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Key Terms Chapter 14: The Somatic Nervous System

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    62665
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    alkaloid
    substance, usually from a plant source, that is chemically basic with respect to pH and will stimulate bitter receptors
    amacrine cell
    type of cell in the retina that connects to the bipolar cells near the outer synaptic layer and provides the basis for early image processing within the retina
    ampulla
    in the ear, the structure at the base of a semicircular canal that contains the hair cells and cupula for transduction of rotational movement of the head
    anosmia
    loss of the sense of smell; usually the result of physical disruption of the first cranial nerve
    anterior corticospinal tract
    division of the corticospinal pathway that travels through the ventral (anterior) column of the spinal cord and controls axial musculature through the medial motor neurons in the ventral (anterior) horn
    aqueous humor
    watery fluid that fills the anterior chamber containing the cornea, iris, ciliary body, and lens of the eye
    ascending pathway
    fiber structure that relays sensory information from the periphery through the spinal cord and brain stem to other structures of the brain
    association area
    region of cortex connected to a primary sensory cortical area that further processes the information to generate more complex sensory perceptions
    audition
    sense of hearing
    auricle
    fleshy external structure of the ear
    basilar membrane
    in the ear, the floor of the cochlear duct on which the organ of Corti sits
    Betz cells
    output cells of the primary motor cortex that cause musculature to move through synapses on cranial and spinal motor neurons
    binocular depth cues
    indications of the distance of visual stimuli on the basis of slight differences in the images projected onto either retina
    bipolar cell
    cell type in the retina that connects the photoreceptors to the RGCs
    Broca’s area
    region of the frontal lobe associated with the motor commands necessary for speech production
    capsaicin
    molecule that activates nociceptors by interacting with a temperature-sensitive ion channel and is the basis for “hot” sensations in spicy food
    cerebral peduncles
    segments of the descending motor pathway that make up the white matter of the ventral midbrain
    cervical enlargement
    region of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of and finer control of muscles of the upper limb
    chemoreceptor
    sensory receptor cell that is sensitive to chemical stimuli, such as in taste, smell, or pain
    chief sensory nucleus
    component of the trigeminal nuclei that is found in the pons
    choroid
    highly vascular tissue in the wall of the eye that supplies the outer retina with blood
    ciliary body
    smooth muscle structure on the interior surface of the iris that controls the shape of the lens through the zonule fibers
    circadian rhythm
    internal perception of the daily cycle of light and dark based on retinal activity related to sunlight
    cochlea
    auditory portion of the inner ear containing structures to transduce sound stimuli
    cochlear duct
    space within the auditory portion of the inner ear that contains the organ of Corti and is adjacent to the scala tympani and scala vestibuli on either side
    cone photoreceptor
    one of the two types of retinal receptor cell that is specialized for color vision through the use of three photopigments distributed through three separate populations of cells
    contralateral
    word meaning “on the opposite side,” as in axons that cross the midline in a fiber tract
    cornea
    fibrous covering of the anterior region of the eye that is transparent so that light can pass through it
    corneal reflex
    protective response to stimulation of the cornea causing contraction of the orbicularis oculi muscle resulting in blinking of the eye
    corticobulbar tract
    connection between the cortex and the brain stem responsible for generating movement
    corticospinal tract
    connection between the cortex and the spinal cord responsible for generating movement
    cupula
    specialized structure within the base of a semicircular canal that bends the stereocilia of hair cells when the head rotates by way of the relative movement of the enclosed fluid
    decussate
    to cross the midline, as in fibers that project from one side of the body to the other
    dorsal column system
    ascending tract of the spinal cord associated with fine touch and proprioceptive sensations
    dorsal stream
    connections between cortical areas from the occipital to parietal lobes that are responsible for the perception of visual motion and guiding movement of the body in relation to that motion
    encapsulated ending
    configuration of a sensory receptor neuron with dendrites surrounded by specialized structures to aid in transduction of a particular type of sensation, such as the lamellated corpuscles in the deep dermis and subcutaneous tissue
    equilibrium
    sense of balance that includes sensations of position and movement of the head
    executive functions
    cognitive processes of the prefrontal cortex that lead to directing goal-directed behavior, which is a precursor to executing motor commands
