Endocrine Control

Chemical Control of Brain and Behavior The Neuroendocrine Link

Patterns of Communication Communication in the nervous system can be: Point-to-point How most of the nervous system is wired Specific connections for specific functions Neurosecretion into the bloodstream The hypothalamus is the key player Targets are distributed Hormones (blood-borne neurotransmitters) reach their targets through the circulatory system Subnetworks controlled from the CNS Autonomic nervous system Diffuse modulatory systems

Types of Hormones Steroids fat-like organic compounds (sex hormones, corticoids ) Steroids pass through target cell membranes, combine with receptor molecules, move into cell nucleus, then helps determine manufacture of specific proteins Protein hormones all others affect target cells in 2 step process = 2nd messenger system: 1st messenger, hormone, combines with receptor on target cell membrane activates an enzyme on the membrane's inside wall That enzyme changes ADP to cyclic AMP (the 2nd messenger) Which triggers enzymes that produce the effect

The Hypothalamus Above pituitary and below thalamus Three zones: lateral medial periventricular Master switchboard of the endocrine system Receives signals from the entire body through the nervous system Sends signals to stimulate or inhibit hormone secretion by other glands (eg. pituitary)

The Periventricular Zone Suprachiasmatic nucleus - synchronize circadian rhythms with light-dark cycles Control neurons for the autonomic nervous system Neurosecretory neurons extend axons down the talk of the pituitary

Tropic Hormones Tropic hormones stimulate or inhibit hormone secretion Releasing hormones = those that stimulate Inhibiting hormones = those that slow secretion At least 9 are made by the hypothalamus These control TSH, GH, LH, FSH, ACTH & prolactin

The Hypothalamus & Homeostasis Homeostasis is the regulatory process that maintains body's internal environment within a narrow physiological range Supervised by neurons in the hypothalamus Includes temperature regulation, regulation of blood volume, regulation of blood pressure, salinity, acidity, oxygenation, and glucose concentration

The Pituitary At the base of the brain Suspended from hypothalamus by a stalk about the size of a bean Acted on by hypothalamus 2 sections: Anterior Lobe Posterior Lobe

The Anterior Lobe Parvocellular neurosecretory cells in the hypothalamus release into a specialized capillary bed called the hyopthalamo-pituitary portal circulation Hypophysiotropic or releasing hormones are secreted These bind to receptors on cells in anterior lobe of pituitary and increase or decrease their secretion of other hormones

Anterior Pituitary Hormones Tropic (affect other glands): FSH ( follicle stimulating hormone ) LH ( lutenizing hormone ) - acts on gonads TSH ( thyroid stimulating hormone ) - stimulates thyroid to produce thyroxin ACTH ( corticotropic hormone ) - affects adrenal cortex MSH (melanocyte stimulating hormone) endorphins Nontropic: Somatotropin (or growth hormone - GH) Prolactin - stimulates milk production

Tropic Hormone Function Example: CRH (corticotropin-releasing hormone is secreted by the parvocellular neurosecretory neurons into the portal system. where it triggers the release of corticotropin. Corticotropin triggers the release of cortisol from the adrenal cortex. Cortisol has many effects One of which is to inhibit the release of CRH from the hypothalamus - the system is self regulating

Posterior Pituitary Does not produce hormones, but stores 2 made by the hypothalamus Magnocellular neurosecretory cells in hypothalamus release two peptide hormones ADH (antidiuretic hormone or vasopressin) keeps blood volume constant by controlling reabsorbtion of H 2 0 in kidneys Oxytocin stimulates contractions of uterus at childbirth

Vasopressin Function At Low blood volume and blood pressure the kidneys secrete renin Renin converts angiotensinogen from the liver into angiotensin I and then to angiotensin II Angiotensin II has direct effects on the kidney and blood vessels to increase blood pressure Angiotensin II is also detected by the subfornical organ in the telencelphalon which is outside the blood brain barrier Subfornical organ neurons project to magnocellular neurosecretory neurons Vasopressin is released to increase water retention in kidney

The Thyroid On the trachea Secretes thyroxine regulates rate of cellular respiration controls metabolic activities including production of proteins & ATP necessary for proper development of nervous system & growth Need iodine to produce thyroxine Too little iodine = enlarged thyroid = goiter

The Parathyroids On the back of the thyroid 4 tiny glands Secrete PTH ( parathyroid hormone ) regulates level of calcium ions & phosphate ions in the blood (necessary for bones, muscles, nerves)

