Human Physiology I — High-Yield Review

Highest-Yield Facts by Unit

Unit 1 — Foundations

• High yield: Negative feedback opposes a change; positive feedback amplifies it (childbirth, action-potential upstroke, clotting).
• Body fluids: ICF (~2/3) vs ECF (~1/3); ECF = interstitial + plasma.

Unit 2 — Membrane Transport

• High yield: Diffusion (down gradient, no energy) vs facilitated (carrier/channel) vs primary active (ATP, Na/K pump) vs secondary active (uses ion gradient).
• Osmolarity = total solutes; tonicity = effect of nonpenetrating solutes on cell volume.

Unit 3 — Neurophysiology

• High yield: Resting potential ≈ −70 mV (K+ leak); Nernst = single-ion equilibrium; GHK = multi-ion.
• Graded potentials = decremental, summate; action potential = all-or-none, threshold-triggered.

Unit 4 — Synaptic Transmission

• High yield: EPSP (depolarizing) vs IPSP (hyperpolarizing); spatial + temporal summation at the axon hillock decide firing.
• Ionotropic = ligand-gated channel (fast); metabotropic = GPCR/second messenger (slow).

Unit 5 — Muscle

• High yield: E-C coupling = Ca²⁺ released from SR binds troponin C → tropomyosin shifts → cross-bridge cycle.
• Cross-bridge: ATP binding → hydrolysis (cock) → power stroke → detachment; rigor mortis = no ATP.

Unit 6 — CNS

• High yield: Cerebellum = coordination; basal ganglia = movement initiation; hippocampus = memory (LTP via NMDA/AMPA).
• Stretch reflex = monosynaptic (muscle spindle); Golgi tendon = inverse myotatic (protection).

Unit 7 — ANS

• High yield: Sympathetic = fight-or-flight (norepinephrine, adrenergic); parasympathetic = rest-and-digest (acetylcholine, muscarinic).
• Both use ACh at ganglia; sympathetic also uses ACh at sweat glands.

Unit 8 — Sensory

• High yield: Phasic receptors adapt (Pacinian = vibration); tonic receptors sustain (nociceptors).
• Dorsal column-medial lemniscus (fine touch) vs spinothalamic (pain/temperature); both cross (contralateral).

Unit 9 — Endocrine

• High yield: Peptide/amine (hydrophilic) → membrane receptors; steroid/thyroid (lipophilic) → intracellular receptors.
• HPA axis (CRH→ACTH→cortisol); HPT axis (TRH→TSH→thyroid); negative feedback throughout.

Comparison Tables

Cumulative Self-Check (20 questions)

1. Differentiate negative from positive feedback.
2. Which compartment holds ~2/3 of body water?
3. Define tonicity.
4. Name the three mechanisms of passive transport.
5. What does the Na⁺/K⁺-ATPase pump do per cycle?
6. What is the approximate resting membrane potential, and which ion dominates it?
7. Differentiate a graded potential from an action potential.
8. Name the two refractory periods and their significance.
9. Differentiate an electrical from a chemical synapse.
10. What is an EPSP, and where does summation occur?
11. Sequence excitation-contraction coupling.
12. What causes rigor mortis?
13. Differentiate the roles of cerebellum and basal ganglia.
14. What is long-term potentiation, and which receptors are involved?
15. Name the neurotransmitter and receptor class for the sympathetic and parasympathetic effectors.
16. Differentiate phasic from tonic receptors.
17. Which pathway carries pain/temperature, and is it ipsilateral or contralateral?
18. Differentiate peptide from steroid hormone signaling.
19. Trace the HPA axis.
20. What is the primary difference between autocrine, paracrine, and endocrine signaling?

Answers and Rationales

1. Negative feedback opposes change (stabilizes); positive feedback amplifies it.
2. Intracellular fluid (~2/3).
3. Effect of nonpenetrating solutes on cell volume.
4. Simple diffusion, facilitated diffusion, osmosis.
5. 3 Na⁺ out, 2 K⁺ in per ATP (electrogenic, maintains gradients).
6. ≈ −70 mV, dominated by K⁺ leak permeability.
7. Graded = decremental/summating; action = all-or-none/propagating.
8. Absolute (no AP) and relative (harder AP); set firing frequency limit and directionality.
9. Electrical = gap junction, fast, bidirectional; chemical = neurotransmitter across cleft, delayed.
10. Excitatory postsynaptic potential (depolarization); summation at axon hillock/trigger zone.
11. AP → T-tubules → DHPR → ryanodine receptor → SR Ca²⁺ release → troponin C → tropomyosin shift → cross-bridge.
12. ATP depletion → myosin cannot detach from actin.
13. Cerebellum = coordination/error correction; basal ganglia = movement initiation/selection.
14. Persistent synaptic strengthening via NMDA and AMPA receptors (memory).
15. Sympathetic = norepinephrine/adrenergic; parasympathetic = acetylcholine/muscarinic.
16. Phasic adapt rapidly (vibration); tonic sustain (nociceptors).
17. Spinothalamic (anterolateral) tract; contralateral.
18. Peptide = membrane receptor + second messenger; steroid = intracellular receptor + gene expression.
19. Hypothalamus (CRH) → anterior pituitary (ACTH) → adrenal cortex (cortisol) with negative feedback.
20. Autocrine (self), paracrine (nearby), endocrine (distant via blood).

Last-Minute Review

• Gradients: concentration + electrical = electrochemical; membrane potential reflects relative permeability (K⁺ at rest, Na⁺ during AP).
• Transport: passive (diffusion/facilitated/osmosis) vs active (primary/secondary) vs vesicular.
• Neurophysiology: resting → graded → threshold → AP (depolarize/repolarize/hyperpolarize) → refractory → saltatory conduction.
• Synapse: presynaptic Ca²⁺ → exocytosis → neurotransmitter → postsynaptic ionotropic/metabotropic → EPSP/IPSP → integration.
• Muscle: E-C coupling → cross-bridge cycle (ATP) → contraction; skeletal vs smooth vs cardiac.
• Sensory: transduction → receptor potential → coding (intensity/duration/location) → pathway.
• Endocrine: hypothalamic-pituitary axes, negative feedback, calcium homeostasis (PTH/calcitonin/D3).

Related

• Subject overview
• Topic 07 — Resting Membrane Potential
• Topic 16 — Excitation-Contraction Coupling
• Topic 33 — Hypothalamic-Pituitary Axis