Skeletal Muscle System

What is the function of the muscular system? How do muscles work?

Generate force for movement, maintain posture, and produce heat. Muscles work through a process where nerve impulses cause them to contract and relax.

What are the various bands that are visible in striated muscle? (why do they look “stripey?”)

The "stripey" or striated appearance of muscle is caused by the precise, repeating arrangement of the contractile proteins actin (thin filaments) and myosin (thick filaments) within functional units called sarcomeres. This organization creates alternating light and dark bands visible under a microscope. 

Distinguish between cardiac, smooth and skeletal muscle tissue. Where are they found? What do they do? How are they controlled? Do they look different?

Cardiac: In walls of heart, Pump blood throughout body, controlled involuntarily, Are striped short, branched fibers typically have sing nucleus connected by intercalated discs

Skeletal: Attached to bone and tendons, Movement of the body or facial expression, Voluntary, appears striated long cylindrical fibers and multinucleated cells

Muscle: Walls are hallow internal organs like stomach, intestines, blood vessels. Moves substances through internal tracts like digestive tracks or blood flow. Involuntary. Nonstriated(smooth) spindle shaped cells and single centrally located nucleus

What are myofibrils? What are the thick and thin filaments? What are they made of (which is actin, which is myosin)?

Myofibrils are fibers that extend along the length of muscle fibers and are the main functional units of muscle contraction. Thick filaments are primarily composed of myosin and has a long tail region and forms a globular head region which can bind to actin and hydrolyze ATP to generate force. Thin filaments are made from actin they polymerize into a two strand helix.

What are the accessory proteins discussed here? What do the accessory proteins do?

Troponin: Calcium-binding protein that regulates the position of the tropomyosin. Tropomyosin: In a resting muscle, strands of tropomyosin bind lengthwise along the groove of the actin filament, covering the myosin-binding sites and preventing actin-myosin interaction. A nerve impulse releases Ca ions and bind to troponin which causes change moving tropomyosin away form the binding sites on the actin. The exposed myosin heads bidn to actin forming cross bridges. They then use energy form ATP hydrolysis to pull th thin filaments past the thick filaments known as the power stroke.

Explain basically how muscle contraction occurs including the sliding filament theory in the level of detail we discussed in class as well as the ultimate result. What happens, how does the muscle contract, how is ATP involved? What happens when the action potential is over? 

A nerve action potential reaches the muscle fiber, causing the sarcoplasmic reticulum to release Ca²⁺. Calcium binds to troponin, which moves tropomyosin off the actin binding sites. This allows myosin heads to attach to actin and perform a power stroke—this is the sliding filament theory, where actin and myosin filaments slide past each other and the sarcomere shortens, producing contraction.

How is ATP involved in muscle contractions

ATP is required to:

1. Reset (cock) the myosin head into a high-energy position.

2. Detach myosin from actin after the power stroke.

3. Pump Ca²⁺ back into the sarcoplasmic reticulum.

What happens when the action potential is over in muscle contractions.

When the action potential ends, Ca²⁺ is pumped back into the SR, tropomyosin covers actin again, cross-bridges stop forming, and the muscle relaxes.

What is a sarcomere?

a structural unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band.

What is a neuromuscular junction? What type of neurons are involved? Which division of the nervous system? What neurotransmitter is released? How does the "signal" to contract reach deep into the muscle fiber? What parts of the cell are specialized in muscles to support/regulate contraction (at the level of detail we discussed in class)?

A neuromuscular junction is where a motor neuron meets a muscle fiber. These neurons are part of the somatic (voluntary) nervous system. They release the neurotransmitter acetylcholine (ACh). The contraction signal travels deep into the muscle through T-tubules, which carry the action potential inside. The sarcoplasmic reticulum (SR) stores and releases Ca²⁺ to start contraction, and myofibrils (with actin and myosin) do the actual contracting.

Where does the energy for muscle contraction come from?

adenosine triphosphate (ATP).

How is cellular respiration involved in muscle contraction? What happens if there is not enough oxygen for sufficient ATP production?

Cellular respiration makes ATP, which muscles need to power the myosin “pulling” during contraction.
If there isn’t enough oxygen, the muscle switches to anaerobic respiration, which makes much less ATP and produces lactic acid, causing the muscle to get tired and sore.

How does exercise affect muscles?

Exercise affects muscles by causing microtears that stimulate repair and growth, leading to increased size and strength through a process called hypertrophy. It also improves the body's ability to use energy and oxygen, enhances neural control, and strengthens the muscles' ability to function, which reduces fatigue and promotes overall muscle health. 

What is creatine phosphate?

a high-energy molecule found primarily in muscle and brain tissue that serves as a rapid energy reserve to quickly regenerate ATP, the primary energy currency of cells.

How do the types of muscle fibers relate to athletic ability?

slow-twitch (Type I) fibers favoring endurance activities and fast-twitch (Type II) fibers favoring power and speed.

