The Hypothalamus

A crucial part of the CNS that takes some part in regulating most organs 3 major functions (we will review 2 today). Regulating release of hormones from pituitary gland. Regulating the ANS; i.e., general visceral motor functions we reviewed last time. Regulating the “appetitive behaviours” (eating, drinking, mating).

A. Anterior-posterior sections of hypothalamus and review key nuclei. The 3 functional zones of the hypothalamus and the nuclei contained therein. Regulation of Pituitary: Parvocellular (anterior) ad magnocellular (posterior) neurosecretory systems. Overview of ANS functional anatomy (sympathetic, parasympathetic systems). Regulation of autonomic functions by descending projections from the hypothalamus. Regional anatomy. A. Anterior-posterior sections of hypothalamus and review key nuclei. B. Descending pathway and sc nuclei. C. Clinical Note: Horner’s Syndrome.

I. 3 Functional Zones General location of hypothalamus: - ventral to thalamus - just over optic chiasm and pituitary stalk (infundibulum). - divided in half by 3rd ventricle

Hypothalamic Nuclei

Hypothalamus (Fig. 15-1, 2)

- a thin nuclei bordering the 3rd ventricle. Periventricular zone - a thin nuclei bordering the 3rd ventricle. - regulates release of endocrine hormones from anterior pituitary gland (See Table 15-1). -uses neurosecretion as a portal vein system, rather than a neurotransmitter across a synapse. Middle zone - regulates hormone release from posterior pituitary. - regulates ANS. Lateral zone - integration and transmission of info from limbic system structures (important in emotional regulation – will view next lecture (limbic system).

3 Functional hypothalamic zones (Fig. 15-14) – Mediolateral zones

Hypothalamic peptides for anterior pituitary (Table 15-1)

II. Regulation of Pituitary: Parvocellular and Magnocellular Neurosecretory Systems Parvocellular system and the anterior pit. - Small-diameter neurons in several hypothalamic nuclei (of periventricular zone) – most medial – regulate anterior pituitary hormone release by neurovascular rather than synaptic transmission.

Parvocellular System (Fig. 15-4A) Note the various nuclei

Neurosecretion and Portal Vein System (Fig. 15-5): Note the path: Parvocellular neurosecretory cells  anterior lobe via portal vein. Chemicals released are peptides, which either promote or inhibit the release of hormones from anterior lobe secretory cells (Table 15-1).

Magnocellular system and the posterior pituitary. - Here, peptide hormones are produced by large-diameter hypothalamic neurons from same nuclei of the middle zone. - Axons deliver these hormones down the infundibular stalk and terminate on fenestral capillaries (“leaky”) of the posterior pit - this is 1 place lacking a BBB.

Magnocellular System (Fig. 15-4B) Note the paraventricular and supraoptic nuclei Hormones: Vasopressin (ADH) – peptide which incr bp by its effects on vascular smooth muscle as well as by promoting H2O reabsorption from DCTs of kidneys to decr urine vol. Oxytocin – incr uterine contraction and milk ejection from mammary glands.

III. Overview of Autonomic Nervous System Sympathetic and Parasympathetic systems – Fig. 15-7. Clearly distinct anatomical locations of preganglionic (central) neurons. Sympathetic: T1  L3 Parasympathetic: brainstem nuclei (reviewed last time): S2  S4 (sacral spinal cord). Also different locations of post-ganglionic neurons.

Fig. 15-7 – The ANS

Sympathetic: peripheral ganglia located relatively close to the spinal cord (sympathetic trunk). Parasympathetic: peripheral ganglia located close to target organs (i.e., terminal ganglia of X). Note: organs distal to splenic flexure of colon served by sacral parasympathetic nuclei. For both systems, anatomical location of central neurons is analogous.

Sympathetic: intermediate zone of spinal cord (intermediolateral cell column) – Fig. 15-9. Parasympathetic: the 4 spinal cord nuclei reviewed last time (general visceral motor column): III, VII, IX, X and in sacral sc intermediate zone.

IV. Descending Projections from the Hypothalamus Regulate Autonomic Functions See Fig. 15-9

Descending pathways controlling autonomic nervous system (Fig. 15-9): From middle functional Zone: parasympathetic n. (using ADH and oxytocin) + several other areas  bs parasym n. (dorsal motor n. of X) + preganglionic neurons (both sym and parasym) of sc.

Fig. 15-8. Note: Mechanism of regulation Is very analogous to the way the Cortex regulates descending Motor pathways and motor Neurons. 1 Difference: Visceromotor Regulation involves the 2-neuron Circuit (pre- and postganglionic) Some bs n. also contribute to autonomic system regulation: Solitary n  intermediolateral n. (also known for chemosensory mechs) - a tie between viscero- sensory and visceromotor.

Ventral lateral medulla - adrenergic descending projections regulating bp. Postmedullary reticular formation - complex “reflex” response involving both visceral and somatic changes; e.g., startle  incr bp. Raphe nuclei – projections from hypothalamus uses serotonin to  spinal autonomous nuclei.

V. Regional Anatomy Sections through the hypothalamus – Schematic of major nuclei – Fig. 15-3. Anterior hypothalamic section, showing preoptic region – Fig. 15-10.

Fig. 15-3 – Major nuclei

Anterior hypothalamus – Fig. 15-10 Note the preoptic region

Paraventricular Nucleus – Fig. 15-11 This nucleus contributes to all 3 functions we have discussed: 1. Parvocellular division  anterior pituitary 2. Magnocellular division  posterior pituitary 3. Autonomic division  descending paths

Posterior Hypothalamus Fig. 15-17. Section reveals mammillary bodies. These, along with Lateral zone noted earlier, play important role in behavioural Regulation and the limbic system.

Mid-medullary Section B. Descending Pathways and Spinal Cord Nuclei Mid-medullary Section Descending fibres In dorsolateral tegmentum. DLF also contains ascending and descending fibres to hypothalamus. Adrenergic cell group in VL medulla – analogous to intermedio- lateral location in sc.

Intermediolateral sympathetic (preganglionic) nucleus in thoracic sc. Parasympathetic preganglionic nucleus in intermediate zone of sacral sc.

Spinal cord nuclei and paths: Fig. 15-21

C. Clinical Note: Horner’s Syndrome – damage to dorsaolateral pons/medulla or any part of descending autonomic control system  disturbance of sympathetic functions: e.g., PICA occlusion. Pupillary constriction on same side. Partial drooping of eyelid. Decr secretory, incr warmth and redness on same side of face. Decr sympathetic function and unopposed parasympathetic function.