9 VIII Glossary

Age-related macular degeneration (AMD): An eye disease that can blur central vision. It happens when aging causes damage to the macula, the part of the eye that controls sharp, straight-ahead vision.

Alzheimer’s disease: A type of dementia; a progressive brain disorder that causes abnormal buildup of proteins that form amyloid plaques and tau tangles that damage neurons and impair communication between neurons, which results in brain shrinkage.

Amygdala: Involved in long-term memory formation and emotional responses.

Anosmia: The loss of the sense of smell.

Anterior columns: Area of white matter in the spinal column between the two anterior horns of gray matter.

Anterior horn: Area of gray matter within the spinal cord that sends out motor signals to the skeletal muscles.

Anterior median fissure: The anterior midline of the spinal cord.

Aqueous humors: A thin, watery fluid found between the cornea and lens of the eye.

Arachnoid mater: A membrane of thin fibrous tissue that forms a loose sac around the CNS and is found in the middle layer of the meninges.

Arachnoid trabeculae: A thin, filamentous mesh deep to the arachnoid.

Ascending tracts: Nervous system fibers within the spinal cord columns that carry sensory information up to the brain.

Association areas: Areas of the brain’s cortex found in the spaces between the primary areas for sensory and motor functions and integrate multisensory information.

Astigmatism: A type of refractive error that causes objects to look blurry or distorted. It happens when the cornea or lens has a different shape than normal, which makes light bend differently as it enters the eye.

Astrocyte: A type of neuroglia of the central nervous system.

Ataxia: A neurological condition characterized by the loss of muscle control, resulting in difficulties with balance, coordination, and movement; often the result of exposure to external substances, focal lesions, or a genetic disorder.

Audiologists: Health care professionals who diagnose, manage, and treat hearing, balance, or ear problems.

Audition: The sense of hearing.

Auditory ossicles: Three small bones in the middle called the malleus (hammer), incus (anvil), and stapes (stirrups).

Aura: A change in function or onset of symptoms that can precede a migraine.

Auricle: A large, fleshy structure on the lateral side of the head; also called the pinna or earlobe.

Autonomic nervous system (ANS): Responsible for involuntary control of the body to maintain homeostasis.

Autonomic tone: Balance between the sympathetic and parasympathetic nervous systems.

Axon: A fiber that emerges from the cell body and sends an electrical nerve impulse to target cells.

Axon terminals: Ends of axons.

Baroreceptors: Type of receptors that sense the increase in blood pressure in the aorta or carotid sinus.

Basal forebrain: Contains nuclei that are important in learning and memory. Alzheimer’s disease is associated with a loss of neurons in this area.

Basal nuclei: Responsible for planning and coordinating movements, along with preventing or suppressing unwanted movements and regulating muscle tone.

BE FAST: A mnemonic to help people remember what to look for in someone who is having symptoms of a stroke; it stands for Balance, Eyes, Face, Arms, and Speech.

Bell’s palsy: A neurological disorder that causes paralysis or weakness on one side of the face.

Bipolar neurons: Have two processes, which extend from each end of the cell body, opposite to each other. One is the axon and one is the dendrite.

Blood-brain barrier (BBB): A physical barrier that restricts what can cross from the blood into the brain.

Brachial plexus: Spinal nerves C4 through T1 reorganize through this plexus to give rise to the nerves of the arms.

Broca’s area: Responsible for the production of language, or controlling movements of muscles responsible for speech. In most people, it is located in the left frontal lobe.

Brodmann’s areas: A system of classification developed in the early 1900s by Korbinian Broadmann to describe the anatomical distinctions within the cortex.

Cardiovascular control center: Heart rate, force of the heart’s contraction, and blood pressure are controlled by the medulla oblongata.

Cataract: Results when the lens of the eye or its attached membrane becomes cloudy or opaque due to the breakdown of proteins in the lens.

Cauda equina: A long bundle of nerves that emerges from the end of the spinal cord and resembles a horse’s tail.

Cell body: The main part of a neuron that contains the nucleus and most of the major organelles.

Central nervous system (CNS): Includes the brain and spinal cord.

Central sulcus: Separates the parietal lobes and the frontal lobes of the brain.

Cerebellum: An area of the brain attached to the brain stem; accounts for 10 percent of the brain’s mass and is covered in folds and grooves like the cerebrum and looks like a miniature version of that part of the brain.

