Phys-Chapter 56

What would lesions in the globus pallidus cause?

-spontaneous and often continuous writhing movements of a hand, an arm, the neck, or the face-movements called athetosis.

What would a lesion in the subthalamus cause?

-sudden flailing movements of an entire limb, a condition called hemiballismus.

How does GABA function?

-GABA always functions as an inhibitory agent. Therefore, GABA neurons in the feedback loops from the cortex through the basal ganglia and then back to the cortex make virtually all these loops negative feedback loops, rather than positive feedback loops, thus lending stability to the motor control systems.

Describe the timing function of the lateral zones of the cerebellar hemispheres

- Another important function of the lateral zones of the cerebellar hemispheres is to provide appropriate timing for each succeeding movement. -In the absence of these cerebellar zones, one loses the subconscious ability to predict how far the different parts of the body will move in a given time. -Without this timing capability, the person becomes unable to determine when the next sequential movement needs to begin. As a result, the succeeding movement may begin too early or, more likely, too late.

What happens to input signals that arrive in cerebellum?

- Each time an input signal arrives in the cerebellum, it divides and goes in two directions: (1) directly to one of the cerebellar deep nuclei and (2) to a corresponding area of the cerebellar cortex overlying the deep nucleus. -Then, a fraction of a second later, the cerebellar cortex relays an inhibitory output signal to the deep nucleus. -Thus, all input signals that enter the cerebellum eventually end in the deep nuclei in the form of initial excitatory signals followed a fraction of a second later by inhibitory signals. -From the deep nuclei, output signals leave the cerebellum and are distributed to other parts of the brain.

Describe the control of movement with reference to motor cortex

- The motor cortex system provides most of the activating motor signals to the spinal cord. It functions partly by issuing sequential and parallel commands that set into motion various cord patterns of motor action. It can also change the intensities of the different patterns or modify their timing or other characteristics. -When needed, the corticospinal system can bypass the cord patterns, replacing them with higher-level patterns from the brain stem or cerebral cortex. The cortical patterns are usually complex; also, they can be "learned," whereas cord patterns are mainly determined by heredity and are said to be "hard wired."

What is the typical function of the cerebellum?

- The typical function of the cerebellum is to help provide rapid turn-on signals for the agonist muscles and simultaneous reciprocal turn-off signals for the antagonist muscles at the onset of a movement. -Then on approaching termination of the movement, the cerebellum is mainly responsible for timing and executing the turn-off signals to the agonists and turn-on signals to the antagonists

One of the principal roles of the basal ganglia in motor control is to function in association with the corticospinal system to control complex patterns of motor activity. What are some everyday tasks that require the basal ganglia?

- An example is the writing of letters of the alphabet. When there is serious damage to the basal ganglia, the cortical system of motor control can no longer provide these patterns. Instead, one's writing becomes crude, as if one were learning for the first time how to write. -Other patterns that require the basal ganglia are cutting paper with scissors, hammering nails, shooting a basketball through a hoop, passing a football, throwing a baseball, the movements of shoveling dirt, most aspects of vocalization, controlled movements of the eyes, and virtually any other of our skilled movements, most of them performed subconsciously.

What lie beneath the cerebellar cortex layers?

- Beneath these cortical layers, in the center of the cerebellar mass, are the deep cerebellar nuclei that send output signals to other parts of the nervous system.

Describe dysmetria and ataxia

- In the absence of the cerebellum, the subconscious motor control system cannot predict how far movements will go. Therefore, the movements ordinarily overshoot their intended mark; then the conscious portion of the brain overcompensates in the opposite direction for the succeeding compensatory movement. -This effect is called dysmetria, and it results in uncoordinated movements that are called ataxia. Dysmetria and ataxia can also result from lesions in the spinocerebellar tracts because feedback information from the moving parts of the body to the cerebellum is essential for cerebellar timing of movement termination.

What is Huntington's characterized by?

- It is characterized at first by flicking movements in individual muscles and then progressive severe distortional movements of the entire body. In addition, severe dementia develops along with the motor dysfunctions.

Why is the mossy fiber input into the Purkinje cell different from climbing fiber input?

- because the synaptic connections are weak, so large numbers of mossy fibers must be stimulated simultaneously to excite the Purkinje cell. -Furthermore, activation usually takes the form of a much weaker short-duration Purkinje cell action potential called a simple spike, rather than the prolonged complex action potential caused by climbing fiber input.

How is it that the cerebellum can be so important when it has no direct ability to cause muscle contraction?

- it helps to sequence the motor activities and also monitors and makes corrective adjustments in the body's motor activities while they are being executed so that they will conform to the motor signals directed by the cerebral motor cortex and other parts of the brain.

Why is tremor of Parkinson's different from other cerebellar disease tremors?

- it occurs during all waking hours and therefore is an involuntary tremor, in contradistinction to cerebellar tremor, which occurs only when the person performs intentionally initiated movements and therefore is called intention tremor.

From a functional POV, how are the anterior and posterior lobes organized?

- the anterior and posterior lobes are organized not by lobes but along the longitudinal axis

What does the term cognition mean?

- the thinking processes of the brain, using both sensory input to the brain plus information already stored in memory

Where do signals go after passing from cerebral cortex to caudate nucleus?

- they are next transmitted to the internal globus pallidus, then to the relay nuclei of the ventroanterior and ventrolateral thalamus, and finally back to the prefrontal, premotor, and supplementary motor areas of the cerebral cortex, but with almost none of the returning signals passing directly to the primary motor cortex. -Instead, the returning signals go to those accessory motor regions in the premotor and supplementary motor areas that are concerned with putting together sequential patterns of movement lasting 5 or more seconds instead of exciting individual muscle movements. -A good example of this would be a person seeing a lion approach and then responding instantaneously and automatically by (1) turning away from the lion, (2) beginning to run, and (3) even attempting to climb a tree. Without the cognitive functions, the person might not have the instinctive knowledge, without thinking for too long a time, to respond quickly and appropriately. -Thus, cognitive control of motor activity determines subconsciously, and within seconds, which patterns of movement will be used together to achieve a complex goal that might itself last for many seconds.

