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Biological Bases of Behaviour Cheat Sheet by

biological bases of behaviour for cuet prep


Scientific study of biological bases of behaviour and mental processes
Scientific study of the nervous system
Nervous System
An extensive system of organs and nerves that are in charge of relaying inform­ation and signals between different parts of the body; composed primarily of specia­lized cells called neurons.
Cell Body
energy source of the neuron, produces nutrients and waste, contains nucleus and DNA
a branching, threadlike extension of the cell body that increases the receptive surface of a neuron. Receives chemical messages from other neurons and cells, sends messages along the neuron if important.
the long, thin, hollow, cylind­rical extension of a neuron that normally carries a nerve impulse away from the cell body. Sends inform­ation through the neuron via the action potential.
Myelin Sheath
the insulating layer around many axons that increases the speed of conduction of nerve impulses. It consists of myelin and is laid down by glia, which wrap themselves around adjacent axons.
Axon Terminals
ending of an axon which releases neurot­ran­smi­tters into a synaptic space near another neuron, muscle, or gland cell.
the specia­lized junction through which neural signals are transm­itted from one neuron (the presyn­aptic neuron) to another (the postsy­naptic neuron).


Excitatory in all cases except in the heart (inhib­itory)
Motor neurons, basal ganglia, pregan­glionic neurons of the autonomic nervous system, postga­ngl­ionic neurons of the parasy­mpa­thetic nervous system, and postga­ngl­ionic neurons of the sympat­hetic nervous system that innervate the sweat glands
Regulates the sleep cycle, essential for muscle functi­oning
Brainstem, hypoth­alamus, and adrenal glands
Increases the level of alertness and wakefu­lness, stimulates various processes of the body
Chromaffin cells of the medulla of adrenal gland
The fight-­or-­flight response (increased heart rate, blood pressure, and glucose produc­tion)
Both excitatory and inhibitory
Substantia nigra
Inhibits unnece­ssary movements, inhibits the release of prolactin, and stimulates the secretion of growth hormone
Neurons of the spinal cord, cerebe­llum, basal ganglia, and many areas of the cerebral cortex
Reduces neuronal excita­bility throughout the nervous system
Sensory neurons and cerebral cortex
Regulates central nervous system excita­bility, learning process, memory
Neurons of the brainstem and gastro­int­estinal tract, thromb­ocytes
Regulates body temper­ature, perception of pain, emotions, and sleep cycle
Hypoth­alamus, cells of the stomach mucosa, mast cells, and basophils in the blood
Regulates wakefu­lness, blood pressure, pain, and sexual behavior; increases the acidity of the stomach; mediates inflam­matory reactions

Electrical Commun­ication

Two types of commun­ica­tion: one within the neuron, one between two or more neurons.
1. Commun­ication within the neuron: Electrical commun­ica­tion.
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.
When neuron gets ready to fire, the sodium floods into the neuron changing the charge and when it reaches the potential threshold and crosses it, the neuron fires.


positively or negatively charged particles.
Resting State
Neuron has more negative ions inside than on the outside. This means that the neuron is polarized.
Active State
Neuron has more positive charge than the outside. This means neuron is depola­rized.
Action Potential
Brief electrical impulse by which inform­ation is gathered by the dendrites and cell body are transm­itted along the axon of a neuron until they hit the axon terminals. Follows the all or none law.

Myelin and Propag­ation of Action Potential

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.
Myelin acts as an insulator that prevents current from leaving the axon; this increases the speed of action potential conduc­tion.
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.
If nodes of Ranvier were not present along an axon, the action potential would propagate very slowly since Na+ and K+ channels would have to contin­uously regenerate action potentials at every point along the axon instead of at specific points. Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon.

Chemical Synapse

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.
This depola­riz­ation causes voltag­e-gated Ca2+ channels to open. Calcium ions entering the cell initiate a signaling cascade that causes small membra­ne-­bound vesicles, called synaptic vesicles, containing neurot­ran­smitter molecules to fuse with 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 neurot­ran­smitter diffuses across the synaptic cleft and binds to receptor proteins on the postsy­naptic membrane.

