Week 12 - hippocampus and limbic system - finished Flashcards
What % of brain mass does the hypothalamus contribute?
Less than 1%
What % of brain mass does the hypothalamus contribute?
Where is the hypothalamus located?
What else is it connected to and how?
Beneath the thalamus, in the walls of the 3rd ventricle and is connected to the pituitary by a stalk
What is the function of the hypothalamus?
Maintains homeostasis.
Also serves the limbic system for emotional expression
- fear
- depression
- pleasure
- rage
What is homeostasis and what are some examples
Maintaining consistent internal conditions within a very narrow range: Temperature pH Blood volume Blood pressure Blood oxygen Blood glucose Electrolyte balance & salinity
What is the structure of the hypothalamus?
Each side of the hypothalamus is divided into 3 zones:
- lateral
- medial
- periventricular
What are the functions of the medial and lateral zones of the hypothalamus?
They connect the hypothalamus to the brainstem, spinal cord and the cortex for the expression and experience of certain emotions.
What does the periventricular zone of the hypothalamus do?
1) Regulated the output of the ANS
2) Influences the pituitary and endocrine regulation
3) Controls circadian rhythms via the suprachiasmatic nucleus
In order to perform these functions it has 3 functionally distinct groups of cells.
Where is the periventricular zone of the hypothalamus located?
Its the area directly surrounding the 3rd ventricle
How many groups of cells are found in the periventriular zone? What are their functions?
3
1) Suprachiasmatic nucleus
- direct retinal input
- monitors daily light/dark cycles
- synchronises circadian rhythms.
2) Cells for the control of the ANS
Connections between the periventricular zone and the autonomic preganglionic nuclei in the brainstem (PS) and spinal cord (S) are essential to autonomic control
Integrates information about body status, anticipates the body’s needs and coordinates a set of both neural and hormonal outputs
3) Neurosecretory neurons:
Axons of neurosecretory neurons project down into the pituitary stalk
Neurohormones are secreted directly into the blood stream
Posterior Pituitary = Neurohypophysis -> CNS
Anterior Pituitary = Adenohypophysis -> gland
What is the solitary nucleus and tract? Where are they located?
Located in the medulla and receives extensive input from the hypothalamus
It is important for the autonomic control and possibly responsible for almost normal control of some autonomic functions even in the absence of the hypothalamus
It coordinates sensory information form the internal organs and outputs to the autonomic brainstem nuclei
What are the functions and divisions of the ANS?
Functions:
Automatic
Involuntary
Complex and highly coordinated functions
Divisions:
Sympathetic
Parasympathetic
Enteric
SNS information:
Fight, Flight, Fright & Sex
Preganglionics from intermediolateral cell column in the thoracolumbar cord
Exit via the ventral root to synapse at the postganglionics
Postganglionics from sympathetic chain ganglia, out with spinal nerves via gray rami communicans
Sympathetic influence:
Increase heart rate
Peripheral vasodilation/ GIT vasoconstriction
Orgasm and ejaculation
Pupillary dilation
Increase glucose production and mobilisation
Dilation of airways
Stimulation of adrenal adrenalin & noradrenalin release
PSNS information:
Rest & digest
Growth, immune responses & energy storage
Preganglionics from autonomic nuclei of brainstem and sacral spinal cord, travel with various cranial & sacral spinal nerves
Parasympathetic ganglia tend to sit within/ local to their target tissues, it is from here that the postganglionic axons extend
Parasympathetic influence
Decrease heart rate
Pupillary constriction
Stimulates salivation and lacrimation
Constricts airways
Stimulates GITl vasodilation/ Peripheral vasoconstriction
Stimulates digestion & insulin release
Stimulates sexual arousal - erection not ejaculation
Enteric division of ANS information:
Embedded in the wall of the oesophagus, stomach, intestines, pancreas and gall bladder are two interconnected plexuses for regulation of GIT function
Auerbach’s Plexus -> Myenteric Plexus
Meissner’s Plexus -> Submucosal Plexus
Both contain autonomic motor & sensory neurons
Contains approx # neurons as entire spinal cord
Can acts to regulate homeostasis with a great deal of autonomy but not entirely
Overall autonomic function:
Innervates secretory glands
Innervates heart to control heart rate, BP & flow
Innervates bronchi to meet O2 demands
Regulates digestive & metabolic functions of the liver, GIT & pancreas
Regulates function of the kidney, urinary bladder, intestines & rectum
Essential to sexual responses of the genitals and reproductive organs
Interacts with the immune system
Functions of the sympathetics & parasympathetics generally oppose each other, so substantial of stimulation of both is incompatible
The two systems function in parallel to balance excitation and inhibition for coordinated and graded control of body systems
What are magnocellular neurons and where are they found? Where do they extend and what do they release?
Found in the hypothalamus
Extend their axons all the way down the pituitary stalk and into the neurohypophysis
They release neurohormones directly into the capillary bed
- Oxytocin: uterine contraction in final stages of child birth and milk ejection from mammary glands
- Vasopressin/ADH: regulates blood volume & salt [C], is released in response to input from cardiovascular pressure receptors & salt [C] sensitive cells in the hypothalamus. Acts directly on the kidney to increase H20 retention & decrease urine production
What are parvocellular neurons and where do they extend? What do they secrete and what do these secretions influence?
They extend into the base of the pituitary stalk & secrete their neurohormones into the capillary bed of the hypothalamopituitary portal system which sits in the base of the stalk and the floor of the 3rd venticle
Neurohormones travel downstream and bind at hormone specific receptors on anterior pituitary cells to exert their effects and either stop or start pituitary hormone release
What hormones are released from the anterior pituitary?
GH: growth hormone TSH: thyroid stimulating hormone ACTH: adrenocorticotropic hormone PROLACTIN FSH: follicle stimulating hormone LH: leutinising hormone
What hormones are released from the anterior pituitary?
GH: growth hormone TSH: thyroid stimulating hormone ACTH: adrenocorticotropic hormone PROLACTIN FSH: follicle stimulating hormone LH: leutinising hormone
