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Nervous System: The entire nerve apparatus, composed of a central part, the brain and spinal cord, and a peripheral part, the cranial and spinal nerves, autonomic ganglia, and plexuses. (Stedman, 26th ed)

What is a Nervous System?

JoVE 10838

The nervous system is the collection of specialized cells responsible for maintaining an organism’s internal environment and coordinating the interaction of an organism with the external world—from the control of essential functions such as heart rate and breathing to the movement needed to escape danger.

The vertebrate nervous system is divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain, spinal cord, and retina—the sensory tissue of the visual system. The PNS contains the sensory receptor cells for all of the other sensory systems—such as the touch receptors in the skin—as well as the nerves that carry information between the CNS and the rest of the body. Additionally, part of both the CNS and PNS contribute to the autonomic nervous system (also known as the visceral motor system). The autonomic nervous system controls smooth muscles, cardiac muscles, and glands that govern involuntary actions, such as digestion. The vertebrate brain is primarily divided into the cerebrum, cerebellum, and brainstem. The cerebrum is the largest, most anterior part of the brain that is divided into left and right hemispheres. Each hemisphere is further divided into four lobes: frontal, parietal, occipital, and temporal. The outermost layer of the cerebrum is called

 Core: Nervous System

The Parasympathetic Nervous System

JoVE 10839

The parasympathetic nervous system is one of the two major divisions of the autonomic nervous system. This parasympathetic system is responsible for regulating many unconscious functions, such as heart rate and digestion. It is composed of neurons located in both the brain and the peripheral nervous system that send their axons to target muscles, organs, and glands.

Activation of the parasympathetic system tends to have a relaxing effect on the body, promoting functions that replenish resources and restore homeostasis. It is therefore sometimes referred to as the “rest and digest” system. The parasympathetic system predominates during calm times when it is safe to devote resources to basic “housekeeping” functions without a threat of attack or harm. The parasympathetic nervous system can be activated by various parts of the brain, including the hypothalamus. Preganglionic neurons in the brainstem and sacral part of the spinal cord first send their axons out to ganglia—clusters of neuronal cell bodies—in the peripheral nervous system. These ganglia contain the connections between pre- and postganglionic neurons and are located near the organs or glands that they control. From here, postganglionic neurons send their axons onto target tissues—generally smooth muscle, cardiac muscle, or glands. Typic

 Core: Nervous System

The Sympathetic Nervous System

JoVE 10840

The sympathetic nervous system—one of the two major divisions of the autonomic nervous system—is activated in times of stress. It prepares the body to meet the challenges of a demanding circumstance while inhibiting essential body functions—such as digestion—that are a lower priority at the moment.

As a student, you may have had the experience of walking into class and finding a surprise exam that you were not expecting. In the moment of realization, you may sense your gut tighten, your mouth goes dry, and your heart starts to race all of a sudden. These are signs of the sympathetic system taking over in preparation to react. While you may not be in immediate danger, the system has evolved to facilitate immediate reaction to stress or threats: blood is directed away from the digestive system and skin to increase energy supplies to muscles. Furthermore, the heart rate, and blood flow increase, and pupils dilate to maximize visual perception. At the same time, the adrenal gland releases epinephrine into the circulatory system. Your body is now primed to take action, whether that means to swiftly flee from danger or fight whatever threat may be at hand. The sympathetic nervous system can be activated by various parts of the brain, with the hypothalamus playing a particularly important role. Sympathetic instructions from the central

 Core: Nervous System

Physiology of the Circulatory System- Concept

JoVE 10625


Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly constant internal environment, which involves continuous regulation of temperature, pH, and other factors. This balanced state is known as homeostasis, which describes the processes by which organisms maintain their optimal internal…

 Lab Bio

What is a Sensory System?

JoVE 10849

Sensory systems detect stimuli—such as light and sound waves—and transduce them into neural signals that can be interpreted by the nervous system. In addition to external stimuli detected by the senses, some sensory systems detect internal stimuli—such as the proprioceptors in muscles and tendons that send feedback about limb position.

