Lecture 16 - Diencephalon and Hypothalamus

Question 1

1) What are the four subdivisions of diencephalon?
2) What is the most dorsal part?
3) Describe its appearance
4) What composes it?
5) What is its fn?
6) What is secreted?

Answer 1

1) epithalamus, subthalamuus, thalamus, hypothalamus
2) epithalamus –> forms caplike covering over thalamus
3) smallest and oldest part
4) pineal body, habenular nuclei and caudal commissure
5) linked to limbic system –> involved in regulating repro fns (mating behavior, postpartum maternal behavior)
6) Melatonin secreted by pineal gland –> involved with biological timing and sleep induction –> set cycles

Question 2

1) What is the result of a lesion on pineal gland? therapy?
2) What results from lesion on habernular nuclei?

Answer 2

1) disrupts sleep cycles –> take supplements of melatonin
2) interrupts maternal instincts

Question 3

1) Where is subthalamus located?
2) T or F: only present in mammals
3) What is its fn?
4) Stimulation results in?
5) What type of section does subthalamus not appear?

Answer 3

1) ventral to thalamus and lateral to hypothalamus
2) true
3) mov’t-focusing fn selecting wanted and suppresing unwanted mov’ts –> generation of rhythmic mov’ts
4) most effective tx for late-stage parkinson’s disease in humans –> relieves some clinical signs
5) mid-saggital section

Question 4

1) What is largest component of diencephalon?
2) What comprises it?
3) What is it’s fn?
4) Where does it receive input from specifically?
5) What tract terminates here?

Answer 4

1) thalamus
2) large number of nuclei –> lateral geniculate (vision) and medial geniculate (hearing)
3) great sensory receiving area (receives sensory input from all sensory pathways EXCEPT olfaction) –> relays to cerebral cortex
4) cerebral cortex
5) spinothalamic tract —> projects to cerebral cortex

Question 5

1) What is most ventral and significant part of diencephalon?
2) Why is it the most significant comp?
3) What is its main fns?

Answer 5

1) hypothalamus
2) lesions cause abnormalities in endocrine, limbic or anutonomic fn
3) maintain HOMEOSTASIS –> regulates three fns:

Endocrine secretion = controls hormone release by pituitary gland

Autonomic Fn = integrates autonomic fn via direct projections to preganglionic autonomic neurons (brainstem and spinal cord)

Emotions and Drives = numerous interconnections with limbic system –> generates behaviors (rage, aggression, escape, etc)

Question 6

1) What are the 3 subdivisions of hypothalamus?
2) Which is the most important division and lies above optic chiasm?
3) name the 3 nuclei that comprise it? Describe fn
4) damage resutls in?

Answer 6

1) supraoptic region, tuber region and mamillary region
2) Supraoptic region
3) Supraoptic nucleus = produce ADH (regulate water excretion by kidney - conserve body water); axons –> post pituitary gland –> ADH released and enters blood

Paraventricular nucleus = produce mainly oxytocin (stimulate myometrial contractions –> parturition)

Suprachiasmatic nucleus = circadian rhythm role –> ability to maintain rhythm on 24hr cycle (body temp, [] of ACTH); connections with pineal gland and melatonin secretion

4) problems with urination, circadian rhythms and temp regulation

Question 7

1) Which hypothalamus subdivision lies directly above pituitary gland?
2) What does it contain?
3) What is narcolepsy a result of?
4) Which subdivision is the most caudal portion?
5) What is it comprised of?
6) What does damage lead to?
7) This region is a main target for what?

Answer 7

1) tuberal region
2) cells that produce orexins (hypocretins) –> control aspects of sleep
3) mutation in orexin receptor gene
4) mamillary region
5) mamillary bodies –> role in memory; assoc with limbic system (learning, paticularly recognition memories)
- thought to add element of smell to memories
6) amnesic syndrome (humans)
7) fornix of hippocampus

Question 8

1) What are the major afferent inputs to hypothalamus? Describe fn and route

Answer 8

1) Nucleus of solitary tract = collects all visceral sensory info from vagus nerve
2) Limbic system = via fornix

amygdala and olfactory cortex (piriform lobe) –> hypothalamus –> regulate behaviors such as eating and repro

3) Retina = via direct branches of optic nerve –> suprachiasmatic nucleus
4) Blood = intrinsic receptors of hypo (thermoreceptors and osmoreceptors) monitor temp and ionic balance
- hypo cells sensitive to hormone [] and glucose levels

Question 9

1) What are the major efferents from hypothalamus? Describe route
4) T or F: hypo can control every endocrine gland and can alter BP, temp and metabolism to maintain homeostasis

Answer 9

1) neural signals –> ANS via projectiosn to brainstem vagal nuclei and preganglionic nuclei in spinal cord
2) neural signals to limbic system (upset clients = overactive limbic system)
3) endocrine signals –> pituitary gland
4) True

Question 10

1) Where is pituitary gland located?
2) What comprises it?
3) Hypo controls endocrine system via what?
4) Describe them
5) What is the hypophyseal portal venous plexus?

