11 - D. Brain stem and cranial nerves

D. Brain stem and cranial nerves

© SPMM Course Hypothalamus  The hypothalamus regulates physiological functions such as eating, drinking, sleeping, and temperature regulation.  The hypothalamus has chemoreceptors that respond to variations in glucose levels, osmolarity, acid balance, etc. It also plays a major role in neuroendocrine control.  The ventromedial hypothalamus acts as the satiety centre while the lateral hypothalamus is the feeding centre. In animals with a lesion of ventromedial hypothalamus hyperphagia and obesity are noted. C. Cerebellum The cerebellum has the important role of preparing a motor plan and predicting balance needed between muscle groups to carry out the intended action smoothly. Cerebellar lesions produce ataxia and coarse intentional tremors, along with hypotonia, past pointing and pendular knee jerk.

Increasingly the role of the cerebellum in cognitive processes has been appreciated. The term cognitive dysmetria (Andreasen) refers to the difficulty in coordinating and monitoring the process of receiving, processing, and expressing information that could result from disrupted cortico-cerebellar circuitry in schizophrenia.

D. Brain stem and cranial nerves The brain stem is made of the midbrain, pons and the medulla. Most of the cranial nerves (9 out of 12) enter or exit the brain from the brainstem.

The midbrain consists of superior (conjugate gaze control) and inferior colliculi (auditory source localization). The substantia nigra is also located in the midbrain along with periaqueductal grey matter that plays an important role in vocalization and freezing response to threat and in pain suppression. Pons is positioned beneath the cerebellum and surrounds the upper half of the 4th ventricle Medulla surrounds inferior part of the 4th ventricle and is continuous with the spinal cord. No. Name Anatomical features I Olfactory Runs on the basal surface of frontal cortex without passing through the thalamus. Formed as an outgrowth of forebrain II Optic Also an outgrowth of the forebrain. Relays via thalamus (geniculate body) III Oculomotor Purely motor function. Supplies four of the six ocular muscles IV Trochlear Purely motor function. Supplies superior oblique (ocular muscle) V Trigeminal Both sensory and motor. Transmits facial sensation and controls jaw muscles VI Abducens Purely motor function. Supplies lateral abducens (ocular muscle) INFERIOR OLIVARY NUCLEUS Inferior olivary nucleus is located in the brainstem and aids in motor coordination by projecting climbing fibers to the contralateral cerebellar cortex via inferior cerebellar peduncle. Inferior olivary lesions lead to appendicular ataxia due to motor incoordination of the contralateral arm and leg. Patients with inferior olivary lesions will fail the finger-nose test, mimicking cerebellar lesion. But unlike cerebellar lesions that result in ipsilateral motor incoordination, the contralateral side is affected in olivary lesions.