ACh esterase is responsible for the breakdown of acetylcholine, which helps eliminate the signal and terminate neurotransmission in the parasympathetic nervous system.
The termination of the calcium signal involves the activity of membrane Ca2+ -ATP-ase, membrane Na+/Ca2+ antiporter, and SR - Ca2+ -ATP-ase, which help decrease intracellular calcium levels.
MLCK is activated by an increase in intracellular calcium levels, which leads to the formation of a calcium-calmodulin complex that activates MLCK.
The adrenal medulla functions as a modified postganglionic neuron that releases epinephrine into the bloodstream.
In the sympathetic nervous system, signal termination is achieved through norepinephrine reuptake, leading to degradation in the cytoplasm, as well as diffusion of transmitters.
MLC-P refers to the phosphorylated form of Myosin Light Chain, which is essential for muscle contraction.
Rho-kinase has an additive effect with MLCK, enhancing the phosphorylation of MLC and thus contributing to stronger contractions.
α1 adrenergic receptors, when stimulated, cause vasoconstriction in blood vessels, particularly in skeletal muscle, contributing to increased blood pressure during sympathetic activation.
Myosin Light Chain (MLC) is a protein that, when phosphorylated by Myosin Light Chain Kinase (MLCK), plays a crucial role in muscle contraction.
Myosin light chain (MLC) is phosphorylated, which allows for the binding of actin and myosin, facilitating smooth muscle contraction.
The fight or flight response is a general activation of the sympathetic nervous system in response to a perceived threat, leading to physiological changes such as increased blood pressure, heart rate, and glucose metabolism.
Sphincters in smooth muscle are normally contracted, maintaining a resting state, but can relax in response to signals before contracting again.
cGMP, activated by nitric oxide (NO), increases the activity of phosphatase, leading to decreased calcium sensitivity and promoting relaxation.
During sympathetic nervous system activation, physiological changes include increased blood pressure, heart rate, enhanced glucose metabolism, and dilated pupils.
The Postganglionic axon is short.
When a ligand binds to the α1 adrenergic receptor, it activates phospholipase C (PLC), leading to inositol trisphosphate (IP3) production and calcium signaling, which promotes contraction.
In the sympathetic nervous system, preganglionic neurons are typically long.
In multiunit smooth muscle, each smooth muscle cell (SMC) has its own innervation, allowing for neural control of contraction.
The Autonomic Nervous System regulates unconscious functions that are important for maintaining homeostasis in the body.
L-type calcium channels are involved in the action potentials of smooth muscle cells, as they are responsible for the influx of Ca2+ that contributes to the plateau phase, unlike voltage-gated sodium channels which are not involved.
The slow actin-myosin cycle in smooth muscle contributes to prolonged contractions and sustained tension with lower energy expenditure.
The adrenal medulla produces norepinephrine (NE) and epinephrine (E), with the conversion of NE to E facilitated by the enzyme N-methyltransferase.
Inputs integrated at the level of autonomic ganglia include different afferents from the periphery, somatic afferents to the CNS, interneurons, further signals from the CNS, and local reflexes.
A mechanism where contraction or relaxation of smooth muscle occurs without a change in membrane potential, typically through ligand binding to receptors.
Dense bodies are structures to which thin filaments are anchored, and they play a role in the contraction of smooth muscle.
The binding of calcium-calmodulin activates myosin light chain kinase (MLCK), which phosphorylates myosin light chain (MLC), leading to contraction of smooth muscle cells.
Therapeutic approaches include blocking transmitter release (acetylcholine), blocking choline reuptake, and inhibiting ACh esterase activity.
An increase in intracellular calcium concentration is crucial for inducing contraction of smooth muscle cells.
Smooth muscle cells are not a homogenous population because there are many differences in their characteristics and functions across different organs, affecting their contraction and relaxation states.
In the esophagus and urinary bladder, the resting state is characterized by a fully relaxed state that can transition to a fully contracted state over time.
There are two synapses involved in the autonomic pathway: one between the preganglionic and postganglionic neurons, and the other at the target cell.
Smooth muscle cells do not utilize voltage-gated sodium channels for action potentials; instead, they rely on L-type calcium channels, making them insensitive to TTX, a specific inhibitor of sodium channels.
The sympathetic division increases heart rate, while the parasympathetic division decreases it, demonstrating counteracting effects on the same target cell.
[Ca2+] IC is a critical regulator of contraction in smooth muscle.
The Postganglionic axon is long.
