Diencephalon - PPT.pptx

Diencephalon The diencephalon (literally, “between brain”) UM1010 Dr Alpana Asurlekar  Learning objectives 1. Outline the structural organisation of the diencephalon 2. What are the three main components of the diencephalon? Where are they located? 3. Name three general funct...

Diencephalon The diencephalon (literally, “between brain”) UM1010 Dr Alpana Asurlekar  Learning objectives 1. Outline the structural organisation of the diencephalon 2. What are the three main components of the diencephalon? Where are they located? 3. Name three general functions of the thalamus. 4. Name three general functions of the hypothalamus. 5. What is the pineal gland’s primary function? 6. Identify parts of diencephalon and function of each part. Development  Facts about Diencephalon Developed from Prosencephalon Below cerebral cortex and above the midbrain Forms the central core of the forebrain Composed largely of grey matter These grey matter areas enclose the third ventricle Parts of Diencephalon:- Consist of 3 paired structures Thalamus + Hypothalamus + Epithalamus (Pineal Gland) Diencephalon corpora quadrigemin a  Thalamus Diencephalon composed of 80% Paired egg-shape structure Thalamus – Greek word meaning “inner room” Consist of 12 nuclei (grey matter areas) which are aggregated cell bodies Each nucleus has a functional speciality Afferent impulses from all senses and all parts of the body converge on the thalamus and synapse with at least one of its nuclei. eg. ventral posterolateral nuclei – receives – general somatic sensory receptors (touch, pressure, pain) eg. The lateral and medial geniculate (Knee shape) body – important – visual and auditory relay centers respectively.  Thalamus Within thalamus information is sorted out and edited Impulse with similar functions are relayed as a group - via internal capsule – to appropriate sensory cortex and – to specific cortical association area. Afferent impulse reaches thalamus- crude recognition of sensation – pleasant or unpleasant Specific stimulus localization and discrimination occur in the cerebral cortex  Thalamus Sensory inputs and all other ascending inputs funnel through thalamic nuclei to reach to cerebral cortex. They are:- eg-  Inputs to help regulate emotion and visceral function from the hypothalamus (via anterior nuclei)  Instruction that help to direct motor activity from the cerebellum (ventral lateral nuclei) and basal nuclei (ventral anterior nuclei) o basal nuclei (ganglia)– role is to plan, programming and coordination of voluntary motor activity (along with cerebrum)  Inputs from memory or sensory integration that are projected to specific association cortices (via pulvinar, lateral dorsal, and lateral posterior nuclei) o Along with limbic system is involved in learning and episodic memory.  Thalamus Plays a key role in mediating sensation, motor activities, cortical arousal(alert), learning, and memory Thus, plays important part in the integration of sensory and motor system Major relay station Most sensory impulse from Spinal cord and brain stem via thalamus reach to cerebrum Relay motor information from cerebrum via thalamus to cerebellum to body  Hypothalamus The hypothalamus is a small but functionally important area of the brain. Weight - little more than 7 grams Location - The hypothalamus lie beneath the thalamus, consists of several structures and form the floor of the third ventricle and the lower part of its lateral walls. Prominent structures composing the hypothalamus are  the supraoptic nuclei,  the paraventricular nuclei, and  the mamillary bodies The supraoptic nuclei consist of grey matter located just above and on either side of the optic chiasma. The paraventricular nuclei is close to the wall of the third ventricle. The midportion of the hypothalamus gives rise to the infundibulum, the stalk leading to the posterior lobe of the pituitary gland (neurohypophysis). The posterior part of the hypothalamus consists mainly of the mamillary bodies, which are involved with the olfactory sense (smell).  Hypothalamus  The hypothalamus is a link between the cerebral cortex the psyche (mind) and lower centres the soma (body).  It links the nervous system to the endocrine system.  Performs many functions which are of the greatest importance both for survival and for the enjoyment of life.  Certain areas of the hypothalamus function as pleasure centres or reward centres for the primary drives such as eating, drinking, and sex. The following list briefly summarizes hypothalamic functions:- Control the autonomic nervous system (ANS)– ANS is part of peripheral nerves and regulates cardiac and smooth muscles, and secretion by glands. Hypothalamus regulates ANS activity by controlling the activities of centres in the brain steam and spinal cord. Eg Blood pressure, rate and force of heart rate, digestive tract motility, eye pupil size and visceral activities.  Hypothalamus Initiate physical responses to emotions – The hypothalamus lies at the heart of the limbic system(Emotional part of the brain). Thus, it acts through ANS pathways to initiate the physical expression of emotion. Eg fearful person has pounding heart, high blood pressure, pallor, sweating, and a dry mouth. Regulate body temperature – Body’s thermostat is in the hypothalamus. Hypothalamic neuros monitor blood temperature and receives inputs from other thermoreceptors (body periphery). Accordingly, the hypothalamus initiates cooling (sweating) or heat-generating actions (shivering) as needed, to maintain relatively constant body temperature.  Hypothalamus Regulate food intake – The “appetite centre” in the lateral part of the hypothalamus and a “satiety centre” located medially. The hypothalamus functions as a crucial part of the mechanism for regulating appetite and therefore the amount of food intake. In response to change of body levels of certain nutrients (glucose , amino acids) or hormones (cholecystokinin, gherlin), the hypothalamus regulates the feeling of hunger and satiety. Regulate water balance and thirst – When body fluids become too concentrated, hypothalamic neuron called osmoreceptors gets activated. Osmoreceptors excite hypothalamic nuclei that trigger the release of antidiuretic hormone (ADH) from posterior pituitary. This ADH causes the kidneys to retain water and stimulate hypothalamic neuron in the thirst centre, causing to feel thirsty and person drink more fluids. Thus, body fluid concentration is back to normal range. Because one of these hormones affects the volume of urine excreted, the hypothalamus plays an indirect but essential role in maintaining water balance.  