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MCAT PHGY > skeletal muscular system > Flashcards

skeletal muscular system Flashcards

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MCAT flashcards
1
Q

what is a tendon?

A

a band of fibrous connective tissue that connects a muscle to bone

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2
Q

explain flexing, extending, abducting, adducting, origin , and insertion?

A

origin - the piece of bone the muscle is attached to closer to the body (shoulder)
insertion - the piece of bone further from the body (forearm)

flexion - decrease joint angle
extension - increase joint angle
abduction - move away from body midline
adduction - move toward body midline

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3
Q

explain the organization of skeletal muscle in increasing complexity

A

1) muscle attached to bone via a tendon
2) each muscle is made up of connective tissue bands called fascicles
3) Each Fascicle is made up of many muscle cells / myocytes / myofibers
4) within each muscle cell, there are myofibrils
5) each fibril is made of actin / myosin filaments

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4
Q

Explain the lines and bands of one sarcomere (myofibril functional unit)

A

Z line to Z line defines sarcomere length
A line: length of myosin including overlap with actin
I line: only actin no overlap included
H zone: only myosin, no overlap included
M line: the centre

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5
Q

upon contraction what occurs to the different regions of the sarcomere?

A

H zone and I band shorten (actin)
A band stays the same (myosin)
Z lines become closer (whole sarcomere shortens)

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6
Q

during contraction, do the thin or thick filaments shorten?

A

no! they simply slide across each-other to shorten the sarcomere

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7
Q

Explain the 4 step power stroke of muscle contraction (actin/myosin interaction)

A
  1. the myosin head contains ADP + Pi. Upon calcium exposure, the myosin head binds to the actin binding site
  2. the myosin head ejects the ADP which induces a conformational change. This is the power stroke
  3. The myosin head binds another ATP molecule which is required for myosin / actin detachment
  4. this ATP molecule is immediately hydrolyzed and ready to go again

note: the bound form of thick/thin is called a cross-bride (formation occurs in step 1

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8
Q

what is tropomyosin and troponin?

A

both are on the thin filament
The power stroke is a spontaneous process. therefore there needs to be inhibitory regulation.

tropomyosin is a long intertwining protein complex that blocks the binding sites on actin
troponin is a globular protein that is attached to the actin and tropomyosin. It also binds calcium. When Ca2+ binds troponin, it shifts tropomyosin out of the way and permits contraction.

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9
Q

explain what occurs in the pre-synaptic neuron and in the cleft of a neuromuscular junction?

A

AP reaches the synaptic knob which triggers voltage gated calcium channels to open. The influx of calcium causes vesicles of acetylcholine to be excreted into the cleft. They diffuse and bind receptors on the motor end plate which are ligand-gated sodium channels (graded potential called the end plate potential)

eventually, acetylcholinesterase degrades acetylcholine

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10
Q

once acetylcholine is released, how does an AP propagate through a myofiber

A
  • acetylcholine stimulates ligand-gated receptors to produce and end plate potential
  • upon meeting threshold, voltage gated sodium channels open and depolarize the cell
  • this depolarization extends down into cell infolding’s called T tubules
  • these allows the depolarization to effect the sarcoplasmic reticulum which opens its voltage gated calcium channels
  • calcium binds troponin –> power stroke
  • calcium is actively pumped back into the SR after the contraction has occurred.
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11
Q

what is the smallest force of contraction called?

A

a twitch

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12
Q

can the size of a twitch change?

A

no

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13
Q

explain how you can generate stronger contraction

A

1) motor unit recruitment: multiple myofibers are innervated by a single somatic neuron (motor unit). If more motor unit’s are acivated at once, more muscle contraction will occur
2) frequency summation (temporal summation) increases the frequency of nerve impulses allowing them to sum on top of each other. this also allows the contraction force to sum on top of each other.

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14
Q

what is tetanus?

A

tetanus is the maximum force of contraction obtained by frequency summation of a muscle.

