DIENCEPHALON II: THE HYPOTHALAMUS NEUROANATOMY
Define Laminae:
Layers of neurons w/in spinal cord towards the back of the cord. Predominantly towards back of cord that perform certain functions.
Oxytocin & vasopressin have been found to have broader roles including:
Learning, anxiety, sexual, and maternal behavior, & aggression
Draw out the flow chart of the general hypothalamus input types:
Take note of the nucleus solitarius & the brainstem reticular formation. Note the direct & indirect paths.
Which function of the hypothalamus relates to: nucleus of the solitary tract, the dorsal motor nucleus of the vagus, the intermediolateral cell column of the spinal cord for autonomic responses.
Temperature control
What am I? I am the most prominent component of the diencephalon due to my size and ease of identification. I have sensory, motor, & cognitive function.
Thalamus
Without looking at the words. Look at the picture on the next slide. What is the structure indicated?
Thalamus
Reticular formation provides input both directly and indirectly via the
Thalamus.
What am I? I functionally relate to basal ganglia.
Subthalamus
Outputs: Projections through the medial forebrain bundle (MFB) and other routes reach the:_____
- Amygdala - Septal Nuclei - Other limbic structures for cognitive responses AKA "maybe I can find the thermostat" when a person is hot/cold
Inputs the the hypothalamus include projections through the dorsal longitudinal fasciculus (DLF) bring information from _____.
- the nucleus of the solitary tract (in the medulla) - the dorsal motor nucleus of the vagus - the intermediolateral cell column
Lateral hypothalamus functions
-important in the control of food and water intake -lateral hypothalamic lesions causes aphasia (inability to swallow) and adipsia (decreased feeling of thirst)
What are the 2 general categories for general input types?
1) From nuclei in the brainstem & spinal cord conveying information about the state of your body 2) From limbic structures like the amygdala, hippocampus, and septal nuclei (structures that lie below the corpus callosum & comprise the medial olfactory area).
In what 3 ways does the hypothalamus regulate autonomic function & drive-related behavior?
1) Has interconnections with visceral parts of the nervous system & receives information used to control: blood glucose, blood pressure, and body temperature. 2) Has interconnections with limbic structures , making you aware of homeostatic needs such as "I'm hungry." 3) Controls the pituitary gland (the pituitary gland produces hormones for our bodies to function (hormonal control).
Look at the hypothalamus picture on the next slide and tell me everything you know about the very important picture.
1- hypothalamic sulcus 2- lamina terminalis 3- optic chiasm 4- jk we don't need to know this. But its the mammillothalamic tract 5- mammillary body 6- median eminence 7- infundibulum 8- posterior pituitary 9- anterior pituitary Know what is anterior, posterior, superior, & inferior. Know the borders of the hypothalamus.
The hypothalamus and the visual pathway are in close proximity to each other. Flip this card and look at the picture. Name the structures numbered. Then check with what is typed.
1- optic nerve 2- infundibulum 3- tuber cinereum 4- oculomotor nerve 5- optic chiasm 6- optic tract 7- crus cerebri 8- mammillary body
LIST THE 4 COMPONENTS TO THE DIENCEPHALON & A BRIEF OVERVIEW OF THEIR FUNCTIONS
1. THALAMUS: 2. HYPOTHALAMUS: 3. EPITHALAMUS 4. SUBTHALAMUS
Medial border of the hypothalamus
3rd ventricle
Hypothalamic regulation of drinking
A part of the preoptic nucleus called the medial preoptic nucleus integrates information from peripheral receptors that detect blood volume and pressure, decreased blood flow, elevated levels of angiotensin hormone, and changes in Osmolality The information is transmitted to the cerebral cortex, which then initiates the necessary behavior to correct a deficit (e.g. sensation of thirst. ***Note location of the vascular organ of lamina terminalis & subfornical organ in the photo***
Horner's syndrome
A sympathetic denervation characterized by: pupillary mitosis (small pupil that fail to dilate ptosis (droopy lid) and anhydrousis (inability to sweat on one side of face). 1st order neuron originates in hypothalamus We can test for location of lesion w/ drug drops
Depression
Affects about 4% of adult population There is a genetic predisposition (about 20% of first degree relatives have it too) Depressed general mood, with loss of interest in normal activities & outside. Symptoms listed above are also characteristic of chronic stress
What are the afferent & efferent connections of the amygdala?
Afferent: From the inferior temporal association cortex, the thalamus, septum and the olfactory tract. Efferent: Its main projection runs in the wall of the lateral ventricle, following the curvature of the caudate nucleus, to terminate ultimately in the hypothalamus
What are the afferents and efferents of temperature regulation?
