The Hypothalamus

A crucial part of the CNS that takes some part in regulating most organs

• 3 major functions (we will review 2 today).

1.Regulating release of hormones from pituitary gland.

2.Regulating the ANS; i.e., general visceral motor functions we reviewed last time.

3.Regulating the “appetitive behaviours” (eating, drinking, mating).

I. The 3 functional zones of the hypothalamus and the nuclei contained therein.

II. Regulation of Pituitary: Parvocellular (anterior) ad magnocellular (posterior) neurosecretory systems.

III. Overview of ANS functional anatomy (sympathetic, parasympathetic systems).

IV. Regulation of autonomic functions by descending projections from the hypothalamus.

V. 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. 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.

B. Middle zone- regulates hormone release from posterior pituitary.

- regulates ANS.

C. 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

A. 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: Parvocellularneurosecretorycells anterior lobevia portal vein.Chemicals releasedare peptides, whicheither promote orinhibit the release ofhormones fromanterior lobe secretory cells(Table 15-1).

B. 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 paraventricularand supraoptic nuclei

Hormones:Vasopressin (ADH) – peptide which incr bp by itseffects on vascularsmooth muscle as well as by promoting H2O reabsorptionfrom DCTs of kidneys todecr urine vol.Oxytocin – incr uterine contraction and milk ejectionfrom 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 pathwayscontrolling autonomicnervous system (Fig. 15-9):From middle functionalZone: parasympatheticn. (using ADH and oxytocin)+ several other areas bsparasym n. (dorsal motor n.of X) + preganglionic neurons(both sym and parasym) of sc.

Fig. 15-8.Note: Mechanism of regulationIs very analogous to the way theCortex regulates descending Motor pathways and motor Neurons.1 Difference: Visceromotor Regulation involves the 2-neuronCircuit (pre- and postganglionic)Some bs n. also contribute to autonomic system regulation:-Solitary n intermediolateral n.(also known for chemosensorymechs) - 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

A. 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. 15-10Note the preoptic region

Paraventricular Nucleus – Fig. 15-11This nucleus contributes to all 3 functions we have discussed:1. Parvocellular division anterior pituitary2. Magnocellular division posterior pituitary3. Autonomic division descending paths

Posterior HypothalamusFig. 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 SectionB. Descending Pathways and Spinal Cord Nuclei

Descending fibresIn dorsolateraltegmentum.DLF also containsascending and descending fibresto hypothalamus.Adrenergic cell groupin VL medulla – analogous to intermedio-lateral location in sc.

1. Intermediolateral sympathetic (preganglionic) nucleus in thoracic sc.

2. 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.