Hypothalamus Regulate sleep awake cycle – The hypothalamus plays an essential role in maintaining the waking state. Presumably, it functions as part of an arousal or alerting mechanism. Acting with other brain regions, the hypothalamus helps regulate sleep. Its suprachiasmatic nucleus sets the timing of the sleep cycle primarily in response to daylight- darkness cues received from the visual pathway. Control endocrine system function – The hypothalamus acts as the helmsman of the endocrine system in two important ways. First, its releasing and inhibiting hormones control the secretion of anterior pituitary gland. Secondly, its supraoptic and paraventricular nuclei produce the hormones ADH and oxytocin. Endocrine control Hypothalamus-pituitary- thyroid axis (HPT axis) The hypothalamic–pituitary–thyroid axis (HPT axis) is under the control of neurons located in the medial region of the PVN that synthesize and release thyrotropin-releasing hormone (TRH) into the pituitary TR portal circulation. The hypothalamus senses low circulating levels H of thyroid hormone (Triiodothyronine (T3) and Thyroxine (T4)) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). Hypothalamus-pituitary- adrenal axis (HPA axis) Stress activates the HPA axis. When the hypothalamus releases the neurotransmitter corticotropin-releasing factor (CRF) that binds to the nearby pituitary gland triggering the release of adrenocorticotropic hormone (ACTH). This hormone travels through body down to the adrenal glands (located at the top of each kidney) triggering the release of cortisol and activating the sympathetic nervous system. As the levels of cortisol in bloodstream increase, multiple systems prepare body to either fight or flee the dangerous situation. The hypothalamo-pituitary-adrenocortical (HPA axis) is required for stress adaptation. Activation of the HPA axis causes secretion of glucocorticoids, which act on multiple organ systems to redirect energy resources to meet real or anticipated demand. Hypothalamus-pituitary- gonadal axis (HPG axis) The HPG axis plays a vital part in the development and regulation of the body's reproductive system. Gonadotropin-releasing hormone (GnRH) is secreted from the Hypothalamus by GnRH-expressing neurons. The anterior portion of the pituitary gland produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonads produce estrogen and testosterone. Fluctuations in this axis cause changes in the hormones produced by each gland and have various local and systemic effects on the body.  Hypothalamus - summary Pituitary gland and trace upward is attached to Hypothalamus Forms the floor of Diencephalon Homeostasis Regulated by 3 systems Control - ANS, Endocrine system via pituitary and Limbic system Initiate physical responses to emotions (hypothalamus lies at heart of limbic system) via ANS Visceral control of the body Maintain/ regulate body temperature Emotional behaviour Hunger centre – regulate Food intake Thirst and water balance (ADH) Sleep awake cycle along with pineal gland  Epithalamus Various small nuclei just outside the thalamus and hypothalamus, collectively referred to as the epithalamus One of the structure is Pineal gland Produces Melatonin Day and night clock of the body Fibers from eyes It gets calcified in old age Changing light levels of the sun and moon throughout the day–night cycle trigger changes in the rate of melatonin secretion. When sunlight levels are high, melatonin secretion decreases When light levels are low, melatonin levels increase proportionally. The changing levels of blood melatonin exhibit a circadian cycle that synchronizes the body’s internal biological clock mechanisms with the day–night cycle of the external environment.  Pineal gland One of the most dorsal portion of the diencephalon, the epithalamus. Forms roof of third ventricle Extend from its posterior border and seen externally in the pineal gland or pineal body Its name comes from the fact that it resembles a pine nut shape. Location- just above the corpora quadrigemina of the midbrain.  Pineal gland The functions of pineal gland :- secretion of the hormone melatonin (sleep inducing signal) body’s biological clock mechanism Antioxidants Along with hypothalamic nuclei Melatonin is a hormone because it is a molecule released into the blood to regulate functions elsewhere in the body. However, melatonin is in fact simply an altered form of the neurotransmitter serotonin. Changing light levels of the sun and moon throughout the day–night cycle trigger changes in the rate of melatonin secretion. When sunlight levels are high, melatonin secretion decreases. When light levels are low, melatonin levels increase proportionally. The changing levels of blood melatonin exhibit a circadian cycle that synchronizes the body’s internal biological clock mechanisms with the day–night cycle of the external environment.  Pineal gland Melatonin is thus often called the “timekeeping hormone”—but because high blood levels of melatonin signal the body that it is time to sleep, it is also called the “sleep hormone”. When a person travels to another time zone, or when the seasons change, the altered sunlight patterns cause corresponding time shifts to the melatonin cycle. Likewise, often subtle changes occur in each melatonin cycle depending on how much moonlight (reflected sunlight) is present each evening. FIGURE 20-14 Melatonin. Graph comparing typical blood melatonin levels throughout the day. Sunlight suppresses melatonin secretion during the day. As the sun goes down, however, melatonin levels begin Any doubt or question then please write to [email protected] Or post question on MS Team chat.