    external ear
    structures on the lateral surface of the head, including the auricle and the ear canal back to the tympanic membrane
    exteroceptor
    sensory receptor that is positioned to interpret stimuli from the external environment, such as photoreceptors in the eye or somatosensory receptors in the skin
    extraocular muscle
    one of six muscles originating out of the bones of the orbit and inserting into the surface of the eye which are responsible for moving the eye
    extrapyramidal system
    pathways between the brain and spinal cord that are separate from the corticospinal tract and are responsible for modulating the movements generated through that primary pathway
    fasciculus cuneatus
    lateral division of the dorsal column system composed of fibers from sensory neurons in the upper body
    fasciculus gracilis
    medial division of the dorsal column system composed of fibers from sensory neurons in the lower body
    fibrous tunic
    outer layer of the eye primarily composed of connective tissue known as the sclera and cornea
    fovea
    exact center of the retina at which visual stimuli are focused for maximal acuity, where the retina is thinnest, at which there is nothing but photoreceptors
    free nerve ending
    configuration of a sensory receptor neuron with dendrites in the connective tissue of the organ, such as in the dermis of the skin, that are most often sensitive to chemical, thermal, and mechanical stimuli
    frontal eye fields
    area of the prefrontal cortex responsible for moving the eyes to attend to visual stimuli
    general sense
    any sensory system that is distributed throughout the body and incorporated into organs of multiple other systems, such as the walls of the digestive organs or the skin
    gustation
    sense of taste
    gustatory receptor cells
    sensory cells in the taste bud that transduce the chemical stimuli of gustation
    hair cells
    mechanoreceptor cells found in the inner ear that transduce stimuli for the senses of hearing and balance
    incus
    (also, anvil) ossicle of the middle ear that connects the malleus to the stapes
    inferior colliculus
    last structure in the auditory brainstem pathway that projects to the thalamus and superior colliculus
    inferior oblique
    extraocular muscle responsible for lateral rotation of the eye
    inferior rectus
    extraocular muscle responsible for looking down
    inner ear
    structure within the temporal bone that contains the sensory apparati of hearing and balance
    inner segment
    in the eye, the section of a photoreceptor that contains the nucleus and other major organelles for normal cellular functions
    inner synaptic layer
    layer in the retina where bipolar cells connect to RGCs
    interaural intensity difference
    cue used to aid sound localization in the horizontal plane that compares the relative loudness of sounds at the two ears, because the ear closer to the sound source will hear a slightly more intense sound
    interaural time difference
    cue used to help with sound localization in the horizontal plane that compares the relative time of arrival of sounds at the two ears, because the ear closer to the sound source will receive the stimulus microseconds before the other ear
    internal capsule
    segment of the descending motor pathway that passes between the caudate nucleus and the putamen
    interoceptor
    sensory receptor that is positioned to interpret stimuli from internal organs, such as stretch receptors in the wall of blood vessels
    ipsilateral
    word meaning on the same side, as in axons that do not cross the midline in a fiber tract
    iris
    colored portion of the anterior eye that surrounds the pupil
    kinesthesia
    sense of body movement based on sensations in skeletal muscles, tendons, joints, and the skin
    lacrimal duct
    duct in the medial corner of the orbit that drains tears into the nasal cavity
    lacrimal gland
    gland lateral to the orbit that produces tears to wash across the surface of the eye
    lateral corticospinal tract
    division of the corticospinal pathway that travels through the lateral column of the spinal cord and controls appendicular musculature through the lateral motor neurons in the ventral (anterior) horn
    lateral geniculate nucleus
    thalamic target of the RGCs that projects to the visual cortex
    lateral rectus
    extraocular muscle responsible for abduction of the eye
    lens
    component of the eye that focuses light on the retina
    levator palpebrae superioris
    muscle that causes elevation of the upper eyelid, controlled by fibers in the oculomotor nerve
    lumbar enlargement
    region of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of muscles of the lower limb
    macula
    enlargement at the base of a semicircular canal at which transduction of equilibrium stimuli takes place within the ampulla
    malleus
    (also, hammer) ossicle that is directly attached to the tympanic membrane
    mechanoreceptor
    receptor cell that transduces mechanical stimuli into an electrochemical signal
    medial geniculate nucleus
    thalamic target of the auditory brain stem that projects to the auditory cortex
    medial lemniscus
    fiber tract of the dorsal column system that extends from the nuclei gracilis and cuneatus to the thalamus, and decussates
    medial rectus
    extraocular muscle responsible for adduction of the eye
