muscle cells

Question 1

what are the three types of muscles?

Answer 1

-skeletal
-smooth
-cardiac

Question 2

give three features of skeletal muscle and its 3 overall functions

Answer 2

-makes up 40% of the mass of the average human body
-usually voluntary contractions
-involves short single contractions or a long and sustained contraction

functions, posture maintenance, motion and heat production

Question 3

explain the striated muscle that makes up skeletal muscle

Answer 3

1. attached to bones via tendons and moves the skeleton
2. divided into fascicles that run parallel
3. each fascicle consists of a bundle of myofibers and this appears striated under electron microscope

Question 4

look at the hierarchical organisation of skeletal muscle

Answer 4

ok

Question 5

What’s a sacromere? What does it contain?

Answer 5

Sections of myofibrils that shorten in muscle contraction. They contain two Z plates 3 myosin filaments, and 4 actin filaments on either side

Question 6

In a sacromere,
What is the I band?
What is the A band?
What is the H zone?
What happens to each of these during muscle contraction? Include z plates

Answer 6

. Sections of the sacromere of actin only
2. Sections of the sacromere where the actin and myosin overlap and myosin only
3. Sections of the sacromere if myosin only

During muscle contraction:
Z plates come together
I bands shorten as actin is pulled over the myosin
H zone shortens as actin overlaps the myosin more
A band stays the same

Question 7

how many myofibres per motor unit in the extraocular muscles that control eye movement?

Answer 7

10-20

Question 8

Give the steps of neural excitation at the neural muscular junction

Answer 8

1. Binding of acetyl choline to its receptors leads to their opening as Na+channels
2. Influx of Na+ leads to local depolarization of the sarcolemma and generation of muscle action potential 3. Depolarisation spreads via T tubules
3. opening of voltage-gated Ca2+ channels in the sarcoplasmic reticulum(SR)
4. massive, rapid movementof Ca2+ from SR into the sarcoplasm
5. Simultaneous contraction of myofibrils → contraction of myofibre

Question 9

watch videos on the sliding filament theory

Answer 9

ok

Question 9

give the role of Ca2+ in muscle contraction

Answer 9

-the calcium ions in skeletal muscle work at actin regulated attraction by moving the troponin-tropomyosin complex off the binding sites allowing actin and myosin to interact

Question 10

give the role of ATP in muscle contraction by detailing the cross bridge cycle

Answer 10

At the end of the power stroke the actin-myosin complex remains intact until ATP becomes available. Upon ATP binding to myosin, myosin head is displaced from actin:- ATP is required for muscle relaxation ATP hydrolysis is needed for return of the myosin head to its resting conformational state- The final product is also the first reactant - the contractile cycle

Question 11

give the steps of electrical inactivity at the myoneural junction to allow muscle relaxation

Answer 11

1. The sarcolemma returns to its resting electrical potential (about-60mV), as does the entire transverse tubule system and the SR membrane
2. Removal of sarcoplasmic Ca2+ (ATP-driven Ca2+ pumps in sarcoplasmic reticulum and mitochondria
3. contractile activity stops and a state of relaxation

Question 12

what do myofibrils consist of?

Answer 12

-thin filament of mainly actin
-thick filament of myosin and each thick filament is surrounded by six thin filaments

Question 13

what is tetany and how does it come about?

Answer 13

its a hypercontracted muscle caused by depletion of ATP due to prolonged period of repetitive muscle stimulation
1. raised sarcoplasmic Ca2+ because no ATP is avaliable to bring Ca2+ into the cisternae of the sarcoplasmic reticulum so Ca2+ remains bound to troponin
2. muscle is highly contracted as no ATP is available to break actomyosin cross bridges

Question 14

give three sources of ATP in the muscle

Answer 14

-creatine phosphate
-anaerobic glycolysis
-aerobic cellular respiration

Question 15

give three types of skeletal myofibers

Answer 15

-slow oxidative fibres. red as they have a high conc of myoglobin, many mitochondria and are very resistant to fatigue
-fast oxidative fibres. also high myoglobin conc and mitochondria and has hugh glycogen stores so generates atp aerobic and anaerobically
- fast glycolytic fibres. low conc of myoglobin and mitochondria, large amounts of glycogen and intense movements of short duration

Question 16

what is rigor mortis and how does it occur?

Answer 16

rigid state of muscles that develops shortly after death
1.loss of energy supplies means ion equilibration
2. Sarcoplasmic reticulum and extracellular Ca2+ leaks into the sarcoplasm
3. raise in Ca2+ conc to high levels
4. exposure of actin binidng sites to myosin
5. uncontrolled contractile activity hastens the total exhaustion of ATP supplies and ends with all or nearly all myosin molecules in actomyosin cross bridges

Question 17

give examples of smooth muscle contraction in humans to carry out bodily functions

Answer 17

1. to regulate air flow in lungs
2. to regulate arterial blood flow
3. move food along the GI tract
4. expel urine from bladder
5. delivering babies
6. iris sphincter and dilators constrict or dilate the pupils

Question 18

give three features of smooth muscle structure

Answer 18

-spindle shape
-single centrally located nucleus
-contractile apparatus due to sarcomere like structure

Question 19

give 5 properties of smooth muscle

Answer 19

-contracts involuntarliy
-able to stretch and maintain tension for a long period of time
-slow shortening velocity
-slow actomyosin atpase so slow crossbridge cycle
-high economy of energy utilization during isometric contraction

Question 20

compare smooth muscle contraction with that of skeletal muscle in
force
velocity
energy consumption

Answer 20

-force smooth 3x less than skeletal
-velocity smooth 100x less than skeletal
-energy consumption smooth 300x less than skeletal