Cerebellum, balance, coordination

Question 1

what does the cerebellum do generally

Answer 1

it is the processing part of the brain
cortex sends info to cerebellum about what movement they want and should be happening
(coming from collateral branches from the corticospinal tract- from cerebral cortx)
cerebellum takes it on board
gets sensory info from muscle spindles, golgi tendon organs (in muscle or joint to say whether the m or tensdon has actually moved)
cerebellum alerts cortex if movement has not happened- ADJUSTMENT MOVEMENT
sends signals via rubrospinal tract from red nucleus- get changing of nucleus
signal back via thalamus to cortex and get correcting signal down corticospinal tract that brings about changing of that movement

Question 2

what is the function of the muscle spindles

Answer 2

in muscles
give info of change of length of muslce

Question 3

what is the function of golgi tendon

Answer 3

found in muscle
give info about tension of muscle

Question 4

what are cerebellar peduncles

Answer 4

connect cerebellum to brain stem and cerebrum

Question 5

what are the 3 types of cerebellar peduncles

Answer 5

inferior- connect cerebellum to medulla
middle- cerebellum to pons
superior- cerebellum to midbrain

they are input and output routes

Question 6

what are the cerebellum lobes

Answer 6

anterior
posterior
flocculonodular lobe (base)

Question 7

what are the different zones of the cerebellum

Answer 7

it is topographically arranged
vermis (centre)- central control
intermediate zone (limb control movement)
lateral zone

Question 8

what are the functional zones of the cerebellum

Answer 8

1. vestibulocerebellum
   –flocculonodular lobe
   –input from vestibular and visual areas
   –output to vestibular nucleus (equilibrium and eye movements
2. spinocerebellum
   –vermis of posterior and anterior cerebellum and intermediate zones
   –input from spinocerebellar and auditory, visual, vestibular systems and sensorimotor cortex
   –output from vermis to fastigial nuclei to vestibular and reticular formation of pons and medullar (antigravity muscles)
   –output from intermediate zone to interposed nuclei to red nucleus to thalamus to cortex (stretch reflexes)
3. cerebrocerebellum
   –lateral zones
   –input from cerebral motor cortex
   –outpit to dentate nucleus to thalamus to motor and premotor cortices
   –creates feedback with cortical sensorimotor system to plan voluntary body and limb movements

Question 9

what are the deep nuclei of the cerebellum

Answer 9

dentate– red nucleus–thalamus–cortex
interposed
fastigial
vestibular

they form the sole output from the cerebellum

Question 10

what are the microscopic structure of the cerebellum
-3 major layers

Answer 10

molecular layer
purkinje cell layer
granule cell layer

Question 11

what happens in the molecular layer

Answer 11

series of axons
integration of info

Question 12

discuss the climbing fibers and the mossy fibers

Answer 12

mossy fibers synapse with the granular layer and interact with the molecular
INDIRECTLY affect purkinje cells

climbing fibers DIRECTLY affect the purkinje cells

They are both EXCITATORY

Question 13

Where do the climbing fibers originate from

Answer 13

olive nucleus

Question 14

are the purkinje cells excitatory

Answer 14

no they are INHIBITORY

Question 15

describe what happens microscopically when there is a new movement occurring

Answer 15

new movement get an increase in firing– excitatory from mossy and climbing fibres
stimulate purkinje
so initial output is inhibitory
when movement is learned the inhibitory output becomes diminished
===>LONG TERM DEPRESSION
PURKINJE become PLASTIC- learning form input

Question 16

what is the order of the deep cerebellar nuclei
lateral to medial (only output from cerebellar)

Answer 16

lateral ->medial
Dentate (lateral zones)
Interposed (intermediate)
Fastigial (vermis)
Vestibular is fed from flocculondular lobe

Dont- DENTATE
Eat- EMBOLIFORM
Greasy- GLOBOSE
Food- FASTIGIAL

Question 17

what are the cerebellum functions

Answer 17

1. acts as a comparator
   (compare descending supraspinal motor signals with ascending afferent info)
2. acts as a timing device
   (3 different kinds of cerebellum)
3. initiating and storing movements
   (modifiable synapse- purkinje- store motor info and update it)

stimulation of cerebellum causes neither sensation nor significant movements
loss of cerebellum–> severe abnormalities of motor function

Question 18

how does alcohol affect the cerebellum

Answer 18

affects neurons in the cerebellum

Question 19

what is the primary role of cerebellum

Answer 19

supplement and correlate activities of other motor areas– correction of rapid muscular movement initiated by cortex (TYPING)

Question 20

what is the secondary and third role of cerebellum

Answer 20

secondary- control of postural mechanisms
third- maintenance of tone of muscles (hyperflexia)

cerebellum informed of movement by cortex before it occurs, cereb processes sensory info to generate an ERROR SIGNAL which is fed back to cortex and movement is adjusted

