Muscles

VTT 235 Anatomy & Physiology

Muscle…

Muscle is one of the four basic tissues of the body.

It is made up of cells that can shorten or contract.

Skeletal muscle is voluntary and is responsible for movement of the bones.

Cardiac muscle is involuntary and is found only in the heart.

Smooth muscle is involuntary and is found all over the body including blood vessels, the bladder, and the intestines.

SKELETAL MUSCLE

Muscle Attachments

Most muscles are attached to bones at both ends by tendons.

A few muscles are attached to bones or to other muscles by aponeuroses. The most prominent aponeurosis is

the linea alba.

Muscle Attachments…

Origin: Site of muscle attachment that is more

stable. The origin has the least amount of

movement during muscle contraction. Insertion:

The site of muscle attachment that undergoes the most movement during contraction.

Muscle Actions

When stimulated by a nerve impulse, a muscle contracts. It shortens by pulling on its attachment

sites to produce movement. A prime mover (agonist) is a muscle

that produces a desired movement. An antagonist opposes the action of

a prime mover.

Muscle Actions…

A synergist is a muscle that contracts at the same time as a prime mover and assists it in carrying out its action.

Fixator muscles stabilize joints to allow other movements to take place.

Muscle Names

Muscles are often named for physical characteristics such as: Action- names can be related to a

muscles function (flexors). Shape Location Direction of fibers Number or heads or divisions Attachment sites

Microscopic Anatomy of Skeletal Muscle

Skeletal muscle cells are huge. They are not very wide, but they

are very long and thin. They are usually referred to as skeletal

muscle fibers because of their length. They have many nuclei located just

beneath the sarcolemma (muscle cell membrane).

Microscopic Anatomy of Skeletal Muscle…

Most of the volume of skeletal muscle fiber is made up of thousands of myofibrils packed together lengthwise. Myofibrils are composed of thousands of

even tinier contractile protein filaments. The two primary proteins that make up the

filaments are: Thin actin filaments. Thick myosin filaments.

Skeletal Muscle Contraction

When a muscle fiber is relaxed, the actin and myosin filaments overlap a little.

When a muscle is stimulated to contract, small levers on the myosin filaments called cross bridges, ratchet back and forth and pull the actin filaments on either side of the myosin filaments towards the center of the myosin filaments.

This causes the filaments to slide over each other and shorten the sarcomere.

Myosin

Actin

Skeletal Muscle Contraction…

Muscle fibers store glucose as glycogen and oxygen as myoglobin.

Muscles utilize aerobic metabolism as long as the oxygen supply is adequate to keep up with the energy needs of the fiber. The maximum amount of energy is

extracted from each glucose molecule.

Skeletal Muscle Contraction…

When the oxygen runs out, muscles switch to anaerobic metabolism. Its not as efficient. Results in lactic acid formation as a byproduct

of incomplete glucose breakdown. Lactic acid accumulates in muscles and makes

them sore. It diffuses back into the blood and goes to the

liver, where it is converted back into glucose.

Heat Production

A considerable amount of energy from muscles is produced in the form of heat.

Under cold conditions, muscles can produce heat by shivering.

CARDIAC MUSCLE

Gross Anatomy

Forms most of the volume of the heart & makes up the majority of the walls of the cardiac chambers.

Cardiac muscle cells form elaborate networks around the cardiac chambers.

Microscopic Anatomy

Cardiac muscle cells are much smaller than skeletal muscle cells.

They only have one nucleus per cell. They are longer then they are wide and

often have multiple branches. The firm end-to-end attachments

between cardiac muscle cells are visible under the microscope as dark, transverse lines between cells (fig. 7-1).

Microscopic Anatomy…

These attachment sites are called interclated disks. The interclated disks securely fasten

the cells together & also transmit impulses from cell to cell to allow large groups of cells to contract in a coordinated manner.

Physiology…

Rather than large numbers of muscle cells contracting at the same time, as in skeletal muscle, cardiac muscle cells contract in a rapid, wavelike fashion.

The impulse that coordinates the contractions spreads from cell to cell across the interclated disks like a wave.

That rapid, wavelike contraction effectively squeezes blood out of the cardiac chambers.

Physiology…

For blood to move through the chambers of the heart, these contractions must be carefully initiated and controlled.

That is the job of the heart’s internal impulse conduction system. This system consists entirely of cardiac

muscle cells. The impulse that starts each heartbeat

begins in the heart’s “pacemaker” the SA node.

SMOOTH MUSCLE

Gross Anatomy

Smooth muscle is found all over the body in two main forms: As large sheets in the walls of some

hollow organs called visceral smooth muscle.