Sensory systems include the visual, auditory, gustatory (taste), olfactory (smell), somatosensory (touch, pain, temperature, and proprioception), and vestibular (balance, spatial orientation) systems. All sensory systems have receptor cells that are specialized to detect a particular type of stimulus. For example, hair cells in the inner ear have cilia that move in the presence of sound waves, while olfactory receptor neurons in the nasal cavity have receptors that bind to odorant molecules. The presence of an appropriate stimulus triggers electrochemical changes in the nervous system. This stimulus typically changes the membrane potential of a sensory neuron, triggering an action potential. The information is then transmitted from the sensory organ to the spinal cord and then the brain, or directly to the brain (as in the visual system). The different types of sensory information—also called modalities—travel in different pathways through the central nervous system, but most

 Core: Sensory Systems

Three-dimensional Tissue Engineered Aligned Astrocyte Networks to Recapitulate Developmental Mechanisms and Facilitate Nervous System Regeneration

1Center for Brain Injury & Repair, Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, 2Center for Neurotrauma, Neurodegeneration & Restoration, Michael J. Crescenz Veterans Affairs Medical Center, 3School of Biomedical Engineering, Drexel University, 4Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, 5Neuroscience Graduate Group, Perelman School of Medicine, University of Pennsylvania

JoVE 55848


Glial Cells

JoVE 10843

Glial cells are one of the two main types of cells in the nervous system. Glia cells comprise astrocytes, oligodendrocytes, microglia, and ependymal cells in the central nervous system, and satellite and Schwann cells in the peripheral nervous system. These cells do not communicate via electrical signals like neurons do, but they contribute to virtually every other aspect of nervous system function. In humans, the number of glial cells is roughly equal to the number of neurons in the brain. Glia in the central nervous system (CNS) include astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes are the most abundant type of glial cell and are found in organized, non-overlapping patterns throughout the brain, where they closely associate with neurons and capillaries. Astrocytes play numerous roles in brain function, including regulating blood flow and metabolic processes, synaptic ion and pH homeostasis, and blood-brain barrier maintenance. Another specialized glial cell, the oligodendrocyte, forms the myelin sheath that surrounds neuronal axons in the CNS. Oligodendrocytes extend long cellular processes that wrap around axons multiple times to form this coating. Myelin sheath is required for proper conduction of neuronal signaling and greatly increases the speed at which these messages travel. Microglia—known as the macrop

 Core: Nervous System

What is the Skeletal System?

JoVE 10863

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid framework for the human body, protects internal organs, and enables movement and locomotion. The human skeletal system consists of the axial and appendicular skeletons. Bone tissue is continuously built up and chewed away by specialized bone cells which are essential to overall health. Dysregulated bone cells and incorrect levels of chemical compounds in the blood lead to bone diseases. The axial skeleton consists of 80 bones and is divided into three regions: the skull, the vertebral column, and the rib cage. The upper portion of the skull—the cranium—consists of eight bones that enclose the brain, while the lower part consists of 14 bones. The vertebral column consists of 33 vertebrae: seven cervical, 12 thoracic, five lumbar, five fused sacral vertebrae, and four fused coccygeal vertebrae. The rib cage adds stability to the vertebral column and also protects the lungs and heart. It consists of 12 pairs of ribs, which attach to the thoracic vertebra via the costovertebral joint. The anterior portion of the rib cage attaches to the sternum—the flat bone at the center of the front of the chest—via the costal cartilages. The first seven ribs on each side are known as true ribs, as their cartilages

 Core: Musculoskeletal System

Anatomically Inspired Three-dimensional Micro-tissue Engineered Neural Networks for Nervous System Reconstruction, Modulation, and Modeling

1Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, 2Center for Brain Injury & Repair, Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, 3Center for Neurotrauma, Neurodegeneration & Restoration, Michael J. Crescenz Veterans Affairs Medical Center, 4School of Biomedical Engineering, Drexel University

