Neural basis of physiological functions

Question 1

Feeding behaviour

Answer 1

• Hypothalamus: Ventromedial hypothalamus acts as satiety centre while lateral hypothalamus acts as a feeding centre
• ghrelin and neuropeptide Y act as mediators of increased appetite (orexigenic)
• leptin, cholecystokinin and serotonin act as mediators of satiety (anorexigenic)

Question 2

Ghrelin

Answer 2

• only orexigenic substance produced outside of the CNS

- synthesised in the gastric mucosa

Question 3

Leptin

Answer 3

• anorexigenic

- synthesised by adipose cells

Question 4

Dopamine and food

Answer 4

• food and food cues increase dopaminergic activity in the nucleus accumbens (reward centre)
• destruction of dopamine pathways reduces eating behaviour
• in obesity, D2 receptors are reduced in the striatum

Question 5

Temperature control

Answer 5

• 2 centres in the hypothalamus
• preoptic anterior hypothalamus acts as the hypothermic centre- stimulation makes you cool down
• posterior hypothalamus acts as the hyperthermic centre-stimulation makes you warm up

Question 6

Hyperthermia

Answer 6

• some drugs may induce malignant hyperthermia but not through the hypothalamic mechanism- this is probably due to abnormal excitation-contraction of skeletal muscles
• also seen in NMS induce by neuroleptic use or levodopa withdrawal

Question 7

Diurnal temperature variation

Answer 7

-lesions in the median eminence reduce diurnal temperature variation

Question 8

Pain

Answer 8

Thalamus is crucial for pain perception nbut higher cortical centres are central to the localisation and interpretation of pain signal

Question 9

Pain fibres

Answer 9

• thin unmyelinated C fibres or sparsely myelinated A-delta fibres carry pain to dorsal horn of the spinal cord
• fast transmission takes place along the lateral spinothalamic route
• slow transmission takes place through reticulothalamic tract to aid subjective sensation

Question 10

Opioid receptors

Answer 10

• opioid receptors in the dorsal horn and possibly in the brain steam (PAG) modulate pain intensity
• descending fibres from serotonergic raphe nuclei also modulate pain perception- this is why TCAs might help with pain

Question 11

Thalamic pain syndrome

Answer 11

• occur in cases of stroke involving thalamoperforating branches of posterior cerebral artery
• patients have a contralateral loss of sensation with burning or aching pain triggered by light cutaneous stimulation

Question 12

Thirst

Answer 12

• subfornical organ and organum vasculosum of the lamina terminalis are circumventricular organs and play vital role in perception of thirst
• hypothalamic paraventricular nucleus is also involved in the regulation of thirst
• Angiotensin II acts as neurotransmitted to send thirst signals to hypothalamus
• hypotension stimulates thirst through baroreceptors on the aorta and carotid

Question 13

ADH

Answer 13

-ADH increases water reabsorption at renal tubules and helps maintain fluid balance

Question 14

SIADH

Answer 14

• syndrome of inappropriate secretion of ADH may result from damage to periventricular and supraoptic hypothalamic nuclei
• may also occur due to carbamazepine or chlorpromaxine
• some tumours such as lung cancer also produce excess ADH
• low sodium and reduced osmolarity is noted in the presence of normal renal excretion of sodium and high urine osmolality

Question 15

Kluver-Bucy syndrome

Answer 15

• bilateral lesions of amygdala and hippocampus
• results in placidity
• hyperorality
• hypersexuality
• hypermetamorphosis (objects are repeatedly examined as if they were novel)

Question 16

Laurence-Moon-Biedl syndrome

Answer 16

• autosomal recessive with genetic locus at 11q13 in most cases
• no hypothalamic lesions
• obesity and hypogonadism
• low IQ, retinitis pigmentosa and polydactyly
• Diabetes insipidus seen

Question 17

Prader Willi syndrome

Answer 17

• associated with paternal deletion (genomic imprinting) at 15q11-q13
• hypotonia
• obesity with hyperphagia
• hypogenitalism
• mental retardation
• short stature
• impaired glucose tolerance
• abnormal control of body temperature and daytime hypersomnolence is related to hypothalamic disturbances

Question 18

Kleine-Levin

Answer 18

• hypothalamix abnormality sometimes preceded by a viral illness
• compulsive eating behaviour with hyperphagia, hypersomnolence, hyperactivity, hypersexuality and exhibitionism
• can resolve in 3rd decade of life

Question 19

Psychogenic polydipsia

Answer 19

• excessive water consumption in the absence of hypovolemia or hypernatraemia
• may lead to water intoxication and serious electrolyte imbalance