MCAT Musculoskeletal muscle

Question 1

Red fibers ( slow twitch) v. White fibers ( fast twitch)

Answer 1

Red fibers are for more sustained contractions and has more mitochondria to carry out oxidative phosphorolaytion and more myoglobin ( carries O2 via heme prosthetic group).

White fibers has less mitochondria and myoglobin. Responsible for fast movements.

Question 2

Tonus

Answer 2

Sustained rhythmic contraction of smooth muscle.

Question 3

Myogenic activity

Answer 3

Contraction without nervous system innervation. Seen in smooth muscle.

Question 4

What makes cardiac muscle different from skeletal and smooth muscle?

Answer 4

Cardiac muscle has properties of both smooth ( innervation via autonomic NS and fire rhythmically) and skeletal muscle ( appears striated under the microscope).

Heart fires rhythmically via intercalated disks; made of desmosomes which prevents cells from separation during the contraction and gap junctions which allows for the cells to fire rhythmically.

Question 5

How many nuclei does each muscle type contains?

Answer 5

Skeletal has many nuclei.

Cardiac has 1-2 nuclei

smooth is uninucleated.

Question 6

Describe the fibers of each muscle type

Answer 6

Skeletal muscle and smooth muscle are bunched while cardiac fibers are branched.

Question 7

Which muscle types contains gap junctions?

Answer 7

Smooth and cardiac muscle.

Question 8

What components of the nervous system control each of the muscle fibers?

Answer 8

Skeletal muscle is controlled the somatic NS ( voluntary control)

Cardiac and smooth muscle are controlled by the autonomic NS ( involuntary control).

Question 9

Striated muscle

Answer 9

Muscle that appears stripped ( sacromeres) under the microscope.

Question 10

Role of titin in the sacromere

Answer 10

anchors actin and myosin together and prevents overstretching.

Question 11

Define each of the zones and bands of the sacromere?

Answer 11

Z-line - represents the boundary of the sacromere.

M-line- line that runs down the center of the sacromere.

I band- represents thin actin

H band- represents thick myosin

A band- the overlap of the I and H bands.

During contraction the myosin pulls towards of the sacromere decreasing the sacromere. This causes a decrease in the I and H bands but NOT the A band.

Question 12

Describe how calcium is released for muscle contraction?

Answer 12

1. Ach binds to ligand gated channels on the sacrolemma.
2. Na+ moves in and depolarize causing an action potential that propagates down the T-tubules to the sacroplasmic reticulum causing the release of calcium down it’s concentration gradient.
3. Calcium binds to tropinin causing a change in tropomyosin and exposing the myosin- binding sites on actin that allows myosin heads to bind to the actin.
4. When depolarizing stimulus is stopped calcium is actively transported back into sacroplasmic reticulum causing the muscle to go back in a resting state.

Question 13

What is the functional unit of cardiac and skeletal muscle?

Answer 13

The sacromere

Question 14

Sacromeres attached to each in end to end are called what? What are a collection of sacromeres composed of?

Answer 14

Myofibrils

A bunch of sacromeres are called myocytes.

Question 15

Where does the the nervous system acts on muscle?

Answer 15

The neuromuscular junction ( also called the motor end plate).

Question 16

Simple twitch

Answer 16

The contraction of a single muscle fiber. Includes the latent period ( release of calcium from sacroplasmic reticulum), contraction period, and relaxation period.

Question 17

Tetanus

Answer 17

When constant stimulation doesn’t allow the muscle to rest.

Question 18

Describe the sliding filament model

Answer 18

Describes how are muscles contracts

1. When fiber is at rest in a high energy conformation ATP is hydrolyzed ( ADP +Pi) on the myosin head. Calcium binds to troponin causing a conformation change in tropomyosin exposing myosin head.
2. The myosin head binds to the actin filament.
3. The dissociation of Pi provides the power stroke where the length of the sacromere decreases.
4. ADP is released from the myosin head. Myosin head is in a low energy state.
5. ATP then binds and breaks apart the cross- bridge link.

6.Hydrolysis of ATP brings it back into the resting, high energy, state.

7. Happens again until calcium is taken back up into the sacroplasmic reticulum

Question 19

What does the muscles use as energy reserves?