Cerebral aqueduct: Area of the brain where the third ventricle opens into and then passes through the midbrain.

Cerebral cortex: The wrinkled outer portion of the cerebrum.

Cerebral hemisphere: The right and left halves (hemispheres) of the cerebrum.

Cerebrospinal fluid (CSF): The fluid that circulates through and around the brain and spinal cord.

Cerebrovascular accident (CVA): The medical term for disruption of blood supply to the brain; commonly called a stroke.

Cerebrum: The iconic gray structure of the human brain that makes up most of the mass of the brain; responsible for higher neurological functions such as memory, emotion, and consciousness.

Cervical plexus: Composed of axons from spinal nerves C1 through C5 and branches into nerves in the posterior neck and head, as well as the phrenic nerve.

Choroid: A layer of highly vascularized connective tissue that provides a blood supply to the eyeball.

Choroid plexus: A specialized structure in the ventricles where ependymal cells come in contact with blood vessels and filter and absorb components of the blood to produce cerebrospinal fluid.

Ciliary body: A muscular structure that is attached to the lens of the eye by suspensory ligaments or zonule fibers.

Cochlea: The auditory portion of the inner ear containing structures to transmit sound stimuli.

Cochlear duct: A space within the auditory portion of the inner ear.

Cognitive abilities: Higher mental functions, such as orientation and memory, language and speech, sensorium, and judgment and abstract reasoning, occurring across regions of the cerebral cortex. If a particular area of the brain becomes injured or diseased, specific cognitive abilities are affected.

Color blindness: Also known as color deficiency; occurs when colors are seen abnormally and is usually a genetic condition that is present at birth in which cones in the retina are completely or partially absent.

Concussion: A mild traumatic brain injury that affects brain function and can include headaches and trouble with concentration, memory, balance, mood and sleep; usually caused by an impact to the head or body.

Conductive hearing loss: Occurs in the outer or middle ear where sound waves are not able to carry all the way through to the inner ear.

Cones: Part of the eye that detects color and functions in bright light.

Cornea: Covers the anterior part of the eye. It allows light to enter, and along with the lens, focuses light onto the retina.

Corpus callosum: White matter deep within the cerebrum that provides the major pathway for communication between the two hemispheres of the cerebrum.

Cranial nerves: Twelve pairs of nerves attached to the brain and primarily responsible for the sensory and motor functions of the head and neck.

Dendrites: Receive information from other neurons at synapses.

Depression: A serious mental illness that causes persistent feelings of sadness and affects how the person acts and perceives the world.

Descending tracts: Nervous system fibers within the spinal cord columns that carry motor commands down from the brain.

Dorsal (posterior) nerve root: Posterior area of the spinal cord where axons responsible for sensory functions enter.

Dorsal (posterior) root ganglion: Most common type of sensory ganglion that have sensory endings in the periphery, such as the skin, and extend into the CNS through the dorsal nerve root.

Dura mater: The outermost layer of the meninges.

Electroconvulsive therapy (ECT): The application of electrical currents to the brain and typically used to treat severe depression that has not responded to other treatments.

Encapsulated ending: Refers to a type of neuron that has sensory nerve endings surrounded in connective tissue to enhance their sensitivity.

Encephalitis: An inflammation of the brain that can be caused by viral or bacterial infections or by a person’s immune system mistakenly attacking brain cells.

Endoneurium: Loose connective tissue that surrounds individual axons.

Enteric nervous system (ENS): A division of the nervous system that controls the smooth muscle and glandular tissue in the digestive system.

Ependymal cell: A neuroglial cell that filters blood to make cerebrospinal fluid.

Epidural space: Space between the dura and the vertebrae.

Epineurium: A layer of fibrous connective tissue that surrounds the outer surface of a nerve.

Equilibrium: The sense of balance.

Eustachian tube: Connects the middle ear to the pharynx and helps equalize air pressure across the tympanic membrane.

Expressive aphasia: Condition in which there is a difficulty in producing speech sounds; often leads to broken or halting speech.

External (outer ear): Consists of the auricle, external auditory canal, and tympanic membrane.

External auditory meatus: The location where the external auditory canal enters the skull.

Exteroceptor: A receptor that is located near a stimulus in the external environment.

Extraocular muscles: Eye muscles that cause movement of the eye within the orbit.

Fascicles: Groups of axons bundled within a nerve.

