BIOG 1440 Lecture Notes - Lecture 11: Cardiac Muscle Cell, Vagus Nerve, Neuromuscular Junction
27 Apr 2018
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Prelim: Wednesday!!! Less than 20 MC questions; 4-5 short answer (3-4 sentences).
Control of Heart Rhythmicity
1. There are two types of acetylcholine receptors
a. Nicotinic type: most neurons and neuromuscular junction (striate muscle)
b. Muscarinic type: cardiac muscle and a few neurons
2. Neurotransmitters and heart rhythm
a. Acetylcholine from vagus nerve allows K+ to flow out; hyperpolarizes cardiac
myocyte → leak takes longer to reach threshold (slows down heart rate)
b. Norepinephrine from sympathetic nerves binds beta 1 receptor (another GPCR)
2nd messenger cascade increases initial [Ca^2+]
i. Depolarizes cardiac myocyte → membrane potential closer to threshold
ii. Increases heart rate
Closed Circuits w/ a Pump (Vertebrates and some invertebrates)
1. Mammals and birds have double circulatory system
2. Closed Circulatory System: vessels
a. Endothelium=innermost layer of artery
b. Smooth muscle=middle layer of artery
c. Outer layer=CT
3. Blood flow velocity (Hemodynamics)
a. A vessel acts as a pipe; physical laws governing fluid mechanics apply. Blood is
viscous.
b. Approximate blood flow as laminar flow (no turbulence).
i. Fluid flows in parallel layers w/o disruption
1. Velocity of external layer is low; internal layer is high
c. Velocity depends on Poiseuille’s Law
4. Diameter (velocity) decreases w/ arborization
a. Aorta (largest artery) → arteries (smaller) → arterioles (smaller) → capillaries (tiny)
b. Microcirculation: circulation in smallest blood vessels (arterioles, capillaries,
venules)
c. Net flow is unchanged from aorta → capillaries but linear velocity is minimal
i. Cross-sectional area is gigantic → goes over a lot of space but moves
slowly
ii. Allows for better transfer of nutrients/oxygen
5. Microcirculatory bed
a. Arterioles control flow to capillaries
6. Microcirculatory flow is under nervous control
a. Vasoconstriction → increases contraction, increased resistance and decreased
flow
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Document Summary
Less than 20 mc questions; 4-5 short answer (3-4 sentences). 2nd messenger cascade increases initial [ca^2+: depolarizes cardiac myocyte membrane potential closer to threshold. Blood is viscous: approximate blood flow as laminar flow (no turbulence). Mostly due to albumin: oncotic pressure is constant and becomes preeminent in capillary bed, fluid is therefore , in bugs . Then recovered due to oncotic pressure: heart is a dorsal vessel, sometimes need accessory heart just to move blood through appendages because the system is inefficient. Open circuits w/ mostly passive flow (vascular plants: pipes in (vascular) plants: xylem and phloem, two separate vascular systems: Xylem: movement of water and minerals: unidirectional flow roots leaves. Phloem: transport of photosynthate and other materials (aas, hormones, minerals: bidirectional flow from sources (leaf) sink (fruit, flower, tuber, root, etc, in herbaceous plants, xylem/phloem occur in vascular bundles. Non uniform lignin pits: complementary systems: Active/passive loading of carbon molecules by sources: water folows by osmosis hydrostatic pressure.
