Functions of the Cerebellum and Brainstem (Week 1, Mod 8)

What is the main branch of white matter in the cerebellum called? What is the gray matter surrounding it called?

Major branch of WM = Arbor vitae (see image)

GM = Cerebellar cortex

From the dorsal view of the cerebellum, it can be split into 3 sections… what are the 2 lateral portions called, and what is the central portion called?

Lateral portions = hemispheres 

Central portion = Vermis

Here is a ventral view of the cerebellum… the rostral portion of the vermis is farther back, the caudal vermis is facing you. What are the 3 structures that are indicated to in this image?

Cerebellar peduncles - the line of 3 white matter tracts; is cut through in this section

• Connection between the cerebrum and cerebellum 

Flocculus - Indicator to the right; found along the inner edges of the hemispheres 

Nodulus - found along the ventral-most part of the vermis 

What are the names of the 3 different cerebellar peduncles?  List them from inside to outside.

1) Rostral cerebellar peduncle 

2) Caudal cerebellar peduncle 

3) Middle cerebellar peduncle

Yes… these are in the right order 

Describe the histology of the cerebellum… What are the 3 layers of gray matter?

Have white matter in the center, but gray matter surrounding it… from innermost to outermost:

• Granule cell layer

• Purkinje cell layer

• Molecular cell layer

What are the 2 kinds of nerve fibers that will communicate outside information TO the cerebellum?

Mossy fibers - the most common in the cerebellum; embedded in the white matter

• Fibers synapse with granular cells in the granular cell layer, brings signal INTO cerebellum

• CAN’T GO FARTHER than the granular cell layer

Climbing fibers

• Come directly from the olivary nucleus… are able to extend into the MOLECULAR LAYER and communicate with the surface, bringing outside info in

• Bypass granular layer

What nerve cell is the only neuron that carries info OUT from the cerebellum?

PURKINJE CELL

• Dendritic fibers extend into the molecular layer, while the cell body has an axon that communicates deep into the cerebellar nuclei 

These are the ONLY cells from which the cerebellum acts through 

What exactly ARE cerebellar nuclei?

Aggregations of neurons (gray matter) that are DEEP within the cerebellum… areas of neuronal activity

KNOW THAT THERE ARE 6 IN TOTAL!!!  Don’t need to know the names 

What is the major function of the of the cerebellum?

The role of the cerebellum is to smooth and coordinate motor function for posture and movement. 

• It acts as a regulator, not a primary initiator, of motor activity.

  • Isn’t in charge of actually moving your limbs, but will CONTROL them to make sure they move correctly (not spastically)

• It modulates the activity of the upper motor neuron (UMN) affecting agonist and antagonist muscles.

What are the 2 main stimuli that the cerebellum RECEIVES / processes?

1) PROPRIOCEPTION

2) Information relevant to the PLANNING AND EXECUTION of motor activity

• Just what was said before; if your cerebrum decides it wants to move, the cerebellum then has to decide HOW you move

What are the 3 different pathways through which proprioceptive info travels to the cerebellum?

Spinocerebellar = From spine to cerebellum; communicates info about the limbs and body

Vestibulocerebellar = from vestibules of the brain to the cerebellum

Tectocerebellar = idk, just know that it has something to do with the position of the head

What are the 2 different pathways through which motor activity planning info travels to the cerebellum?

1) Corticopontocerebellar = from cortex → pons → cerebellum

• Cortex decides you want to move, then cerebellum has to determine HOW you move

2) Via Olivary Nucleus - Takes in input from EXTRAPYRAMIDAL system of the cortex

Which efferent neurons in the cerebellum are INIHIBITORY, and which are EXCITATORY?

Inhibitory:

• PURKINJE CELLS 

• Most of them synapse in the deep cerebellar nuclei

Excitatory:

• Deep cerebellar nuclei neurons

  • Are excitatory nuclei of pyramidal and extrapyramidal systems; can NEVER be inhibitory 

So essentially, the Purkinje cells act to INHIBIT the deep cerebellar nuclei!

• Helps to make movements smooth and controlled 

The 3 peduncles also act as carriers of information… what kind of afferent and efferent info does the ROSTRAL cerebellar peduncle transport?

Afferent:

• Info from ventral spinocerebellar pathway

Efferent:

• Carries info to thalamus and midbrain

The 3 peduncles also act as carriers of information… what kind of afferent and efferent info does the MIDDLE cerebellar peduncle transport?