Grey Matter and White Matter

Gray Matter
made up of clusters of neuronal bodies
In the brain, the majority of gray matter is found superf­icially comprising the cerebral cortex. Smaller clusters of gray matter are found deep within the white matter comprising the subcor­tical struct­ures, such as basal ganglia and dience­phalon. Every unit of gray matter in the brain which is outside of the cortex is called the nucleus.
the gray matter comprises its inner part and has a charac­ter­istic butterfly shape when observed on cross-­sec­tion.
White Matter
composed of their myelinated axons
The white matter, consisting of spinal cord pathways, is located externally surrou­nding the gray matter.
In the brain, the white matter composes its inner part.

Peripheral Nerves

Cranial Nerves
emerge from the cranium (brain­/br­ain­stem)
There are 12 pairs of cranial nerves
Spinal Nerves
leave the CNS via the spinal cord.
31 spinal nerve pairs
Afferent or sensory neurons
carry inform­ation towards the CNS
Efferent or motor neurons
the ones transm­itting impulses from the CNS

Peripheral Nervous System

A nervous system division composed of all the neural tissue found outside the cranial vault and vertebral canal.
Anatomical components
Peripheral nerves (spinal nerves, cranial nerves, autonomic nerves) Ganglia
Functional Components
Autonomic nervous system (ANS) - involu­ntary part in control of cardiac, smooth and glandular cells. It consists of sympat­hetic and parasy­mpa­thetic divisions. Somatic nervous system (SNS) - voluntary part in control of skeletal muscles and processing of somatic sensation.
Transmits motor and sensory inform­ation between the central nervous system and peripheral body tissues.

Parietal Lobe

Parietal Lobe
located just underneath the parietal bone, lying posterior to the frontal lobe and anterior and superior to the temporal and occipital lobes
anterior border of the parietal lobe is demarcated by the central sulcus, and the posterior border is formed by an imaginary line that extends between the pariet­ooc­cipital sulcus (super­iorly) and the preocc­ipital notch (infer­iorly)
can be divided into three regions. The most anterior portion of the parietal lobe is the postce­ntral gyrus which runs parallel to the central sulcus
Functi­onally, this area is known as the primary somato­sensory cortex
This region receives sensory inform­ation from all sensory receptors that provide inform­ation related to temper­ature, pain (spino­tha­lamic pathway), vibration, propri­oce­ption and fine touch (dorsal column pathway). Thus, the postce­ntral gyrus of the frontal lobe is mainly involved in processing various types of sensory inform­ation
remainder of the parietal lobe can be divided into two main regions: the superior and inferior parietal lobules, which are separated anatom­ically by the intrap­arietal sulcus. The superior parietal lobule contri­butes to sensor­imotor integr­ation while the inferior parietal lobule contri­butes to auditory and language functions.

Temporal Lobe

Temporal Lobe
largely occupies the middle cranial fossa, and its name relates to its proximity to the temporal region­/bone of the skull
separated from the frontal and parietal lobes superiorly by the lateral sulcus (Sylvian fissure). It extends ventrally from this fissure to the inferior surface of the cerebral cortex. Dorsally, it extends to an arbitrary line running between the pariet­ooc­cipital sulcus and the preocc­ipital notch
contains the cortical areas that process hearing, as well as sensory aspects of speech and memory
The primary auditory area, also known as the transverse gyri of Heschl, is located on the internal, superior part of the superior temporal gyrus. It is a specia­lized region of cortex primarily respon­sible for the reception of auditory inform­ation
Auditory inform­ation is further processed within the secondary auditory area. This lies posterior to the primary auditory area in the superior temporal gyrus, at the pariet­ote­mporal junction (Werni­cke’s region in the dominant hemisp­here), and receives impulses from the primary auditory area and thalamus.
the middle and inferior temporal gyri are respon­sible for visual percep­tion. The middle temporal gyrus is associated with the perception of movement within the visual field; whereas the inferior temporal gyrus contains the fusiform face area (FFA), which is necessary for face recogn­ition