JoVE 55609


In vivo Optogenetic Stimulation of the Rodent Central Nervous System

1Department of Psychiatry, University of Pittsburgh Medical Center, 2Department of Bioengineering, Stanford University, 3Department of Brain and Cognitive Sciences, Picower Institute for Learning and Memory, Massachusetts Institute of Technology, 4Department of Neurobiology and Behavior, Cornell University, 5Department of Psychiatry and Behavioral Sciences, Stanford University

JoVE 51483


Generation of 3-D Collagen-based Hydrogels to Analyze Axonal Growth and Behavior During Nervous System Development

1Molecular and Cellular Neurobiotechnology, Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Parc Científic de Barcelona, 2Department of Cell Biology, Physiology, and Immunology, Universitat de Barcelona, 3Center for Networked Biomedical Research on Neurodegenerative Diseases (CIBERNED), 4Institute of Neuroscience, University of Barcelona

JoVE 59481



JoVE 10910

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior portion of the neural tube will give rise to the brain, with the rest forming the spinal cord. The central portion of the ectoderm that bends to generate the neural tube is aptly called the neural ectoderm, while the areas that flank it—along the periphery of the embryo—are the surface ectoderm. However, at the junction of the neural and surface ectoderm lies another population of cells, called the neural crest. As the neural folds (the edges of the elevating neural tube) begin to appear, neural crest cells (NCCs) can be visualized in their tips through the expression of characteristic markers, like the Pax7 transcription factor. As development proceeds and the neural folds fuse, NCCs can be observed either in the top-most portion of the neural tube or migrating along this structure’s sides towards lower regions of the embryo. To migrate, N

 Core: Reproduction and Development

An Introduction to Developmental Neurobiology

JoVE 5207

Developmental neuroscience is a field that explores how the nervous system is formed, from early embryonic stages through adulthood. Although it is known that neural progenitor cells follow predictable stages of proliferation, differentiation, migration, and maturation, the mechanisms controlling the progression through each stage are incompletely understood. Studying…


Neural Regulation

JoVE 10835

Digestion begins with a cephalic phase that prepares the digestive system to receive food. When our brain processes visual or olfactory information about food, it triggers impulses in the cranial nerves innervating the salivary glands and stomach to prepare for food.

The cephalic phase is a conditioned or learned response to familiar foods. Our appetite or desire for a particular food modifies the preparatory responses directed by the brain. Individuals may produce more saliva and stomach rumblings in anticipation of apple pie than of broccoli. Appetite and desire are products of the hypothalamus and amygdala—brain areas associated with visceral processes and emotion. After the cephalic phase, digestion is governed by the enteric nervous system (ENS) as an unconditioned reflex. Individuals do not have to learn how to digest food; it happens regardless of whether it is apple pie or broccoli. The ENS is unique in that it functions (mostly) independent of the brain. About 90% of the communication are messages sent from the ENS to the brain rather than the other way around. These messages give the brain information about satiety, nausea, or bloating. The ENS, as part of the peripheral nervous system, is also unique in that it contains both motor and sensory neurons. For example, the ENS directs smooth muscle movements that churn and propel food al

 Core: Nutrition and Digestion

An Introduction to Neurophysiology

JoVE 5201

Neurophysiology is broadly defined as the study of nervous system function. In this field, scientists investigate the central and peripheral nervous systems at the level of whole organs, cellular networks, single cells, or even subcellular compartments. A unifying feature of this wide-ranging discipline is an interest in the mechanisms that lead to the generation and…


An Introduction to Neuroanatomy

JoVE 5204

Neuroanatomy is the study of nervous system structures and how they relate to function. One focus of neuroanatomists is the macroscopic structures within the central and peripheral nervous systems, like the cortical folds on the surface of the brain. However, scientists in this field are also interested in the microscopic relationships between neurons and glia - the two…


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…


Neuron Structure

JoVE 10842

Neurons are the main type of cell in the nervous system that generate and transmit electrochemical signals. They primarily communicate with each other using neurotransmitters at specific junctions called synapses. Neurons come in many shapes that often relate to their function, but most share three main structures: an axon and dendrites that extend out from a cell body.

