Refers to neurons, synapses, or receptors where acetylcholine is used as the neurotransmitter.

For example, cholinergic neurons release acetylcholine as their neurotransmitter.

In cholinergic synapses, acetylcholine is released from the presynaptic neuron, and it acts on acetylcholine receptors in the plasma membrane of the postsynaptic cell.

Cholinergic receptors are those that respond to acetylcholine as the physiological ligand. The two major types are nicotinic and muscarinic cholinergic receptors (may also be referred to as nicotinic and muscarinic acetylcholine receptors).

Cholinergic drugs are compounds that mimic the action of acetylcholine by binding to and activating cholinergic receptors.

Excessive appetite or consumption of food. It may be associated with damage to the hypothalamus. Also referred to as polyphagia.

Hyperphagia

Hyperphagia

The A band is the region of a striated muscle sarcomere that contains myosin thick filaments. In fact, the A band is the entire length of the thick filament of the sarcomere. Its length is approximately 1 μm. The center of the A band is located at the center of the sarcomere (M line).

H zone
I band
M line
Z disk

The absolute refractory period refers to a period during the action potential. This is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. The absolute refractory period starts immediately after the initiation of the action potential and lasts until after the peak of the action potential. Following this period, the relative refractory period begins.

Relative refractory period

Neuronal Action Potential - Refractory Periods

An enzyme found in the synaptic cleft at cholinergic synapses. It degrades acetylcholine to choline and acetate and, thus, terminates the action of acetylcholine at the synapse. Neither choline nor acetate can bind to acetylcholine receptors (nicotinic or muscarinic).

Leading toward a region or structure of interest.

In the nervous system, afferent fibers (i.e., neurons) transmit information from a peripheral receptor to the spinal cord or the brainstem. Afferent neurons are also referred to as sensory neurons.

In the kidneys, the afferent arteriole carries blood to the glomerular capillaries.

Efferent

An agonist is a molecule that binds to a receptor and activates a physiological response similar to that induced by the naturally occurring physiological ligand of the receptor. Therefore, agonist binding to a receptor mimics the action of the natural ligand.

For example, acetylcholine (ACh) is the naturally occurring physiological ligand that activates nicotinic and muscarinic acetylcholine receptors. Nicotine is an agonist of nicotinic ACh receptors (nAChR), and muscarine is an agonist of muscarinic ACh receptors (mAChR).

Antagonist

All-or-nothing is usually used when describing the action potential. It refers to the well-known observation that an action potential always occurs in its full size (i.e., full magnitude of voltage change).

Many physiologists use all-or-nothing and all-or-none interchangeably.

Important Features of the Neuronal Action Potential

An antagonist is a molecule that binds to a receptor, however, it does not activate the physiological response induced by the naturally occurring physiological ligand of the receptor. Moreover, once bound to the receptor, an antagonist prevents the physiological ligand from activating the receptor. Therefore, antagonist binding to a receptor prevents or blocks the action of the natural ligand.

For example, acetylcholine (ACh) is the naturally occurring physiological ligand that activates nicotinic and muscarinic acetylcholine receptors. Tubocurarine and succinylcholine are antagonists of the nicotinic ACh receptor (nAChR), and atropine is an antagonist of the muscarinic ACh receptor (mAChR).

Agonist

The most distal sphincter in the gastrointestinal (GI) tract.

The region of the neuron cell body from which the axon originates. The axon hillock is generally the site of action potential initiation. It is also referred to as the initial segment.

Ca²⁺

Calcium (Ca²⁺) is a divalent cation. It plays an important role in physiological processes such as muscle contraction and synaptic transmission. Calcium is also an intracellular messenger.

The extracellular concentration of Ca²⁺ is about 2 mM. The intracellular concentration of Ca²⁺ is about 70 nM.

