LAst neuro

Describe the Putamen

It processes major body movement control

Draw and describe the connections between the vestibulocerebellum and vestibular nuclei. What is this pathway's purpose?

The vestibulocerebellum is concerned with balance and eye movements and with the position of the head in space. The flocculonodular lobe receives inputs from the vestibular system and also from the visual system. Its output goes to the vestibular nuclei via the inferior peduncle. It is the only part of the cerebellum where the outputs do not go via the deep cerebellar nuclei.

Describe purkinje cells

Their cell bodies are found in the purkinje cell layer of the cerebellar cortex and their axosn project into the outtermost layer of the cerebellar cortex. The dendrites of the purkinje cell extend out in a singular plane--they are very flat like with a japenese fan. They receive excitatory signalling from parallel fibers and climbing fibers and send inhibitory stimuli to the deep nuclei

Striatum

the caudate nucleus and putamen together

What connects the putamen to the caudate?

the nucleus accumbens

What's the difference between planning and execution?

Planning requires the prefrontal association cortex which controla motivation, emotional behaivor and mood. The basal ganglia and cerebellum are also involved. Execution of the plan invovles the motor cortex with feedback control from the periphery to the cerebellum.

The cerebellum feeds information through the deep cerebellar nuclei to:

*the motor cortex, through the ventrolateral nucleus of the thalamus *the red nucleus *the reticular formation *the vestibular nucleus

What is cerebellar hypotonia?

A decrease in the resistance to the stretch of skeletal muscles. When we passively stretch a muscle, there is some resistance to this muscle movement. The degree of this resistance is referred to as muscle tone. Muscle tone is the reflexion of the fact that there is always some msucle contraction at rest in the absence of movement. This reflects inputs from higher center including the cerebellum. Since the cerebellum provides excitatory inputs to the spinal cord lower motor neurons that supply skeletal muscles, lesions of the cerebellum that decrease this excitatory output would result in decreased resting muscle coontraction.

Describe the nucleus accumbens

Although the nucleus accumbens is anatomically a part of the basal ganglia, functionally it belongs in the limbic system for it is a apart of the reward system and is involved in the processing of motivation, aversion, and learning. It does control of affect: the nuanced emotional reactions. Due to its participation in the rewards system, we see a lot of activation of dopamine in this region whenever we have rewarding behaviors or rewarding stimulus. Note: due to its ties with reward, this area is looked at in adictions

climbing fibers

Axons that originate in the inferior olive, ascend through the inferior cerebellar peduncle, and synapse into the cerebellum--the olive receives information from the spinal cord, cortical, and subcortical structures. The ascened along the purkinje cell axon, to the cell body, and wrap their synaptic terminals around the dendrites of the purkinje cells. These climbing fibers provide excitatory input to the purkinje cells which will then send inhibitory signals to the deep nuclei.

What's the difference between mossy fibers and climbing fibers?

Both types of fibers make stimulatory synapses with deep cerebellar nuclei as well as synapsing with cells in the cerebellar cortex. However, while mossy fibers provide sensory information, the climbing fibers are providinf "motor plan" information, thats, they are telling the cerebellum what movements are beign planned so that the cerebellum can facilitate them.

Explain how lesions in the basal ganglia can result in hyperkinesis.

Damage to the basal ganglia can reduce the output from these nuclei and removes activation of the indirect loop. This reduced output removes inhibition of the thalamic nuclei. The increased thalamic output to the premotor cotex results in an inability to stop unwanted movements.

What is the role of dopamine on the substantia niagra?

Dopamine, from the substantia nigra facillitates release of inhibition. People who have deficient dopamine production, have an overall decrease in motor output and need to make greater exertional effort to move.

How does the cerebellum end up modulating commands from the cerebral cortex?

Fibers from the primary motr area in the cerebral cortex that synapse with motor neurons in the spinal cord, sendconenctions to the pontine nuclei and the inferior olive. These nuclei project into the cerebellum so that the cerebellum receives a copy of the motor instructions going to skeletal muscles. At the same time, sensory information is routed directly to the deep cerebllar nuclei from the spinal cord and vestibular nuclei. Within the cerebellum, the actual movement as signalled from the peripheral receptors os compared with the original commands from the primary motor area. If necessary, the cerebellum sends information to fine tuen the movement.

