscle fibers
• PERIMYSIUM penetrates into the muscle and
  covers fascicles

9.2 / 9.2
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• MUSCLE FIBERS- individual cells
• ENDOMYSIUM envelopes muscle fibers

9.2 / 9.2
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MICROSCOPIC ANATOMY of SKELETAL MUSCLE FIBER

• SARCOLEMMA- membrane around the muscle cell- many
  openings

sarcolemma
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MICROSCOPIC ANATOMY of SKELETAL MUSCLE FIBER

• T TUBULE- small openings in the sarcolemma that
  allow ions to enter deep into the muscle fiber

T TUBULE
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MICROSCOPIC ANATOMY of SKELETAL MUSCLE FIBER

• SARCOPLASMIC RETICULUM- Specialized smooth
  endoplasmic reticulum that stores Calcium ions to
  release it on demand

Sarcoplasmic reticulum
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Description of SARCOMERE
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• Each muscle fiber is made of many repeating
  chains called SARCOMERES.
• SARCOMERES connect at an area called the Z-DISC

Z-disc
9.4 / 9.4
Sarcomere
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• Each fiber contains multiple myofibrils
• MYOFIBRIL bundles of contractile elements- 2
  types of filaments myosin and actin

Nucl.
9.7 / 9.7
Nucl.
Mitoch.
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MYOFIBRILS

• ACTIN- thin myofilament that connects to the
  Z-disc
• MYOSIN- thick myofilament that does not connect
  to Z disc

Myosin
Actin
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• Muscle as a whole appears to have striations
  caused by alternating light and dark bands.
• DARK BANDS called A Bands- Where there is myosin
• LIGHT BANDS- called I Bands- where myosin is
  lacking

A band
I band
9.4 / 9.4
Sarcomere
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MYOFIBRIL

• I bands thin actin filaments enter sarcomere
  from each Z line
• I bands are long and thread-like
• Actin forms framework for myosin to pull on

IV
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Neuromuscular junction

• Where neurons and muscle cells meet (they dont
  actually touch)
• SYNAPTIC CLEFT- tiny gap between neuron and
  muscle cell.

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• Steps in a Muscular Acitvation
• STEP 1 Impulse reaches the axon terminal
  (neuromuscular junction)
• One muscle fiber gets input from one neuron

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• STEP 2 -Axon terminal releases thousands of
  vesicles containing a small chemical cube
  (acetylcholine)
• STEP 3- Acetylcholine drifts across the synaptic
  cleft and binds to receptors opening up the tubes
  for Na ions to DEPOLARIZE the cell
• -depolarization is all or nothing

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• STEP 4- depolarization sends an electrical
  muscle impulse in the muscle fiber
• STEP 5- Muscle impulse travels down sarcolemma
  and enters the T-tubules (holes) and causes
  release of Ca2 from sarcoplasmic reticulum
• Step 6- An extracellular enzyme
  (acetylcholinesterase) destroys the leftover
  acetylcholine thus stopping contraction

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Steps in a Muscular Acitvation
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Steps in contraction of sarcomere SLIDING
FILAMENT THEORY

• STEP 1- In resting fibers
• Cytoplasmic Ca2 concentration is normally low
• Because Ca2 is low- chemicals block actin
  binding sites for myosin

Tropomyosin
Troponin
Myosin
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• STEP 2. Ca2 binds to actin causing the
  configuration change and opening up binding sites
  for myosin
• STEP 3- Myosin head binds to actin via
  cross-bridges then changes its shape and pulls
  actin together
• STEP 4- ATP is used to break myosin cross-bridges
  

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• STEP 5-Myosin can rebind to another actin
  sub-unit and repeats the process as long as Ca2
  levels are high and ATP is available
• RIGOR MORTIS happens after death because no more
  ATP is made to break actin/myosin cross-bridges

ADPPheat
ATP
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• A band thick myosin fibers
• myosin subunits have small protein regions that
  pull on actin called MYOSIN HEADS or CROSSBRIDGES

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• I bands and A bands must overlap
• H zone central region of A band between ends of
  I band- will get smaller when muscle contracts

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• When Ca2 levels are elevated, troponin changes
  its conformation (shape) and causes tropomyosin
  to move and exposes binding sites on actin for
  myosin

9.11 / 9.10
Mysoin binding sites
Ca2
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SLIDING FILAMENT THEORY
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MOTOR UNIT

• One nerve cell (neuron) and all the skeletal
  muscle cells it stimulates
• One neuron can have one axon terminal (ending
  point) or many depending on the muscle stimulated

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5 GOLDEN RULES of Skeletal Muscle

• 1. All Muscles cross at least one joint
• 2. Typically, the bulk of the muscle lies
  proximal to the joint crossed.
• 3. All muscles have at least two attachments-
  origin and insertion
• 4. Muscles can only pull, they never push
• 5. During contraction , the muscle insertion
  moves toward the origin