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.
Gonads secrete the same set of hormones secreted by the adrenal cortex in the form of androgens. The release of hormones by the gonads is regulated by the release of gonado­trophin stimul­ating hormone of the pituitary gland.
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.
There is a pair of testis in men that secrete the hormone testos­terone as the primary sex hormone. The hormone is respon­sible for the develo­pment of the male sex organs as well as the develo­pment of secondary sex charac­ter­istics in men.
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.
The synthesis and release of sex hormones by the gonads are regulated by two hormones secreted by the pituitary; lutein­izing hormone and follic­le-­sti­mul­ating hormone.
These hormones also work as sex hormones by helping in the formation of male and female gametes.

Pituitary Gland

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 (Adeno­hyp­oph­ysis)
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.
Anterior Pituitary (AP) Hormones
Growth hormone (GH) Other names: somato­tropic hormone or somato­tropin Precursor cells: somato­trophs in the AP Target cells: almost all tissues of the body
GH acts almost on every type of cell. Its principal targets are bones and skeletal muscles. It has direct metabolic effects on fats, proteins, and carboh­ydrates and indirect actions that result in skeletal growth. Direct Metabolic Functions: GH is anabolic. It stimulates the growth of almost all tissues of the body that are capable of growing (increase in the number of cells). GH also increases the rate of protein synthesis in most cells of the body and decreases the rate of glucose utiliz­ation throughout the body (diabe­togenic action). Also, it increases the mobili­zation of fatty acids from adipose tissue and increases levels of free fatty acids in the blood. Indirect Actions on Skeletal Growth: GH stimulates the production of IGF-1 from hepato­cytes. IGF-1 mediates the growth­-pr­omoting effects of GH on the skeleton. IGF-1 exerts direct actions on both cartilage and bone to stimulate growth and differ­ent­iation. These effects are crucial for growth during childhood to the end of adoles­cence.
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.
Follic­le-­sti­mul­ating hormone (FSH) and lutein­izing hormone (LH) Precursor cells: gonado­trophs in the AP Target cells: gonads (ovaries and testes) Mechanism of action: FSH and LH bind to G protei­n-c­oupled receptors to activate adenylyl cyclase enzyme, which in turn increases intrac­ellular cAMP. cAMP activates protein kinase A (PKA) that phosph­ory­lates intrac­ellular proteins. These phosph­ory­lated proteins then accomplish the final physio­logic actions. Regula­tion: FSH and LH secretion are under the control of the hypoth­alamic gonado­tro­pin­-re­leasing hormone (GnRH). Physio­logical Functions: FSH and LH regulate the functions of the ovaries and the testes. In females, FSH stimulates growth and develo­pment of follicles in prepar­ation for ovulation and secretion of estrogens by the mature Graafian follicle. LH triggers ovulation and stimulates the secretion of proges­terone by the corpus luteum. In males, FSH is required for sperma­tog­enesis, and LH stimulates testos­terone secretion by Leydig cells.
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 (Neuro­hyp­oph­ysis)
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.
Oxytocin Precursor cells: parave­ntr­icular and supraoptic nuclei in the hypoth­alamus Target cells: myoepi­thelial cells of the mammary glands and the uterine muscles (myome­trium) in women and myofib­roblast cells in the semini­ferous tubules in men. Mechanism of action: oxytocin acts on its target cells via a G-protein coupled receptor, which activates phosph­olipase C that in turn stimulates phosph­oin­ositide turnover. This causes increased intrac­ellular calcium concen­tra­tion, which activates the contra­ctile machinery of the cell. Regula­tion: oxytocin is released in response to an afferent neural input to the hypoth­alamic neurons that synthesize the hormone. Suckling and uterine stimul­ation by the baby’s head during delivery are the major stimuli for oxytocin release. It is subject to positive feedback regula­tion. Physio­logical Functions: oxytocin stimulates milk ejection from the breast in response to suckling (milk ejection reflex). It causes contra­ction of myoepi­thelial cells surrou­nding the ducts and alveoli of the gland and therefore milk ejection. Oxytocin also stimulates uterine contra­ction during labor to expel the fetus and placenta.
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.

