Microstructure and function of human muscle systems

Question 1

What are the five tissue types?

Answer 1

-Epithelium(sheets of cells)
-Connective tissue(Support and strength)
-Blood
-Muscle tissues
-Neural tissues(CNS and nerves)

Question 2

What are the different classes of muscles?

Answer 2

1. Striated(Striped)
   a. Skeletal
   b. Cardiac
2. Non-striated
   a. Smooth muscle
3. Myoepithelium
   a. Contraction of glands, iris of eye
4. Myofibroblasts
   a. In healing wounds

Question 3

What do skeletal muscles operate and link?

Answer 3

-Operates the skeleton
-Links bones and tendons

Question 4

Where are smooth muscle found?

Answer 4

-Generally internal organs like the gut, lungs, blood vessels(which control blood pressure), uterus and bladder

Question 5

What is the function of skeletal muscle and what type of control is it?

Answer 5

-Rapid contraction to escape danger but subject to fatigue
-Voluntary control

Question 6

What is the function of cardiac muscle and what type of control is it?

Answer 6

-Quite rapid
-Resists fatigue
-Can contract regularly for 90+ years
-Involuntary control

Question 7

What is the function of smooth muscle and what type of control is it?

Answer 7

-Slower contraction but very powerful
-Energy efficient
-Susceptible to very little fatigue
-Able to stretch more than skeletal and cardiac muscles
-Usually the control is involuntary

Question 8

What is the structure of skeletal muscle?

Answer 8

1. Epimysium
2. Fascicles
3. Perimysium

Question 9

What are fascicles?

Answer 9

Little bundles

Question 10

What is muscle surrounded by, how is it seen and what is its diameter

Answer 10

-Surrounded by epimysium
-Seen by eye
-Diameter of 1-20cm

Question 11

What is the fascicle surrounded by, how is it seen and what is its diameter?

Answer 11

-Surrounded by perimysium
-Seen by eye
-1-5 mm

Question 12

What is a muscle fibre(a cell) surrounded by, what is it seen by and what is its diameter?

Answer 12

-Surrounded by Endomysium and plasma membrane
-Seen by light microscope
-30-100 micrometers

Question 13

what are myofibrils(in a cell) seen by and what is its diameter?

Answer 13

-Seen by light microscope and transmission electron microscopy
-1-2 micrometers

Question 14

What does skeletal muscle look like under high magnification with H&E stain?

Answer 14

-Very long(up to 4cm)
-Giant thread-like cells with thousands of nuclei:
-Multinucleate or syncytial cells

Question 15

How are skeletal muscle fibres formed?

Answer 15

-Skeletal muscle fibres are formed by thousands of precursor cells in the embryo(myoblasts) fusing together

Question 16

What proteins are the core of the contractile apparatus?

Answer 16

Made of many molecules of the proteins myosin and actin

Question 17

Why is meat(muscle) rich in protein?

Answer 17

Meat(muscle) is rich in protein because it is largely made of actin and myosin protein filaments

Question 18

What are the steps in the contractile mechanism?

Answer 18

-In longitudinal section the actin and myosin filaments line up like this. This diagram represents a relaxed muscle
-Sliding of actin past myosin generates muscle contraction
-Therefore the I bands get narrower and A does not
-Z line contains alpha actinin, a protein to which actin attaches

Question 19

What is a sacromere

Answer 19

The contractile unit, from one z line to the next

Question 20

What are the steps in neural stimulation of skeletal muscles via motor end-plates?

Answer 20

-Action potential spreads over the fibre’s plasma membrane
-Then special intracellular membrane systems carry the signal to all parts of this cell
-Diffusion is not fast enough
-Membrane systems:
-T-(transverse) tubules convey stimulus from plasma membrane rapidly inside fibre. Then they pass it to sarcoplasmic reticulum which is a specialised form of endoplasmic reticulum

Question 21

What is the structure of cardiac muscles?

Answer 21

-Have much smaller fibres, joined end to end by specialised junctions, intercalated disks
-Have striations as found in skeletal muscle
-Intercalated disk, the strong end to end junctions between fibres
-Actin filaments are attached to the disks

Question 22

What happens to skeletal muscle suffering from duchenne muscular dystrophy under microscope with H&E stain?

Answer 22

Smaller fibres, more connective tissue between.
Damage, death and repair of fibres
occurring.

Question 23

What is the Fascia adherens in cardiac muscle fibres and whats it for? What is attached to it?

Answer 23

-Special sheet-like intermediate junction between fibres, for strong adhesion
-Actin attached

Question 24

What is the function of gap junctions in cardiac muscle fibres?

Answer 24

-Ionic communication, to coordinate contraction wave

Question 25

What are desmosomes for in cardiac muscle fibres?

Answer 25

Desmosome for adhesion

Question 26

What do branching fibres provide in cardiac muscles?

Answer 26

Branching fibres provide extra strength, curvature and resistance to splitting(by high pressure blood)

Question 27

What does a small diameter of fibres in cardiac muscles allow?

Answer 27

-Smaller diameter fibres(than skeletal muscles) allow rich blood supply and additional connective tissue, for strength

Question 28

What does numerous mitochondria in cardiac muscle allow?

Answer 28

-Numerous mitochondria allow respiration, continuous energy supply, resistance to fatigue

Question 29

What do intercalated disks give in cardiac muscles?

Answer 29

-Intercalated disks give very strong attachments and ionic communication between fibres

Question 30

How does contraction in cardiac muscle occur?

Answer 30

-Myogenic stimulus(Muscle generated)
-Action potential starts from pacemaker region in right atrium and carries a wave of contraction across heart, assisted by ion diffusion through gap junctions in the intercalated disks
-Purkinje fibres(Larger, modified cardiac muscle fibres)
-Carry stimulus rapidly to ventricles

Question 31

Is smooth muscle striated?

Answer 31

Smooth muscle is not striated

Question 32

Are smooth muscles voluntarily controlled?

Answer 32

-Also called ‘involuntary’ muscle, as not normally under conscious control

Question 33

What is the structure of smooth muscles?

Answer 33

-No myofibrils
-No striation
-No complex membrane systems
-Spindle shaped fibre
-Junctions between fibres
-Near the membrane is a basic form of sarcoplasmic reticulum

Question 34

What is the function of dense bodies in smooth muscles?

Answer 34

anchors for contraction
-Dense bodies are found in smooth muscle and function like Z lines

Question 35

What are qualities of smooth muscle?

Answer 35

tissue stronger, more elastic, more energy-efficient. Well adapted to constant activity in organs

Question 36

What do dense bodies in smooth muscles contain and and what do they function as?

Answer 36

-Contain alpha actinin and actin attaches to them