    mesencephalic nucleus
    component of the trigeminal nuclei that is found in the midbrain
    middle ear
    space within the temporal bone between the ear canal and bony labyrinth where the ossicles amplify sound waves from the tympanic membrane to the oval window
    multimodal integration area
    region of the cerebral cortex in which information from more than one sensory modality is processed to arrive at higher level cortical functions such as memory, learning, or cognition
    neural tunic
    layer of the eye that contains nervous tissue, namely the retina
    nociceptor
    receptor cell that senses pain stimuli
    nucleus cuneatus
    medullary nucleus at which first-order neurons of the dorsal column system synapse specifically from the upper body and arms
    nucleus gracilis
    medullary nucleus at which first-order neurons of the dorsal column system synapse specifically from the lower body and legs
    odorant molecules
    volatile chemicals that bind to receptor proteins in olfactory neurons to stimulate the sense of smell
    olfaction
    sense of smell
    olfactory bulb
    central target of the first cranial nerve; located on the ventral surface of the frontal lobe in the cerebrum
    olfactory epithelium
    region of the nasal epithelium where olfactory neurons are located
    olfactory sensory neuron
    receptor cell of the olfactory system, sensitive to the chemical stimuli of smell, the axons of which compose the first cranial nerve
    opsin
    protein that contains the photosensitive cofactor retinal for phototransduction
    optic chiasm
    decussation point in the visual system at which medial retina fibers cross to the other side of the brain
    optic disc
    spot on the retina at which RGC axons leave the eye and blood vessels of the inner retina pass
    optic nerve
    second cranial nerve, which is responsible visual sensation
    optic tract
    name for the fiber structure containing axons from the retina posterior to the optic chiasm representing their CNS location
    organ of Corti
    structure in the cochlea in which hair cells transduce movements from sound waves into electrochemical signals
    osmoreceptor
    receptor cell that senses differences in the concentrations of bodily fluids on the basis of osmotic pressure
    ossicles
    three small bones in the middle ear
    otolith
    layer of calcium carbonate crystals located on top of the otolithic membrane
    otolithic membrane
    gelatinous substance in the utricle and saccule of the inner ear that contains calcium carbonate crystals and into which the stereocilia of hair cells are embedded
    outer segment
    in the eye, the section of a photoreceptor that contains opsin molecules that transduce light stimuli
    outer synaptic layer
    layer in the retina at which photoreceptors connect to bipolar cells
    oval window
    membrane at the base of the cochlea where the stapes attaches, marking the beginning of the scala vestibuli
    palpebral conjunctiva
    membrane attached to the inner surface of the eyelids that covers the anterior surface of the cornea
    papilla
    for gustation, a bump-like projection on the surface of the tongue that contains taste buds
    photoisomerization
    chemical change in the retinal molecule that alters the bonding so that it switches from the 11-cis-retinal isomer to the all-trans-retinal isomer
    photon
    individual “packet” of light
    photoreceptor
    receptor cell specialized to respond to light stimuli
    premotor cortex
    cortical area anterior to the primary motor cortex that is responsible for planning movements
    primary sensory cortex
    region of the cerebral cortex that initially receives sensory input from an ascending pathway from the thalamus and begins the processing that will result in conscious perception of that modality
    proprioception
    sense of position and movement of the body
    proprioceptor
    receptor cell that senses changes in the position and kinesthetic aspects of the body
    pupil
    open hole at the center of the iris that light passes through into the eye
    pyramidal decussation
    location at which corticospinal tract fibers cross the midline and segregate into the anterior and lateral divisions of the pathway
    pyramids
    segment of the descending motor pathway that travels in the anterior position of the medulla
    receptor cell
    cell that transduces environmental stimuli into neural signals
    red nucleus
    midbrain nucleus that sends corrective commands to the spinal cord along the rubrospinal tract, based on disparity between an original command and the sensory feedback from movement
    reticulospinal tract
    extrapyramidal connections between the brain stem and spinal cord that modulate movement, contribute to posture, and regulate muscle tone
    retina
    nervous tissue of the eye at which phototransduction takes place
    retinal
    cofactor in an opsin molecule that undergoes a biochemical change when struck by a photon (pronounced with a stress on the last syllable)
    retinal ganglion cell (RGC)
    neuron of the retina that projects along the second cranial nerve
    rhodopsin
    photopigment molecule found in the rod photoreceptors
    rod photoreceptor
    one of the two types of retinal receptor cell that is specialized for low-light vision
    round window
    membrane that marks the end of the scala tympani
