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Nerve Fibers: Slender processes of Neurons, including the Axons and their glial envelopes (Myelin sheath). Nerve fibers conduct nerve impulses to and from the central nervous system.

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

Cranial Nerves Exam I (I-VI)

JoVE 10091

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


During each section of the neurological testing, the examiner uses the powers of observation to assess the patient. In some cases, cranial nerve dysfunction is readily apparent: a patient might…

 Physical Examinations III

Cranial Nerves Exam II (VII-XII)

JoVE 10005

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


The cranial nerve examination follows the mental status evaluation in a neurological exam. However, the examination begins with observations made upon greeting…

 Physical Examinations III

Sensory Exam

JoVE 10113

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


A complete sensory examination consists of testing primary sensory modalities as well as cortical sensory function. Primary sensory modalities include pain, temperature, light touch, vibration,…

 Physical Examinations III

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers

1Department of Orthopaedic Surgery, University of Michigan Medical School, 2Department of Molecular & Integrative Physiology, University of Michigan Medical School, 3Department of Biomedical Engineering, University of Michigan Medical School, 4Department of Surgery, Section of Plastic Surgery, University of Michigan Medical School

JoVE 52695

 Bioengineering

Motor Units

JoVE 10871

A motor unit consists of two main components: a single efferent motor neuron (i.e., a neuron that carries impulses away from the central nervous system) and all of the muscle fibers it innervates. The motor neuron may innervate multiple muscle fibers, which are single cells, but only one motor neuron innervates a single muscle fiber.

Lower motor neurons are efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. The cell bodies of lower motor neurons are located in the spinal cord or brain stem. Those in the brainstem transmit nerve signals through the cranial nerve, and primarily control muscles in the head and neck. Lower motor neurons originating in the spinal cord send signals along the spinal nerve, and primarily control muscles in the limbs and body trunk. A lower motor neuron fires an action potential that, at once, contract all skeletal muscle cells that the neuron innervates. Thus, motor units are functional units of skeletal muscle. The size of a motor unit, or the number of muscle fibers the lower motor neuron innervates, varies depending on the size of the muscle and the speed and precision the movement requires. Muscles in the eyes and fingers, which require rapid, precise control, are generally controlled by small motor units. In these units, motor neurons connect to a small number of muscle f

 Core: Biology

Thermosensation

JoVE 10860

Peripheral thermosensation is the perception of external temperature. A change in temperature (on the surface of the skin and other tissues) is detected by a family of temperature-sensitive ion channels called Transient Receptor Potential, or TRP, receptors. These receptors are located on free nerve endings. Those detecting cold temperatures are closer to the surface of the skin than the nerve endings detecting warmth. These thermoTRP channels, while temperature selective, have relatively non-selective cation permeability. There are at least three types of receptors that are activated by cold, of which TRPM8 and TRPA1 are particularly sensitive. TRPM8 has a temperature sensitive range of about 10-26 oC (50-79 oF), and is largely associated with the perception of non-painful, or innocuous, cold. Menthol, a compound found in mint leaves, can also activate this receptor, which helps explain why this flavor is often perceived as cool. When temperatures are low enough to feel painful (i.e., noxious cold), TRPA1 receptors are activated. TRPA1 receptors respond to any temperature lower than 17 oC (~63 oF). There are at least seven receptors that respond to heat. Of these, five respond to temperatures in the innocuous warmth range: TRPM2 (23-38 oC, or ~73-100oF), TRPC5 (26-38 oC, or ~79-

 Core: Biology

The Spinal Cord

JoVE 10872

The spinal cord is the body’s major nerve tract of the central nervous system, communicating afferent sensory information from the periphery to the brain and efferent motor information from the brain to the body. The human spinal cord extends from the hole at the base of the skull, or foramen magnum, to the level of the first or second lumbar vertebra.

The spinal cord is cylindrical and contains both white and grey matter. In the center is the central canal, which is the remnant of the lumen of the primitive neural tube and is part of the internal system of cerebrospinal fluid cavities. In cross-section, the grey matter surrounding the central canal appears butterfly-shaped. The wings of the butterfly are divided into dorsal and ventral horns. The dorsal horn contains sensory nuclei that relay sensory information, and the ventral horn contains motor neurons that give rise to the axons that innervate skeletal muscle. White matter surrounds the gray matter and contains large numbers of myelinated fibers. The white matter is arranged into longitudinal bundles called dorsal, lateral, and ventral columns. Three membranes surround the spinal cord: the pia adheres closely to the surface of the spinal cord, followed by the arachnoid, and the dura mater—the tough outermost sheath. The spinal cord is divided into four different r

 Core: Biology
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