What role does the vestibulocerebellum play in equilibrium that cannot be provided by other neuronal machinery of the brain stem?

-A clue is the fact that in people with vestibulocerebellar dysfunction, equilibrium is far more disturbed during performance of rapid motions than during stasis, especially when these movements involve changes in direction of movement and stimulate the semicircular ducts. -This suggests that the vestibulocerebellum is important in controlling balance between agonist and antagonist muscle contractions of the spine, hips, and shoulders during rapid changes in body positions as required by the vestibular apparatus.

All movements of body are pendular, hence they have a tendency to "overshoot," like the arm for example due to its momentum. Describe what happens when overshooting does occur in a person whose cerebellum has been destroyed. Also describe what would happen if the cerebellum is intact.

-If overshooting does occur in a person whose cerebellum has been destroyed, the conscious centers of the cerebrum eventually recognize this and initiate a movement in the reverse direction attempting to bring the arm to its intended position. -But the arm, by virtue of its momentum, overshoots once more in the opposite direction, and appropriate corrective signals must again be instituted. Thus, the arm oscillates back and forth past its intended point for several cycles before it finally fixes on its mark. This effect is called an action tremor, or intention tremor. - if the cerebellum is intact, appropriate learned, subconscious signals stop the movement precisely at the intended point, thereby preventing the overshoot and the tremor. -This is the basic characteristic of a damping system. All control systems regulating pendular elements that have inertia must have damping circuits built into the mechanisms. For motor control by the nervous system, the cerebellum provides most of this damping function.

Describe the efferent pathways of the cerebellum

-A pathway that originates in the midline structures of the cerebellum (the vermis) and then passes through the fastigial nuclei into the medullary and pontile regions of the brain stem. This circuit functions in close association with the equilibrium apparatus and brain stem vestibular nuclei to control equilibrium, as well as in association with the reticular formation of the brain stem to control the postural attitudes of the body. -A pathway that originates in (1) the intermediate zone of the cerebellar hemisphere and then passes through (2) the interposed nucleus to (3) the ventrolateral and ventroanterior nuclei of the thalamus and then to (4) the cerebral cortex, to (5) several midline structures of the thalamus and then to (6) the basal ganglia and (7) the red nucleus and reticular formation of the upper portion of the brain stem. This complex circuit helps to coordinate mainly the reciprocal contractions of agonist and antagonist muscles in the peripheral portions of the limbs, especially in the hands, fingers, and thumbs. -A pathway that begins in the cerebellar cortex of the lateral zone of the cerebellar hemisphere and then passes to the dentate nucleus, next to the ventrolateral and ventroanterior nuclei of the thalamus, and, finally, to the cerebral cortex. This pathway plays an important role in helping coordinate sequential motor activities initiated by the cerebral cortex.

Why does administering L-Dopa work in Parkinson's patients but not dopamine itself?

-Administration of dopamine itself does not have the same effect because dopamine has a chemical structure that will not allow it to pass through the blood-brain barrier, even though the slightly different structure of l-dopa does allow it to pass.

Describe treatment with L-Dopa in Parkinson's patients

-Administration of the drug l-dopa to patients with Parkinson's disease usually ameliorates many of the symptoms, especially the rigidity and akinesia. The reason for this is believed to be that l-dopa is converted in the brain into dopamine, and the dopamine then restores the normal balance between inhibition and excitation in the caudate nucleus and putamen

Describe the anatomy of the cerebellum

-Anatomically, the cerebellum is divided into three lobes by two deep fissures -the anterior lobe -the posterior lobe -the flocculonodular lobe.

What is dysarthria and how does it occur?

-Another example in which failure of progression occurs is in talking because the formation of words depends on rapid and orderly succession of individual muscle movements in the larynx, mouth, and respiratory system. -Lack of coordination among these and inability to adjust in advance either the intensity of sound or duration of each successive sound causes jumbled vocalization, with some syllables loud, some weak, some held for long intervals, some held for short intervals, and resultant speech that is often unintelligible. This is called dysarthria.

What is it that arouses us from inactivity and sets into play our trains of movement? In other words, what drives us to action?

-Basically, the brain has an older core located beneath, anterior, and lateral to the thalamus-including the hypothalamus, amygdala, hippocampus, septal region anterior to the hypothalamus and thalamus, and even old regions of the thalamus and cerebral cortex themselves-all of which function together to initiate most motor and other functional activities of the brain. -These areas are collectively called the limbic system of the brain

Describe treatment of Parkinson's by destroying part of feedback circuitry in basal ganglia

-Because abnormal signals from the basal ganglia to the motor cortex cause most of the abnormalities in Parkinson's disease, multiple attempts have been made to treat these patients by blocking these signals surgically. -For a number of years, surgical lesions were made in the ventrolateral and ventroanterior nuclei of the thalamus, which blocked part of the feedback circuit from the basal ganglia to the cortex; variable degrees of success were achieved, as well as sometimes serious neurological damage. -In monkeys with Parkinson's disease, lesions placed in the subthalamus have been used, sometimes with surprisingly good results

What is cerebellar nystagmus and how does it occur?

-Cerebellar nystagmus is tremor of the eyeballs that occurs usually when one attempts to fixate the eyes on a scene to one side of the head. -This off-center type of fixation results in rapid, tremulous movements of the eyes rather than steady fixation, and it is another manifestation of failure of damping by the cerebellum. -It occurs especially when the flocculonodular lobes of the cerebellum are damaged; in this instance it is also associated with loss of equilibrium because of dysfunction of the pathways through the flocculonodular cerebellum from the semicircular ducts.

