2 - Anatomy/Physiology

Question 1

What are the layers of the wall of the eyeball?

Answer 1

1) Fibrous (corneosclera) - anterior cornea is refractive; posterior sclera maintains shape of eye
2) Uvea - composed of Iris, Choroid Bodies and Choroid; contains smooth muscle to control pupil size and lens shape; choroid is contains vessels for the nourishment of deeper layers of the eye
3) Retina - pigmented and neural retina for photosensation

Question 2

What are the layers of the cornea?

Answer 2

1) Corneal Epithelium - stratified epithelium innervated by CN V(1); quickly regenerated in the event of injury; covered in microvilli which assist in maintaining the tear film on the eye
2) Corneal Stroma - thick layer of orthogonal collagen fibers arranged to provide transparency; avascular;
3) Corneal Endothelium - single layer of cells important for metabolic exchange and supplying nutrients for the cornea

Question 3

What are the intra-occular muscles of the eye? What are their innervation? Function?

Answer 3

1) Dilator Pupillae - dilates pupil - sympathetic fibers from Superior Cervical Ganglion
2) Sphincter Pupillae - constrict pupil - parasympathetic fibers from Ciliary Ganglion
3) Ciliary Muscle - controls shape of lens via zonular fibers connected to ciliary bodies - parasympathetic fibers from Ciliary Ganglion

Question 4

Describe the flow path of Aqueous Humor.

Answer 4

1) Formed by the ciliary epithelium of the ciliary bodies
2) Empties into posterior chamber
3) Flows through pupil into the anterior chamber
4) Absorbed by the Trabecular Meshwork
5) Drains into Canal of Schlemm
6) The Canal drains into Aqueous Veins which then drain into (blood) Veins of the Sclera

Question 5

What are the layers of the Retina?

Answer 5

(posterior to anterior)

1) Retinal Pigmented Epithelium (RPE) - acts as a back-barrier of the retina; highly pigmented to absorb excess light and prevent glare; primary component of BBB and phagocytosis of the eye
2) Outer Segment Rods/Cones - outer (posterior) portion of the rods/cones are photosensitive and initiate light-sensitive sensory signaling;
3) Inner Segment Rods/Cones - inner portion contains the nuclei
4) Synapse bwtn Rods/Cones and Bipolar Cells
5) Bipolar Cell bodies
6) Synapse btwn Bipolar Cells and Ganglion Cells
7) Ganglion Cell bodies
8) Ganglion Cell axons

Question 6

What are the layers of the Lens?

Answer 6

1) Capsule - THICK basement layer around the lens
2) Epithelium - thin layer of simple cuboidal epithelium
3) Fibers - elongated epithelium that lose their nuclei and become filled with crystallins

Question 7

Describe the structure and location of the tympanic cavity.

Answer 7

1) air filled cavity in the petrous temporal bone
2) lower portion -> tympanic cavity proper, immediately internal to the tympanic membrane; upper portion -> epitympanic recess
3) roof -> tegmen tympani (thin petrous bone) separates cavity from cranial cavity
4) floor -> thin plate separates cavity from jugular fossa; tympanic branch of CN IX transits wall to form tympanic plexus
5) medial wall -> promontory = basal turn of the cochlea; facial canal = bulge above promontory; oval and round window
6) posterior wall -> aditus = opening to mastoid air cells via mastoid antrum; chorda tympani = from facial n. that courses over membrane before exiting; pyramidal eminence = contains stapedius muscle w/ tendon emerging from the tip
7) lateral wall -> tympanic membrane with malleus and incus; tympanic nerve courses across
8) anterior wall -> opening to the canal of the tensor tympani; opening to the pharyngotympanic tube; thin wall over internal carotid a.

Question 8

Describe the function of the auditory ossicles.

Answer 8

1) Malleus (hammer): long handle on the the membrane with its head articulating with the incus in the epitympanic recess
2) Incus (anvil): long process extends back down into the tympanic cavity proper to articulate with stapes
3) Stapes (stirrup): footplate sits in oval window
Muscles:
1) Tensor tympani: attached to the cartilage of the auditory tube and inserts on the handle of the malleus; CN V3; tenses tympanic membrane and dampens sound conduction
2) Stapedius: attached to the pyramidal eminence and inserts on the neck of the stapes; CN VII; lifts foot plate off oval window, dampening sound

Question 9

Describe the form and function of the cochlea.

Answer 9

1) set within the bony labyrinth; central core is of bony modiolus which contains the Spiral Ganglion
2) spiral lamina is a bony ridge that wraps around modiolus and contains the cochlear duct
3) within spiral lamina, space is divided into three areas: scala vestibuli (perilymph), cochlear duct(endolymph) and scala tympani(perilymph)
4) oval window is at opening of scala vestibuli; round window is at end of scala tympani; these two meet at the helicotrema
5) sound travels from the oval window, through the scala vestibuli, into the cochlear duct where the organ of corti is located,into the scala tympani and is dissipated at the round window
6) organ of corti is composed of sensory hair cells (inner and outer) and supporting hair cells (phalangeal and pillar); techtorial membrane overlies the hair cells and provides the “shearing force” for the sensory hair cells
7) outer wall is lined by stratified cuboidal epithelium overlying connective tissue; this is where endolymph is secreted

Question 10

Describe the components of the semilunar canals.