Femoral nerve: One of the major nerves from the lumbar plexus.

Fibrous tunic: The outermost layer of tissue of the eye.

Fight-or-flight response: Controlled by the sympathetic division of the autonomic nervous system.

Fourth ventricle: The space between the cerebellum and the pons and upper medulla oblongata; narrows into the central canal of the spinal cord.

Fovea: A small area in the macula lutea of the eye; visual acuity is greatest at this point.

Free nerve ending: A neuron that has dendrites embedded in tissue that receive a sensation.

Frontal lobes: Regions of the cerebral cortex deep to the frontal bone, which is also superior to the lateral sulcus.

Ganglion: In the PNS, a collection of neuron cell bodies in the PNS.

General sense: A sense that is distributed throughout the body, such as touch or pain.

Glaucoma: A chronic, progressive eye disease that leads to vision loss due to damage to the optic nerve.

Gray matter: Regions within the nervous system structures with many cell bodies and dendrites.

Guillain-Barré syndrome: An autoimmune disorder where the immune system mistakenly attacks some peripheral nerves. This damage interferes with the transmission of signals, leading to muscle weakness and other symptoms.

Gustation: The sense of taste.

Gustatory receptor cells: Cells found in taste buds that are responsible for taste.

Gyrus: A ridge on a wrinkle of the cerebral cortex.

Hair cells: Mechanoreceptors cells found in the ear that convert sound vibrations into nerve impulses.

Hemorrhagic strokes: Result from bleeding in the brain due to a ruptured blood vessel.

Hippocampus: Involved in long-term memory formation and emotional responses.

Huntington’s disease: A rare, progressive genetic disease that causes deterioration of neurons in the brain and affects a person’s movements, thinking ability, and mental health.

Hyperopia (farsightedness): Makes nearby objects look blurry. It happens when the eyeball grows too short from front to back, or when there are problems with the shape of the cornea or lens.

Hypothalamus: A major region of the diencephalon; the major regulator of homeostasis and also controls temperature, appetite, thirst, and sleep.

Incus: Latin term for a small bone in the middle ear; also called the anvil.

Inferior colliculus: Inferior pair of colliculi of the midbrain’s tectum; neurons within the inferior colliculus project to the thalamus, which then sends auditory information to the cerebrum for the conscious perception of sound.

Inferior oblique: An extraocular eye muscle that coordinates eye movements.

Inferior rectus: An extraocular eye muscle that coordinates eye movements.

Integration: Process of the central nervous system that requires the analysis of sensory information and development of thoughts, emotions, and conscious experiences in the brain.

Interneurons: Connect sensory neurons to motor neurons and are responsible for interpreting sensory information, storing information, and for decision-making. Most neurons in the central nervous system are interneurons; also referred to as association neurons.

Interoceptor: A receptor that interprets stimuli from internal organs and tissues.

Iris: The colored part of the eye.

Ischemic strokes: Caused by a blockage in an artery in the brain from a blood clot or embolism.

Judgment and abstract reasoning: Refers to making sense of concepts and making appropriate decisions.

Kinesthesia: A general sense referring to body movement.

Lacrimal duct: Area of the eye responsible for draining tears into the nasal cavity.

Lacrimal gland: Gland that produces tears in the eye.

Lateral columns: The white matter on either side of the spinal cord, between the posterior horn and the anterior horn.

Lateral horn: Area of gray matter found in the thoracic, upper lumbar, and sacral regions; contains cell bodies of motor neurons of the autonomic nervous system.

Lateral rectus: An extraocular eye muscle that coordinates eye movements.

Lateral sulcus: Separates the temporal lobe from the other regions of the brain.

Lateral ventricles: Two ventricles within each cerebral hemisphere of the brain.

Lens: A part of the eye that focuses light rays.

Limbic cortex: The region of the cerebral cortex that is part of the limbic system.

Limbic lobe: Includes structures that are involved in emotional responses, as well as structures that contribute to memory; has strong connections with the hypothalamus and influences the state of its activity on the basis of emotional state.

Limbic system: A collection of structures involved in emotion, memory, and behavior.

Longitudinal fissure: The large groove between the two sides of the cerebrum that separates the cerebrum into two distinct halves.

Lumbar plexus: Arises from all the lumbar spinal nerves and gives rise to nerves innervating the pelvic region and the anterior leg.

