Hypothalamus Flashcards
All integrated hypothalamic responses are composed of an:
- Endocrine component
- Behavioral component
- Autonomic component
What is homeostasis?
What are the four general features?
Property of a system either open or closed that regulates the internal environment and tends to maintain stable and constant conditions
- Constancy in an open system requires mechanisms to maintain constancy
- Steady state conditions require that if there is a tendency to change, there are factors to resist change
- regulating systems are cooperative and work together or successively
- Organized self government
What structure surrounds the hypothalamus?
What is the benefit of this?
The circle of Willis surrounds the hypothalamus so there is a lot of collateral blood flow making strokes in this area less likely to cause damage
What is the overarching function of the hypothalamus?
To maintain homeostasis.
Destruction of the hypothalamus is not compatible with life
What are the sensory inputs into the hypothalamus?
- Extroreceptors for light, temperature, odorants
2. Info about the internal environment like BP, glucose level, blood osmolarity
What controls the actions of the hypothalamus?
Neuroendocrine control that feedback onto the hypothalamus like
- Glucocorticoid
- Thyroid hormone
- Estrogen and testosterone
What are the 4 motor outputs of the hypothalamus?
- Anterior and posterior pituitary
- Cerebral cortex
- Motor neurons in the brainstem and spinal cord
- Autonomic preganglionic neurons
What are the borders of the hypothalamus?
Rostrally- optic chiasm
Laterally- optic tracts and cerebral peduncles
Caudally- mammillary bodies
What are the three rostral to caudal divisions of the hypothalamus?
- Anterior zone
- tuberal hypothalamus
- Posterior part
What nuclei are in the anterior part of the hypothalamus and what are their functions?
- Preoptic area
- Paraventricular hypothalamic nucleus (PVH)
- supraoptic nucleus (SON)
PVH and SON regulate anterior and posterior pituitary function. The magnocellular neurons in both secrete ADH and oxytocin
What is the function of the tuberal hypothalamic region?
What are the two main nuclei with secretory function and what does each secrete?
What other nuclei are present and what do they do?
This region contains cells that secrete releasing factors into to pituitary portal system (ant. Pituitary) at the zone of the median eminence
PVH parvocellular neurons secrete corticotropin releasing hormone, thyroid releasing hormone and somatostatin
Arcuate nuclei release growth hormone releasing hormone and dopamine
Ventral and dorsomedial nuclei integratevautonomic and endocrine functions
What are the roles of the posterior portion of the hypothalamus?
What is the prominent structure?
What is generated in the posterior part and what does it regulate?
The mammillary bodies are the prominent structure
The posterior portion integrate autonomic and behavior
Histamine is generated and it regulates arousal
What region of the hypothalamus integrates autonomics with endocrine function?
What region integrates autonomics with behavior?
Tuberal region
Posterior part
What are the five exteroceptive ways the hypothalamus gathers information?
Visual Somatosensory Visceral Olfactory Limbic/multimodal
What are five interoceptive ways the hypothalamus gathers info?
Temp Sodium Osmolarity Glucose Circumventricular organs
What are the three major things the hypothalamus integrates with the sensory signals it receives?
- Homeostasic set points
- Circadian signals
- Allostatic signals (attack or threat, presence of a mate)
Where do the magnocellular cells of the PVH project?
Where do the parvocellular neurons of the PVH project?
Magnocellular- posterior pituitary
Parvocellular- anterior pituitary
What are the three broad categories for output from the hypothalamus?
- Autonomic (parasympathetic and sympathetic)
- Endocrine (to ant. and post pituitary and autonomics)
- Behavioral (motor automation, arousal, autonomics)
What are the three medial to lateral divisions of the hypothalamus?
- Paraventricular (on edge of third ventricle)
- Medial zone
- Lateral zone
What two major structures are in the paraventricular zone of the hypothalamus?
What ventricle do they surround?
Arcuate nucleus is just lateral to the third venticle and regulates food and water intake via ADH
The median eminence is at the floor of the third ventricle and is where the portal system that takes hormones to the ant. Pituitary
What major structures are in the medial zone of the hypothalamus?
As a general rule, where do these structures project?
Ventromedial and dorsomedial nuclei and the anterior and posterior hypothalamic areas
These structures project to neighboring hypothalamic regions which control endocrine and autonomic outputs
What is the major structure of the lateral zone?
What two major neuropeptide system are found in the LHA?
Medial forebrain bundle which connects the hypothalamus with forebrain structures and the brainstem.
Melanin concentrating hormone (MCH)- increase feeding behavior and weight
Orexins (ORX) aka hypocretins - increase awakefullness (absence causes narcolepsy)
What is the major cause of disruption to the hypothalamus?
Pituitary tumors that are growing.
This would be a major concern if the patient presents with tunnel vision because the pituitary tumor could press on the optic chiasm
What neurons of the hypothalamus directly influence the pituitary?
Magnocellular neurons from the PVH and supraoptic nucleus axons extend down the neural lobe into the posterior pituitary
What neurons from the hypothalamus indirectly influence the pituitary?
The parvocellular neurons of the PVH and Arcuate nuclei secrete hormones to the portal circulation in the median eminence which release hormones into the anterior pituitary
What are hypothalamic projection neurons?
