Lecture 2: Introduction and Muscles

What is the comparative method?

Examining patterns across species to infer past evolutionary processes.

Why do many land animals have invaginated breathing organs?

Because this trait is adaptive for living on land.

How does variation within a species help biologists?

It reveals which traits are most advantageous under natural selection.

What was shown in deer mice at high altitude?

Mice with higher VO2​ (thermogenic capacity) were more likely to survive harsh winters.

How does physiology differ across populations (e.g., plains vs mountains)?

High-altitude populations average higher VO2 due to colder, harsher conditions.

What is a clade?

A group of organisms with shared derived characteristics.

What did icefish teach us about evolution?

Myoglobin (Mb) was lost four times in the icefish clade, showing when and why traits can disappear.

What is homeostasis?

Maintaining relative stability of the internal environment.

What are the parts of a feedback control system?

Regulated variable → sensors → integrating center → effectors → compensatory response (negative feedback).

What is negative feedback?

A response that counteracts a change to restore the set point.

What is the difference between a conformer and a regulator?

• Conformer: internal conditions change with the environment.

• Regulator: internal conditions are kept constant.

Can one species be both?

Yes—depends on the variable (e.g., salmon conform for temperature but regulate blood Cl⁻).

What are the three muscle types in vertebrates?

Skeletal, smooth, and cardiac.

Where is smooth muscle found?

Blood vessels, GI tract, uterus; it has no striations.

What defines skeletal muscle?

Usually attached to bones; striated; used for movement.

What makes cardiac muscle unique?

Shares traits of skeletal and smooth muscle; many gap junctions.

What is a sonic muscle?

A specialized muscle (e.g., in toadfish) that produces sound to attract mates.

What properties can muscles vary in?

Size, morphology, microscopic structure, strength, velocity, energetic efficiency.

What is a muscle fiber?

A long, narrow, excitable cell.

What triggers muscle contraction?

An increase in intracellular Ca²⁺.

What is excitation–contraction coupling?

Linking membrane excitation to Ca²⁺-driven contraction.

What are myofibrils made of?

Repeating units called sarcomeres.

What is a sarcomere?

The functional unit of contraction between two Z-lines.

What are A bands and I bands?

• A band: thick (myosin) filaments

• I band: thin (actin) filaments

What is the H zone?

Region of the A band with only myosin (no overlap).

What is the M-line?

Middle of the H-zone; holds myosin filaments together.

What anchors myosin to the Z-line?

The protein titin.

What makes up thick filaments?

Myosin molecules (hundreds per filament).

What is myosin made of?

• 2 heavy chains

• 2 regulatory light chains

• 2 essential light chains

• 2 globular heads

What does the myosin head do?

Binds actin and hydrolyzes ATP to generate force.

What makes up thin filaments?

Actin (G-actin → F-actin) plus regulatory proteins.