Shared Flashcard Set

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BMB 2 Week 1
first week of bmb module 2
121
Biology
Graduate
05/05/2014

Additional Biology Flashcards

 


 

Cards

Term

 

 

 

3 Groups of Somatosensory Pathways

Definition
  • dorsal colum/medial lemniscus
  • anterolateral pathways
  • spinocerebellar
Term

 

 

 

Dorsal Column/Medial Lemniscus system

(DCMLS)

Definition
  • discriminative touch (2 point discrimination)
  • pressure
  • vibration
  • conscious proprioception (position sense)
Term

 

 

Neurons in the

Dorsal Column/Medial Lemniscus system

Definition
  • 1st order cells in dorsal root ganglion(DRG): ascend via dorsal columns (DRG are outside spinal cord)
  • 2nd order cells in dorsal column nuclei(n gracilis, n cuneatus): cross midline and ascend in medial lemniscus
  • 3rd order cells in ventral posterior lateral(VPL) nucleus of the thalamus
Term

 

 

 

Sensory Homunculus and blood supply

Definition
  • supplied by the ACA and MCA
  • ACA supplies medially and tends to deal with the leg foot and toes
  • MCA supplies the lateral surface of brain and affects face hands and upper body
Term

 

 

 

 

Higher order processing

(somatosensory)

Definition
  • cortex combines information from different receptor types to form higher order perceptions(size, texture, shape)
  • exaples of deficits: difficulty discriminating texter, or size/shape of objects
  • agraphesthesia: inability to identify letters drawn on the skin
  • astereognosia: inability to name objects held against skin
Term

 

 

 

Projections of somatosensory cortex

(to other cortical areas)

Definition
  • primary somatosensory cortex(postcentral gyrus): brodmanns areas 3-1-2
  • projects of somatosens ctx to:
  • parietal cortex: contributes to internal representation of the body and outside world
  • motor cortex: provides essential information about body position, muscle status
Term

 

 

 

Projections of Somatosens ctx

to subcortical areas

Definition
  • to lower levels of somatosens pathways: spinal cord dorsal horn, dorsal column nuclei, VPL
  • modiefies the processing and flow of sensory information
Term

 

 

 

Phantom Limb

Definition
  • phantom limb= perception of a body part that is not present
  • likely because of activity within an intact cortex is perceived as origination within the missing limb
  • phantom pain is bad 
  • may help with use of prosthetic
Term

 

 

 

Assessing DC/ML function

Definition
  • two-point discrimination (calipers)
  • vibration (tunning fork)
  • proprioception: report passive limb movement(with closed eyes), and romberg test
Term

 

 

 

Romberg Test

Definition
  • patient stands, feet together, eyes open
  • assess sway
  • patient closes eyes
  • re-assess sway
  • postivie: increased swaying with eyes closed. indicates loss of proprioceptive info carried in DC/ML
  • swaing is less with eyes open because visual system compensates for loss of position sense
Term

 

 

 

Tabes dorsalis

Definition
  • tabes means decay
  • major symptom is ataxia (uncoordinated movts) due to degeneration of the dorsal columns
  • occurs during tertiary stage of syphilis
Term

 

 

 

Antereolateral System

(spinothalamic)

information

Definition
  • pain
  • temperature
  • crude touch-poorly localized or identified
  • damage causes loss of pain and temperature sensation
Term

 

 

 

Pain/Nociceptive information

Definition
  • fast pain: sharp, well localized, carried by A delta fibers in periphery
  • slow pain: dull aching or burning, carried by c fibers in periphery
Term

 

 

 

Primary Afferents for

Fast Pain

Definition
  • A delta fibers
  • enter cord and asc or desc a few levels
  • terminate in laminae I and V
  • substance P neurotransmitter
  • ascending pathway is spinothalamic
Term

 

 

 

Primary Afferents for 

Slow Pain

Definition
  • C fibers
  • enter cord and asc or desc a few levels
  • terminate in laminae I and II (substantia gelatinosa)
  • substance P neurotransmitter
  • ascending pathways are spinoreticular (spinoreticulothalamic) or spinotectal (spinomesencephalic)
  • these hava a lot more synapses (contributes to slow)
Term

 

 

 

Spinothalamic pathway

Fast pain

Definition
  • 1st order neuron: Adelta fibers with cell body in DRG (ascend/descend a few segments in dorsolateral tract)
  • 2nd order neuron: cell bodies in lamina I, V. Axon crosses in ventral white commissure
  • 3rd order neuron: VPL of thalamus. Axon projects to postcentral gyrus via posterior limb of internal capsule
  • responsible for localization of pain
Term

 

 

 