Describe the globose and emboliform nuclei

In humans, these are not separate nuclei and are referred to as the interposed nucleus. The interposed nucleus is involved in regualtion of muscle stretch reflexes and in coordinating agonist/antagonist muscle activity. It receives information from limb and trunk muscles and from the medial part of the cerebellar hemisphere. It sends information to the red nucleus via the superior cerebellar peduncle.

What are the symptoms of Huntington's disease

In these patients we see choreiform movements (unintended movements that look compsed or choreographed). We also see the onset of dementia. These guys can think they're fien when they're not

Describe the cereballar inputs

Information begins in the frontal/parietal cortex. Information is then either relayed to the pontine nuclei where it then goes straight through the middle cerebellar pedunlce (does motor input from the motor cortex) to the cerebellar cortex/deep nuclei, or to the red nucleus which sends information to the inferior olive which transmits it through the inferior cerebellar peduncle to the cerebellar cortex/deep nuclei (learning signal from cortex, the basis for motor learning). Information from the spinal cord and vestibuvlar nuclei also come in through the inferior cerebellar peduncle to the cerebellar cortex/deep nuclei. Note: descending information crosses the midline to enter the oppsite side of the cerebellum while spinal cord and vestibular information is ascending ipsilaterally

Describe Parkinson's disease

It is a bradykinetic disorder that primarily affects the neurons that exist in the substantia niagra. It selectively targets these dopamine neurons resulting in an inability to produce enough dopamine to synergize the direct and indirect pathways within the striatum: without these neurons projecting to the striatum we're not able to selectively activate the direct and inhibit the indirect pathway when we intend a movement activation.

Describe Huntington's disease

It is a hyperkinetc disorder that involves a failure of supression of movement. This is an autosomal dominant diorder where we see 100% penetrance in carriers of the gene. The huntington's gene, codes for the Huntington's protein, develops an unusally large number of CAG repeats within it. The problem with this is that these expanded CAG repeats are neurotoxic and affect the D2 cells in the striatum. This results in increased action of the Gloubc pallidus external segment (it is not receiving the inhibiton signal from the striatum) which causes decrease in the indirect pathway and an increase in the direct pathway.

Describe the fastigial nucleus

It is involved in the control of standing and walking and also in the tracking of movement by our eyes (saccadic eye movements). It receives information from Purkinje cells in the vermis. It sends information to the vestibular nuclei in the brain stem via the inferior cerebellar peduncle.

Describe the dentate nucleus

It is involved in the planning and control of movement and also has additional functions in cognition and spatial orientation. It receives information from the premotor cerebral cortex and from the lateral part of the cerebellar hemispheres. It sends information through the superior cerebellar peduncle to the red nucleus and thalamus where it is relayed to the premotor cortex and, for cognition to the parietal cortex.

Describe the basal ganglia

It is the area of the brain responsible for initiating wanted movements and supressing unwanted movements. The basal ganlgia are composed of different groups of grey matter nuclei foudn in both cerebral hemispheres surroinding the diencephalon. THey comprise the: *striatum: dorsal (composed of the putamen and the caudate) and ventral (nucleus accumbens and the olfactory tubercle). *globus pallidus: internal and external *Subthalamic nucleus *substantia nigra (which lies on the midbrain) Note: hte midbrain itself is not part of the basal ganglia. Furthermore, the ventral striatum is associated with the limbic system--it plays an important role in reward-related functions

Describe the caudate nucleus

It is the ram's horns. It is primarily involved with occular motor control: where the eyes go, the mind goes

Describe the substania nigra

It plays a critical role in the function and modulation of basal ganglia behavior. It consists of teo different regions: *substania nigra pars compacta: has axons that project up to the striata and release dopamine to modulate the signalling within the striatum *substantia nigra pars reticulata: has axons that consists of the primary output pathways from the basal ganglia back to the thalamus before the information is relayed to the

Describe the functions of the cerebellum

It provides moment to moment adjustment of behavior through integration of inputs. This provides learning facillitation in the presence of errors. Similar to the basal ganglia, the cerebellum does not have output to lower motor neurons but has direct input to the central nervous system. The cerebellum has two primary functions: 1. To coordinate on-going multijointed movement (ex. upper arm, lower arm, and hand coordination to reach out and grab a cup) 2. To coordinate ongoing sequentive cognitive processes (ex: problem solving) The cerebellum has three function parts: the spinocerebellum, the cerebrocerebellum, and the vestibulocerrebellum