    rubrospinal tract
    descending motor control pathway, originating in the red nucleus, that mediates control of the limbs on the basis of cerebellar processing
    saccule
    structure of the inner ear responsible for transducing linear acceleration in the vertical plane
    scala tympani
    portion of the cochlea that extends from the apex to the round window
    scala vestibuli
    portion of the cochlea that extends from the oval window to the apex
    sclera
    white of the eye
    semicircular canals
    structures within the inner ear responsible for transducing rotational movement information
    sensory homunculus
    topographic representation of the body within the somatosensory cortex demonstrating the correspondence between neurons processing stimuli and sensitivity
    sensory modality
    a particular system for interpreting and perceiving environmental stimuli by the nervous system
    solitary nucleus
    medullar nucleus that receives taste information from the facial and glossopharyngeal nerves
    somatosensation
    general sense associated with modalities lumped together as touch
    special sense
    any sensory system associated with a specific organ structure, namely smell, taste, sight, hearing, and balance
    spinal trigeminal nucleus
    component of the trigeminal nuclei that is found in the medulla
    spinothalamic tract
    ascending tract of the spinal cord associated with pain and temperature sensations
    spiral ganglion
    location of neuronal cell bodies that transmit auditory information along the eighth cranial nerve
    stapes
    (also, stirrup) ossicle of the middle ear that is attached to the inner ear
    stereocilia
    array of apical membrane extensions in a hair cell that transduce movements when they are bent
    stretch reflex
    response to activation of the muscle spindle stretch receptor that causes contraction of the muscle to maintain a constant length
    submodality
    specific sense within a broader major sense such as sweet as a part of the sense of taste, or color as a part of vision
    superior colliculus
    structure in the midbrain that combines visual, auditory, and somatosensory input to coordinate spatial and topographic representations of the three sensory systems
    superior oblique
    extraocular muscle responsible for medial rotation of the eye
    superior rectus
    extraocular muscle responsible for looking up
    supplemental motor area
    cortical area anterior to the primary motor cortex that is responsible for planning movements
    suprachiasmatic nucleus
    hypothalamic target of the retina that helps to establish the circadian rhythm of the body on the basis of the presence or absence of daylight
    taste buds
    structures within a papilla on the tongue that contain gustatory receptor cells
    tectorial membrane
    component of the organ of Corti that lays over the hair cells, into which the stereocilia are embedded
    tectospinal tract
    extrapyramidal connections between the superior colliculus and spinal cord
    thermoreceptor
    sensory receptor specialized for temperature stimuli
    topographical
    relating to positional information
    transduction
    process of changing an environmental stimulus into the electrochemical signals of the nervous system
    trochlea
    cartilaginous structure that acts like a pulley for the superior oblique muscle
    tympanic membrane
    ear drum
    umami
    taste submodality for sensitivity to the concentration of amino acids; also called the savory sense
    utricle
    structure of the inner ear responsible for transducing linear acceleration in the horizontal plane
    vascular tunic
    middle layer of the eye primarily composed of connective tissue with a rich blood supply
    ventral posterior nucleus
    nucleus in the thalamus that is the target of gustatory sensations and projects to the cerebral cortex
    ventral stream
    connections between cortical areas from the occipital lobe to the temporal lobe that are responsible for identification of visual stimuli
    vestibular ganglion
    location of neuronal cell bodies that transmit equilibrium information along the eighth cranial nerve
    vestibular nuclei
    targets of the vestibular component of the eighth cranial nerve
    vestibule
    in the ear, the portion of the inner ear responsible for the sense of equilibrium
    vestibulo-ocular reflex (VOR)
    reflex based on connections between the vestibular system and the cranial nerves of eye movements that ensures images are stabilized on the retina as the head and body move
    vestibulospinal tract
    extrapyramidal connections between the vestibular nuclei in the brain stem and spinal cord that modulate movement and contribute to balance on the basis of the sense of equilibrium
    visceral sense
    sense associated with the internal organs
    vision
    special sense of sight based on transduction of light stimuli
    visual acuity
    property of vision related to the sharpness of focus, which varies in relation to retinal position
    vitreous humor
    viscous fluid that fills the posterior chamber of the eye
    working memory
    function of the prefrontal cortex to maintain a representation of information that is not in the immediate environment
    zonule fibers
    fibrous connections between the ciliary body and the lens
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