Course: Anatomy & Physiology I (BIOL 2301 + BIOL 2101) · Silver Oak University (fictional sample) · Prof. Navarro
Module: Week 10 of 16 · Fall 2026 · in-person, two 75-minute lectures + one weekly lab
Objective covered: Objective 5 — Describe skeletal-muscle structure (down to the sarcomere) and explain the sliding-filament mechanism and the steps of contraction, in order, including the neuromuscular junction.

This file holds two pieces: (A) the Module 10 Overview page ("Start Here") and (B) the Welcome Announcement that drips out when the module opens. Dates below assume a Tuesday/Thursday lecture pattern with Week 10 meeting Tue Nov 3 and Thu Nov 5, a lab that same week, and end-of-week work due Sunday Nov 8, 11:59 p.m. Adjust the day-of-week and times to match your section.

(A) Module 10 Overview — Start Here

Welcome to Week 10: How a Muscle Actually Moves

This is your home base for the week. Read it first, then work the checklist below from top to bottom. Everything you need is linked inside the module.

Last week you built the skeleton and its joints. This week we power them. You decide to lift a cup, and a fraction of a second later your forearm flexes — and in that sliver of time a stunningly ordered chain of events fires: a nerve signals, a chemical crosses a tiny gap, an electrical wave sweeps the muscle, calcium floods out of storage, and millions of microscopic molecular "hands" grab and pull. This week we slow that instant down, name the contractile machinery down to the sarcomere, and learn the steps of contraction in their exact order. Two old habits carry us: structure determines function, and — new this week — order matters.

The week's big question

"What are the parts of the muscle that actually contract, and in what exact order do the events run from a nerve firing to a filament sliding?"

By Friday you'll name the muscle hierarchy down to the sarcomere, tell actin (thin) from myosin (thick), explain why the filaments slide rather than shrink, and narrate the contraction sequence — ACh → action potential → calcium → troponin/tropomyosin → cross-bridge — without a misstep.

By the end of this week, you can…

Use this as a checklist. If you can do all four out loud, you're ready for the quiz.

• [ ] Walk the skeletal-muscle hierarchy (muscle → fascicle → fiber → myofibril → sarcomere) and name the sarcomere as the contractile unit, bounded by Z discs, with actin = thin and myosin = thick filaments.
• [ ] Explain the sliding-filament model — the thin filaments slide past the thick filaments toward the center so the Z discs pull closer; the filaments themselves do not shorten.
• [ ] Put the steps of contraction in order: motor-neuron AP → ACh at the NMJ → muscle AP down the T-tubules → Ca²⁺ from the sarcoplasmic reticulum → Ca²⁺ binds troponin → tropomyosin uncovers actin's binding sites → myosin cross-bridges pull (power stroke, needs ATP) → relaxation.
• [ ] Tie structure to function — explain why a fiber rich in mitochondria resists fatigue, and why ATP is needed for both contraction and relaxation (and why rigor mortis happens without it).

What's due this week, and when

Work these in order — each one gets you ready for the next.

Heads-up on the AI tools: you'll use a chatbot to draft and explain, and then you judge its work against what we cover in class. Chatbots routinely scramble the contraction steps (putting calcium before the action potential, or forgetting the NMJ), claim the filaments shorten, or swap actin and myosin. Catching the model is the point — in the tutorial, the assignment, and the lab.

Late policy reminder: 10% off per day late. If life happens, reach out before the deadline — I'd much rather hear from you early.

How to succeed this week

• Lead with the idea, not the jargon. A contraction is just nerve says go → chemical crosses → muscle fires → calcium comes out → the gate opens → the hands pull. Learn that plain story first; the names (ACh, troponin, sarcoplasmic reticulum) snap onto it after.
• Memorize two tiny hooks. "Actin is thin; myosin is thick." And "The filaments slide, they don't shrink."
• Drill the order until it's automatic. Five beats: ACh → action potential → calcium → troponin/tropomyosin → cross-bridge/slide. Say them in the car. This week, the sequence is the single most-tested idea, and it's the one a chatbot scrambles.
• Keep ATP in two places. It powers the pull (the power stroke) and the release/reset — which is exactly why a body in rigor mortis locks up when the ATP runs out.
• Treat the chatbot as a smart intern, not an oracle. It drafts; you check — especially the order of the steps. That habit is the whole semester in miniature, and in physiology the order is the meaning.

You don't need to memorize every band of the sarcomere — you need the parts that do the work (actin, myosin, Z disc), the one big idea (sliding), and the one sequence (the steps). Come to class ready to narrate a contraction out loud. See you Tuesday.

(B) Welcome Announcement — Module 10

Release setting: post on the module's start day (offset = 0 days), i.e., Tue Nov 3, 2026 — not before. If your platform won't preserve the scheduled date on import, post this as a draft labeled "Release: Tue Nov 3."

Subject: Welcome to Week 10 — the split-second chain that moved your hand 💪

Hi everyone, and welcome to Week 10!

Quick thought experiment before we start: right now, decide to make a fist — and do it. It felt instant. But in that fraction of a second, a precise, ordered chain fired inside your forearm: a nerve signaled, a chemical (acetylcholine) crossed a tiny gap, an electrical wave swept the muscle, calcium poured out of storage, a molecular gate swung open, and tiny myosin "hands" grabbed actin and pulled. You felt none of the steps — this week we name every one, in order.

This week — Muscle Tissue & the Physiology of Contraction — we tackle the big question: What parts of a muscle actually contract, and in what exact order do the events run from a nerve firing to a filament sliding? By Friday you'll zoom from a whole muscle down to the sarcomere, tell actin (thin) from myosin (thick), explain why the filaments slide rather than shrink, and walk the contraction sequence without a stumble.

Three things not to miss:
1. Lecture Tutorial 10 — work through the sarcomere, the sliding-filament idea, and the steps of contraction with one approved chatbot (Gemini, Claude, or ChatGPT) and submit the share link. You'll catch the model when it scrambles the order. Due Sun Nov 8.
2. Lab 10 ("Feel the Fatigue"), Quiz 10, Discussion 10, and Assignment 10 also close Sun Nov 8 — the lab has you measure your own grip fatigue, no equipment needed, then tie the curve back to ATP and the sliding-filament cycle.
3. Open the Start Here page first — it lays out everything in order with due dates.

One promise: this is the week the molecules stop being abstract. By Friday, the next time you pick something up, you'll be able to narrate exactly what your muscle did — step by step — and you'll know why your grip gives out when the ATP runs low.

Bring your curiosity (and your own two hands) to class on Tuesday.

See you soon,
Prof. Navarro