intro to neuro - exam ii

homeostatic systems

use our behavior to keep things balanced

negative feedback

maintain homeostatic mechanisms if a desired set point is deviated from, compensatory action begins

hypovolemic thirst

stimulated by low extracellular/intravascular volume

triggered by loss of water VOLUME, concentration is NOT changed. Baroreceptors in blood vessels and heart detect the initial drop. brain activates thirst and salt craving. arteries constrict to raise BP.

osmotic thirst

stimulated by high extracellular solute concentration.

hypovolemia

release of vasopressin (antidiuretic hormone). constricts blood vessel and so reduces blood flow to bladder.

what occurs in diabetes insipidus?

vasopressin is not produced - kidneys send more urine to the bladder resulting in the chronic thirst

pituitary adenoma

benign tumor of pituitary gland due to secretion of too much vasopressin

angiotensin cascade

if blood volume decreases, kidneys release renin which trigger formation of angiotensin ii

what happens if vasopressin secretion is low?

low blood pressure constriction resulting in being more thirsty

what happens if vasopressin secretion is high?

high blood pressure constriction resulting in not being very thirsty

what are the effects of the release of angiotensin ii?

1. blood vessels constrict raising blood pressure
2. brain triggers drinking
3. vasopressin is released


1. aldosterone is released

where does angiotensin ii act in order to initiate drinking?

angiotensin ii acts in the SUBFORNICAL ORGAN to signal other brain sites to initiate drinking.

osmotic thirst

if you intake salt such as eating potato chips; in the cell water can pass semipermeable membrane but salt cannot causing the cells to shrink and blood concentration to increase

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OSMOSENSORY neurons in anterior hypothalamus (OVLT) respond to rise in blood osmotic pressure. their cell membranes shrink and open mechanical-gated Na channels

how do OVLT neurons respond to increased osmotic pressure?

They cause the pituitary to release antidiuretic hormone.

at the start of a diet, why does basal metabolic rate fall?

to prevent losing weight

basal metabolic rate

energy required to fuel the brain/body and maintain temperature. 75% of energy expenditure in average sedentary student.

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avg 1/3 of women who failed to lose weight had LOW BMRs

heredity accounts for 40% of a person’s BMR but ACTIVITY can INCREASE it

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regular exercise - converts fat to muscle - more muscle speeds up basal metabolism - faster metabolism burns more calories - weight loss/natural weight control

glucose is the _____

principal fuel for energy

glycogen is ______

glucose stored for short term in the liver

glycogenesis ______

converts glucose to glycogen using pancreas hormone INSULIN

lipids are ______

used for long-term storage, are fat tissue

brain integrates ____ __and__ ______ levels w/ other signals to decide when to stop/start eating

insulin and glucose

what do fat cells produce and secrete into the bloodstream?

leptin

what can defects or sensitivity in leptin production cause in animals?

it can give a FALSE low report of body fat causing animals to OVEREAT

obese people = leptin-resistant

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over-nutrition INFLAMES hypothalamus - (obesity/diabetes/heart disease)

ghrelin

appetite stimulant

where is ghrelin released?

released by stomach/gut endocrine cells

when does ghrelin rise and drop?

rises during fasting; drops after eating

prader-willi syndrome

genetic disease that causes a sense of never being full or satisfied. ghrelin levels are elevated.

hypothalamus is the ____ control center

hunger

lateral hypothalamus

lesions - refusal to eat

ventromedial hypothalamus

lesions cause obesity

what do ventromedial animals do?

the animals overeat until they become obese and this increased weight stabilizes. this new weight is then maintained even after food challenges.

what do lateral hypothalamus animals do?

these animals stop eating but resume and stabilize their weight at a new, lower level

what are the two types o neurons in the hypothalamus?

