The Muscular System

Chapter 7

• http://www.youtube.com/watch?v=RsWNyqnHQ2I

Muscle

• One of the 4 basic tissues of bodyOne of the 4 basic tissues of body

• Made up of cells that can shorten Made up of cells that can shorten (contract(contract))

• Three different types of muscleThree different types of muscle 1.skeletal muscle

Controlled by conscious mind and moves bones of skeleton.

2.cardiac muscleFound 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)

• 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

• 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

• 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 One nerve fiber and all muscle fibers it innervates

• Muscles that make small, delicate movements have only a Muscles that make small, delicate movements have only a few muscle fibers per nerve fiber in each motor unitfew muscle fibers per nerve fiber in each motor unit

• Large, powerful muscles may have a hundred or more Large, powerful muscles may have a hundred or more muscle fibers per motor unitmuscle 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.

SQSQ

IMIM

Intramuscular Injections: : dogs/catsdogs/cats

Intramuscular InjectionsIntramuscular Injections: Horse: Horse

Intramuscular Injections: Cow: Cow

• Keep all injections in front of shoulderKeep all injections in front of shoulder• Inject straight in, not at angle (IM)Inject straight in, not at angle (IM)• Never inject more than 10 cc’sNever inject more than 10 cc’s• Do not inject into manure stained skin Do not inject into manure stained skin • Multiple inj sites: >5” apartMultiple 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.