Spinoreticular pathway

Slow Pain

Definition
  • 1st order neurons: C fibers with cell body in DRG (can ascend/descend in dorsolateral tract of lissauer)
  • Higher order: 2nd order cell bodies in lamina I and II. Axons of these and other 2nd order cells(in other sp cord laminae) project bilaterally to reticular formation at several levels of brainstem
  • projections to intralaminar nuclei of thalamus. then axons project via posterior limb of internal capsule too: postcentral gyrus, insula and anterior cingulate gyrus
  • insula and anterior cingulate gyrus are particularly important for affective (suffering) aspects of pain
Term

 

 

 

Spinotectal tract

Definition
  • aka spinomesencephalic tract
  • similar to spinoreticular tract, except axons end in superior colliculus and periaqueductal gray
  • part of slow pain
Term

 

 

 

Random Pain Pathway facts

Definition
  • spinoreticular esp important for attention, awareness, and levels of consciousness
  • access to limbic system contributes to suffering component of pain
  • note: redundancy of pathways limits the effectiveness of surgical intervention to alleviate pain by cutting tracts
Term

 

 

 

Unilateral Spinal Cord Lesion

Definition
  • ipsilateral loss of discrim touch
  • contralateral loss of pain/temp
  • these are at levels lower than lesion
Term

 

 

 

Spinal Cord Lesion

Definition
  • lesion of anterolateral tract produces contralateral analgesia(loss of pain sensation)
  • lesion of ventral white commissure produces bilateral analgesia, in a ring around the body in the dermatomes corresponding to the lesion
  • discriminative touch can be spared
Term

 

 

 

Lateral Medullary Lesion

Definition
  • produces contralateral analgesia
  • no loss of discriminative touch
Term

 

 

 

Medial medullary lesion

Definition
  • no loss of pain and temperature
  • contralateral loss of discriminative touch 
Term

 

 

 

Pons or Midbrain lesions

Definition
  • ALS and DC/ML fibers run close to one another as they ascend to the thalamus
  • lesions of both patways lead to contralateral anesthesia (loss of all sensations)
Term

 

 

 

Thalamic Pain Syndrome

Definition
  • lesions in the thalamus can cause analgesia but this can change to chronic pain after a few months
  • this is a form of central pain, meaning pain that arises in the CNS
Term

 

 

 

Somatosensory Cortex Lesion

Definition
  • somatosensory cortex is important for localizing pain
  • however , suffering aspects of pain are still felt after loss of somatosensory cortex
Term

 

 

 

Visceral Pain

Definition
  • also known as referred pain
  • pain that originates in viscera but is percieved in somatic areas
  • conveyed within anterolateral system by neurons concerned with cutaneous pain
  • example: pain arising from hypoxia in heart arises in upper chest and left arm
  • pathway runs along DC/ML and projects to insula for suffering aspect
  • in spinal cord, axon ascends along midline of fasciculus gracilis
  • surgical transection of medial part of dorsal columns can offer relief of visceral pain
Term

 

 

 

Spinocerebellar pathways

Definition
  • non-conscious proprioception
  • different from conscious proprioception conveyed by DC/ML system
  • main pathways are dorsal spinocerebellar and cuneocerebellar
  • other ones are ventral and rostral spinocerebellar pathways but are smaller then main ones
Term

 

 

 

Dorsal Spinocerebellar Path

Definition
  • trunk, leg (C8 and below) lower body
  • 1st order cell body in DRG: C8-L2 axon enters Clarkes nu directly, below L2 axon ascends in F. gracillis to clarkes nu
  • 2nd order cell body in Clarkes Nuc(C8-L2): axon ascends ipsilaterally in dorsal spinocerebellar tract and enters cerebellum via inferior cerebellar peduncle
Term

 

 

 

Cuneocerebellar Pathway

Definition
  • arm, neck(upper limb, upper trunk)
  • 1st order cell body in DRG: axon enters cord above C8 and ascends ipsilaterally in fasciculus cuneatus
  • 2nd order: cell body in external cuneate nu(caudal medulla): axon ascends ipsilaterally in cuneocerebellar tract and enters cerebellum via inferior cerebellar peduncle
Term

 

 

 

Ventral Spinocerebellar path

(other spinocerebellar)

Definition
  • lower trunk, leg
  • 1st order axon enters cord and ends on 2nd order cell around ventral horn
  • 2nd order axon: crosses midline in ventral white commisure and ascends contralaterally, then entrers via super cerebellar peduncle and recrosses within cerebellum
  • double crossed; enters via SCP
Term

 

 

 