Neurons that dont regulate endocrine function but rather regulate behavior by projecting the regions outside of the hypothalamus/pituitary axis
What are the three zones of the median eminence?
Ependymal layer
Internal zone
External zone
What specialized cell in the ependymal layer sends signals to other layers of the median eminence?
Tannycytes
What is the major function of the ependymal layer of the median eminence?
To form a barrier from the CSF in the third ventricle and to prevent the movement of releasing factors back into the hypothalamus
What is the internal zone of the median eminence composed of?
- Axons of the SON and PVH magnocellular neurons en route to the posterior pituitary
- Axons of hypophysiotropic neurons to the external layer of the median eminence
- Supportive cells
What is found in the external layer of the median eminence?
The exchange point where hypothalamic releasing factors enter the portal system
It contains terminals for :
Peptide release
Monoamine release (NE and dopamine)
What are the three lobes of the anterior pituitary (adenohypophysis) ?
Pars distalis
Pars intermedia
Pars tuberalis
What are the two divisions of the neurohypophysis (posterior pituitary)?
Pars nervosa
Infundibular stalk and median eminence
What bone does the pituitary gland sit in?
Sells turcica
What two components make up the hypophyseal stalk?
Infundibular stalk of post pituitary surrounded by pars tuberalis of ant. Pituitary
How does olfactory information reach the hypothalamus?
Directly via the olfactory bulbs
How does visual input reach the hypothalamus?
What nucleus does the input go to?
What is the function of the nucleus?
Via retinal fibers through the optic chiasm.
The fibers synapse on the suprachiasmAtic nucleus which regulates circadian rhythm including circadian hormone secretion, body temp, behavior
How does visceral information from the heart lungs and GI tract enter the hypothalamus?
- Direct input from the nucleus of the solitary tract
2. Several relays
How do somatic sensory afferents reach the hypothalamus?
Via the Spinothalamic tract
How does auditory information reach the hypothalamus?
Through a relay from the brainstem reticular formation
How do inputs from the hippocampal formation (limbic areas) reach the hypothalamus?
Via the fornix.
The fornix leaves the dorsal end of the hippocampus, loops ventrally and caudally around the hypothalamus and splits into two.
1. Diffuse innervation of the hypothalamus
2. Tight bundle (column of fornix) directly onto mammillary bodies
How does the Amygdala give input to the hypothalamus?
Via the stria terminalis which loops similarly to the fornix (hippocampal input to the hypothalamus)
What would occur if forebrain afferents to the hypothalamus were severed?
Organized emotional response is generated in the hypothalamus but it is regulated by the forebrain afferents. Severing this connection would create profound rage for minimal stimulation.
What are the afferents to the mammillary bodies?
What are the efferents?
The fornix, ventral and dorsal tegmental nuclei
Principal mammillary tract which bifurcated into:
- Mamillotegmental tract which descends to the brainstem
- Mamillathalamic tract which goes to the anterior thalamic nuclei
What efferents from the hypothalamus arise from the lateral region?
- MCH and ORX neurons ascend through the medial forebrain bundle and provide reciprocal innervation to the forebrain
Iimbic structures - Descending fibers from lateral hypothalamus and PVH go to brainstem and spinal structures for autonomic control and the reticular formation
What are the major ways the hypothalamus controls endocrine function?
- Magnocellular neurosecretory system- cell bodies from SON and PVH project along the optic chiasm to enter the median eminence where it is continuous with the posterior pituitary. They secrete ADH and oxytocin
- Parvocellular neurosecretory system- near Arcuate nucleus and PVH (near third ventricle) run into median eminence, release hormones into capillary loops which feel into hypophyseal portal veins which go to anterior pituitary
How does the hypothalamus play a role in autonomic regulation ?
PVH, lateral hypothalamic area and dorsomedial nuclei innervate parasympathetic preganglionic neurons in the medulla and sympathetic preganglionic neurons in the spinal cord
How does oxytocin have a role in the autonomic regulation of the body?
It activates gastric secretion and cardiac inhibitory vagal motor neurons (parasympathetic)
In addition to directly synapsing on autonomic preganglionic cells, what other path does the hypothalamus use to regulate autonomic function?
Axons get sent through the medial forebrain bundle to the brainstem autonomic control regions
How does leptin regulate sympathetic outflow?
Leptin is a signal to tell you to not eat.
When you fast, TRH levels go down because you don’t want to metabolize.
This decreases leptin to tell your body to eat.
Lack of leptin is linked with lower oxygen consumption
Lesions to the Ventromedial nucleus of the hypothalamus causes what?
Overeating and obesity because it removes the leptin receptors telling you you are full.
What happens to behavior if the lateral hypothalamus is lesioned?
Aphagia (starvation) occurs
How do descending pathways and ascending pathways influence eating control in the hypothalamus?
Descending pathways facilitate automatic behavior like chewing
Ascending pathways innervate that cerebral cortex and are involved in overall behavioral arousal
A MCH knockout displays what?
Decreased feeding and body weight
An ORX knockout displays what?
Narcolepsy
What is narcolepsy?
Clinically, what triggers narcolepsy?
An autoimmune disorder with the selective destruction of orexin neurons.
In a person with narcolepsy, there will be no orexin in the CSF
It is triggered by pleasurable or interesting stimuli