Answer 10

1) 3 canals at ~90 degrees to each other
2) contain central ampullae, in which is a raised epithelial ridge (crista ampullaris) which is covered by a gelatenous structure (cupula)
3) filled with endolymph
4) cupula has the same sp. gravity as the endolymph, therefore when the head turns, the endolymph and cupula “lag” behind the skull’s rotation placing shear stress on hair cells and initiating sensory pathway
5) type I/II hair cells have a single cilium (kinocillum) and many stereocillia (microvilli)
6) supporting cells have irregular shapes and secrete contents of the cupula

Question 11

Describe the components of the utricle and saccule.

Answer 11

1) utricle: sac at the opening to the semilunar ducts; senses gravity and HORIZONTAL linear movement
2) saccule: sac at the opening to the cochlear duct; senses gravity and VERTICAL linear movement
3) macula contains type I/II hair cells and supporting cells; covered by otolithic membrane which is then covered with otoconia
4) due to the greater density of the otoconia, when there is linear acceleration, the otoconia “lag” behind and cause shear stress on the hair cells, initiating the sensory pathway

Question 12

What is detection threshold?

Answer 12

• the minimum level necessary for human perception of sound
• normal human hearing range 20Hz - 20kHz
• most sensitive 2-5kHz
• human speech~4kHz

Question 13

Describe the conduction of sound through the ear.

Answer 13

1) sound waves are collected and selectively amplified by the auricle and the external auditory meatus
2) vibration of the tympanic membrane is transferred to the oval window by the ossicles
3) amplification is~18:1 due to: 1)reduction in size from tympanic membrane to oval window, 2) lever/piston action of the ossicles
4) sound conduction can be attenuated by the contraction of 1) tensor tympani: tensing the membrane limits vibration; 2) stapedius: lifting the foot process off the oval window
5) wave is conducted through the perilymph of the scala vestibuli and through the basement membrane of the cochlear duct, then through the scala tympani and dissipated at the round window
6) pressure difference across the basement membrane causes displacement of and shear stress on the hair cells of the organ or corti
7) the movement relative to the tectoral membrane produces an electrical signal and initiates the sensory pathway

Question 14

How is frequency of sound discriminated? Amplitude?

Answer 14

1) Place: as the wave is propagated within the inner ear, the area of maximum basement membrane displacement is dependent on the frequency of the sound -> the hair cells that are most displaced produce the greatest signal, which is characteristic of a certain frequency (topotonic organization)
2) Phase-Lock: the frequency detected at the tip of the cochlear duct is ~200Hz, but the ear is able to sense as low as 20Hz since the entire basement membrane can oscillate as a wave at a low frequency -> the CNS then determines the time between the bursts of resultant APs to determine the frequency
3) Amplitude is identified by the increased firing rate of the appropriate region of the cochlear nerve, and by the recruitment of neighboring regions of the nerve

Question 15

Describe the Auditory (sensory) pathway.

Answer 15

1) signals from the inner(95%) and outer(5%) hair cells travel to the CNS via Cochlear n.(VIIIc) and synapse in the upper medulla on the Dorsal and Ventral Cochlear N.
2) the axons that synapse on the Dorsal Cochlear N. cross via the Dorsal Acoustic Stria to the contralateral Lateral Lemniscus and travel up to the Inferior Colliculus (lower midbrain)
3) the axons that synapse in the Ventral Cochlear N. travel to the BILATERAL Superior Olivary N. (providing biaural signals to each SOC)
4) the SOC provides localization of the sound and axons from here travel up the ipsilateral Lateral Lemniscus to the Inferior Colliculus
5) from the IC, axons travel through the Brachium of the IC and synapse in the Medial Geniculate Body of the Thalamus
6) neurons then travel to the Primary Auditory Cortex (Gyri of Herschle)
7) connections are then made to the secondary auditory cortex, including Wernicke’s Area for higher processing and association
8) some neurons from the SOC give rise to the efferent Olivocochlear Bundle which travels back to synapse on the inner hair cells of the ear -> provide an inhibitory signal that can be used to selectively filter frequencies -> cocktail party effect

Question 16

What is Meniere’s Disease?

Answer 16

• sensorineural hearing loss due to abnormal production of endolymph in the membranous labyrinth
• affects both vestibular and auditory functions

Question 17

Describe the Weber and Rinne Tests.

Answer 17

1) Weber: tuning fork on the vertex of the skull; sensironeural hearing loss -> louder on the unaffected side; conductive hearing loss -> louder on affected side
2) Rinne: tuning fork on mastoid process and in front of ear; sensironeural hearing loss -> both ways are softer then normal, but air is louder than bone; conductive-> bone is louder than air in affected ear

Question 18

Describe the stimulation of the Utricle and Saccule.

Answer 18

1) Utricle is connected to the semilunar canals and is sensitive to Horizontal Linear acceleration
2) Saccule is connected to the cochlear duct and is sensitive to Vertical Linear acceleration
3) movement of the head/hair cells relative to the endolymph/otolithic membrane/otoconia cause bending of the cilia and kinocilium -> bending towards kinocilium = depolarization
4) cilia/kinocilia are oriented on either side of the striola with the kinocilia aligned towards the striola (utricle) or away (saccule); the curved nature of the striola provides greater differentiation for the tilt of the head in multiple planes

Question 19

Describe the stimulation of the semilunar ducts.

