Hypothalamus & Temperature Regulation Flashcards
Pathways connecting hypothalamus to autonomic systems
- Fibers travel in dorsal longitudinal fasiculus
- Hypothalamic neurons ==> preganglionic neurons of the SNS and PNS
- Sympathetic: The preganglionic neurons of the sympathetic nervous system are located in the intermediolateral column of the thoracic and upper 3 lumbar segments of the spinal cord (T1-L3),
- Parasympathetic: the preganglionic neurons of the parasympathic nervous system are located in brainstem nuclei and in the sacral spinal cord.
Pathways connecting hypothalamus to somatic motor system
- Hypothalamic neurons==> reticular formation near the motor nuclei of the cranial nerves
- somatic motor neurons in turn innervate skeletal muscle.
- By coordinating activity in these neurons with actions of autonomic neurons ==> organize and initiate complex activities that require both somatic and autonomic responses
- e.g. vomiting, laughing, crying, and facial expressions
- activities required for maintenance of homeostasis such as chewing and swallowing.
Efferent tracts of the hypothalamus (to autonomic/somatic nervous system)
- Dorsal longitudinal fasiculus: to autonomic nuclei in the brainstem reticular system and spinal cord
- Medial forebrain bundle: to brainstem reticular formation (somatic motor)
- Mammillotegmental tract: from the mammillary bodies to the midbrain reticular formation (tegmentum)
Pathways connecting hypothalamus to endocrine system
- hypothalamus regulates hormone release from anterior nad posterior lobes of pituitary
- anterior pituitary
- hypothalamus synthesizes adn releases hormones into the hypothalamo-pituitary portal circulation ==>
- release of hormones from glandular cells of ant. pituitary
- posterior pituitary
- neurons from supraoptic and paraventricular nucleus ==> vasopressin & oxytocin ==>
- stored @ posterior pituitary until release
Pathways connecting hypothalamus w/limbic system
- Connection w/limbic system ==> appropriate initiation of motivated behaviors + integration of emotion and sensation
- Fornix: afferent/efferent connections between hippocampus and mamillary bodies
- Stria terminalis: afferent/efferent connections between amygdala and the anterior and tuberal regions of hypothalamus
- Medial forebrain bundle: afferent/efferent connections between hypothalamus and prefrontal cortex and septum
- mamillothalamic tract is an efferent pathway connecting the mammillary bodies with the anterior thalamus.
Role of autonomic nervous system in homeostasis/emotion response (general)
- Somatic reactions – escape, fighting, biting, hissing, facial expressions
- Autonomic reactions – blushing, dryness of mouth, sweating, GI reactions, fainting
- Endocrine reactions – activation of adrenal cortex and medulla
Role of autonomic nervous system in emotions
- SNS:
- Blushing - vasodilation
- Fainting - vasodilation
- White face- vasocontriction
- Sweating
- Dry mouth
- PNS: GI effects - butterflies
Role of autonomic nervous system in homeostasis
- body temp = sweating regulation
- water balance = H2O reabsorption
- body weight/hunger = stomach growling
Characteristics of neuroendocrine fxn of hypothalamus/control of anterior pituitary
- (midline/paraventricular regions) hypothalamus synthesizes/releases hormone ==> hypothalamo-pituitary portal circulation ==> release of hormones from anterior pituitary
- ant. pituitary hormones ==> regulate hormones @ peripheral endocrine organs
- thus, hypothalamus indirectly regulates most of endocrine system
Characteristics of neuroendocrine fxn of hypothalamus/control of posterior pituitary
- hormones of the posterior pituitary, vasopressin/ADH and oxytocin are made by neurons in the supraoptic (SON) and paraventricular nuclei (PVN)
- They are transported down the axons of these neurons to the posterior pituitary where they are released directly into the general circulation for transport to their distant target tissues.
Vasopressin acts on the kidneys to increase water reabsorption and on the vasculature to cause vasoconstriction. Oxytocin causes constriction of smooth muscle in the uterus and mammary glands and thereby plays important roles in parturition and lactation.
Endocrine response (initiated by hypothalamus) : body temp regulation, water balance, body weight regulations
- body temp = thyroxin
- water balance = vasopressin
- body weight regulation = insulin/glucagon (ANS) & epinephrine
Somatic motor (initiated by hypothalamus) : body temp regulation, water balance, body weight regulations
- body temp
- exercise (voluntary)
- shivering (involuntary)
- drinking warm liquid, using blankets
- seeking cool environment
- water balance
- thirst ==> drinking beverages
- body weight regulation
- hunger ==> chewing/swallowing
Fever and Pyrogen definition
- fever = regulated increase in body temp
- pyrogen = fever-producing agents
Hypothalamic mechanisms ==> fever
- Fever is produced by the actions on the POAH of one or more of the cytokines (interleukin 1 [IL-1], interleukin 6 [IL-6], tissue necrosis factor [TNF] and interferon).
- IL-1 acts in a non BBB region in the hypothalamus: the OVLT (organumvasculosum of the lamina terminalis).
- ==> endothelial cells in this region to produce prostaglandin E2.
- PGE2 ==> POAH and decreases the activity of the thermoreceptors ==>
- resetting the hypothalamic temperature “set point” to a higher level.
Role of the hypothalamus in generation of circadian rhythm
- Retina ==> info about light/dark cycles ==> SCN
- SCN generates endogenous rhythms even w/out exogenous information
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- SCN generates endogenous rhythms even w/out exogenous information
Location of major nuclei of hypothalamus: suprachiasmatic, paraventricular nucleus, supraoptic nucleus
- suprachiasmatic = just superior to optic chiasm (more anterior vs. paraventricular/supraoptic)
- supraoptic = superior to optic chiasm, lateral w/in hypothalamus, posterior to suprachiasm
- paraventricular = superior to optic chiasm, medial w/in hypothalamus, posterior to suprachiasm
Location of hypothalamic nuclei: posterior nucleus, mamillary body
- mamillary body/posterior nucleus mark the posterior aspect of hypothalamus
