Identify the labeled structures.
• lateral to the third ventricle, inferior to the thalamus (below hypothalamic sulcus
• between anterior commissure and optic chiasm anteriorly and the midbrain tegmentum (including red nucleus) posteriorly
• Connected to the posterior pituitary via the Infundibulum or pituitary stalk
Identify the numbered structures.
The Pituitary gland lies in the ____ ___ just above the ____ sinus.
The Pituitary gland lies in the Sella turcica (Turkish saddle) just above the sphenoid sinus (this allows the pituitary gland to be accessed by a transphenoidal surgical approach through the nasal cavity).
What is the anatomical relationship of the pituitary gland and the optic chiasm? What is the significance of this relationship?
What dura surrounds the pituitary gland?
What bounds teh sella turcica laterally on both sides?
Note the location of the pituitary in the sella turcica and its location just posterior and inferior to the optic chiasm.
It is surrounded by dura: the diaphragma sella is the superior part of the dura.
The sella turcica is bounded laterally on both sides by the cavernous sinus.
Because of the proximity of the Pituitary Gland to the Optic Chiasm, Pituitary tumors (adenomas) can compress the chiasm and cause visual field defects (bitemporal hemianopsia) along with endocrine issues.
What other tumors/masses in the sellar or supracellar region can cause bitemporal hemianopsia?
Other tumors or masses in the sellar or supracellar region could also produce this symptom, including meningiomas, craniopharyngiomas, optic or hypothalamic gliomas, etc.
What is the function of the OVLT (organum vasculosum of the lamina terminalis)?
Where is it located?
Located in the LT = lamina terminalis: OVLT (Organum vasculosum of the lamina terminalis) located here; functions to sense blood osmolarity and therefore lacks a blood brain barrier
Key for attached pic: A = Anterior Commissure; O = Optic Chiasm; Inf = Infundibulum; M= Mammillary Body; P = preoptic, a= anterior, t = Tuberal region (which includes tuber cinereum (gray swelling) and the median eminence protruding from it; this is continuous with the Infundibulum (Inf) which projects to the pituitary; po= posterior
What is the relationship btwn the hypothalamus and 3rd ventricle?
Hypothalamus (H) forms the walls and floor of the inferior portion of the Third Ventricle (3).
Identify the labeled structures.
Explain the embryological origins of the anterior and posterior pituitary.
Anterior Pituitary is formed by a thickened area of ectodermal cells in the roof of the developing oral cavity that invaginate to form Rathke’s pouch.
Posterior Pituitary forms from evagination of the floor of the diencephalon.
Developmental defects in Rathke's pouch can give rise to what kind of tumor? What sx can present with this type of tumor?
Developmental defects in Rathke’s pouch can give rise to a Craniopharyngioma (benign childhood tumor). Can compress optic chiasm causing bitemporal hemianopsia (can be confused with a pituitary tumor for this reason). Larger tumors can compress the hypothalamus (especially satiety center thereby causing obesity).
Most common supratentorial tumor. Calcification is common (tooth enamel-like)
What are the functions of the hypothalamus?
Functions of Hypothalamus: maintains homeostasis of the internal environment via autonomic and endocrine systems and also exerts control of external environment via motor behavior responses mediated by both the reticular formation and the limbic and autonomic system.
Homeostasis: controlling hunger, thirst, temperature, sexual desire, sleep-wake cycle, etc.
Limbic system mechanisms: emotion and drive –related behaviors
(1) Maintain homeostasis in body; physiological variables maintained in narrow range (or set points) (blood pH, CO2, O2, etc.)
(2) controls the release of 8 major hormones by the pituitary gland
(3) temperature regulation
(4) control of food and water intake for body weight and body water regulation
(5) sexual behavior and reproduction
(6) control of daily cycles in physiological state and behavior
(7) mediation of emotional responses (fear, rage, pleasure) and other drive-related behavior (e.g. sexual, feeding) through autonomic visceromotor centers/ control mechanisms.
