BIO 304 . Human Anatomy & Physiology . Week 4

Week 4 Workbook — Muscle & Nervous (Start)

Days 13 through 16 . Print one packet, work the whole week.

Print this whole packet at the start of the week and use it as you work through the videos and interactive notes for the days listed below. Each day starts on a fresh page so it’s easy to keep them organized.

Day 13 · Skeletal Muscle Microanatomy
Day 13 · Motor Units & Muscle Mechanics
Day 14 · Sliding Filament & Cross-Bridge Cycle
Day 15 · Neurons & Resting Membrane Potential
Day 16 · Action Potentials & Synaptic Transmission

Day 13

Skeletal Muscle Microanatomy

BIO 304 . WEEK 4 . MONDAY . LAB WORKBOOK

Skeletal Muscle Microanatomy

From whole muscle down to the sarcomere: the structural ladder of contractile tissue.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Today you will draw the muscle hierarchy from the outside in, then a single sarcomere in detail. Use two boxes below. Box A is for the hierarchy. Box B is for the sarcomere close-up. Sketch, do not trace.

Box A. Hierarchy (whole muscle to myofibril)

Directions

Draw a long oval representing a whole muscle (cross-section). Wrap it in a thin line. Label that line Epimysium.
Inside the oval, draw three or four smaller circles. Each is a fascicle. Wrap one of them with a thin line. Label that line Perimysium.
Inside one fascicle, draw several smaller circles. Each is a muscle fiber (cell). Wrap one with a thin line. Label that line Endomysium.
Inside one muscle fiber, draw a stack of long rods. Each rod is a myofibril. Label one Myofibril.
Above your hierarchy, write the order of wrappings from outside to inside in one short sentence.

Draw here. Sketch by hand.

Box B. Sarcomere close-up

Directions

Draw a long rectangle. Mark the left and right ends with vertical lines. Label both lines Z line.
In the center, draw a vertical line. Label it M line.
Between the two Z lines, draw thick filaments (myosin) in the middle and thin filaments (actin) extending from each Z line.
Bracket and label the A band (the full length of the thick filaments).
Bracket and label the I band (the region with only thin filaments).
Bracket and label the H zone (the central thick-only region).
Draw a T-tubule entering from above and a sarcoplasmic reticulum wrapping the myofibril. Label both.

Draw here. Sketch by hand.

1C. Structures to label (15)

After you finish each drawing, label every structure below directly on your sketch.

Epimysium
Perimysium
Endomysium
Muscle fiber (cell)
Myofibril
Sarcomere
Z line
M line
A band
I band
H zone
Thick filament (myosin)
Thin filament (actin)
T-tubule
Sarcoplasmic reticulum

Part 2 of 2

Physiology Lab

2A. Mechanism trace: from action potential to power stroke

An action potential has just arrived at the sarcolemma of a muscle fiber. List the next 8 events that lead to a single power stroke. For each event, name WHERE it happens (which structure), WHAT moves (ion or molecule), and what changes STRUCTURALLY at the sarcomere.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. The I band shortens dramatically during contraction, but the A band barely changes length. Explain why, in terms of which filaments make up each band.

2. A toxin disrupts the triad junctions specifically (the points where T-tubules meet the SR). Predict the effect on contraction and explain at which step the cycle fails.

3. A muscle is stretched so far that thick and thin filaments no longer overlap. Predict the tension the muscle can generate at this length, and justify your answer using the cross-bridge mechanism.

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.

Day 13

Motor Units & Muscle Mechanics

BIO 304 . WEEK 4 . MONDAY . LAB WORKBOOK

Motor Units and Muscle Mechanics

Motor unit organization, recruitment, summation, and fatigue.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

You will draw two motor units side by side. One is small (for fine control, like an extraocular eye muscle). One is large (for power, like the quadriceps). The contrast in your drawing should make the size principle obvious.

Box A. Two motor units, side by side

Directions

On the LEFT, draw a small circle for a motor neuron cell body in the ventral horn of the spinal cord. Extend an axon downward.
Branch the axon into 5 short terminals, each ending on a different muscle fiber. Draw 5 short ovals as the muscle fibers.
Label this side Small motor unit (eye muscle).
On the RIGHT, draw another cell body and axon. Branch it into many terminals (draw 12 to 20). Draw the same number of muscle fibers.
Label this side Large motor unit (quadriceps).
Add labels: Motor neuron cell body, Axon, Axon terminal, Neuromuscular junction, Muscle fiber.