Describe the spinocerebellum

It provides refined movements of peripheral limbs throught the spinal cord--it is involved in carryout out (executing) motor functions. It is divided into two primary structures: 1. The vermis, which is the middle part, is primary concerned with the middle of the body in terms of modulating muscle movement control. Its putput leaves the cerebellum via the deep fastigial nucleus 2. The sides of the vermis (the medial part of the cerebellar hemisphere) control the peripheral limbs (like in the primary motor cortex, we see that there are multiple representations of different body parts along the distribution of the cerebellar cortex). Its output leaves via the deep interposed nucleus. The spinocerebellum also receives sensory (proprioceptive) inputs from the periphery via the inferior olivary nucleus in the medulla as well as from the audiory and visual systems. Its outputs leave the cerebellum through the superior peduncle and project to the red nucleus.

Describe the sequence of events when a mossy fiber or climbing fiber is stimulated

Mossy fiebrs and climbing fibers send collateral branches to the deep cerebellar nuclei on their way to synapsing with granule cells (mossy fibers) or directly with Purkinje cells (climbing fibers). Therefore, the first response is excitiation of these deep cerebellar nuclei that results in activation of their target neurons. THis is the deep excitatory loop. Excitiation of the Purkinje cells foloows as the signal reaches the cerebellar cortex. This results in teh purkinje axons releasing GABA in the deep cerebellar nuclei with inhibition of the output from these nuclei. This is the cortical inhibitory loop. THis excitaion of the purkinje cells has only a short duration so the inhibiton of the deep cerebellar nuclei is rapidly removed. How much the purkinje cells modulate and attenuate the amount of deep cerebellar nuclear excitation depends on the release of GABA inhibitory signalling from the Purkinje cells. This is the result of summation from parallel fibers and climbing fibers that excite the Purkinje cell, and basket cells and stellate cells that provide inhibitory signalling to the purkinje cell. This pattern of excitation, inhibition, and modulation provides coded messages to the target neurons.

Describe what would occur with lesions to the flocculonodular lobe

Outputs directly to the vestibular nuclei that affect eye movements. Lesion in this lobe result in a type of nystagmus -- a type of oscillary eye movement where the eye slowly drifts off its target before rapidly returning to it. The vestibulat nuclei are also concerned with balance, so lesion here cause people to feel unsteady on their feet and to be in fear of falling. They are unsteady with their eyes open or shut.

Describe granule cells

THere are more granule cells than all other CNS cells combined. The granule cell axon ascends into the molecular layer where it bifurcates, forming the parallel fibers that synapses with purkinje cell dendrites. Granule cells are excitatory, using glutamine as their neurotransmitter.

Describe the purkinje cell layer of the cerebellum

The Purkinje cell layer contains the Purkinje cell bodies. Their dendrites are found in the molecular layer and their axons run deep into the cerebellum to synapse on cells in the deep cerebellar nuclei. The Purkinje cell is inhibitory and uses GABA as its neurotransmitter.

Describe the descending cerebellar outputs

The cerebellar cortex has ipsilateral information coming in from the spinal cord and the vestibular nuclei and also has primarily ipsilateral output descending back down to the spinal cord. In terms of motor correction we have that information primarily from the fastigial deep nuclei going to the superior colliculus and the reticular formation via the inferior cerebellar peduncle before descending down the anterior medial white matter of the spinal cord. The anterior white matter column, is going to be primarily focused on teh postural control of our motor movements. We also have cerebellar output that goes through the inferior cerebellar peduncle directly to the vestibular nuclei before descending down the spinal cord to provide the feedback pathways. Those feedback movements include the side to side adjsutment as we have lateral shifting as well as responding to forward rotation of the head (which will extend our arms out to break our fall). In many cases we are going to see that our cerebellar output is going to involve bilateral responses. So that information is relayed through the superior cerebellar peduncle where it synapses in the superior colliculus where it converges with other descending information from the cerebellum into the spinal cord pathway.

Describe the cerebelalr cortex

The cerebellar cortex has three distinc cell layers; from outside in these are the molecular layer, Purkinje cell layer, and granule cell layer. The molecular layer contains the dendrites of the purkinje cells whose cell bodies are found in the purkinje cell layer. Nerve endings of climbing fibers form strong excitatory synapses with these purkinje cell dendrites. The molecuar layer also contains the bifurcations of the granule cells that form the parallel fibers that also synapse with the purkinje cell dendrites. The purkinje cell layer contains the purkinje cell bodies. Their dendrites are found in the molecular layer and their axosn run deep into the cerebellum to synapse on cells in the deep cerebellar nuclei The Purkinje cell is inhibitory and uses GABA as its neurotransmitter. The granule cell layer contains the granule cell bodies. Mossy fibers form excitatiory synapses with the granule cells. Each granule cell receives input from multiple mossy fibers, and each mossy finer influences several granule cells. The terminals are exceptionally large.