Mnemonic: TAN HATS: Thirst and water balance, Adenohypophysis (regulates anterior pituitary hormone release), Neurohypophysis (neurohypophysis releases ADH and OCT synthsized in hypothalamus), Hunger, Autonomic regulation, Temperature, Sexual urges
What are central program generators? Where are they located? What is their function? What is their relationship to the hypothalamus?
Central Program Generators
• Neural networks in brainstem and spinal cord that act as pattern generators for rhythmical, automatic movements such as breathing, chewing and walking
• Shivering and panting responses for temperature regulation
• centers for cardiovascular and respiratory responses (to heart and diaphragm) in medulla
• others for swallowing, sexual mating behavior, etc
Hypothalamus regulates above functions through connections to central program generators.
How does the hypothalamus regulated body water? Where does it receive inputs from for blood osmolarity?
How does the hypothalamus regulate satiety? From where does it receive inputs to regulate satiety?
- Body water regulation (via angiotensin II/antidiuretic hormone, thirst mechanisms, etc); inputs for osmolality via OVLT to supraoptic nucleus (SON)-synthesizes ADH
- Satiety or feeding centers (via inputs from nucleus of solitary tract (NST) regarding stomach distension or lack thereof). Nucleus of the solitary tract contains GVA and SSA fibers from CNs VII, IX, and X. Note that signals from satiety can be overriden by the cortex-keep eating when full
What functions does the "biological clock" in the hypothalamus regulate?
Where does the hypothalamus receive input from for synchronization of diurnal rhythms? To what nucleus of the hypothalamus does it synapse in?
Regulates body functions that :
1. vary at different times of the day (e.g., body temperature, hormone secretion, hunger)
2. vary over a period of many days (e.g. menstrual cycle)
• Projections from the retina to the hypothalamus (suprachiasmatic nucleus specifically) supply the clock with day-night information needed for synchronizing diurnal (circadian) rhythms.
• Lesions of the hypothalamus often disrupt the sleep-wake cycle and circadian rhythms.
Where does the suprachiasmatic nucleus (SCN) project to?
Where do the mammillary bodies of the hypothalamus receive input from?
SCN: Regulates circadian rhythms, receives direct retinal input; outputs to pineal gland: synthesizes melatonin
Mammillary body: Input from hippocampus
What is Wernicke-Korsakoff encephalopathy/syndrome?
What is it caused by? What population is it often seen in?
What are the symptoms/consequences?
Wernicke Korsakoff encephalopathy or syndrome:
- Bilateral necrosis of mammillary bodies due to thiamine (Vitamin B1) deficiency and seen most commonly in chronic alcoholic. (also may see degeneration in Dorsomedial and anterior nuclei of thalamus)
- See triad of 1) ataxia, 2) abnormal eye movements such as Horizontal gaze palsy, nystagmus, opthalmoplegia (weak eye movements) and 3) a confused state.
- Left with anterograde and retrograde amnesia. (remember that the mammillary bodies receive projections from the hippocampus)
- Also frontal lobe dysfunction including impaired judgment, poor impulse control.
- Often unaware of their memory deficits and “confabulate” or make up stories to questions versus saying they do not remember
What are the major inputs to the hypothalamus?
1. Retina (for regulation of circadian rhythms)
2. Brainstem and spinal cord
3. Limbic system connections including those from the orbitofrontal and cingulate cortex (i.e. limbic cortex), the hippocampus (via the fornix to mammillary bodies), amygdala, ventral striatum and septal nuclei.
What is the function of the connections of the brainstem and spinal cord to the hypothalamus via the median forebrain bundle (MFB) and the dorsolateral funinculus (DLF)? What is the direction of travel of these tracts?
Brainstem and spinal cord via Medial forebrain bundle (MFB) and Dorsolateral funiculus (DLF). The MFB is a bidirectional collection of fibers running through the hypothalamus at multiple levels; it interconnects caudal areas such as the brainstem tegmentum and reticular formation with the hypothalamus. The DLF is also bidirectional and runs between brainstem autonomic-visceral regions and the hypothalamus. Hypothalamic inputs include Viscerosensory ones from brainstem nuclei (e.g. the solitary tract) as well as from a “Central Autonomic Network” in widespread brain regions).
What are the outputs of the hypothalamus?