The lowest part of the female uterus facing the vaginal canal. It is cylindrical in shape and 2-3 cm long. A cervical canal runs the entire length of the cervix and connects the lumen of the vaginal canal to the lumen of the uterus. The opening of cervical canal into the uterus is called the internal os, and the opening into the vagina is called the external os.

An integral membrane protein which contains a pore through which ions, water, or polar molecules permeate. For any given channel, the pore is usually very selective for the particular ion or molecule. For example, sodium (Na⁺) channels are very selective for Na⁺ over other cations.

The channel pore may be constitutively open, or it may be gated to the open state by various stimuli such as chemical ligands, voltage, temperature, or mechanical stimulation of the membrane.

Refers to the concentration gradient of an ion or molecule. The concentration gradient may exist across a biological membrane, where the concentration is higher on one side of the membrane compared to the other side. Concentration gradient may also exist in a solution without an apparent barrier separating the area of higher concentration from the area of lower concentration. In both cases, the free energy that results from the concentration difference drives the movement of the ion/molcule from the area of higher concentration to the area of lower concentration. In free solution, the ion/molecule simply diffuses down its gradient. Movement across a biological membrane is more complicated and is a function of lipid solubility of the ion/molecule as well as the presence of channels or transport proteins that can allow the ion/molecule to cross the membrane (see Lipid Bilayer Permeability and Summary of Membrane Transport Processes).

Electrical gradient
Electrochemical gradient

CI⁻

The main anion (negatively charged ion) of the extracellular fluid.

Cloride (Cl⁻) plays an important role in several physiological processes such as the action potential of skeletal muscle cells, CO₂ transport in blood (via Cl⁻/bicarbonate exchange across the plasma membrane of red blood cells), and many other processes.

The extracellular concentration of Cl⁻ is about 110 mM. The intracellular concentration of Cl⁻ is about 10 mM.

The semi-solid, partially-digested contents of the stomach that exit via the pyloric valve to enter the duodenum (initial region) of the small intestine.

A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na⁺ or H⁺) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In cotransport, the direction of transport is the same for both the driving ion and driven ion/molecule (into the cell or out of the cell).

An example is the Na⁺/glucose cotransporter (SGLT), which couples the movement of Na⁺ into the cell down its electrochemical gradient to the movement of glucose into the cell against its concentration gradient.

Cotransport is also commonly referred to as symport.

Transport proteins that are involved in this type of transport are referred to as cotransporters or symporters.

Symport

Secondary active transport
Exchange

Lecture notes on Secondary Active Transport

A potent blocker of nicotinic cholinergic receptors (nicotinic acetylcholine receptor, nAChR) found at the neuromuscular junction. At small doses, curare can lead to muscle weakness. At high doses, curare can lead to paralysis of skeletal muscles, which would also result in asphyxiation (and ultimately death) due to paralysis of the diaphragm. Curare was commonly the active agent of poison arrow.

See Wikipedia

An electrophysiological technique in which the current passing across the cell membrane is controlled experimentally, and the membrane voltage is measured.

Voltage clamp

Neuronal Action Potential - Pharmacological Inhibition of Na⁺ and K⁺ Channels

The flow of charge. In electrical wires and electronic circuits, current is carried by electrons. In physiological solutions, current is carried by ions in solutions.

Voltage

The first region (i.e., most proximal region) of the small intestine. Chyme leaving the stomach (through the pyloric valve) first enters the duodenum. The contents of the duodenum empty into the jejunum (middle region of the small intestine). In adult humans, the duodenum is about 25-38 cm (10-15 inches) long.

Jejunum
Ileum

Leading away from a region or structure of interest.

In the nervous system, efferent fibers (i.e., neurons) transmit information from the central nervous system to peripheral effector organs (i.e., muscles or glands). Therefore, the cells bodies of efferent neurons reside within the central nervous system, whereas their axonal projections exit the central nervous system to make synaptic contact with effector organs in the periphery. Efferent neurons are also referred to as motor neurons.