Gap junctions are specialized intercellular connections that allow for direct communication between smooth muscle cells, facilitating coordinated contractions.
Depolarization refers to the change in membrane potential that can occur due to neighboring cells, neural stimulation, or mechanical activation, leading to contraction.
Rho-kinase inhibits the function of phosphatase, leading to increased phosphorylation of MLC and stronger contractions.
The FIRST synapse is between the preganglionic axon and the postganglionic neuron, where acetylcholine (ACh) is released and binds to nicotinic acetylcholine receptors (nAChR).
The neurotransmitter released at the FIRST synapse in both the parasympathetic and sympathetic systems is acetylcholine (ACh).
Rhythmic fluctuations in membrane potential that can lead to action potentials and correlate with contraction in smooth muscle cells.
Nerves originating from the thoracic and lumbar regions of the spinal cord, with cervical nerves not included in the ANS.
E refers to epinephrine, which is released from the adrenal medulla and acts as a hormone in the sympathetic system.
A varicosity is a swelling along the axon that contains neurotransmitter vesicles, allowing for the release of neurotransmitters to affect multiple target cells rather than a single cell.
MLCK, or myosin light chain kinase, mediates the phosphorylation of myosin light chains, which is essential for the binding of actin and myosin during smooth muscle contraction.
The main divisions of the Autonomic Nervous System are the Parasympathetic, Sympathetic, and Enteric nervous systems.
In the parasympathetic system, the ganglia are located close to the target cell, while in the sympathetic system, they are located close to the CNS/spinal cord.
Slow waves are fluctuations in membrane potential that can lead to the formation of action potentials at certain points, playing a crucial role in the rhythmic contraction of smooth muscle.
N-methyltransferase is an enzyme expressed in the adrenal medulla that is responsible for the conversion of norepinephrine to epinephrine, and its expression is dependent on high levels of steroid hormones.
Initially, only electrotonic potential changes occur, followed by the summation of all signals, which can lead to the generation of an action potential.
Smooth muscle cells are uninucleated, small, and not striated, with thin and thick filaments present.
Receptor number is tightly regulated and can change depending on age and hormonal effects, leading to dynamic expression patterns and tissue-specific cellular responses.
MLC phosphorylation is essential because it changes the conformation of the myosin heavy chains, enabling the interaction necessary for contraction of smooth muscle cells.
Receptors are pharmacological targets because their activity can be efficiently modulated by agonists and antagonists, influencing the physiological responses of the autonomic nervous system.
Rho-kinase phosphorylates MLC, increasing calcium sensitivity and allowing for the same contraction with less intracellular calcium.
The SYMPATHETIC synapse involves membrane-NE-transporter inhibition, inhibition of the NE-carrier in vesicles, and blocking NE synthesis, which alters neurotransmitter activity.
The Bayliss effect is the phenomenon where mechanical changes, such as increased vessel pressure, induce depolarization and subsequent contraction of smooth muscle.
Normally partial tone in smooth muscle refers to a state where the muscle is partially contracted, allowing for increased contraction and subsequent relaxation when stimulated.
Changes in the electrical charge across the membrane of smooth muscle cells that can lead to action potential formation and subsequent contractile force.
ATP is required for muscle contraction in smooth muscle, similar to its role in skeletal muscle.
The ganglion is located close to the spinal cord, specifically in pre/paravertebral ganglia.
The contracted/relaxed form of smooth muscle refers to the state of smooth muscle cells, which can be fully relaxed, fully contracted, or in a state of partial tone depending on the organ and physiological conditions.
A Preganglionic neuron originates in the CNS and synapses with a postganglionic neuron located in a peripheral ganglion, which then connects to the target cell.
Norepinephrine (NE) is more effective than epinephrine (E) at α1 adrenergic receptors, leading to greater vasoconstriction.
The depolarization phase involves L-type voltage-gated Ca2+ channels, while the repolarization phase involves voltage-gated late K+ channels.
The Preganglionic axon is long, as it is close to the organ.
The types of adrenergic receptors activated by norepinephrine include α1, α2, β1, β2, and β3 receptors.
The phosphorylation of IP3R leads to the inhibition of calcium entry into the cell, which induces relaxation.
cGMP activates phosphatase, which contributes to the relaxation of smooth muscle.
Rho-GTP is a molecular switch that activates Rho-kinase, which plays a role in regulating smooth muscle contraction by phosphorylating myosin light chain (MLC).
