Hypothalamus Flashcards
What is the role of the hypothalamus in regulating autonomic function?
Hypothalamic neurons innervate preganglionic sympathetic and preganglionic parasympathetic neurons
What is the role of the hypothalamus in regulating somatic motor response?
Hypothalamic neurons innervate UMNs in the cranial nerve nuclei which project to LMNs innervating skeletal muscle, i.e. muscles of facial expression; the hypothalamus coordinates autonomic/somatic responses such as laughing, crying, etc.
What is the role of the hypothalamus in the posterior pituitary?
The hypothalamus directly releases vasopressin and oxytocin from the paraventricular nucleus (PVN) and supraoptic nucleus (SON) via axons that terminate in the posterior pituitary, where the hormones are absorbed into the blood stream
What is the role of the hypothalamus in the anterior pituitary?
The hypothalamus releases releasing and inhibiting factors into the hypothalmo-pituitary portal circulation; these hormones regulate the release of other hormones from the glandular anterior pituitary
What do hypothalamic osmoreceptors do?
Located in the organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO) of the anterior hypothalamus; monitor plasma osmolality and temperature
Non-shivering thermogenesis
Caused by release of NE onto brown fat cells by sympathetic nervous fibers, increasing their catabolism; brown adipose tissue produces UCP1 which uncouples the proton-motive force from ATP-production, generating heat
Autonomic regulation of heat loss
Vasodilation - can increase blood flow to skin from nearly 0% to 30% of total cardiac output
Sweating - under sympathetic control
How is the anterior hypothalamus involved in thermoregulation?
Thermoreceptors in the preoptic anterior hypothalamus (POAH) generate action potentials at a frequency proportional to local temperature; increases in firing rate induce heat loss mechanisms
How is the posterior hypothalamus involved in thermoregulation?
Neurons in the hypothalamus receive strong excitatory input from cutaneous cold receptors; excitation of these neurons induces heat gain mechanisms
How do the anterior and posterior hypothalamic neurons coordinate thermoregulation?
POAH cells tonically inhibit the cells of the posterior hypothalamus; when POAH cells reduce their firing rate in response to a decrease in local temperature they release the posterior hypothalamus cells from inhibition, inducing heat gain mechanisms
Substantial excitation of posterior hypothalamic neurons to induce heat gain mechanisms requires release of POAH inhibition + activation of cutaneous cold receptors
How do pyrogens produce fever?
Pyrogens decrease the activity of thermoreceptors in the POAH, tricking the body into thinking that it’s cold; POAH neurons activate thermogenic responses (vasoconstriction, shivering), which raise the temperature of the body over the normal set point
When the pyrogen dissipates, the POAH thermoreceptors are released from inhibition and respond to the higher body temperature by increasing their firing rate, which initiates heat dissipating mechanisms
Endogenous pyrogens - how do they cause fever?
Cytokines (IL-1, IL-6, TNF, interferon) released by macrophages in response to bacterial and viral infection; induces endothelial cells of the OVLT in the hypothalamus to produce PGE2, which diffuses into the POAH and decreases the activity of thermoreceptors, resetting the hypothalamic temperature “set point” to a higher level
Where is the primary circadian clock of the body?
Suprachiasmatic nucleus (SCN) of the hypothalamus; receives direct innervation from the retina and projects to the pineal gland, which releases melatonin
Sham rage
Observed when the hypothalamus is disconnected form higher brain areas but remains connected to the brainstem and spinal cord
Disconnecting the hypothalamus from the brainstem abolishes the sham rage, indicating that the hypothalamus initiates somatic and autonomic reactions to sensory input even in the absence of cortical input, but that cortical input is necessary to modulate appropriate comportment
