Chapter 11 - Musculoskeletal System Flashcards
What are the three types of muscle?
Cardiac, skeletal, and smooth muscle
Skeletal muscle is innervated by the ___________.
Somatic nervous system
What is the function of the skeletal muscle?
Controls voluntary movement
What is the function of smooth muscle?
Control involuntary movement
Characteristics of skeletal muscle
Striated, multinucleated, contains actin and myosin in repeating units called sarcomeres, mature cells are suspended in G0 phase (don’t divide)
What are the two types of fibers in skeletal muscle?
- Red fibers/slow-twitch - high myoglobin and high iron, many mitochondria, use aerobic respiration
- White fibers/fast-twitch - low myoglobin, low iron
Characteristics of smooth muscle
Uninucleated, no striations, myogenic activity, actin and myosin not in organized units; control the gut, viscera, blood vessels
Characteristics of cardiac muscle
1-2 nuclei per cell, striated, myogenic activity, innervated by autonomic NS, contains actin & myosin units in repeating units of sarcomeres, cardiac cells can undergo mitosis
Nerves that innervate the heart are responsible for _______?
Regulating the rhythm of the heart. The parasympathetic (vagus) nerve lowers HR while the sympathetic nerves increase HR.
Cardiac muscle cells are connected via _________. What is the purpose of this?
Intercalated discs, these discs house gap junctions which allow ions to flow directly from one cell to another for a rapid action potential.
What is the basic contractile unit of skeletal muscle?
A sarcomere
What makes up a sarcomere?
Thick myosin filaments and thin actin filaments that are connected to the proteins: troponin and tropomyosin
Troponin and tropomyosin attach to what part of the sarcomere?
To the thin filaments (actin)
Myosin is (always/sometimes) bound to actin unless the actin binding sites are blocked by tropomyosin.
always, myosin has a high affinity for actin such that it will always be bound unless blocked by tropomyosin
Multiple sarcomeres form a _________.
Myofibril
What is the outline of the gross structure of muscle cells starting from sarcomere?
Sarcomere —> myofibril —> muscle fiber —> fascicle —> skeletal muscle
What are the Z lines in a sarcomere?
They are zigzag lines at the end of both sides within each sarcomere unit, which define the boundaries of an individual sarcomere. Think “Z” is the end of the alphabet, just like the end of the sarcomere.
They shorten with contraction.
What is the A band?
It includes the total length of the myosin filaments as well as part of the actin filaments that overlap. Think “A” band as in it contains ALL of the myosin filament.
The distance STAYS the same with contraction.
What is the H zone?
Includes only a portion of myosin thick filaments. Think “H” is a thick letter, so it only contains the thick filament and NONE of the actin filaments.
H zone distance decreases with contraction.
What are the I bands?
They are the portion of the sarcomere which contain only thin actin filaments. Think of “I” as a thin letter which contains only thin filaments.
These also shorten with contraction.
What is the M line?
It is a line that runs down the middle of the sarcomere, that is the middle of the myosin filaments.
The distance between M lines in 2 sarcomeres decreases during contraction.
During contraction what part of the sarcomere stays the same?
A band
How does an action potential travel in a sarcomere?
The sarcolemma, cell membrane of a muscle fiber, is capable of propagating an action potential and distributing that action potential to all the sarcomeres in the myofibril though the T tubules which are perpendicular to the myofibril itself.
True or false:
Without calcium, muscle contraction wouldn’t occur.
True, calcium is necessary to bind to troponins which allows for bound tropomyosins configuration to change. This exposes actin binding sites to which myosin binds to.
Just like action potential, muscle fibers contain an _________.
all of nothing response, meaning they either contract or they don’t
How can you obtain a stronger muscle force?
Your nerve cells will recruit more muscle fibers to contract.
A simple twitch (response of a single muscle fiber) can be divided into 3 phases:
Latent period - AP spreads to muscle and calcium gets released from the sarcoplasmic reticulum
Contraction period - calcium binds to troponin, allowing myosin to bind to actin, muscle contracts
Relaxation period - calcium unbinds stopping contraction from occurring
What is the function of osteoclasts?