Question 21

what are some clinical features of cerebellar dmage

Answer 21

HYPOTONIA
reduced input from deep cerebellar nuclei
INCOORDINATION/ATAXIA
asynergy
dysmetria
dysdiadochokinesis
DYSARTHRIA
NYSTAGMUS
disruption between vestibular nucleus and oculomotor nuclei
PALATAL TREMOR, MYOCLONUS
rare
hypertrophy of inferior olive- damage to dentate nucleus of cerebellum and red nucleus in midbrain

Question 22

what system generates our sense of balance

Answer 22

vestibular system

Question 23

discuss the ear and

Answer 23

pinna collects and focuses sound waves
external auditory canal (skin lined) ends up at tympanic membrane
middle ear is air filled chamber, bounded by tympanic membrane and oval window

eustachian tube connects middle ear to nasophyarynx, allows pressure equalisation

outer, middle, inner ear

Question 24

what is the membranous labyrinth

Answer 24

filled with endolymph
encased in temporal bone
auditory part is cochlea

Question 25

what are the two vestibular parts

Answer 25

otolith organs* (two parts)- detect GRAVIT, HEAD TILT
semicircular canals- detect HEAD ROTATION

*saccular (vertical)
*utricle (horizontal)

Question 26

what are the hair cells of saccule

Answer 26

mechanoreceptors that respond to minute movement changes
consists of one large KINOCILIUM and 50-150 stereocilia
cochlea–they lose their kinocilium with age
vestibular– do not lose kinocilium with age

perception of tilting/movement depends of movement of microcilia to kinocilia

Question 27

discuss otolithic organs

Answer 27

detect changes in linear acceleration (i.e. that experienced as a car starts) and head angle
• Each hair cell synapses on an axon of vestibular nerve (part of CN VIII)
• Otoliths are particles of calcium carbonate; they are denser than the endolymph
• Otoliths are pulled by gravity and move gelatinous cap in same direction; cilia of hair cells are deflected

Question 28

what is the mechanotransduction in hair cells

Answer 28

a 0.5 micron movement of the kinocilium open/closes hair cell cations
if cilia move towards kino
k channels open – depolarisation, increase in frequency down nerve
NT released down vestibular never
tells brain there is movement in that direction
if away close k channels and hyperpolarisation
occurs in utricles and saccules

Question 29

what happens in semicircular canals (ampulla)

Answer 29

Sensitive to angular acceleration
• Hair cells clustered in sensory
epithelium, crista ampullaris
• Hair cells project into gelatinous
cupula, all hair cells orientated in
same direction
• As head rotates canal moves but
endolymph stays put, this bends the
hair cells and they either excite or
suppress transmitter release
depending on direction of
movement

Question 30

describe the vestibular nervous pathway

Answer 30

Vestibular axons from CN VIII make
direct connections to vestibular
nucleus & cerebellum
• Axons from otolith organs project to
lateral vestibular nucleus, which
project via vestibulospinal tract to
spinal motor neurons – posture
• Axons from semicircular canals
project to medial vestibular nucleus,
which project via medial longitudinal
fasiculus to motor nerves of trunk
and neck muscles – keeps head
straight as body moves

Question 31

how does the semicircular canals control eye movements

Answer 31

VESTIBULO-OCULAR REFLEX
• Direct stimulation of ampullary nerves
elicits specific eye movements
• Stimulation of afferents from left
horizontal canal causes eyes to turn
right (vestibulo-ocular reflexes)
• Specific adaption to allow gaze to
remain steady during head movement
• Lateral recti – cranial nerve VI
(abducens nucleus)
• Medial recti – cranial nerve III
(oculomotor nucleus)

Question 32

describe meniere’s disease

Answer 32

vertigo, nausea, tinnitus, hearing loss
The vestibular apparatus is bathed in endolymph
• Normally drains to venous sinus
• Meniere’s cause is unknown, but there is an excessive accumulation of
endolymph and damage to hair cells
• Accumulation of endolymph is probably due to poor drainage

Question 33

why does increased pressure in the endolymph cause both tinnitus/hearing loss and dizziness

Answer 33

increased endolymph in cochlear affects hearing
damage of hair cells means you dont get signals

Question 34

what is vertigo

Answer 34

sensation of turning or rotation in space in absence of actual rotation

nausea, vomiting, gait ataxia
caused by debris from otolithic membrane adhering to cupula in ampulla of posterior semicircular canal
can be due o lesions of vestibular aspect of CNVIII or central lesions affecting brainstem vestibular nuclei.

treatment– manipulation of head, to cause calcium crystal move back to where should be