What would destruct of small portions of lateral cerebellar cortex do?

-Destruction of small portions of the lateral cerebellar cortex seldom causes detectable abnormalities in motor function. -In fact, several months after as much as one half of the lateral cerebellar cortex on one side of the brain has been removed, if the deep cerebellar nuclei are not removed along with the cortex, the motor functions of the animal appear to be almost normal as long as the animal performs all movements slowly. -Thus, the remaining portions of the motor control system are capable of compensating tremendously for loss of parts of the cerebellum.

How does dopamine function?

-Dopamine also functions as an inhibitory neurotransmitter in most parts of the brain, so it also functions as a stabilizer under some conditions.

What starts on the turn-on/turn-off pattern of agonist/antagonist contraction at onset of movement?

-signals from cerebral cortex -these signals pass thru noncerebellar brain stem and cord pathways directly to agonist muscle to begin the initial contraction

Describe how excitation and inhibition of deep cerebellar nuclei occurs

-In execution of a rapid motor movement, the initiating signal from the cerebral motor cortex or brain stem at first greatly increases deep nuclear cell excitation. -Then, another few milliseconds later, feedback inhibitory signals from the Purkinje cell circuit arrive. -In this way, there is first a rapid excitatory signal sent by the deep nuclear cells into the motor output pathway to enhance the motor movement, but this is followed within another small fraction of a second by an inhibitory signal. -This inhibitory signal resembles a "delay-line" negative feedback signal of the type that is effective in providing damping. That is, when the motor system is excited, a negative feedback signal occurs after a short delay to stop the muscle movement from overshooting its mark. Otherwise, oscillation of the movement would occur.

Down the centre of the cerebellum, a narrow band called the vermis is separated from remainder of cerebellum by shallow grooves. What is the function of this area?

-In this area, most cerebellar control functions for muscle movements of the axial body, neck, shoulders, and hips are located.

How does hypotonia occur in reference to cerebellar issues?

-Loss of the deep cerebellar nuclei, particularly of the dentate and interposed nuclei, causes decreased tone of the peripheral body musculature on the side of the cerebellar lesion. -The hypotonia results from loss of cerebellar facilitation of the motor cortex and brain stem motor nuclei by tonic signals from the deep cerebellar nuclei.

What is cognitive control of motor activity?

-Most of our motor actions occur as a consequence of thoughts generated in the mind

What are ballistic movements?

-Most rapid movements of the body, such as the movements of the fingers in typing, occur so rapidly that it is not possible to receive feedback information either from the periphery to the cerebellum or from the cerebellum back to the motor cortex before the movements are over. -These movements are called ballistic movements, meaning that the entire movement is preplanned and set into motion to go a specific distance and then to stop. -Another important example is the saccadic movements of the eyes, in which the eyes jump from one position to the next when reading or when looking at successive points along a road as a person is moving in a car.

What is past pointing and how does it occur?

-Past pointing means that in the absence of the cerebellum, a person ordinarily moves the hand or some other moving part of the body considerably beyond the point of intention. -This results from the fact that normally the cerebellum initiates most of the motor signal that turns off a movement after it is begun; if the cerebellum is not available to do this, the movement ordinarily goes beyond the intended mark. Therefore, past pointing is actually a manifestation of dysmetria.

Describe the control of movement with reference to spinal level

-Programmed in the spinal cord are local patterns of movement for all muscle areas of the body-for instance, programmed withdrawal reflexes that pull any part of the body away from a source of pain. -The cord is the locus also of complex patterns of rhythmical motions such as to-and-fro movement of the limbs for walking, plus reciprocal motions on opposite sides of the body or of the hindlimbs versus the forelimbs in four-legged animals. -All these programs of the cord can be commanded into action by higher levels of motor control, or they can be inhibited while the higher levels take over control.

What causes the turn-off signal for agonist muscles at termination of movement?

-Remember that all mossy fibers have a second branch that transmits signals by way of the granule cells to the cerebellar cortex and eventually, by way of "parallel" fibers, to the Purkinje cells. -The Purkinje cells in turn inhibit the deep nuclear cells. This pathway passes through some of the smallest, slowest-conducting nerve fibers in the nervous system: that is, the parallel fibers of the cerebellar cortical molecular layer -Also, the signals from these fibers are weak, so they require a finite period of time to build up enough excitation in the dendrites of the Purkinje cell to excite it. -But once the Purkinje cell is excited, it in turn sends a strong inhibitory signal to the same deep nuclear cell that had originally turned on the movement. Therefore, this helps to turn off the movement after a short time.

What are the abnormal movements of Huntington's caused by?

-The abnormal movements of Huntington's disease are believed to be caused by loss of most of the cell bodies of the GABA-secreting neurons in the caudate nucleus and putamen and of acetylcholine-secreting neurons in many parts of the brain. -The axon terminals of the GABA neurons normally inhibit portions of the globus pallidus and substantia nigra. This loss of inhibition is believed to allow spontaneous outbursts of globus pallidus and substantia nigra activity that cause the distortional movements.

Where do the dorsal tracts enter cerebellum and where do they terminate? How about ventral tracts?

-The dorsal tract enters the cerebellum through the inferior cerebellar peduncle and terminates in the vermis and intermediate zones of the cerebellum on the same side as its origin. -The ventral tract enters the cerebellum through the superior cerebellar peduncle, but it terminates in both sides of the cerebellum.

Which is the oldest of all portions of the cerebellum?