Describe acending output from the cerebellar cortex

The cerebellar cortex sends information to the deep cerebellar nuclei (dentate/interposed) . The information then crosses the midline going to the opposite side of the body and either ascends to the VL complex in the thalamus and up to the primary motor and premotor cortices, or down to the superior colliculus (this information directs behavioral responses toward specific points in egocentric ("body centered" space). A third output destination from the cerebellum to the brainstem is the red nucleus. The importance of the red nucleus in humans deminishes around the age of two as we progress from crawling around on all fours to walking on two legs--the red nucleus continues to remain important in animals who continue to walk around on all fours throughout their entire life. In humans, we see the myelination of the axon pathways is involved with the progression of moving from crawling to walking and the red nucleus does still have a role in coordinating arm swing and maybe some movement of the upper and lower arms.

Describe the structure of the cerebellum

The cerebellum sits above the pons and midbrain. It comprises just 10% of the brain's total volume but contains more neurons than any other single brain structure. There are several distinct regions in the cerebellum that receive inputs from different areas of the brain and spinal cord and have outputs to different motor systems. The cerebellum is also composed of 3 different lobes: *Anterior lobe: concerned with unconcioous proprioception *posterior lobe: concerned with fine motor control *flocculobodular lobe: concerned with vestibular feedback, head/eye tracking Note: the primary fissure separates the anterior lobe from the posterior lobe and the posterolateral dissure separates the posterior lobe from the flocculonodular lobe

Describe the cerebrocerebellum

The cerebrocerebellum consists of the lateral part of the cerebellar hemispheres. It is involved in the planning of movements but it also has cognitive functions. It receives inputs from the cerebral crtex (principally the parietal lobe) via the pontine nuclei in the pons. Its output leaves via the dentate nucleus and passes to the motor and premotor cortices in the frontal lobe of the cerebrum as well as the red nucleus, and, for cognitive functions, to the parietal lobe of the cerebrum. This gives us refined movement of controled motor skills directed by the cerebrum. We also see most of our cognitive, multistep processing facillitated by the neurons here

Draw and describe the connections between the cerebrocerebellum and the motor nuclei. What is this pathway's purpose?

The cerebrocerebellum is involved in the planning of movements. It also has cognitive functions. It consists of the lateral part of the cerebellar hemispheres. It receives inputs from the cerebral cortex (principally the parietal lobe) via the pontine nuclei in the pons. Its output leaves via the dentate nucleus and passes via the ventrolateral nucleus of the thalamus to the motor and premotor cortices in the frontal lobe of the cerebrum, and, for cognitive functions, to the parietal lobe of the cerebrum.

Describe the deep cerebellar nuclei

The deep nuclei of the cerebellum receive inputs from the CNS and from the cerebellar cortex through the Purkinje cells and output information to other parts of the brain and spinal cord. With the exception fo the output of the flocculonodular lobe that goes directly to the vestibualr nuclei in the brain stem (medulla and pons), all other outputs go through the deep nuclei. Thus, these do processing of cerebellar inputs. There are three: *The dentate nucleus: invovled with processing of information from the cerebrocerebellum *The interposed nuclei: involved with the processing of information within the spinocerebellum *The fastigial nucleus: involved with processing of information from the vestibulocerebellum

Whats the difference between the cerebellum and the primary motor cortex?

The function of the primary motor cerebral cortez is encoding movement intention and movement dimension- force, direction, and amplitude (speed). In contrast, the cerebellum's function is error correction of motor learning and movement-to-movvement adjustment of behavior through integration of executive commands with sensory input. So, for example, it helps maintain balance and posture. It also coordinates ongoing, multi-jointed movement and coordinates ongoing sequential cognitive processed including problem solving. Damage to the cerebellum doesn't prevent a person from moving, but it does make actions hesistant and clumsy, and affects balance and gait.

Describe the granule cell layer of the cerebellum

The granule cell layer contains the granule cell bodies. Mossy fibers form excitatory synapses with the granule cells. Each granule cell receives input from multiple mossy fibers, and each mossy fiber influences several granule cells. Terminals are exceptionally large.

