Hypothalamus+and+Pituitary

=**Hypothalamus and Pituitary**=


 * 1. Understand the locations and precise boundaries of the hypothalamus.**

__Superior Boundary__ is the hypothalamic sulcus, a groove in the wall of the 3rd ventricle separating the hypothalamus from the thalamus. The __Anterior Boundary__ is the Lamina Terminalis which is the terminal end of the developing neurotube. The __Inferior border__ lies around the Optic chiasm / Infundbibulum / Median eminence / mammillary bodies. The __Posterior border__ is an imaginary line to pineal body from mammillary bodies.


 * 2. In general terms, learn the names and general positions (zones) of the hypothalamus and know their associated functions.**

__Periventricular zone:__ adjacent to ventricle on either side, with neuroendocrine nuclei influiencing the pituitary gland __Medial zone:__ boundary goes through fornix (which is a path to mammillary bodies from hippocampus) receiving inputs regarding the limbic system, hippocampus, amygdale, related to emotion. __Lateral zone:__ Influences autonomic nervous system


 * 3. Have an understanding of the main afferent and efferent connections of the hypothalamus.**

__Retino-hypothalamic tract__is a one way tract, light comes in from retina and signals the superchiasmatic nucleus. __Fornix__ is primarily unidirectional from hippocampus to the mammillary nuclei. __Stria terminalis__ carries information from the amygdale, monitoring emotions. __Corticohypothalamic tract__bidirectionally connects cingulate cortex and frontal cortex __Median Forebrain Bundle__ bidirectionally connects: amygdale, olfaction from olfactory organs, and reticular formation. __Diffuse pathway from Brainstem__ from spinal cord to brainstem to midbrain to hypothalamus.
 * Afferents:**

__Dorsal-longitudinal fasciculus of Schutz__ ending on brainstem / spinal cord nuclei and is the return pathway from diffuse ascending afferents from the hypothalamus providing control for autonomics. __Hypothalamo-spinal pathway__ is another means of communication with spinal cord bypassing the midbrain __Mammillothalamic tract__ forms part of the limbic loop going to anterior thalamic nucleus as part of the limbic system.
 * Efferents**


 * 4. Learn the details of the hypothalamohypophyseal tract and the pituitary portal system.**

The __Hypothalamo-hypophyseal tract__forms a direct link between hypothalamus and posterior pituitary creating a neurosecritiory system. It consists of magnacellular neurons originating from the Paraventricular Nucleus and Supra-optic Nucleus. This system secrets Vasopressin (ADH) and Oxytocin (smooth muscle contraction).

The __ Pituitary portal system__ uses primary capillary bed in median eminence then heads down through pituitary stalk into anterior pituitary where it breaks up into second capillary bed (made up of sinusoids). This system uses several nuclei: Infundibular nucleus, Periventricular nuclei, Tuberal nuclei, and others. Nuclei gather axons as tubero-infundibular tract reach first capillary bed, release neuropeptides (releasing hormones) into circulation of capillary plexus, the releasing hormones travel to second capillary bed where they influence cells of anterior pituitary and stimulate either release or inhibition of another set of pituitary hormones into systemic circulation to target organ


 * 5. Review the hypothalamic-anterior pituitary-target as a reference for understanding feedback loops.**

The Anterior pituitary releases a releasing hormone (Gonadotrophic releasing hormone) into 1st capillary bed, anterior pituitary responds positively by releasing hormone (FSH and LH) to target organs (ovary) releases product (estrogen). The signal to the hypothalamus to regulate its influence on the pituitary must integrate information from three feedback loops:

__Short loop feedback:__ Anterior pituitary hormone influence on the hypothalamus such as FSH and LH

__Long loop feedback:__ Hypothalamus influenced by target hormone such as ovary’s product inhibiting hypothalamus

__Ultra-Short loop feedback:__ hypothalamus influences itself (by releasing hormone neuropeptide)


 * 6. Understand the mechanisms for hypothalamic action (be able to site examples).**

Hypothalamic control of all mechanisms is reflexive in nature receiving input from two sources: neuronal input- comes via numerous circuits, or hormonal input – involved in feedback loops. The response to this input can be either: Neuronal response- seen in its influence on behaviors and the autonomic nervous system, or Hormonal response- seen in release of anterior / posterior pituitary hormones.

__Temperature Regulation__ information comes from skin (e.g. “too hot”) and from temperature sensitive receptors in the brain that determine temperature of the blood. The sensory neurons ascend up the spinal cord and give off collaterals to reticular formation- is ventral to 4th ventricle. Information ascends from reticular formation to the anterior hypothalamus where it will send descending information to spinal cord ends in brainstem and spinal cord autonomic nuclei inducing sweating and other regulatory functions. “Too cold” will cause posterior hypothalamic nucleus (heat conservation) to send similar descending information to autonomic nuclei to regulate temperature and sends information to ventral horn in spinal cord to induce shivering. It can also use hormonal pathway: use anterior pituitary to increase the activity of the thyroid gland pathway to raise basal metabolic rate.

__Baroreceptor reflex__reacts to changes in blood pressure are determined in carotid sinus with afferents go through CN IX to the Nucleus Tractus Solitarius (NTS). The NTS sends interneuron within brainstem over to Motor Nucleus of CN X which uses vagus nerve to influence the heart rate. NTS also sends another set of neurons ascending to the hypothalamus ending in the paraventricular nucleus which sends descending information to influence the brainstem / spinal cord nuclei changing heart rate as well.

__Reproductive Activity Regulation__ influences the menstrual cycle through hormonal pathway (releasing hormones - anterior pituitary – ovary - feedback). Mating behavior is regulated in pre-optic nucleus and dorsomedial nucleus have neurons sensitive to hormone levels (females to estrogen, males to testosterone) and the hormone is thus part of the stimulus trigger. As levels elevate the hypothalamus sends descending signal to end on motor neurons of spinal cord causing female rats to “present” in a state of lordosis. Control of lactation depends on sensory stimulus from nipple afferents ascend to end in brainstem reticular formation which sends neurons that end in superoptic / paraventricular nucleus. The 	superoptic axons go to posterior pituitary and induces the release of oxytocin into circulation whichstimulates SMC in the breast to contract resulting in lactation.


 * 7. Review hypothalamic control of the ANS.**

Lateral zone


 * 8. Describe the influence of emotion on hypothalamic mechanisms.**

Medial zone


 * 9. Describe the cascade of events and the role of the hypothalamus in response to stress.**

Diagram on p. 102