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15
Q

muscle contraction requires ATP. It mainly gets this through glycolysis and the kreb cycle. However during contraction, these mechanisms cannot reform ATP (from ADP +Pi) fast enough. What occurs?

A

another molecule called phosphate creatine is hydrolyzed and quickly converts ADP back to ATP for further muscle contraction

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16
Q

What it Rigor mortis?

A

when you die, you can no longer generate ATP. As a result, all of your ATP gets used up (hydrolyzed) which allows your muscles to contract. With no ATP, thick/think filaments stay bound

Rigor Mortis = rigidity after death

17
Q

what is myoglobin?

A

this is a protein with a very high affinity for oxygen (also has 4 subunits like heme). It pulls oxygen of Hb and stores it for aerobic use. Prior to fermentation

18
Q

what are the characteristics of Type 1 slow twitch muscle?

  • other names
  • mitochondria
  • contraction speed
  • fatigue resistance
  • examples
A
  • other names —- Red oxidative / slow oxidative
  • mitochondria — many mitochondria
  • contraction speed —- slow
  • fatigue resistance —- high
  • examples — used in marathons, posture, etc.
19
Q

what are the characteristics of Type 2A fast twitch muscle?

  • other names
  • mitochondria
  • contraction speed
  • fatigue resistance
  • examples
A
  • other names — red fast oxidative
  • mitochondria — quite a few (why its called red)
  • contraction speed — intermediate
  • fatigue resistance — intermediate
  • examples — contractions that last 30 min or less. E.g. running a 800 meter race.
20
Q

what are the characteristics of Type 2B fast twitch muscle?

  • other names
  • mitochondria
  • contraction speed
  • fatigue resistance
  • examples
A
  • other names — White fast twitch
  • mitochondria — few (why its white)
  • contraction speed — fast
  • fatigue resistance —- low
  • examples — shot put, jump shot, punch
    explosive movements
21
Q

Skeletal, Smooth, and Cardiac muscle. Compare

  1. appearance
  2. syncytium
  3. cause of depolarization
  4. Action Potential graph
  5. T tubule presence
  6. Protein regulators of contraction
  7. nervous system affects
A

Skeletal | Smooth | Cardiac
1. appearance
striated, smooth, Striated

  1. syncytium
    Structural syncytium, functional, functional
    Cardiac muscle intercalated discs = gap junctions
  2. cause of depolarization
    influx of sodium, influx of sodium, influx of calcium and sodium
  3. Action Potential graph
    Skeletal = similar to neuron. Na+ influx, K+ efflux
    Smooth = slow waves potential which eventually (with NS help) reaches threshold. Na+ influx, K+ efflux
    Cardiac node = slow leaky Na+ channels lead to threshold. Ca++ influx, K+ efflux
    Cardiac muscle = Na+ influx, Ca++ influx with K+ efflux (plateau), K+ efflux
  4. T tubule presence
    Cardiac and skeletal muscle = T tubules
    Smooth = no T tubes
  5. Protein regulators of contraction
    Cardiac and skeletal muscle = troponin binds calcium which displaces tropomyosin. Myosin head (which has hydrolyzed ATP to ADP) can now bind.
    Smooth = Calmodulin binds calcium which activates myosin light chain kinase (MLCK) which phosphorylates a myosin head which activates it.
  6. nervous system affects
    skeletal –> somatic nervous system impulses
    cardiac –> SNS uses NE to speed up contraction
    PNS uses Ach to slow contraction
    smooth –> PNS Ach stimulates contraction, SNS NE inhibits contraction
22
Q

Where does the calcium come from in cardiac, smooth, and skeletal muscle for contraction

A 
skeletal = entirely from the SR 
Cardiac = partially from SR, partially ECF 
smooth = entirely ECF
23
Q

what is the axial skeleton?

A

the skull, vertebral column, and rib cage. All other bones are the appendicular bones

24
Q

What are the three main cell types of connective tissue?

