Chapter 15 Chemical Control of the Brain and Behavior

Introduction (a) Synaptic Connections –Point-to-point is the most common form Restricts synaptic communication Brain areas with expanded influence over space and time Secretory hypothalamus with its multiple targets Autonomic nervous system (ANS) networks Diffuse modulatory systems However, in (b), (c), & (d) we have several exceptions:

Ernst & Berta Scharrer – proposed that magnocellular neurosceretory neurons released chemicals into the capilary bed of the posterior lobe.

The CNS has three basic neural outputs… one somatic motor, and two that are from the ANS… sympathetic and parasympathetic.

The Enteric Division (“little brain”) of the ANS is found in a variety of locations within the digestive system. This is called the “little brain” because it has sensory nerves, interneurons, and autonomic motor neurons. The enteric division of the ANS consists of TWO different networks: Myenteric (Auerbach’s) Plexus – Submucous (Meissner’s) Plexus -

Homeostasis of a variety of regulatory processes: Regulates body temperature and blood composition Hypothalamus commands in cold weather –Shiver, goosebumps, turn blue Hypothalamus commands in hot weather –Turn red, sweat The Secretory Hypothalamus

Structure of the Hypothalamus

Pathways to the Pituitary use two neurohormones –Oxytocin Lactation, suppress hypothalamic function –Vasopressin (ADH) Regulate blood volume and salt concentration The Secretory Hypothalamus

Communication between kidneys and brain: The Secretory Hypothalamus With the release of ADH, the kidney will be stimulated to release RENIN. Renin (angiotensinogenase) - an enzyme that participates in the body's renin- angiotensin system (RAS) mediating extracellular volume and arterial vasoconstriction. It regulates the body's mean arterial blood pressure. Angiotensinogen, Angiotensin I & II are then released via the liver to stimulate the subfornical organ (on the fornix) to stimulate the hypothalamus which in turn stimulates via the hypothalamic hypophyseal tract, the posterior pituitary gland to produce ADH. High ADH is associated with thirst.

Hypothalamic Control of the Anterior Pituitary –Controlled by parvocellular neurosecretory cells Secrete hypophysiotropic hormones (many kinds, GHRN, GnRH as two examples Hypophyseal Portal circulation serves as the way the hypothalamus and anterior pituitary communicate –Pituitary cells secrete or stop secreting hormones The Secretory Hypothalamus

Stress Response –Periventricular hypothalamus secretes CRH into portal circulation –ACTH released into circulation –ACTH stimulates cortisol release from adrenal cortex. The Secretory Hypothalamus

Divisions of autonomic nervous system (ANS) –Sympathetic division Increased heart rate and blood pressure Depressed digestive function Mobilized glucose reserves –Parasympathetic division Slower heart rate, fall in pressure Increased digestive functions Stop sweating The Autonomic Nervous System

ANS Circuits versus Somatic Motor System The Autonomic Nervous System

The subdivisions here show how the individual with spinal cord injury may maintain function via parasympathetic control.