Afferents about body temperature: 1- locally (thermosensitive neurons in the preoptic nucleus of the anterior hypothalamus) 2- rest of the body (ex/skin) sends information via the spinoreticular tract in the spinal cord Efferents The hypothalamic nucleus sends axons to synapse on the preganglionic thoracolumbar lateral horn neurons of the spinal cord, directing blood flow into the skin and activating sweat glands.
What are the 4 of the 6 limbic structures that we should know about? These structures are tasked with ensuring that we have the appropriate behaviors to our environment. Can you say where 3 are located in a sagittal section of the brain?
Amygdala, Hippocampus, Basal Ganglia, & Cingulate Gyrus ***The hypothalamic nuclei location is also important to note in this picture.
Which part of the hypothalamus is involved in temperature regulation?
Anterior hypothalamus
Regions related to the subdivisions of the hypothalamus: longitudinal?
Anterior region: above the optic chiasm, extending anteriorly to the lamina terminalis A tuberal region: above and including the tuber cinereum Posterior region: above and including the mammillary bodies
Which function of the hypothalamus relates to: the limbic system, sympathetic & parasympathetic connections.
Attack & Defense
The hypothalamus regulates what function and behavior
Autonomic functions & drive-related behavior
The state of arousal is communicated by connections that originate in the
Brainstem
Interior border of the hypothalamus
Consists of: the optic chiasm, tuber cinereum, & mammillary bodies ****The tuber cinereum shows a small swelling, the median eminence, immediately behind the infundibulum (funnel) atop the pituitary stalk
Medial hypothalamus
Contains various nuclei, only some of which have well-defined functions such as: Supraoptic nucleus which produces vasopressin (antidiuretic hormone) which is released from the posterior pituitary Paraventricular nucleus synthesizes oxytocin which is released from the posterior pituitary Suprachiasmatic nucleus contains osmosensitive neurons that are activated by changes in blood Osmolality
What does the word diencephalon mean & where is it located in the brain? What separates the diencephalon from other brain components? What separates its pair structures medially?
Diencephalon means 'in between' & it is a paired structure deep within the brain. The diencephalon is separated from the other brain components by the internal capsule on the sides & medially the right and left side are separated by the 3rd ventricle.
Monoamine refer to the particular neurotransmitters:
Dopamine, noradrenaline, & serotonin
What am I? I contain the pineal gland which secretes melatonin for circadian rhythms (sleep)
Epithalamus
The functions of the hypothalamus result in homeostasis and survival of the individual and species. What are they?
FAT GRAMS 1. Reproduction 2. Growth 3. Metabolism 4. Food & Fluid Intake 5. Attack & Defense 6. Temperature control 7. Sleep - wake cycle 8. Aspects of memory
What clinical manifestations related to hypothalamic dysfunctions caused by tumors, congenital malformations, & head injuries?
Gross obesity, disturbances of autonomic control, excessive sleepiness, and memory loss.
Magnocellular neurons located in supraoptic and paraventricular nuclei give rise to a tract known as _______. Where does the tract descend too? What hormones does it produce?
Hypothalamohypophyseal tract (or supraopticohypophyseal tract) This tract descends to the neurohypophysis (posterior lobe) This tract produces the hormones oxytocin & vasopressin (ADH)
What am I? I contain the pituitary gland. I serve the autonomic & limbic systems.
Hypothalamus
In Latin limbus means...
In Latin limbus means border. "Limbic" describes the set of structures that line the edge of the cortex
How does the hypothalamus play a role in sexual arousal in females?
In females estrogen rich neurons are contained within the ventromedial nucleus.
Explain the input and output of the hypothalamus in regards to room temperature.
Input: visceral parts of the limbic system gather information on body temperature & send it to the hypothalamus which decides what changes are needed. Output: A signal is then sent to the brain responsible for making those changes. So if the hypothalamus detects that you are warm then the behavioral response would be to check if we can change the room temperature
The hypothalamus is able to integrate signals from _______________ and make appropriate adjustments.
Internal organs and fluid-filled cavities. These are the inputs
Hypothalamic connections with visceral nuclei and limbic structures are ________.
Largely reciprocal
Oxytocin
Liberated by magnocellular neurons in response to suckling of the breast. Once in the bloodsteam, it causes the expression of milk by stimulating myoepithelial cells surrounding the lactiferous ducts of the breast. Stimulates contraction of the uterine muscles during labor.
