436 Review for Lec 7

What type of response does the SNS mediate.

-this system is responsible for Fight or flight responses. the SNS releases NE+Epi to stimulate the opening of pacemaker HCN channels. this depolarizes SA node faster, increases heart rate and BP. It hyperactivates HCN channels instead of having Na+ slowly enter the cell to reach threshold, in enters much faster. this also shortens the pause at the AV-node. Epi also has the effect to get more Ca++ into the SR for stronger contraction.

Adrenergic

1. activated by, characteristic of, or secreting epinephrine or related substances, particularly the sympathetic nerve fibers that liberate norepinephrine at a synapse when a nerve impulse passes. 2. any agent that produces such an effect. See also under receptor.

Epinephrine (EPI)

A catecholamine hormone of the adrenal medulla that is the most potent stimulant of the sympathetic nervous system, resulting in increased heart rate and force of contraction, vasoconstriction or vasodilation, relaxation of bronchiolar and intestinal smooth muscle, glycogenolysis, lipolysis, and other metabolic effects. Also called adrenaline.

Vagus nerve

A nerve that supplies nerve fibers to the pharynx (throat), larynx (voice box), trachea (windpipe), lungs, heart, esophagus, and intestinal tract, as far as the transverse portion of the colon. The vagus nerve also brings sensory information back to the brain from the ear, tongue, pharynx, and larynx. The vagus nerve is the tenth cranial nerve. It originates in the medulla oblongata, a part of the brain stem, and extends all the way down from the brain stem to the colon. Complete interruption of the vagus nerve causes a characteristic syndrome in which the soft palate droops on the side where damage occurred, and the gag reflex is also lost on that side. The voice is hoarse and nasal, and the vocal cord on the affected side is immobile. The result is difficulty swallowing (dysphagia) and speaking (dysphonia). The vagus nerve has several important branches, including the recurrent laryngeal nerve.

What Neuraltransmitters are used by the ANS?

ACh Norepernephren (NE) Epinepheran (EPI)

Where is EPI from?

Adrenal Medulla.

What is an ECG? What is it NOT? What events do the P-wave, QRS-complex, and T-wave represent?

An electrical activity record of the heart, using surface electrodes (can be done on any animal) Basis of ECG: heart behaves like a dipole: a separation of electrically charged regions, so momentarily, one region can be polarized, another region depolarized (i.e. dipole's direction changes with time). Depolarization of a cell can be recorded from cell's surface. The large extracellular potential changes occurring with thousands of heart cells depolarizing, repolarizing almost in synchrony can be seen at the body surface. P-Wave: atrial depolarization QRS-complex: ventricular depolarization : atrial re-polarizating simultaneously T-wave: ventricular repolarization

What in general is the profile and time frame Cardiac contracting cells?

Cardiac contractile cells recive Ca++ from both the SR and outside the cell. these cells have a sarcomere. contractile cells have a resting membrane potential- as Na+ and Ca++ start leaking in via GJ from PMC or another activated contractile cell- it starts to depolarize and reach threshold. when that cell reaches threshold the VGNa+C that depolarizes the cell. once depolarized, the VGNa+C closes. (there are 2 different VGNa+C. one is fast and the other slow. the fast one opens first). now the fast VGK+C opens. 100ms after the Fast VGK+C opened, the VGCa++C opens. this results in a much slower repolarization (which is referred to as the Ca++ plateau. 100ms after the VHCa++C opened it closes and the slow VGK+C opens. that repolarizes the cell and brings it back to the RMP. this whole process takes about 350ms.

What is the function of EPI?

EPI stimulates the opening of pacemaker HCN channels. this depolarizes the SA faster increasing HR which increases blood flow which in turn brings more oxygen to the body. EPI hyper activates the HCN channels. this causes Na+ to come into the cells faster and causing them to reach threshold faster. EPI also decreases the wait time on the AV-node. EPI also increases the rate at which Ca++ in absorbed into the SR. this decreases the refractory time that allows for the cells to be able to contract sooner.

Pacemaker potential

In the pacemaking cells of the heart (e.g., the sinoatrial node), the pacemaker potential (also called the pacemaker current) is the slow, positive increase in voltage across the cell's membrane (the membrane potential) that occurs between the end of one action potential and the beginning of the next action potential.

Acetylcholine (ACh)

It acts on both the peripheral nervous system (PNS) and central nervous system (CNS) and is the only neurotransmitter used in the motor division of the somatic nervous system.

What in general is the profile and time frame of Cardiac Pacemaker cells?