Lumbar puncture: A procedure in which a needle is inserted through the dura and arachnoid layers to withdraw cerebrospinal fluid.

Malleus: Latin term for a small bone in the middle ear; also called the hammer.

Medial rectus: An extraocular eye muscle that coordinates eye movements.

Medulla oblongata: The most inferior of the brain stem before it transitions into the spinal cord.

Memory: Refers to how the brain stores and remembers information. It is a function of the temporal lobe.

Meninges: Membranes of the outer surface of the CNS that are composed of connective tissues.

Meningitis: An inflammation of the meninges; can be caused by infection, bacteria, or viruses.

Microglia: A type of macrophage but are smaller than most other neuroglia. When macrophages encounter diseased or damaged cells, they ingest and digest those cells or the pathogens that cause disease.

Middle ear: Part of the ear separated from the outer ear by the tympanic membrane and  transmits sound waves from the tympanic membrane to the partition between the middle and inner ears through a chain of tiny bones.

Migraine: A neurological condition consisting of recurrent headaches that are moderate to severe in intensity.

Motor neurons: Neurons found in the PNS that carry information to other motor neurons, muscles, or glands; also known as efferent neurons.

Multiple sclerosis (MS): An autoimmune disease that causes inflammation and destruction of the myelin in the central nervous system.

Multipolar neurons: Any neurons that are not unipolar or bipolar. They have one axon and two or more dendrites. Most neurons in the human body are multipolar.

Myelin: A lipid-rich, insulating substance made from neuroglia within some axons.

Myelin sheath: Composed of myelin that surrounds an axon and helps increase the speed of electrical signals along the axon.

Myopia (nearsightedness): Makes far-away objects look blurry. It happens when the eyeball grows too long from front to back, or when there are problems with the shape of the cornea or the lens.

Nerve: A bundle of axons in the PNS.

Nerve plexus: Axons from different spinal nerves that come together and form networks of nerve fibers.

Neural tunic: Another name for the eye’s retina; it contains the rods and cones responsible for photoreception.

Neuroglia: Include a variety of cells that support the neurons in their communication activities.

Neurologist: A physician who specializes in the diagnosis and treatment of disorders and conditions related to the brain, spinal cord, nerves, and muscles.

Neurology: The study of the nervous system and the structure and function of all of its parts.

Neurons: The communicating cells of the nervous system.

Neurosurgeon: A physician who specializes in diagnosing and treating conditions that affect the nervous system. They also perform surgery and prescribe nonsurgical treatments.

Nociceptors: A type of neuron that perceives pain.

Node of Ranvier: A gap within the myelin covering an axon.

Nucleus: A collection of neuron cell bodies in the CNS.

Occipital lobes: Regions of the cerebral cortex deep to the occipital bone.

Olfaction: The sense of smell.

Olfactory bulb: Part of the frontal lobe of the brain that receives impulses related to smell.

Oligodendrocyte: The neuroglia that insulate axons with myelin in the central nervous system.

Optic disc: An area at the back of the eye in the retina where there are no photoreceptors; commonly called a “blind spot.”

Optic nerve: The area where nerve impulses generated by rods and cones of the eye are sent to the brain.

Organs of Corti: Structures in the ear that change sound waves into neural signals.

Orientation: Being aware of your immediate circumstances, such as your name, date, and location; this ability occurs in the prefrontal cortex.

Orthostatic hypotension: Also known as postural hypotension; a condition where blood pressure drops significantly when a person stands up, often causing dizziness, lightheadedness, or fainting.

Otitis media: An inflammation or infection of the middle ear that is often caused by an upper respiratory infection, resulting in fluid build-up in the eustachian tubes, fever, and ear pain.

Palpebral conjunctiva: A thin membrane that lines the inner surface of each eyelid.

Papillae: Raised bumps on the tongue that contain taste buds.

Parasympathetic division: A division of the autonomic nervous system associated with the “rest and digest” response. This division increases activities like digestion and decreases others like heart rate and blood pressure.

Paresthesias: Tingling sensations.

Parietal lobes: Regions of the cerebral cortex deep to the parietal bones. They are superior to the lateral sulcus and directly behind the frontal lobe.

Parieto-occipital sulcus: Separates the parietal and occipital lobes of the brain.

Parkinson’s disease: A progressive neurological disorder that affects an individual’s ability to move. It is caused by the deterioration of neurons in the brain that produce dopamine.