Afferent:

• Info from cortico-ponto-cerebellar pathway

DOES NOT TRANSPORT EFFERENT INFO 

The 3 peduncles also act as carriers of information… what kind of afferent and efferent info does the CAUDAL cerebellar peduncle transport?

Receives MOST of the afferent info

Afferent:

• From DORSAL spinocerebellar pathway

• Reticular formation 

• Olivary nucleus 

• Vestibular nuclei 

• Etc.

Efferent:

• Info TO reticular formation and vestibular nuclei 

What are the 3 functional SUBDIVISIONS of the cerebellum?

1) Vestibulocerebellum

• AKA archicerebellum 

• Flocculo-nodular lobe (STRUCTURES ON THE VENTRAL PORTION OF THE CEREBELLUM (Flocculus and nodulus)) → These control the vestibules

2) Spinocerebellum

• AKA paleocerebellum

• Is the vermis and paravermis → control hypermetria and spasticity

3) Cerebrocerebellum

• Is the cerebral hemispheres → control dysmetria and tremors

What is the “menace” response?

Eyes closing when you wave a hand in from of them; is a cerebellar reflex, if cerebellum not working well then this response will not be present

What general clinical signs would you see if there is cerebellar dysfunction?

• Mentation: Normal

• Hypermetria, dysmetria (ipsilateral): cerebellar ataxia

• Intention tremors

• Some cases head tilt (contralateral) and nystagmus → Paradoxical vestibular: Lesions in the foculonodular lobe. The side of the lesion has increase activity due to lack of inhibition.

What are the 3 main functions of the brainstem?

• Conduction: All information relayed from the body to the cerebrum and cerebellum and vice versa must traverse the brainstem.

• Cranial nerves function: Cranial nerves III-XII emerge from the brainstem.

• Integrative functions: Involved in cardiovascular system control, respiratory control, alertness, awareness and consciousness.

REMEMBER THESE!!!

Rodrigo said he’d cry if you didn’t

What are the 10 cranial nerves that are associated with the brainstem, and where in the brainstem do they originate from?

What is the cardiovascular center of the brainstem? Where in the brainstem is it found, and what are its functions?

Found in the medulla oblongata of the brainstem

• Regulation of heart rate.

• Change of blood pH and CO2 —> modulated by chemoreceptors → signals brainstem

• Change of blood pressure —> modulated by baroreceptors in aortic and carotid bodies → signals brainstem to DECREASE blood pressure

• Acts by sending nerve impulse to pacemaker via autonomic fibers

Injury to the brainstem could cause heart failure and death

What is the Cushing Reflex?

Is the hypertension and bradycardia that is caused by INCREASED INTRACRANIAL PRESSURE on the brainstem

• This is why you monitor a patient’s blood pressure if they have any sort of brain swelling 

What is the respiratory center of the brainstem? Where in the brainstem is it found, and what are its functions?

Are again found in the medulla oblongata AND the pons of the brainstem

• Control the rate and depth of respiratory movements.

• Injury may lead to respiratory failure.

• Change of blood pH and CO2 —> Chemoreceptors

What are the 4 kinds of abnormal breathing patterns that can be seen with brainstem lesions?

1) Cheyne-Stokes Respiration:

• Periods of respiration during which the total volume of a breath becomes shallow, then gets progressively deeper, then gets progressively SHALLOWER again

• Followed by periods of significant apnea (see image) 

2) Biot’s Respiration:

• Periods or “clusters” of rapid respiration of near-equal depth, followed by regular periods of apnea 

3) Apneustic Respiration:

• Prolonged inspiratory phase, followed by a prolonged expiratory phase

• Commonly believed to be apneic phases 

4) Ataxic Respiration:

• Completely irregular breathing pattern

• Increasing episodes of apnea 

What is the ascending reticular activating system (ARAS) of the brainstem? What is its function?

Is a reticular formation:

• Collection of neuronal cell bodies that form an ill-defined meshwork in the central core of the brainstem

• Found through the caudal diencephalon to the medulla oblongata

Is responsible for the AWAKE state, level of consciousness, and sleep

What are the 6 grades of mental status (alertness), starting from least to most severe.

What are the 6 neurological signs of brainstem dysfunction?

• •Mentation: Normal, obtunded, stupor or coma

• •Head tilt and wide base stance can be seen

• •Cranial nerves III-XII can show deficits

• •Ipsilateral proprioceptive deficits

• •Abnormal heart rate

• •Abnormal breathing pattern