Pacemaker cells:cycle from depolarization to repolarization. They cycle through action potentials and are what keeps the heart beating. Pacemaker cells take the place of Somatic motor neuron. In a normal heart, the frequency of beats will be set by a group of pacemaker cells called the SA-node and the polarize at the fastest spontaneous rate. Pacemaker cells have different rates 1)SA-node: this group sets the pace for the entire heart (normal heart). they are linked together via gap junctions to the neighboring contractile cells. they are also going to link to other pacemaker cells via gap junctions. 2)Interatrial/ internoble pathways. the interatrial goes to the left atrium while the internoble leads to the AV-node. 3)AV-nod (atrial ventricular node): this group of pacemaker cells is the only electrical communication between the atrial and the ventricals. the AV-node is connected to the bundle of hiss which branches into the left and right bundle branches. 4) the left and right bundle branches go down the center of the heart via matrix material heart cells. than go through the heart wall into the ventricles via the Purkinje fibers. 5) Purkinje Fibers Pacemaker cells make a protein called HCN channel. this is what gives the pacemaker cells their unique property. HCN channel (hyperpolarized activity cyclic nucleotide channels). hyperpolarized activity means as soon as these cells are activated, it opens up this happens to be a servian channel. As soon as these cells hyperpolarize they never have a resting membrane potential. this is because once the HCN channels open up we start having sodium slowly leak into the cell which means going up to the cells threshold. pacemaker cells do not have sarcoeres.

Plateau phase

Phase 4, or the resting potential, is stable at ≈−90 mV in normal working myocardial cells. Phase 0 is the phase of rapid depolarization. The membrane potential shifts into positive voltage range. This phase is central to rapid propagation of the cardiac impulse (conduction velocity, θ=1 m/s). Phase 1 is a phase of rapid repolarization. This phase sets the potential for the next phase of the action potential. Phase 2, a plateau phase, is the longest phase. It is unique among excitable cells and marks the phase of calcium entry into the cell. Phase 3 is the phase of rapid repolarization that restores the membrane potential to its resting value.1

Pilocarpine

Pilocarpine is a cholinergic drug, that is, a drug that mimics the effects of the chemical, acetylcholine which is produced by nerve cells. Acetylcholine serves as a messenger between nerve cells and between nerve cells and the organs they control.

PVC (Pre-Ventricular Contraction)

Premature ventricular contractions (PVCs) are extra, abnormal heartbeats that begin in one of your heart's two lower pumping chambers (ventricles). These extra beats disrupt your regular heart rhythm, sometimes causing you to feel a flip-flop or skipped beat in your chest. Premature ventricular contractions are very common — they occur in most people at some point.

Purkinje fibers

Purkinje fibers are a unique cardiac end-organ. Further histologic examination reveals that these fibers are split in atria and ventricles walls. The electrical origin of atrial Purkinje fibers arrives from the sinoatrial node.

What is similar/different between skeletal muscle and cardiac muscle?

Similar: The basic contractile unit is the sarcomere. they both get Ca++ from the SR. They both have T-tubules. They both Have cross bridging and Thick and thin filaments sarcomeres will slide over each other. Cardiac muscle cells cannot hit tetanus. Cardiac muscle cells cannot stay contracted. Cardiac Muscle cells have slow and fast Ca++ channels that give it much longer refractory period that lets the cell almost completely relax. Differences: Unlike skeletal muscle cell which can be very long, cardiac muscle cells are small (considered to be more normal sized) they do not have fibers that stretch lengthwise or around or horizontal. instead these smaller cells are linked to one another via intercalated discs. cardiac cells have gap junctions that allows for electrical communication between cells. The T-tubules in cardiac muscle cells are small indented grooves. An important difference between cardiac muscle cells and skeletal muscle cells is that we do need Ca++ to cause cross bridging some of that Ca++ is going to come from the SR but a lot of it will come from outside the cell. To relax, the cardiac cells are going to pump some of the Ca++ into the SR but it is also going to pump some of it outside the cell. the cardiac muscle cells do not need neuron to activate it, instead they will be activated by pacemaker cells. the pacemaker cells take the place of somatic motor neuron.

How many divisions are there and what are they?

Sympathetic nervous system- this is responsible for fight or flight. Most sympathetic receptor release Norepi (Noradenaline) or Epinephren. these receptor are referred to as Adrenergic. Parasympathetic nervious system is responsible for rest and digest. all of these neurons are dual innervated andrelease ACh. these respeptor are all nicotinic recptors and are all accutstory. Any neuron that produces ACh is called a Cholinergic neuron. The Parasympathetic Nervous system is going to use the Vagus Cranial Nerve X.

SA node

The SA node is the heart's natural pacemaker. The SA node consists of a cluster of cells that are situated in the upper part of the wall of the right atrium (the right upper chamber of the heart). The electrical impulses are generated there.

How does the ans affect HR?

The SNS can speed it up with the release of EPI. the PNS can slow it down with the release of ACh.

Bundle of His

The bundle of His is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node (located between the atria and the ventricles) to the point of the apex of the fascicular branches via the bundle branches.

Internodal fibers/pathway

The impulse travels from the SA node through the internodal pathways to the atrioventricular node (AV node). The AV node is responsible for conduction of the impulse from the atria to the ventricles.