Where is the hippocampus located and what roles does it play?
Located under the cerebral cortex in the medial temporal lobe, one on each side of the brain. Shaped like a seahorse. In charge of consolidating information for short/long term memory & spatial information.Enables navigation.
Which structures relate to the subdivisions of the hypothalamus: longitudinal?
Mammillary bodies Tuber cinereum Median eminence arises from the tuber cinereum and narrows into the infundibulum, to which the pituitary gland is attached
Monoaminergic projections ascend in the _____.
Medial forebrain bundle
Hypothalamic regulation of rage and fear responses.
Mood and food go together! The lateral and ventromedial nuclei are concerned with mood as well as food.
Why are the pituitary gland secretions called neuroendocrine?
Neuro: because it has dendrites & axons & conducts nerve impulses Endocrine: because they liberate their secretions into capillary beds ***the secretions are peptides, synthesized in clumps of granular Endoplasmic reticulum & packaged in Golgi complexes
The pituitary gland secretions are controlled by 2 sets of:
Neuroendocrine cells: parvocellular & magnocellular (depending on size like in the retina) Magnocellular (large) reach the posterior lobe of the pituitary gland Parvocellular (small) neurons reaching the median eminence
Which structure relates to food and fluid intake (a function of the the hypothalamus)?
Nucleus solitarius of the medulla for BP & osmolarity
Visual field testing can help us determine what in regards to the hypothalamus?
Pituitary lesions Notice that nasoretinal fibers cross at chiasm for peripheral/temporal vision.
We know that the hypothalamus and the visual pathway are in close proximity to each other. What is the main take away?
Pituitary tumors can press against the optic chiasm and cause vision deficits
The hypothalamus sends an output signal to which structure in order to influence wakefulness and sleep?
Reticular formation (brainstem nuclei)
Hypothalamic regulation of eating is influenced by what hormone?
Serotonin can influence appetite by inhibiting the lateral nucleus. Anorexics tend to have a raised level of serotonin production, and bulimics a reduced level.
Master clock for most circadian rhythms. Can you label it in a cross section?
The Suprachiasmatic nucleus is the master clock for most circadian rhythms and information from the retina helps get these rhythms synchronized with the 24 hour day. Notice that the Suprachiasmatic nucleus is just over the optic chiasm in the picture.
Adenohypophysis (anterior pituitary or master gland) regulates ___ & involves what hormones?
The adenohypophysis regulates stress, growth, reproduction and lactation by secreting: 1) adrenocorticotropic hormone (ACTH) 2) luteinizing hormone (LH) 3) follicle-stimulating hormone (FSH) 4) thyroid-stimulating hormone (TSH) 5) growth hormone 6) prolactin
Where is the amygdala located? Can you identify it on a coronal cross section?
The amygdala is located in the deep, frontal portion of the temporal lobe. It is connected to several components of the limbic system.
Hypothalamic Regulation of Eating
The arcuate nucleus is sensitive to glucose levels and to various peptides secreted by the stomach and or adipocytes that stimulate feeding behavior. It also integrates information from the lateral & ventromedial hypothalamus.
Where in a coronal cross section of the brain would we be able to see the subthalamic nucleus?
The boundaries are not well defined by the subthalamic nucleus is underneath the thalamus. It is caudal to a cross section showing the hypothalamus.
What anatomical structure is surrounds the hypothalamus at the base of the brain?
The circle of willis
The hypothalamus is strongly connected with the limbic system. These connections are involved in what type of behavior?
The connections between the hypothalamus and the limbic system are involved in adaptive behavior, which includes the ability to learn new responses based on previous experience (the memory). Think of it as homeostasis in the "social environment".
The hippocampus is connected to the parts of the brain involved in emotional behavior, one of them is the
The hippocampus is connected to the parts of the brain involved in emotional behavior, one of them is the mammillary body in the hypothalamus. ***take note that the hippocampus and the mammillary bodies are connected
The limbic system includes:
The hippocampus, cingulate cortex, olfactory cortex, & amygdala.
Superior border of the hypothalamus
The hypothalamic sulcus separates the hypothalamus from the thalamus
In order for the hypothalamus to exert control over internal organs what does it need to send a signal to?
The hypothalamus exerts control over the autonomic nervous system ( preganglionic sypathetic & parasympathetic neurons) of the autonomic nervous system.
The hypothalamus receives input (directly or indirectly?) from the retina. It does this how?