1. mainly back to same regions (except retina !!) with addition of pituitary for endocrine control mechanisms.
2. Mammillothalamic tract to anterior nucleus of thalamus which then relays to widespread limbic cortical areas.
3. There are direct descending pathways to the brainstem autonomic nuclei and the intermediolateral cell column of the spinal cord. The descending sympathetic hypothalamics initially run in the medial forebrain bundle and then in the lateral brainstem and spinal cord and synapse on the preganglioninc sympathetic neurons in the lateral horn to activate them.
What is the result of a lesion of the descending sympathetic pathways above T1?
When lesioned above T1 the patient ends up with an ipsilateral Horner’s Syndrome (e.g. PICA syndrome and Brown Sequard syndrome at or above T1).
Dorsolateral Funiculus in rostral medulla: Parasympathetic fibers follow same pathways but synapse on parasympathetic brainstem motor nuclei (e.g. DMN of Vagus) and also extend to sacral spinal cord level.
Thus, the Hypothalamus is an integrating center of autonomic functions.
Attached is depiction of Hypothalamus controlling sympathetic neurons in the intermediolateral cell column of the thoracolumbar spinal cord (T1 –L2).
Explain the afferent and efferent source of fibers in the baroreceptor reflex and the role of the hypothalamus in the baroreceptor reflex.
Baroreceptor Reflex: Visceral afferents (GVA : CN IX and X) from Solitary tract (S) carry blood pressure information from baroreceptors in carotid sinus and aortic arch to DMN of X which projects to terminal ganglia of heart and influence heart rate. Interconnections between the Hypothalamus and the DMN of X allow the hypothalamus to powerfully regulate this reflex.
Explain the temperature regulation and water balance reflexes.
Temperature Regulation Reflex: temperature sensing neurons in hypothalamus generate either heat dissipation (sweating and cutaneous vasodilation) OR heat conservation (cutaneous vasoconstriction) and heat production (shivering, mediated by reticulospinal pathways)
Water Balance Reflex: a “neurohumoral” reflex. Blood osmolarity-sensitive neurons in anterior hypothalamus connect with ADH neurons. When osmolarity is too high, increased ADH released and more water resorption occurs in kidney collecting tubules (opposite response with low blood osmolarity).
List the areas of the brain involved in drive-related behavior?
What is drive related behavior?
Drive –related Behavior: Implemented by the Hypothalamus and interconnected brainstem regions:
1. Nucleus of solitary tract (GVA: VII, IX, X)
2. Parabrachial nuclei : around Superior Cerebellar Peduncle (SCP)
3. Reticular formation (RF) in brainstem
4. The periaqueductal gray (PAG)
• Protection: enemies/attackers/the elements
• Sexual behavior/procreation
• Well being
• Cardiovascular and Respiratory Control (for survival)
Where are the parabrachial nuclei located?
What is their function?
Parabrachial nuclei [around Superior Cerebellar Peduncle (SCP) * ] convey visceral, pain & temperature information to hypothalamus, amygdala and thalamus (which then relays to insular cortex); Convey subjective sense of well-being to higher centers involved in drive and emotion.
What are the functions of the insular cortex?
What is the function of its connections with the amygala?
The insular cortex has gustatory, pain and autonomic functions. Its connections with the amygdala are involved in fear conditioning.
What is the function of the reticular formation in drive related behavior?
Reticular Formation (RF): Central program generators (CPG) for coordinated autonomic responses located in RF. CPGs are local neural networks that produce rhythmic patterned motor outputs. These include centers for cardiovascular and respiratory responses in medulla and others for swallowing, micturition (pontine center), defecation, and sexual function. They coordinate autonomic motor neurons with lower motor neurons.
What is the function of the periaqueductal gray in drive behavior?
The periaqueductal gray (PAG): around aqueduct in midbrain; origin of descending pain pathways, also organizes complex responses to environmental situations with guidance from cerebral cortex, amygdala and hypothalamus.
Example: In frightened animal signals from PAG to Central Program Generators (CPGs) in brainstem initiate tachycardia, piloerection, back arching, hissing and sometimes analgesia.