Rostral Spinocerebellar pathway

Definition
  • upper trunk, arm
  • 1st order axon enters cord and ends on 2nd order cells in cord scattered rostral to clarkes nucleus
  • 2nd order axon ascends ipsilaterally: enters via inferior cerebellar peduncle
Term

 

 

 

Lesions of Spinocerebellar paths

Definition
  • loss of spinal input to the cerebellum leads to clumsy, uncoordinated movts, called ataxia
  • clinically, we'll consider only dorsal spinocerebellar and cuneocerebellar tracts, so: a lesion causes an ispilateral deficit (ataxia)
Term

 

 

 

Trigeminal Pathways

Definition
  • discriminate touch, pain and temperature, and other
  • chief(principal or main) sens nu: discriminative touch, etc (pressure, vibration, conscious proprioception)
  • spinal V nu (caudal part): pain and temp
  • mesencephalic nu: some reflexes
Term

 

 

 

Internal Capsule Topography

Definition
  • axons from DC/ML and trigeminal pathways maintain topography through posterior limb of internal capsule
  • trigeminal(face) axons near genu
  • axons from bady travel increasingly caudally(posterior) along posterior limb (Arm, trunk, leg)
Term

 

 

 

Jaw Jerk Reflex

Definition
  • tap jaw
  • reflex closing of jaw
  • peripherally, tests only CN V
  • centrally, tests Mesencephalic V and motor V
Term

 

 

 

Corneal Reflex

Definition
  • touching cornea produces direct response(close touched eye), and consensual response(close opposite eye)
  • pain fibers in ophthalmic branch of CN V to
  • spinal V nu to
  • reticular formation to
  • bilateral proj to VII nucleus to
  • VII nerve
Term

 

 

 

Lateral Medulla Lesions

CN V pathways

Definition
  • interrupts spinal V tract and nucleus
  • ipsilateral analgesia for face 
Term

 

 

 

Lateral Pons Lesion 

CN V pathways

Definition
  • interrupts all incoming V fibers
  • ipsilateral anesthesia for face 
Term

 

 

 

Alternating hemianalgesia

Definition
  • alternating means a deficit on one side of face and opposite side of body thus
  • example is ipsilateral face and contralateral body
  • example is laterally medullary lesion: spinal V tract and nu and ascending fibers of anterolateral system
Term

 

 

 

Sensory Transduction mechanisms

Definition
  • direct transduction (mechanoreceptor): stimulus directly opens channels (fast)
  • indirect transduction (olfactory receptor): stimulus activates a secondary messenger pathway that then opens channels (slow)
Term

 

 

 

Adaption of Receptors and Neurons

Definition
  • slow adaption: a raise in the constant stimulus causes a constant spike potential
  • rapid adaption the raise in stimulus constant causes a bunch of spike potentials at the raise but then no more 
Term

 

 

 

Receptive fields and perception

Definition
  • receptive field is region of skin that causes firing of neurons
  • differ in size and location
  • for primary somatosensory neurons, this appears to be based on branching pattern of receptor neurons underneath the skin
  • receptive field size is basis for two-point discrimination
Term

 

 

 

Somatic sensibility

Definition
  • somatic sensation arises from information provided by a variety of receptors distributed throughout the body (4 major sub-modalities)
  • dicriminative touch: recognition of size, shape and texture of objects and their movt across skin
  • proprioception:the sense of static position and movnt of the limbs and body
  • nociception: signaling tissue damage or chemical irritation, percieved as pain or itch
  • temerature sense: warmth and cold
Term

 

 

 

pseudo-unipolar neurons

Definition
  • false unipolar cause it has two branches but they are connected
  • bypass the cell body (straight into spinal cord from stimulus)
  • peripheral processes ramify within the skin or muscle and central processes synapse with neurons in spinal cord and higher levels
Term

 

 

 

somatosensory receptor types

Definition
  • mechanoreceptors
  • proprioceptors
  • thermoceptors
  • nociceptors
Term

 

 

 

Cutaneous (skin) mechanoreceptors

Definition
  • specialized to receive tactile information
  • respond to mechanical deformation of tissue (stretch, touch, pressure, vibration)
  • best studied in glabrous (hairless) portion of the hand (palm and fingertips)
  • these regions of the skin surface are specialized for providing a high-def neural image of manipulated objects
  • first layer in ridges has merkel cell-neurite complex, then meissner corpuscle that is closest to skin, but in different layer
  • then ruffini ending and lastly pacinian corpuscle
Term

 

 

 

Merkel Cell Afferents

Definition
  • slowly adapting
  • 25% of mechanoreceptors
  • fingertips, info from epidermis
  • highest spatial resolution (because they are small)
  • points, ridges and curvature
  • info about form and texture
Term

 

 

 