NPY/AgRP (pro-appetite) & POMC/CART (anti-appetite)

NPY/AgRP neurons

produce neuropeptide Y and agouti-related peptide - stimulate appetite and LOWER metabolism = weight GAIN

POMC/CART

produce pro-opiomelanocortin and cocaine - inhibit appetite and RAISE metabolism = weight LOSS

how does overeating cause brain damage?

overeating - hypothalmic inflammation - inhibits neurogenesis, resets your set point

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high-calorie diets cause HYPOTHALMIC SCARRING and MICROGIAL ACTIVATION and fewer POMC neurons (which are normally activated by leptin to block eating and increase energy expenditure)

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but brain can recover, if overeating stops - newborn hypothalmic cells can become POMC neurons

anorexia nervosa

restricting or binge-eating/purging type, refusal to maintain body weight, fear of weight gain, body image disturbance

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other sx - thinning of bones, brittle hair/nails/yellow skin, mild anemia, severe constipation, low BP, drop in body temp, amenorrhea (HYPOTHYROIDISM)

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HIGHEST mortality rate of any psychiatric disorder

bulimia

recurrent binge eating, recurrent inappropriate compensatory behavior, at least 2x/week for three months, purging - making themselves throw up

teen girls with anorexia have a ___ __insula and__ ______ orbitofrontal cortex

larger; larger

larger insula - active when you experience disgust

larger orbitofrontal cortex - area that tells you ‘you shouldn’t do that’

how do we treat obesity?

EAT LESS = daily defecit of 200 cal is good. this is the MOST IMPORTANT part and most difficult. eat until hungry then stop. lifestyle change for YEARS. self-monitoring/social support = ESSENTIAL

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EXERCISE MORE = a LOT. strenuous activity over 200 minutes per week for a long time with calorie restriction works. not just walking.

gastric bypass surgery

weight loss avg 25% and is long-lasting; reduces ghrelin and increases PYY and GLP-1 reducing hunger

surgical creation of a tiny stomach

how does the stress response activate?

it activates the sympathetic nervous system via hypothalmic control

what does the adrenal cortex secrete?

cortisol

what is cortisol?

stress hormone that increases blood glucose and breaks down protein

what does the adrenal medulla release?

epinephrine and norepinephrine

hypothalamus and pituitary stimulate the adrenal glands to release

epinephrine, norepinephrine, and cortisol

what does epinephrine, norepinephrine, and cortisol do during acute stress?

epinephrine and norepinephrine = increase output from heart and liberate glucose

cortisol = provide sustained release of energy to cope

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results in boosted immune system

what do stress hormones stimulate?

they stimulate astrocytes to release fibroblast growth factor 2 leading to the formation of new neurons

how can chronic stress be harmful?

interferes w/ memory, appetite, sexual desire and performance

depletes energy and disrupts mood

increases body inflammation

compromises the immune system

what hormones are released during the chronic stress suppress immune system?

DAMPs - danger/damage-associated molecular patterns

what is the process of DAMPs during chronic stress?

1 - at rest miRNAs balance out DAMPs

2 - acute stress = adrenaline and norepinephrine cause immune cells to release DAMPs

3 - after stress = balance is restored by cortisol

4 - chronic stress = low-grade excess production od DAMPs or block of miRNAs

when stressed we revert to our ________

primitive survival brain

post traumatic stress disorder

develops in response to a stressful event of exceptionally threatening or catastrophic nature (assault/car wrecks/rape)

what are sx of PTSD?

re-experiencing (flashbacks/nightmares), avoiding people or situations associated w event, hyper-arousal symptoms (panic)

what is the treatment for PTSD?

behvaioral desensitization, ecstacy

what is the natural course of PTSD?

many recover without treatment within months/years of treatment (50% natural remission by 2 years) but may have significant impairment of social/occupational functioning. treatment means -20% more people w PTSD recover. generally 33% remain symptomatic for 3 yrs + w/ greater risk of secondary problems

how does stress lead to damage in the brain?

the frontal cortex and hippocampus volume is reduced in combat veterans w PTSD and in victims of childhood abuse. cortical tissue is reduced in torture victims.

damage due to stress is caused by?

cortisol resulting in increased receptor sensitivity

how does social/personality influence affect physioogy?

introverts w/ HIV have higher virus titers than extroverts with HIV. possibly due to link between introversion and norepinephrine level; NE level higher in introverts which blocks the immune system

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married adults have lower cortisol levels than never-married or previously married people

what are some buddhist coping strategies for stress?

meditation, mindfulness, lovingkindness, morality, and impermanence

what system helps resilience during and/or after stress?

ecB system.

what synthesis does chronic stress (cortisol) impair?

