Neuroscience Flashcards
Define “Hypothalamus”
= Small structure at the base of the brain, made up of many different nuclei which control diff. bodily functions (they all talk to each other)
- integration of autonomic, endocrine, behavioural responses for homeostatic regulation of internal environment for adaptation to continuously changing external environment
- master controller of ANS
- beneath the thalamus, connected to pituitary gland (just above the pituitary) –> Posterior pituitary is part of the hypothalamus!!
- extends from near the optic chasm to the mammillary bodies
Functions of the hypothalamus
1) Control of ANS
2) Neuroendocrine control
3) Reproductive
4) H2O Balance/exchange
5) Sodium balance/exchange
6) Body energy balance/exchange
7) Drive and emotions
8) Circadian rhythms
9) Body temperature regulation
Major Function of the
SUPRAOPTIC NUCLEUS
Water balance
Major Function of the
SUPRAOCHIASMATIC NUCLEUS
Biological Clock
Major Function of the
VENTROMEDIAL NUCLEUS
Satiety
Major Function of the
PARAVENTRICULAR NUCLEUS
Water balance, stress, feeding
- works with lateral for feeding functions, but takes a bit more time
Major Function of the
LATERAL NUCLEUS
Feeding centre
- works with the paraventricular nucleus
Major Function of the
PREOPTIC/ANTERIOR HYPOTHALAMIC REGION
Blood pressure, Body temperature
(Vasodilation = PNS)
- 2 nuclei
Major Function of the
POSTERIOR HYPOTHALAMUS
Blood pressure, Body temperature
Vasoconstriction = SNS
Major Function of the
BASOMEDIAL HYPOTHALAMUS
Anterior/Posterior Pituitary Releasing Factors
Effect of stimulation of the Posterior Hypothalamus?
–> Sympathetic (fight or flight)
- INCREASES Blood Pressure
- INCREASES Heart Rate
- DECREASES Gastrointestinal motility
- DILATES Pupils (therefore, see more)
Effect of stimulation of the Anterior Hypothalamus?
–> Parasympathetic (rest and digest)
- DECREASES blood pressure
- DECREASES heart rate
- INCREASES gastric motility
- CONSTRICTS pupils
How do the supraoptic and paraventricular nuclei interface with the pituitary gland?
Through the axon terminals of both nuclei (this is how hormones are transported)
What hormones are produced in the hypothalamus and released directly into circulation? Which nuclei produces the hormones?
Oxytocin (paraventricular nuclei)
ADH (supraoptic nuclei)
The _______ hypothalamus secretes _________, which reach the __________ ________ gland via the _____________.
The basomedial hypothalamus secretes releasing hormones, which reach the anterior pituitary gland via the hypophyseal portal system.
What is a neural-humoral reflex?
An example?
Neural input/stimulus –> activates neural system –> hormone release in system
i.e. oxytocin = positive feedback system
3 main stimuli known to elicit thirst and the release of vasopressin (ADH)?
- low ECF
- low Osmolarity
- low Arterial blood pressure
How is water loss regulated?
- multiple initial stimuli stimulate the decrease in ECF and decreased arterial BP –> causes a change in the left atrial stretch receptors
- this signal sent to hypothalamus, stimulates hypothalamic neutrons
- vasopressin release from pituitary (anterior –> pituitary)
- causes arteriolar vasoconstriction (relieves arterial BP)
- increases H2O permeability in distal/collecting tubes
which increases H2O reabsorption and decreased
urine output –> increase plasma vol. (relieves low ECF)
How is water intake controlled?
- INCREASED osmolarity
- stimulates hypothalamic osmoreceptors
- this stimulates hypothalamic neutrons
- increases thirst
- drink water –> DECREASES (relieves) plasma osmolarity
Define “obesity”
Having abnormal/excessive fat accumulation that presents a risk to an individual’s health
What is BMI?
Body Mass Index = Mass/(Height^2) = kg/metres^2
- obese = BMI ≥ 30
- tells us how at risk we are for developing certain diseases/illnesses
- problem = doesn’t take into account muscle mass (therefore, it’s a crude measurement)
- now we look at waist:hip ratio instead
Why do we eat and over-eat?