Meissner Afferents

Definition
  • rapidly adapting, make up 40% mechanoreceptors
  • tips of dermal papillae adjeacent to the primary ridges
  • closest to skin surface
  • elongated receptors, formed by connective tissue capsule comprising schwann cell lamellae
  • more sensitive than merkels to skin deformation
  • has larger receptive fields then merkel
Term

 

 

 

Paccinian Afferents

Definition
  • rapidly adapting, 10-15% of mechanoreceptors
  • deep in dermis or subcutaneous tissue
  • onion-concentric layers of membrane surrounding a single afferent fiber
  • very sensitive-respond to 10 nanometers skin displacement
  • large rceptive fields
  • detect vibrations transmitted through objects that contact the hand or are grasped
Term

 

 

 

Ruffini afferents

Definition
  • slowly adapting, 20% of mechanoreceptors
  • elongated, spindle shaped capsulated, deep in skin
  • ligaments and tendons
  • long axis of the corpuscle parallel to stretch lines of the skin
  • sensitive to the cutaneous stretching 
  • info about finger position and hand conformation
Term

 

 

 

muscle spindles

Definition
  • signal changes in muscle length (proprioceptions)
  • activate motor neuron to extrafusal muscle fibers
  • muscle stretch
  • tension on intrafusal fibers
  • activates nerve endings
  • activate mechanically gated ion channels
  • action potentails
  • group Ia and II afferent fibers
  • spindle recieves motor input too
Term

 

 

 

Golgi Tendon Organ

Definition
  • proprioceptor that is a mechanoreceptor
  • signal changes in muscle tension
  • are formed by branches of group 1b afferents distributed among collagen fibers that form the tendons
  • each GTO is arranged in series with 10-20 extrafusal muscle fibers (in series btw muscle and tendon)
Term

 

 

 

Descriptive Features of pain

Definition
  • pain threshold: minumum stimulus that elicits pain-indicator of the health of the CNS and PNS
  • pain tolerance: degree of pain a subject can tolerate before experiencing physical or emotional impairment
  • pain hypersensitivity: pathological condition
Term

 

 

 

Separate pain

Definition
  • noxious stimulus-Adelta fibers activated first(larger diameter)-sharp pain first
  • increase stimulus intens-c fibers(small d) get activated-slower, delayed second pain(dull)
  • distinct mechanisms of pain perception; independent pathways(proven by selective anesthetized fibers)
Term

 

 

 

Capsaicin

Definition
  • activates TRP channel on C fibers (heat and acid also open it)
  • these are polymodal nociceptors(activated by other agents)
  • inject capsaicin into skin-burning sensation
  • elicits hyperalgesia to thermal and mechanical stimuli
  • paradox-repeaded applications of capsaicin act as analgesic-due to desensitization of the TRP receptor
  • desensitization allows you to use it to treat pain
Term

 

 

 

Vanilloid Receptor (VR)

 

Definition
  • member of the TRP family(transient receptor)
  • same family as somatosensory receptors
  • occurs on the free nerve endings of C and Adelta fibes
  • activated by heat+capsaicin;heat only;acid
  • activated by different heat levels: 45 is uncomfortable;52 is higher heat threshold
  • transduction mechanisms are similar to other somatosensory receptors-but trigger is a noxious stimulus
Term

 

 

 

Classification and distribution of nociceptors

Definition
  • mechanonociceptors-mechanical tissue damage
  • thermo-nociceptors-heat or cold tissue damage
  • chemo-nociceptors-chemical tissue damage
  • nociceptors found in muscles, joints, visceral organs ect-activated by ischemia
  • nociceptors can also transduce non-painful stimuli-low levels of heat or cold that dont cause tissue damage and therefore dont cause pain
  • not all nociceptor activation produces pain
Term

 

 

 

Catagories of pain

Definition
  • physiological pain-nociception
  • inflammatory pain-inflammation
  • neuropathic pain-pathological
  • neuroimmune pain
Term

 

 

 

Nociceptive Pain, transient ouch

Definition
  • direct activation of nociceptors
  • tissue damage-release of bradykinin ect-leads to activation of nociceptors to release subs P which causes inflammatory response
  • inflam response activates more nociceptors
  • peripheral sensitization of pain-hyperalgesia
Term

 

 

 

Neuropathic Pain

Definition
  • chronic
  • initiated by lesion in PNS or CNS
  • nerve sprouting and rewiring from hyperactivity
  • allodynia-pain evoked by a normally nonpainful stimulus
  • hyperalgesia-exaggerated pain evoked by normally moderately painful stimulus
Term

 

 

 