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Muscular system anatomy

• 600 skeletal muscles
• Origin the immovable connection anchor
• Insertion movable connection
• Muscles may have 1 origin and 1 insertion, OR
  more of both

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Muscles work in groups

• Prime mover -one that predominately causes the
  motion
• Synergists nearby muscles assisting with
  motion
• Fixators- hold a bone still or stabilize origin
  (core muscles or girdle muscles)
• Antagonist (opposes a motion) - relaxes

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JOINT MOTIONS

• 1. Flexion decrease joint angle (elbow curl)
• 2. Extension increase joint angle (straighten
  elbow)
• Hyperextension extend past anatomical
  position (sometimes painful)

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JOINT MOTIONS

• 3. Abduction move away from midline (lift arm
  sideways)
• 4. Adduction move toward midline (let arm fall)

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JOINT MOTIONS

• 5. Rotation move around an axis (twist arm)
  (turn head)
• 6. Circumduction move in a circular path (ball
  and socket joints)

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SPECIAL JOINT MOVEMENTS

• FOOT AND ANKLE
• 7. Dorsiflexion lift foot
• 8. Plantar flexion pointing toes downward
• 9. Eversion sole outwards
• 10. Inversion sole inwards (cause of sprained
  ankles)

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SPECIAL JOINT MOVEMENTS

• RADIUS AND ULNA
• 11. Supination palms up (cup of soup)
• 12. Pronation palms down

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SPECIAL JOINT MOVEMENTS

• THUMB
• 13. OPPOSITION- allows thumb to touch the ends
  of other fingers opposable thumb

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SPECIAL JOINT MOVEMENTS

• 14. Protraction thrust outward (jaw)
• 15. Retraction pull it back (jaw)
• 16. Depression make lower (jaw or ribs)
• 17. Elevation make higher (jaw or ribs)

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NAMING OF SKELETAL MUSCLES

• CLUES TO FOLLOW
• DIRECTION OF MUSCLE -
• rectus straight oblique angle
• MUSCLE SIZE-
• maximus, minimus, longus
• 3. LOCATION- many muscles are named for their
  location- temporalis

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NAMING OF SKELETAL MUSCLES

• NUMBER OF ORIGINS-
• biceps, triceps, quadriceps-
• ACTION OF MUSCLE-
• extensor, flexor, adductor
• SHAPE OF MUSCLE-
• deltoid- triangular rhomboid- rhombus
• LOCATION OF ORIGIN OR INSERTION

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DEPOLARIZATION / REPOLARIZATION

• In resting cell there is a high concentration of
  K inside the cell and Na outside the cell.
• When enough acetylcholine diffuses across
  synaptic cleft gates open and Na rushes into
  the cell causing DEPOLARIZATION.
• K ions diffuse out of the cell and the
  SODIUM-POTASSIUM PUMP is used to REPOLARIZE the
  cell.
• - 3 sodiums are pumped out to every 2 potassiums
  pumped in

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GRADED RESPONSES (pg 172)

• I. Muscle mechanics
• THRESHOLD STIMULUS
• muscle fiber contracts only after the stimulating
  impulse reaches a minimum voltage ? threshold
  stimulus (image a muscle stimulation machine)

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• III. Measuring muscle responses
• once stimulus exceeds threshold fibers in the
  motor unit will contract and relax called a
  TWITCH

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• B. REFRACTORY
• interval after contraction during which the
  muscle fiber WILL NOT respond
• During this time muscle cell is repolarizing

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• C. SUMMING OF CONTRACTIONS
• a muscle fiber can increase its contraction
  strength with successive stimuli
• the effect may be due to incomplete calcium
  pumping out of cytoplasm
• incomplete relaxation between contractions allows
  one contraction to build on another

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• RECRUITMENT
• as the load is increased on a muscle, additional
  motor units can be brought into the contraction
• power muscles (ex. quadriceps) have motor units
  with thousands of fibers
• finesse muscles have comparatively few fibers
  per unit more control (1 neuron per 10 muscle
  fibers)

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• SUSTAINED CONTRACTIONS
• small motor units are active first
• larger power units become active a little later
• continuous muscle contraction consists of many
  motor units becoming active (some relaxing and
  contracting) but maintaining a summed force
• muscle tone - resting contractions of a few
  fibers (posture)

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TETANUS

• When muscle stimulation is so fast that there is
  no refractory period- muscle stays contracted.
• (muscle stimulation machine turned up too high)

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TYPES OF CONTRACTIONS

• ISOTONIC - myofibrils shorten producing tension
  (moving weight through a range of motion)
• ISOMETRIC produce tension without shortening
  (pushing on an immovable object)

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MUSCLE FATIGUE / OXYGEN DEBT

• Oxygen debt
• 1.When metabolism uses up available oxygen the
  cell uses anaerobic metabolism to try to maintain
  ATP via lactic acid production
• 2. Prolonged oxygen debt causes a significant
  increase in lactic acid levels (lowered pH)
  the burn and later muscle pain