Genetic Changes + Lifestyle Factors + Physiological Signals
We overeat due to lifestyle factors and social habits
we override physiological signals
What are lifestyle factors that contribute to food intake?
- taste and smell permeability
- availability
- clock
- cues and social habits
Your “COGNITIVE AND EMOTIONAL BRAIN”
What are genetic changes that contribute to food intake?
= changes in genes that make you want to eat (can’t control!!)
- epigenetic = gene expression changed
- imprinting
Your “COGNITIVE AND EMOTIONAL BRAIN”
What are physiological signals that contribute to food intake?
= parts in your body that provide signals telling you to eat/not eat; often overrided
Energy Balance = Energy Intake - Energy Expenditure (aim for this to be 0)
Your “METABOLIC BRAIN”
What is Leptin?
= hormone produced by fat cells (adipose tissue) = a satiety signal
- main physiological signal for food intake
- lot of fat = produce a lot of leptin = signals hypothalamus, resulting in … decreased food intake, increased expenditure, increased blood pressure
- high levels activate arcuate nucleus, a satiety centre
- low levels activate lateral + paraventricular nuclei, feeding centre
What’s the function of Orexin?
- when it’s present, it causes an INCREASE in appetite
- housed in Lateral Hypothalamic Nucleus
- orexin release is inhibited by excess leptin
What’s the function of NPY?
- it’s release is inhibited with high leptin levels
- causes an increase in food intake
What’s the function of POMC?
- Activated with high leptin levels –> releases alpha-MSH
- causes increased energy expenditure and inhibits food intake
What’s the function of the paraventricular nucleus in regards to food intake?
- part of the feeding centre
- directly increases hunger by increasing energy expenditure once alpha-MSH binds to its MC4-R
What’s the function of the dorsomedial hypothalamus in regards to food intake?
- responds to NPY
- Low leptin levels cause activation of this pathway –> NPY binds to NPY-R –> stimulates dorsomedial hypothalamus –> increases food intake
What’s the function of the lateral hypothalamus in regards to food intake?
- part of the feeding centre
- releases orexin in response to low leptin
What is Metabolic Syndrome?
= group of conditions that puts you at higher risk for developing type 2 diabetes, heart diseases, other heart problems
If you have 3 OR MORE of…
- high fasting blood glucose levels
- high blood pressure
- high level of triglycerides
- low levels of HDL
- abdominal obesity (too much fat around your waist)
- -> the more of the conditions you have = higher risk of developing the diseases
- -> unsure what causes metabolic syndrome (maybe related to insulin resistance? Genetic, old age, lifestyle also plays a role)
What are the end points when a person starts this metabolic syndrome disease process?
Diabetes, hyperlipidemia, hypertension
–> Atherosclerosis
High risk of stroke and cardiac arrest
What % of global health care used towards alleviation of metabolic syndrome?
75%
What is Anorexia Nervosa?
= psychological disorder where you see yourself as heavier than you really are
- BMI
What is Bulimia Nervosa?
= psychological disorder involving binge eating and then throwing it up (purging) to maintain a certain image
- involves both frontal cortex and limbic system
What are Circadian Rhythms?
= natural pattern of physiological/behavioural processes that are timed to a near 24hr period
- drive by natural dark-light cycles, but will persist under constant environmental conditions
- controlled by SUPRACHIASMATIC Nucleus (biological clock) –> controls melatonin release
- LED lights alter cycle by tricking the system, it suppresses melatonin levels leading to decreased ability to fall asleep
Examples of circadian rhythms
- Sleep
- Food/H2O Intake
- Urine production
- most at bed, also when you wake up
- Blood pressure
- highest in the AM, rises until noon, decreases @ 6-7pm
- Platelet aggregation
- platelets come together at night
- White blood cell production
- Body temperature changes
- during the day
- Hormone release
- corticosterone (cortisol), LH, melatonin
- Menstrual cycle
- longer cycle
Define Thermoregulation
= homeostatic regulation of normal body temp within narrow limits
Heat Input + Heat Production = Heat Loss
What are the 4 ways that heat can be produced? Which is the most effective?
- METABOLIC ACTIVITY = heat byproduct from any biochemical reaction
- NON-SHIVERING THERMOGENESIS = hormonal release (T3/T4) that causes an increase in heat production, without muscle contractions
- MUSCLE ACTIVITY = generates heat when you work out
- SHIVERING = involuntary rhythmic muscle contractions
- –> most efficient way!!