Describe the molecular layer of the cerebellum

The molecular layer contains the dendrites of the Purkinje cells whose cell bodies are found in the Purkinje cell layer. Nerve endings of climbing fibers form strong excitatory synapses with these Purkinje cell dendrites. The molecular layer also contains the bifurcations of the granule cells that form the parallel fibers that also synapse with the Purkinje cell dendrites.

Describe the process for the execution of movement

The motor cortex initiates the execution of a movement using its connection to α motoneurons through the cortico-spinal tract. It also informs the cerebellum and basal ganglia. When muscles begin to contract, proprioceptive information from muscle spindles, Golgi tendon organs and joint mechanoreceptors feeds back to spinal interneurons and, through the spinocerebellar tract, to the cerebellum. The cerebellum now compares the actual movement with the motor cortex instruction it received and fine tunes the response by signaling back through the thalamus to the motor cortex, and sending information to brain stem nuclei that supply spinal cord interneurons. At the same time, the basal ganglia are accentuating the desired movements through stimulation of thalamic feedback to the motor cortex (direct loop) while inhibiting other conflicting cortical motor activity by inhibiting thalamic support for these (indirect loop).

What are the symptoms of parkinson's disease

The signs and symptoms of Parkinson's disease are going to be akinesia (lack of ability to initiate movement behaviors) or bradykinesia (the slowing of movements as they are attended). We'll see general rigidity throughout the body and the development of a resting tremor--inbitility to supress unintended motor behaviors (inability to activate the indirect pathway). Another pronounced aspect of Parkinson's disease is reduced facial expression along with shuffling gait. Note: Eventually these patients all develop some form of dementia.

Draw and describe the connections between the spinocerebellum and the motor nuclei. What is this pathway's purpose?

The spinocerebellum is involved in executing motor functions. It consists of the vermis, whose output leaves the cerebellum via the deep fastigial nucleus, and the medial part of the cerebellar hemisphere, whose output leaves via the deep interposed nucleus. It receives sensory (proprioceptive) inputs from the periphery via the inferior olivary nucleus through the olivocerebellar tract, as well as from the auditory and visual systems through the reticular formation and vestibular nucleus. Its outputs leave the cerebellum through the superior peduncle and project to the red nucleus. The red nucleus, in turn, projects to the inferior olive, thus providing a feedback loop to the spinocerebellum. Note: the red nucleus also projects to the spinal motor nerves through the rubrospinal tract and affects muscle movements, particularly in the upper limbs.

Describe the pathology behind Parkinson's disease

The substantia nigra compacta contains dopaminergic neurons. It is not known why in some people there is a progressive loss of these neurons but when some 80% or more have been lost, symptoms and signs of parkinsons disease begin to be seen. The role of the basal ganglia is to provide a cosntant inhibitory input to prevent inappropriate motor activity. When a movement is desired, the inhibition for this is reduced through the direct lop, while the indirect loop continued to inhibit other motor activity. Dopamine from the substantia nigra facilitates this release of inhibition, People who have deficient dopamine production have an overal decrease in motor output and need to make greater exertional effort to move.

Describe what would occur vermal region

The vermal region supplies the trunk. A lesion here would affect the way the person walks--their gait. People with damage here have a wide stance and hesitant walk with irregular steps, stops, ad starts, and a tendency to veer to one or other side.

Describe the cerebellar peduncles

They provide our white matter tract areas for the cerebellum. There are three: *Superior peduncle: concerned with cerebellar output, largely to teh motor cortex * Middle peduncle: where motor input enters the cerebellar processing loops from the pons *Inferior peduncle: where we have input for motor learning from the medulla oblongata (lower down than the middle peduncle) Information enters through the inferior and middle cerebellar peduncles, is processed in the cortex of the cerebellum with additional processing done by the deep cerebellar nuclei .

Describe ataxia

This is an inability to perform movements accurately. Manifestations include defects in accurately locating objects in space (dysmetria) --for example, not being able to touch your nose accurately (finger-nose test) or touch a finger accurately. There is also an inability to perform rapid alternating rotational movements (called dysdiadochokinesia). And tehre may be a tremor when a person ahs to move a lim--intention tremor (there is no tremor at rest). Note: damage to the cerebellum results in ipsilateral motor issues

Describe the vestibulocerebellum

This is made up of two regions: the flocculus (lateral) and the nodulus (medial)--may be referred to as the floccularnodualr group. This is the oldest part of the cerebellum and is concerned with balance and eye movements and with the position of the head in space (vestibular feedback). It receives inputs from the vestibular and visual systems. Its output goes to the vestibular nuclei via the inferior peduncle. It is the only part of the cerebellum where the outputs do not go via the deep cerebellar nuclei.

