Exam 2 Study Guide—Potential Essays & Short Answers

Compare and contrast cholinergic and adrenergic receptors

Cholinergic receptors bind with acetylcholine and includes both nicotinic and muscarinic receptors. A nicotinic receptor is also simultaneously an ion channel in addition to a ligand gated channel with channel linked receptors. They can be found at skeletal neuromuscular junctions and all autonomic ganglia. These receptors are always excitatory. The muscarinic receptors act with the help of G proteins and their linked receptors to gate K channels. These receptors are located at parasympathetic stimulated effector cells. There effects can be either excitatory or inhibitory. Adrenergic receptors bind with norepinephrine and epinephrine, and include alpha and beta receptors. The receptors are linked to G proteins and use second messengers. Alpha 1 receptors are the most common type and usually elevate the calcium inside of the cell in order to cause smooth muscle contraction or glandular secretion by exocytosis. Alpha 2 receptors are inhibitory so they inhibit cAMP to slow gut motility. Beta receptors are used to elevate intracellular cAMP, which results in the phosphorylation of intracellular proteins. Beta 1 receptors are found in the heart and respond to sympathetic innervation and epinephrine in order to speed up heart rate. Beta 2 receptors respond to epinephrine to dilate airways and skeletal muscle vasculature.

Describe the events, in order, associated with excitation, contraction, and relaxation of muscle

To get the excitation and contraction of a muscle the action potential first releases calcium from the sarcoplasmic reticulum. T tubules are used to help spread the action potential rapidly to all parts of the fiber. Inside the T tubules, there are calcium voltage gated channels that become activated to release calcium from calcium release channels in the sarcoplasmic reticulum. Calcium will then bind with troponin to effect a conformation change which will result in the rotation of tropomyosin off of the actin binding site. The activated myosin head will immediately bind and the cross-bridge cycle will ensue. The muscle twitch, or the contractile activity, will last much longer than the action potential. For the muscle to relax, calcium has to be returned to the sarcoplasmic reticulum; this is done by a primary active Ca pump. When the action potentials stop, the pump will remove the calcium and the actin binding sites get covered to result in relaxation.

Define, describe, and explain every aspect of an action potential

An AP is a rapid rise & fall in voltage or membrane potential across a cellular membrane. This is a transient all-or-none reversal of the membrane polarity, so the amplitude of the response is independent of stimulus intensity. An electrical signal is present that can be propagated by nerve and muscle cells so there's no decrement and amplitude is constant, making an AP good for long distance communication. APs are initiated by GPs; they require a threshold potential to be initiated. The essential proteins are Na & K VG channels. When APs are initiated VG Na channels open from the Na in GPs and membrane becomes highly permeable to sodium. VG channels found initially at axon initial segment, & along axon. When a series of APs is initiated down axon membrane=propagation occurs & therefore nerve impulse. When more Na enters cell more channels open; the upstroke of AP causes positive feedback cycle that depolarizes cell to +50mv. Cell now needs to be repolarized; K VG channels open, K leaves, & voltage returns to resting value. Membrane has diminished excitability right after an AP, so refractory period occurs; this is when there's a moment where neuron cant respond to second stimulus b/c the channel needs to ensure one way conduction of impulses.

Compare and contrast a graded potential and an action potential

Graded potentials occur in dendrites and cell bodies. Their essential protein is chemically gated channels. They are initiated by sensory stimuli in sensory transduction, neurotransmitter in synaptic transmission, or a spontaneous pacemaker event. Graded potentials are used to initiate action potentials. In order for threshold potential to be reached the graded potentials have to be summed; temporal and spatial summation are possible. They can also be both excitatory and inhibitory, so both depolarization and hyperpolarization can occur. Graded potentials are used to carry information for short distances so there isn't much regeneration and they spread passively. They are amplitude modulated; the amplitude varies with the strength of the stimulus and will decrease with increasing distance from the initiation site. Action potentials occur in axons and their essential proteins are Na and K voltage gated channels. They are used for rapid long distance communication since they are actively propagated, and to release neurotransmitters from the axon terminal. When graded potentials reach threshold, then action potentials are initiated. In contrast to graded potentials, action potentials can not be summed because they have an all-or-none response. Their amplitude is constant unlike a graded potential so action potentials are conducted without decrement. Action potentials are always caused by a depolarization followed by repolarization when K leave the axon. Lastly, action potentials are frequency modulated; their frequency varies with the strength of the stimulus.

