Transcript Topic 16
Biology 463 - Neurobiology Topic 16 Chemical Control of the Brain and Behavior Lange Introduction (a) Synaptic Connections – Point-to-point is the most common form • Restricts synaptic communication However, in (b), (c), & (d) we have several exceptions: Brain areas with expanded influence over space and time • (b) Secretory hypothalamus with its multiple targets • Autonomic nervous system (ANS) networks • Diffuse modulatory systems 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. Notice how this covers all muscle types. The Enteric Division of the ANS is found in a variety of locations within the digestive system. Enteric ANS 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 - Interestingly, the two plexi will control the two muscle layers for peristalic movement through the digestive system. The Secretory Hypothalamus • Homeostasis of a variety of regulatory processes: Regulates body temperature and blood composition • Hypothalamus commands in cold weather – Shivering & goosebumps (blue appearance) • Hypothalamus commands in hot weather – (Red appearance), sweating 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: With the release of ADH, the kidney will be stimulated to release RENIN. Renin (angiotensinogenase) - an enzyme that participates in the body's reninangiotensin 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. The Secretory Hypothalamus Hypothalamic Control of the Anterior Pituitary – Controlled by parvocellular neurosecretory cells • Secrete hypophysiotropic hormones (many kinds, GHRN, GnRH as two examples • Hypophyseal Portal Systemic 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. Cortisol Releasing Hormone (CRH) The Autonomic Nervous System Divisions of autonomic nervous system (ANS) – Sympathetic division • Increased heart rate and blood pressure • Depressed digestive function • Mobilized glucose & glycogen reserves – Parasympathetic division • Slower heart rate, fall in pressure • Increased digestive functions • Slowing of 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. END.