Limbic System & Hypothalamus

What is the hypothalamus?

• Small part of diencephalon sitting below thalamus

• Connected by a stalk to anterior/posterior lobes of pituitary gland

• Coordinates drive related behavior

What are the general functions of the hypothalamus?

• Homeostasis

• Regulates endocrine output

• Regulates body temp, blood comp, blood volume, BP, salinity, pH, oxygen, glucose, growth, reproduction

Describe the posterior pituitary.

• Made of dense bed of capillaries & axons

• Release 2 hormones:

  • Vasopressin (ADH) → stimulate kidneys to retain water

  • Oxytocin → uterine contractions & milk production, anti-anxiety during breastfeeding, social bonding, intimacy

Describe the anterior pituitary.

• Releases 6 hormones:

  • ACTH → adrenal glands produce adrenalin & cortisol

  • TSH → thyroid regulate metabolism

  • FSH → sperm & egg production

  • LH → testosterone & progesterone production

  • Prolactin → breast milk production

  • GH → child growth & muscle

  • Melaonocyte-Stimulating (MSH) → skin pigmentation

How does the hypothalamus control the anterior pituitary?

• Cells of hypothalamus secrete releasing factors & inhibiting factors

• Go to hypophyseal portal system

• Specifically selects which hormone is increasing/decreasing in circulation

What are the 3 ways the hypothalamus exerts its effects?

1. Control of endocrine system → hormones in bloodstream

2. Autonomic control → adjusts PNS & SNS motor output

3. Somatic motor control → responds to visceral sensations

How does the hypothalamus regulate temperature?

• Does NOT let it change more than ½ °F

• Acts before blood temp changes

• Signals from skin thermoreceptors & cognitive awareness of environment

• Vasoconstriction → conserve heat

• Vasodilation → release heat (cool down)

• Shivering → involuntary heat generation

• Behavioral changes → seek warmth, add/remove clothes, sit under fan

• HypoT → anterior pituitary → TSH → increase/decrease metabolism

How does the hypothalamus regulate BP?

• Modulates baroreceptor reflex

• Controls the release of ADH to regulate circulating blood volume

• Prompts conscious self to use somatic motor system to get up & rehydrate

How does the hypothalamus regulate satiety (fullness)?

• Satiety center → detects rising glucose & shuts down urge to feed

• Appetite center → detects falling glucose & initiates feeding

• Low blood sugar → anger, irritability, hangry

What is Horner’s Syndrome?

• Loss of sympathetic innervation to the head

• Miosis → pupil constriction

• Ptosis → eyelid droop

• Anhidrosis → lack of sweating at head/face

• Pale skin → Harley Quinn sign

What are some causes of Horner’s syndrome?

• Damage to lateral hypothalamus → sympathetic output

• Damage do descending sympathetic pathway from hypoT to IML (PICA stroke)

• Damage to ascending sympathetic axons from superior cervical ganglia, traveling with carotid artery

What is autonomic dysreflexia?

• SC lesions T6 and above

• Lose top-down communication from hypT to IML

• Sympathetic neurons of iML become hypersensitive

• Noxious stimuli below lesion initiates exaggerated reflex response

• Vasoconstriction → increased BP

• HypoT signals CN X (Vagus) to decrease BP → slow HR

• Sudden increase in BP with bradycardia, pounding headache, pupillary constriction, & anxiety

• Must remove stimuli to resolve hypertension

• SIT THEM UP

What are some common noxious stimuli that cause autonomic dysreflexia?

• Over filled urinary bladder

• Fecal impaction

• UT

• Bed sore

• Skin pinched in chair

What is the limbic system?

• Structures responsible for initiating reactions & behaviors associated with reproduction, survival drives, & emotional responses

• Cingulate gyrus, parahippocampal gyrus, amygdala, hippocampus

• Bridge b/w higher voluntary thought centers & ANS & endocrine system

• Helps guide our actions & form new memories

Describe the parahippocampal gyrus.

• Medial temporal lobe

• Meeting ground for afferent projections to hippocampus for memory

Describe the cingulate gyrus.

• Broad belt of cortex around corpus callosum

• Posterior → receive memories to compare to current environment for proper motor planning & response

• Anterior → influences decision making by exploring previously learned alternatives, initiates crying, active with chronic pain

Describe the hippocampus

Create new declarative memories

Describe the amygdala

• Almond shaped in medial temporal lobe, deep to uncus

• Response to emotional stress

• Associated with fear, rage, & anxiety

• Place emotional stamp on experience

• Unconscious emotion → intuition

• Learning whether a fact is “bad” or “not bad”

What are the connections of the amygdala?

• Receives input from temporal lobe, pre-frontal cortex, cingulate gyrus, olfactory, & hippocampus

• Sends info to hypoT, septal nuclei, & hippocampus

Describe the mammillary bodies.

• Part of hypot

• Accepts afferent info on memory formation from hippocampus through fornix

• Sends info to anterior nuclei of thalamus

• Important for consolidation (strengthening) of new memories

• Damaged by chronic alcoholism

Describe septal nuclei

• Component of medial wall of inferior frontal lobe, anterior to hypoT

• Functions as pleasure center

• Reciprocal connections with hippocampus & amygdala