What are the functional differences between the cerebrocerebellum, vestibulocerebellum and spin cerebellum?

Answer:

Vestibulocerebellum is the part of cerebellum which is also known as the floculonodular lobe of the cerebellum. Arch cerebellum is another name given to it. Its main role is to receive inputs from both the vestibular nerves. Moreover, it receives information from both of the semicircular canals.  Vestibular nuclei, vestibular nerves and semicircular canals are involved in maintaining the balance and equilibrium of the body. Information received is then sent back to medial and lateral vestibular nerve. In addition to this, this part of cerebellum also receives visual information from the superior follicular. Cerebro-ponto-cerebello pathway is a visual pathway related to vestibulocerebrum.

This is the only portion of cerebellum which receives sensory input from nerves. Additionally, purkinje cells of the cerebellum leave it to go deeper in the cerebellum and reach the deep cerebella nuclei directly. They synapse in the dorsolateral brain stem in the vestibular nuclear complex. (Benagiano, Rizzi, & Lorusso, 2018)

Vertigo and Nystagmus are two conditions which occur when and if the vestibulocerebellum is damaged. An amazing function of vestibulocerebellum is to compensate the damage occurring to it by adapting to the damage. To elaborate, if inner ear is damaged but vestibulocerebellum is intact, damage will be compensated with time. However, if vestibulocerebellum is damaged itself, compensation will not occur.

Vestbulo-ocular reflex is used to check for the cerebellar plasticity. This reflex is an indication or measure of the adaptation to the vestibular damage by checking for the eyes stabilization during movements.

Spin cerebellum also known as pale cerebellum consist of the vermis and paarvermis of cerebellum. It is involved in regulating the movements of the body and limbs. In addition to regulating the tone of muscles it is also helpful in adapting the body to the changing patterns.

Spin cerebellum is involved in maintain the position of body as it contains sensory maps of all parts of the body. Fibres from proximal portions of limbs and trunk go to vermis, whereas para vermis receives information from distal parts of the limbs. Feed forward is a term associated with the cerebellum because it can predict the position of the body in future by its proprioreceptive input.

Input of Spinocerebellar is from the dorsal column of spinal cord, trigeminal nerve, auditory system, visual system and Spinocerebellar tract. Output goes to fastigial nuclei and other deep cerebella nuclei. From here, fibres are sent to both of the cerebral hemisphere and brain step. Fibres to brainstem project via reticular formation and vestibular nuclei in the pons and medulla oblongata respectively. Fibres to cerebrum cortex project via thalamus as well as midbrain.In this way modulation to the motor systems is provided. (Bickel, Gregory, & Dean, 2011)

Cerebrocerebellum located in the lateral parts of the cerebral hemispheres is also known as neocerebellum and pontocerbellum.

Cerebral cortex sends information to the pontine nuclei via corticopontine fibres which then goes to cerebellum through the middle cerebllar peduncles .Here the axons terminate giving small branches in the form of mossy fibres. Neocerellum csonsisiting of te lateral cerebllar hemisphere receives its biggest input in this form through the cerebrum. In addition, it is connected to the dentate nuclei through purkinje cell axons and then information goes to thalamus and afterwards relays in the cerebrum.

Therefore, neocerebrum is involved in the regulation of motor information which comes from cerebrum.Its also involved in evaluation of sensory information and plans movements. It plans movements forehand and prepares body for it. Purely cognitive functions also are regulated by neocerebellum. In addition, “procedural learning” also comes under the territory of neocerebellum. Bike riding, skiing, driving all such activities are learnt due to cerebellum. Intention tremor is a disease in which limb movements do not coordinate because all movements either undershoot or overshoot. This happens when lateral hemisphere of cerebellum is damaged. (Boland, Lin, & Engel, 2011)

What is  the  largest  source  of  input  to  the  cerebellum? 

Answer:

Largest source of input to the cerebellum is the cerebral cortex. Ans largest part of cerebellum is cerebrocerebellum which receives most of the information coming from cerebral cortex. Pathways coming to cerebellum from cerebrum arise from the frontal lobe, anterior parietal lobe and posterior lobe. Visual pathways origante from association areas of the cerebrum , and project to cerebellum. Before reaching the cerebellum all the pathways originating from cerebrum and destined from cerebellum relay in the pontine nuclei.

Crebrocerebllum is involved in the speech, cognitive functions and all the very skilled movements.Its also involved in the learning of movements like skiing.

What  does  cerebellar  ataxia  reveal  about  normal  functioning  of  the  cerebellum? 

Answer:

Ataxia means the uncontrolled body movements which manifest in the form of incoordinations of movements of limbs and unsteadiness of gait and posture. Ataxia can lead to problematic speech, uncontrolled force and range of movements, disordered rhythm and rate of movements and problem with starting and ending a movement. (D.Schmahmann, 2018)

Cerebellum is involved in maintaining the posture of body and regulating the body movements.If ataxia occurs due to the cerebellar involvement it is known as cerebllar ataxia. Cerellar ataxia is best described by lack of coordination of muscles and unsteady movements caused by the cerebellar atrophy or cerebellar disease.

Cerebellar ataxia is mere a symptom and not a condition itself.Its an ataxia caused by the cerebellar damage which can be casued by several reasons like geneteic factors, alcoholism,infection,hypothyroidism,head trauma,cerebral palsy and can be idiopathic.Cerebellum ataxia is an indication of the abnormal functioning of the cerebellum.

Spinal Cord

1.Diagram the myotatic (knee-jerk) spinal reflex, showing the afferent and efferent neurons and the interneuron (local  circuit  neuron).

