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Motor Neurons: Neurons which activate muscle cells.

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: Musculoskeletal System

Motor Maps

JoVE 10175

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California


One principle of brain organization is the topographic mapping of information. Especially in sensory and motor cortices, adjacent regions of the brain tend to represent information from adjacent parts of the body, resulting in maps of the…

 Neuropsychology

An Introduction to Motor Control

JoVE 5422

Motor control involves integration and processing of sensory information by our nervous system, followed by a response through our skeletal system to perform a voluntary or involuntary action. It is vital to understand how our neuroskeletal system controls motor behavior in order to evaluate injuries pertaining to general movement, reflexes, and coordination. An improved understanding of motor …

 Behavioral Science

Cross-bridge Cycle

JoVE 10870

As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

When ATP, that is attached to the myosin head, is hydrolyzed to ADP, myosin moves into a high energy state bound to actin, creating a cross-bridge. When ADP is released, the myosin head moves to a low energy state, moving actin toward the center of the sarcomere. Binding of a new ATP molecule dissociates myosin from actin. When this ATP is hydrolyzed, the myosin head will bind to actin, this time on a portion of actin closer to the end of the sarcomere. Regulatory proteins troponin and tropomyosin, along with calcium, work together to control the myosin-actin interaction. When troponin binds to calcium, tropomyosin is moved away from the myosin-binding site on actin, allowing myosin and actin to interact and muscle contraction to occur. As a regulator of muscle contraction, calcium concentration is very closely controlled in muscle fibers. Muscle fibers are in close contact with motor neurons. Action potentials in motor neurons cause the release of the neurotransmitter acetylcholine in the vicinity of muscle fibers. This ge

 Core: Musculoskeletal System

Muscle Contraction

JoVE 10869

In skeletal muscles, acetylcholine is released by nerve terminals at the motor end plate-the point of synaptic communication between motor neurons and muscle fibers. Binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle stimulation. Individuals with the disorder myasthenia gravis, develop antibodies against the acetylcholine receptor. This prevents transmission of electrical signals between the motor neuron and muscle fiber and impairs skeletal muscle contraction. Myasthenia gravis is treated using drugs that inhibit acetylcholinesterase (allowing more opportunities for the neurotransmitter to stimulate the remaining receptors) or suppress the immune system (preventing the formation of antibodies). Unlike skeletal muscles, smooth muscles present in the walls of internal organs are innervated by the autonomic nervous system and undergo involuntary contractions. Contraction is mediated by the interaction between two filament proteins-actin and myosin. The interaction of actin and myosin is closely linked to intracellular calcium concentration. In response to neurotransmitter or hormone sig

 Core: Musculoskeletal System

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: Musculoskeletal System

Explant Culture of Neural Tissue

JoVE 5209

The intricate structure of the vertebrate nervous system arises from a complex series of events involving cell differentiation, cell migration, and changes in cell morphology. Studying these processes is essential to our understanding of nervous system function as well as our ability to diagnose and treat disorders that result from abnormal development. However, neural…

 Neuroscience

Embryonic Stem Cell Culture and Differentiation

JoVE 5332

Culturing embryonic stem (ES) cells requires conditions that maintain these cells in an undifferentiated state to preserve their capacity for self-renewal and pluripotency. Stem cell biologists are continuously optimizing methods to improve the efficiency of ES cell culture, and are simultaneously trying to direct the differentiation of ES cells into specific cell types that could be used in…

 Developmental Biology

An Introduction to Stem Cell Biology

JoVE 5331

Cells that can differentiate into a variety of cell types, known as stem cells, are at the center of one of the most exciting fields of science today. Stem cell biologists are working to understand the basic mechanisms that regulate how these cells function. These researchers are also interested in harnessing the remarkable potential of stem cells to treat human diseases.


Here,…

 Developmental Biology

Isolation and Culture of Oculomotor, Trochlear, and Spinal Motor Neurons from Prenatal Islmn:GFP Transgenic Mice

1Department of Neurology, Boston Children's Hospital, 2FM Kirby Neurobiology Center, Boston Children's Hospital, 3Department of Neurology, Harvard Medical School, 4Medical Genetics Training Program, Harvard Medical School, 5Department of Ophthalmology, Boston Children's Hospital, 6Department of Ophthalmology, Harvard Medical School, 7Broad Institute of M.I.T. and Harvard, 8Howard Hughes Medical Institute, 9Department of Neurology, Kokura Memorial Hospital, 10Department of Genetics, Albert Einstein College of Medicine

Video Coming Soon

JoVE 60440

 JoVE In-Press

The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy

1Physiology and Bosch Institute, University of Sydney, 2Motor Neuron Disease Research Group, Australian School of Advanced Medicine, Macquarie University, 3Advanced Microscopy Facility, Bosch Institute, University of Sydney

