The Muscular System

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The Muscular System

• Chapter 7

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• http//www.youtube.com/watch?vRsWNyqnHQ2I

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Muscle

• One of the 4 basic tissues of body
• Made up of cells that can shorten (contract)
• Three different types of muscle
• skeletal muscle
• Controlled by conscious mind and moves bones of
  skeleton.
• cardiac muscle
• Found only in heart
• smooth muscle
• Found throughout body but controlled by
  unconscious mind

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Terminology

• Myo- generally refers to muscle
• Sarco- muscle cells

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Skeletal Muscle

• Moves the bones of the skeleton
• Also may generate heat
• Also called voluntary striated muscle
• Obvious striped pattern microscopically of light
  and dark bands.

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Skeletal Muscle Gross Anatomy

• Generally have a thick central portion called a
  belly.
• Have two attachment sites that join muscle to
  whatever tissues they move when they contract.
• Generally attach via tendons.
• May be attached via aponeuroses- broad sheets of
  connective tissue (example linea alba of ventral
  midline)
• Origin- the end that is generally more stable
  than the other. Does not move when muscle
  contracts.
• Insertion- site that undergoes most of the
  movement during contraction.

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Muscle Actions

• Only function is to contract when stimulated to
  do so by a nerve impulse.
• Usually work in groups
• Some muscles provide most of the movement
• Others provide stability to nearby joints
• A prime mover (agonist) describes a muscle or
  muscle group that directly produces a desired
  movement.
• An antagonist is a muscle or muscle group that
  directly opposes the action of a prime mover.

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More terms

• Synergist- a muscle that contracts at the same
  time as a prime mover and assists it in carrying
  out action.
• Fixator- stabilizes joints to allow other
  movements to take place.

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Muscle Naming Conventions

• Muscles are generally named by
• Action
• Function (flexors and extensors)
• Shape
• What it looks like (deltoid muscle)
• Location
• Where it is in the body (biceps brachii)
• Direction of Fibers
• Rectus muscles- means straight
• Number of heads or Divisions
• Number of attachment sites (biceps, triceps, etc)
• Attachment sites
• Origin and insertion sites

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Selected Muscles

• Cutaneous Muscles
• Muscles of the skin
• Have little or no attachment to bone
• Actually see fascia (connective tissue) causing
  movement
• Cutaneous trunci- makes back twitch, used during
  neurological exams.
• Head and Neck Muscles
• Control facial expressions, enable chewing and
  move sensory structures
• Include
• Masseter- chewing muscle
• Splenius-extend head and neck
• Trapezius-extend head and neck
• Brachiocephalicus-extends head and neck and pulls
  front leg forward
• Sternocephalicus-extends from sternum to the base
  of the skull and lowers neck. (flexor)

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6 IS THE MASSETER MUSCLE
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29 IS THE SPLENIUS
7 IS PART OF THE TRAPEZIUS SPECIFICALLY THE
CLAVO- TRAPEZIUS
2 IS ALSO PART OF THE TRAPEZIUS-THE
ACROMIO-TRAPEZIUS
28 IS THE SPINOTRAPEZIUS
https//homes.bio.psu.edu/people/faculty/waters/tu
torial_project/cat_frames_maps/muscular/setup_html
/brachium_extensors_label_index.html
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• Abdominal Muscles
• Function to support the abdominal organs
• Help to flex back, aid in defecation, urination,
  vomiting, respiration and parturition.
• Layers from outside in
• External abdominal oblique
• Internal abdominal oblique
• Rectus Abdominis
• Transversus abdominis
• Thoracic Limb Muscles
• Function mainly in locomotion
• Latissimus dorsi- extends from spinal cord to
  humerus and flexes shoulder
• Pectoral muscles- extend from sternum to humerus
  and act as adductors of front leg to keep them
  under the animal
• Deltoid muscles-abducts and flexes shoulder joint
• Biceps brachii-flexes elbow joint
• Triceps brachii- extends elbow joint
• Extensor carpi radialis-extends the carpus
• Deep digital flexor-flexes the digit

