0428 - Muscle Histology - EG

Question 1

Define each of the three muscle groups as either voluntary/involuntary and striated/non striated

Answer 1

Voluntary - skeletal
Involuntary - smooth, cardiac

Striated - skeletal, cardiac
Non-striated - smooth

Question 2

The plasma membrane of skeletal muscle is known as?

Answer 2

sarcolemma

Question 3

The cytoplasm of skeletal muscle is known as?

Answer 3

sarcoplasm

Question 4

The endoplasmic reticulum of skeletal muscle is known as?

Answer 4

sarcoplasmic reticulum

Question 5

muscle fibres are surrounded by?

Answer 5

endomysium

Question 6

Muscle fibres are arranged into bundles known as what?

Answer 6

fascicles

Question 7

Fascicles are surrounded by?

Answer 7

perimysium

Question 8

The muscle belly is surrounded by?

Answer 8

epimysium

Question 9

Why are muscle cells multinucleated? Where are the nuclei found?

Answer 9

Because many myoblasts fuse together to form a single muscle cell. The nuclei are found peripherally.

Question 10

List some contrasting features between type 1 and type 2 skeletal muscles.

Answer 10

Type 1 - slow contraction, aerobic, use oxidative phosphorylation, have many mitochondria and large amounts of myoglobin which give a red colour.

Type 2 - Fast contraction, anaerobic, use glycolysis, rich in glycogen, have a white colour.

Question 11

If stained muscle using a succinic dehydrogenase stain or NADH-TR stain, how are type 1 and type 2 muscles distinguished?

Answer 11

type 1 fibres stain dark and type 2 fibres stain pale.

Question 12

What makes a muscle appear striated?

Answer 12

The ordered arrangement of myofibril contractile proteins.

Question 13

The dark A band of a sarcomere represents?

Answer 13

section containing thick myosin filaments

Question 14

The light I band of a sarcomere represents?

Answer 14

section containing thin actin filaments

Question 15

The Z bands anchor which filaments?

Answer 15

actin filaments

Question 16

Which bands of the sarcomere become narrower with contraction?

Answer 16

I and H bands

Question 17

What is a motor unit?

Answer 17

A motor neuron and the muscle fibres it supplies.

Question 18

What is the neurotransmitter released at the neuromuscular junction?

Answer 18

acetylcholine

Question 19

Duchenne Muscular Dystrophy is inherited via what type of simple Mendelian inheritance? What is the protein affected?

Answer 19

x-linked disorder, results in abnormalities in the gene encoding dystrophin protein, which normally concentrates at the plasma membrane over Z bands where it links to cytoplasmic actin. Results in degeneration of muscle fibres and proliferation of endomysial connective tissue.

Question 20

Where is the nucleus in smooth muscle cells?

Answer 20

Central.

Question 21

In comparison to skeletal muscle which has Z lines, what do smooth muscle cells have?

Answer 21

Dense bodies which act as anchor points in the cytoplasm, and attachment junctions, which act as anchor points on the cell membrane.

Question 22

How are the contractile proteins arranged in smooth muscle? What happens when they contract?

Answer 22

In a criss-cross arrangement, so when contract the cell goes from an elongated shape to a plump shape.

Question 23

What is the difference between single unit (unitary)smooth muscle and multiunit smooth muscle? What are some examples of each type?

Answer 23

Single unit cells have extensive communications via gap junctions between adjacent cells so that they can contract as a single unit, examples in the gastrointestinal tract and uterus.
Multiunit cells are independent from their neighbours and are capable of finer control, such as ciliary muscles of the eye and piloerector muscles of skin.

Question 24

What is the difference between phasic and tonic contraction?

Answer 24

Phasic refers to the muscle exhibiting rhythmic or intermittent activity, often by single unit type muscle.
Tonic referes to the muscle continuously maintaining a level of tone, for example in blood vessels, often by multiunit type muscle.

Question 25

Compare and contrast cardiac myocytes with skeletal and smooth muscle cells.

Answer 25

Cardiac myocytes similar as elongated cells, have central nuclei like smooth muscle yet are also striated with sarcoplasmic reticulum and T tubules similar to skeletal muscle. Cardiac muscle is unique with branching fibres and intercalated discs

Question 26

What is the function of intercalated discs?

Answer 26

Specialised junctions between cells permit the rapid spread of contractile stimuli due to areas of low electrical resistance, so the fibres can contract almost simultaneously.

Question 27

What are the 3 types of membrane contacts from which intercalated discs arise?

Answer 27

Fascia adherens - sites of actin filament insertion

Desmosomes - anchor intermediate filaments

Gap junctions - pores with low electrical resistance for ion transfer

Question 28

Cardiac muscle is innervated by the autonomic nervous system - what is the effect of sympathetic and parasympathetic stimulation?

Answer 28

sympathetic increases heart rate, while parasympathetic decreases heart rate.

Question 29

What is hypertrophic cardiomyopathy?

Answer 29

myocardial dysfunction due to haphazard hypertrophy of myocytes and interstitial fibrosis, causing overal myocardial hypertrophy.