Neuroimmune pain

Definition
  • immune signaling remote from injury site
  • migroglial induced inflam
  • affects nociceptive relay neurons(second order) in spinal cord
  • hyperactivity in VPL neurons, increased microglial based inflam in thalamus
  • increased pain perception in cortex
Term

 

 

 

Mechanisms of phantom pain

Definition
  • part of the axon of a nociceptor still exists after amputation; when you sever an axon it sometimes becomes hyperexcitatory (keeps firing)
  • another way is getting rid of inhibitory nociceptors, so without stimulus, the pain keeps firing
Term

 

 

 

Visceral Pain

Definition
  • via the DC/ML system
  • afferents from the pelvic/abdominal viscera-> spinal cord->2ndorder neuron in dorsal horn of the lumbar sacral spinal cord -> give rise to anterolateral systems that contribute to visceral pain
  • other neurons are the intermediate gray region of spinal cord near the central canal; send axons through dorsal columsn near midline and through arcuate fibers that form contralateral medial lemniscus that synapse with Ventral-posterior thalamus
Term

 

 

 

local circuit neuron

Definition
  • makes connections only inside the dorsal horn
  • contains enkephalin (inhibits)
Term

 

 

 

Sensitization to pain

Definition
  • prolonged hyper-responsiveness to pain-pain sensation increases with repeated stimulation, even though stimulation intensity does not increase
  • transcription-independent (early onset)
  • transcription-dependent (late onset)
Term

 

 

 

Transcription-independent

Definition
  • early onset
  • windup: homosynaptic: repeated stimulus that compounds: lasts 500ms
  • activity dependent CS: heterosynaptic (must have two synapses interacting):Abeta fiber and C fiber: last 10 mins to hours
  • Long Term Potentiation (LTP): homosynaptic: last several minutes to hours
Term

 

 

 

Transcription-dependent

Definition
  • late onset and lasts much longer
  • activity dependent: get localized changes in transcription at synapse
  • ativity independent: start off with inflammation and you end up releasing enzymes(COXs) that migrate along spinal cord
Term

 

 

 

Papilledema

Definition
  • choked or swollen disk
  • increased intracranial pressure(through subarachnoid space) leads to swollen head of optic nerve 
  • constricts optic nerve and central retinal artery
Term

 

 

 

Refractive Power

Definition
  • focusing?
  • measured in diopters
  • total refractive power of eye is around 60 diopters
  • cornea is 42 and lens is 18 (lens can accomadate)
Term

 

 

 

Lens Curvature control

Definition
  • used for accomadation
  • edinger-westphal nucleus (part of CN III group)
  • ciliary ganglion and ciliary muscle
  • to focus on nearby objects you contract ciliary muscles; it reduces tension on zonule fibers and increases curvature of lens
  • to focus on distant objects: relax ciliary muscle; increases tension on zonule fibers, decreases curvature of lens
Term

 

 

 

Depth of Field

Definition
  • narrow depth of field comes from an increase in aperture (dilation of pupil from iris); subject is in focus, foreground and background are blurry 
  • Wide depth of field comes from reduced aperture (pupil constriction); focus is good extending into foreground and background
  • dilation done by ppilary dilator(radial) muscles contracting (sympathetic)
  • constriction done by sphincter muscles contract
Term

 

 

 

Focusing eye (problems)

Definition
  • emmetropia: normal vision
  • myopia (nearsighted): eyeball elongated: object focused in front of retina
  • hyperopia(farsighted): eyeball shortened: object focused behind the retina
  • presbyopia: age related loss of lens focusing ability with age; due to thickening of lens, reducing its ability to round, NOT due to any age related changes in ciliary muscles (start to need reading glasses eventually)
Term

 

 

 

Light Hyperpolarization

Definition
  • several biochemical steps first happen when light hits a photoreceptor
  • decreases cGMP concentration
  • closes Na/Ca channels(gated by cGMP
  • hyperpolarizes cell because the positive ions cannot come in
  • less neurotransmitter released onto next cell in pathway (bipolar cell)
Term

 

 

 

Phototransduction in rods

Definition
  • photon absorbed by photopigment
  • photopigment is a GPCR:lightabsorb chromophore retianl(Vit A aldehyd) coupled to an opsin protein
  • type of opsin tunes the wavelength sensitivity of the photopigment; different opsins across rods and cones
  • photopigment in rods is rhodopsin
  • 11 cis retinal converts to all trans retinal when light
  • activates Gprotein transducin that activates a phosphodiesterase
  • the PDE hydrolyzes cGMP leading to lower concentrations and eventually hyperpolarization
  • provides huge signal amplification
Term

 

 

 

Light and Dark Adaptation

Definition
  • to adapt to ongoing light stimuli a dissociation of retinal from opsin as well as other biochemical changes
  • to adapt to reduced light, a reassociation of retianl and opsin
  • rods more sensitive, but cones have more acuity 
Term