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EXTERNAL ABDOMINAL OBLIQUE
RECTUS ABDOMINUS
INTERNAL ABDOMINAL OBLIQUE
TRANSVERSUS ABDOMINUS
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SPINODELTOID
CLAVODELTOID
ACROMIODELTOID
LATTISSIMUS DORSI
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LATERAL HEAD OF THE TRICEPS
MEDIAL HEAD OF THE TRICEPS
LONG HEAD OF THE TRICEPS
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EXTENSOR CARPI RADIALIS LONGUS
EXTENSOR CARPI RADIALIS BREVIS
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• Pelvic Limb Muscles
• Involved mainly in locomotion
• Gluteal muscles- extend from bones of pelvis to
  trochanters of femur
• Hamstring Muscles- Help to extend hip joint and
  flex stifle joint
• Biceps Femoris
• Semimembranosus
• Semitendinosus
• Quadriceps Femoris- main extensor of the stifle
  joint
• Gastrocnemius muscle- calf muscle, extensor of
  the hock.

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• Muscles of Respiration
• Increase and decrease size of thoracic cavity
• Inspiratory Muscles
• Diaphragm
• External intercostal muscles
• Expiratory muscles
• Internal intercostal muscles
• Abdominal muscles

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Microscopic Anatomy of Skeletal Muscle

• Muscle cells
• Are very large in size
• Have a threadlike or fiberlike shape.
• Usually are multi-nucleated
• Made up of smaller myofibrils composed of actin
  (thin) and myosin (thick)
• Network of sarcoplasmic reticulum (similar to
  ER)
• Stores Ca for muscle contraction

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• A band- large dark band made up of myosin
  filaments
• I Band- large light band made up of actin
  filamaments
• Z line- dark band in center of I band, disk that
  is viewed as a line and is attachment site for
  actin filaments.
• Sarcomere- area from one z line to the next z
  line. Basic contracting unit of skeletal muscle.
  When all sarcomeres contract, leads to overall
  muscle fiber shortening.

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Neuromuscular Junction

• Skeletal muscle is under voluntary control
• If nerve supply is interrupted for long period of
  time, muscle will atrophy (shrink down)
• Neuromuscular junctions- sites where the ends of
  motor nerve fibers connect to muscle fibers.
  Space is actually a synaptic space.

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Neuromuscular Junction Continued

• Synaptic vesicles - sacs at end of a nerve fiber
  contain neurotransmitter (e.g., acetylcholine)
• Acetylcholineneurotransmitter chemical that
  travels across synapse to activate muscle fiber
• Attaches to receptor on sarcolemma
• Acetylcholinesteraseenzyme in the synaptic space
  that removes acetylcholine
• If muscle is to contract again, another impulse
  must be sent

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Motor Unit

• One nerve fiber and all muscle fibers it
  innervates
• Muscles that make small, delicate movements have
  only a few muscle fibers per nerve fiber in each
  motor unit
• Large, powerful muscles may have a hundred or
  more muscle fibers per motor unit

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Connective Tissue Terminology

• Endomysium- each individual skeletal muscle fiber
  is surrounded by this delicate connective tissue
  layer.
• Fascicles- groups of skeletal muscle fibers
• Perimysium- connective tissue that binds together
  fascicles.
• Epimysium- fibrous connective tissue that
  surrounds groups of fascicles.

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Physiology of Skeletal Muscle

• Initiation of Muscle Contraction and Relaxation
• Nerve impulse comes down motor nerve fiber,
  reaches neuromuscular junction and acetylcholine
  is released into synaptic space.
• Acetylcholine binds to receptors on surface of
  sarcolemma (cell membrane) of the muscle fiber.
• This starts impulse that travels along sarcolemma
  and through the T tubules to the interior of the
  cell.
• Once impulse reaches sarcoplasmic reticulum it
  causes release of stored calcium ions (Ca) into
  the sarcoplasm (cytoplasm).
• As Calcium diffuses into myofibrils, initiates
  contraction process which is powered by ATP.
• As contraction occurs, Calcium is pumped back out
  of myofibrils which shuts down contraction
  process.
• Both relaxation and contraction requires energy.

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Mechanics of Muscle Contraction

• When a muscle fiber is relaxed, actin and myosin
  overlap a little.
• When stimulated cross bridges (levers on the
  myosin filaments) ratchet back and forth and pull
  the actin filaments on both sides toward center
  of the myosin filaments.
• Sliding of filaments shortens sarcomere, thereby
  causing contraction.