The neuronal cell body—the soma— houses the nucleus and organelles vital to cellular function. Extending from the cell body are thin structures that are specialized for receiving and sending signals. Dendrites typically receive signals while the axon passes on the signals to other cells, such as other neurons or muscle cells. The point at which a neuron makes a connection to another cell is called a synapse. Neurons receive inputs primarily at postsynaptic terminals, which are frequently located on spines—small bumps protruding from the dendrites. These specialized structures contain receptors for neurotransmitters and other chemical signals. Dendrites are often highly branched, allowing some neurons to receive tens of thousands of inputs. Neurons most commonly receive signals at their dendrites, but they can also have synapses in other areas, such as the cell body. The signal received at the synapses travels down the dendrite to the soma, where the cell can proce

 Core: Nervous System

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

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

The Blood-brain Barrier

JoVE 10841

The blood-brain barrier (BBB) refers to the specialized vasculature that provides the brain with nutrients in the blood while strictly regulating the movement of ions, molecules, pathogens, and other substances. It is composed of tightly linked endothelial cells on one side and astrocyte projections on the other. Together they provide a semipermeable barrier that protects the brain and poses unique challenges to the delivery of therapeutics. The BBB is made up of a variety of cellular components, including endothelial cells and astrocytes. These cells share a common basement membrane and together regulate the passage of components between the circulation and the interstitial fluid surrounding the brain. The first type of cellular component, specialized endothelial cells, make up the walls of the cerebral capillaries. They are connected by extremely tight and complex intercellular junctions. These junctions create a selective physical barrier, preventing simple diffusion of most substances, including average to large-sized molecules such as glucose and insulin. A second cell type, astrocytes, are a type of glial cell of the central nervous system which influences endothelial cell function, blood flow, and ion balance in the brain through interaction and close association with cerebral vasculature. They provide a direct link between the vasculature

 Core: Nervous System

The Resting Membrane Potential

JoVE 10845

The relative difference in electrical charge, or voltage, between the inside and the outside of a cell membrane, is called the membrane potential. It is generated by differences in permeability of the membrane to various ions and the concentrations of these ions across the membrane.

The membrane potential of a cell can be measured by inserting a microelectrode into a cell and comparing the charge to a reference electrode in the extracellular fluid. The membrane potential of a neuron at rest—that is, a neuron not currently receiving or sending messages—is negative, typically around -70 millivolts (mV). This is called the resting membrane potential. The negative value indicates that the inside of the membrane is relatively more negative than the outside—it is polarized. The resting potential results from two major factors: selective permeability of the membrane, and differences in ion concentration inside the cell compared to outside. Cell membranes are selectively permeable because most ions and molecules cannot cross the lipid bilayer without help, often from ion channel proteins that span the membrane. This is because the charged ions cannot diffuse through the uncharged hydrophobic interior of membranes. The most common intra- and extracellular ions found in the nervous tissue are potassium (K+), sodium (Na+…

 Core: Nervous System

Animal Diversity- Concept

JoVE 10637

Kingdom Animalia is composed of a range of organisms united by a set of common characteristics. Barring a few exceptions, animals are multicellular eukaryotes that move, consume organic matter, and reproduce sexually. Although these attributes are shared, species within this kingdom are also extremely diverse. This diversity is due to adaptation of each species to a different niche. The niche…

 Lab Bio

Cell Division- Concept

JoVE 10571

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, cell division allows organisms to transfer their genetic material to their offspring. For a unicellular organism, cellular division generates a completely new organism. For multicellular organisms, cellular division produces new cells for…

 Lab Bio

An Introduction to Cellular and Molecular Neuroscience

JoVE 5213

Cellular and molecular neuroscience is one of the newest and fastest growing subdisciplines in neuroscience. By investigating the influences of genes, signaling molecules, and cellular morphology, researchers in this field uncover crucial insights into normal brain development and function, as well as the root causes of many pathological conditions.