2-AG synthesis

habituation to stress is due to _____

increased eCB system activity

biology of aggression

behavior intended to harm

reactive aggression

impulsive, provoked, emotional

proactive aggression

premeditated, unprovoked, emotionless

how does the amygdala relate to aggression in people?

aggressive men/women have a small amygdala. seizure activity in amygdala increases aggression.

murderers have higher activity of the amygdala and hypothalamus. removing the amygdala reduces aggression in 33-100% of patients.

in aggressive teens, areas of brain linked w feeling good AMYGDALA AND STRIATUM become active when they watch pain inflicted on others

reactive aggressors

lower activity in prefrontal cortex, behave recklessly, overreact to provocation, and are sexually promiscuous; e,g, road rage

proactive aggressor

associated w psychopathy. they have less autonomic response to stress, impaired amygdala function, ex. boston bombers

sociopaths

incapable of remorse - may commit very violent acts

where does all sensory processing begin?

receptors cells

a stimulus to the receptor produces a _________. if the potential is big enough, the receptor generates as__ ________.

graded potential; action potential

coding

patterns of action potentials in a sensory system

what are the three ways a stimulus can be encoded?

1 - a single neuron can convey stimulus intensity by changing the FREQUENCY of its action potentials

2 - MULTIPLE neurons can act in parallel - as the stimulus strengthens, more neurons are recruited

3 - Different neurons respond to different ranges (range fractionation)

range fractionation

different cells have different thresholds for firing over a range of stimulus intensities

somatosensory system detects

pain and touch

what are the five touch receptors?

free nerve endings (pain/temp)

merkel’s disc (touch)

meissner’s corpuscle (touch)

pacinian corpuscle (vibration)

ruffini’s ending (stretch)

what pathway do temperature receptors use?

pain. pathway

what neurons does pain use?

small unmyelinated (slow) C fibers = dull pain

large myelinated (fast) A-delta fibers = sharp pain

TRPV is the

spice of life

capsaicin

melts body fat, slows atherosclerosis, lowers BP, fights diabetes, lowers body weight

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the “hot” in chilies, activates C fibers via TRVP1 and is neurotoxic

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banned in equestrian sports - hypersensitive horses are more motivated to jump hurdles

vibration perception

\-pacinian corpuscle, unipolar cell, dorsal root ganglion, mechanically gated

what are the two parallel touch systems?

tonic and phasic receptors - sensory cortex is organized this way too

tonic receptors

slow or no decline in action potential frequency

phasic receptors

adapt quickly by decreased frequency

receptive field

part of the world sensory neurons respond to, property of each single sensory neuron, differ in size and shape

touch receptive fields

put an electrode in ONE neuron in sensory cortex and poke around on skin until you find spot that makes that neuron fire, on-center and off-surround

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touch in center = maximal firing

touch in surrounding = decreased firing

touch far away = no effect

most sensory pathways pass through the _______ to end in sensory cortex

thalamus

what are the two parallel tactile systems?

one for touch and vibration = dorsal column

one for pain and temperature = spinothalmic

somatosensory cortex - the homunculus

cortical map represent the innervation of a body region; larger body regions have smaller areas and vice versa

what happens after amputation occurs in the brain?

the somatosensory cortex reorganizes

what are the three different perceptions of pain?

cognitive system, motivational-affective system, and sensory-discriminative system

cognitive system - pain perception

‘men don’t cry‘ - linked with behavior and acting an appropriate way when in pain

WILL - frontal cortex

motivational affective system - pain perception

motor response mechanism. attention is directed elsewhere. for example, breaking your wrist in the middle of the game but not noticing until after the game is over

EMOTION - anterior cingulate cortex

sensory-discriminative system - pain perception

can verbally describe pain, ex. “my broken wrist hurts”

SENSORY - somatosensory cortex

free nerve endings

origin of pain. nerve endings in skin have specialized receptors to respond to temperature change, chemicals, and tissue energy

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note especially substance P - a neurotransmitter

congenital insensitivity to pain

inherited mutated sodium channel in pain fibers in dorsal root ganglia

cause pts to not notice pain, ex. baby w this chews on fingers but doesn’t notice and proceeds to chew fingers off

man on fire

congential hypersensitivity to pain - severe burning pain, erythema, triggered by mild warmth, autosomal dominant

how does pain helps us in everyday life?

low levels of pain during everyday tasks tell us when a certain movement or prolonged posture is harmful. even during sleep, mild pain makes us toss and turn enough to prevent bedsores or skeletal strain.

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ex. a woman w pain insensitivity developed progressive degeneration of her joints and spinal vertebrate causing skeletal deformation/infection eventually leading to death

spinothalmic system transmits

pain and temperature