Answer 19

1) three ducts oriented at 90deg to each other and paired with a canal in the opposite ear (Anterior-Posterior; Horizontal-Horizontal)
2) sensory hair cells sit within the crista ampullaris and are embedded in the capsule (which extends across the canal)
3) during angular rotation, the endolymph displaces the cupula and causes bending of the cilia
4) bending of the cilia towards the kilocilium causes depolarization, and vise versa
5) after prolonged, constant acceleration, the endolymph will equalize and rotation will no longer be perceived by the vestibular system

Question 20

Describe the Vestibular-Ocular Reflex.

Answer 20

1) communication between the vestibular system and extraocular muscles allows for tracking of objects while the head moves
2) rotation is sensed by the hair cells of the semilunar canals
3) signal travels via vestibular n. (VIIIv) to vestibular nucleus
4) axons then travel via the Medial Longitudinal Fasciculus (MLF) to the Extraoccular Cranial Nerve Motor Nerve N.
5) CN III, IV and VI then control extraocular movement to maintain desired position (slow phase)
6) when the eye has reached end of range, it “snaps” back to focus on another object (saccade/fast phase)

Question 21

Describe the vestibular sensory pathway.

Answer 21

1) Hair cells connect to bipolar neurons from the vestibular ganglion,which then project axons via Vestibular n. (VIIIv) to the Vestibular N. (Superior, Inferior, Medial, Lateral) on the lateral floor of the 4th ventricle
2) some neurons of the vestibular nucleus and travel to the cerebellum via the ICP
3) Neurons from the Medial Vestibular N. form the Medial Vestibular Tract and synapse BILATERALLY in the Cervical Spinal Cord to coordinate head and neck movements
4) neurons from the Lateral Vestibular N. for the Lateral Vestibular Tract that project IPSILATERALLY to all levels of the Spinal Cord to participate in “righting reflex”
5) neurons from Inferior Vestibular N. project to the cerebellum forming the Vestibulocerebellar Fibers; these particpate in balance and posture and cancellation of the VOR for tracking via head mvmt
6) neurons also project to the CN nuclei for CN III, IV and VI to influence extraocular eye mvmt via the VOR

Question 22

What are the structures in the parotid gland?

Answer 22

Lateral/Superficial

1) Facial Nerve -> enters in the posteriomedial surface, crosses superficial to the below structures and divides into its terminal branches
2) Retromandibular Vein -> formed by the union of the superficial temporal vein and the maxillary veins
3) External Carotid A -> terminates in superficial temporal and maxillary a.

Question 23

What are the components of the fascia of the orbit?

Answer 23

1) Periorbita: periosteum of the bones of the orbit; it is continuous with the covering of the optic canal posteriorly and the orbit septum/facial bones anteriorly
2) Bulbar Sheath: thin membrane that covers the eyeball except the cornea; it is perforated by the ciliary nerve/vessels and ocular tendons
3) Muscular Fascia: continuous posteriorly with the periorbita and anteriorly with the bulbar sheath; anteriorly extensions come out to the lacrimal and zygomatic bones to form the medial and lateral check tendons

Question 24

What are the visual fields of each eye?

Answer 24

1) visual fields are the areas that each eye can see
2) both eyes can see a central binocular zone
3) this zone is broken up into nasal and temporal, then upper and lower quadrants
4) each eye also has a monocular crescent in the periphery region that only it can see -> this is represented in the nasal retina due to the refraction of the eye

Question 25

What are retinal ganglion cells?

Answer 25

1) ganglion cells represent the output for the retina
2) M-Ganglion Cells: larger, more numerous cells that predominate in the periphery
- receive input from rods and cones and most sensitive to image movement
- the have fast conduction that supports their ability for localization
- project to layers 1 & 2 of the Lateral Geniculate Body of the Thalamus
3) P-Ganglion Cells: smaller cells that are found predominately in the center of the retina and receive input from the cones
- used for high acuity site and color coding
- slow conduction, so less useful for tracking/localization
- project to layers 3-6 of the LGB

Question 26

Describe the optic partial decussation.

Answer 26

• in the optic chiasm the fibers from the nasal visual hemifield crosses to the contralateral side
• this means that each optic tract (after chiasm) contains the ipsilateral temporal hemifield and the contralateral nasal hemifield
• since the images received by the retina are inverted/reversed; an image from the right is “seen” by the right nasal retina and the left temporal retina -> then during the partial decussation, the signal from the nasal retina crosses to the contralateral side -> the signal for the right image is completely sent to the left LBG and optic cortex

Question 27

Describe the visual pathway.