Pituitary Gland

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 (Adeno­hyp­oph­ysis)
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.
Anterior Pituitary (AP) Hormones
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)

Occipital Lobe

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 occipital lobe is separated superiorly from the parietal lobe by the pariet­ooc­cci­pital sulcus. Anteri­orly, it is separated from the temporal lobe by an imaginary line called the lateral pariet­ote­mporal line, that extends from the termin­ation of the pariet­ooc­cipital sulcus superi­orly, and to the preocc­ipital notch inferi­orly.
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 intrao­cci­pital sulcus, which is formed as an extension of the intrap­arietal sulcus, separates the superior and middle gyri (if present)
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).
A fissure known as the calcarine sulcus begins slightly above the occipital pole just behind the pariet­ooc­cipital sulcus. The calcarine sulcus divides the medial aspect of the occipital lobe into the cuneate gyrus (cuneus) superiorly and the lingual gyrus inferi­orly.
The calcarine sulcus also marks the location of the primary visual cortex which is respon­sible for visual percep­tion.
The occipital lobe is identified as the main visual processing centre. It is associated with color determ­ina­tion, facial recogn­ition, depth percep­tion, visuos­patial processing and even plays a role in memory formation. The occipital lobe not only enables visual perception but allows us to process and interpret visual inform­ation.

Action Potential

An action potential is defined as a sudden, fast, transi­tory, and propag­ating change of the resting membrane potential.
Cells which can generate action potential
Muscle cells and Neurons
an action potential is generated when a stimulus changes the membrane potential to the values of threshold potential. The threshold potential is usually around -50 to -55 mV. This means that any subthr­eshold stimulus will cause nothing, while threshold and suprat­hre­shold stimuli produce a full response of the excitable cell.


is the initial increase of the membrane potential to the value of the threshold potential. The threshold potential opens voltag­e-gated sodium channels and causes a large influx of sodium ions.
During depola­riz­ation, the inside of the cell becomes more and more electr­opo­sitive, until the potential gets closer the electr­och­emical equili­brium for sodium of +61 mV.
This phase of extreme positivity is the overshoot phase
After the overshoot, the sodium permea­bility suddenly decreases due to the closing of its channels. The overshoot value of the cell potential opens voltag­e-gated potassium channels, which causes a large potassium efflux, decreasing the cell’s electr­opo­sit­ivity.
Repola­riz­ation always leads first to hyperp­ola­riz­ation, a state in which the membrane potential is more negative than the default membrane potential. But soon after that, the membrane establ­ishes again the values of membrane potential.

Synaptic Transm­ission

is the place where inform­ation is transm­itted from one neuron to another.
usually form between axon terminals and dendritic spines. There are also axon-t­o-axon, dendri­te-­to-­den­drite, and axon-t­o-cell body synapses.
Pre-sy­naptic neuron
The neuron transm­itting the signal
Post-s­ynaptic neuron
The neuron receiving the signal.
These design­ations are relative to a particular synaps­e—most neurons are both presyn­aptic and postsy­naptic.
Two Types
Chemical and Electrical

Central Nervous System

the CNS is the supreme command center of the body
consists of two organs which are continuous with each other; the brain and spinal cord.
are enveloped and protected by three layers of meninges, and encased within two bony struct­ures; the skull and vertebral column, respec­tively.
brain consists of the cerebrum, subcor­tical struct­ures, brainstem and cerebellum
spinal cord continues inferiorly from the brainstem and extends through the vertebral canal