They break down bone tissue
Would the hormone calcitonin released by the thyroid support or inhibit the proliferation of osteoclasts?
Calcitonin would inhibit the proliferation of osteoclasts. Calcitonin acts to decrease blood calcium levels, therefore less osteoclasts would mean less bone breakdown, and less calcium released from the bone.
What constitutes a motor unit?
The nerve axon terminal and the myocytes (muscle fibers) it innervates.
What is the role of the sarcoplasmic reticulum?
To release calcium.
When calcium is released by the sarcoplasmic reticulum, it binds to (troponin/tropomyosin) which triggers a change in the conformation of (troponin/tropomyosin).
Troponin, tropomyosin
Troponin and tropomyosin are both bound to (myosin filaments/actin filaments).
Actin filaments
Explain the cross bridge cycle (myosin binding to actin) in steps.
- Calcium binds to troponin, inducing conformational change and exposing actin filaments.
- Myosin which has ADP+Pi attached to it, binds to the exposed actin site.
- ADP+Pi are released from myosin, causing the power stroke to occur.
- A new ATP binds to myosin, causing myosin to be released from actin.
- Finally the attached ATP is hydrolyzed to ADP which allows the myosin head to cock back into a straight position.
What is summation in terms of muscle contraction?
This is when the muscle fibers are exposed to frequent stimulation by the nerve axons, so it doesn’t give the muscle time to relax. Contractions therefore end up combining to become longer without a relaxation period.
Tetanus occurs when ….?
Muscle contraction is so frequent that the muscle can’t relax at all and it just looks like one big slope on a graph.
How does an action potential travel from a neuron to a muscle cell and reach the sarcoplasmic reticulum so calcium can be released?
AP travels across the axon of a neuron —> post-synaptic potential across at the muscle cell which causes Na channels to fire across the muscle cell membrane —> those AP reach a long indent in the membrane called a T tubule —> t tubule contains protein complexes which bridge with the sarcoplasmic reticulum —> cause Calcium ions to release
What types of muscles contain gap junctions?
Smooth and cardiac muscles
What is creatine phosphate?
A substance that is used by the body to make ATP from during strenuous exercise after all the ATP stores have been depleted in the muscle. It starts to be used about 10sec into a strenuous exercise.
After the first 60secs of strenuous exercise, how does the body supply muscles with ATP?
It utilizes glycolysis by breaking down glycogen stores to glucose, which is oxidized to generate ATP.
Glycolysis is more likely to be used by which type of muscle fiber?
Fast-twitch (white) muscle fibers because they have very few mitochondria so they utilize ways to make ATP outside mitochondrial use.
A side effect of anaerobic metabolism is …?
Lactic acid
Aerobic cellular respiration is likely to be used during a (sprint/2 mile jog).
2 mile jog
The human skeletal system is divided into two parts, what are they?
Axial - Skull, vertebral column, ribcage, and hyoid bone (in the neck used for swallowing)
Appendicular - bones of the limbs, humerus, radius, ulna, carpals, etc, pelvic bones, and scapula, and clavicle
What is the function of tendons?
They attach muscle to bone
What is the function of ligaments?
They attach bone to bone.
Shivering is a (voluntary/involuntary) response controlled by what region of the brain?
Involuntary, hypothalamus
What happens physiologically while shivering?
Core muscle groups under the skin undergo rapid contractions which generate heat.
Spongy bone contains (red or yellow bone marrow) in its interwoven pocket like spaces.
Red bone marrow
The site of blood cell production occurs in the red or yellow bone marrow?
Red bone marrow
What kind of tissue is the bone made of?
Connective tissue derived from embryonic mesoderm.
Spongy bone characteristics
Lattice structure, cavities inside are filled with either yellow or red bone marrow, located at bulbous ends of long bones, makes up more internal parts of flat & irregular bones
Compact bone characteristics
Dense and strong, no pore like appearance, it surrounds the outside of all bones, and makes up the shaft of long bones
Anatomy of a long bone: three parts
Epiphysis - bulbous ends
Metaphysis - connecting part to the middle
Diaphysis - long cylindrical middle part shaft
What is the epiphyseal plate made of?
