Neuropsychology

Autonomic Nervous System
Sympathetic
Parasympathetic
Enteric System

Pituitary Control
Hypothalamic Nuclei & Hormones
Regulation of Drives (Hunger, Thirst)
Brainstem Regulation Areas

The Hypothalamus

The Hypothalamus comprises the most ventral part of the diencephalon, lying lateral to the walls of the third ventricle. It is very old phylogenetically and exerts an influence over almost every aspect of the body's functions. This prominence in body regulation is why it has been referred to as the head ganglion of the autonomic and endocrine system. Examples of its influence include the control of respiratory, cardiovascular and body temperature, feeding and drinking, sexual behavior, and emotional responses such as drive, motivation and emotion. The major mechanism by which the hypothalamus works to achieve such control is to directly produce, or stimulate the pituitary to produce, hormones that circulate in the bloodstream. These homones selectively control a number of autonomic functions, including general growth, lactation and uterine contractions during birth.

The Paraventricular and supraoptic nuclei transmit two hormones to the posterior section of the pituitary gland, oxytocin and antidiuretic hormone. Oxytocin controls uterine contraction and antidiuretic hormone controls water excretion by the kidneys.

The Dorsomedial Nucleus is a less distinct aggregate of cells whose function is not clear. It is believed that it plays a role in the "hunger-satiety/feeding" role of the ventromedial hypothalamic nucleus and lateral hypothalamic area. It may also play a role in the neuroendocrine system and insulin secretion.

The Anterior Hypothalamic Nucleus produces parasympathetic responses such as reduced heart rate and enhanced activity of the gastrointestinal tract when stimulated.

The Preoptic nucleus plays a role in regulating sex hormones, which in turn regulate reproductive cycles, such as the menstrual cycle in females. Cells in the preoptic area also aid in the control of heart rate, blood pressure and body temperature.

The Suprachiasmatic nucleus receives direct input from the retina and is instrumental in maintaining circadian (day-night) rhythms.

The Anterior Pituitary secretes growth hormone, thyrotropin, corticotrophin, follicle stimulating hormone, luteinizing hormone, and prolactin.

The Posterior Hypothalamic Nucleus produces sympathetic responses when stimulated, such as increasing heart rate and inhibiting gastrointestinal activity.

The Ventromedial hypothalamic (VMH) nucleus plays a role in agonistic and feeding behavior. Lesions here produce hyperphagia and obesity. The Lateral hypothalamic area (LHA), which is not depicted in this image but lies to one side of these nuclei, mediates the stimulation of appetite so that lesions here produce aphagia or starvation. The control of hunger motivation therefore represents a balance of influence from these two centers, the VMH being designated as the "satiety center" and the LHA as the "feeding center". The VMH has also been demonstrated to play some role in aggression. When this area is released from cortical control, "sham rage" is produced which is characterized by extreme savage behavior.

The Mammillary body is considered part of the hypothalamus and limbic system. It interacts with brain stem nuclei utilizing the mammillo-tegmental tract. The fornix represents its connections with the hippocampus. The mammillothalamic tract represents a prominent connection with the thalamus.

The Arcuate nucleus, also known as the infundibular nucleus, consists of a group of cells which are in close contact with the wall of the third ventricle. Their role is uncertain, but may have something to do with hormonal secretion.

The Infundibulum, also known as the pituitary stalk, is the connection between the hypothalamic nuclei and the pituitary.

The Posterior Pituitary contains vasopressin and oxytocin secreted by cells of the supraoptic and paraventricular nuclei of the hypothalamus.