Biological Bases of Behaviour Cheat Sheet by rentasticco

Two types of commun­ica­tion: one within the neuron, one between two or more neurons.

Within the axon of the neuron is negatively charged potassium, surrounded by positively charged sodium when the neuron is at rest, or it is ready to fire.

The speed of conduction of an action potential along an axon is influenced by both the diameter of the axon and the axon’s resistance to current leak.

The nodes of Ranvier are gaps in the myelin sheath along the axon. These unmyel­inated spaces are about one micrometer long and contain voltage gated Na+ and K+ channels. Flow of ions through these channels, partic­ularly the Na+ channels, regene­rates the action potential over and over again along the axon. This ‘jumping’ of the action potential from one node to the next is called saltatory conduc­tion.

When an action potential reaches the axon terminal it depola­rizes the membrane and opens voltag­e-gated Na+ channels. Na+ ions enter the cell, further depola­rizing the presyn­aptic membrane.

Fusion of a vesicle with the presyn­aptic membrane causes neurot­ran­smitter to be released into the synaptic cleft, the extrac­ellular space between the presyn­aptic and postsy­naptic membranes.

The male and female gonads are endocrine glands that produce sex hormones essential for the develo­pment of reprod­uctive organs and the proper functi­oning of the process of reprod­uction.

The male gonads are called testes, whereas the female gonads are called ovaries. The sex hormones secreted by the male and female gonads are different but perform more or less similar functions.

The gonads occur in the form of ovaries in women. There are two ovaries in women that secrete two hormones, estrogen, and proges­terone that are respon­sible for different processes like ovulation, menstrual cycle, and develo­pment of secondary sex characters in women.

These hormones also work as sex hormones by helping in the formation of male and female gametes.

The pituitary endocrine gland, which is located in the bony sella turcica, is attached to the base of the brain and has a unique connection with the hypoth­alamus. The pituitary gland consists of two anatom­ically and functi­onally distinct regions, the anterior lobe (adeno­hyp­oph­ysis) and the posterior lobe (neuro­hyp­oph­ysis). Between these lobes lies a small region called the interm­ediate lobe. The hypoth­alamus regulates the pituitary gland secretion.

The anterior pituitary is derived from embryonic ectoderm. It secretes five endocrine hormones from five different types of epithelial endocrine cells. The release of anterior pituitary hormones is regulated by hypoth­alamic hormones (releasing or inhibi­tory), which are synthe­sized in the cell bodies of neurons located in several nuclei that surround the third ventricle.

Growth hormone (GH) Other names: somato­tropic hormone or somato­tropin Precursor cells: somato­trophs in the AP Target cells: almost all tissues of the body

Prolactin Precursor cells: mainly from lactot­rophs in the AP Target cells: main target cells are mammary glands and gonads Mechanism of action: binds to peptide hormone receptor (single transm­embrane domain) to activate the JAK2-STAT intrac­ellular signaling pathway similar to that of GH Regula­tion: Like GH, dual hypoth­alamic inhibitory (from dopamine) and stimul­atory hormones (PRH) regulate prolactin secretion. The predom­inant hypoth­alamic influence is inhibi­tory. Physio­logical Functions: The main functions of prolactin are stimul­ating mammary gland growth and develo­pment (mammo­graphic effect) and milk production (lacto­genic effect). It also has effects on the hypoth­ala­mic­-pi­tui­tar­y-g­onadal axis and can inhibit pulsatile GnRH secretion from the hypoth­alamus.

Adreno­cor­tic­otr­ophic hormone (ACTH) Precursor cells: cortic­otrophs in the AP Target cells: cells in the cortex of the adrenal glands (adren­oco­rtical cells) Mechanism of Action: ACTH binds to its G-protein coupled receptors on the adreno­cor­tical cells. Similar to TSH, FSH, and LH, it activates adenylyl cyclas­e-P­KA-cAMP system to phosph­orylate several proteins, which in turn achieve the final physio­logic functions. Regula­tion: ACTH secretion is under the control of the hypoth­alamic cortic­otr­opi­n-r­ele­asing hormone (CRH). It is subject to negative feedback regulation Physio­logical functions: the main function of ACTH is to stimulate the secretion of adrenal cortex hormones (mainly glucoc­ort­icoids) during stress.

The posterior pituitary is neural in origin. Unlike the anterior pituitary, the posterior pituitary is connected directly to the hypoth­alamus via a nerve tract (hypot­hal­amo­hyp­oph­yseal nerve tract). It secretes two hormones: oxytocin and antidi­uretic hormone (ADH) or vasopr­essin. The hormones are synthe­sized by the magnoc­ellular neurons located in the supraoptic and parave­ntr­icular nuclei of the hypoth­alamus. The hormones are transp­orted in associ­ation with neurop­hysins proteins along the axons of these neurons to end in nerve terminals within the posterior pituitary.