Perception: Refers to the central processing of sensory stimuli into a meaningful pattern. Perception is dependent on sensation, but not all sensations are perceived.

Perineurium: Fibrous connective tissue that surrounds a group of axons or fascicles.

Peripheral nervous system (PNS): Includes all of the parts of the nervous system found outside of the brain and spinal cord.

Peripheral neuropathy: Weakness, numbness, and pain caused by peripheral nerve damage and commonly a result of diabetes and peripheral vascular disease.

Photoreceptors: Specialized receptor cells in the retina that respond to light stimuli.

Phrenic nerve: Nerve that connects to the diaphragm at the base of the thoracic cavity.

Pia mater: A thin fibrous membrane that follows the bumps and grooves of the gyri and sulci.

Pinna: A large, fleshy structure on the lateral side of the head; also called the auricle or earlobe.

Pons: The main connection between the cerebellum and the brain stem; with the medulla oblongata, it regulates respirations.

Postcentral gyrus: The primary somatosensory area; all the tactile senses, as well as more general senses of the body such as proprioception (body position) and kinesthesia (movement), are processed in this area.

Posterior columns: Area of white matter in the spinal column between the two posterior horns of gray matter.

Posterior horn: Area of gray matter within the spinal cord responsible for sensory processing.

Posterior median sulcus: The posterior middle of the spinal cord.

Precentral gyrus: Found in the frontal lobe and contains the primary motor cortex. The primary motor cortex has voluntary control over skeletal muscles.

Presbyopia: A type of refractive error that makes it hard for middle-aged and older adults to see things up close because the lens in the eye gets harder and less flexible and stops focusing light correctly on the retina.

Proprioception: A general sense referring to body movement.

Proprioceptor: A receptor located near a moving part of the body, such as a muscle, that interprets position and movement.

Psychiatrist: A physician who specializes in mental health and substance use disorders.

Pupil: The black hole in the center of the iris that allows light to enter the eye.

Pyramids: Two large white matter lateral bulges formed from the descending motor tracts of the medulla oblongata.

Pyramidal decussation: The defining landmark of the medullary-spinal border where motor tracts cross over to the opposite side of the brain, explaining why the right side of the brain controls the left side of the body and vice versa.

Receptive aphasia: Aphasia associated with Wernicke’s area where there is a loss of understanding of what is being spoken.

Reflex: A quick predictable automatic response to a stimulus and occurs without a conscious decision by the brain to perform it.

Refractive errors: A common type of vision problem that occurs when the shape of a person’s eye prevents light from focusing correctly on their retina.

Response: A reaction to a stimulus perceived by our senses; responses can be voluntary or involuntary.

Rest and digest response: Controlled by the parasympathetic division of the autonomic nervous system.

Reticular formation: Area of gray matter throughout the brain stem that is related to sleep and wakefulness and general brain activity and attention.

Retina: The innermost layer of the eye, which contains the rods and cones responsible for photoreception.

Rods: Part of the eye that detects shades of black and grey but does not function in bright light.

Saccule: Specialized structures in the ear responsible for sensing head position.

Sacral plexus: Comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4 to supply nerves to the posterior leg.

Satellite cells: A type of neuroglia in the peripheral nervous system that provides support to neurons.

Schizophrenia: A serious mental illness caused by genetics, imbalanced neurotransmitters in the brain, and environmental factors.

Schwann cell: A type of neuroglia in the peripheral nervous system that insulates axons with myelin.

Sciatica: Refers to pain that travels along the sciatic nerve from the buttocks and down the back of the leg; most often happens when a herniated disk or an overgrowth of bone puts pressure on the lumbar spine nerve roots, causing inflammation, pain, and possible numbness in the affected leg.

Sciatic nerve: The most significant nerve to come from the sacral plexus and extends across the hip joint and is most commonly associated with sciatica.

Sclera: A tough protective structure that is part of the fibrous tunic of the eye.

Semicircular canals: Three ring-like extensions adjacent to the vestibule of the eye and responsible for sensing movement.

Sensation: Refers to receiving information from the environment that activates sensory receptor cells; a major function of the nervous system.

Sensorineural hearing loss: Occurs when the inner ear or the vestibulocochlear nerve becomes damaged. It is the most common type of hearing loss and can be a result of aging, exposure to loud noise, injury, disease, certain drugs, or an inherited condition.

Sensorium: Refers to interpretation of sensory stimuli.