JoVE 52220

 Neuroscience

Dissection of Local Ca2+ Signals in Cultured Cells by Membrane-targeted Ca2+ Indicators

1Japan Science and Technology Agency, PRESTO, 2Laboratory for Developmental Neurobiology, RIKEN Center for Brain Science, 3École Normale Supèrieure, Institut de Biologie de l'ENS (IBENS), Institut national de la santè et de la recherche mèdicale (INSERM), Centre national de la recherche scientifique (CNRS), École Normale Supèrieure, PSL Research University

JoVE 59246

 Neuroscience

Using Unidirectional Rotations to Improve Vestibular System Asymmetry in Patients with Vestibular Dysfunction

1Department of Physiology, Shahid Beheshti University of Medical Sciences and Health Services, 2Audiology and Dizziness Center, Dey General Hospital, 3Department of Speech-Language Pathology, SUNY Buffalo State, 4Department of Rehabilitation Science, School of Public Health and Health Professions, State University of New York at Buffalo, 5Center for Hearing and Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo

JoVE 60053

 Behavior

Short-Term Free-Floating Slice Cultures from the Adult Human Brain

1Department of Biochemistry and Immunology, Ribeirão Preto Medical School, University of São Paulo, 2Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, 3Department of Pathology and Forensic Medicine, Ribeirão Preto Medical School, University of São Paulo, 4Department of Anatomy, Institute of Biosciences, São Paulo State University, 5Clinical Hospital at the Ribeirão Preto Medical School, University of São Paulo

Video Coming Soon

JoVE 59845

 JoVE In-Press

Low-Cost Gait Analysis for Behavioral Phenotyping of Mouse Models of Neuromuscular Disease

1Department of Neurology, Duke University School of Medicine, 2Duke Center for Neurodegeneration & Neurotherapeutics, Duke University School of Medicine, 3Biomedical Sciences Graduate Program, University of California San Diego, 4Department of Neurobiology, Duke University School of Medicine, 5Department of Cell Biology, Duke University School of Medicine

JoVE 59878

 Behavior

Ex Vivo Oculomotor Slice Culture from Embryonic GFP-Expressing Mice for Time-Lapse Imaging of Oculomotor Nerve Outgrowth

1Department of Ophthalmology, Boston Children's Hospital, 2Department of Ophthalmology, Harvard Medical School, 3F.M. Kirby Neurobiology Center, Boston Children's Hospital, 4Department of Neurology, Boston Children's Hospital, 5Department of Neurology, Harvard Medical School, 6Howard Hughes Medical Institute

JoVE 59911

 Neuroscience

Conversion of Human Induced Pluripotent Stem Cells (iPSCs) into Functional Spinal and Cranial Motor Neurons Using PiggyBac Vectors

1Department of Biology and Biotechnology Charles Darwin, Sapienza University of Rome, Italy, 2Center for Life Nano Science, Istituto Italiano di Tecnologia, Italy, 3Laboratory of Stem Cell biology and Molecular Embryology, The Rockefeller University, USA, 4Department of Physiology and Pharmacology, Sapienza University of Rome, Italy

JoVE 59321

 Neuroscience

Spinal Cord Lateral Hemisection and Asymmetric Behavioral Assessments in Adult Rats

1Department of Spinal Cord Injury and Repair, Trauma and Orthopedics Institute of Chinese PLA, General Hospital of Jinan Military Region, 2Institute of Military Cognitive and Brain Sciences, Academy of Military Medical Sciences, 3Spinal Cord and Brain Injury Research Group, Stark Neurosciences Research Institute, Department of Neurological Surgery and Goodman Campbell Brain and Spine, Indiana University School of Medicine, 4Program in Medical Neuroscience, Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, 5Shandong University Affiliated Shandong Cancer Hospital and Institute

Video Coming Soon

JoVE 57126

 JoVE In-Press

Simultaneous Recordings of Cortical Local Field Potentials and Electrocorticograms in Response to Nociceptive Laser Stimuli from Freely Moving Rats

1CAS Key Laboratory of Mental Health, Institute of Psychology, 2Department of Psychology, University of Chinese Academy of Sciences, 3Research Center of Brain Cognitive Neuroscience, Liaoning Normal University, 4Neuroscience Research Institute, Peking University, 5Department of Neurobiology, School of Basic Medical Sciences, Peking University, 6Key Laboratory for Neuroscience, Ministry of Education/National Health and Family Planning Commission, Peking University, 7Department of Pain Management, State Key Clinical Specialty in Pain Medicine, Second Affiliated Hospital of Guangzhou Medical University

JoVE 58686

 Behavior
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