Antidi­uretic Hormone (ADH) or Vasopr­essin Precursor cells: parave­ntr­icular and supraoptic nuclei of the hypoth­alamus. Target cells: renal distal convoluted tubules and collecting duct and vascular smooth muscle cells. Mechanism of action: similar to oxytocin, it acts on its target cells via a G-protein coupled receptor, which activates phosph­olipase C that in turn stimulates phosph­oin­ositide turnover and causes an increase in intrac­ellular calcium concen­tration which in turn achieves the final physio­logic actions. Regula­tion: The main stimulus for ADH release is an increase in osmolality of circul­ating blood. Osmore­ceptors located in the hypoth­alamus detect this increase and activate the parave­ntr­icular and supraoptic nuclei to release ADH. It also releases in response to hypovo­lemia. Physio­logical Functions: ADH binds to V2 receptors on the distal tubule and collecting ducts of the kidney to up-reg­ulate aquaporin channel expression on the basola­teral membrane and increase water reabso­rption. It, as its name suggests, also acts as a vasoco­nst­rictor upon binding to V1 receptors on the arteriolar smooth muscle.

The pituitary endocrine gland, which is located in the bony sella turcica, is attached to the base of the brain and has a unique connection with the hypoth­alamus. The pituitary gland consists of two anatom­ically and functi­onally distinct regions, the anterior lobe (adeno­hyp­oph­ysis) and the posterior lobe (neuro­hyp­oph­ysis). Between these lobes lies a small region called the interm­ediate lobe. The hypoth­alamus regulates the pituitary gland secretion.

The anterior pituitary is derived from embryonic ectoderm. It secretes five endocrine hormones from five different types of epithelial endocrine cells. The release of anterior pituitary hormones is regulated by hypoth­alamic hormones (releasing or inhibi­tory), which are synthe­sized in the cell bodies of neurons located in several nuclei that surround the third ventricle.

Growth hormone (GH) Other names: somato­tropic hormone or somato­tropin Precursor cells: somato­trophs in the AP Target cells: almost all tissues of the body Transport: 60% circulates free and 40% bound to specific GH-binding proteins (GHBPs)

The occipital lobe lies just underneath the occipital bone. It forms the most posterior portion of the brain and is found behind both the parietal and temporal lobes.

The supero­lateral aspect of the occipital lobe presents with three notable gyri: the superior, middle and inferior occipital gyri. The superior occipital gyrus is the clearly defined gyrus on the lateral surface of the occipital lobe.

The lateral occipital sulcus (also known as the inferior occipital sulcus) separates the inferior occipital gyrus from the superior, or the middle occipital gyrus (if present).

The calcarine sulcus also marks the location of the primary visual cortex which is respon­sible for visual percep­tion.

the CNS is the supreme command center of the body

are enveloped and protected by three layers of meninges, and encased within two bony struct­ures; the skull and vertebral column, respec­tively.

spinal cord continues inferiorly from the brainstem and extends through the vertebral canal

The hypoth­alamus is the region in the ventral brain which coordi­nates the endocrine system. It receives many signals from various regions of the brain and in return, releases both releasing and inhibiting hormones, which then act on the pituitary gland to direct the functions of the thyroid gland, adrenal glands, and reprod­uctive organs and to influence growth, fluid balance, and milk produc­tion.

The thyrot­rop­in-­rel­easing hormone is a tripeptide that stimulates the release of thyroi­d-s­tim­ulating hormone and prolactin from the anterior pituitary gland. The gonado­tro­pin­-re­leasing hormone triggers sexual develo­pment at the onset of puberty and maintains female and male physiology after that by contro­lling the release of follic­le-­sti­mul­ating hormone and lutein­izing hormone. The growth hormon­e-r­ele­asing hormone stimulates the secretion of growth hormone by the anterior pituitary. The cortic­otr­opi­n-r­ele­asing hormone stimulates the release of adreno­cor­tic­otropic hormone from the anterior pituitary. Somato­statin inhibits the release of both growth hormone and thyroi­d-s­tim­ulating hormone, and various intestinal hormones. Dopamine inhibits the release of prolactin from the anterior pituitary, modulates motor-­control centers, and activates the reward centers of the brain. Prolactin functions mainly to promote lactation but also helps regulate reprod­uction, metabo­lism, and the immune system.

The thyroid is an endocrine gland. Its location is in the inferior, anterior neck, and it is respon­sible for the formation and secretion of the thyroid hormones as well as iodine homeos­tasis within the human body. The thyroid produces approx­imately 90% inactive thyroid hormone, or thyroxine (T4), and 10% active thyroid hormone, or triiod­oth­yronine (T3). Inactive thyroid hormone is converted periph­erally to either activated thyroid hormone or an altern­ative inactive thyroid hormone.

The thyroid gland is respon­sible for the production of iodoth­yro­nines, of which there are three. The primary secretory product is inactive thyroxine, or T4, a prohormone of triiod­oth­yro­nine, or T3. T4 is converted to T3 periph­erally by type 1 deiodinase in tissues with high blood flow, such as the liver and kidneys. In the brain, T4 is converted to active T3 by type 2 deiodinase produced by glial cells. The third iodoth­yronine is called reverse T3, or rT3. rT3 is inactive and forms by type 3 deiodinase activity on T4.