What are the main heat loss mechanisms? What’s the % breakdown?
- Convection (35%)
- Radiation (34%)
- Evaporation (27%)
- Conduction (1%)
What is RADIATION?
= transfer of heat energy as EM waves
What is CONDUCTION?
= transfer from warmer to cooler object through direction contact
- heat transferred through movement of thermal energy from molecule to adjacent molecule
- not very effective
What is CONVECTION?
= transfer of heat energy by air currents
- used to cool ourselves down, transfer of warmth to the air molecules around you
- cool arm warmed by body via conduction rises, and is replaced by more cool air
What is EVAPORATION?
= conversion of liquid (sweat) into gaseous vapour
- helps cool us down
- brings fluid to surface of body via sweat glands (active process)
- process requires heat, which is absorbed from the skin
What are thermoreceptors?
= sensory receptors that detect absolute and relative changes in temperature
- unmyelinated nerve endings
- detect relative changes in hot or cold within a range
What are the two types of thermoreceptors? Where are they located?
- Warm Receptors –> Dermis
2. Cold Receptors –> Dermis (located deeper within)
Internal environment factors/actions and external environment factors/actions that interact in the
Physiological Response to the Cold
- REGULATION OF ENDOCRINE SECRETION
- Hypothalamus detects fall in the temperature
- releases TSH-RH (thyroid stimulating hormone releasing hormone)
- TSH-RH acts at the anterior pituitary to increase TSH secretion
- TSH stimulates thyroid to release thyroxine (hormone)
- thyroxine acts act cells to increase basal metabolic rate –> increases heat production + temperature - REGULATION OF ANS ACTIVITY
- Hypothalamus detects fall in temp., stimulates SNS
- leads to constriction of blood vessels in skin –> less blood will flow to skin –> reduces heat loss
- increased SNS activity stimulates shivering (piloerection in animals) –> increases heat production/reduces heat loss - REGULATION OF EMOTIONS/MOTIVATED BEHAVIOUR
- cold is a stimulus for goal directed, motivated behaviours (seeking shelter, turning up thermostat, putting on sweater)
- lead to reduced heat loss
What the “hypothalamic set point mechanism”? What is the set-point temperature?
= a genetically determined value that is present from brith
37˚C
What is the effect of stimulation of the POSTERIOR hypothalamus on Temperature regulation?
Posterior = heat promoting/heat-loss centre
- responsible for activating sweat glands and dilating blood vessels when hot
- activating skeletal muscles and constricting blood vessels when cool
What is the effect of stimulation of the ANTERIOR hypothalamus on Temperature regulation?
- stimulates posterior hypothalamus heat loss mechanism
- detect increases in temp. which get relayed to posterior hypothalamus –> blood perfuses (permeates) the anterior hypothalamus)
Different ways to measure body temp. and their effectiveness
- Rectal = most effective
- Tongue = 2nd most effective
- Armpits = least effective
What is Fever?
= body’s response to a foreign object
- increased body temp. will denature proteins
- Interleukin-1 (byproduct of phagocytic cells/lymphokines) goes to hypothalamus, raises body’s set point to accommodate this protein destruction
- babies are great thermoregulatory (due to high SA: volume ratio)
What is Heat Exhaustion?
= when we thermoregulate so well that we end up losing too much water so the blood volume decreases, BP decreases, enter circulatory shock (decreased MAP and decreased CO)
- can cause heat stroke if not treated quickly
Heat –> cutaneous arteriolar dilation and excessive sweating —> Hypovolemia –> circulatory shock
What is Heat Stroke?
= severe elevation in core temp. and the inability to bring it back to set point (poor thermoregulation)
- high temps. impair CNS and damage organs and tissues
Symptoms of Heat Stroke
- extremely hot body temp.
- red, hot, dry skin
- rapid, strong pulse
- headache
- dizziness/nausea
- confusion/unconsciousness
- body isn’t regulated (therefore, don’t sweat)
Possible Treatments for Heat Stroke
- stay somewhere cool
- apply cold compress to neck, armpits, groin
- give fluids
- elevate feet
- have person lie down