The Plateau phase is a period during the action potential in smooth muscle cells characterized by a maintained depolarization, lasting around 10 seconds, which is crucial for the generation of force.
Contraction in smooth muscle requires much less ATP compared to skeletal muscle, making it more energy-efficient.
Postganglionic neurons in the adrenal medulla are specialized cells that have lost their axons, which prevents them from forming typical synapses.
Nerves originating from cranial nerves 3, 7, 9, 10 and from the sacral spinal cord segments S2-S4.
The main neurotransmitter at the SECOND synapse in the parasympathetic system is acetylcholine (ACh).
Effector cells in the parasympathetic system have muscarinic acetylcholine receptors (mAChR).
The Preganglionic axon is short.
The two systems are the sympathetic nervous system and the parasympathetic nervous system, which work in opposition to regulate bodily functions.
cAMP induces phosphorylation of MLCK by PKA, resulting in a phosphorylated form of MLCK (MLCK-P) that decreases calcium sensitivity.
Myofilaments in smooth muscle consist of thin filaments made of actin and tropomyosin, and thick filaments made of myosin, which includes two heavy chains and two light chains that bind to each heavy chain, forming the final structure.
An example is the β1 adrenergic receptor, which can be influenced by various drugs to modulate its activity.
The heavy chains of myosin in smooth muscle are different from those in skeletal muscle, with specific subunits that contribute to the unique properties of smooth muscle contraction.
Calcium-channel inhibitors can block the action potentials in smooth muscle cells, indicating the reliance on calcium influx for action potential generation.
Neural signals modulate the activity of single-unit smooth muscle, influencing the frequency and strength of contractions without initiating them.
Organs that are regulated solely by the sympathetic division, such as most vascular smooth muscle, which primarily induces vasoconstriction through alpha-1 adrenergic receptors.
The primary neurotransmitter used at the SECOND synapse in the sympathetic system is norepinephrine (NE).
Dual innervation allows the sympathetic and parasympathetic divisions to induce different responses in the same organ, depending on which division is stimulated.
It means that a single postganglionic autonomic axon can connect to multiple target cells, allowing for widespread effects on tissues rather than a direct connection to just one cell.
Autonomic neurotransmitters are chemical messengers that regulate unconscious autonomic functions, which are crucial for maintaining the body's homeostasis, such as heart rate, pupillary response, and blood pressure.
Phosphatase dephosphorylates MLC-P, which is a critical step in the regulation of muscle contraction.
Electrical pacemaker cells, such as interstitial cells of Cajal, generate constant changes in membrane potential that propagate via gap junctions, influencing smooth muscle contraction.
cAMP, stimulated by β2-adrenergic receptors, induces a mechanism that decreases calcium sensitivity and promotes relaxation of smooth muscle.
A nicotinic receptor is a ligand-dependent ion channel that generates a fast excitatory postsynaptic potential (EPSP).
The adrenal gland produces high levels of steroid hormones, which create a local concentration necessary to induce the formation of epinephrine.
The parasympathetic division stimulates the production of non-viscous, enzyme-rich saliva, while the sympathetic division promotes the secretion of viscous, mucinous saliva.
Gap junctions connect smooth muscle cells, allowing for coordinated contraction.
Spontaneous contractions in single-unit smooth muscle allow for basal activity and are modulated by neural signals, enabling the muscle to respond to physiological needs.
The adrenal medulla is a part of the sympathetic division that contains modified postganglionic neurons which have lost their axons, allowing them to release neurotransmitters directly into the bloodstream.
Acetylcholine is the transmitter common to both the sympathetic and parasympathetic divisions.
Epinephrine (E) has a higher affinity for β2 adrenergic receptors compared to norepinephrine (NE), leading to vasodilatation in certain blood vessels.
Both smooth and skeletal muscles involve the sliding of thin and thick filaments to achieve contraction.
Calcium acts as an important regulator in smooth muscle contraction, being released into the cytoplasm upon receptor activation.
Smooth muscle does not have T tubules, while skeletal muscle does.
The action potential in smooth muscle cells has a smaller amplitude, lasts longer, and involves different ion channels compared to action potentials in other cell types.
The ganglion is located near or within the organ, very close to the target cell.
Counteracting effects refer to the opposing actions of the sympathetic and parasympathetic divisions on similar cell types, such as the pupillary sphincter and pupillary dilator.
A change in membrane potential that can be induced by neighboring cells or ligand-dependent mechanisms, leading to contraction.
