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Cardiac Exam II: Auscultation

JoVE 10124

Source: Suneel Dhand, MD, Attending Physician, Internal Medicine, Beth Israel Deaconess Medical Center


Proficiency in the use of a stethoscope to listen to heart sounds and the ability to differentiate between normal and abnormal heart sounds are essential skills for any physician. Correct placement of the stethoscope on the chest…

 Physical Examinations I

Motor Exam II

JoVE 10095

Source:Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurology, Brigham and Women's/Massachusetts General Hospital, Boston, Massachusetts, USA


There are two main types of reflexes that are tested on a neurological examination: stretch (or deep tendon reflexes) and superficial reflexes. A deep tendon…

 Physical Examinations III

Abdominal Exam II: Percussion

JoVE 10090

Source: Alexander Goldfarb, MD, Assistant Professor of Medicine, Beth Israel Deaconess Medical Center, MA


Medical percussion is based on the difference in pitch between the sounds elicited by tapping on the body wall. The auditory response to tapping depends on the ease with which the body wall vibrates, and is influenced by underlying…

 Physical Examinations II

Respiratory Exam II: Percussion and Auscultation

JoVE 10041

Source: Suneel Dhand, MD, Attending Physician, Internal Medicine, Beth Israel Deaconess Medical Center


Learning the proper technique for percussion and auscultation of the respiratory system is vital and comes with practice on real patients. Percussion is a useful skill that is often skipped during everyday clinical practice, but if…

 Physical Examinations I

Physical Properties Of Minerals II: Polymineralic Analysis

JoVE 10001

Source: Laboratory of Alan Lester - University of Colorado Boulder


The physical properties of minerals include various measurable and discernible attributes, including color, streak, magnetic properties, hardness, crystal growth form, and crystal cleavage. These properties are mineral-specific, and they are fundamentally related to a particular mineral’s chemical make-up and …

 Earth Science

Photosystem I

JoVE 10752

Like Photosystem II (PS II), Photosystem I (PS I) captures photons and transports them through chlorophyll molecules into a reaction center. In PS I, the photons reenergize the electrons that have entered PS I from PS II. From the reaction center, the high energy electron is sent through an electron transport chain and ultimately joins with an additional electron and a proton to reduce NADP+ into NADPH. Thus, similar to PS II that captures energy to generate ATP, PS I captures energy to create NADPH. The pigments of the light-harvesting complex in Photosystem I absorb photons and relay the energy to the reaction center (P700). Following oxidation, a high-energy electron is passed from the specialized pair of chlorophyll a to the primary electron acceptor. This time, however, the missing electrons from the chlorophyll a pair are replaced by the electrons traveling from Photosystem II (instead of splitting of water as in PS II). On their way from PS II to PS I, the electrons pass through the electron transport chain, comprising the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. Once the electron was excited in the reaction center of PS I, it enters a second electron transport chain—the protein complex ferredoxin. The single electron then joins with another electron and a proton (H+)

 Core: Biology

Life Histories

JoVE 10941

Constrained by limited energy and resources, organisms must compromise between offspring quantity and parental investment. This trade-off is represented by two primary reproductive strategies; K-strategists produce few offspring but provide substantial parental support, whereas r-strategists produce much progeny that receives little care. These strategies are related to an organism’s survival likelihood across its lifespan, which is represented by a survivorship curve. Three general types of survivorship curves are exhibited by organisms that: tend to live long lives (Type I, K-strategists); are equally likely to die at all ages (Type II); or have high early mortality rates, but long lifespans if they survive into adulthood (Type III, r-strategists). An organism’s life history includes all the events occurring across its lifespan, including birth, development, sexual maturation, reproduction, and death. Trade-offs involving the patterns and timing of life history events (notably survival and reproduction) across different ages and developmental stages represent different life history strategies. R-strategists and K-strategists make distinct reproductive compromises between the number of offspring and level of parental care, or offspring quantity versus quality. R-strategists (r

 Core: Biology

Classification of Skeletal Muscle Fibers

JoVE 10868

Skeletal muscles continuously produce ATP to provide the energy that enables muscle contractions. Skeletal muscle fibers can be categorized as type I, type IIA, or type IIB based on differences in their contraction speed and how they produce ATP, as well as physical differences related to these factors. Most human muscles contain all three muscle fiber types, albeit in varying proportions. Type I, or slow oxidative, muscle fibers appear red due to large numbers of capillaries and high levels of myoglobin, an oxygen-storing protein. Type I muscle fibers contain more mitochondria, which produce ATP through oxidative phosphorylation, than type II fibers. Slow oxidative muscle fibers use aerobic respiration, involving oxygen and glucose, to produce ATP. In addition to contracting more slowly than type II fibers, type I fibers receive nerve signals more slowly, contract for longer periods, and are more resistant to fatigue. Type I fibers primarily store energy as fatty substances called triglycerides. Type II, or fast, muscle fibers often appear white. Relative to type I fibers, type II fibers receive nerve signals and contract more quickly, but contract for shorter periods and fatigue more quickly. Type II muscle fibers primarily store energy as ATP and creatine phosphate. Type IIA, or fast oxidative, muscle fibers primarily u

 Core: Biology
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