Describe the indirect pathway of the basal ganglia

This is our signal to stop. It is called the indirect pathway because we go through the globu pallidus external segment and the subthalamic nucleus before converging on the internal segment of the globus pallidus: We have signalling from the cerebral cortex that's going to activate neurons in the caudate and putamen (the striatum). Those nuclei will then cause transient inhibition of the globus pallidus external and internal segments. Inhibiton from the globus pallidus external causes disinhibition of the subthalamic nucelus which will activate the globus pallidus internal segment to increase the tonic inhibition on the Va/VL complex of the thalamus preventing the signal of movement--this prevents conflicting movements. Note: in this pathway we find the D2 medium spiny axons of the substansia pars compacta which inhibit the indirect pathway --alowing for movement

Describe the direct pathway for the basal ganglia loop

This pathway is our move signal. It reinforces the planned movements originating in the premotor cortex: striatum(-) -> Globus pallidus (-) --> VA/VL complex of the thalamus (+) --> motor corex which sends information to the lower motor neurons When the putamen of the striatum is activated via descending input from the cerebral cortex and input from the substantia pars compacta, it will inhibit the globus pallidus (internal segment) which disinhibits the VA/VL complex of the thalamus so that the VA/VL complex of the thalamus can activate the motor cortex. At the same time, dopaminergic neurpns from the substantia nigra pars compacta are also activating inhbitory neurons in the striatum through dopamine D1 receptors, thus reinforcing the inhibitory output from the striatum to the GPi . Note: all signalling except that from the globus, pallidus internal segment is transient--that from the globus pallidus internal segment is tonic. In the direct pathway we are looking at medium spiny neurons from the substansia nigra that express D1 receptors

Describe what would occur with lesions to the cerebellar hemispheres

This region of the cerebellum supplies the limbs. Lesions here result in intention tremor, problems with rapid alternating movements (dysdiadochokinesia) and lcating objects in space (dysmetria), as well as hypotonia.

What is the important of the substantia pars compacta in movement modulated by the cerebellum?

Under normal circumstances, the signalling from teh cerebral cortex is going to activate the direct adn indirect basal ganglian pathways simultaneously resulting in a lack of no movement or discoordinated movement. To have functional movement behaivors, this is where we see the substania nigra pars compacta having functional effects by releasing dopamine into the striatum. THe dopamine will act on the D1 receptor neurons in the striatum and activate the direct pathway. That same dopamine is also going to act on the D2 receptor neurons and that is goign to inhibit the indirect pathway. And so with this modulation that comes from dopamine release through the axons projjectign through the substansia nigra, we're able to coordinate the signal for creating a movement by turning on the direct pathway and turning off the indirect pathway

Where is the flocculonodular lobe?

beneath the posterolateral fissure

deep excitatory loop

conssting of the mossy fibers which activate the deep cerebellar nuclei and ascend to the granule cell Note:: when both the parallel fibers and climbing fibers fire together, this is where we see motor learning occur

What is the folia of the cerebellum?

grey matter; this will be around the arbor vitae like leaves (folia)

cortical inhibitory loop

mossy fiber --> parallel fiber--> purkinje fiber which will send inhibitory signals to the deep cerebellar nuclei involved in fine tuning reflexes: instead of yelling at max volume when we try to speak, the purkinje fibers helps us fine tune the volume. In other words, the inhibitory loop modulates the excitation of the deep excitatory loop--this is where see most of the corection for our motor output as well as our cognitice processes occur

mossy fibers

the axons of the pontine nuclei, spinal cord, reticular nuclei, vestibular nuclei, and some og the somatosensory receptors are all of this type. They come into the cerebellar cortex and synapse onto granule cells in the granule cell layer. The granule cell then sends its axons to the molecular layer where they will bifurcate into parallel fibers. The parallel fibers will extend in two different directions through the cerebellar cortical areas. They end up synapsing on the dendrites of purkinje cells. These parallel fibers provide excitatory input to the purkinje cells which will then send inhibitory signals to the deep nuclei.

What is the arbor vitae?

white matter of the cerebellum; meaning the tree of life they look like tree branches , folia (like leaves) surrounds them