As small, discrete groups of cells called multiunit smooth muscle.

Microscopic Anatomy

Smooth muscle cells are small and spindle shaped with a single nucleus center.

Because their contractile units are not organized into regular, parallel sarcomeres, individual smooth muscle cells can shorten to a greater extent than the other types of muscle cells.

Physiology- Visceral Smooth Muscle

Visceral smooth muscle is found in the walls of many soft internal organs.

Contractions occur in large, rhythmic waves.

These contractions can be very strong for example: Peristaltic contractions Uterine contractions

Physiology- Multiunit Smooth Muscle

Multiunit smooth muscle is small and delicate.

It is found where delicate contractions are needed: Iris & ciliary body of the eye. Walls of small blood vessels. Air passages in the lungs.

SELECTED SKELETAL MUSCLES

Muscles you will need to identify for your lab practical

Muscles of the Face

Masseter- closes the jaw

Thoracic Limb Muscles Extrinsic Shoulder-

1. Trapezius- elevates the scapula.

2. **Latissimus dorsi- flexes the shoulder.

3. **Brachiocephalicus- advances the limb or draws the head laterally.

Thoracic Limb Muscles

Extrinsic Shoulder-4. Serratus

ventralis- supports the trunk.

5. Superficial pectoral- adducts and advances the limb.

6. Deep pectoral- draws the limb caudally (flexes the shoulder).

Thoracic Limb Muscles

Intrinsic shoulder-7. Deltoid- flexes the

shoulder.8. Brachialis- flexes

the elbow.

Thoracic Limb Muscles

Intrinsic shoulder-9. Biceps brachii-

extends the shoulder and flexes the elbow.

10. **Triceps brachii- extends the elbow, the long head flexes the shoulder.

Forearm Muscles 11.) Extensors-

A-Extensor Carpi Radialis- extends the carpus, flexes the elbow.

B- Common Digital Extensor- extends the digits & carpus.

C- Lateral Digital Extensor- extends the digits & carpus.

D- Extensor Carpi Ulnaris- flexes the carpus.

Thoracic Limb Muscles

12.) Flexors- A- Flexor Carpi

Radialis- flexes the carpus.

B- Flexor Carpi Ulnaris- flexes the carpus.

C- Superficial Digital Flexor- flexes the carpus & digits.

D- Deep Digital Flexor- flexes the carpus & digits.

Thorax Muscles Intercostals- involved in

respiration Diaphragm- separates the

thoracic and abdominal cavities, main muscle of respiration.

Trunk Muscles

13. Epaxials- Lies above the

vertebral column. supports the spine.

14. Hypaxials- Lies below the

vertebral column. They flex the neck &

tail contributes to the flexion of the vertebral coloumn.

Pelvic Limb Muscles 15.) **Superficial

Gluteal- abducts the limb.

Middle Gluteal- Extends the thigh.

Deep Gluteal- extends the limb.

Pelvic Limb Muscles Hamstring Group-

extends the hip, stifle, & tarsus, flexes the stifle.

All originate from the ischiatic tuberosity, 16.) Biceps femoris-

Inserts into the patella. 17.) **Semitendinosus-

Inserts into the tibia. 18.)

**Semimembranosus- Inserts into the femur &

tibia.

Pelvic Limb Muscles 19.) **Gracialis-

Originates in the pelvic symphysis.

Inserts into the medial side of the stifle.

Adducts the limb. 20.) **Sartorius-

Originates in the ilium.

Inserts into the medial side of the stifle.

Flexes the hip & stifle.

Pelvic Limb Muscles 21.) Quadriceps

femoris- Rectus femoris-

Originates in the ilium. Inserts into the patella. Flexes the hip, extends the

stifle.

Vastus: lateralis, medialis, intermedius- Originates in the proximal

femur. Inserts into the patella. Extends the stifle.

Pelvic Limb Muscles 22.) Adductor-

Originates in the ventral surface of the hip bones.

Inserts into the femur. Adducts the limb.

23.) **Gastrocnemius- Originates in the caudal

surface of the femur. Inserts into the

calcanean tuberosity. Extends the tarsus,

flexes the stifle.

Abdominal Muscles 24.) Obliques:

External- extends from the ribs to the ventral midline.

Internal- muscle fibers run obliquely and cross with the external oblique.

25.) Transversus abdominus- the deepest abdominal muscle terminating at the linea alba.

26.) Rectus abdominus- two long, straight muscles extending from the sternum along the ventral abdomen.

27.) **Linea Alba- the fibrous cord formed by the joining of the abdominal muscles.

THE END