Chemical control of brain and behaviour Flashcards
What are the 3 components of the nervous system that operate in expanded space and time?
-secretory hypothalamus –> directly secrete chemicals into the bloodstream.
-autonomic nervous system –> controlled neurally by the hypothalamus, ANS simultaneously controls the responses of many internal organs, blood vessels and glands
-The third component exists throughout the entirety within the CNS and consists of several related cell groups that differ with respect to the transmitter they use. All these cell groups extend their spatial reach with highly divergent axonal projections and prolong their actions by using metabotropic postsynaptic receptors. –>members of this component of the NS are called the diffuse modulatory system of the brain –> diffuse system regulates level of arousal and mood
where does the hypothalamus sit? and size
Below the thalamus, along the walls of the third ventricle. –> connected by a stalk to the pituitary gland which dangles below the base of brain, just above mouth
makes up less than 1% of brains mass
what does the hypothalamus integrate?
-somatic and visceral responses in accordance with the needs of the brain
-a lesion in hypothalamus –> disruptions of widely dispersed bodily functions
what is homeostasis with respect to the hypothalamus?
-the maintenance of the body’s internal environment within a narrow physiological range –> hypothalamus regulates these levels
what are the functional zones of the hypothalamus?
-each side has 3 functional zones:
-lateral, medial and periventricular
describe the connections of the functional zones of hypothalamus
the lateral and medial zones have extensive connections with the brainstem and the telencephalon and regulate certain types of behaviour, the periventricular zone receives much of its input from the other 2 zones
where does the periventricular zone of the hypothalamus lie?
-lie right next to the wall of the third ventricle
what cells groups constitute the periventricular zone of the hypothalamus?
-suprachiasmatic nucleus (SCN) –> lies just above the optic chiasm –> these cells receive direct retinal innervation and function to synchronize circadian rhythms with daily light-dark cycle
-other cells in this zone control the ANS and regulate the outflow of the sympathetic and parasympathetic innervation of the visceral organs
-the third group, called neurosecretory neurons, extend axons down toward the stalk of the pituitary gland –> command our attention
describe the pituitary gland in a living brain
-in a brain lifted out of the head, pituitary gland dangles below the base of the brain
-in a living brain pituitary gland is held in a cradle of bone at the base of the skull
why does the pituitary gland require this level of protection ?
it is the “mouthpiece” from which much of the hypothalamus “speaks” to the body
what are the lobes of the pituitary gland?
posterior and anterior –> hypothalamus controls the 2 lobes in different ways
describe the magnocellular neurosecretory cells of the hypothalamus
-largest of the hypothalamus neurosecretory cells
-extend axons down the stalk of the pituitary gland and into the posterior lobe
- (ernst and Berter Scharrers) –> these neurons release chemical substances directly into the capillaries of the posterior lobe –> the substances releases into the blood by neurons are called neurohormones.
what do the magnocellular neurosecretory cells release?
-two neurohormones into bloodstream, oxytocin and vasopressin
describe oxytocin
-peptide containing a chain of 9 amino acids
-levels rise during sexual or intimate behaviours and promote social bonding
-crucial role during final stages of childbirth by causing uterus to contract and facilitating delivery of newborn –>also stimulates ejections of milk from mammary glands
describe vasopressin (aka antidiuretic hormone (ADH))
-peptide containing a chain of 9 amino acids
-regulates blood volume and salt concentration
-when body is deprived of water, the blood volume decreases and blood salt concentration increases –> these changes are detected by pressure receptors in the cardiovascular system and salt concentration-sensitive cells in the hypothalamus, respectively
-vasopressin-containing neurons received information about these changes and respond by releasing vasopressin, which acts directly on the kidneys and leads to water retention and reduced urine production
under conditions of lowered blood volume and pressure, communication between brain and kidneys…
occurs in both directions
what happens when there is low blood pressure?
Kidneys secrete an enzyme into the blood called renin. Elevated renin sets off a sequence of biochemical reactions in the blood. Angiotensinogen, a large protein released from the liver, is converted by renin to angiotensin I, which breaks down further to form another small peptide hormone, angiotensin II. Angiotensin II has direct effects on the kidney and blood vessels, which help increase blood pressure.
describe angiotensin II and subfornical organ
angiotensin II in the blood is also detected by the subfornical organ, a part of the telencephalon that lacks a blood-brain barrier. Cells in the subfornical organ project axons into the hypothalamus where they activate, among other things, the vasopressin-containing neurosecretory cells. In addition, the subfornical organ activates cells in the lateral area of the hypothalamus, somehow producing an overwhelming thirst that motivates drinking behaviour.
what part of the pituitary is the gland?
anterior lobe is the actual gland
what does the anterior lobe of the pituitary gland do?
