Propulsion Tissue Histology

Question 1

The basic fundamental properties of propulsion tissues are? (4)

Answer 1

Contractility
Excitability
Conductivity
Elasticity

Question 2

State 5 general functions of propulsion tissues.

Answer 2

a. Locomotion
b. Maintenance of body shape
c. Heat generation
d. Transport/movement of substances within the body
e. Expulsion of substances from the body

Question 3

In order to perform their functions, what cellular organelles do propulsion tissues have in abundance (4)?

Answer 3

• numerous contractile filaments (actin and myosin)
• numerous mitochondria to provide energy
• highly modified and well developed sarcoplasmic reticulum which sequesters and releases calcium necessary for contraction mechanism
• cell membrane invaginations (T-tubules) which increase transmission into the sarcoplasmic reticulum

Question 4

How are muscle tissues classified?

Answer 4

Functionally, based on whether they are under voluntary or involuntary (autonomic) control by the nervous system.
Structurally, based on the arrangement of contractile filaments i.e. if actin and myosin are regularly arranged, striated and if they are irregularly arranged, non-striated.

Question 5

State the 3 categories of propulsion tissue.

Answer 5

1. Skeletal muscle - striated and voluntary
2. Cardiac muscle - striated and involuntary
3. Smooth muscle - non-striated and involuntary

Question 6

The following are contractile cells distinct from muscle cells. Where are they found and what are their roles?
1. Myoepithelial cells
2. Myofibroblasts
3. Myoid cells
4. Pericytes

Answer 6

1. Myoepithelial cells - found in secretory portion of exocrine glands. Their contractions aid in expelling the secretions through the duct of the exocrine gland as in sweat glands, parotid glands amongst others.
2. Myofibroblasts - found in connective tissues; responsible for contraction of wounds during healing hence reducing the size of a scar
3. Myoid cells - found on the basal side of the seminiferous tubules of the testis. They aid in transport of spermatozoa through the tubules.
4. Pericytes - found on capillaries. They regulate vascular diameter and hence capillary blood flow.

Question 7

Actin and myosin form ________.

Answer 7

myofilaments

Question 8

Myosin are thick, dark and anisotropic (alters polarized light) (A band) while actin are thin, light and isotropic (doesn’t alter polarized light) (I band). TRUE or FALSE?

Answer 8

TRUE

Question 9

Actin and myosin myofilaments are arranged perpendicular to the direction of cellular contraction and form myofibrils responsible for muscle contraction. TRUE or FALSE?

Answer 9

FALSE. Actin and myosin myofilaments are arranged parallel to the direction of cellular contraction and form myofibrils responsible for muscle contraction.

Question 10

How do the cells of skeletal muscles appear histologically?

Answer 10

elongated, cylindrical striated cells with multinucleated peripheral nuclei

Question 11

State the location of skeletal muscles.

Answer 11

• muscles which are associated with the skeleton (are connected to bones by tendons).
• platysma muscles
• voluntary sphincters of inner organs

Some info. about platysma:
This is a thin sheet-like muscle that lies superficially within the anterior aspect of the neck.

Question 12

Skeletal muscles are innervated by the _______________ nervous system.

Answer 12

somatic [hence under voluntary control]

Question 13

Which theory explains the mechanism of contraction of myofibrils?

Answer 13

Sliding filament theory

Question 14

Myofibrils have some bands and lines depending on the distribution and interconnection of myofilaments. List them and what they comprise.

Answer 14

I - band: actin filaments
A - band: myosin filaments which may overlap with actin filaments
Z - line: band of connections between actin filaments; zone of apposition of actin filaments belonging to two neighbouring sacromeres
M - line: band of connection between myosin filaments
H - zone: zone of myosin only (NO overlap with actin filaments) within the A - band

Question 15

The smallest contractile units of myofibrils are called ____________.

Answer 15

sarcomeres

Question 16

Write the sarcomere formula.

Answer 16

S = ½ I + A + ½ I

Question 17

Skeletal muscles are stimulated by nerve impulses carried by ______(a)_______ of motor neurons. The _____(a)______ form synapse-motor end plate. The excitatory transmitter is _______(b)________. Invaginations of the sarcolemma form the _________(c)________ system which “leads” the excitation into the muscle fiber. Close to the border between A- and I- bands of the myofibrils, __________(c)__________ are in close apposition with cisternae of sarcoplasmic reticulum. This association is called a _____(d)_____.

Answer 17

(a) axons
(b) acetylcholine
(c) T-tubule
(d) triad

Question 18

The action potential of excitation from T-tubule opens the ___________ channels of the sarcoplasmic reticulum. ___________ can now move from stores in the sarcoplasmic reticulum into the cytoplasm surrounding the myofilaments.

Answer 18

calcium

Question 19

Sites of interaction between actin and myosin are in resting muscle cells “hidden” by ________(1)_______. _________(1)________ is kept in place by a complex of proteins collectively called _________(2)________.

Answer 19

(1) tropomyosin
(2) troponin

Question 20

The binding of calcium to troponin-C induces a conformational change in the troponin-tropomyosin complex which permits the interaction between myosin and actin and, as a consequence of this interaction, ________________ will occur. [Diagram]

Answer 20

contraction

Question 21

_______________________ are small cells which are closely apposed to muscle fibers within the basal lamina which surrounds the muscle fiber. They may regenerate muscle fibers in case of damage.

Answer 21

Satellite cells

Question 22

Individual muscle fibers are surrounded by a delicate connective tissue septa (delicate network of reticular fibers) called the _______(1)______. Large numbers of parallel muscle fibers are grouped into fascicles, and the connective tissue sheath surrounding each fascicle is called the _________(2)________. Numerous fascicles form a whole muscle and a connective tissue sheath called the __________(3)_________.

Answer 22

(1) endomysium
(2) perimysium
(3) epimysium

Question 23

State differences between red and white muscle fibers.

Answer 23

• Red muscle fibers are comparatively thin and contain large amounts of myoglobin and mitochondria while white muscle fibers (cells) are thicker and contain less myoglobin.
• Red fibers contain an isoform of myosin with low ATPase activity, hence contraction is therefore slow while ATPase activity of the myosin isoform in white fibers is high and contraction is fast.

Question 24

Red muscles are used when sustained production of force is necessary e.g. in the control of posture. True or False?

Answer 24

True

Question 25

A) Groups of muscle fibers innervated by one motor neuron and its branches are called _____________________.

B) Skeletal muscle fibers contract spontaneously. True or False?

Answer 25

A) motor units
B) False. Skeletal muscle fibers do not contract spontaneously.

Question 26

State the location, function, and unit of cardiac muscle.

Answer 26

Location: the heart
Function: involuntary, rhythmic contraction
Unit: cardiomyocyte (cell)

Question 27

How do cardiac muscles look like structurally?

Answer 27

The fibers are not simple cylindrical units but display branching.
Majority of cardiac muscles have a single central nucleus, but a few have 2 nuclei.
The fibers are made up of separate cells joined end to end by intercalated discs that consist of gap junctions and desmosomes.

Question 28

In terms of control, cardiac muscle is both _______________ and ______________.

Answer 28

autonomous and involuntary

Question 29

List the structural proteins in muscle. (They provide proper alignment, elasticity and extensibility.)

Answer 29

Titin
Myomesin
Nebulin
Dystrophin

Question 30

Give the reasons for identifying smooth muscle histologically.

Answer 30

Non-striated
Spindle shaped cells
Single centrally placed nucleus