Answer 27

1) Light is sensed by the retina and the signal is passed to M(periphery) and P(central) ganglion cells
2) they travel through the optic nerve (CN II) to the optic chiasm where they undergo a partial decussation and form the optic tracts
3) the majority of fibers then travel to the Lateral Geniculate Body of the Thalamus (pirate hat)
4) some fibers travel to the: 1)suprachiasmic nucleus in hypothalamus and affect circadian rhythm; 2)the superior colliculus via the brachium of the s. colliculus to control reflex responses to light; 3) the pretectal area via the brachium of the s. coll. to control pupillary reflex
5) in the LBG the fibers synapse in 6 layers according to original side and ganglion type-> Ipsilateral: 2, 3, 5; Contralateral: 1,4, 6; M-Cell-> 1, 2 (Magnocellular); P-Cell-> 3-6 (Parvocellular)
6) from the LBG the fibers travel to the primary optic cortex located above and below the calcarine sulcus in the occipital lobe
7) travel in two tracts(optic radiations or geniculocalcarine tract): fibers from the lower visual field travel up through the internal capsule to the upper bank of the calcarine sulcus; fibers from the upper visual field travel down, around the inferior horn of the lateral ventricle (meyer’s loop) to the lower bank of the calcarine sulcus
8) in the primary visual cortex (V1) the axons from the LBG synapse in Layer IV -> some convergence of information occurs here but segregation is maintained as related to eye and M/P cells
9) axons from LBG layers 2,3,5 align in columns distinct from those from layers 1,4,6; additionally, axons from M cells (LBG layers 1,2) go to different sublayers than those from P cells (LGB layers 3-6)
10) ~75% of primary visual cortex is from the central 15deg of vision including the fovea and mucula
11) projections then go to Visual Association Cortices: M-Pathway(Dorsal) travels from V1 to the Superior Parietal Cortex (where); P-Pathway(Ventral) travels from V1 to the Inferior Temporal Cortex(what)

Question 28

What are the scotopic, mesopic and photopic levels?

Answer 28

• different levels of illumination
  1) Scotopic: low light(less than starlight) where only rods are used -> poor acuity and no color
  2) Mesopic: intermediate light (starlight to indoor lighting) where both rods and cones are used -> improved, but still poor acuity and some color
  3) Photopic: bright light (sunlight) where cones are used and rods are saturated (or close) -> high acuity and good color

Question 29

Describe the stimulation of photoreceptors.

Answer 29

1) in the dark both rods and cones have cGMP-gated Na channels open and are depolarized causing release of inhibitory neurotransmitter(NT) on bipolar and horizontal cells
2) when exposed to light, the cGMP-gated Na channels close and the cell hyperpolarize causing less inhibitory NT release
3) rods converge on bipolar cells at ~50:1 where cones maintain 1:1
4) for On-Center bipolar cells, light causes greater depolarization which then causes excitation of the ganglion cell
5) the ganglion cells then send axons to form the CN II via the optic disc

Question 30

What is meant by on-center, off-surround antagonism?

Answer 30

1) light causes hyperpolarization of photoreceptor, less inhibitory NT released, increaesed signal at the bipolar/ganglion cell
2) light causes hyperpolarization of the horizontal cell, which then releases less inhibitory NT on neighboring photoreceptor ->
3) this causes the neighboring photoreceptor to release more inhibitory NT on its bipolar cell and thus less of signal
4) this process helps to accentuate distinctions between light and dark -> increased firing in light and decreased firing next to light

Question 31

How is color perceived in the eye?

Answer 31

1) three cones: blue, green and red
2) each is most sensitive to its own color wavelength, but red is most sensitive to light as well
3) there is considerable overlap between red and green, but also some with blue
4) it is the comparison of the excitation of the multiple cones that allow for determination of the color
5) blue cones are not in the center of the fovea to provide better acuity by preventing chromatic aberration (blurring due to the different wave lengths of the color as it refracts through the eye)

Question 32

What is the function of CN VI in eye movements? Path?

Answer 32

1) Abducens Nucleus is in the dorsal pons in the floor of the IV ventricle in the genu of CN VII
2) it sends fibers to the ipsilateral lateral rectus for ipsilateral abduction
3) it sends Abducens Interneuclear Neurons (AINs) to the contralateral occulomotor nucleus to stimulate contraction of the contralateral medial rectus
4) this provides for conjugate gaze of the lateral and medial rectus but does NOT provide for convergence

Question 33

Describe the function/path of the Trochlear Nerve.

Answer 33

1) the trochlear Nucleus is in the upper pons/lower midbrain dorsal to the cerebral aqueduct
2) axons travel dorsally around the aqueduct, CROSS in the isthmus and then exit the brain stem
3) it then travels in the free end of the tectorial cerebelli, along the wall of the cavernous sinus and through the superior orbital fissure
4) it terminates in the contralateral Superior Oblique
5) Function:
- when looking forward, the S.O. acts to intort, depress, and slightly abduct eye
- when looking medially, the S.O. is the primary depressor of the eye

Question 34

What is the function/path of the Occulomotor nerve?

Answer 34

1) Occulomotor complex (nucleus) is in the upper midbrain/pretectal region, medially and ventral to the PAG and cerebral aqueduct
2) divided into two regions: 1) Somatic motor neurons -> LMNs for the superior, inferior, and medial rectus, the inferior oblique and the levaetor palpebrae superioris; 2) Edinger-Westphal Neurons -> preganglionic parasympathetic neurons that will travel to the ciliary ganglion and then on to form the short ciliary fibers that will pierce the sclera and innervate the ciliary bodies and sphincter puppilae
3) axons exit the brainstem at the superior pontine angle and travel in the cavernous sinus and through the superior orbital fissure

Question 35

What are the non-cranial nerve nuclei CNS eye movement centers?