 

 

 

Color Blindness

Definition
  • normally red green color blind
  • protanopia is loss of L cone function (red) (long wavelengths)
  • deuteranopia is loss of m cone function (green) medium wavelength
Term

 

 

 

Fovea

Definition
  • means pit, actual indentation
  • slightly towards the temporal side
  • photoreceptors clustered in fovea
  • macula lutea surrounds fovea and also dense in photoreceptors
  • both have better resolution then rest of the eye
  • in this area, the cell bodies and bipolar and galngion cells are moved out of the way so that theres a direct path to the photoreceptors
  • only cones in the fovea (very densly packed)
  • high rods density surrounding the fovea
Term

 

 

 

off center receptive fields

Definition
  • work by using a different glutamate receptor on the bipolar cell
  • its glutamate receptor is excitatory instead of inhibatory like in on center 
Term

 

 

 

Color and brightness contrast

 

Definition
  • there are ON-center and OFF-center cells
  • can encode brightness contrast (if surround has same color sensitivity)
  • can encode color contrast (if surround has different color sensitivity)
  • examples are ON green off red or vice versa for both on and off center fields
Term

 

 

 

M-type Ganglion cells

Definition
  • magnocellular= large cells
  • large receptive field
  • prefer brief/moving stimuli
  • little if any color information
  • provides information about motion and spatial location
  • project to lateral geniculae nucleus layers 1 and 2(IM channel)
Term

 

 

 

P-Type Ganglion Cells

Definition
  • parvicellular=small cells
  • smaller receptive field
  • respond well to sustained stimuli
  • mediate color and form vision
  • project to lateral geniculate nucleus layers 3-6 (IP channel)
Term

 

 

 

Functional Properties of 

Lateral Geniculate Nucleus

Definition
  • separate layers for ipsi and contra inputs
  • separate layers for M and P inputs
  • receptive fields similar to retinal ganglion cells
  • systematic representation of retina(retinotopy) and visual field (visuotopy)
Term

 

 

 

Inferior and superior retina

Definition
  • inferior retina is the top visual field
  • superior retina is the bottom visual field
  • superior retina goes back to the cuneus in the occipital lobe
  • inferior retina goes to the lingual gyrus in the occipital lobe
  • these are seperated by the calcarine sulcus
Term

 

 

 

Myers loop

Definition
  • part of the optic radiations
  • carry some of the information from the inferior retina to the lingual gyrus 
  • the myers loop is when some of the optic radiations dip down into the temporal lobe
  • important for lesions and blood supply questions
Term

 

 

 

Pathways for V1

Definition
  • regardless of which pathway, first step is down V2
  • then the dorsal (spatial vision) pathway goes into MT and up into the parietal lobe (location and direction of motion)
  • the ventral (object recognition) pathway flows into V4 and beyond into the temporal lobe (form and color) 
Term

 

 

 

Scotoma

Definition
  • a part of the retina with reduced or non-functional vision
  • deficit 
  • part of retina responding to a certain visual field
Term

 

 

 

Anopia

Definition
  • lack of vision in a portion of the visual field
Term

 

 

 

Homonymous and heteronymous

(visual deficits)

Definition
  • homo is a deficit in the same part of the visual field viewed by both eyes (they are congruent)
  • heter are deficits that are not in the same part of the visual field for each eye
Term

 

 

 

visual field lesions

Definition
  • hemianopia: lesions may affect half of the visual field
  • quadrantanopia: lessions may affect one quarter of the visual field
Term

 

 

 

Suprachiasmatic Nucleus

Definition
  • found in the hypothalamus
  • recieves direct input from the retina
  • deals with circardian rhythyms (24hour light/dark cycle)
Term

 

 

 

Pretectal Nucleus

Definition
  • recieves direct retinal stimulation from a branch of the fibers running to the LGN
  • deals with pupillary light reflex
  • pretectal nucleus projects intralaterally to the edinger-westphal nucleus (CN III)
  • also projects contralaterally to the other pretectal nucleus
  • shine light in one eye and see both pupils constrict
  • lesioning optic tract causes a weaker pupillary reflex (because one tract carries info from both eyes)
Term

 

 

 

Pupillary Dilation

Definition
  • hypothalamic projections
  • intermediolateral horn of spinal cord to superior cervical ganglion to pupillary dilator muscles in iris
  • sympathetic NS
Term

 

 

 

Horner's Syndrome

Definition
  • loss of sympathetic inpute to the eye/face
  • pupillary constriction (miosis)
  • partial ptosis(drooping eyelid)
  • anhidrosis (loss of facial sweating)
Term