Cartilaginous structure filled with mitotic cells that contribute to growth
What is the function of ligaments?
To attach bone to bone
What happens to muscle contraction if there is no calcium present?
Muscle contraction cannot occur if there is no calcium release.
What happens to muscle contraction if there is no ATP present?
A condition called rigor mortis which causes the muscles to be stuck in a contracted position because the myosin heads cannot detach from actin since there is no ATP binding after the power stroke.
To perform a delicate movement, recruitment of (few/many) motor units is necessary.
Few
To perform a gross movement, recruitment of (few/many) motor units is necessary.
Many
What is the role of ATP in muscle contraction?
- It binds to myosin, to allow the release of the myosin head from the actin filament.
- It must be hydrolyzed after binding to myosin, so myosin can go back to a straight position.
What is myoglobin?
An iron and oxygen binding protein that contains only 1 subunit, capable of holding 1 O2 molecule
Where is myoglobin found and what is the purpose of it?
It is found in cardiac muscle and skeletal muscle cells; the purpose of it is when muscles use up available oxygen, there is an additional mechanism of obtaining oxygen to keep aerobic respiration going for as long as possible
What are osteocytes?
They are mature bone cells derived from osteoblast which are surrounded by a mineral matrix.
Components of bone matrix
Organic - collagen, glycoproteins
Inorganic - calcium, phosphate, hydroxide ions which together form a compound hydroxyapatite
Structure of bony matrix
Circles called lamellae that surround a longitudinal channel called a Haversian canal (contain blood vessels and nerve fibers)
Where are osteocytes located in the bone?
Between lamellar rings in small spaces called lacunae.
Lacunae are connected through tiny channels called canaliculi which allow for exchange nutrients & wastes.
What are the 4 classification of bones?
Long bones – femur, humerus
Short bones – tarsals, carpals
Flat bones – skull, sternum
Irregular bones – hip, vertebrae
What kind of tissue is cartilage composed of? Describe the characteristics of cartilage.
It’s composed of connective tissue mostly collagen. It is very elastic, found in the nose, ears, and vertebrae, and is avascular (no innervation of blood vessels).
What are the two types of joints?
Movable and immovable
Example of an immovable joint
Bones that are fused together to form sutures; joints in the skull
Example of a movable joints
Hinge joints like elbow and knee, ball-and-socket joints like shoulder and hip (these contain a synovial capsule w/ synovial fluid in them
Example of an antagonistic pair of muscles in the body
Biceps and triceps in the upperarm
Which two hormones increase the resorption of bone (bone breakdown)?
Parathyroid hormone, and vitamin D
AAMC FL SB #16: Which event is directly mediated by a ligand-gated ion channel? Answer is C
A. Release of Ca2+ from the sarcoplasmic reticulum of a muscle fiber to initiate muscle contraction
B. Influx of Na+ across the axon membrane of a somatic neuron during action potential propagation
C. Influx of Na+ across the motor end plate resulting in the depolarization of the muscle fiber membrane
D. Re-entry of Ca2+ back into the sarcoplasmic reticulum of a muscle fiber to end muscle contraction
A. Ca2+ from the sarcoplasmic reticulum is released by voltage gated Ca2+ channels on its membrane.
B. Somatic neurons are those which control skeletal muscles. Key word is axon membrane which only has voltage gated Na channels. Influx of Na++ through voltage-gated Na channels allows the AP to propagate down the axon.
C. This situation refers to the synapse between a neuron & muscle cell. What causes the influx of Na across the motor end plate is the binding of acetylcholine released from the presynaptic neuron to the ligand gated Na channel on the post-synaptic muscle cell, allow Na to rush in.
D. Re-entry of Ca back into sarcolemma is NOT due to a ligand binding. It is due to a Ca2+ ATPase pump (primary active transport).