In the kidneys, the efferent arteriole carries blood away from the glomerular capillaries.

Afferent

Movement of a substance out of the cell.

Efflux is reported as a rate. It is the amount of substance that moves through a given area of the plasma membrane per unit time.

Flux
Influx
Unidirectional flux
Net flux

In biological solutions, electrical gradient refers to the electrical potential that acts on an ion to drive the movement of the ion in one or another direction (see Resting Membrane Potential - Establishment of the Membrane Potential).

Chemical gradient
Electrochemical gradient

Refers to the balance of chemical and electrical gradients that act on an ion, particularly as it relates to the movement of an ion across a biological membrane (see Resting Membrane Potential - Establishment of the Membrane Potential and Resting Membrane Potential - Nernst Equilibrium Potential).

Chemical gradient
Electrical gradient

Electrogenic pumps are primary active transporters that hydrolyze ATP and use the energy released from ATP hydrolysis to transport ions across biological membranes leading to the translocation of net charge across the membrane.

For example, the Na⁺/K⁺ ATPase (sodium pump) is an electrogenic pump because during every transport cycle, it transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell. This leads to the movement of one net positive charge out of the cell making this process electrogenic.

Electrogenic

Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).

Endocrine glands contain clusters of endocrine cells, whose function is to is to release hormones into the bloodstream.

Endocrine glands are ductless glands in that their secretions do not enter a duct (as for example with salivary glands). Rather, endocrine glands release their secretions (i.e., messenger molecules) into the interstitial fluid in highly vascularized regions, where the molecules then enter the bloodstream. The chemical messenger molecule that is released into the bloodstream is referred to as a hormone.

Endocrine cell
Hormone

A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na⁺ or H⁺) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In exchange, the driving ion and the driven ion/molecule are transported across the biological membrane in opposite directions.

An example is the Na⁺/Ca²⁺ exchanger (NCX), which couples the movement of 3 Na⁺ ions into the cell down its electrochemical gradient to the movement of 1 Ca²⁺ ion out of the cell against its electrochemical gradient.

Exchange is also commonly referred to as antiport.

Transport proteins that are involved in this type of transport are referred to as exchangers or antiporters.

Antiport

Secondary active transport
Cotransport

Lecture notes on Secondary Active Transport

Protrusion or bulging of one or both eyeballs out of the orbit. It may be caused by swelling of orbital tissue in response to trauma, or by hyperthyroidism (especially primary hyperthyroidism).

It is also referred to as exophthalmus, exophthalmia, proptosis, or exorbitism.

Exophthalmos (Wikipedia)

Facilitated diffusion (or facilitated transport) is a form of passive transport across biological membranes and refers to carrier-mediated transport of molecules/ions down a concentration gradient. Facilitated transport is mediated by facilitative transporters (also referred to as uniporters).

Facilitated Diffusion

The rate of movement of a substance across an interface. The interface could be the plasma membrane (separating the intracellular or extracellular fluid compartments), an epithelial sheet separating two compartments, or where two solutions of different composition meet.

Flux is reported as a rate. It is the amount of substance that moves across a given interface per unit time.

Influx
Efflux
Unidirectional flux
Net flux

GABA

GABA is an inhibitory amino acid neurotransmitter in the central and peripheral nervous systems. It is the most abundant inhibitory neurotransmitter in the nervous system. During embryonic development, GABA acts as an excitatory neurotransmitter at some central synapses. GABA is a classical neurotransmitter. Its action is exerted via the activation of GABA_A, GABA_B, and GABA_C receptors. GABA_A and GABA_C receptors are ligand-gated chloride channels, whereas GABA_B receptors are G protein coupled receptors. At GABAergic synapses, the action of GABA is terminated by GABA transporters (GAT), which transport GABA from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Glutamate (Glu, E) is one of the standard twenty (20) amino acids used by cells to synthesize peptides, polypeptides, and proteins. It has a molecular weight of 147.13 g/mol. Its side chain has a pK_a of 4.07 and, therefore, glutamate has a net negative charge at physiological pH.