Answer 35

1) Horizontal Gaze Center: area in the pontine reticular formation (near abducens nuclei) that influences the ipsilateral lateral rectus in conjugate horizontal eye movement
2) Vertical Gaze Center: area in the reticular formation of the rostral mesencephalon (near the occulomotor n.) that influences CN III and IV in the conjugate vertical eye movements
3) Vestibular Nuclei: in the lower pons and upper medulla that relays vestibular information to the CN III, IV, and VI in support of the Vestibular Occular Reflex

Question 36

How does the vestibular ocular reflex happen?

Answer 36

1) head motion causes stimulation of the vestibular n. (CN VIIIv)
2) VIIIv synapses in the Vestibular N. in the upper medulla and lower pons
3) those that synapse in the Inferior and Superior (?) Vestibular N. send axons to the Abducens, Trochlear and OMC Nuclei to cause contraction of the appropriate occular muscles
4) this coordinated action allows for maintained focus on an object while the head is moving; can be overridden by the cerebellar input to allow for tracking via head movement

Question 37

What are the subdivisions of the cerebellum?

Answer 37

1) Vestibulocerebellum: the lower portion of the cerebellum -> the flocculonodular lobe
2) Spinocerebellum: central portion -> the vermis (minus the nodulus) and the paraveral zones of the hemispheres
3) Pontocerebellum: the lateral zones of the cerebellar hemispheres

Question 38

What are the tracts that connect to the cerebellum? Path?

Answer 38

Vestibularcerebellum
1) Vestibulocerenellar: from the ipsilateral vestibular nucleus and ganglion -> travel via the ICP
2) Olivocerebellar: fibers from the contralateral Inferior Olivary Nucleus enter via the ICP to relay information to each of the subdivisions of the cerebellum -> vestibular N. to vestibulocerebellum; spinal motor feedback to the spinocerebellum; frontal lobe motor input (via red N.) to pontocerebellum –> are CROSSED, diffuse connections that terminate in climbing cells
Spinocerebellum:
3) Pontocerebellar: from the contralateral pontine nucleus which communicate with diffuse cerebral areas (frontal, temporal and occipital) via the red N. -> are CROSSED fibers that enter via MSP
Spinocerebellum:
4) Posterior Spinocerebellar Tract(PSCT): originates in the Dorsal Nucleus of Clark with proprioceptive information from ipsilateral muscle groups -> ascends ipsilaterally and enters via ICP
5) Cuneaocerebellar Tract(CCT): originates in the Accessory Cuneat Nucleus and is the upper limb analogue of PSCT -> enters via ICP
6) Anterior Spinocerebellar Tract(ASCT): originates in the gray matter of the lumbar and sacral segments and carries golgi tendon information -> ascends contralateral ASCT and then crosses (again) via the SCP
7) Spino-Reticulo-Cerebellar Pathway: path from several nuclei in the reticular system which extends the Spinoreticular Tract into the cerebellum via the ICP
8) Trigeminocereballar Fibers: Fibers from each of the 3 ipsilateral sensory nuclei of CN V to the cerebellum via a corresponding peducle -> Spinal V Nucleus = ICP, Principal Sensory Nucleus = MCP, Mesencephalic Nucleus of V = SCP

** everything uncrossed EXCEPT -> Pontocerebellar, Olivocerebellar and ASCT (which is double crossed)

Question 39

Describe the cytoskeleton of the cerebellum.

Answer 39

1) Granule Layer: composed of mossy fibers that form excitatory synapse with granule cells which bifurcate to form two parallel fibers.
- mossy fibers also make excitatory synapses with deep cerebellar nuclei
- The parallel fibers form excitatory synapses on distal Purkinje cells and the inhibitory interneurons (golgi, basket and stellate cells)
- the synapse of the mossy, granule and golgi cell form the Mossy Fiber Glomerulus which is surrounded by a glial capsule
2) Purkinje Cell Layer: composed of purkinje cell bodies which emit numerous dendrites that extend into the Molecular Layer
- dendrites synapse with numerous other cells -> parallel fibers of the granule cells, stellate and basket inhibitory interneurons,
- also synapse with climbing fibers via the Olivocerebellar (from IOC)
- Purkinje are the ONLY output of the cerebellar cortex -> make inhibitory synapses on the deep cerebellar nuclei via GABA
3) Molecular Layer: formed primarily by the Purkinje dendrites and the interneurons they synapse with (see above)
- climbing fibers are powerful excitatory and synapse in 1:1
- Basket cells are powerful inhibitory

Question 40

What are the major differences between Mossy and Climbing fibers?

Answer 40

1) Mossy Fibers: the majority of afferent fibers in the cerebellum
- synapse with granule fibers which bifurcate and then synapse with a large number of Purkinje cells
- produces a diffuse signal averaging that allows the Purkinje fiber to process a large amojnt of information simultaneously
- supports moment-to-moment coordination and regulation
2) Climbing Fibers: travel from the Inferior Olivary Cortex and bind 1:1 on Purkinje cells
- have a large influence on only the one Purkinje cell -> influence cell sensitivity and may participate in motor learning

Question 41

What are the efferent cerebellar pathways?