-The flocculonodular lobe is the oldest of all portions of the cerebellum; it developed along with (and functions with) the vestibular system in controlling body equilibrium

Describe control of movement with respect to the basal ganglia

-The basal ganglia are essential to motor control in ways entirely different from those of the cerebellum. Their most important functions are (1) to help the cortex execute subconscious but learned patterns of movement and (2) to help plan multiple parallel and sequential patterns of movement that the mind must put together to accomplish a purposeful task. -The types of motor patterns that require the basal ganglia include those for writing all the different letters of the alphabet, for throwing a ball, and for typing. Also, the basal ganglia are required to modify these patterns for writing small or writing very large, thus controlling dimensions of the patterns. -At a still higher level of control is another combined cerebral and basal ganglia circuit, beginning in the thinking processes of the cerebrum to provide overall sequential steps of action for responding to each new situation, such as planning one's immediate motor response to an assailant who hits the person in the face or one's sequential response to an unexpectedly fond embrace.

What is the function of the basal ganglia?

-The basal ganglia help to plan and control complex patterns of muscle movement, controlling relative intensities of the separate movements, directions of movements, and sequencing of multiple successive and parallel movements for achieving specific complicated motor goals

How is the cerebellum similar to the basal ganglia?

-The basal ganglia, like the cerebellum, constitute another accessory motor system that functions usually not by itself but in close association with the cerebral cortex and corticospinal motor control system.

How does the cerebellum aid the cerebral cortex?

-The cerebellum aids the cerebral cortex in planning the next sequential movement a fraction of a second in advance while the current movement is still being executed, thus helping the person to progress smoothly from one movement to the next. -Also, it learns by its mistakes-that is, if a movement does not occur exactly as intended, the cerebellar circuit learns to make a stronger or weaker movement the next time.

Describe control of movement with reference to cerebellum

-The cerebellum functions with all levels of muscle control. It functions with the spinal cord especially to enhance the stretch reflex, so when a contracting muscle encounters an unexpectedly heavy load, a long stretch reflex signal transmitted all the way through the cerebellum and back again to the cord strongly enhances the load-resisting effect of the basic stretch reflex. -At the brain stem level, the cerebellum functions to make the postural movements of the body, especially the rapid movements required by the equilibrium system, smooth and continuous and without abnormal oscillations. -At the cerebral cortex level, the cerebellum operates in association with the cortex to provide many accessory motor functions, especially to provide extra motor force for turning on muscle contraction rapidly at the start of a movement. Near the end of each movement, the cerebellum turns on antagonist muscles at exactly the right time and with proper force to stop the movement at the intended point. Furthermore, there is good physiologic evidence that all aspects of this turn-on/turn-off patterning by the cerebellum can be learned with experience. -The cerebellum functions with the cerebral cortex at still another level of motor control: it helps to program in advance muscle contractions that are required for smooth progression from a present rapid movement in one direction to the next rapid movement in another direction, all this occurring in a fraction of a second. The neural circuit for this passes from the cerebral cortex to the large lateral zones of the cerebellar hemispheres and then back to the cerebral cortex. -The cerebellum functions mainly when muscle movements have to be rapid. Without the cerebellum, slow and calculated movements can still occur, but it is difficult for the corticospinal system to achieve rapid and changing intended movements to execute a particular goal or especially to progress smoothly from one rapid movement to the next.

During which activities is the cerebellum especially vital?

-The cerebellum is especially vital during rapid muscular activities such as running, typing, playing the piano, and even talking. -Loss of this area of the brain can cause almost total incoordination of these activities even though its loss causes paralysis of no muscles.

What is the function of the cerebellum?

-The cerebellum plays major roles in the timing of motor activities and in rapid, smooth progression from one muscle movement to the next. -It also helps to control the intensity of muscle contraction when the muscle load changes and controls the necessary instantaneous interplay between agonist and antagonist muscle groups.

Where does the cerebellum continuously receive info from?

-The cerebellum receives continuously updated information about the desired sequence of muscle contractions from the brain motor control areas; it also receives continuous sensory information from the peripheral parts of the body, giving sequential changes in the status of each part of the body-its position, rate of movement, forces acting on it, and so forth.

What does the cerebellum do with the info it receives?

-The cerebellum then compares the actual movements as depicted by the peripheral sensory feedback information with the movements intended by the motor system. -If the two do not compare favorably, then instantaneous subconscious corrective signals are transmitted back into the motor system to increase or decrease the levels of activation of specific muscles.

Besides timing movements of body, what else can the cerebrocerebellum (lateral lobes) do?

-The cerebrocerebellum (the large lateral lobes) also helps to "time" events other than movements of the body. For instance, the rates of progression of both auditory and visual phenomena can be predicted by the brain, but both of these require cerebellar participation. -As an example, a person can predict from the changing visual scene how rapidly he or she is approaching an object. -A striking experiment that demonstrates the importance of the cerebellum in this ability is the effects of removing the large lateral portions of the cerebellum in monkeys. Such a monkey occasionally charges the wall of a corridor and literally bashes its brains because it is unable to predict when it will reach the wall. - It is quite possible that the cerebellum provides a "time-base," perhaps using time-delay circuits, against which signals from other parts of the central nervous system can be compared; it is often stated that the cerebellum is particularly helpful in interpreting rapidly changing spatiotemporal relations in sensory information.

Describe the climbing fiber type

-The climbing fibers all originate from the inferior olives of the medulla. There is one climbing fiber for about 5 to 10 Purkinje cells. -After sending branches to several deep nuclear cells, the climbing fiber continues all the way to the outer layers of the cerebellar cortex, where it makes about 300 synapses with the soma and dendrites of each Purkinje cell. -This climbing fiber is distinguished by the fact that a single impulse in it will always cause a single, prolonged (up to 1 second), peculiar type of action potential in each Purkinje cell with which it connects, beginning with a strong spike and followed by a trail of weakening secondary spikes. This action potential is called the complex spike.

What does the dementia of Huntington's result from?

-The dementia in Huntington's disease probably does not result from the loss of GABA neurons but from the loss of acetylcholine-secreting neurons, perhaps especially in the thinking areas of the cerebral cortex.