Sensory neurons: Neurons found in the PNS that carry sensory information to the spinal cord or brain; also known as afferent neurons.

SLUDD: An acronym associated with some functions of the parasympathetic nervous system and stands for Salivation, Lacrimation, Urination, Digestion, and Defecation.

Somatic nervous system (SNS): Responsible for conscious perception of the environment (senses) and voluntary motor responses to that perception by the contraction of skeletal muscles.

Somatosensation: The general sense of touch.

Special sense: Any sensory system that is localized to a specific organ structure, namely, the senses of smell, taste, sight, hearing, and balance.

Spinal nerves: Nerves connected to the spinal cord; all spinal nerves are mixed nerves with combined sensory and motor axons that separate into two nerve roots.

Stapes: Latin term for a small bone in the middle ear; also called the stirrup.

Stimulus: An agent that causes a change in homeostasis or the environment.

Stroke: The medical term for disruption of blood supply to the brain; also called a cerebrovascular accident (CVA).

Subarachnoid space: Area containing the trabeculae and is filled with circulating cerebrospinal fluid.

Subdural hematoma: Occurs when a blood vessel near the surface of the brain bursts, causing blood to build up between the brain and the brain’s tough outer lining. It is a life-threatening problem because it causes increased pressure that compresses the brain and can result in loss of consciousness, paralysis, or death.

Subdural space: The space between the dura and the middle layer or arachnoid mater.

Substantia nigra: Structure found in the midbrain that is responsible for regulating automatic skeletal muscle movements, such as swinging your arms when you walk.

Sulcus: A groove between two gyri of the cerebral cortex.

Superior colliculus: Superior pair of colliculi of the midbrain’s tectum; activity in the superior colliculus is related to orienting the eyes to a sound or touch stimulus.

Superior oblique: An extraocular eye muscle that coordinates eye movements.

Superior rectus: An extraocular eye muscle that coordinates eye movements.

Sympathetic division: A division of the autonomic nervous system associated with the “fight-or-flight” response; it increases body activities that are crucial for survival in a potentially dangerous situation and will decrease body activities that aren’t essential.

Synapse: Where two neurons (or a neuron and muscle) meet.

Synaptic end bulb: An enlarged tip of an axon terminal that makes connection with the target at the synapse.

Taste buds: The structures responsible for taste.

Tectum: Region of the midbrain composed of four nuclei or “bumps” known as the colliculi.

Temporal lobes: Regions of the cerebral cortex deep to the temporal bones and located on each side of the brain.

Thalamus: Relays information between the cerebral cortex and the brain stem, spinal cord, and nerves; all sensory information, except for the sense of smell, passes through and is processed within the thalamus.

Thermoreceptors: A type of neuron that perceives temperature.

Third ventricle: Connected to the lateral ventricles and is the space between the left and right sides of the diencephalon.

Thoracolumbar system: Another name for the sympathetic nervous system.

Tract: A bundle of axons, or fibers, found in the CNS.

Traumatic brain injuries (TBIs): Head injuries that can range from mild concussions to severe brain injuries causing death; are often due to falls, motor vehicle accidents, sports injuries, or violence.

Tympanic membrane: Eardrum; vibrates when sound waves hit it.

Umami: A Japanese word that means “delicious taste” and is often translated to mean savory; recently discovered as a fifth taste.

Unipolar neurons: Have only one process emerging from the cell. True unipolar cells are only found in invertebrate animals.

Utricle: Specialized structures in the ear responsible for sensing head position.

Vascular tunic (uvea): The middle layer of the eye and mostly composed of the choroid, ciliary body, and iris.

Ventral (anterior) nerve root: Anterior area of the spinal cord where axons responsible for motor functions enter.

Ventricles: Open spaces within the brain that are lined with ependymal cells where cerebrospinal fluid (CSF) circulates.

Vestibule: A region of the inner ear that is responsible for balance.

Visceral sense: A general sense referring to body movement.

Vision: The special sense of sight that is based on light stimuli entering through the eyes.

Visual acuity: The sharpness of vision.

Vitreous humor: A viscous or jelly-like fluid found in the posterior cavity of the eye.

Wernicke’s area: Responsible for speech comprehension.

White matter: Regions within the nervous system structures with many myelinated axons.

Zonule fibers: Suspensory ligaments that connect the ciliary body and lens of the eye.