Answer 41

1) Vestibulocerebellum: Purkinje fibers project DIRECTLY to all four Vestibular N. to influence righting reflex, head/face stability and cancellation of VOR
2) Spinocerebellum (Vermal) Path: originates in Vermal Cerebellum and terminates in Fastigial Nucleus. From there it projects to the vestibular and reticular nuclei to influence vestibulospinal and retinulospino tracts -> proximal and axial muscles to control balance and posture; also generate walking patterns
4) Spinocerebellum (Paravermal) Path: originate in the paravermal area and synapse on the globus and emboliform nuclei. From there axons project to the contralateral Red N. and VLp (thalamus N.) via the SCP and project to the primary motor cortex and associate areas. These are CROSSED fibers and affect IPSILATERAL rubrospinal and corticospinal tracts for fine motor skill
5) Pontocerebellar: originate in the Pontocerebellum, synapse in the Dentate N. and project to the contralateral Red N. and thalamus, which continue to motor planning areas of the frontal cortex. Affect the Corticospinal and Rubrospinal tract and thus assist in initiation of movement and complex mvmt planning.

Question 42

What arteries supply the different regions of the cerebellum?

Answer 42

1) PICA: the inferior 1/2 of the cerebellum to include the nodulus
2) SCA: the superior 1/2 of the cerebellum, but does not “meet” the PICA area on the ventral side; it stops above the superior/middle peducles
3) AICA: covers the area between the PICA and SCA on the ventral side to include the peduncles and flocculus

Question 43

What is the structure of the Temporal-Mandibular Joint?

Answer 43

1) it is an articulation between the underside of the squamous temporal bone (mandibular fossa and articular tubercle) and the condyle/head of the mandible
2) the TMJ contains two layers of fibers forming the fibrous capsule; the upper attach the articular disc to the mandibular fossa and articular tubercle; the lower attaches the disc to the condyl
3) the articular disc is an oval plate of dense CT divides the joint into an upper and lower portion
4) ligaments limit the motion of the joint:
- Temprormandibular Lig: attaches the zygomatic process of temporal bone to neck of the condyle
- Sphenomandibular Lig: from the spine of the sphenoid bone to the lingula and the internal surface of the neck of the condyle
- Stylomandibular Lig: from the styloid process to the angle of the mandible

Question 44

What is Kisselbach’s Plexus?

Answer 44

-it is the arterial plexus in the nares that is composed of branches from the facial artery, opthalmic artery and maxillary artery

Question 45

What are the components of the Basal Ganglia?

Answer 45

1) caudate, putamen, globus pallidus, amygdala
2) substania nigra and subthalamic nucleus frequently included
3) striatum = caudate + putamen
4) lentiform nucleus = putamen + globus pallidus
5) corpus striatum = caudate + putamen + globus pallidus

Question 46

What is the pathway of the Basal Ganglia?

Answer 46

1) Basal ganglia modulates the amount of excitatory input from the thalamus to the cortex via a Direct and Indirect Pathway
2) The Direct Pathway consists of input from the cerebral cortex to the striatum spiny neurons (+Glu)
3) the striatum then projects to the Medial Pallidal Segment (MPS) and Substantia Nigra, pars reticulata (SNr) (-GABA/Substance P)
4) it then projects to the Thalamus VA and VLa (-GABA)
5) the Thalamus then projects to the supplemental motor cortex (+Glu)
6) the Indirect Pathway utilizes spiny neurons to connect to the Lateral Pallidal Segment (-GABA/Enkephalin)
7) it then projects to the Subthalamic Nucleus (-GABA)
8) it then projects to the MPS and SNr (+Glu)
9) Overall; DIRECT = facilitate movement; INDIRECT = suppress movement

Question 47

What is the effect of Dopamine on the Basal Ganglia?

Answer 47

1) Dopaminergic neurons from the SNc project to synapse w/ three types of neurons in the Striatum
2) Spiny Neurons (GABA/Substance P) have D1 receptors which make dopamine excitatory -> facilitates DIRECT
3) Spiny Neurons (GABA/Enkephalin) have D2 receptors which make dopamine inhibitory -> suppress INDIRECT
4) Aspiny Neurons (ACh) interneurons -> excitatory w/ Spiny neurons (GABA/Enkephalon) in the indirect pathway; Dopamine is inhibitory to these neurons, making them inhibitory to the Spiny of the indirect path -> suppress INDIRECT
5) OVERALL -> dopamine release acts to facilitate movement

Question 48

What are the components subdivisions of the Thalamus?

Answer 48

1) Lateral Group: Ventral Tier (Ventral Anterior, Ventral Lateral, Ventral Posterior) and Dorsal Tier(Lateral Dorsal, Lateral Posterior)
2) Anterior Group
3) Medial Group
4) Posterior Group: Pulvinar, Medial and Lateral Geniculate Bodies

Question 49

What are the functions of the nuclei of the Thalamus?