Describe the control of movement with reference to hindbrain

-The hindbrain provides two major functions for general motor control of the body: (1) maintenance of axial tone of the body for the purpose of standing and (2) continuous modification of the degrees of tone in the different muscles in response to information from the vestibular apparatuses for the purpose of maintaining body equilibrium.

What's the function of the intermediate zone of the cerebellar hemisphere?

-The intermediate zone of the hemisphere is concerned with controlling muscle contractions in the distal portions of the upper and lower limbs, especially the hands and fingers and feet and toes.

What's the function of the lateral zone of the cerebellar hemisphere?

-The lateral zone of the hemisphere operates at a much more remote level because this area joins with the cerebral cortex in the overall planning of sequential motor movements. -Without this lateral zone, most discrete motor activities of the body lose their appropriate timing and sequencing and therefore become incoordinate

Describe the mossy fiber type

-The mossy fibers are all the other fibers that enter the cerebellum from multiple sources: from the higher brain, brain stem, and spinal cord. -These fibers also send collaterals to excite the deep nuclear cells. Then they proceed to the granule cell layer of the cortex, where they, too, synapse with hundreds to thousands of granule cells. -granule cells send extremely small axons up to the molecular layer on the outer surface of the cerebellar cortex. Here the axons divide into two branches that extend in each direction parallel to the folia -there are many of the parallel nerve fibers because there are many granule cells per Purkinje cell. It's into this molecular layer that dendrites of Purkinje cells project and the many parallel fibers synapse with each Purkinje cell

What 3 things happen to the ballistic movements when cerebellum is removed?

-The movements are slow to develop and do not have the extra onset surge that the cerebellum usually provides - the force developed is weak -the movements are slow to turn off, usually allowing the movement to go well beyond the intended mark. -Therefore, in the absence of the cerebellar circuit, the motor cortex has to think extra hard to turn ballistic movements on and again has to think hard and take extra time to turn the movement off. Thus, the automatism of ballistic movements is lost

Describe the planning of sequential movements by lateral zones

-The planning of sequential movements requires that the lateral zones of the hemispheres communicate with both the premotor and the sensory portions of the cerebral cortex, and it requires two-way communication between these cerebral cortex areas with corresponding areas of the basal ganglia. -It seems that the "plan" of sequential movements actually begins in the sensory and premotor areas of the cerebral cortex, and from there the plan is transmitted to the lateral zones of the cerebellar hemispheres. Then, amid much two-way traffic between cerebellum and cerebral cortex, appropriate motor signals provide transition from one sequence of movements to the next. -An interesting observation that supports this view is that many neurons in the cerebellar dentate nuclei display the activity pattern for the sequential movement that is yet to come while the present movement is still occurring. -Thus, the lateral cerebellar zones appear to be involved not with what movement is happening at a given moment but with what will be happening during the next sequential movement a fraction of a second or perhaps even seconds later. -To summarize, one of the most important features of normal motor function is one's ability to progress smoothly from one movement to the next in orderly succession. In the absence of the large lateral zones of the cerebellar hemispheres, this capability is seriously disturbed for rapid movements.

Describe the signals transmitted in the dorsal spinocerebellar tract

-The signals transmitted in the dorsal spinocerebellar tracts come mainly from the muscle spindles and to a lesser extent from other somatic receptors throughout the body, such as Golgi tendon organs, large tactile receptors of the skin, and joint receptors. -All these signals apprise the cerebellum of the momentary status of (1) muscle contraction, (2) degree of tension on the muscle tendons, (3) positions and rates of movement of the parts of the body, and (4) forces acting on the surfaces of the body.

Describe how the ventral spinocerebellar tracts work

-The ventral spinocerebellar tracts receive much less information from the peripheral receptors. Instead, they are excited mainly by motor signals arriving in the anterior horns of the spinal cord from (1) the brain through the corticospinal and rubrospinal tracts and (2) the internal motor pattern generators in the cord itself. -Thus, this ventral fiber pathway tells the cerebellum which motor signals have arrived at the anterior horns; this feedback is called the efference copy of the anterior horn motor drive.

The nervous system uses the cerebellum to coordinate motor control functions at three levels. What are they?

-The vestibulocerebellum. This consists principally of the small flocculonodular cerebellar lobes that lie under the posterior cerebellum and adjacent portions of the vermis. It provides neural circuits for most of the body's equilibrium movements. -The spinocerebellum. This consists of most of the vermis of the posterior and anterior cerebellum plus the adjacent intermediate zones on both sides of the vermis. It provides the circuitry for coordinating mainly movements of the distal portions of the limbs, especially the hands and fingers. -The cerebrocerebellum. This consists of the large lateral zones of the cerebellar hemispheres, lateral to the intermediate zones. It receives virtually all its input from the cerebral motor cortex and adjacent premotor and somatosensory cortices of the cerebrum. It transmits its output information in the upward direction back to the brain, functioning in a feedback manner with the cerebral cortical sensorimotor system to plan sequential voluntary body and limb movements, planning these as much as tenths of a second in advance of the actual movements. This is called development of "motor imagery" of movements to be performed.

Describe the basket cells and stellate cells of the cerebellum

-These are inhibitory cells with short axons. Both the basket cells and the stellate cells are located in the molecular layer of the cerebellar cortex, lying among and stimulated by the small parallel fibers. -These cells in turn send their axons at right angles across the parallel fibers and cause lateral inhibition of adjacent Purkinje cells, thus sharpening the signal in the same manner that lateral inhibition sharpens contrast of signals in many other neuronal circuits of the nervous system.

Where are basal ganglia located?