Answer 19

Use of creatine- detach phosphate from ATP and add it to creatine, in times of stress the processed is reversed to make the ATP.

Use of myoglobin and increased oxygen delivery to the muscles.

Question 20

Oxygen debt

Answer 20

The amount of oxygen needed by the muscles and the amount of oxygen present in the muscles.

Question 21

What are the two types of skeletons?

Answer 21

Endoskeleton is when the skeleton is inside the body.

Exoskeleton is when skeleton encases the organism ( think insects).

Question 22

Slow twitch ( type 1) oxidative fibers

Answer 22

Contract at a slower rate and is more resistance to fatigue.

Uses aerobic respiration to generate ATP and so has a lot of mitochondria, myoglobin, and an extensive capillary network.

Question 23

Describe fast glycolytic fibers ( 2X) and fast oxidative glycolytic fibers ( 2A)

Answer 23

Fast glycolytic fibers ( 2X) primarily uses anaerobic respiration for energy and so produces more H+ and fatigues easily as a result.

Fast oxidative glycolytic ( type 2A) fibers has intermediate fatigue and uses both aerobic and anaerobic respiration.

Question 24

Where does bone strength comes from?

Answer 24

Compact bone

Question 25

Describe spongy bone

Answer 25

Contains trabeculae ( responsible for the sponge properties) in-between trabeculae is cavities that contains two types of bone marrow:

Red marrow- composed of homopoietic stem cells which are capable of differentiating into any cell type in the body.

Yellow marrow- contains fat cells and are inactive.

Question 26

Describe the structure of long bones.

Answer 26

A long cylindrical section called the diaphysis which leads to a spread out section called the metaphysis and terminates at the epiphysis.

The epiphysis contains epiphyseal growth plates which contains mitotic stem cells. These plates are open until puberty.

Outside of the diaphysis contains periosteum which serves as sight of attachement for muscle.

Question 27

Tendons v. Ligaments

Answer 27

Tendons attaches muscle to bone while ligaments attaches bone to bone via joints.

Question 28

What are the two cell types involved in building and maintaining bone?

Answer 28

• Osteoclasts - resorbs bone ( breaks it down)
• Osteoblasts - builds bone.
• Both are needed in maintaining bone*h

Question 29

What are the roles of calcitonin and PTH in bone formation/ resorption?

Answer 29

Calcitonin works to decrease blood calcium levels by increasing bone formation.

PTH works to increase blood calcium levels by increasing bone resorption.

Question 30

What is cartilage composed of?

Answer 30

Composed of chondrin which consists of chondrocytes. It’s avascular and not innervated.

Question 31

What are the ways to create bone?

Answer 31

• Endochondral ossification - creating bone by the hardening of cartilage.

*Intramembranous ossification- creation of bone via embryonic connective tissue.

Question 32

What are the 2 types of joints?

Answer 32

Movable joints- you can move them ( ie. hinge joints, ball and socket)

Immovable joints- create fused bones called sutures ( ie. the skull).

Question 33

Synovial capsule

Answer 33

Encloses joint cavity and secretes synovial fluid which serves to lubricate the joint.

Question 34

Articular cartilage

Answer 34

Coats the articular surfaces and lubricates them so they can withstand impact better.

Question 35

Origin v. Insertion

Answer 35

The origin is the part of muscle with larger bone attachment. The insertion is the part of the bone where there is less muscle attached.

Muscles can work in antagonistic or synergistic pairs.

Question 36

Flexor v. Extensor

Answer 36

Flexor movement that decreases the angle across a joint.

Extensor is movement that increases the angle across a joint.

Question 37

Abductor v. Adductor

Answer 37

Abductor is the movement of a limb away from the midline.

Adductor is the movement of a limb toward the midline.

Question 38

Medial rotation v. lateral rotation

Answer 38

Medial rotation is the rotation of the axis of the limb away from the midline.

Lateral rotation is the rotation of the axis of the limb toward the midline.

Question 39

Within a sacromere what’s the sign of great contractile force potential?

Answer 39

Great overlap of the I and H bands but not so much overlap that it’s already contracted ( when the I bands are completely overlapped with each other).

Question 40

How to identify optimal contraction force of a sarcomere?

Answer 40

Greater overlap of the I and H bands means a greater contraction force.
Just make sure that the sarcomere isn’t already contracted.