Muscle tissue

Question 1

Name the three contractile cells that function as single-cell contractile units, and state the function of each

Answer 1

Myoepithelial Cells - Important component of certain secretory glands – expel secretions from glandular acini.
Pericytes - Smooth muscle cells that surround the blood vessels
Myofibroblasts - Cells that have a contractile role in addition to secreting collagen – important for tissue healing after tissue damage,
leads to scar formation.

Question 2

What are the three types of muscle cells?

Answer 2

Skeletal muscle
Smooth muscle
Cardiac muscle

Question 3

What are the key features of skeletal muscle tissue?

Answer 3

-Striated due to the arrangement of contractile proteins
-Elongated, multinucleate, contractile
-Contraction is controlled by motor nerves

Question 4

What is a motor unit?

Answer 4

Individual nerve fibres that branch within the muscle to supply a group of muscle fibres is called a MOTOR UNIT.

Question 5

What happens to a muscle if the nerve supplying it becomes damaged?

Answer 5

If the nerve supply is damaged, the muscle cannot be stimulated to contract, which leads to atrophy of the muscle

Question 6

The connective tissue coverings of a skeletal muscle, listed
from superficial to deep, are
(a) endomysium, perimysium, and epimysium.
(b) endomysium, epimysium, and perimysium.
(c) epimysium, endomysium, and perimysium.
(d) epimysium, perimysium, and endomysium.

Answer 6

(d) epimysium, perimysium, and endomysium.

Question 7

Describe the organization of a muscle from the gross muscle to the the smallest functional unit of a muscle.
Also state the connective tissue covering of each layer

Answer 7

Muscle is made up of a group or bunch of fascicles covered by epimysium
A fascicle is made up of a group of muscle fibres/cells covered by perimysium
Individual muscle fibres are covered by endomysium
Each muscle fibre is made up of myofibrils
Each myofibril is made up of sarcomeres
Each sarcomeres is made up contractile proteins (actin and myosin)

Question 8

What would be the difference between fascicles of muscles in the hand and those of muscles in the arm?

Answer 8

Muscles in the hand have small fasciculi because they are responsible for fine movement
Muscles in the arm have large fasciculi because they are responsible for gross movement

Question 9

what do skeletal muscle fibers look like in the transverse section?

Answer 9

Pink-stained
They have a polygonal shape
nucleus is at the periphery

Question 10

What do muscle fibers look like in the longitudinal section?

Answer 10

Striations are more visible
More nuclei per muscle fiber can be seen

Question 11

What is the precursor of skeletal muscle?

Answer 11

Myoblasts

Question 12

Describe the embryogenesis of skeletal muscle

Answer 12

1. Mesenchymal cells become myoblasts
2. The myoblasts fuse to form elongated myotubes
3. Synthesis of contractile proteins
4. Form myofilaments
5. cross striations become visible

Question 13

What cells are responsible for muscle regeneration after damage?

Answer 13

Satellite cells.
Satellite cells enter mitosis after muscle damage and fuse to form differentiated muscle fibers

Question 14

How are newly regenerated skeletal muscle fibres different from normal skeletal muscle fibres?

Answer 14

Newly regenerated muscle fibers have a centrally located nucleus rather than in the periphery

Question 15

True or False:
Smooth muscle needs innervation in order for it to contract

Answer 15

False

Contractility is an essential property of smooth muscle that occurs
INDEPENDENDTLY OF INNERVATION; however, the autonomic nervous
system, hormones and metabolites influence contractility to meet
changing functional demands.

Question 16

Describe the structure of smooth muscle

Answer 16

The cells are small, with a single nucleus.
The fibers are bound together in irregular branching fasciculi.
Bundles of contractile proteins ‘criss-cross’ the cell and are
inserted into anchoring points within the cytoplasm and cell
membrane.

Question 17

Why is smooth muscle not striated?

Answer 17

Contractile proteins of smooth muscle are not arranged in
myofibrils – thus, smooth muscle cells are not striated.

Question 18

How does a smooth muscle look like when it contracts?

Answer 18

Contraction of smooth muscle results in shortening of the cell due
to the criss-cross nature of the arrangement of contractile proteins.
When contracted, the cells assumes a globular shape in contrast to
its elongated shape in its relaxed state. The shape of the nucleus is
sometimes spiral-shaped in a contracted cell.

Question 19

Describe smooth muscle when seen in transverse section

Answer 19

Cells appear as if they are of different diameter.
• Nuclei are included in the plane of section where fibres
have been cut through the widest diameter.
• Plump nuclear shape and central location of nucleus in
cytoplasm

Question 20

Describe smooth muscle when seen in longitudinal section

Answer 20

Elongated, spindle-shaped cells with tapered ends that are
sometimes bifurcated.
Contain one nucleus, centrally located at widest part of cell.

Question 21

Which type of muscle has features of both skeletal and smooth muscle?

Answer 21

Cardiac muscle

Question 22

Describe the structure of cardiac muscle

Answer 22

Cardiac myocytes are cylindrical cells with a central nucleus, the
ends of the fibres are split into smaller branches.
Delicate collagen, that is similar to endomysium, lies between
fibres.
Similar arrangement of contractile proteins; therefore, does
appear striated (however, not as distinct as skeletal muscle).

Question 23

What is the specialized intercellular junction found between cardiac muscle cells?

Answer 23

Intercalated discs

Question 24

State the functions of intercalated discs

Answer 24

1. Provide points of anchorage for myofibrils.
2. Permit rapid spread of contractile stimuli from one cell to another

Question 25

Describe the cardiac muscle cells in transverse section

Answer 25

Have a centrally located nucleus, with a large ring of
surrounding cytoplasm.

Question 26

Describe the cardiac muscle cells in longitudinal section

Answer 26

Cardiac myocytes contain one to two nuclei and an
Extensive cytoplasm.
Elongated nuclei that are generally centrally located.
Striations not as easily visible as skeletal muscle.
Intercalated discs mark cellular boundaries.

Question 27

What is muscular dystrophy?

Answer 27

Weakness and ‘wasting away’ of muscles due to a defect in one
of the proteins involved in muscle function.
Muscle does not function correctly and fibres undergo
progressive damage with repeated contraction, ultimately leading
to death of muscle cells.