Synthesize and secrete a wide range of hormones that regulate secretions from other glands throughout the body –> together constituting the endocrine system
what does the pituitary hormones act on?
gonads, thyroid glands, adrenal glands and mammary glands
what controls the anterior pituitary?
the secretory hypothalamus, under the control of neurons in the periventricular area called parvocellular neurosecretory cells.
–anterior pituitary was traditionally describe as body’s “master gland” –> but anterior pituitary controlled by hypothalamus so hypothalamus is true master gland of the endocrine system
how does the neurons in the periventricular area of the hypothalamus communicate with the anterior lobe?
-the parvocellular neurosecretory cells of the periventricular area do not extend all the way down into the anterior lobe, instead communicate with their targets via the bloodstream
-these neurons secrete what are called the hypophysiotropic hormones into a uniquely specialised capillary bed at the floor of the third ventricle
-these tiny blood vessels run down the stalk of the pituitary and branch in the anterior lobe –> this network of blood vessels is called the hypothalamo-pituitary portal circulation
-hypophysiotropic hormones secreted by the hypothalamic neurons into the portal circulation travel downstream until they bind to specific receptors on the surface of pituitary cells –> activation of these receptors causes the pituitary cells to either secrete or stop secreting hormones into the general circulation
Where are the adrenal glands located and what do they consist of?
-located above the kidneys
-consist of two parts, a shell called the adrenal cortex and a centre called the adrenal medulla
what does the adrenal cortex produce?
a steroid hormone, cortisol
what happens when cortisol is released into bloodstream?
-cortisol acts throughout the body to mobilise energy reserves and suppress the immune system, preparing us to carry on in the face of life’s various stresses
what is a good stimulus for cortisol release?
-stress, ranging from physiological stress, such as a loss of blood, to positive emotional stimulation, such as falling in love; to psychological stress, such as anxiety over an upcoming exam
What cells determine whether a stimulus is stressful or not?
-parvocellular neurosecretory cells that control the adrenal cortex determine whether a stimulus is stressful or not –> as defined by the release of cortisol
where do parvocellular neurosecretory cells lie?
-in periventricular hypothalamus
what do parvocellular neurosecretory cells release?
a peptide called corticotropin hormone (CRH) into the blood of the portal circulation
where does CRH travel to after being secreted into the portal circulation by the parvocellular neurosecretory cells?
-travels the short distance to the anterior pituitary, where, within about 15 seconds, it stimulates the release of corticotropin, or adrenocorticotropic hormone (ACTH)
what happens after ACTH is released?
ACTH enters the general circulation and travels to the adrenal cortex where, within a few minutes, it stimulates cortisol release
describe cortisol in blood
-blood levels of cortisol are, to some extend, self-regulated
-cortisol is a steroid, a class of biochemicals related to cholesterol –> is a lipophilic (“fat-loving”) molecule, which dissolves easily in lipid membrane and readily crosses the blood-brain barrier
How does the brain ensure cortisol levels don’t get to high?
in the brain cortisol interacts with specific receptors that lead to inhibition of CRH release, thus ensuring that circulating cortisol levels don’t get too high
describe prednisone
-synthetic form of cortisol
-frequently used to suppress inflammation, but when administered for several days, the prednisone circulating in the bloodstream fools the brain into thinking that naturally release levels of cortisol are too high and shutting down the release of CRH and the adrenal cortex
what happens when there is an abrupt discontinuation of prednisone?
-does not give the adrenal cortex enough tie to ramp up cortisol production and can thus result in what is called adrenal insufficiency
describe adrenal insufficiency
-can occur as a result of abrupt cessation of prednisone
-among the symptoms of adrenal insufficiency are severe abdominal pain and diarrhoea, extremely low blood pressure, and changes in mood and personality.
-feature of rare disorder called Addison’s disease –> degeneration of adrenal gland
What is Cushing’s disease?
-pituitary gland dysfunction that results in elevated levels of ACTH and consequently, cortisol.
-symptoms include rapid weight gain, immune suppression, sleeplessness, memory impairment, and irritability.
-symptoms of Cushings disease is common side effects for prednisone treatment