In the blood, the sensitive process of calcium and phosphate homeos­tasis is maintained primarily by an approp­riately functi­oning parath­yroid gland. The parath­yroid gland is comprised of 4 small glands located poster­iorly to the thyroid in the middle aspect of the anterior neck. The parath­yroid gland secretes parath­yroid hormone (PTH), a polype­ptide, in response to low calcium levels detected in the blood. PTH facili­tates the synthesis of active vitamin D and calcitriol (1,25-­dih­ydr­oxy­cho­lec­alc­iferol) in the kidneys. In conjun­ction with calcit­riol, PTH regulates calcium and phosphate. PTH effects are present in the bones, kidneys, and small intest­ines. As serum calcium levels drop, the secretion of PTH by the parath­yroid gland increases. Increased calcium levels in the serum serve as a negati­ve-­fee­dback loop signaling the parath­yroid glands to stop the release of PTH.

The pancreas is a composite organ, which has exocrine and endocrine functions. The endocrine portion is arranged as discrete islets of Langer­hans, which are composed of five different endocrine cell types (alpha, beta, delta, epsilon, and upsilon) secreting at least five hormones including glucagon, insulin, somato­statin, ghrelin, and pancreatic polype­ptide, respec­tively.

Source: Beta cells of islets of the pancreas. Synthesis: Insulin is a peptide hormone. The insulin mRNA is translated as a single­-chain precursor called prepro­ins­ulin, and removal of its signal peptide during insertion into the endopl­asmic reticulum generates proins­ulin. Within the endopl­asmic reticulum, proinsulin is exposed to several specific endope­pti­dases, which excise the C peptide (one of three domains of proins­ulin), thereby generating the mature form of insulin. Insulin is secreted from the cell by exocytosis and diffuses into islet capillary blood. C-peptide is also secreted into the blood in a 1:1 molar ratio with insulin. Although C-peptide has no establ­ished biological action, it is used as a useful marker for insulin secretion. Transport: insulin circulates entirely in unbound form (T1/2 = 6 min). Main Target cells: hepatic, muscle and adipocyte cells (i.e., cells specia­lized for energy storage). Mechanism of action: Insulin binds to a specific receptor tyrosine kinase on the plasma membrane and increases its activity to phosph­orylate numerous regulatory enzymes and other protein substr­ates. Regulation of its secretion: Plasma glucose level is the main regulator of insulin secretion. The change in the concen­tration of plasma glucose that occurs in response to feeding or fasting is the main determ­inant of insulin secretion. Modest increases in plasma glucose level provoke a marked increase in plasma insulin concen­tra­tion. Glucose is taken up by beta cells via glucose transp­orters (GLUT2). The subsequent metabolism of glucose increases cellular adenosine tripho­sphate (ATP) concen­tra­tions and closes ATP-de­pendent potassium (KATP) channels in the beta cell membrane, causing membrane depola­riz­ation and an influx of calcium. Increased calcium intrac­ellular concen­tration results in an increase of insulin secretion. Increased plasma amino acid and free fatty acid concen­tra­tions induce insulin secretion as well. Glucagon is also known to be a strong insulin secret­agogue. Physio­logical functions: Insulin plays an important role to keep plasma glucose value within a relatively narrow range throughout the day (glucose homeos­tasis). Insulin’s main actions are (1) In the liver, insulin promotes glycolysis and storage of glucose as glycogen (glyco­gen­esis), as well as conversion of glucose to trigly­cer­ides, (2) In muscle, insulin promotes the uptake of glucose and its storage as glycogen, and (3) in adipose tissue, insulin promotes uptake of glucose and its conversion to trigly­cerides for storage.

The adrenal gland is made up of the cortex and medulla. The cortex produces steroid hormones including glucoc­ort­icoids, minera­loc­ort­icoids, and adrenal androgens, and the medulla produces the catech­ola­mines, epinep­hrine, and norepi­nep­hrine. This brief article reviews the physiology of the adrenal gland and highlights the relevance of unders­tanding the clinical syndromes of excess and defici­ency.

The adrenal cortex takes part in steroi­dog­enesis, producing glucoc­ort­icoids, minera­loc­ort­icoids, and androgen precur­sors. It has 3 distinct functional and histol­ogical zones: the zona glomer­ulosa (outermost layer), the zona fascic­ulata (middle layer), and the zona reticu­laris (innermost layer).[1] Each layer produces steroid hormones from the precursor choles­terol. However, the specific steroid hormone produced differs in each layer because of zonal specific enzymes. The zona glomer­ulosa produces minera­loc­ort­icoids, the zona fascic­ulata produces glucoc­ort­icoids, and the zona reticu­laris produces androgen precursors (mostly DHEA with some andros­ten­edi­one).

The hypoth­ala­mic­-pi­tui­tar­y-a­drenal (HPA) axis is involved in the production of glucoc­ort­icoids and adrenal androgens from the zona fascic­ulata and zona reticu­laris. In response to circadian rhythms or stressors, parave­ntr­icular neurons (PVN) in the hypoth­alamus make and secrete cortic­otr­opi­n-r­ele­asing hormone (CRH).