Unit 6 equilibrium

Question 1

Equilibrium

Answer 1

Ability to maintain orientation of the body & its parts in relation to external space
Proprioceptive, Visual & Vestibular systems

Question 2

Visual System: Receptors

Answer 2

Located in retina
retina is outgrowth of diencephalon
Transduce light information
Rods
night vision
grayscale
Cones
day vision
color

Question 3

Visual System: Pathways

Answer 3

Three pathways
Geniculostriate pathway
primary visual pathway; high resolution system
vast majority of axons follow this pathway

Tectal pathway
to superior colliculus
visual tracking & some reflexes

Hypothalamic pathway
helps entrain circadian rhythms

Question 4

Geniculostriate Pathway

Answer 4

Hemidecussation at the optic chiasm
signal from each visual field to reach contralateral cerebral hemisphere

Question 5

optic nerve → ______ _______ → optic tract → LGN → internal capsule & optic radiation → primary visual (striate) cortex

Answer 5

optic chiasm

Question 6

Geniculostriate Pathway
Lateral genicular nucleus (part of thalamus)

Answer 6

Synapses in Lateral Genicular Nucleus (LGN)
part of thalamus
Parvocellular layers
4 superior layers
2 for each eye
primarily encode color & form
Magnocellular layers
2 inferior layers
1 for each eye
primarily encode movement & contrast

Question 7

Parvocellular layers

Answer 7

4 superior layers
2 for each eye
primarily encode color & form

Question 8

Magnocellular layers

Answer 8

2 inferior layers
1 for each eye
primarily encode movement & contrast

Question 9

Geniculostriate Pathway
2nd order neuron

Answer 9

2nd order neurons travel through internal capsule, then optic radiation
Superior pathway carries information from inferior visual field
Inferior pathway carries information from superior visual field
Meyer’s loop
part of inferior pathway of optic radiation
passes laterally into temporal lobe before turning posteriorly
i.e., temporal lobe damage may cause a deficit to superior (and contralateral) visual field

Question 10

Hemianopia of ipsilateral eye

Answer 10

know it

Question 11

Bitemporal hemianopia

Answer 11

know it

Question 12

contralateral homonymous hemianopia

Answer 12

Know it

Question 13

contralateral homozygous superior quadrantanopia

Answer 13

Know it

Question 14

Geniculostriate Pathway
3rd synapse

Answer 14

synapse in primary visual cortex (area 17) in occipital lobe
superior pathway projects to region of cortex superior to calcarine sulcus
i.e., inferior visual field
inferior pathway projects to region of cortex inferior to calcarine sulcus
i.e., superior visual fields
also, foveal inputs reach more caudal areas & peripheral visual fields progressively more rostral

Question 15

Geniculostriate Pathway
Association areas

Answer 15

Pathways from association visual (areas 18/19) areas maintain functional distinctions seen in LGN
dorsal pathway
“where” pathway
motion & location
LGN magnocellular → dorsal extrastriate cortex →→ parietal lobe
ventral pathway
“what” pathway
color & detailed form
LGN parvocellular → ventral extrastriate cortex →→ temporal lobe
lesion = motion blindness

Question 16

Lesion of Ventral Pathway

Answer 16

color blindness
achromatopsia
inability to recognize faces
prosopagnosia

Question 17

achromatopsia

Answer 17

Color blindness

Question 18

prosopagnosia

Answer 18

inability to recognize faces

Question 19

Lesion of Dorsal Pathway

Answer 19

Motion blindness

“people were suddenly here or there but I have not seen them moving

Question 20

Tectal Pathway

Answer 20

bypasses LGN
1.Synapse in pretectal nucleus, then to Edinger-Westphal nucleus
subserves pupillary light reflex
Or..
2.Synapse in superior colliculus
visual tracking
ocular reflexes (e.g., looming)
via tectospinal tract

Question 21

Hypothalamic Pathway

Answer 21

light-sensitive ganglion cells reach suprachiasmatic nucleus of the hypothalamus
helps entrain circadian rhythms to light-dark cycle

Question 22

semicircular canals/ducts

Answer 22

measure angular acceleration (rotation) of the head
attached to vestibule

Question 23

vestibule

Answer 23

contains utricle & saccule
otolithic organs
measure linear acceleration
both dynamic & static

Question 24

Semicircular Canals

Answer 24

Three ducts
orthogonal to each other
Sense angular acceleration
dynamic rotation
Hair cells extend into cupula
rotation increases (or decreases) AP frequency