In the nervous system, glutamate is an excitatory amino acid neurotransmitter. In fact, glutamate is the most abundant excitatory neurotransmitter in the nervous system. Glutamate is a classical neurotransmitter. Its action is exerted via the activation of glutamate receptors (GluR), some of which are ligand-gated ion channels (ionotropic receptors), and some are G protein coupled receptors (GPCRs, metabotropic receptors). At glutamatergic synapses, the action of glutamate is terminated by glutamate transporters (EAAT, excitatory amino acid transporter), which transport glutamate from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Glycine (Gly, G) is one of the standard twenty (20) amino acids. At a molecular weight of 75.07 g/mol, it is the smallest of the 20 amino acids used by cells to synthesize peptides, polypeptides, and proteins.

In the nervous system, glycine is also an inhibitory amino acid neurotransmitter. Glycinergic synapses are most commonly found in brain stem and spinal cord circuits. Glycine is a classical neurotransmitter. Its action is exerted via the activation of ionotropic glycine receptors (GlyR), which are ligand-gated chloride channels. At glycinergic synapses, the action of glycine is terminated by glycine transporters (GlyT), which transport glycine from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Hyperthyroidism refers to a pathophysiological condition in which the thyroid gland produces and releases abnormally high levels of the thyroid hormones (T₃ and T₄).

The symptoms of hyperthyroidism may include high metabolic rate, weight loss, nervousness, excess heat production, tachycardia, and tremor.

Two main forms of hyperthyroidism exist: (1) Primary hyperthyroidism, and (2) Secondary hyperthyroidism.

In primary hyperthyroidism, the thyroid gland produces high levels of the thyroid hormones, either as a result of a secretory tumor of the thyroid gland, or under the control of thyroid stimulating immunoglobulins (such as in Graves' disease).

Secondary hypothyroidism is caused by high levels of thyroid stimulating hormone (TSH) produced by the anterior pituitary gland. TSH then stimulates the thyroid gland to produce excessive amounts of the thyroid hormones.

Hypothyroidism
Euthyroidism

Surgical removal of the pituitary gland (hypophysis).

Hypophysis

Hypothyroidism refers to a pathophysiological condition in which the thyroid gland does not produce sufficient amounts of the thyroid hormones (underactive thyroid), leading to abnormally low levels of the thyroid hormones (T₃ and T₄).

The symptoms of hypothyroidism may include reduced metabolic rate, chronic fatigue, weight gain, myxedema, and depression.

Three main forms of hypothyroidism exist: (1) Primary hypothyroidism, (2) Secondary hypothyroidism, and (3) Tertiary hypothyroidism.

In primary hypothyroidism, the thyroid gland itself is incapable of producing normal levels of the thyroid hormones.

Secondary hypothyroidism is caused by low levels of thyroid stimulating hormone (TSH). TSH, produced by the anterior pituitary gland, is required to stimulate the thyroid gland to produce the thyroid hormones.

Tertiary hypothyroidism is caused by low levels of thyrotropin releasing hormone (TRH). TRH, produced by the hypothalamus, is required to stimulate the anterior pituitary gland to produce TSH which, in turn, is required to stimulate the thyroid gland to produce the thyroid hormones.

Primary hypothyroidism
Secondary hypothyroidism
Tertiary hypothyroidism

Hyperthyroidism
Euthyroidism

The I band is the region of a striated muscle sarcomere that contains thin filaments. This region is closest to the Z disk, and is the lightest region of the sarcomere when viewed in under the light or electron microscope. The I band is occupied by the thin filaments only. Each Z disk runs through the middle of the I band. Therefore, half of each I band belongs to one sarcomere, and the other half belongs to the neighboring sarcomere. The I band shortens as the muscle contracts and the sarcomere shortens.

