Cerebellum and Its Connections

Cerebellum and Its Connections

CHAPTER OBJECTIVES

To review the structure and functions of the cerebellum

A fifty-six-year-old woman is examined by a neurologist for a variety of complaints, including an irregular swaying gait and a tendency to drift to the right when walking. Her family recently noticed that she has difficulty in keeping her balance when standing still, and she finds that standing with her feet apart helps her keep her balance.

On examination, she has diminished tone of the muscles of her right upper limb, as seen when the elbow and wrist joints are passively flexed and extended. Similar evidence is found in the right lower limb. When asked to stretch out her arms in front of her and hold them in position, she demonstrates obvious signs of right-sided tremor. When asked to touch the tip of her nose with the left index finger, she performs the movement without any difficulty, but when she repeats the movement with her right index finger, she either misses her nose or hits it due to the irregularly contracting muscles. When she is asked to quickly pronate and supinate the forearms, the movements are normal on the left side but jerky and slow on the right side. A mild papilledema of both eyes is found. No other abnormal signs are seen.

The right-sided hypotonia, static tremor, and intention tremor associated with voluntary movements, right-sided

GROSS APPEARANCE

The cerebellum is situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli. It is the largest part of the hindbrain and lies posterior to the fourth ventricle, the pons, and the medulla oblongata. The cerebellum is somewhat ovoid in shape and constricted in its median part. It consists of two cerebellar hemispheres joined by a narrow median vermis. The cerebellum is connected to the posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the superior, middle, and inferior cerebellar peduncles.

To describe the afferent and efferent connections of the cerebellum within the central nervous system dysdiadochokinesia, and the history are characteristic of right-sided cerebellar disease. A computed tomography scan reveals a tumor in the right cerebellar hemisphere.

Understanding the structure and the nervous connections of the cerebellum and, in particular, knowing that the right cerebellar hemisphere influences voluntary muscle tone on the same side of the body enable the neurologist to make an accurate diagnosis and institute treatment.

The cerebellum plays a very important role in the control of posture and voluntary movements. It unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions, together with the relaxation of their antagonists. Students should commit the functions of the connections of the cerebellum to the remainder of the central nervous system to memory, as this will greatly assist in the retention of the material. In this chapter, great emphasis is placed on the fact that each cerebellar hemisphere controls muscular movements on the same side of the body and that the cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem.

The cerebellum is divided into three main lobes: the anterior lobe, the middle lobe, and the flocculonodular lobe. The anterior lobe may be seen on the superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure. The middle lobe, sometimes called the posterior lobe, which is the largest part of the cerebellum, is situated between the primary and uvulonodular fissures. The flocculonodular lobe is situated posterior to the uvulonodular fissure. A deep horizontal fissure that is found along the margin of the cerebellum separates the superior from the inferior surfaces but has no morphologic or functional significance.