Draw here. Sketch by hand.

Box B. Twitch summation (force vs time)

Directions

Draw an x-axis (time) and a y-axis (force).
On the same axes, sketch three force traces stacked vertically by frequency.
Trace 1: single twitches at 1 Hz. Force rises and falls completely between each stimulus. Label Single twitches.
Trace 2: stimulation at 10 Hz. The second twitch starts before the first finishes; force adds up. Label Wave summation.
Trace 3: stimulation at 30 Hz. Twitches fuse into a smooth, sustained plateau. Label Complete tetanus.
Below the graph write one sentence: why does higher frequency produce more force?

Draw here. Sketch by hand.

1C. Structures to label (10)

After you finish each drawing, label every structure below directly on your sketch.

Motor neuron cell body
Axon
Axon terminal
Neuromuscular junction
Muscle fiber
Small motor unit
Large motor unit
Single twitch
Wave summation
Complete tetanus

Part 2 of 2

Physiology Lab

2A. Fiber type comparison table

Fill in the table below. Use one short phrase per cell. After the table, answer the two interpretation questions in complete sentences.

Property	Type I (slow oxidative)	Type IIa (fast oxidative)	Type IIx (fast glycolytic)
Myosin ATPase rate
Mitochondria density
Capillary supply
Fatigue resistance
Primary energy system

Which fiber type would dominate the postural muscles of the back? Justify in one sentence.

A 100-meter sprinter and a marathon runner are tested. Whose calves would have a higher percentage of Type IIx fibers? Whose would have the most mitochondria? Justify each.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Eye muscles are innervated by very small motor units (only a handful of fibers each). Explain why this design works beautifully for precision tracking but would fail for lifting a heavy object.

2. Apply the size principle. A person picks up a coffee cup. Then the same person attempts a deadlift. Which motor units are recruited in each case, and in what order?

3. Train a sprinter on explosive jumping and a marathoner on long slow distance for six months. Predict which fiber type each adapts most strongly and the physiological mechanism behind the adaptation.

3. What to submit

Day 14

Sliding Filament & Cross-Bridge Cycle

BIO 304 . WEEK 4 . TUESDAY . LAB WORKBOOK

Sliding Filament and the Cross-Bridge Cycle

How calcium, ATP, actin, and myosin convert chemical energy into mechanical force.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

You will draw the cross-bridge cycle as a 4-step loop. Draw a large square. At each corner, draw what myosin and actin look like at that step. Use arrows to show the direction of the cycle (clockwise).

Box A. The 4-step cross-bridge cycle

Directions

Draw a large square that fills the box.
Top-left corner: COCKING. Draw a myosin head in its high-energy, cocked position. Label it. Note that ATP has just been hydrolyzed to ADP plus Pi, both still bound to myosin.
Top-right corner: BINDING. Draw the myosin head attached to actin. Note that calcium has bound troponin and tropomyosin has shifted to expose the actin binding site.
Bottom-right corner: POWER STROKE. Draw the myosin head pivoted, pulling actin toward the M line. Note that ADP and Pi are released.
Bottom-left corner: DETACHMENT. Draw the myosin head with a NEW ATP bound, released from actin. Note that ATP binding is required for detachment.
Connect the corners with clockwise arrows. Mark every step where ATP is consumed or required.

Draw here. Sketch by hand.

Box B. Calcium release and reuptake

Directions

Draw the sarcolemma at the top of the box, with an action potential arriving (use a small arrow).
Draw a T-tubule diving down from the sarcolemma into the cell.
Draw the sarcoplasmic reticulum wrapping a myofibril below.
Add arrows showing Ca-squared-plus flowing OUT of the SR into the cytoplasm during stimulation.
Draw a second small panel beside this one labeled Relaxation. Show the SR Ca-squared-plus ATPase pumping calcium BACK into the SR.
Label every structure: Sarcolemma, T-tubule, Sarcoplasmic reticulum, Triad, SR calcium ATPase.

Draw here. Sketch by hand.

1C. Structures to label (15)

After you finish each drawing, label every structure below directly on your sketch.