A band
H zone
M line
Z disk

The last region (i.e., most distal region) of the small intestine. Ileum receives the contents of the jejunum and, in turn, the contents of ileum leave the small intestine by emptying into the cecum. In adult humans, the ileum is about 2-4 meters (about 6.5-13 feet) long.

Duodenum
Jejunum

Not permeable. Not allowing the passage of substances. Impermeable refers to a property of a membrane or channel pore in preventing or restricting the passage of substances. For example, the lipid bilayer portion of biological membranes is highly impermeable to ions and large polar molecules.

See also permeable.

Permeable
Permeability
Permeant
Impermeant

Lipid Bilayer Permeability

Not permeant. Incapable of passing through or penetrating. Impermeant refers to the inability of a substance (e.g., ion or molecule) to cross (i.e., permeate or penetrate) a biological membrane or channel pore. For example, it can be said that ions are membrane impermeant.

See also permeant.

Permeant
Permeability
Permeable
Impermeable

Lipid Bilayer Permeability

Movement of a substance into the cell.

Influx is reported as a rate. It is the amount of substance that moves through a given area of the plasma membrane per unit time.

Flux
Efflux
Unidirectional flux
Net flux

A glycoprotein released by parietal cells (also know as oxyntic cells) located in the fundus region of the stomach. Intrinsic factor is required for vitamin B₁₂ absorption in the small intestine.

In electrophysiological convention, a negative current value or downward deflection of a current trace is typically referred to as an inward current. A negative current value (i.e., inward current) can reflect either the movement of positive ions (cations) into the cell or negative ions (anions) out of the cell.

Neuronal Action Potential - Pharmacological Inhibition of Na⁺ and K⁺ Channels

The middle region of the small intestine between the duodenum and the ileum. The jejunum receives the contents of the duodenum and, in turn, its contents empty into the ileum. In adult humans, the jejunum is about 2.5 meters (about 8 feet) long.

Duodenum
Ileum

Chemical warfare agent belonging to sulfur (or sulphur) mustards. Causes severe chemical burns and water blisters (i.e., it is a vesicant). It is cytotoxic, mutagenic, and carcinogenic.

Sulfur mustard (Wikipedia)

Net flux represents the amount of substance moved in or out of the cell. It is the mathematical difference between influx and efflux.

Net flux = Influx − Efflux

Similar to influx and efflux, net flux is reported as a rate. It is the net amount of substance that moves through a given area of the plasma membrane per unit time.

Flux
Influx
Efflux
Unidirectional flux

Surgical removal of one or both ovaries.

Also known as ovariectomy

Ovariectomy

In electrophysiological convention, a positive current value or upward deflection of the current trace is typically referred to as an outward current. A positive current value (i.e., outward current) can reflect either the movement of positive ions (cations) out of the cell or negative ions (anions) into the cell.

Inward current

Neuronal Action Potential - Pharmacological Inhibition of Na⁺ and K⁺ Channels

Surgical removal of one or both ovaries.

Also known as oophorectomy

Oophorectomy

Permeability refers to the ease with which molecules cross biological membranes. It may also refer to the ease with which ions or molecules pass through the pore of channel proteins.

Permeable
Impermeable
Permeant
Impermeant

Lipid Bilayer Permeability

Permeable refers to a property of a membrane or channel pore in allowing substances to pass through. For example, the lipid bilayer portion of biological membranes is highly permeable to fat-soluble molecules, but is not permeable to ions and large polar molecules.

See also impermeable.

Impermeable
Permeability
Permeant
Impermeant

Lipid Bilayer Permeability

Permeant refers to the ability of a substance (e.g., ion or molecule) to cross (i.e., permeate or penetrate) a biological membrane or channel pore. For example, it can be said that fat-soluble molecules are membrane permeant.

See also impermeant.