Answer 49

Relay Nuclei (Motor)
1) VA: basal ganglia to motor planning area of cortex
2) VLa: basal ganglia to motor planning area of cortex
3) VLp: cerebellum to motor planning area and primary motor
4) DM: assists with eye coordination btwn basal ganglia and cortex, but major function is limbic
Relay (Limbic System)
1) AN: mammillary bodies/HF via fornix to cingulate
2) LD: limbic subcortical regions to cingulate
3) DM: amygdala to prefrontal -> emotions
Relay (Sensory)
1) VPL: sensory from body to cortex
2) VPM: sensory from head to cortex
3) VPMpc (parvocellular): taste via solitary tract to cortex
4) LGB: visual from CN II to visual cortex
5) MGB: auditory from lateral lemniscus to auditory cortex
6) DM:l olfaction to olfactory cortex
7) Pu: visual to secondary visual cotrices (attention)
Diffuse
1) VA: from intralaminar nuclei to frontal lobe
2) Intralaminar N.: from ascending systems maintaining consciousness and STT to widespread cerebral cortex
Subthalamic: reticulus nucleus has diffuse local connections with the lateral thalamus and does not project to neocortex

Question 50

What is the Hypophysial Portal System?

Answer 50

1) part of the hypothalamic control of the pituitary gland, specifically the anterior/endocrine lobe
2) hypothalamic nuclei (arcuate, supraoptic and paraventricular) synapse on the Primary Capillary Plexus in the infundibular stem and median eminance
3) they secrete releasing and inhibitory factors into the primary capillary plexus
4) this plexus carries the factors to the anterior lobe of the pituitary and transfer them to the Secondary Capillary Plexus via portal veins
5) the secondary capillary plexus carry the factors to and deliver them to the anterior lobe of the pituitary
6) the anterior pituitary cells secrete hormones into the general circulation

Question 51

Describe the hypothalamic influence on Autonomic Function.

Answer 51

Parasympathetic
1) Medial and Lateral areas of the Hypothalamus receive input from numerous area (brainstem, amygdala, cortex, insula)
2) output parasympathetic stimulation via the Vagus and Sacral Parasympathtic innervation
3) causes increased parasympathetic activation -> decreased HR, BP and increased GI activity
Sympathetic
1) Lateral and Posterior regions receive imput from numerous regions
2) project axons to brainstem and spinal cord at the IML nuclei (T2-L3)
3) to increase sympathetic activation (increase HR, BP and decrease GI motility)

Question 52

Describe the Hypothalamic influence on Stress Response.

Answer 52

1) stress is sensed by the cortical and limbic stuctures for external danger and the brainstem and circumventricular systems for interal danger
2) this is relayed to the hypothalamus which releases Coricotropin Releasing Factor from the Paraventricular N.
3) this causes the release of Adrenocorticotropic Hormone to be released from the anterior pituitary cells into the blood stream
4) the ACTH causes the adrenal cortex to release glucocorticoids (cortisol) into the blood stream which promotes liver gluconeogenesis and reduces inflammation and immune reactions
5) the glucocorticoids then inhibit further release of CRF from the hypothalamus and ACTH from the anterior pituitary

Question 53

Describe the Hypothalamic influence on Fluid Balance.

Answer 53

1) fluid osmolarity is determined by the cicumventricular organs and BP by via brainstem/autonomic sensory input
2) this information is sent to the Supraoptic and Paraventricular Nuclei
3) when BP falls or blood is hyperosmotic (low volume), these nuclei release Vasopressin (ADH) via their axons that project into the Posterior Lobe of the pituitary
4) ADH is released directly into the blood stream and acts as a vasocontrictor and an anti-diuretic to prevent water loss and restore blood pressure and osmolarity

Question 54

What is the hypothalamic influence on Reproduction and Affiliative Behaviors?

Answer 54

1) supraoptic and paraventricular nuclei receive input indicating uterus stretch (labor) and/or suckling
2) axons project to the posterior lobe of the pituitary gland and secrete oxytocin into the blood stream
3) oxytocin induces parturition and milk let down for a pregnant mother
4) it is also thought to participate in maternal behaviors such as nesting, maternal protective response and maternal bonding

Question 55

What are the hypothalamic influences on the circadian rhythm?

Answer 55

1) light (irradiant light) is sensed on the retina and some fibers stimulate the suprachiasmic nucleus
2) when stimulated, the SCN influences the endocrine glands to prepare body for the appropriate activity level
3) pineal gland produces melatonin at night to promote sleep
4) adrenal gland produces glucocorticoids and the liver releases glucose just prior to waking
5) there is also an affect to modulate attention and awaking

Question 56

What is the hypothalamic influence on Temperature Regulation?

Answer 56

1) somatosensory signals provide conscious temperature sensation which is directed to Primary Sensory Cortex to illicit appropriate compensating actions
2) signals are also sent to Median Preoptic Nucleus from the STT and Spinal V via the parabrachial nucleus of the pons
3) for Heat Reduction: the preoptic n. projects neurons to the brainstem to activate sympathetic cutaneous vasodilation and increaesed sweating to remove heat by evaporation
4) for Heat Production/Retention: the preoptic n. removes its inhibition of a posterior hypothalmic nucleus which results in activation of the brainstem/spinal cord to induce shivering
- the preoptic n. also induces the sympathetic system to cause central-core vasodilation and cutaneous vasocontriction, thus minimizing heat lost to the environment
- the preoptic n. also release Thyrotropin-releasing Hormone (TRH) in the tuberohypophysial portal system, causing the anterior pituitary cells to release Thyrotropin Stimulating Hormpone (TSH), which causes the Thyroid to release more hormone and thus increase metabolic rate (long term)

Question 57

What is the hypothalamic influence on Fever?