Myosin head (cocked)
Myosin head (bound)
Myosin head (post power stroke)
Actin binding site
Troponin
Tropomyosin
Calcium (Ca2+)
ATP
ADP + Pi
Power stroke arrow
Sarcolemma
T-tubule
Sarcoplasmic reticulum
Triad
SR Ca2+ ATPase

Part 2 of 2

Physiology Lab

2A. Sequencing puzzle: from nerve to power stroke

Below are 10 events involved in producing a single power stroke. They are listed in SCRAMBLED order. Rewrite them in the correct sequence in the numbered space provided. Start with the motor neuron action potential and end with the power stroke.

Scrambled events:

Voltage-gated calcium channels open at the axon terminal.
Myosin head pivots and pulls actin toward the M line.
Acetylcholine binds nicotinic receptors on the sarcolemma.
Action potential reaches the axon terminal of the motor neuron.
Calcium binds troponin; tropomyosin shifts off the binding site.
Sarcolemma depolarizes; action potential travels along T-tubules.
Sarcoplasmic reticulum releases calcium into the cytoplasm.
Acetylcholine is released into the synaptic cleft.
Myosin head binds the exposed site on actin (cross-bridge forms).
ATP is hydrolyzed; myosin head cocks into its high-energy position.

Your sequence (write the events in correct order):

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Rigor mortis sets in hours after death. Explain the molecular mechanism using your cycle drawing. Which step cannot proceed, and why?

2. Curare blocks the nicotinic acetylcholine receptor at the neuromuscular junction. At which step does the entire chain stall, and what is the patient's clinical picture?

3. Malignant hyperthermia is caused by a mutation that makes the SR calcium release channel hyperactive in response to certain anesthetics. Walk through the cycle and explain why body temperature climbs so rapidly.

3. What to submit

Day 15

Neurons & Resting Membrane Potential

BIO 304 . WEEK 4 . THURSDAY . LAB WORKBOOK

Neurons and Resting Membrane Potential

Neuron anatomy, glia, and how the resting potential is built and maintained.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Two drawings today. Box A is a labeled neuron. Box B is a close-up of a patch of resting membrane showing the pumps, channels, and ion distribution responsible for the resting potential.

Box A. The neuron

Directions

Draw a cell body (soma) as an irregular circle. Show a nucleus inside.
Add 3 to 5 short branched dendrites projecting from the soma.
Extend a single long process from the opposite side. Label its base Axon hillock.
Wrap the axon with discrete myelin segments. Show at least 2 unmyelinated gaps. Label one gap Node of Ranvier.
Identify which cell type makes the myelin: if CNS, an oligodendrocyte; if PNS, a Schwann cell. Pick one and label it.
End the axon in several axon terminals (small swellings). Label one.

Draw here. Sketch by hand.

Box B. Resting membrane close-up

Directions

Draw a horizontal rectangle representing a patch of plasma membrane. Label the top Outside (extracellular) and the bottom Inside (cytoplasm).
Draw a Na-K ATPase pump straddling the membrane. Show arrows: 3 Na-plus leaving the cell, 2 K-plus entering, ATP being consumed.
Draw at least 2 K-plus leak channels in the membrane. Show K-plus leaking OUT down its gradient.
On the outside, write a large Na-plus and a small K-plus. On the inside, write a small Na-plus and a large K-plus. (Show which ion is more concentrated where.)
Indicate charge: a row of minus signs lining the inside of the membrane and plus signs lining the outside.
In the corner, write the resting potential value: about negative 70 millivolts.

Draw here. Sketch by hand.

1C. Structures to label (14)

After you finish each drawing, label every structure below directly on your sketch.

Dendrites
Cell body (soma)
Nucleus
Axon hillock
Axon
Myelin sheath
Node of Ranvier
Schwann cell or oligodendrocyte
Axon terminal
Na+/K+ ATPase
K+ leak channel
Na+ (high outside)
K+ (high inside)
Resting membrane potential (-70 mV)

Part 2 of 2

Physiology Lab

2A. Calculation: who builds the resting potential?

Use your Box B drawing as the reference. Answer each question. Show short work where math is involved.

1. Per ATP, the Na+/K+ ATPase moves 3 Na+ out and 2 K+ in. What is the NET charge moved across the membrane per cycle, and in which direction?

2. Does this NET pump activity make the inside more negative or more positive on its own? Explain.

3. The membrane is also leaky to K+. Which direction does K+ flow through these leak channels at rest, and why (give the gradient driving it)?

4. Of the two mechanisms (pump electrogenicity vs K+ leak), which contributes MORE to the -70 mV resting potential? Justify in one or two sentences.