Autorhythmicity

The quality of being autorhythmic, or generating its own rhythm, as for example the cells of the cardiac muscle do.

Briefly describe the ANS anatomically.

The sympathetic goes from T1-L2. the Sweat gland, blood vessels, and adrenal gland are only innervated by the SNS. the SNS is able to be activated simultaneously because of the Sympathetic Chain Ganglion. The Chain Ganglion is where neuronal cell bodies group together and rides along the spinal cord. if any of these neurons sense an AP it will will spread the AP's up and down the Sympathetic Chain Ganglion so that everything can be activated at once in the body. The Parasympathetic Nervous System is located at the midbrain/ hindbrain and S1-S4 The ANS is dual innervated meaning the Parasympathetic and Sympathetic systems innervate the same things.

Norepinephrine (NE)

a catecholamine, which is the principal neurotransmitter of postganglionic adrenergic neurons, having predominant α-adrenergic activity; also secreted by the adrenal medulla in response to splanchnic stimulation, being released predominantly in response to hypotension. It is a powerful vasopressor and is used, in the form of the bitartrate salt, to restore the blood pressure in certain cases of acute hypotension and to improve cardiac function during decompensation associated with congestive heart failure or cardiovascular surgery.

Syncitium

a multinucleate mass of cytoplasm resulting from fusion of cells

Intercalated discs

a specialized intercellular attachment of cardiac muscle cells comprising gap junctions, fascia adherens, and occasionally desmosomes.

Desmosomes

a structure by which two adjacent cells are attached, formed from protein plaques in the cell membranes linked by filaments.

Agonist

a substance that initiates a physiological response when combined with a receptor.

Antagonist

a substance that interferes with or inhibits the physiological action of another.

Atropine

an anticholinergicand antispasmodic alkaloid used as the sulfate salt to relax smooth muscles and increase and regulate the heart rate by blocking the vagus nerve, and to act as a preanesthetic antisialagogue, an antidote for various toxic and anticholinesterase agents and as an antisecretory, mydriatic, and cycloplegic.

Sinus venosus

an enlarged pouch that adjoins the heart, is formed by the union of the large systemic veins, and is the passage through which venous blood enters the heart in lower vertebrates and in embryos of higher forms

Gap junctions

are a specialized intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells

HCN(hyperpolarization- activated cyclic-nucleotide channels)

are intermembrane proteins that serve as nonselective ligand-gated cation channels in the plasma membranes of heart and brain cells.

AV node

he AV node is an area of specialized tissue between the atria and the ventricles of the heart, specifically in the posteroinferior region of the interatrial septum near the opening of the coronary sinus, which conducts the normal electrical impulse from the atria to the ventricles.

What is the ANS?

it regulates involuntary actions. it is part of the peripheral nervous system. they tend to be dual innervation. Exceptions are adrenal gland, sweat glands and blood vessels. All have sympathetic innervation only.

What are the functions of the desmosomes?

large proteins that extend outside the cell and wrap together live velcro. they form tight connections so the cardiac cells do not pull apart.

Cholinergic

parasympathomimetic; stimulated, activated, or transmitted by choline (acetylcholine); said of the sympathetic and parasympathetic nerve fibers that liberate acetylcholine at a synapse when a nerve impulse passes. 2. an agent that produces such an effect.

what are the functions of Gap Junctions?

provide passageways for molecules to go from inside one cell to another- because of this cells have electrical continuity and propagation throughout the heart. if you depolarize one cell it will spread to all other cells it is associated with via gap junctions. this can be referred to as "Communication of ions" or "electrical communication". cells can open and close but if you depolarize the cell, the Ca++ and Na+ inside that cell can diffuse to the next and cause it to reach threshold. Gap junctions make the Atrial and Ventricular cells behave as one. Technically cells linked to one another via gap junctions are referred to as Syncitium.

Myogenic

taking place or functioning in ordered rhythmic fashion because of the inherent properties of cardiac muscle rather than specific neural stimuli <a myogenic heartbeat>

What is a pacemaker potential? What causes the pacemaker potential?

the slow upward climb to threshold is referred to as pacemaker potential. the reason behind them not having a resting membrane potential is due to the HCN channels slowly leaking Na+ into the next cell.

What nerves are involved and where do they synapse in the heart?

there are no nerves innervating the heart

Why can't cardiac myocytes summinate?

this is because of the VGCa++C give the Cardiac Myocytes a very long refractory period. during the refractory period, the muscle almost completely relaxes and you cannot stimulate a muscle during a refractory period. this makes it impossible for them to summinate.

What type of response does the PSNS mediate?

this is responsible for rest and digest. ACh is going to promote the opening of the VGCa++C . So if you have the HCN channels open allowing Na+ in but now your also allowing K+ out, it is going to take longer to reach threshold. because it takes longer to reach threshold, that is going to slow down the HR. it also slows down the AV-node response and decreases arterial contraction but it does not change the contractility of the ventricle.