-They are located mainly lateral to and surrounding the thalamus, occupying a large portion of the interior regions of both cerebral hemispheres

Describe the principal pathways through the basal ganglia for executing learned patterns of movement

-They begin mainly in the premotor and supplementary areas of the motor cortex and in the somatosensory areas of the sensory cortex. Next they pass to the putamen (mainly bypassing the caudate nucleus), then to the internal portion of the globus pallidus, next to the ventroanterior and ventrolateral relay nuclei of the thalamus, and finally return to the cerebral primary motor cortex and to portions of the premotor and supplementary cerebral areas closely associated with the primary motor cortex.

Where do the excitatory and inhibitory influences to the deep nuclear cell in the functional unit come from?

-This cell is continually under both excitatory and inhibitory influences. -The excitatory influences arise from direct connections with afferent fibers that enter the cerebellum from the brain or the periphery. -The inhibitory influence arises entirely from the Purkinje cell in the cortex of the cerebellum.

Describe treatment of Parkinson's using L-Deprenyl

-This drug inhibits monoamine oxidase, which is responsible for destruction of most of the dopamine after it has been secreted. Therefore, any dopamine that is released remains in the basal ganglial tissues for a longer time. -In addition, for reasons not understood, this treatment helps to slow destruction of the dopamine-secreting neurons in the substantia nigra. -Therefore, appropriate combinations of l-dopa therapy along with l-deprenyl therapy usually provide much better treatment than use of one of these drugs alone.

In human beings, the lateral zones of the two cerebellar hemispheres are highly developed and greatly enlarged. Why is this significant?

-This goes along with human abilities to plan and perform intricate sequential patterns of movement, especially with the hands and fingers, and to speak.

Where do the inputs to the putamen circuit come from? Also describe its outputs

-Thus, the putamen circuit has its inputs mainly from those parts of the brain adjacent to the primary motor cortex but not much from the primary motor cortex itself. -Then its outputs do go mainly back to the primary motor cortex or closely associated premotor and supplementary cortex.

Describe treatment of Parkinson's using transplanted fetal dopamine cells

-Transplantation of dopamine-secreting cells (cells obtained from the brains of aborted fetuses) into the caudate nuclei and putamen has been used with some short-term success to treat Parkinson's disease. However, the cells do not live for more than a few months.

What are 2 important capabilities of the brain in controlling movement?

-Two important capabilities of the brain in controlling movement are (1) to determine how rapidly the movement is to be performed and (2) to control how large the movement will be. -For instance, a person may write the letter "a" slowly or rapidly. Also, he or she may write a small "a" on a piece of paper or a large "a" on a chalkboard. Regardless of the choice, the proportional characteristics of the letter remain nearly the same. -these timing and scaling functions are poor in patients with severe lesions of the basal ganglia (sometimes nonexistent)

What is intention/action tremor and how does it occur?

-When a person who has lost the cerebellum performs a voluntary act, the movements tend to oscillate, especially when they approach the intended mark, first overshooting the mark and then vibrating back and forth several times before settling on the mark. -This reaction is called an intention tremor or an action tremor, and it results from cerebellar overshooting and failure of the cerebellar system to "damp" the motor movements.

What is dysdiadochokinesia and how does it occur?

-When the motor control system fails to predict where the different parts of the body will be at a given time, it "loses" perception of the parts during rapid motor movements. -As a result, the succeeding movement may begin much too early or much too late, so no orderly "progression of movement" can occur. One can demonstrate this readily by having a patient with cerebellar damage turn one hand upward and downward at a rapid rate. -The patient rapidly "loses" all perception of the instantaneous position of the hand during any portion of the movement. As a result, a series of stalled attempted but jumbled movements occurs instead of the normal coordinate upward and downward motions. This is called dysdiadochokinesia.

Describe the internal capsule of the brain

-almost all motor and sensory nerve fibers connecting the cerebral cortex and spinal cord pass through the space that lies between the major masses of the basal ganglia, the caudate nucleus and the putamen. This space is called the internal capsule of the brain.

When does the vestibulocerebellum originate phylogenetically in reference to vestibular apparatus in inner ear?

-both of them originate at same time

What happens after destruction of lateral zones of cerebellar hemispheres along with their deep nuclei (dentate nuclei)?

-can lead to extreme incoordination of complex purposeful movements of the hands, fingers, and feet and of the speech apparatus.

What nucleus plays a major role in the cognitive control of motor activity?

-caudate nucleus

What do the basal ganglia consist of?

-caudate nucleus -putamen -globus pallidus -substantia nigra -subthalamic nucleus

What would removal of the cerebellum do?

-causes body movements to become highly abnormal

How does the cerebellum learn by its mistakes?

-changes occur in the excitability of appropriate cerebellar neurons, thus bringing subsequent muscle contractions into better correspondence with the intended movements.

What are the types of afferent inputs to the cerebellum?

-climbing fiber type -mossy fiber type

What would lesions in lateral zones of cerebellum cause?

-complex movements (such as those required for writing, running, or even talking) to become incoordinate and lacking ability to progress in orderly sequence from one movement to the next. Such cerebellar lesions are said to cause failure of smooth progression of movements.

Where are the deep cerebellar nuclei?

-deep beneath the folded mass of cerebellar cortex

Where does the output from the cerebellar functional unit come from?

-deep nuclear cell

What are the 3 deep cerebellar nuclei?

-dentate -interposed -fastigial -The vestibular nuclei in the medulla also function in some respects as if they were deep cerebellar nuclei because of their direct connections with the cortex of the flocculonodular lobe.

Describe balance b/w excitation and inhibition at the deep cerebellar nuclei

-direct stimulation of the deep nuclear cells by both the climbing and the mossy fibers excites them. -By contrast, signals arriving from the Purkinje cells inhibit them. -Normally, the balance between these two effects is slightly in favor of excitation so that under quiet conditions, output from the deep nuclear cell remains relatively constant at a moderate level of continuous stimulation.

What neurotransmitters are known to function within the basal ganglia?