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

Primary Neuronal Cultures

JoVE 5214

The complexity of the brain often requires neuroscientists to use a simpler system for experimental manipulations and observations. One powerful approach is to generate a primary culture by dissecting nervous system tissue, dissociating it into single cells, and growing those cells in vitro. Primary cultures make neurons and glia easily accessible to the…


Physiological Correlates of Emotion Recognition

JoVE 10297

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

The autonomic nervous system (ANS) controls the activity of the body's internal organs and regulates changes in their activity depending on the current environment. The vagus nerve, which innervates many of the internal organs, is an…


Hormonal Regulation

JoVE 10836

Hormones regulate a significant portion of digestion through activation of the neuroendocrine system. The neuroendocrine system of digestion contains many different hormones all with multiple functions that are both, directly and indirectly, involved in digestion.

Starting in the stomach, when proteins are detected by sensory neurons of the enteric nervous system, the pyloric gland is stimulated to release gastrin. In turn, this hormone induces the release of histamine. Combined, they initiate the production of hydrochloric acid which facilitates digestion—turning food into chyme. When the pH of the stomach becomes more acidic, a negative feedback loop halts the production of both hormones. The chyme then moves to the duodenum, where several hormones are released—each with multiple functions. Some inhibit digestion in the stomach. Gastric inhibitory peptide (GIP) slows stomach churning. Secretin inhibits gastric juice production and, along with cholecystokinin (CCK), induces the pyloric sphincter between the stomach and duodenum to close. This limits the volume of chyme in the duodenum, pacing the rate of digestion. Once the chyme is in the duodenum, secretin prompts the release of bicarbonate from the pancreas. This reduces the acidity of the chyme, protecting the sensitive lining of the duodenum and setting up an optimal environment

 Core: Nutrition and Digestion

Hypothalamic-Pituitary Axis

JoVE 10879

The response to stress—be it physical or psychological, acute or chronic—involves activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. The HPA axis is part of the neuroendocrine system because it involves both neuronal and hormonal communication. Its function is to regulate homeostatic systems—metabolic, cardiovascular, and immune—providing the necessary means to respond to a stressor. In response to stress, the neurons in the hypothalamus release corticotropin-releasing hormone, or CRH, into the bloodstream. CRH takes a short journey to the pituitary gland where it stimulates the release of adrenocorticotropic hormone, or ACTH. The site of action for ACTH are the adrenal glands which lay just on the surface of the kidneys. When stimulated, the adrenal glands release two types of stress messages. Neural stimulation initiates the first message—the release of epinephrine and norepinephrine from the adrenal medulla. This activates the sympathetic nervous system resulting in elevated heart rate, blood flow, and respiration—processes designed to activate states of alertness and arousal. These two chemicals are also referred to as adrenaline and noradrenaline, respectively. ACTH initiates the second message—the release of glucocorticoids by the adrenal cortex. In humans, cortisol is the primary hormone

 Core: Endocrine System

An Introduction to Behavioral Neuroscience

JoVE 5210

Behavioral neuroscience is the study of how the nervous system guides behavior, and how the various functional areas and networks within the brain correlate to specific behaviors and disease states. Researchers in this field utilize a wide variety of experimental methods ranging from complex animal training techniques to sophisticated imaging experiments in human subjects. …


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

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

Hair Cells

JoVE 10854

Hair cells are the sensory receptors of the auditory system—they transduce mechanical sound waves into electrical energy that the nervous system can understand. Hair cells are located in the organ of Corti within the cochlea of the inner ear, between the basilar and tectorial membranes. The actual sensory receptors are called inner hair cells. The outer hair cells serve other functions, such as sound amplification in the cochlea, and are not discussed in detail here. Hair cells are named after the hair-like stereocilia that protrude from their tops and touch the tectorial membrane. The stereocilia are arranged by height and are attached by thin filaments called tip links. The tip links are connected to stretch-activated cation channels on the tips of the stereocilia. When a sound wave vibrates the basilar membrane, it creates a shearing force between the basilar and tectorial membranes that moves the hair cell stereocilia from side to side. When the cilia are displaced towards the tallest cilium, the tip links stretch, opening the cation channels. Potassium (K+) then flows into the cell, because there is a very high concentration of K+ in the fluid outside of the stereocilia. This large voltage difference creates an electrochemical gradient that causes an influx of K+ once the channels are opened. This influx o

