MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF THE SELF-REGULATION OF BODY FUNCTIONS

THE BRAIN

6. DIENCEPHALON

6.2. PHYSIOLOGY OF THE Diencephalon

The thalamus contains about 40 nuclei, which are clusters of neuronal Cell bodies. From a functional perspective, they are divided into specific and nonspecific nuclei.

Specific nuclei are sensory in nature. They receive sensory input from receptors via ascending sensory pathways and process it before it reaches the Cerebral Cortex. The only sensory tract that passes "in transit" through the thalamus to the cortex is the olfactory pathway. The thalamus is often figuratively described as the Relay station for sensory information.

The nonspecific nuclei of the thalamus are part of the reticular formation. They give rise to ascending pathways that fan out and terminate on Neurons across various Regions of the cortex, increasing their excitability. Damage to the nonspecific thalamic nuclei leads to impaired consciousness.

In the metathalamus, a group of specific nuclei forms the medial and lateral geniculate bodies. Neurons of the medial geniculate body receive and process auditory information from the auditory nuclei of the Medulla Oblongata and Midbrain, serving as the subcortical auditory center. The lateral geniculate bodies act as the subcortical visual centers.

The Hypothalamus consists of clusters of nuclei that function as the highest subcortical autonomic centers, regulating the Functions of all Internal Organs and maintaining the constancy of the body's internal environment.

In experimental settings, stimulation of the posterior hypothalamic nuclei produces effects characteristic of sympathetic Nervous system activation: ARTERIAL Blood PRESSURE rises, Heart rate and contractility increase, breathing becomes more frequent, pulmonary ventilation increases due to bronchodilation; gastrointestinal motility, secretion, and absorption are inhibited; blood glucose levels rise; and METABOLISM and Energy production increase.

Conversely, stimulation of the anterior hypothalamic nuclei produces opposite effects characteristic of the Parasympathetic division of the Autonomic Nervous System.

The middle region of the hypothalamus contains chemosensitive neurons that detect changes in osmotic pressure, glucose concentration, and the Temperature of the blood and the CEREBROSPINAL FLUID of the Third ventricle. They effectively "monitor" the state of the body's internal environment, allowing the hypothalamus to regulate internal Homeostasis.

The hypothalamus regulates all Types of Metabolism, body temperature, endocrine gland functions, and The activity of all major systems—cardiovascular, respiratory, digestive, and urogenital.

The hypothalamus houses centers associated with behavioral reactions, including sexual and defensive behaviors.

The hypothalamus regulates emotional behavior and contains centers for satiety, hunger, and thirst. It plays a role in the Sleep-wake cycle and is directly linked to the Endocrine System. Neurosecretory neurons in the posterior hypothalamus produce Hormones such as antidiuretic hormone, which regulates Water-salt balance, and oxytocin, which regulates uterine contractions and Mammary Gland Function. The anterior hypothalamus produces precursor hormones for the anterior Pituitary Gland.