 

 

 

Argyll-Robertson pupil

Definition
  • result of late stage syphilis infection of CNS
  • small pupils with weak pupillary light reflex; but visual acuity is good and pupil can constrict during accomodation
  • lesion in pretectum or pathway to edinger-Westphal nucleus, rather than in sensory pathway or within Edinger-westphat nucleus
Term

 

 

 

Accomodation to 

Near Vision

Definition
  • lens thickening: edinger-westphat path to ciliary muscles
  • pupillary constriction: edinger-westphat path to sphincter muscles
  • convergence: contract medial rectus-external eye muscles
Term

 

 

 

Parts of the ear

Definition
  • external ear: external auditory meatus, and tympanic membrane
  • middle ear: malleus-> incus -> stapes, eustachian tube, round and oval window
  • inner ear: cochlea, semicircular canals, otolith organ (saccule)
  • cochlear nerve and vestibular nerve
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Endolymph

Definition
  • found in membranous labyrinth
  • high potasium and low sodium
  • 0 to +90mV potential
  • requires Na/K ATPase
  • modified epithelial cells or stria vascularis
  • tight junctions
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Vestibular receptor organs

Definition
  • otolith organs: utricle and saccule (static balance)
  • semicircular canals: anterior ventrical, posterior ventrical and horizontal (angular acelleration)
  • utricle large space at confluence of semicircular canal and contains its receptor the macula
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The Utricle

Definition
  • located at confluence of semicircular canals
  • hair cells surrounded by supporting cells
  • hair cells (stereocilia) project into a gelatinous layer, the otolithic membrane
  • otoconia (rocks) is sitting on top of the gelatinous membrane
  • fluid is bathed in endolymph(membranous labyrinth
  • has map of all different directions of movnt based on arangement of hair cells
  • striola is dividing line 
  • does forward and back while saccule does up and down
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Vestibular Hair cell

Definition
  • has 40 to 70 stereocilia that differ in length
  • contain tight junctions to prevent endolymph leakage
  • kinocillium is the largest stereocila 
  • links between tips of stereocilia and contain potassium channels (open when you mechanically move the stereocilia)
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Transduction in Hair Cells

Definition
  • at rest, K leaks into the stereocilia from endolymph and gets pumped out into the extracellular space
  • causes a little bit of NT to be released and spontaneous activity
  • pushing from short to long stereocilia causes K to come in and excitation (depolarization) and release of more NT
  • pushing in other direction closes channels into tips, causing less K in and hyperpolarization (less NT released)
  • pushing them off axis (90 degrees) nothing happens
Term

 

 

 

Semicircular Canals

Definition
  • contain endolymp and at each end there is a swelling called an ampulla
  • have ampulary crest with hair cells that project up into a gelatinous matrix called cupula
  • endolymph pushes against cupula during angular acceleration causing displacement (hair cells work like the other ones)
  • one hair cell can distinguish btw moving head to left or right
  • all hair cells allighned in one direction for a specific ampulary crest 
  • function as antagonistic pairs(right and left)
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Lateral vestibulospinal pathway

Definition
  • senses change in orientation with respect to gravity and have muscle contraction to counteract the tilt
  • stimulated by angular acc or tilt in any direction (saccule)
  • activates primarily axial muscles
  • reflex doesnt develop immediatly
  • unilateral pathway
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Medial Vestibulospinal Pathway

Definition
  • stabilizes position of the head in space
  • involves semicircular cannals and medial vestibular nucleus
  • descending bilateral projections travel in medial longitudinal fasciculus 
  • if you rotate you body in one direction, reflex movnt of head in the other direction (continue looking at object that you were looking at before)
  • pathway only goes down to cervical cord
Term

 

 

 

Vestibular-occular reflex

Definition
  • medial vestibular nucleus recieves info that head turned one direction and sends it to the abducens and occulomotor nuclei
  • net affect is that in the first ms after a head turn the eyes move in oposite direction to stay focused on the visual field
  • stimulated by the semicircular canals
  • can addapt using cerebellum 
  • nystagmus is slow eye mvt away and they fast eye movnt back to the way the head is going
  • damage to the medial long fasc (multiple sclerosis) results in disconjugate movnts of left and right eye(internuclear opthalmoplegia)
Term

 

 

 

benign paroxysmal positional vertigo

Definition
  • perceived bodily motion, sensation of spinning
  • brief periods, often after sleeping
  • calcium carbonate crystals lodged in semicircular canal
  • crystals cause stimulus
Term

 

 

 

endolymphatic hydrops (menieres disease)