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Characteristics of Muscle Contraction

• All or nothing principle
• An individual muscle fiber either contracts
  completely when it receives an impulse or not at
  all.
• Movements vary in strength due to number of
  muscle fibers stimulated.
• Nervous system sends out impulse based on muscle
  memory- or idea of how many fibers need to be
  stimulated for that particular activity.

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Phases of twitch contraction

• 1. Latent phase
• Brief pause between nerve stimulus and beginning
  of actual contraction (lasts about 0.01 seconds)
• 2. Contracting phase
• Actual contraction is taking place (lasts about
  0.04 seconds)
• 3. Relaxation phase
• When cells go back to a relaxed state (lasts
  about 0.05 seconds)

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Chemistry of Muscle Contraction

• Primary source of energy is ATP
• When ATP loses a phosphate group (remember
  cellular respiration?) energy is released.
• CP (creatine phosphate) is responsible for
  converting ADP back to ATP so that it is ready to
  provide energy again.
• ATP and CP require glucose and oxygen to operate
  effectively.
• Muscle fibers may store glucose and oxygen in
  glycogen or myoglobin (oxygen attached to a
  protein)
• Myoglobin can release oxygen during strenuous
  exercise (process is called aerobic metabolism)
• Anaerobic metabolism occurs when not enough
  oxygen is stored. By product is lactic acid, a
  by-product of incomplete glucose breakdown.

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Heat Production

• Considerable amount of energy produced in
  muscles is in form of heat.
• This heat is used to help maintain internal
  temperature.
• Shivering.

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Cardiac Muscle

• Also known as involuntary striated muscle
• Only found within the heart
• Cardiac muscle cells are much smaller than
  skeletal muscles cells and only contain one
  nuclei per cell (size)
• Are longer than wide and have multiple branches.
• This forms a branching network of cells.
• Contain intercalated disks- where cells attach
  one to another.
• Also transmit impulses from cell to cell.
• This allows entire groups of cells to contract
  together at the same time.

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Physiology of Cardiac Muscle

• No external stimulation required.
• Rate and rhythm of contraction is due to SA
  (sinoatrial node) of heart located in the wall of
  the right atrium.
• Impulse follows a controlled path through the
  conduction system of the heart.
• This helps to transmit, delay, and redirect each
  impulse so that the cardiac muscle cells in the
  walls of the heart chambers contract in
  coordinated manner.
• Groups of cardiac cells adopt the contraction
  rate of the most rapid cell in the group.
• Cardiac cells contract in rapid, wavelike
  fashion.
• This helps to squeeze blood out of chambers of
  the heart

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Nerve Supply of Heart

• Heart rate is modified by Autonomic Nervous
  System
• sympathetic and parasympathetic systems
• Sympathetic fibers stimulate heart to beat harder
  and faster as part of "fight or flight response
• Parasympathetic fibers inhibit cardiac function,
  causing heart to beat more slowly and with less
  force, part of feed or breed response.

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Smooth Muscle

• Called nonstriated involuntary muscle or
  involuntary muscle.
• Found in two forms
• Visceral smooth muscle
• Large sheets of cells in the walls of some hollow
  organs
• Multiunit smooth muscle
• Small, discrete groups of cells.

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Smooth muscle anatomy

• Small and spindle shaped with single nucleus.
• Actin and myosin criss-cross cell and correspond
  to z lines of skeletal muscle.

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Visceral Smooth Muscle

• Found in walls of many soft internal organs that
  are known as viscera.
• Instead of fine movements, work in waves of
  motion.
• Does not need external stimulation.
• If stretched, will contract more strongly.
• This is part of parasympathetic or feed or
  breed system.

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Multiunit Smooth Muscle

• Small and delicate
• Found in areas were small delicate motions are
  needed.
• Iris and ciliary body of the eye
• Walls of small blood vessels
• Around small air passageways in the lungs.
• Are NOT automatic. Do require specific impulses
  from autonomic nerves to contract.

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Intramuscular Injections dogs/cats

• SQ
• IM

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Intramuscular Injections Horse
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Intramuscular Injections Cow

• Keep all injections in front of shoulder
• Inject straight in, not at angle (IM)
• Never inject more than 10 ccs
• Do not inject into manure stained skin
• Multiple inj sites gt5 apart

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Rigor Mortis

• Lack of oxygen at death causes calcium to spill
  out of sarcoplasmic reticulum
• This causes contraction of many of the muscle
  fibers
• Uses up all oxygen, no more is available which
  means muscles get stuck in contracted position.