General Anatomy (Muscle Tissue)

Question 1

What are the functions of muscle tissues?

Answer 1

▪ generation of movements
▪ stabilization of the position of the body
▪ control of the volume of the organs
smooth muscle - sphincters
▪ motion of the substances in the body
blood, lymph, urine, air, food and fluids, sperm
▪ generation of body heat
voluntary and involuntary contractions of skeletal striated muscle

Question 2

What are the three types of muscle tissues?

Answer 2

• Smooth muscle tissue
• striated muscle tissue/skeletal
• Cardiac striated muscle tissue

Question 3

What are the special terms for muscles?

Answer 3

• plasma membrane - sarcolemma
• Cytoplasm - Sarcoplasm
• Smooth endoplasmic reticulum - Sarcoplasmic reticulum
• Mitochondria - Sarcosomes

Question 4

How are skeletal muscles supported by?

Answer 4

Connective tissue frameworks

Question 5

What are the functions of connective tissue frameworks?

Answer 5

1. Transmits the force of contraction through aponeurosis & tendons.
2. Carries blood vessels and nerves – blood vessels penetrate the connective tissue septa & form rich capillary network in the endomysium.

Question 6

What are the concept of muscle fibres

Answer 6

Muscle—muscle fibre bundle—muscle fibre—myofibrils—myofilaments

Question 7

What is epimysium?

Answer 7

Dense connective tissue sheath surrounding the entire muscle

Question 8

What is endomysium?

Answer 8

loose connective tissue composed of reticular fibers supporting individual muscle fibers.

Question 9

What are the light microscopic observation?

Answer 9

▪ Each muscle fiber is an elongated, unbranched cylindrical cell.
▪ It has many flat nuclei located beneath the sarcolemma.
▪ It shows cross-striations of alternate dark (A/H) and light (I) bands with Z line intersecting
I band.
▪ Each muscle fiber is made of compactly packed long cylindrical myofibrils in the sarcoplasm arranged parallel to the long axis.
▪ The distance between two Z lines is a contractile unit called Sarcomere.

Question 10

What is the arrangement of myofilaments in the sarcomere?

Answer 10

▪ Sarcomere consists of 2 types of myofilaments arranged parallel to the long axis of myofibril.
▪ Thick filaments – composed mainly of the protein myosin and occupy the A/H band.
▪ Thin filaments – composed mainly of the protein actin and also tropomyosin and troponin (occupy the I band)

Question 11

What is the contraction mechanism?

Answer 11

1. During contraction there is NO SHORTENING of individual thick and thin myofilaments
2. There is an increase in the degree of overlap between the filaments.
3. Sliding filament theory – under the influence of energy release by ATP + calcium ion released from sarcoplasmic reticulum, the thin and thick filaments slide over one another causing shortening of sarcomere.
4. In this process, the A band remains constant in width whereas the I band and H zone become narrow and Z lines are drawn closer together.

Question 12

What is the transverse tubule-sarcoplasmic reticulum complex?

Answer 12

▪ To provide uniform contraction of all muscle fibers, the skeletal muscle possesses a system of transverse (T) tubules.
▪ The function of T-TUBULES is to conduct impulses from the surface of the cell (SARCOLEMMA) down into the cell and, specifically, to another structure in the cell called the SARCOPLASMIC RETICULUM.
▪ Finger-like invaginations of the sarcolemma extending into the sarcoplasma to surround each myofibril at the region of HI/AI junction (the junction between H/A and I bands).
▪ The T tubules are embraced on either side by the terminal cisternae of the sarcoplasmic reticulum forming a SR-T tubule-SR complex called triad – present at the junction of I and H/A bands of each sarcomere.

Question 13

What is the functional significance of the triad?

Answer 13

▪Depolarisation of the sarcolemma is rapidly disseminated throughout the sarcoplasm by the T tubule system.
▪Resulting in the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm causing contraction.
▪ When depolarization ceases, the Ca+ is actively transported back into the sarcoplasmic reticulum cisternae→muscle relaxes.

Question 14

What are some abnormal contraction?

Answer 14

▪spasm – involuntary contraction of one muscle
• cramp – painful spasm
• tetanus – multiple spasms of skeletal muscles
▪tic – involuntary twiches of muscles, usually under voluntary control
▪tremor – rhythmical, involuntary contractions of opposite groups of muscles
▪fasciculations – involuntary, short twiches on motor unit visible under the skin
▪fibrilace – spontaneous contractions of fibres of one muscle that aren ́t visible under the skin

Question 15

What are the innervation of skeletal muscles?