Impermeant
Permeability
Permeable
Impermeable

Lipid Bilayer Permeability

Physiology is the study of how living systems function. The scope of physiological studies ranges from the subcellular level (molecules and organelles) all the way to the level of the whole organism and how organisms adapt to vastly different environmental conditions such as hot, cold, dry, humid, or high altitude.

What is Physiology?

Gradual hearing loss associated with aging.

Peptide hormone produced by the anterior pituitary gland. Prolactin is best known for its action in stimulating the mammary glands to produce milk (lactation).

Prolactin is known to be involved in many other physiological processes including enlargement of the mammary glands in preparation for milk production, sexual gratification, metabolism, regulation of the immune system, and others.

Prolactin (Wikipedia)

A period of rapid physical growth and change, brought about by hormonal changes, that culminates in sexual maturity. In most human girls and boys, it starts between the ages of 10 and 14 and it is complete by the age of 16 in most girls, and by the age of 17 in most boys.

Adrenarche
Menarche
Pubarche
Thelarche

Surgical removal of the fallopian tube.

Secondary active transport is a type of active transport across a biological membrane in which a transport protein couples the movement of an ion (typically Na⁺ or H⁺) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

This transport process is referred to as active transport because the driven ion/molecule is transported against a concentration or electrochemical gradient. It is referred to as secondary active transport because no ATP hydrolysis is involved in this process (as opposed to primary active transport). The energy required to drive transport resides in the transmembrane electrochemical gradient of the driving ion.

Secondary active transport is also referred to as ion-coupled transport. Those utilizing Na⁺ as the driving ion are called Na⁺-coupled transporters. Those utilizing H⁺ as the driving ion are called H⁺-coupled transporters.

Two types of secondary active transport exist: cotransport (also known as symport) and exchange (also known as antiport). Na⁺/glucose cotransporter and H⁺/dipeptide cotransporter are examples of cotransporters. Na⁺/Ca²⁺ exchanger and Na⁺/H⁺ exchanger are examples of exchangers.

Cotransport
Symport
Exchange
Antiport

Lecture notes on Secondary Active Transport

Na⁺

The main cation (positively charged ion) of the extracellular fluid.

Sodium (Na⁺) plays an important role in several physiological processes such as the action potential of neurons and muscle cells, secondary active, sodium-coupled transport of ions, nutrients, neurotransmitters across the plasma membrane of cells, and many other processes.

The extracellular concentration of Na⁺ is about 145 mM. The intracellular concentration of Na⁺ is about 15 mM.

A rectangular signal waveform used in physiological studies to perturb (i.e., challenge) the system under study. The response of the system to the pulse is then studied carefully to learn about how the system responds to challenges.

Examples include pulses of voltage or current in electrophysiological experiments. Other examples include pulses of light, pressure, temperature, ligand, etc.

A square-wave pulse is defined by the amplitude and duration of the pulse, as well as by the frequency at which the pulse is applied to the system under study.

Neuronal Action Potential - Introduction

Square wave (Wikipedia)

Synaptic pathology. Any pathophysiological condition that leads to abnormal function of synapses within the nervous system. The pathology may be due to pre-synaptic and/or post-synaptic mechanisms, or may involve glial cells surrounding synapses.

TEA

An inhibitor of voltage-gated potassium (K⁺) channels.

TEA is a quaternary ammonium cation (positively charged ion). It is also commonly used as a cation replacement for sodium (Na⁺) in physiological buffers used in ion replacement experiments.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

The condition of hearing a sound in the absence of an external sound stimulus. The sound may be ringing, buzzing, whistling, or hissing. The sound may be soft, loud, low-pitched, or high-pitched. It may be heard in one ear or both ears (simultaneously or independent of one another).

Tinnitus (Wikipedia)

An electrophysiological technique in which the voltage of a cell membrane is controlled experimentally, and the current passing across the membrane is measured.

Current clamp

Neuronal Action Potential - Pharmacological Inhibition of Na⁺ and K⁺ Channels