5. Predict the resting potential of a cell that has lost ALL its K+ leak channels but still has a working Na+/K+ ATPase.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Ouabain blocks the Na+/K+ ATPase. Predict the resting membrane potential at: (a) 5 seconds, (b) 5 minutes, (c) 5 hours after exposure. Explain the trajectory.

2. Match each glial cell to one function: astrocyte, oligodendrocyte, microglia, Schwann cell, ependymal cell. Pick from: makes myelin in CNS; makes myelin in PNS; immune surveillance; blood brain barrier support; produces CSF.

3. A neuron in cold seawater has a resting potential of -90 mV instead of -70 mV. Propose one mechanistic explanation involving the Na+/K+ ATPase or the K+ leak channels.

3. What to submit

Day 16

Action Potentials & Synaptic Transmission

BIO 304 . WEEK 4 . FRIDAY . LAB WORKBOOK

Action Potentials and Synaptic Transmission

Phases of the action potential, propagation, and how chemical synapses pass the signal on.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Two drawings today. Box A is the action potential graph with channel-state bars. Box B is the chemical synapse. Be precise: the values on the y-axis matter.

Box A. Action potential graph

Directions

Draw an x-axis (time, in milliseconds) and a y-axis (membrane voltage, mV, from -90 to +40).
Plot a single action potential. Start at the resting potential (-70 mV). Rise to threshold (-55 mV). Spike up to about +30 mV. Fall through 0 back down. Dip slightly below -70 mV (afterhyperpolarization) before returning to rest.
Label each phase on the curve: Resting, Threshold, Depolarization, Peak, Repolarization, Hyperpolarization, Return to rest.
Below the graph, draw 3 horizontal bars showing when these channels are OPEN, aligned with the curve above: Voltage-gated Na+ (activation gate), Voltage-gated Na+ (inactivation gate closes during peak), Voltage-gated K+.
Mark the absolute refractory period and the relative refractory period on the time axis.

Draw here. Sketch by hand.

Box B. Chemical synapse

Directions

Draw an axon terminal (presynaptic) at the top. Inside it, sketch a cluster of synaptic vesicles. Label them.
Show voltage-gated Ca-squared-plus channels in the presynaptic membrane, with arrows of Ca-squared-plus entering when an AP arrives.
Draw the synaptic cleft as a small gap below.
Draw the postsynaptic membrane below the cleft. Show ligand-gated receptors embedded in it.
Show neurotransmitter molecules being released into the cleft and binding the postsynaptic receptors.
Label: Action potential arriving, Voltage-gated Ca2+ channel, Synaptic vesicle, Neurotransmitter, Synaptic cleft, Postsynaptic receptor.

Draw here. Sketch by hand.

1C. Structures to label (16)

After you finish each drawing, label every structure below directly on your sketch.

Resting potential (-70 mV)
Threshold (-55 mV)
Peak (+30 mV)
Depolarization
Repolarization
Hyperpolarization
Absolute refractory period
Relative refractory period
Voltage-gated Na+ channel
Voltage-gated K+ channel
Axon terminal
Voltage-gated Ca2+ channel
Synaptic vesicle
Neurotransmitter
Synaptic cleft
Postsynaptic receptor

Part 2 of 2

Physiology Lab

2A. Sequence the synapse

Number the following 7 events in the correct order at a chemical synapse, starting from the action potential arriving at the axon terminal and ending with a change in the postsynaptic neuron's membrane potential.

Scrambled events:

Neurotransmitter binds receptors on the postsynaptic membrane.
Action potential arrives at the axon terminal.
Voltage-gated calcium channels open; calcium flows in.
An EPSP or IPSP is generated in the postsynaptic neuron.
Synaptic vesicles fuse with the presynaptic membrane.
Neurotransmitter diffuses across the synaptic cleft.
Neurotransmitter is released into the synaptic cleft.

Your sequence (write the events in correct order):

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Saltatory conduction is much faster than continuous conduction. Explain the structural reason in terms of where voltage-gated channels cluster and what the action potential actually does between nodes.

2. Why does a neuron need an inactivation gate on its voltage-gated Na+ channel? Predict what propagation would look like if this gate did not exist. Why is unidirectional conduction important?

3. SSRIs immediately block serotonin reuptake (within minutes), yet clinical relief from depression takes 4 to 6 weeks. Propose a mechanism for this lag. What downstream changes might account for it?