The hypothalamus receives input directly from the retina. It does this by having retinal ganglion cells terminate at the Suprachiasmatic nucleus on each side of the anterior hypothalamus. The superchiasmatic nucleus receives information from the retina and uses information to synchronize with the 24 hour day.
HPA axis mediates responses to stress. What is hpa?
The hypothalamus-pituitary-adrenal axis mediates responses to stress. After a physiological, physical, or physiologically stressful event, the body attempts to restore homeostasis. Brainstem structures notice various physiological stressors & limbic system input about emotion. The brainstem structures notify the paraventricular nucleus in the hypothalamus CRH is released by the paraventricular nucleus—> ACTH is released from anterior pituitary—> cortisol is released from the adrenal cortex of the kidney. Cortisol activates the bodies energy stores. ***notice the location of the paraventricular nucleus in the photo
The lateral boundary of the hypothalamus
The internal capsule
Anterior border of the hypothalamus
The lamina terminalis
The limbic system is believed to comprise the neural basis of _____.
The limbic system is believed to comprise the neural basis of emotion.
What is another word for the protuberance shown on the tuber cinereum?
The median eminence
The production and secretion of each of the major anterior pituitary hormones are regulated by peptides released from ______. Those peptides include...
The median eminence neurons of the hypothalamus. Those peptides include: thyrotropin-releasing hormone (TRH), corticotropin releasing hormone (CRH), gonadotropin releasing hormone, & growth releasing hormone.
Hypothalamic Outputs: The hypothalamus can initiate appropriate motor behavioral repertoires of an instinctive kind because of....
The nucleus accumbens has connections with the limbic system and the limbic part of the corpus striatum (the nucleus accumbens)
What contributes information to the nucleus solitarius? Where is the nucleus solitaries in the CNS?
The nucleus solitaries is located in the medulla & it receives information from baroreceptors & chemoreceptors which it then conveys to the hypothalamus. This is one example of an input system. - The circulating blood provides physical (Temperature, Osmolality), chemical (blood glucose, acid- base state) and hormonal signals of the state of the body. - The nucleus solitarius of the medulla projects to the hypothalamus, conveying information collected by the autonomic nervous system concerning the pressure within the smooth-muscled walls of organs (baroreceptors) and the chemical constituents of the fluid-filled cavities) chemoreceptors.
Posterior border of the hypothalamus
The tegmentum of the midbrain (general area on the ventral side of the midbrain)
The tuber cinereum primarily constitutes the nerve fibers from the hypothalamus to the pituitary gland. Rather than provide signaling to the gland many of these fibers act as...
The tuber cinereum primarily constitutes the nerve fibers from the hypothalamus to the pituitary gland. Rather than provide signaling to the gland many of these fibers act as... The source of the substances released by the posterior lobe of the pituitary gland. The tuber cinereum really just functions as the rapid high concentration, hormonal route between the hypothalamus, the median eminence, and the pituitary gland. From the pituitary gland these hormones can enter into the circulation.
In general anatomy we talked about the aortic arch and the carotid sinus. Why are these relevant?
These are relevant because they have baroreceptors (receptors in the walls of the blood vessels that sense the stretch) caused by the blood pressure, & these receptors send signals to the midbrain and the midbrain sends signals to the hypothalamus. Once the signals reach the hypothalamus then the hypothalamus acts on the sympathetic (fight & flight) & parasympathetic (rest & digest) systems to influence blood pressure. Baroreceptors—> midbrain—> hypothalamus—> sympathetic or parasympathetic system Ex/ if we need to increase heart rate & stroke volume then the sympathetic system can influence blood vessels namely by causing vasoconstriction and vasodilation. The parasympathetic system can decrease heart rate & stroke volume (the opposite).
Without looking at the words. Look at the picture on the next slide and label the structures indicated. We are considering the gross dissection of the diencephalon.
Top Box: Thalamus Right Box: Pineal Gland Bottom Box: Hypothalamus
ADH stimulates..? What happens if we withdraw or stop ADH secretions?
Water retention & raises blood pressure by contracting arterioles. Withdrawal of ADH secretion results in diabetes insipidus: not related to DM, caused by hormonal problems, leads to body being unable to handle fluid (ex/thirst & urination) Diabetes insipidus is brought about by interruption of the hypothalamohypophyseal pathway- sometimes by tumors in the region, sometimes by head injury.
How does the hypothalamus play a role in sexual arousal in men?
Within the medial part of the preoptic nucleus in a subset of neurons, the 3rd interstitial nucleus of the anterior hypothalamus is rich in androgen receptors and they are activated by circulating testosterone.