Question 25

Saccule and Utricle

Answer 25

Chambers within vestibule that contain macula receptors that sense linear acceleration utricle = horizontal saccule = vertical

Question 26

Macula

Answer 26

Patch of hair cells with their stereocilia & one kinocilium buried in a gelatinous otolithic membrane gelatin weighted with granules called otoliths otoliths add to the density & inertia enhance the sense of gravity and motion hair cells bend when otolithic membrane experiences acceleration

Question 27

Vestibular Nuclei

Answer 27

Four brainstem nuclei (inferior, medial, lateral, & superior) Receive input from vestibular sensors via CN VIII vestibulocochlear n. Efferents to: nuclei controlling eye muscles (VOR) cerebellum thalamus/cerebral cortex conscious perception skeletal muscles compensate for head movement lateral vestibular tract all body regions (balance adjustments) medial vestibular tract cervical only (stabilizes head) descends via MLF

Question 28

Vestibuloocular Reflex (VOR)

Answer 28

Gaze stays fixed when head is moved Extremely fast shake book vs. shake head short reflex loop 3 neurons Ascending portion travels on medial longitudinal fasciculus (MLF)

Question 29

Nystagmus

Answer 29

Rapid eye movement in opposite direction of VOR Physiological ‘resets’ gaze when head movements are too large for VOR compensation Pathological spontaneous, unnecessary, exaggerated may indicate neuropathology Caloric warm or cold water is placed in ear to induce nystagmus i.e, clinical test

Question 30

Eye Movement

Answer 30

6 muscles/3 cranial nerves oculomotor n. (III) medial/superior/inferior rectus & inferior oblique mm. trochlear n. (IV) superior oblique m. abducens n. (VI) lateral rectus m. Upper Motor neurons in cortical eye fields, basal ganglia, & cerebellum Lower motor neurons in specific brainstem nuclei oculomotor, trochear, & abducens

Question 31

Eye Fields

Answer 31

Frontal eye fields initiate saccades lesion = inability to look to contralateral side Supplementary eye fields sequence of multiple saccades? Parietal eye fields smooth pursuit (with cerebellum) see next slide

Question 32

Smooth Pursuit

Answer 32

Requires parietal eye fields & (flocculonodular) cerebellum Can overshoot/dysmetria

Question 33

Basal Ganglia

Answer 33

Caudate & SNpr Damage e.g., Parkinson’s or Huntington’s involuntary saccades slowed smooth pursuit

Question 34

Cerebellum

Answer 34

Adjust VOR new glasses adjust change in eye movement when converging on near or far objects

Question 35

Medial Longitudinal Fasciculus

Answer 35

Bilateral tracts between midbrain & cervical region primarily from abducens n. (VI) to oculomotor n. (III) Ascending to CN III, IV, VI (for VOR) Descending medial vestibulospinal tract coordinate head/eye movements Lesions (esp. multiple sclerosis) deficits to lateral conjugate gaze cannot move both eyes together vestibular nystagmus lack of head/eye coordination

Question 36

Auditory PathwayOuter & Middle Ear

Answer 36

Sense sound information Auricle → external auditory canal → tympanic membrane → ossicles → cochlea Sound causes tympanic membrane to vibrate which causes movement of the ossicles malleus → incus → stapes tensor tympani & stapedius mm. attach to ossicles contraction limits ossicle movement protective reflex too slow for noises with fast onset (e.g., gunshots) good for building sounds (e.g., thunder) primarily dampens vibrations from your own voice

Question 37

Inner ear

Answer 37

Organ of Corti (within cochlea) vibration of basilar membrane activates hair cells inserted into the tectorial membrane = transduction (of sound vibration into APs)

Question 38

Hair Cells

Answer 38

Just about the coolest freakin’ cells in the world tip links open trap doors ions flow into cell, creates local potential, that may become APs

Question 39

Auditory Pathway - Neural Pathway

Answer 39

Hair cells → spiral ganglia (=bipolar neurons of CN VIII) → cochlear nuclei (in medulla) → inferior colliculus (bilaterally; some is used for auditory startle reflexes) (via lateral lemniscus) → thalamus (medial genicular body) → temporal lobe (primary & association auditory cortex)

Question 40

Olfaction

Answer 40

sense of smell CN I bypasses thalamus Reaches orbitotemporal cortex

Question 41

Gustation

Answer 41

sense of taste CNs VII, IX, & X synapse in nucleus of the solitary tract (NTS) via central tegmental tract thalamus (VPM) middle insular cortex