 Core: Sensory Systems


JoVE 10852

The sense of smell is achieved through the activities of the olfactory system. It starts when an airborne odorant enters the nasal cavity and reaches olfactory epithelium (OE). The OE is protected by a thin layer of mucus, which also serves the purpose of dissolving more complex compounds into simpler chemical odorants. The size of the OE and the density of sensory neurons varies among species; in humans, the OE is only about 9-10 cm2. The olfactory receptors are embedded in the cilia of the olfactory sensory neurons. Each neuron expresses only one type of olfactory receptor. However, each type of olfactory receptor is broadly tuned and can bind to multiple different odorants. For example, if receptor A binds to odorants 1 and 2, receptor B may bind to odorants 2 and 3, while receptor C binds to odorants 1 and 3. Thus, the detection and identification of an odor depend on the combination of olfactory receptors that recognize the odor; this is called combinatorial diversity. Olfactory sensory neurons are bipolar cells with a single long axon that sends olfactory information up to the olfactory bulb (OB). The OB is a part of the brain that is separated from the nasal cavity by the cribriform plate. Because of this convenient proximity between the nose and brain, the development of nasal drug applications is widely studied, especially in cases

 Core: Sensory Systems

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

Histological Staining of Neural Tissue

JoVE 5206

In order to examine the cellular, structural and molecular layout of tissues and organs, researchers use a method known as histological staining. In this technique, a tissue of interest is preserved using chemical fixatives and sectioned, or cut into very thin slices. A variety of staining techniques are then applied to provide contrast to the visually uniform sections. In …


What is Cell Signaling?

JoVE 10985

Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate to respond to the environment.

Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch information, while photoreceptors in the retina can detect light. Most cells, however, have evolved to respond to chemical signals, including hormones, neurotransmitters, and many other types of signaling molecules. Cells can even coordinate different responses elicited by the same signaling molecule. Typically, cell signaling involves three steps: (1) reception of the signal, (2) signal transduction, and (3) a response. In most signal reception, a membrane-impermeable molecule, or ligand, causes a change in a membrane receptor; however, some signaling molecules, such as hormones, can traverse the membrane to reach their internal receptors. The membrane receptor can then send this signal to intracellular messengers, which transduces the message into a cellular response. This intracellular response may include a change transcription, translation, protein activation, or many

 Core: Cell Signaling


JoVE 10853

When we hear a sound, our nervous system is detecting sound waves—pressure waves of mechanical energy traveling through a medium. The frequency of the wave is perceived as pitch, while the amplitude is perceived as loudness.

Sound waves are collected by the external ear and amplified as they travel through the ear canal. When sounds reach the junction between the outer and middle ear, they vibrate the tympanic membrane—the eardrum. The resulting mechanical energy causes the attached ossicles—a set of small bones in the middle ear—to move. The ossicles vibrate the oval window, the outermost part of the inner ear. In the labyrinth of the inner ear, the sound wave energy is transferred to the cochlea—a coiled structure in the inner ear—causing the fluid within it to move. The cochlea contains receptors that transduce mechanical sound waves into electrical signals that can be interpreted by the brain. Sounds within the hearing range vibrate the basilar membrane in the cochlea and are detected by hair cells on the organ of Corti, the site of transduction. Along the primary auditory pathway, the signals are sent through the auditory nerve to the cochlear nuclei in the brainstem. From here, they travel to the inferior colliculus of the midbrain and up to the thalamus, and then to the primary auditory cortex. Along this pat

 Core: Sensory Systems

Action Potentials

JoVE 10844

Neurons communicate by firing action potentials—the electrochemical signal that is propagated along the axon. The signal results in the release of neurotransmitters at axon terminals, thereby transmitting information in the nervous system. An action potential is a specific “all-or-none” change in membrane potential that results in a rapid spike in voltage.