Answer 10

1) beneath brain
2) 2 distinct parts: neural part - adenohypophysis (post pit.) and a glandular comp derived from oral epithelium - adenohypophysis (ant pit)
3) two routes: direct and indirect pathway
4) Directly - by secretion of neuroendocrine prdts into general circulation via vasculature of post pit gland (ADH and oxytocin)

Indirctly - by secretion or releasing factors into local hypophyseal portal venous plexus

5) vascualr plexus –> carriers RFs from base of hypo (eminence) –> ant pit –> controls release and synthesis of ant pit hormones (via transport of RFs)

Question 11

1) Give example of indirect hypothalamus control via hypophyseal protal venous plexus

Answer 11

1) RFs from hypo (TRH) –> Adenohypophysis (TSH) –> Thyroid (T3 and T4)

Question 12

1) What are 6 major fns of hypothalamus?

Answer 12

1) controls release of 8+ hormones by hypophysis
2) temperature regulation
3) control of food and water intaek
4) sexual behavior and reproduction
5) control of daily cycles in physiological state and behavior
6) mediation of emotional responses

Question 13

1) What are the direct effects on endocrine system from hypo?
2) Where is oxytocin produced?
3) What is its fn?

Answer 13

1) secretion of oxytocin and ADH into circulation
2) by neurons in paraventricular nuclei of hypo
3) -acts on uterine smooth m –> stim myometrial contractions and accelerates parturition
- Activates milk letdown reflex in response to suckling (stim contraction of myoepithelial cells in mammary gland)
- Acts on amygdala –> enhance bonding btw male and female once mated and btw mother and newborn

Question 14

1) What is ADH produced by?
2) What is its fn?
3) capillary density is highest where?
4) inc in what? stimulate release of what?

Answer 14

1) by neurons in supraoptic nucleus
2) inc reabsorption of water in kidneys –> dec urine production –> conserves body water
3) supraoptic nucleus
4) inc in blood osmolarity –> release of ADH

Question 15

1) What is diabetes insipidus?
2) what causes it?
3) its commonly assoc with what?
4) How to diagnose?
5) Tx?
6) Which pituitary comp secretes ADH and oxytocin?

Answer 15

1) disorder of water balance –> loss of control of water excretion due to a failure of production/transport/release of ADH into bloodstream from neurohypophysis
2) trauma or disease of pituitary or hypo
3) tumors of adenohypophysis which compress neurohypophysis
4) imagery of pituitary with + finding of tumor; water deprivation test –> animal unable to produce more concentrated urine as water intake is restricted
5) sx or intranasal, oral or SQ injection of desmopressin
6) neurohypophysis (post pit)

Question 16

1) What are the indirect effects on endocrine system from hypo?
2) What is Hyperadrenocorticoidism?
3) What are the symptoms?
4) Tx?

Answer 16

1) production and release of hypothalamic RFs –> stimulate or inhibit release of hormones from adenohypophysis (ant pit)
2) also called Cushing’s disease –> accompanies tunmors of adenohypophysis –> produce excess ACTH

***one of most common diseases of middle-aged/older dogs

3) -extremely hungry, poor hair coat (thinning, loss), obesity (bloated abdomen and potbelly due to inc in fat in abdomen, inc liver size, stretching abdominal wall), muscle weakness lethargy and lameness (excesss cortisol –> protein breakdown)
4) Sx to remove pituitary tumor; radiation to control tumor growthh; medication to destroy cortisol producing cells in adrenal cortex

Question 17

1) How does hypo control ANS?
2) What is the segregation of fn?
3) Ex of disease state

Answer 17

1) projects parasympathetic vagal nuclei and preganglionic sympathetic nuclei –> control autonomic fn –> HR, vasoconstriction, digestion, sweating ,etc
2) stimulate rostral hypo –> parasympathetic responses (dec HR)

stimulate caudal hypo –> sympathetic responses (inc HR, vasoconstriction)

3) alterations in CV fn as a result of abscesses of hypo (dec HR)

Question 18

1) What are the two temp reguation centers of hypo?
2) which one is the heat loss center?
3) How does it work?
4) Lesions cause?
5) Which one is the heat conservation center?
6) How does it work?
7) Leiosn cause?

Answer 18

1) rostral and caudal hypo
2) rostral hypo
3) warm blood –> antipyretic substances/impulses from heat receptors –> pantign, vasodilation and sweating –> red BT
4) hyperthermia
5) caudal hypo
6) cool blood –> pyrogenic substances/input from cold receptors –> shiver and vasoconstriction –> inc BT
7) hypothermia and disturbances in sweating mech

Question 19

1) how does hypo control water and food intake?
2) lesions cause?

Answer 19

1) controls body weight and appetite and water intake
2) cause abnormal eating and drinking behavior
- ventromedial hypo –> voracious appetite –> obesity
- lateral-most hypo –> loss of appetite –> anorexia