Neural Control of Motivational Behaviour

Question 1

What is the role of the lateral hypothalamus in hunger?

Answer 1

Hunger centre (relays information about the requirement for hunger)

Question 2

What is the role of the medial hypothalamus in hunger?

Answer 2

The periventricular nucleus lies here which is involved in stimulating satiety

Question 3

What may be a consequence of a lesion in the lateral hypothalamus?

Answer 3

Anorexia due to damage to the hunger centre

Question 4

What may be a consequence of a lesion to the medial hypothalamus?

Answer 4

Obesity due to damage to the satiety centre in the periventricular nucleus

Question 5

What are the internal stimuli involved in the control of feeding?

Answer 5

Stomach contractions (hunger pain), glucose, insulin, ghrelin and ,eptin levels as well as internal cues detected in the arcuate nucleus of the hypothalamus which projects information to the periventricular nucleus (satiety centre)

Question 6

Where is ghrelin produced?

Answer 6

Fundus of stomach and pancreatic cells

Question 7

What is the function of ghrelin?

Answer 7

Promotes eating by stimulating neurones in the arcuate nucleus which then project to the periventricular nuclei to inhibit neurones –> inhibits satiety and therefore encourages eating. Therefore ghrelin encourages eating

Question 8

What internal stimuli encourage feeding?

Answer 8

Ghrelin

Question 9

What internal stimuli discourage feeding?

Answer 9

Cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1)

Question 10

What is the function of cholecystokinin (CKK)?

Answer 10

CCK released into blood (made in small intestine epithelia) and travels to hypothalamus –> acts on cells of arcuate nucleus to produce satiety

Question 11

What causes the release of pancreatic enzymes and bile?

Answer 11

CCK release from the small intestine epithelia

Question 12

What is the function of glucagon-like peptide 1 (GLP-1)?

Answer 12

Hormone released as consequence of food in the gut and acts on arcuate cells to produce satiety and also stimulates insulin secretion

Question 13

How does ghrelin work to encourage feeding?

Answer 13

Ghrelin stimulates NPY/AGRP neurones in ventromedial arcuate nucleus; this inhibits satiety centre and stimulates eating.

Question 14

How do CCK, GLP-1 and leptin work to discourage feeding?

Answer 14

CCK, GLP and leptin stimulate POMC (MSH) neurones in dorsolateral arcuate nucleus; this stimulates satiety centre and inhibits eating

Question 15

Where is the subfornical organ located?

Answer 15

Wall of the 3rd ventricle in the hypothalamus

Question 16

Describe the role of the subfornical organ in thirst

Answer 16

Osmoreceptors are present which detect the osmolarity of the blood, the organ then projects to the medial preoptic nucleus and is connected to the limbic system to regulate sense of thirst but also activates the cells of the paraventricular nucleus and supraoptic nucleus to cause the release of ADH to reduce urine flow and prevent greater osmolarity developing

Question 17

Where is the supraoptic nucleus located?

Answer 17

Above the optic chiasm

Question 18

Where is the paraventricular nucleus located?

Answer 18

Around the 3rd ventricle

Question 19

How does ADH reduce water loss in urine?

Answer 19

Via aquaporins, increased reabsorption of urea and increased sodium reabsorption (so water follows)

Question 20

What is the dentate/pectinate line?

Answer 20

Where the rectum joins the anal canal

Question 21

Describe the internal anal sphincter

Answer 21

A ring of smooth muscle (involuntary) which surrounds the anus (sympathetic efferents maintain the contraction of this ring tonically)

Question 22

Describe the external anal sphincter

Answer 22

Ring of skeletal (voluntary) muscle surrounding the internal anal sphincter

Question 23

How is continence ordinarily maintained?

Answer 23

By the tonic contraction of the internal anal and external anal sphincters

Question 24

How does the body inform us that we need to defecate?

Answer 24

When foecal matter enters rectum from sigmoid colon –> stretches rectal walls –> activates stretch receptors –> afferents synapse on dorsal horn of sacral spinal cord –> spinothalamic tract –> genital area of somatosensory cortex –> conscious awareness of need to defecate

Question 25

Describe the ano-rectal reflex

Answer 25

The internal anal sphincter relaxes due to inhibition of sympathetic nerves which innervate it. The pressure increases on the external anal sphincter (faecal matter) which stimulates stretch receptors in the perianal tissue and triggers the urge to defecate

Question 26

What happens if someone consciously decides not to defecate?

Answer 26

Voluntary effort increases contraction of external sphincter and puborectalis muscle, and rectal afferents adapt to stretch and stop firing (acclimatization). The anorectal reflex ceases and the internal anal sphincter muscle contracts again (due to re-established sympathetic stimulation), which reinforces the external anal sphincter

Question 27

What happens during defecation?

Answer 27

Involves parasympathetic reflexes and the individual allows the external sphincter to relax (voluntarily), and the movement of the faeces downwards in the rectum reduces the stretch of the upper aspect of the rectum. This decreased stretch causes an increase in smooth muscle contraction above the faecal matter to propel the faeces downwards by peristalsis.

Question 28

Define ‘diuresis’

Answer 28

Production of urine by the kidney

Question 29

What is the trigone?

Answer 29

neck of the bladder

Question 30

Define ‘micturition’

Answer 30

The ejection of urine from the urinary bladder through the urethra to the outside of the body

Question 31

What is the innervation to the internal urethral sphincte and detrusor muscle of the bladderr?

Answer 31

Sympathetic efferents via the hypogastric nerve

Question 32

Neurologically, what happens during filling and storage of urine in the bladder?

Answer 32

Internal urethral sphincter stimulated to maintain tonic contraction (mediated by adrenergic alpha 1 receptors) and detrusor muscle stimulation by sympathetic efferents tonically inhibit contraction (inhibitory action mediated by adrenergic B3 receptors)

Question 33

What receptors are present in the internal urethral sphincter?

Answer 33

Adrenergic alpha 1 receptors which cause excitatory action to the muscle when stimulated by sympathetic efferents

Question 34

What receptors are present in the detrusor muscle of the bladder?

Answer 34

Adrenergic beta 3 receptors, which cause inhibitory action to the muscle when stimulated

Question 35

How does the body inform us that we need to urinate?

Answer 35

As bladder fills –> walls stretched –> activates afferents in pelvic nerves –> spinothalamic tract –> genital somatosensory cortex –> perception of bladder fullness

Question 36

What happens if the conditions aren’t appropriate for urination when necessary?

Answer 36

individual tightens the external urethral sphincter (voluntary muscle).

Question 37

What stimulates the micturition reflex?

Answer 37

When conditions are appropriate to urinate, a signal is sent from forebrain –> pons (micturition centre AKA Barrington’s nucleus) –> activates micturition reflex

Question 38

Describe the micturition reflex

Answer 38

Micturition centre in pons activates descending fibres in reticulospinal tract –> inhibit sympathetic and osmatic outputs to internal and external urethral sphincters –> activates parasympathetic efferents –> stimulates detrusor muscle –> bladder contracts –> urine flows out of urethra –> positive feedback to continue detrusor contraction

Question 39

What does the contraction of the detrusor muscle of the bladder involve?

Answer 39

A parasympathetic reflex that is mediated by muscarinic receptors (M3)