2. .Compare  the  uncrossed  ventral  corticospinal  tract  with  the  crossed  lateral corticospinal  tract  with  regard  to  origin,  location,  and  function.  Where are  the gracile  and  cuneate  nuclei? 

Answer:

Crossed lateral corticospinal tract: 

Lateral corticospinal tracts are the largest part of the corticospinal tracts. Origin, location and function of these tracts is given below: 

Origin: These tracts consist of descending motor pathways which originate from the cerebral cortex carrying motor signals from the brain cortex to the target organ or muscle through the spinal cord. (Matthews, 2000)

Location: These tracts descend upto the pyramids of lower medulla (medulla oblongata) on the same side where they decussate to the opposite side of the spinal cord. This point is also known as cervicomedullary junction. These fibres then extend throughout the spinal cord on the contralateral side. On a transverse section of spinal cord, they appear as an oval area medial to the posterior spinocerebellar tract and anterior to the posterior column. 

Function: Function of the crossed lateral corticospinal tracts is the ipsilateral control of fine movement of limbs.

Uncrossed ventral corticospinal tracts:  10 percent of the fibres travelling in corticopinal tract are the ventral or anterior corticospinal tracts. There origin, location and function is explained below: 

Origin: Fibers of the ventral corticospinal tracts are originated from the cerebral cortex carrying motor fibers to their target location. (Miall, 2016)

Location: Ventral corticospinal tract fibres do not decussate at the level of pyramids and travel on the ipsilateral side. They are present only in the upper part of spinal cord lying near to the anterior median fissure.

Function: Function of anterior corticospinal tract is to control proximal muscles, like the muscles of the trunk

Gracile nucleus is a dorsal column nuclei located in the medulla oblongata. It is involved in the prioporeception and sensations of fine touch of the lower part of the body. It gives rise to gracile tubercle on medulla.

Cuneate nucleus is also a dorsal column nucleus of medulla oblongata. It gives rise to cuneate tubercle lateral to the gracile tubercle.Its also involved in the sensations of touch and propioreception but of the upper part of the body (Moskowitz & Schroeppel1, 2010)

3. Due to a spinal injury, a patient lost pain and temperature sensation on the left half of his body, from the waist down. Where was his injury? Where would you expect loss of tactile sensation in this patient?

Answer: -

The condition explained in the question is known as Brown-Sequard Syndrome. It is a rare syndrome resulting from an incomplete spinal cord injury. In this type of injury, only one side of spinal cord is damaged most commonly in the cervical region, but it may occur anywhere throughout the length of the spinal cord.

In this syndrome, sensations of pain and temperature are lost on the opposite side of the body below the level of the injury, and sensation of touch also known as tactile sensation is lost on the same side of the body below the level of lesion. 

In the given question, as pain and temperature sensations are lost below the level of waist on the left half of the body, so the waist line is the level of spinal injury with the right portion of the spinal cord being affected at this level. It can also be said as right hemisection injury of spinal cord at level of waist line. (P.Selvaduraia, H.Hardinga, & A.Corbe, 2018)

In addition to this, tactile sensation will be lost on the right side of the body of this person below the waist as tactile sensations are lost on the ipsilateral side of the body below the level of injury.

4. Define the motor unit. What is spinal shock? 

Answer:

Motor unit: A motor unit consists of a number of functionally alike muscle fibers which are innervated by a single somatic nerve. The numbers of muscle fibers in a motor unit vary greatly. Number of muscle fibers can be very fine and small or can be huge.

Once the axons of an efferent (motor) neuron enter the muscle they divide into small branches and all these branches of axon supply various muscle fibers in a muscle unit. However, there is no overlap in the supply of the muscle fibers. Each motor unit is supplied by an individual nerve. Each muscle in the body is supplied by a large number of efferent neurons. Similarly, each efferent neuron can supply a large number of muscle fibers in a motor unit.

Spinal shock: Spinal shock occurs right after a spinal injury and is characterized by the autonomic dysfunction and the loss of reflexes completely or partially. Loss of reflexes occur below the level of injury Autonomic dysfunction occurs in the form of hypotension and bradycardia. Spinal shock is a reversible condition in most of cases and reflexes come back after sometime. Spinal shock occurs due to the partial and often complete transaction of the spinal cord. Spinal cord has four phases based on the severity and reversibility or permanency of the shock. (Prsa & Thier, 2016)

References of Neurobiology

Benagiano, V., Rizzi, A., & Lorusso, L. (2018). The functional anatomy of the cerebrocerebellar circuit: A review and new concepts. journal of comparative neurology , 769-789.

Bickel, C. S., Gregory, C. M., & Dean, J. C. (2011). Exercise Physiology > Fundamentals of Exercise Physiology > Neural Control of Movement . Euorpean journal of applied physiology , 10.

Boland, R. A., Lin, C. S.-Y., & Engel, S. (2011). Adaptation of motor function after spinal cord injury: novel insights into spinal shock. BRIAN , 495-505.

D.Schmahmann, J. (2018). The cerebellum and cognition. Neuroscience letters , 5.

Matthews, P. B. (2000). The human stretch reflex and the motor cortex. new trends in neurobiology , 87-91.

Miall, R. C. (2016). Cerebellum: Anatomy and Function. neuroscience in 21st century , 1277-1295.

Moskowitz, E., & Schroeppel1, T. (2010). Brown-Sequard syndrome . BMJ journals , 1.

P.Selvaduraia, L., H.Hardinga, I., & A.Corbe, L. (2018). Cerebral abnormalities in Friedreich ataxia: A review. Neuroscience and Behavioral revies , 349-406.

Prsa, M., & Thier, P. (2016). Cerebellum: Eye Movements. Neuroscience in 21st century , 1297-1314.