neural control of motivational behaviour Flashcards
what are circumventricular organs?
structures where the BBB is leaky at some points bc of fenestrated capillaries
where are circumventricular organs found?
surround the ventricular system
name some circumventricular organs
area postrema posterior pituitary median eminence subfornical organ subcommissural organ pineal gland
what can cause blood osmolarity to increase?
o if total body water is low bc of sweating/lack of drinking t
what senses blood osmolarity?
sensed by osmoreceptor cells in the subfornical organ – a circumventricular organ
explain the pathway of detecting high blood osmolarity and how this is kept under control?
- subfornical organ detects
high blood osmolarity - activates cells in medial preoptic nucleus of hypothalamus
- nucleus projects into limbic system –> regulates thirst
- cells of the paraventricular and supraoptic nucleus are also activated
- their axons project to the posterior pituitary –> release ADH –> reduce urine -> reduce water loss in urine -> prevents blood osmolarity rising even further
which nucleus makes us feel thirst?
medial preoptic nucleus
where is the paraventricular nucleus found?
around the 3rd ventricle
where is the supraoptic nucleus found?
above the optic chiasm
what are the 3 effects of ADH to decrease loss of water?
- aquaporins: more move into the collecting duct epithelial membranes. water moves into renal medulla - less urine, higher conc
- increases collecting duct permeability to urea
- stimulates Na+ reabsorption in the ascending loop of Henle through the Na+ K+ 2CL- cotransporter. Increases osmolarity of medullary extracellular fluid -> more water reabsorbed from collecting ducts
what does the body do when water is lost by sweat during heat stress?
we drink more water to compensate
Body also increases aldosterone secretion and decreases atrial natriuretic peptide secretion -> decreases sodium loss in urine -> compensates for sodium loss in the sweat and prevents hyponatraemia
which 2 factors initiate feeding behaviour?
o External cue – immediate availability of food
o Internal cue – sense of hunger from inside your body
what is the major store of energy in mammals?
adipose tissue
what is weight maintained by?
o Adipostatic model – factors released by fat target the hypothalamus to control feeding and maintain weight
o Intestinal absorption - altering intestinal transit time –> altering absorption of caloric material in the intestine
describe the early evidence for the role of the hypothalamus in appetite?
o Patients with pituitary tumours pressing up on the hypothalamus demonstrated voracious appetite, morbid obesity and hypogonadism – known as adiposogenital syndrome
what do lesions in the lateral hypothalamus cause?
anorexia
what do lesions in the medial hypothalamus cause?
obesity
what does the ventromedial satiety centre do?
inhibited feeding when stimulated
what stimuli does the hypothalamus respond to to regulate food intake?
o Internal stimuli – contraction of the stomach, the levels of various blood chemicals e.g. glucose, insulin, ghrelin, cholecystokinin and leptin
o External stimuli – sight and smell of food
what does whether we eat food or not depend on?
the balance between external stimuli (how attractive the food is) and internal stimuli (how hungry we feel)
what does the arcuate nucleus detect?
internal cues e.g. levels of blood hormones
what do arcuate lesions do?
destroy the animal’s ability to detect internal signals
o If presented with palatable food, it will eat until it can physically eat no more
o If presented with unpalatable food, it will starve to death as it has no ability to detect internal hunger signals
what are the main cell types in the arcuate and periventricular nuclei?
o ‘Agouti-related peptide*’ (AGRP) & ‘Neuropeptide Y’ neurones (NPY) neurones
o ‘Cocaine & amphetamine related transcript’ neurones (CART) & ‘Pro-opiomelanocortin (POMC)’ neurones
what is ghrelin?
hunger hormone
protein hormone produced by special ghrelinergic cells