A

Adipocytes, chondrocytes, osteocytes

are all CT cells

25
Q

Connective tissue is essentially cells and the matrix the cells secrete. The matrix includes 2 main types of fibres and a ground substance made up of 2 proteins. What are these?

A

fibres are collagen and elastin.

The ground substance is made up of proteoglycans which have carbohydrate chains called glycosaminoglycans (GAG’s). Carbohydrates are very hydrophilic which is why the connective tissue draws water to it.

26
Q

what are loose and dense connective tissue

A

loose - more cells and ground matrix and less fibres such as areolar tissue.
dense - contains lots of fibres such as tendons and bone.

27
Q

What are flat, long, diaphysis, epiphysis, compact, and spongey bone??

A

the two main types of bone are flat and long bone.

flat bone is a concrete sheath with spongey bone underneath.
long bone is made up of a tube of compact bone called the diaphysis and on each end is compact bone called the epiphysis. within the tube their is spongey bone.

28
Q

what is red and yellow bone marrow? Where are they found

A

Red bone marrow is the site of hematopoiesis (blood cell production) and is found inside flat spongey bone.

yellow bone marrow is found in diaphysis spongey bone and is simply fat

29
Q

what is hydroxyapatite?

A

the crystal calcium phosphate material that surrounds the collagen network that creates bone

30
Q

explain the osteon, central canal, lamellae, canaliculi, and lucanae!
bone organization

A

the osteon is the basic unit of bone
within the center of each osteon is a central canal which has tiny rings surrounding it called lamellae.

within each osteon, the central canal has branches called caniliculi which extend into spaces called lucinae. Within each lucinae is an osteocyte.

31
Q

What are the three types of cartilage, what is their function

A
  1. Hyaline cartilage - strong but flexible, found in most locations such as joints where its also called articular cartilage
  2. Elastic cartilage - more flexible such as the pinna of the ear
  3. Fibrous cartilage - more rigid such as vertebral columns
32
Q

what is endochondral ossification ?

A

this is bone growth through the use of ostoblasts and chondroblasts. Hyaline cartilage is lay down first, and then invading osteoblast cells lay down bone.

33
Q

what is intramembranous ossification ?

A

this is the formation of bone stemming from embryonic stem cells called mesenchymes. This is how flat bone is produced

34
Q

explain briefly the development of bone for long bones.

A

each kid has a sheet of hyaline cartilage between the epiphysis and diaphysis called the epiphyseal plate.

upon growth hormone and other factors, chondroblasts form cartilage extending the plate. Then osteoblasts lay down bone (ossification) and get trapped in lucinae then becoming osteocytes.

The ossification process eventually catches up to the dividing chondrocyte cells which fuses the D with the E.

35
Q

what are synarthroses, amphithroses, and diarthroses?

A

these refer to different joints of the body

joints with no movement = synarthroses
joints with little movement = amphi
joints with lots = dia

36
Q

What is calcitrol? What is its effects on bone, the kidneys, and the gut?

A

Calcitrol is the active form of vitamin D (the kidneys are responsible for converting vitamin D to calictrol)

Calcitrol is a hormone which increases blood calcium

  1. on bone: stimulates osteoclasts slighly
  2. on kidneys: increases reabsorption of phosphorus
  3. on gut: increases absorption of phoshorus and calcium
37
Q

Explain the effects of PTH and calcitonin on bone, gut, kidneys.

A

PTH released from parathyroid increases blood Ca++

  1. bone –> PTH stimulates osteoclasts
  2. kidneys –> increases Ca++ reabsorption and encourages vitamin D conversion to calcitrol
  3. The gut –> increases intestinal absorption of Ca++ via calcitrol

Calcitonin from C cells of the thyroid decreases blood Ca+

1) bone –> inhibit osteoclasts
2) kidneys –> promote Ca++ secretion / decrease re-ab
3) gut – N/A

MCAT PHGY (8 decks)

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