Structures of The Brain

is the largest part of the brain, divided into two hemisp­heres – a left and a right – by the falx cerebri along the longit­udinal cerebral fissure.
Each hemisphere can then be subdivided into lobes that are named according to the cranial bones under which they reside.
It is an ovoid structure that resides in the posterior cranial fossa, inferior to the tentorium cerebelli. It has an outer grey matter cortex and white matter intern­ally.
Brain Stem
is the distal part of the brain that is made up of the midbrain, pons, and medulla oblongata.
Parts of the Brain Stem
Medulla oblongata
is the narrowest and most caudal part of the brainstem. It is a funnel­-like structure.
The medulla develops from the myelen­cep­halon, which is a secondary brain vesicle that arises from the rhombe­nce­phalon (the hindbr­ain). The other secondary brain vesicle to arise from the hindbrain is superior to the myelen­cep­halon and gives rise to the pons.
resembles a dome-like structure with numerous striations across its surface. It is widest in the middle and tapers toward the lateral extrem­ities.
function: to house the pontine nuclei and to facilitate cortic­opo­nto­cer­ebellar commun­ica­tion. It also enables commun­ication between the left and right hemisp­heres of the cerebe­llum.
is the shortest segment of the brainstem. It extends caudally from the base of the thalamus to the superior roof of the fourth ventricle.
Reticular formation
The reticular formation is a vast network of neurons that are involved in mainta­ining consci­ousness and initiating arousal. This neuronal tract extends from the spinal cord to the dience­phalon and occupies different parts of the brainstem throug­hout.
The nuclei of the reticular formation are situated deep within the brainstem along its vertical axis. On each half of the brainstem, there is a lateral, medial, and median group of nuclei. The combined effect of this collection of nuclei are related to the regulation of the circadian rhythm, coordi­nates the respir­atory and antigr­avity muscles, modifies reflex activity, and also helps to coordinate the muscles of facial expres­sion.

Frontal Lobe

Frontal Lobe
largest lobe of the brain comprising almost one-third of the hemisp­heric surface
frontal lobe forms the most anterior portion of the cerebral hemisphere and is separated from the parietal lobe poster­iorly by the central sulcus, and from the temporal lobe poster­oin­fer­iorly by the lateral sulcus
The most anterior portion of the frontal lobe is known as the frontal pole
is made up of three cortical surfaces: a lateral, medial and inferior surface
lateral surface of the frontal lobe contains four principal gyri: the precen­tral, superior frontal, middle frontal, and the inferior frontal gyri
medial (inter­hem­isp­heric) surface extends down to the cingulate sulcus and consists mainly of the parace­ntral lobule (an extension of the precentral and postce­ntral gyri), and the medial extension of the superior frontal gyrus
nferior surface contains the olfactory tract and olfactory bulb, the straight gyrus and the four orbital gyri
the entire frontal cortex of the frontal lobe is divided into three parts: the prefrontal cortex, motor cortex and Broca’s area
Prefrontal cortex
encomp­asses the superior, middle and inferior frontal gyri of the frontal lobe
It plays a crucial role in the processing of intell­ectual and emotional inform­ation, including aggres­sion, and facili­tates judgement and decisi­on-­making
Motor cortex
corres­ponds to the precentral gyrus of the frontal lobe. The precentral gyrus contains the primary motor cortex
which is respon­sible for integr­ating signals from different brain regions to modulate motor function. The primary motor cortex is where the cortic­ospinal tract origin­ates.
Encomp­assing part of the middle and inferior frontal gyri, just rostral to the premotor region, is an area called the frontal eye fields
which is respon­sible for voluntary control of conjugate (horiz­ontal) eye movements
Broca's Area
inferior frontal gyrus is divided into three parts: i) the pars opercu­laris, ii) the pars triang­ularis, and iii) the pars orbitalis
Pars opercu­laris refers to the most dorsal part of the gyrus
pars triang­ularis is the middle triang­ula­rly­-shaped part
the pars orbitalis represents the most ventral part of the gyrus
the pars opercu­laris and triang­ularis in the dominant hemisphere are referred to as Broca’s speech area
Broca’s area is respon­sible for producing the motor component of speech, which includes verbal fluency, phonol­ogical proces­sing, grammar processing and attention during speech