Definition
  • debilitating
  • severe, recurrent episodes
  • progressive
  • increased endolymphatic pressure (membranes can burst)
  • vertigo, spontaneous nystagmus, auditory symptoms
  • eventual loss of reeptor cells unless controled
Term

 

 

 

Wallenberg Syndrome

Definition
  • vestibular nuclei are supplied by posterior inferior cerebellar artery
  • vertigo and nystagmus (short term) are effects of loss of PICA circulation
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Middle Ear Muscles

Definition
  • tensor tympani muscle: attached to malleus, CN V
  • stapedius muscle: attached to stapes, CN VII
  • dampen movement of middle ear ossicles to control vibrations during loud sounds
  • reduce distortion of loud sounds, and can be protective 
Term

 

 

 

Otosclerosis

Definition
  • calcification of the foot plate of the stapes that locks it in place
  • keeps it from vibrating to the extent that it should
  • reduce sensitity to sound (by several decibles)
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Cochlea Cross section

Definition
  • Scala vestibuli (connected to oval window) on top, scala media, then scala tympani on bottom
  • reissners membrane btw vestibuli and media
  • vestibuli and tympani filled with perilymph 
  • scala media contains endolymph (about +90 mV)
  • basilar membrane seperating media from tympani 
  • tectorial membrane in scala media
  • stria vascularis in scala media wall creates endolymph
Term

 

 

 

Organ of Corti

Definition
  • sits on top of basilar membrane
  • contains receptor cells (hair cells): inner and outer (more)
  • afferent and efferent nerve fibers
  • tectoral membrane sitting on top of organ of corti
  • 95% of inner hair cells connected to NS, provide almost all of info of sound
  • outer hair cells recieve input from the CNS, contracts at rate of sound, have contact with tectoral membrane
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Transmission of Mechanical energy

to the cochlea

Definition
  • stapes moves in and out of oval window(scala vestibuli) in response to sound vibration
  • pressure waves move up sca vestibuli through the perilymph 
  • pressure waves move across the scala media and basilar membrane on their way into scala tympani (basilar membrane vibrates)
  • increased pressure in perilymph of scala tympani is relieve at round window
  • high frequency sounds cause maximum vibration nearer to base of cochlea
  • low frequency sounds cause maximum vibration nearer to apex of cochlea
Term

 

 

 

Upward and downward deflection of

basilar membrane

Definition
  • upward deflection causes stereocilia to be moved from short to tall, opening the potassium channels and depolarizing the receptor
  • in the downward phase the stereocilia are moved from tall to short, causing K channels to close and hyperpolarization
  • outer hair cells pivotal for supply full sensitivity and selectivity (one from another) for sound because they are where the vibrations are largest
  • efferent inervation adjusts outer hair cells to protect them from sensitivity
Term

 

 

 

Ascending auditory pathway

(brainstem)

Definition
  • dorsal (vertical locali) and ventral (timing) cochlear nuclei
  • acoustic stria are fiber pathways leaving cochlear nuclei that cross midline in pons-meddula junx in the trapezoid body and goes to the superior olive nuclei(lower pons)
  • superior olive compares sound levels (loudness) from the two ears (1st point in aud system it occurs)
  • superior olive also provides olivarcochlear fibers that are efferent to outer hair cells
  • ascending tracts go from crossing over to join the lateral lemniscus in pons-midbrain
  • next is inferior colliculus, to brachium of this to the medial geniculate body in thalamus
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Ascending auditory pathway

(cerebrum)

Definition
  • ascending tracts (contralateral) go through brachium of inferior colliculs to the medial geniculate of the thalamus 
  • unilateral auditory radiation then projects up to the cerebral cortex (superior bank of temporal lobe) 
  • cortical area 41; primary auditory cortex that recieves info from the medial geniculate nucleus
  • low frequencies in more anterior parts and high frequencies more posterior part of primary auditory cortex
  • can then project to cortical area 22, secondary auditory gyrus 
Term

 

 

 

Wernicke's Area

Definition
  • part of area 22(temporal lobe), supramarginal and angular gyrus in parietal lobe
  • involved in speech perception on left side of brain
  • supplied by left MCA
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causes of hearing loss

Definition
  • age
  • exposure to loud sounds
  • genetic syndromes
  • toxic substances that can kill haircells (antitumor agents and a certain type of antibiotics)
  • acoustic neuroma(vestibular schwannoma) swan cell tumor thats slow growing and effects both vestibular and auditory but auditory first because cerebellum can compensate
Term

 

 

 

cochlear implant

Definition
  • sound seperated electronically by a microphone
  • a recieved inside the skull then processes this
  • provides systematic stimulation pattern inside the auditory nerve.
  • allows speech perception
  • the electrode array goes into the cochlea
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