Hypothalamus Flashcards
How does the hypothalamus mediate homeostasis?
It controls:
1) autonomic nervous system (projections to sympathetic and parasympathetic neurons)
2) endocrine system: via anterior and posterior pituitary gland
3) motivated homeostatic behaviors (feeding, drinking,…)
What is the organization of the hypothalamic nuclei?
Divided into 3 regions from medial to lateral:
1) periventricular area: periventricular nucleus (subchiasmic nuclei)
2) medial hypothalamic area: (cortex, hindbrain)
3) lateral hypothalamic nuclei: (cortex, hindbrain)
What is the organization of the medial hypothalamic area?
4 regions from rostral to caudal
1) Preoptic area
2) anterior (supraoptic) region
3) middle (tuberal) region
4) posterior (mammillary) region
How does the hypothalamus control the posterior pituitary?
Magnocellular neurosecretory cells located in the supraoptic nucleus and the paraventricular nucleus.
They secrete two hormones into the capillary bed in the posterior pituitary:
Oxytocin - love, social bonding
Vasopressin - water retention, less urine production
How does the hypothalamus control the anterior pituitary?
Parvocellular neurosecretory cells located in the paraventricular nucleus
They secrete releasing hormones into the hypothalamic-pituitary portal circulation
Receptors for hypothalamic hormones cause anterior pituitary cells to release or stop releasing their hormones into blood
What is released during stress response? What does this element do?
Release of cortisol
Cortisol:
- releases glucose into your bloodstream
- increases blood pressure for increased physical activity
- stimulates brain for more intense awareness
- immune system activity is reduced to save energy for physical activity
What is the HPA axis?
1) stress
2) Parvocellular neurosecretory neurons release corticotropin-releasing hormones (CRH)
3) Anterior pituitary releases ACTH (adrenocorticotropic hormone)
4) ACTH acts on adrenal cortex which releases cortisol
5) cortisol inhibits CRH release
What is the difference btw sympathetic and parasympathetic?
Sympathetic: fight or flight
Parasympathetic: rest and digest
What does the ANS innervate?
Smooth muscle, cardiac muscle, gland cells
Explain what anabolism and catabolism are
Anabolism: when the blood is filled with nutrients
Catabolism: during fasting; between meals
How is energy stored?
2 forms: glycogen in liver and skeletal muscle
Triglycerides in adipose tissue (fat)
How does the adipose tissue communicate with brain?
Ob gene codes for a protein called leptin which is released by adipocytes (fat cells)
Leptin is a hormone that communicates with the brain about fat reserves:
- elevated leptin levels in blood activates hypothalamus and decreases feeding behavior
- decreased leptin levels in blood activates hypothalamus and increased feeding behavior
What do Ob-/Ob- mice lack? Conséquence?
Both copies of the gene and the mice are obese: brain thinks fat reserves are low
How does leptin interact with hypothalamus? What does the*** control?
Leptin activates leptin receptors on neurons in Arcuate nucleus of hypothalamus
The arcuate nucleus controls paraventricular nucleus (ANS, endocrine system) and the lateral hypothalamic area (activates homeostatic motivated behavior = feeding)
What are the effects of elevated leptin levels in hypothalamus?
Elevated leptin levels lead arcuate neurons to the release of peptide transmitters called alphaMSH and CART. They inhibit feeding behavior
What do decreased leptin levels entail?
Arcuate neurons responding to decreased levels of leptin release the peptide transmitters NPY and AgRP which stimulate feeding behavior
What are the 4 modulatory systems?
Norepinephrine system
Serotonin system
Acetylcholine system
Dopamine system
Explain the norepinephrine system (Origin, Target, What it’s involved in)
NE
Origin: locus coerulus in pons
Target: Most of CNS
Activated by new, unexpected stimuli
Controls: attention, arousal, sleep-wake
Explain the serotonin system
Origin, Target, What it’s involved in
5-HT
Origin: raphe nuclei in brainstem
Target: Most of CNS
Part of Reticular Activating System, involved in wakefulness and sleep
Controls arousal, sleep-wake, pain, mood
LSD acts similar to it, simulates dreams while awake
Explain the acetylcholine system for memory (Origin, Target, What it’s involved in)
ACh
Origin: basal forebrain complex—> arousal, sleep wake, learning and memory
Target: Cerebral cortex + Hippocampus
first cells to die in Alzheimer’s
Explain the dopamine system in movement (Origin, Target, What it’s involved in)
DA
Origin: substantia nigra
Controls the facilitation of initiation/inhibition of movement, death of cells leads to Parkinsons
Explain the dopamine system in reward (Origin, Target, What it’s involved in)
Origin: Ventrotegmental Area (VTA)
Target: Nucleus accumbens, frontal cortex
Involved in reward and reinforcement, learning and memory
Cocaine, amphetamines act on this, serving as reuptake inhibitor
Diffuse Modulatory System
Within brain, 4 modulatory NT’s, cell body in brainstem, NT release diffused throughout extracellular fluid, widespread influence.
Explain the acetylcholine system for sensory input (Origin, Target, What it’s involved in)
ACh
Origin: Pontomesencephalotegmental cortex
Target: Dorsal Thalamus
Involved in: Organizing sensory Input
Autonomic Nervous System
- One switch that turns on and off, activating a network all connected to various points.
- Regulates smooth/cardiac muscle and glands (mostly involuntary)
- Through sympathetic/parasympathetic/enteric division
- There isn’t much of a fine tuning.
Sympathetic Division: uses, where and NT’s used
- 4 F’s (fight, flight, fear, sex)
- Pre Ganglionic: ACh, Post Ganglionic: NT
- Thoracic/Lumbar (Think of running, punching, HR regulation)
Parasympathetic Division: uses, where and NT’s used
- Digestion, resting, recovering
- Both ACh for pre and post ganglion
- Cervical/Sacral (think of crapping)
Enteric Division
- “Gut brain”
- Neurons in GI Tract, embedded in smooth muscle and help food move along