Endocrine System

Endocrine System
consists of a series of glands that produce chemical substances known as hormones
hormones are chemical messengers that must bind to a receptor in order to send their signal
hormones are secreted into the bloods­tream and travel throughout the body, affecting any cells that contain receptors for them
Imbalances in hormones are related to a number of disorders.


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 hypoth­alamus functions in conjun­ction with the pituitary gland through the hypoth­ala­mic­-pi­tuitary axis. The hypoth­alamus itself contains several types of neurons that release different hormones. The thyrot­rop­in-­rel­easing hormone (TRH), gonado­tro­pin­-re­leasing hormone (GnRH), growth hormon­e-r­ele­asing hormone (GHRH), cortic­otr­opi­n-r­ele­asing hormone (CRH), somato­statin, and dopamine are released from the hypoth­alamus into the blood and travel to the anterior pituitary.
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.

Thyroid Gland

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.
T3 is respon­sible for affecting many organs and tissues throughout the body, which can, in summary, is the effect of increasing metabolic rate and protein synthesis. Parafo­lli­cular cells, or C cells, are respon­sible for the production and secretion of calcit­onin. Calcitonin opposes parath­yroid hormone to decrease blood calcium levels and maintain calcium homeos­tasis.
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.
These iodoth­yro­nines are composed of thyrog­lobulin and iodine. Thyrog­lobulin is formed from amino acids in a basal to apical fashion within the thyroid cells themse­lves. Thyrog­lobulin is then secreted into the follicular lumen, where it is enzyma­tically combined with iodine to form iodinated thyrog­lob­ulin. Endosomes containing this iodinated thyrog­lobulin then fuse with lysosomes, which enzyma­tically release the thyrog­lobulin from the resultant thyroid hormone. The thyroid hormones are next released from the cell while the remaining thyrog­lobulin is deiodi­nated and recycled for further use.

Parath­yroid Gland

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.

Adrenal Gland

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.
Adrenal Cortex
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).
Hypoth­ala­mic­-Pi­tui­tar­y-A­drenal (HPA) Axis
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).
CRH binds receptors on the anterior pituitary gland, which leads to the synthesis of ACTH (or cortic­otr­ophin) from pre-pr­o-o­pio­mel­ano­cortin (pre-P­OMC). Of note, cleavage of POMC also yields other hormones such as alpha-­mel­ano­cyt­e-s­tim­ulating hormone (MSH). ACTH from the anterior pituitary is released into the circul­ation and engages the melano­cortin type 2 receptors (MC2-R) in the zona fascic­ulata of the adrenal cortex predom­inantly to induce the synthesis of glucoc­ort­icoids. It is a GPCR and has an associated protein (MRAP) produced by the adrenal that appears to function as a chaperone to escort MC2-R to the cell surface to allow engagement by ACTH.C­irc­ulating glucoc­ort­icoids negatively feedback on the hypoth­alamus (long loop) and the anterior pituitary (short loop), suppre­ssing the release of CRH and ACTH, respec­tively. This prevents the continued rise of glucoc­ort­icoid levels. ACTH is released from the anterior pituitary in a pulsatile pattern that parallels the fluctu­ating levels of cortisol. Both ACTH and cortisol levels rise to a peak in the morning (6:00 AM to 8:00 AM) and decline throughout the day, reaching their nadir at around midnight.
Adrenal Medulla and the Sympat­hetic Nervous System
The sympat­hetic nervous system regulates the secretion of epinep­hrine and norepi­nep­hrine from the adrenal medulla.


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