Hormonal Regulation of Calcium

The Adrenals Located on top of each kidney Each is like 2 separate glands Inside = Adrenal medulla Outside = Adrenal Cortex

The Adrenal Medulla In response to nerves signals from the sympathetic division of the autonomic nervous system, secretes epinephrine & norepinephrine Fight or flight - like stepping on the accelerate with the brake on Response to stress: increases blood pressure, heart rate, breathing, dilates pupils, increases metabolism

Adrenal Cortex Secretes more than 50 hormones corticoids Include: Aldesterone controls reabsorbtion of Na+ & K+ by the kidney Cortisol (hydrocortisone) controls glucose uptake by cells Androgens sex hormones

The Pancreas Also an exocrine gland produces digestive enzymes Islets of Langerhans a group of cells within the pancreas, function as endocrine glands Secrete insulin and glucagon which have opposite effects: Insulin lowers level of glucose in blood; without it glucose cannot enter body cells Glucagon triggers breakdown of glycogen to glucose .

The Gonads Gamete producing organs, also produce hormones female = estrogen male = androgen, testosterone both produce secondary sex characteristics, involved in reproduction

The Autonomic Nervous System Three divisions: Sympathetic Parasympathetic Enteric

Sympathetic Division Disynaptic pathway: releases acetylcholine onto sympathetic ganglion and norepinephrine postsynaptically Sympathetic ganglia form sympathetic chain along side the spinal cord Functions Dilates pupil Inhibits salivation and tearing Constricts blood vessels Accelerates heart rate Stimulates glucose release from liver Inhibits digestion Stimulates orgasm

Parasympathetic Division Disynaptic pathway: releases acetylcholine onto parasympathetic ganglion and acetylcholine postsynaptically Ganglia are scattered all over the place Functions: Constricts pupil Stimulates salivation and tearing Slows heart rate Stimulates digestion Stimulates release of insulin from pancreas Stimulates sexual arousal

Yin & Yang These two divisions generally oppose each other in effect Only one is activated at a time Sympathetic division is activated during a crisis: fight/flight/fright/sex - the 4 F's Parasympathetic division is active over long periods of time

Enteric Division Involves little direct brain function Semi-autonomous double: Auerbach's plexus and Meissner's plexus Found in esophagus, stomach, intestines, pancreas, and gall bladder Functions to control digestion Master control comes from the parasympathetic and sympathetic divisions

Autonomic/ Endocrine Link Central control of the ANS Periventricular zone of hypothalamus Nucleus of the solitary tract Integrates sensory inputs from internal organs and has outputs to the autonomic ganglia

Diffuse Modulatory Systems General characteristics: Core of each system is a small number of neurons, several thousand Core neurons are in central core of brain and brainstem Connections of one core neuron may affect 100,000 postsynaptic neurons widely dispersed Synapses by core neurons release into extracellular fluid rather than at standard synapses

Noradrenergic System Core neurons are in the locus coeruleus in the pons Targets are spinal cord, cerebellum, hypothalamus, thalamus, and most of neocortex Noradrenalin is released Functions are complex Involved in regulation of attention, arousal, and sleep-wake cycles Core neurons are activated by novel, non-painful sensory stimuli General increase of brain responsiveness

Serotonergic System Core neurons are in the Raphe nuclei in the brainstem from the pons to the medulla Targets are spinal cord, cerebellum, hypothalamus, thalamus, basal ganglia, and all of neocortex Serotonin is released Function - complex Core neurons are most active when animal is awake, least active during sleep Also involved in control of mood and some types of emotional behavior May work together with noradrenergic system during general arousal

Dopaminergic System Core neurons are in the substantia nigra and the ventral tegmental area , both in the floor of the midbrain Targets are the striatum and the frontal lobe of neocortex Dopamine is released Function: Part of the reward system for certain adaptive behaviors involved in addiction Malfunctions may lead to psychiatric disorders

Cholinergic System Core neurons are in the basal forebrain complex basal nucleus of Meynert innervates most of neocortex Medial septal nuclei innervate hippocampus Core neurons are also in the pontomesencephalo-tegmental complex in pons and midbrain tegmentum Innervate the thalamus and cortex Acetylcholine is released Function - largely confused Alzheimer's starts with these cholinergic neurons General arousal and sleep-wake cycles May have some role in memory

Endocrine Control

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Endocrine Control