-dopamine pathways from the substantia nigra to the caudate nucleus and putamen - gamma-aminobutyric acid (GABA) pathways from the caudate nucleus and putamen to the globus pallidus and substantia nigra -acetylcholine pathways from the cortex to the caudate nucleus and putamen, -multiple general pathways from the brain stem that secrete norepinephrine, serotonin, enkephalin, and several other neurotransmitters in the basal ganglia, as well as in other parts of the cerebrum. -In addition to all these are multiple glutamate pathways that provide most of the excitatory signals that balance out the large numbers of inhibitory signals transmitted especially by the dopamine, GABA, and serotonin inhibitory transmitters

The cerebellum also receives important sensory signals directly from the peripheral parts of the body mainly through four tracts on each side, two of which are located dorsally in the cord and two ventrally. What are the 2 important ones?

-dorsal spinocerebellar tract -ventral spinocerebellar tract

Why is the cerebellum called "the silent area of the brain?"

-electrical excitation of the cerebellum does not cause any conscious sensation and rarely causes any motor movement.

What does loss of flocculonodular lobes and adjacent portions of vermis of cerebellum (which constitute the vestibulocerebellum) cause?

-extreme disturbance of equilibrium and postural movements

What would lesions of the substantia nigra cause?

-extremely severe disease of rigidity, akinesia, and tremors known as Parkinson's disease

What would multiple small lesions in the putamen lead to?

-flicking movements in the hands, face, and other parts of the body, called chorea.

What is a "folium?"

-fold of cerebellum

Where do basal ganglia receive input from and where does the output from them go?

-from the cerebral cortex itself and also return almost all their output signals back to the cortex.

How does Parkinson's disease (paralysis agitans) result?

-from widespread destruction of that portion of the substantia nigra (the pars compacta) that sends dopamine-secreting nerve fibers to the caudate nucleus and putamen

What are the functional units of the cerebellum made of?

-functional unit centers on a single, very large Purkinje cell and on a corresponding deep nuclear cell.

Describe causes of Parkinson's in relation to dopamine

-he dopamine secreted in the caudate nucleus and putamen is an inhibitory transmitter; therefore, destruction of the dopaminergic neurons in the substantia nigra of the parkinsonian patient theoretically would allow the caudate nucleus and putamen to become overly active and possibly cause continuous output of excitatory signals to the corticospinal motor control system. These signals could overly excite many or all of the muscles of the body, thus leading to rigidity. -Some of the feedback circuits might easily oscillate because of high feedback gains after loss of their inhibition, leading to the tremor of Parkinson's disease.

What is Huntington's disease (Huntington's chorea)?

-hereditary disorder that usually begins causing symptoms at age 30 to 40 years

The intermediate zone of each cerebellar hemisphere receives 2 types of info when movement performed. What are they?

-information from the cerebral motor cortex and from the midbrain red nucleus, telling the cerebellum the intended sequential plan of movement for the next few fractions of a second -feedback information from the peripheral parts of the body, especially from the distal proprioceptors of the limbs, telling the cerebellum what actual movements result

Describe the abnormal gene that causes Huntington's

-it has a many-times-repeating codon, CAG, that codes for multiple extra glutamine amino acids in the molecular structure of an abnormal neuronal cell protein called huntington that causes the symptoms.

What are the 3 major layers of the cerebellar cortex?

-molecular layer -Purkinje cell layer -granule cell layer

Describe the afferent tracts that originate in each side of the brain stem

-olivocerebellar tract, which passes from the inferior olive to all parts of the cerebellum and is excited in the olive by fibers from the cerebral motor cortex, basal ganglia, widespread areas of the reticular formation, and spinal cord -vestibulocerebellar fibers, some of which originate in the vestibular apparatus itself and others from the brain stem vestibular nuclei-almost all of these terminate in the flocculonodular lobe and fastigial nucleus of the cerebellum - reticulocerebellar fibers, which originate in different portions of the brain stem reticular formation and terminate in the midline cerebellar areas (mainly in the vermis).

What causes the reduction of the psychic drive for motor activity that can cause akinesia in Parkinson's?

-opamine secretion in the limbic system, especially in the nucleus accumbens, is often decreased along with its decrease in the basal ganglia.

Describe the corticopontocerebellar pathway

-originates in the cerebral motor and premotor cortices and also in the cerebral somatosensory cortex. -It passes by way of the pontile nuclei and pontocerebellar tracts mainly to the lateral divisions of the cerebellar hemispheres on the opposite side of the brain from the cerebral areas. -it's an afferent pathway

Describe the turning-on of output signals from cerebellum

-parallel signals are sent by way of the pontile mossy fibers into the cerebellum. -One branch of each mossy fiber goes directly to deep nuclear cells in the dentate or other deep cerebellar nuclei; this instantly sends an excitatory signal back into the cerebral corticospinal motor system, either by way of return signals through the thalamus to the cerebral cortex or by way of neuronal circuitry in the brain stem, to support the muscle contraction signal that had already been begun by the cerebral cortex. -As a consequence, the turn-on signal becomes even more powerful than it was at the start because it becomes the sum of both the cortical and the cerebellar signals. This is the normal effect when the cerebellum is intact, but in the absence of the cerebellum, the secondary extra supportive signal is missing. -This cerebellar support makes the turn-on muscle contraction much stronger than it would be if the cerebellum did not exist.

What is personal neglect syndrome?

-person with right posterior parietal cortex lesion will always try to avoid using his or her left arm, left hand, or other portions of his or her left body for the performance of tasks, or even wash this side of the body almost not knowing that these parts of his or her body exist.

What indirect aspects of motor control are the lateral zones concerned with?

-planning of sequential movements -timing of sequential movements

What is an important cortical area which is the locus of the spatial coordinates for motor control of all parts of the body. as well as the relation of the body and its parts to all its surroundings? What would lesions of this area cause?