Neurons typically have a resting membrane potential of about -70 millivolts (mV). When they receive signals—for instance, from neurotransmitters or sensory stimuli—their membrane potential can hyperpolarize (become more negative) or depolarize (become more positive), depending on the nature of the stimulus. If the membrane becomes depolarized to a specific threshold potential, voltage-gated sodium (Na+) channels open in response. Na+ has a higher concentration outside of the cell as compared to the inside, so it rushes in when the channels open, moving down its electrochemical gradient. As positive charge flows in, the membrane potential becomes even more depolarized, in turn opening more channels. As a result, the membrane potential quickly rises to a peak of around +40 mV. At the peak of the action potential, several factors drive the potential back down. The influx of Na+ slows because the Na+ channels start to inactiv

 Core: Nervous System


JoVE 10780

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause Waardenburg Syndrome Type 4, or WS4, which can cause defects in pigmentation, hearing impairments, and an absence of intestinal contractions necessary for elimination. This diversity of phenotypes results from the expression pattern of SOX10 in early embryonic and fetal development. SOX10 is found in neural crest cells that form melanocytes, which are involved in pigmentation and also in the early development of the ear. SOX10 is also expressed in nerve tissue that eventually contributes to the enteric nervous system in the gut, which controls the contractions necessary for waste elimination. In this way, SOX10 exhibits pleiotropic effects, because it influences multiple phenotypes. Pleiotropy can arise through several mechanisms. Gene pleiotropy occurs when a gene has various functions due to encoding a product that interacts with multiple proteins or catalyzes multiple reactions. For example, in humans, an abnormal copy of the SOX10 gene, in which a region is deleted, can lead to developmental defects that include a white forelock, different-colored irises (e.g., one blue and one brown), and regions of unpigmented skin. These traits are all symptoms of a di

 Core: Classical and Modern Genetics


JoVE 10912

During embryogenesis, cells become progressively committed to different fates through a two-step process: specification followed by determination. Specification is demonstrated by removing a segment of an early embryo, “neutrally” culturing the tissue in vitro—for example, in a petri dish with simple medium—and then observing the derivatives. If the cultured region gives rise to cell types that it would normally generate in the embryo, this means that it is specified. In contrast, determination occurs if a region of the embryo is removed and placed in a “non-neutral” environment—such as in a dish containing complex medium supplemented with a variety of proteins, or even a different area of the embryo itself—and it still generates the expected derivatives. Specification and determination are two sequential steps in the developmental pathway of a cell, which precede the final stage of differentiation, during which mature tissues with unique morphologies and functions are produced. To study specification, researchers must first understand the normal derivatives of different regions of an embryo. To accomplish this, fate maps are often used, which are generated by dyeing or labeling cells early in embryonic development, culturing whole embryos and monitoring where the marked cells end up. For example, such te

 Core: Reproduction and Development


JoVE 10906

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal distribution of cell contents ensures that there are enough cytoplasm and nutrients to nourish the early stages of development. Second, during oogenesis, meiosis “arrests” at two distinct points: once during embryonic growth and a second time during puberty. In mammals, oocytes are suspended in prophase I until sexual maturation, at which point meiosis I continues under hormonal influence until an egg precursor cell is released into a fallopian tube. At ovulation, the precursor exits the ovary and, only if fertilization occurs, is stimulated to complete meiosis II and form a complete egg. Defects during oogenesis can result in severe consequences. In particular, problems with chromosome segregation during either meiosis I or meiosis II may lead to an embryo being aneuploid, meaning that it contains an abnormal number of chromosomes. Increased age elevates a woman

 Core: Reproduction and Development
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