Answer 15

▪ Skeletal muscle is richly innervated by myelinated motor nerves (axons) branch out within the perimysium.
▪ At the site of innervation, the axon loses its myelin sheath and forms a dilated termination called the motor end-plate or neuromuscular junction.
▪ Synaptic vesicles contain neurotransmitter acetylcholine.
▪ Between the axon and the muscle is a space called the synaptic cleft – in which lies an amorphous basal lamina matrix from the muscle fiber.

Question 16

What is motor unit?

Answer 16

▪ Skeletal muscle is richly innervated by myelinated motor nerves (axons) branch out within the perimysium.
▪ At the site of innervation, the axon loses its myelin sheath and forms a dilated termination called the motor end-plate or neuromuscular junction.
▪ Synaptic vesicles contain neurotransmitter acetylcholine.
▪ Between the axon and the muscle is a space called the synaptic cleft – in which lies an amorphous basal lamina matrix from the muscle fiber.

Question 17

What is the rule of motor unit?

Answer 17

the smaller the motor unit, the less force it produces, and the more graded the force production of the entire muscle.

Question 18

What happens in fine movements?

Answer 18

Now think about your eye muscles. They are small. They have many fewer muscle fibers. They have to be able to contract in tiny amounts so that your eyes can make tiny movements rather than jumping all over as they look around. These muscles need to have small motor units.

Question 19

What happens in coarse movements?

Answer 19

Your quadriceps muscles are huge, containing many thousands of muscle fibers. They also need to be able to produce a lot of force, since they help support your body to stand up. So quadriceps muscles should have pretty large motor units. Since there are so many muscle fibers overall in these muscles, it won’t cause our motion to be too jerky if we have large motor units. And we will get a lot of force out of them.

Question 20

What are sensory receptors?

Answer 20

• Muscle spindles - sensory endings around specialized skeletal muscle cells; complex structure and function; sensory neurons are sensitive to stretch and signal changes in muscle length.
• They convey length information to the central nervous system via afferent nerve fibers. This information can be processed by the brain to determine the position of body parts
• Muscle spindles are found most densely in muscles that are used for fine control (ex. interosseus muscles of hand).

Question 21

What are golgi tendon organs?

Answer 21

located in muscle tendons; anatomy simple; sensitive to tension in tendon; act to inhibit motor nerve activity if tension becomes excessive.

Question 22

What are responses of tendon organs?

Answer 22

when muscle contracts against a large load (isometric contraction), tendon organs fire intensely.
When contract against a moderate load (isotonic contraction), tendon organ firing reflects amount of force needed to move load.
Passive stretch or tendon tap does NOT excite tendon organs.

Question 23

What is troponin?

Answer 23

▪ Troponin is a contractile protein that normally is not found in serum. It is released only when muscle necrosis occurs.
▪ Troponin originates within the sarcomere of both cardiac and striated skeletal muscle. Each sarcomere is comprised of actin and myosin filaments, which interact to produce a muscle contraction.
▪ Each tropomyosin molecule is associated with a troponin complex, which regulates actin-myosin binding. The cTn complex is composed of three units: Troponin T (TnT), Troponin I (TnI), and Troponin C (TnC).
▪ While troponin is found in both skeletal and cardiac muscle, the high specificity of cTn for cardiomyocyte necrosis is conferred by unique peptide sequences present in cTn, but absent in skeletal troponin (sTn).
▪ Cardiac troponins T and I are the preferred markers for myocardial injury as they have the highest sensitivities and specificities for the diagnosis of acute myocardial infarction.

Question 24

What are the characteristics of smooth muscles?

Answer 24

1. Elongated spindle-shaped cells.
2. No striations.
3. Single elongated nucleus central in position.
4. Surround the viscera.

Question 25

What are the functions of smooth muscles?

Answer 25

1. Supplied by autonomic nerves – involuntary control.
2. Respond slowly to stimuli.
3. Capable to sustain contraction – do not fatigue easily.
4. Regulate the internal environment e.g. digestion, circulation, secretion, excretion.
5. Less dependent on nervous control – contract automatically, spontaneously.