What are the diseases we discussed related to the excitation of muscle fibers and what aspect is impaired (basics here)?

In AL S, motor neurons in the spinal cord and brainstem degenerate, and muscle fibers atrophy

– Myasthenia gravis is an autoimmune disease that attacks acetylcholine receptors on muscle fibers, reducing signal transmission

How do cardiac muscles contract? What is the function of the SA node? Voluntary? (we'll also do more on this later)

Contract through calcium-induced calcium release(CICR). Sinoatrial node serves as the heart’s pacemaker which is Involuntary

Where do you find smooth muscle? Is it striated? Voluntary?

What are the major functions of the skeletal system?

Provide structure and protection to the body

The skeleton comes in three forms: what are they? How do they work? Who (general) has which kind? Advantages/disadvantages?

Hydrostatic skeleton

• What it is: Fluid-filled body that muscles push against.

• Who has it: Worms, jellyfish.

• How it works: Muscles squeeze the fluid to change shape and move.

• Pros: Flexible, good for burrowing.

• Cons: Not good for heavy support.

2. Exoskeleton

• What it is: Hard outer shell.

• Who has it: Insects, crabs.

• How it works: Muscles pull on the inside of the shell.

• Pros: Strong protection.

• Cons: Must molt to grow; heavy.

3. Endoskeleton

• What it is: Hard skeleton inside the body.

• Who has it: Vertebrates (humans, dogs, fish).

• How it works: Muscles attach to bones and pull to move.

• Pros: Can grow with the organism; good support.

• Cons: Less external protection.

What are antagonistic muscles?

pairs of muscles that work in opposition to create movement

What are the major roles of the vertebrate endoskeleton? What are they made of? What does each part do (covered in detail in questions below).

The vertebrate endoskeleton has four major roles:

1. Support – holds the body up.

2. Protection – shields organs (skull, ribs, spine).

3. Movement – provides places for muscles to attach and pull on.

4. Blood cell production & mineral storage – bones make blood cells and store calcium/phosphorus.

It’s made of bone and cartilage:

• Bone gives strong support, protects organs, stores minerals, and makes blood cells.

• Cartilage provides flexible support and reduces friction in joints.

What are the appendicular & axial skeleton.

The axial skeleton is the central core of the body, including the skull, vertebral column, ribs, and sternum, and its primary function is to protect vital organs. The appendicular skeleton is made up of the limbs and the girdles that attach them to the axial skeleton (pectoral and pelvic girdles) and is responsible for movement

What are the 3 types of connective tissues in vertebrate skeletal systems? Where are they found? What are tendons? Why aren't they fully/solely in the skeletal system.

The 3 connective tissues in vertebrate skeletal systems are:

1. Bone – hard tissue found in the skeleton; supports, protects, stores minerals, makes blood cells.

2. Cartilage – flexible, smooth tissue found in joints, nose, ears, and between ribs.

3. Ligaments – tough bands that connect bone to bone at joints.

Tendons are strong cords that connect muscle to bone.
They aren’t fully part of the skeletal system because they involve the muscular system too—they transfer muscle force to bones so movement can happen.

What is the function of cartilage? Function of ligaments?

Cartilage covers bone surfaces to reduce friction and provides shock absorption, while ligaments connect bone to bone to provide joint stability and limit movement. Cartilage is a flexible padding between bones, whereas ligaments are strong, fibrous connective tissues that hold joints together. 

What are the 3 types of bone cells? What do osteoclasts and osteoblasts do?

Osteoblasts: Build

Osteoclasts: Break down and release calcium

Osteocytes

What is red bone marrow? Where is it found? What is produced there?

Red bone marrow is a spongy, jelly-like tissue inside bones that produces blood cells. In adults, it is primarily found in the pelvis, sternum, ribs, vertebrae, skull, and the upper parts of the femur and humerus. It generates red blood cells, white blood cells, and platelets from stem cells. 

What is bone remodeling? When does it occur? In response to what?

Bone remodeling is the continuous process of breaking down old bone (resorption) and building new bone (formation). It occurs throughout a person's life and is triggered by age, physical stress on bones, hormones, and the body's need to maintain blood calcium levels. 

What happens when bone reabsorption outpaces bone deposition? When is this more likely to occur? Why? How can someone reduce risk of this?

If bone resorption (breaking down old bone) happens faster than bone deposition (building new bone), bones become weak, thin, and brittle—this leads to osteoporosis.

This is more likely in:

• Older adults, especially post-menopausal women, because lower estrogen speeds up bone loss.

• People with low calcium/vitamin D, little exercise, or long-term inactivity.

To reduce risk:

• Do weight-bearing exercise (walking, lifting).

• Get enough calcium and vitamin D.

• Avoid smoking and excess alcohol.

• Maintain overall healthy diet and activity.