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The Muscular System
Chapter 7
• http://www.youtube.com/watch?v=RsWNy
qnHQ2I
Muscle
• One of the 4 basic tissues of body
• Made up of cells that can shorten
(contract)
• Three different types of muscle
1. skeletal muscle
Controlled by conscious mind and moves bones of
skeleton.
2. cardiac muscle
Found only in heart
3. smooth muscle
Found throughout body but controlled by
unconscious mind
Terminology
• Myo- generally refers to muscle
• Sarco- muscle cells
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.
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.
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.
More terms
• Synergist- a muscle that
contracts at the same time as
a prime mover and assists it
in carrying out action.
• Fixator- stabilized joints to
allow other movements to
take place.
Muscle Naming Conventions***
• Muscles are generally named by:
• Action
• Function (flexors and extensors)
• Shape
• What it looks like (deltoid muscle)
• Location
• Where it is at in 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
•
•
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)
Know these
•
•
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
Know these
• 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.
• Muscles of Respiration
• Increase and decrease size of thoracic
cavity
• Inspiratory Muscles
• Diaphragm
• External intercostal muscles
• Expiratory muscles
• Internal intercostal muscles
• Abdominal muscles
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
Know these
• 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.
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.
Neuromuscular Junction
Continued
• Synaptic vesicles - sacs at end of a
nerve fiber; contain neurotransmitter
(e.g., acetylcholine)
• Acetylcholine—neurotransmitter
chemical that travels across synapse to
activate muscle fiber
• Attaches to receptor on sarcolemma
• Acetylcholinesterase—enzyme in the
synaptic space that removes
acetylcholine
• If muscle is to contract again,
another impulse must be sent
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
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.
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.
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.
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.
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)
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.
Heat Production
• Considerable amount of energy produced
in muscles is in form of heat.
• This heat is used to help maintain internal
temperature.
• Shivering.
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.
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
Nerve Supply of Heart
•
Heart rate is modified by Autonomic Nervous
System
• sympathetic and parasympathetic systems
1. Sympathetic fibers stimulate heart to beat
harder and faster as part of "fight or flight
response”
2. Parasympathetic fibers inhibit cardiac function,
causing heart to beat more slowly and with
less force, part of “feed or breed” response.
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.
Smooth muscle anatomy
• Small and spindle shaped with single
nucleus.
• Actin and myosin criss-cross cell and
correspond to z lines of skeletal muscle.
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.
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.
Intramuscular Injections:
dogs/cats
SQ
IM
Intramuscular Injections: Horse
Intramuscular Injections: Cow
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Keep all injections in front of shoulder
Inject straight in, not at angle (IM)
Never inject more than 10 cc’s
Do not inject into manure stained skin
Multiple inj sites: >5” apart
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.