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Thalamus: Paired bodies containing mostly gray substance and forming part of the lateral wall of the third ventricle of the brain. The thalamus represents the major portion of the diencephalon and is commonly divided into cellular aggregates known as nuclear groups.

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

Vision

JoVE 10858

Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed. Light is absorbed by the rod and cone photoreceptor cells at the back of the retina, causing a decrease in their rate of neurotransmitter release. In addition to detecting photons of light, color information is also encoded here, since different types of cones respond maximally to different wavelengths of light. The photoreceptors then send visual information to bipolar cells near the middle of the retina, which is followed by projection to ganglion cells at the front of the retina. Horizontal and amacrine cells mediate lateral interactions between these cell types, integrating information from multiple photoreceptors. This integration aids in the initial processing of visual information, such as detecting simple features, like edges. Along with glial cells, the axons of the retinal ganglion cells make up the optic nerve, which transmits visual information to the brain. The optic nerve partially cro

 Core: Biology

Case Studies

JoVE 11019

There are many research methods available to psychologists in their efforts to understand, describe, and explain behavior and the cognitive and biological processes that underlie it.



In 2011, the New York Times published a feature story on Krista and Tatiana Hogan, Canadian twin girls. These particular twins are unique because Krista and Tatiana are conjoined twins,…

 Core: Psychology

Somatosensation

JoVE 10859

The somatosensory system relays sensory information from the skin, mucous membranes, limbs, and joints. Somatosensation is more familiarly known as the sense of touch. A typical somatosensory pathway includes three types of long neurons: primary, secondary, and tertiary. Primary neurons have cell bodies located near the spinal cord in groups of neurons called dorsal root ganglia. The sensory neurons of ganglia innervate designated areas of skin called dermatomes. In the skin, specialized structures called mechanoreceptors transduce mechanical pressure or distortion into neural signals. In hairless skin, most disturbances can be detected by one of four types of mechanoreceptors. Two of these, Merkel disks and Ruffini endings, are slow-adapting and continue to respond to stimuli that remain in prolonged contact with the skin. Merkel disks respond to light touch. Ruffini endings detect deeper static touch, skin stretch, joint deformation, and warmth. The other two major cutaneous mechanoreceptors, Meissner corpuscles and Pacinian corpuscles, are rapidly-adapting. These mechanoreceptors detect dynamic stimuli, like those required to read Braille. Meissner corpuscles are responsive to delicate touch and pressure, as well as low-frequency vibrations. Pacinian corpuscles respond best to deep, repetitive pressure and high-frequency vibrations. Information detected

 Core: Biology

Hearing

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: Biology

Gustation

JoVE 10851

Gustation is a chemical sense that, along with olfaction (smell), contributes to our perception of taste. It starts with the activation of receptors by chemical compounds (tastants) dissolved in the saliva. The saliva and filiform papillae on the tongue distribute the tastants and increase their exposure to the taste receptors.

Taste receptors are found on the surface of the tongue as well as on the soft palate, the pharynx, and the upper esophagus. On the tongue, taste receptors are contained within structures called taste buds. The taste buds are embedded within papillae, which are visible on the tongue surface. There are three types of papillae that contain taste buds and their receptors. Circumvallate papillae are the largest papillae and are located near the back of the tongue. Foliate papillae resemble folds on the side of the tongue. Fungiform papillae are found across the front three-quarters of the tongue but are less concentrated in the middle of the tongue. There are five basic tastes: salty, sour, sweet, bitter, and savory (or umami). The perception of salty taste is caused by tastants that release sodium ions upon dissolution. Sour taste, by contrast, is produced by the release of hydrogen ions from dissolved acidic tastants. Salty and sour tastants produce a neural response by depolarizing the membrane directly (salty tastants) or via ion chan

 Core: Biology

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: Biology

The Vestibular System

JoVE 10856

The vestibular system is a set of inner ear structures that provide a sense of balance and spatial orientation. This system is comprised of structures within the labyrinth of the inner ear, including the cochlea and two otolith organs—the utricle and saccule. The labyrinth also contains three semicircular canals—superior, posterior, and horizontal—that are oriented on different planes. All of these structures contain vestibular hair cells—the sensory receptors of the vestibular system. In the otolith organs, the hair cells sit beneath a gelatinous layer called the otolithic membrane, which contains otoconia—calcium carbonate crystals—making it relatively heavy. When the head is tilted, the otolithic membrane shifts, bending the stereocilia on the hair cells. In the semicircular canals, the cilia of the hair cells are contained within a gelatinous cupula, which is surrounded by endolymph fluid. When the head experiences movements, such as rotational acceleration and deceleration, the fluid moves, bending the cupula and the cilia within it. Similar to the auditory hair cells, displacement towards the tallest cilium causes mechanically-gated ion channels to open, depolarizing the cell and increasing neurotransmitter release. Displacement towards the shortest cilium hyperpolarizes the cell and decreases neurotr

 Core: Biology

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: Biology

Nociception

JoVE 10873

Nociception—the ability to feel pain—is essential for an organism’s survival and overall well-being. Noxious stimuli such as piercing pain from a sharp object, heat from an open flame, or contact with corrosive chemicals are first detected by sensory receptors, called nociceptors, located on nerve endings. Nociceptors express ion channels that convert noxious stimuli into electrical signals. When these signals reach the brain via sensory neurons, they are perceived as pain. Thus, pain helps the organism avoid noxious stimuli. The immune system plays an essential role in pain pathology. Upon encountering noxious stimuli, immune cells such as mast cells and macrophages present at the site of injury release inflammatory chemicals such as cytokines, chemokines, histamines, and prostaglandins. These chemicals attract other immune cells such as monocytes and T cells to the injury site. They also stimulate nociceptors, resulting in hyperalgesia—a more intense response to a previously painful stimulus, or allodynia—a painful response to a normally innocuous stimulus such as light touch. Such pain sensitization helps protect the injured site during healing. In some cases, pain outlives its role as an acute warning system if sensitization fails to resolve over time. Chronic pain—persistent or recurrent pain lasting longer than t

 Core: Biology
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