Chapter 8 Test Yourself

Test Yourself 8.1

What is muscle?

• One of four basic tissues

  • Epithelial, Connective, Nervous, Muscle

• Consists of muscle cells

  • Excitability; respond to stimuli (nerve impulse)

  • Contractability; shorten when stimulated

  • Extensibility; stretch when pulled

  • Elasticity; return to original shape/length after stimulation

• Provide motion, maintain posture, generate heat

Test Yourself 8.1

What are the three types of muscle and what are some of the general characteristics of each type?

• Skeletal

  • Voluntary striated, moves the skeleton

• Smooth

  • Involuntary, found in eyes, airways and lungs, stomach, intestines, bladder, blood vessels, reproductive tract

• Cardiac

  • Involuntary, pumps the heart from beginning to end of life

Test Yourself 8.2

What is the difference between a tendon and an aponeurosis?

• Tendon: attaches muscle to bone, continuation of epimysium (fibrous connective sheathe around skeletal muscle)

• Aponeurosis: broad sheet of fibrous connective tissue (ex: linea alba)

Test Yourself 8.2

What is the origin of a muscle? The insertion?

Origin: Stable site where a muscle originates (ex: biceps originate around scapula)

Insertion: Site that moves the most when muscle contracts (ex: biceps insert around elbow)

Test Yourself 8.2

Why might it be of clinical importance to know the origin and insertion of a muscle?

Can help identify injury, injury risk, and find the appropriate treatment?

Test Yourself 8.3

Describe a skeletal muscle cell in terms of cell size, shape, number of nuclei, and appearance under the microscope.

• Size: Very long (several in. long), but not wide (up to 80 mm in diameter)

• Shape: Threadlike/fiberlike

• # of Nuclei: Up to 100 nuclei per cell on the edge of the cell beneath sarcolemma (cell membrane)

• Appearance: Striations, appearance can vary depending on type of muscle tissue

Test Yourself 8.3

What are the differences among a skeletal muscle fiber, a skeletal muscle myofibril, and a skeletal muscle protein filament?

• Fiber

  • Entire muscle cell; long, cylindrical, multinucleated

  • Consists of hundreds to thousands of myofibrils, packed lengthwise

• Myofibril

  • Made of repeating sarcomeres

  • Consist of thousands of tinier protein filaments

• Protein filament

  • Individual actin and myosin filaments that make up the myofibril

Test Yourself 8.3

Which contractile protein filaments make up the dark bands of skeletal muscle cells? Which make up the light bands?

• Dark

  • A-bands

  • Myosin, thick filaments

  • Dark due to dense myosin and actin overlap

• Light

  • I-bands

  • Actin, thin filaments

  • Light due to sparse actin only

Test Yourself 8.3

What is a sarcomere and what are its components?

A contractile unit of myofibril. Has a disc at both ends called the Z line / Z disc. Consists of actin and myosin. Actin connect to the Z lines, myosin float in between the Z lines.

Test Yourself 8.4

What ion, released from the sarcoplasmic reticulum by a nerve impulse, starts the contraction process in a muscle fiber?

Calcium (Ca2+)

Test Yourself 8.4

What molecules in muscle act as the “batteries” to power the sliding of the actin and myosin filaments? What molecules function as the “battery chargers”?

Battery: ATP

Charger: Creatine phosphate

• Donates phosphate group to ADP to quickly regenerate ATP

Test Yourself 8.4

If individual muscle fiber contractions obey the all-or nothing principle, how does an animal control the size and strength of its muscular movements?

Controlling the number of muscle fibers it stimulates in certain parts of the body.

• Fine movements = smaller # of muscle fibers

• Powerful movements = larger # of muscle fibers

Test Yourself 8.4

What is myoglobin and why is it important?

Large, red protein molecule that can store and release large amounts of oxygen. Myoglobin can release its stash of oxygen molecules to resupply the fiber during strenuous muscle contractions.

Test Yourself 8.4

Why does an animal breathe heavily for a while after heavy exercise?

“Oxygen debt”. Buildup of lactic acid in the muscles. Gets absorbed into bloodstream, taken to the liver, turned back into glucose via process that requires oxygen.

Test Yourself 8.4

Describe a cardiac muscle cell in terms of size, shape, number of nuclei, and appearance under the microscope.

