Motivational behaviour Flashcards
Which part of the brain detects blood osmolarity?
The hypothalamus
Osmoreceptor cells within with organ detect blood osmolality?
Subfornical organ
Describe the location of the subfornical organ
In the wall of the third ventricle
Outside the blood brain barrier
Next to interventricular foramen
How does stimulation of osmoreceptors in subfornical organ lead to behavioural thirst?
Subfornical organ projects to medial preoptic nucleus of hypothalamus
This connects to limbic system and regulates sense of thirst
When medial preoptic nucleus is activated we feel subjectively thirsty
Where can the subfornical organ activate cells?
Paraventricular nucleus (third ventricle) Supraoptic nucleus (above optic chiasm) Medial preoptic nucleus
What is the effect of activating cells in paraventricular nucleus and supraoptic nucleus?
Release ADH and reduce urine flow
What 3 effects does ADH have?
1- additional aquaporins move into membrane of collecting duct epithelial cells
2- increase permeability of collecting duct to urea
3- stimulate sodium reabsorption by increasing activity of Na+/K+/2Cl- cotransporter
By what 2 inputs does a non-obese person regulate their weight?
1- regulation of input
2- reulating intestinal absoprtion by altering intestinal transit time
Result of lesions in lateral hypothalamus in terms of weight?
Anorexia
Result of lesions in medial hypothalamus in terms of weight?
Obesity
What two structures does a medial hypothalamus lesion effect? What is the impact of this?
Arcuate and periventricular nuclei
Causes overeating as no concept of satiety
Why do scientists think that a lateral lesion to hypothalamus leads to anorexia?
There is an orexigenic centre (hunger centre) located here
What are internal stimuli in terms of regulating weight?
Contractions of stomach, levels of blood chemicals such as glucose
What are external stimuli in terms of regulating weight?
Sight and smell of food
What role does the arcuate nucleus have in terms of weight regulation?
Detection of internal cues such as blood hormones
Perojects to periventricular and ventromedial nuclei (satiety centre)
What is the result of arcuate lesions?
Destroy ability to detect internal signals
What happens if you present an animal with arcuate lesion with palatable food?
Will eat until physically cannot carry on: as no internal satiety signals
What happens if you present an animal with arcuate lesion with non palatable food?
It will starve to death as it can’t detect internal hunger signals
What produces ghrelin and where is it mainly found?
Produced by oxyntic gland cells
Mainly found in fundus of the stomach and to a lesser degree in other parts of gut
Name 2 factors that cause ghrelin release
Stomach contractions
High insulin levels
How does ghrelin stimulate eating
Stimulates neurons in the arcuate nucleus that contain neuropeptide Y and agouti-related peptide
Project to periventricular nuclei and inhibit neurons there
Inhibits satiety and releases eating behaviour
How is ghrelin responsible for hedonic aspect of eating?
Stimulates dopamine pathway in the brain
What does circulating leptin levels give brain a reading of?
Total energy storage (total adipose tissue in the body)
What is a high circulating leptin level associated with?
Chronically reduced appetite
How may leptin levels relate to obesity?
Relative leptin insensitivity causing chronic overeating
How does leptin affect fertility?
Low level of leptin prevent gonadotrophic hormones from being released
When is cholecystokinin (CCK) secreted?
Secreted in the duodenum when the chyme moves from stomach to duodenum
What cells does CCK act upon?
Dorsal part of arcuate nucleus to promote satiety
Effect of release of CCK?
Release of digestive enzymes from pancreas and bile from gallbladder
What is the impact of release of glucogaon like peptide 1
Produces rapid satiety by action on arcuate cells
Stimulates insulin secretion
Where are oxyntomodulin and PYY released from?
Enteroendocrine cells
What is the impact of oxyntomodulin?
Delays gastric emptying and decreases gastric acid secretion
What is the impact of PYY?
Increases ileal absorption, slows gastric emptying and delays gallbladder and pancreatic secretion
Name the 4 main hormones that inhibit eating
CCK, GLP-1, oxyntomodulin, PYY
What happens when satiety-inducing hormones reach arcuate nucleus?
Stimulate dorsolateral arcuate nucleus that contain pro-opiomelancortin
These neurons stimulate cells in periventricular satiety centre and stop feeding
Define diuresis
Production of urine by the kidney
Define trigone
The neck of the bladder
How is urine expelled from the bladder during diuresis
Detrusor muscles contract bladder
What is the effect of sympathetic efferents travelling via hypogastric nerve on muscles to do with bladder?
Maintains tonic contractions of internal urethral sphincter
Tonically inhibit contraction of detrusor muscle
What muscle is internal urethral sphincter made of?
Smooth
What receptors mediate the excitatory and inhibitory effect of this innervation?
Inhibitory on detrusor: beta receptors
Excitatory on sphincter: alpha receptors
How is the filling of the bladder detected?
Bladder becomes stretched
Stretch receptors detect stretch and activate afferents in the pelvic nerves
Where do the afferents in the pelvic nerves synapse and what impact does this have?
Afferents synapse on spinothalamic tract
This relays to genital area of somatosensory cortex to person has sense of bladder fullness
What happens if the bladder is full but conditions are not appropriate for micturition?
External urethral sphincter tightens
Lower motor neurons controlling this muscle run in the pudendal nerves
What happens if bladder is full and conditions are appropriate for micturition?
Signal sent from forebrain to pons where micturition centre is situated
nucleus activates the micturition reflex
What happens during the micturition relflex?
Activates descending fibres in reticulospinal tract– inhibits sympathetic and somatic output controlling sphincters
Activates parasympathetic efferents which stimulates detrsuor muscle in wall of bladder.
Causes bladder to contract and urine flows out
How is it ensured that contraction continues until bladder empties?
Once detrusor contraction begins, afferents in muscle increase activity by positive feedback so contraction continues until bladder is empty
What receptors mediate contraction of bladder
M3 type muscarinic receptors
Where are the mucus secreting glands located in the anal canal?
Below to pectinate or dentate line (grooved line where rectum meets anal canal)
What surrounds the internal anal sphincter?E
External anal sphincter (ring of skeletal muscle)
What maintains continence?
Tonic contraction of internal and external anal sphincters
What receptors detect the filling of the sigmoid colon?
Stretch receptors activated because when sigmoid colon fills it stretches the wall of the rectum
Where do stretch receptors in the rectal wall synapse and what effect does this have?
Afferents of stretch receptors synapse on cells in dorsal horn of sacral spinal cord
Transmitted via spinothalamic tract to genital area of somatosensory cortex
What reflex does stretch of rectal afferents activate?
Ano-rectal reflex
What triggers the concious desire to defecate?
Pressure increase on external anal sphincter
What happens if the person decides not to defecate?
Voluntary effort increases contraction of external sphincter and puborectalis muscle
Gradually, rectal afferent adapt to enlarged rectal dimensions and stops firing
Anorectal reflex ceases and internal anal sphincter contracts again
When is urge to defecate increased again after deciding not to defecate?
When next bolus of stool material arrives from sigmoid colon
What happens when person decides to defecate?
Allow external sphincter to relax
Movement of faeces down reduces stretch of upper park
Causes increased contraction of smooth muscle in this region
Propels faeces downward by peristalsis
Is the ano-rectal reflex parasympathetic or sympathetic
Para