Answer 57

1) fever can be caused by exposure to pyrogens (proteins, breakdown products, lipopolysaccharide toxins, bacterial toxins) which act on the hypothalamus to release prostaglandins which will raise the body’s “set point”
2) once the set point is raised, the body perceives it as too cold (even though the temp is above normal) and begins to raise the temp
3) the preorbital n. induces heat production and conservation through central vasodilation, cutaneous vasocontriction, and stimulation of more Thyroid Hormone to increase metabolic rate
4) once the new set point is reached, the person no longer “feels” chilled -> no shivering
5) once the pyrogen is removed or an anti-pyretic is administered, the hypothalamus stops producing prostaglandins and the set point begins to lower/normalize
6) the body perceives the temp as too high, so begins to reduce it by reversing the previous stimuli and causing cutaneous vasodilation and sweating

Question 58

What is the olfactory pathway?

Answer 58

1) chemoreceptors are sensitive to a wide range of odors allows for chemical analysis based on the different sensitivities
2) the receptors synapse on the bipolar neurons
3) the bipolar neurons penetrate the cribriform plate and synapse on the mitral cells in the olfactory bulb
4) collaterals of the mitral cells synapse in the Anterior Olfactory Nucleus which then sends projections to the contralateral olfactory bulb via the medial olfactory stria and anterior commissure
5) the remaining mitral cells project via the lateral olfactory stria to the olfactory cortex which is made of the pyriform lobe and entorhinal cortex
6) from the primary olfactory cortex axons are sent to the thalamus(DM) via the amygdala or orbitofrontal cortex

Question 59

What are the components of the Limbic System?

Answer 59

1) Limbic Lobe: cingulate, subcollasal and parahippocampal gyri
2) Subcortical center: amygdala, septal nuclei, basal forebrain
3) Diencephalic nuclei: anterior thalamus and mammillary bodies

Question 60

Describe the cytoarchitecture of the Hippocampus.

Answer 60

1) composed of three parts: the dentate gyrus, the hippocampus proper and the subiculum
2) the flow of information (generally) from dentate to hippocampus proper to subiculum and then to the fornix, though fibers from the h.proper can bypass the subiculum to synapse in the fornix directly
3) the primary input is to the dentate from the enterhinal cortex where it synapses with small granule cells; their dendrites in the outer molecular layer, their cell bodies in the intermediate/granule layer and axons passing through the inner polymorphic layer to reach the h.proper
4) in the h.proper they synapse with pyrimidal cells with a largely same architecture; their axons project either into the subiculum or the fornix
5) in the subiculum some axons project back to the enterhinal cortex, but most form a sheet of anxons (alveus) that accumulate lateral to the HF to form the fimbria of the fornix
6) the fornix travels in the ventricle to end in the septum pellucidum as the column of the fornix, and caudally at the mammilary bodies and AN of the thalamus

Question 61

What is the Papez Circuit?

Answer 61

• a simplified overview of the control of emotional expression
  (1) Cingulate Gyrus -> (2)Hippocampus -> (3)Mammillary Bodies -> (4) Anterior Thalamus -> (1)

Question 62

What is the septum? What is it’s function?

Answer 62

1) septum is a series of nuclei ventrolateral the septum pellucidum that is thought to be responsible for determining if a stimulus is pleasurable
2) received input from the hippocampus via the fornix, from the amygdala via the stria terminalis and the amygdalafugal path, and from the hypothalamus and midbrain via the medial forebrain bundle
3) this highly integrated information is sent back to the hippocampal formation, hypothalamus and the habenula

Question 63

What is the structure and function of the amygdala?

Answer 63

1) collection of nuclei located anterior to the hippocampul formation and deep to the uncus
2) integrates multiple inputs to determine if stimuli is negative or harmful; important for focusing attention and fight/flight response
3) receives inputs from temporal lobe, direct olfactory input, and limbic and autonomic information from orbitofrontal lobe, cingulate gyrus, hypothalamus, and midbrain tegmentum
4) output is sent to numerous locations to initiate the fight/flight response -> PAG (pain suppression), autonomics, reticular formation, hypothalamus (stress response), DM of thalamus (fear)
5) the major efferent tract are ventral amygdalofugal tract and stria terminalis

Question 64

What is the nucleus accumbens?

Answer 64

• located at the junction of the caudate and putamen, rostral to anterior commissure
• “cocaine nuclei” -> pleasurable/addictive stimuli

Question 65

What is the basal forebrain?

Answer 65

• area ventral to the anterior commissure and deep to the anterior perforated substance
• part of the substantia innominata and contains the nucleus basalis of Meynert
• this nucleus is a major cholinergic producer and sends projections throughout the cortex

Question 66

What are some examples of lateralized cerebral function?

Answer 66

1) handedness -> right: ~90% are right-handed, which is also strongly associated with left being dominant for language
2) math -> left: calculations and problem solving in linear fashion
3) music -> right/left: right is better w/ chords/melodies, but left is better with tone/duration/rhythm
4) spatial reasoning -> right: better at perceiving and manipulating 2D/3D images
5) emotion -> right: better at coding/decoding emotional states and recognizing faces
6) language -> left: perceive written or spoken words