Hypothalamus & Temp Regulation Flashcards
Describe the location of the hypothalamus and some key nuclei (those with functions
discussed in detail).
Forms the ventral-most part of the diencephalon, specifically the floor of the third ventricle and
much of the walls.
- regulates the
majority of endocrine glands via its regulation of the pituitary gland
-extensive
interconnections with the limbic system and autonomic nervous systems
General boundaries: Anterior: optic chiasm Posterior: mesencephalon Dorsal: thalamus Ventral: pituitary (hypophysis) Medial: third ventricle
Nuclei: paraventricular nuc lateral and medial preoptic nuclei anterior nuc suprachiasmatic nuc Supraoptic nuc Arcuate nuc ventromedial nuc Dorsomedial nuc
Describe the pathways connecting the hypothalamus with the autonomic NS.
-Hypothalamic neurons innervate the preganglionic neurons of the sympathetic and
parasympathetic nervous systems.
-pregang symp neurons intermediolateral column of thoracic and upper three segment of the spinal cord (T1-L3)
-pregang parasymp in brainstem nuclei and SC (CN III, VII, IX, X, and sacral SC in pelvic splanchnic nerve.)
-synapse on postganglionic neurons located in autonomic ganglia outside CNS. These post-ganglionic neurons then innervate smooth muscle, cardiac
muscle, or glands in their target organs
Describe the role of the autonomic nervous system in homeostasis and emotional
responses.
The ability of the hypothalamus to regulate the ANS is
critical for its role in maintaining homeostasis as well as for the physiological correlates of emotion
(e.g., heart palpitations, sweaty palms, blushing)
How does the hypothal regulate the autonomic and somatic motor systems?
Efferent projections to:
- autonomic centers and preganglionic neurons
- motor nuclei in brainstem
Efferent pathways are neural and humoral.
Neural (hypothal to autonomic and somatic nervous systems):
A. Dorsal longitudinal fasiculus: to autonomic nuclei in the brainstem reticular system and
spinal cord
B. Medial forebrain bundle(mfb): to brainstem reticular formation
C. Mammillotegmental tract: from the mammillary bodies to the midbrain reticular formation
(tegmentum).
Note: Pathways a and b also carry afferent information (visceral sensory) to the hypothalamus
How does the hypothalamus regulate Somatic Motor Responses?
Hypothalamic neurons innervate upper motor neurons in the brainstem reticular formation
which then project to the lower motor neurons that innervate skeletal muscle.
Hypothalamic regulation of the endocrine system.
- direct and indirect
- Direct: posterior pituitary:
- vasopressin and oxytocin are made by neurons in the supraoptic and paraventricular nuclei–>transported to posterior pituitary. APs signal for release directly into general circulation. Vasopressin –>kidneys to increase water reabsorption or on vascular smooth muscle to cause vasoconstriction. Oxytocin–>constriction of SM in uterus and mammary glands (parturition and lactation)
- Both hormones also act on brain to modulate behavior
Indirect: Anterior pituitary: hypothal synthesizes/releases hormones into the hypothalamo pituitary portal circulation that regulate the release of hormones from the glandular
cells of the anterior pituitary (LH, GH, ACTH, PRL, TSH, FSH, etc). Portal system carries hormones to anterior pituitary w/o dilution into general circ. Ant pit hormones regulate release of various hormones from peripheral endocrine organs
Neural afferents to hypothalamus from brainstem
- dorsal longitudinal fasciculus
- medial forebrain bundle
Other inputs:
- direct input from retina
- processed sensory info from limbic areas (hipp/amyg)
- visceral sensation via nucleus of solitary tract
Humoral inputs to hypothalamus
Humoral afferents:
- temp
- osmolality
- glucose
- peripheral hormones
Regions with fenestrated capillaries (no BBB)–circumventricular organs:
OVLT–organum vasculosum lamina terminalis (sensitive to osmolarity of blood)
subfornical regions (responds to chemical composition of blood; angiotensin II acts here to induce thirst)
posterior pituitary
median eminence (leptin–from white adipocytes–acts on median eminence)
How does the hypothalamus recruit motivated behavior pathways?
Projections to limbic system–amygdala, hippocampus, etc.
Neural connections (reciprocal w/ afferent and efferent):
-fornix: connects hippocampus with mammillary bodies
- Stria terminalis: connects amygdala with the anterior and tuberal regions of hypothalamus
- Medial forebrain bundle (mfb): connects hypothalamus with prefrontal cortex and septum
-strictly efferent neural pathway, the mammillothalamic tract, carries information
from the mammillary bodies of the hypothalamus to the anterior nucleus of the thalamus.
Pathway for integrating behavior with time.
Light information from specialized retinal ganglion
cells that are photosensitive travels directly to the suprachiasmatic nucleus of the
hypothalamus via the retinohypothalamic tract. Important for entraining circadian rhythms to the environmental light/dark cycle
Hypothalamus and Emotional behavior
- hypothalamus is responsible for initiating the coordinated autonomic and behavioral responses
that constitute emotional expression (higher centers like limbic system modulate emotional expression to situation)
Sham rage
- Dissociation of the rage response from the appropriate environmental context
- Observed when hypothalamus is disconnected from higher brain areas (decorticate), but hypothal is still connected to brainstem and SC. (animals=aggressive, irritable); in response to inappropriate stimuli
Disconnecting hypothal from brainstem gets rid of sham rage.
- Tells us coordinated response require hypothal(?)
- More discrete regions involved in sham rage: dorsomedial and ventromedial nuc.
Heat production
-Maintain temp @ 37 deg C (98.6F)
=thermal set point of body.
-Heat production:
basal metabolic rate (heat produced as a by-product of metabolism; thyroxin increase–>increase basal heat production thru altering basal metab rate)
-Exercise
-Shivering (involuntary), but somatic control
-Non-shivering thermogenesis (infants, small mammals w/ brown fat deposits increase catabolic activity of tissue; release of NE onto brown fat cells by symp n fibers; NE activates UCP1–>H+ion channel in mitochondrial membrane in brown fat cells–>heat w/o ATP production
Heat loss
- heat flow to skin (sympathetic vasomotor control)
- sweating (eccrine gland under symp control)
Behavioral mechanisms of temp regulation
- putting on clothing, turn up heat etc when too cold
- less awareness/involvement for lowering temperature because increased circulation to skin and increased sweating are efficient at preventing body temp raises.