-posterior parietal cortex -Damage to this area does not produce simple deficits of sensory perception, such as loss of tactile sensation, blindness, or deafness. Instead, lesions of the posterior parietal cortex produce an inability to accurately perceive objects through normally functioning sensory mechanisms, a condition called agnosia

The large lateral zones of the cerebellar hemispheres have no direct input of info from peripheral body and the communication b/w the lateral zones and cerebral cortex is not with primary cerebral motor cortex. What do the lateral zones communicate with?

-premotor area -primary and association somatosensory areas

What are the 2 major circuits of the basal ganglia?

-putamen circuit -caudate circuit

What is Parkinson's characterized by?

-rigidity of much of the musculature of the body -involuntary tremor of the involved areas even when the person is resting at a fixed rate of three to six cycles per second -serious difficulty in initiating movement, called akinesia -postural instability caused by impaired postural reflexes, leading to poor balance and falls -other motor symptoms including dysphagia (impaired ability to swallow), speech disorders, gait disturbances, and fatigue.

When learning new motor act, cerebellum's timing of helping with the act are incorrect for precise performance of movement, but it eventually adjusts and learns how to do it. How do these adjustments occur?

-sensitivity levels of cerebellar circuits themselves progressively adapt during the training process, especially the sensitivity of the Purkinje cells to respond to the granule cell excitation. Furthermore, this sensitivity change is brought about by signals from the climbing fibers entering the cerebellum from the inferior olivary complex. -Under resting conditions, the climbing fibers fire about once per second. But they cause extreme depolarization of the entire dendritic tree of the Purkinje cell, lasting for up to a second, each time they fire. -During this time, the Purkinje cell fires with one initial strong output spike followed by a series of diminishing spikes. -When a person performs a new movement for the first time, feedback signals from the muscle and joint proprioceptors will usually denote to the cerebellum how much the actual movement fails to match the intended movement. And the climbing fiber signals in some way alter long-term sensitivity of the Purkinje cells. -Over a period of time, this change in sensitivity, along with other possible "learning" functions of the cerebellum, is believed to make the timing and other aspects of cerebellar control of movements approach perfection. When this has been achieved, the climbing fibers no longer need to send "error" signals to the cerebellum to cause further change.

Besides the spinocerebellar tracts, where else does the cerebellum get signals from?

-signals are transmitted into the cerebellum from the body periphery through the spinal dorsal columns to the dorsal column nuclei of the medulla and then relayed to the cerebellum. -Likewise, signals are transmitted up the spinal cord through the spinoreticular pathway to the reticular formation of the brain stem and also through the spino-olivary pathway to the inferior olivary nucleus. Then signals are relayed from both of these areas to the cerebellum. -Thus, the cerebellum continually collects information about the movements and positions of all parts of the body even though it is operating at a subconscious level.

What is one of the major problems in controlling balance?

-the amount of time required to transmit position signals and velocity of movement signals from the different parts of the body to the brain. -Even when the most rapidly conducting sensory pathways are used (spinocerebellar afferent tracts), there is still some delay. The feet of a person has moved some distance during that time. -Therefore, it is never possible for return signals from the peripheral parts of the body to reach the brain at the same time that the movements actually occur.

Why are the neural connections b/w the caudate nucleus and the corticospinal motor control system different from the putamen circuit?

-the caudate nucleus extends into all lobes of the cerebrum, beginning anteriorly in the frontal lobes, then passing posteriorly through the parietal and occipital lobes, and finally curving forward again like the letter "C" into the temporal lobes. -Furthermore, the caudate nucleus receives large amounts of its input from the association areas of the cerebral cortex overlying the caudate nucleus, mainly areas that also integrate the different types of sensory and motor information into usable thought patterns.

Where do the deep cerebellar nuclei receive signals from?

-the cerebellar cortex -the deep sensory afferent tracts to the cerebellum.

What must occur for serious and continuing dysfunction of the cerebellum to happen?

-the cerebellar lesion usually must involve one or more of the deep cerebellar nuclei-the dentate, interposed, or fastigial nuclei.

What happens after the intermediate zone of the cerebellum has compared the intended movements with the actual movements?

-the deep nuclear cells of the interposed nucleus send corrective output signals (1) back to the cerebral motor cortex through relay nuclei in the thalamus and (2) to the magnocellular portion (the lower portion) of the red nucleus that gives rise to the rubrospinal tract. -The rubrospinal tract in turn joins the corticospinal tract in innervating the lateral most motor neurons in the anterior horns of the spinal cord gray matter, the neurons that control the distal parts of the limbs, particularly the hands and fingers.

Which portions of the cerebellar hemispheres don't have topographical representations of the body?

-the large lateral portions of the cerebellar hemispheres do not have topographical representations of the body. -These areas of the cerebellum receive their input signals almost exclusively from the cerebral cortex, especially from the premotor areas of the frontal cortex and from the somatosensory and other sensory association areas of the parietal cortex. -It is believed that this connectivity with the cerebral cortex allows the lateral portions of the cerebellar hemispheres to play important roles in planning and coordinating the body's rapid sequential muscular activities that occur one after another within fractions of a second.

How is it possible for the brain to know when to stop a movement and perform the next sequential act when the movements are performed rapidly?

-the signals from the periphery tell the brain how rapidly and in which directions the body parts are moving. -It is then the function of the vestibulocerebellum to calculate in advance from these rates and directions where the different parts will be during the next few milliseconds. The results of these calculations are the key to the brain's progression to the next sequential movement. -Thus, during control of equilibrium, it is presumed that information from both the body periphery and the vestibular apparatus is used in a typical feedback control circuit to provide anticipatory correction of postural motor signals necessary for maintaining equilibrium even during extremely rapid motion, including rapidly changing directions of motion.

What is a similarity b/w Purkinje cells and deep nuclear cells?

-they both fire continuously -the output activity of both these cells can be modulated up or down