• Size:

  • Smaller than skeletal muscles

• Shape:

  • Longer than they are wide, branching

• # Nuclei

  • 1 nucleus per cell

• Appearance:

  • Striated, attached end to end, dark transverse lines called intercalated discs

Test Yourself 8.5

What are intercalated discs and why are they important to the functioning of cardiac muscle?

They securely fasten the cells together and also transmit impulses from cell to cell to allow large groups of cardiac muscle cells to contract in a coordinated manner

Test Yourself 8.5

Describe the effect of a cardiac muscle’s nerve supply on its functioning.

Not needed to initiate the contractions of cardiac muscle, the heart does have a nerve supply that can modify its activity

• Nerves to the heart are from both divisions of the autonomic portion of the nervous system; sympathetic and parasympathetic systems

  • Sympathetic fibers stimulate the heart to beat harder and faster as part of the fight-or-flight response

  • Parasympathetic fibers do the opposite in that they inhibit cardiac function, thereby causing the heart to beat more slowly and with less force when the body is relaxed and resting

Test Yourself 8.5

What is the general effect of sympathetic nervous system stimulation on cardiac muscle? What is the effect of parasympathetic nervous system stimulation?

• Sympathetic fibers stimulate the heart to beat harder and faster as part of the fight-or-flight response

• Parasympathetic fibers do the opposite in that they inhibit cardiac function, thereby causing the heart to beat more slowly and with less force when the body is relaxed and resting

Test Yourself 8.6

Describe a smooth muscle cell in terms of its size, shape, number of nuclei, and appearance under the microscope.

• Size:

  • small

• Shape:

  • spindle-shaped

• # Nuclei:

  • 1 nucleus per cell

• Appearance:

  • Nonstriated, smooth + homogenous, actin and myosin crisscross rather than overlap

Test Yourself 8.6

What are the main differences between visceral smooth muscle and multi-unit smooth muscle?

Visceral smooth:

• large and relatively powerful

• formed into large sheets that function as a single, large unit

• found in the walls of many in ternal soft organs, which are also known by the general name viscera

• form large sheets in the walls of organs such as the stomach, intestine, uterus, and urinary bladder

• experiences large, rhythmic waves of contraction

Multi-unit smooth:

• small and delicate

• individual smooth muscle cells or small groups of cells

• found where small, delicate contractions are needed, such as the iris and ciliary body of the eye, the walls of small blood vessels, and around small air passageways in the lungs

• contractions of multi-unit smooth muscle are not automatic. They require specific impulses from autonomic nerves to contract

Test Yourself 8.6

Describe the effect of nerve stimulation on the functioning of visceral smooth muscle versus multi-unit smooth muscle.

Visceral smooth:

• has a nerve supply that is not necessary to initiate contractions but serves to modify them

• nerve supply to smooth muscle consists of the sympathetic and parasympathetic divisions of the autonomic nervous system

Multi-unit smooth:

• contractions of multi-unit smooth muscle are not automatic. They require specific impulses from autonomic nerves to contract

• actions of multi-unit smooth muscle are specific and carefully controlled. This allows fine control of actions

Test Yourself 8.6

What is the general effect of sympathetic nervous system stimulation on visceral smooth muscle? What is the effect of parasympathetic nervous system stimulation?

• effects of the two are the reverse of what is seen in cardiac muscle. Sympathetic stimulation decreases visceral smooth muscle activity, and parasympathetic stimulation increases it

Test Yourself 8.6

What are the main differences in the structures and functions of skeletal muscle, cardiac muscle, and smooth muscle?

Cardiac

• Structures: Striated, branched, mononucleated, intercalated discs, gap junctions & desmosomes, t-tubules

• Functions: Involuntary, pumps the heart; both divisions of the autonomic portion of the nervous system: sympathetic and parasympathetic systems

Skeletal

• Structures: Striated, cylindrical, multinucleated (on the sides), myofibrils made of repeating sarcomeres (actin & myosin), bundled into fascicles > surrounded by endomysium > perimysium > epimysium

• Functions: Voluntary, generate force for movement, maintain posture, stabilize, produce heat; somatic division of peripheral nervous system

Smooth

• Structures: Nonstriated, mononucleated, spindle-shaped, no sarcomeres (dense bodies instead)

• Functions: Regulate processes in hollow organs; found in the walls of hollow organs such as blood vessels, the gastrointestinal tract, and the respiratory system; sympathetic and parasympathetic divisions of the autonomic nervous system (reverse effects of cardiac)