Explain the sliding filament theory of muscle contraction

In muscles, the proteins are not able to contract but instead what happens is the thick and thin filaments(myosin and actin) slide past each other making the sarcomere shorten. There is a repetitive cycle of events that need to occur for the sliding filament mechanism. First, the formation of cross-bridges between actin and myosin has to happen, so there needs to be a binding. In addition, a bending, or stroking, of the myosin head occurs to release the cross-bridge; this event has a ratchet like motion. To energize the cross-bridge the ATP needs to go through hydrolysis; this occurs at activation. The sarcomeres that are in a fiber will all shorten together causing the fiber as a whole to shorten as well. When ATP binds to myosin it decreases myosin's affinity for actin and causes detachment; this is an allosteric regulation of protein activity. The myosin head is active by the splitting of ATP by myosin ATPase; the ADP and P will leave the head at a power stroke.

Describe the relation between structure and function of muscles

Muscles have a structural hierarchy which consists of muscle(organ), fascicles, muscle fibers(cell), myofibrils, and myofilaments. The myofibrils are made up of cytoskeleton elements known as actin and myosin. Thick filaments are made of myosin molecule and thin filaments are made of actin, which are contractile proteins. Actin also contains other proteins such as tropomyosin and troponin. Myosin has binding sites for both actin and ATP, known as myosin ATPase site. The elements are arranged in bands. Dark bands are known as A bands, which are made from myosin. There are also light bands that are called I bands, made from actin. There is a cytoskeletal protein that connects the thin filaments known as a "Z disc". An M line is another protein that functions in supporting the thick filaments. A sarcomere is what is in Z disc to Z disc and is the functional unit of a muscle. Muscles are used for movement in the body and also in internal organs such as the heart, intestines, and blood vessels. They are also energy transducers that change chemical energy into mechanical energy. Skeletal muscle contractions provide movement, posture, joint stability, and heat production; they are able to conduct action potentials, contract or shorten in response to a stimulus, stretch or extend by load or antagonistic muscle, and return to their original shape due to the presence of elastic fibers

Compare & contrast sensory transduction, synaptic transmission, and signal transduction

Sensory transduction is a mechanism that relays information form the binding of a signal molecule to a receptor in a target cell's plasma membrane which initiates an intracellular response. This event occurs in sensory receptors and it functions to change the sensory stimulus form of energy into an electrical form of energy as graded potentials and then action potentials; these can be propagated along sensory neuron axons to the brain for interpretation. The gating of a channel by voltage, chemical, or mechanical means is the transduction event. In hair cells, the sound waves are transduced from the bending of the cilia where there are mechanically gated channels. This process can also include synaptic transmission, because after the hair cells are bent, K enters the cell and VG Ca channels are gated, and the Ca causes the exocytosis of NT. In the rods and cones of the eye, a cis/trans conformation in a pigment molecule occurs because of the light energy; this causes the shape of the protein to change which will also gate a channel. Synaptic transmission is the process in which an electrical impulse, or action potential, reaches synaptic vesicles where neurotransmitters are released, and then the neurotransmitters carry the signal across the synaptic cleft to bind to a receptor that is on the post-synaptic cell. This event occurs in a synapse, where a neuron is able to communicate with another neuron or an effector, or a sensory neuron can synapse with a sensory receptor. When sodium enters the axon terminal through voltage gated channels, this causes voltage gated Ca channels to open. Ca then enters the axon terminal to bind with synaptotagmin, a protein, and then it causes the exocytosis of neurotransmitters from the synaptic vesicles. The neurotransmitters diffuse across the synaptic cleft and bind with their receptor. When they bind it initiates a response inside of the post-synaptic cell, which is known as signal transduction. Where a messenger molecule binds to a receptor and initiates a response inside the effector or target cell, is where the event of signal transduction occurs. The messenger molecule can either be a neurotransmitter or a hormone. There are a couple of different responses that can occur. The gating of a channel that is an intrinsic part of the receptor can occur like with ACh and nicotinic receptors. Another response could be the gating of a channel using G protein activation; this occurs with ACh and muscarinic receptors. Also, second messengers could be produced inside the target cell using G proteins. If a G protein coupled receptor is involved, a subunit comes off and moves through the membrane when a specific neurotransmitter or hormone binds to it. The G protein subunit can directly open a channel, activate adenylate cyclase(an enzyme) to catalyze the making of a second messenger like cAMP, or it can activate phospholipase C, another enzyme, so that Ca can be released from the endoplasmic reticulum. Second messengers, like cAMP and calcium, carry out the message and effects stimulated by the first messenger within the cell. cAMP is able to activate a kinase to phosphorylate an effector protein; the effector protein can be a transporter, enzyme, or motor protein. Ca can cause phosphorylation with calmlodulin, a secretion by exocytosis, or cause muscle contraction.

Describe the advantages of signal transduction

Signal transduction is a mechanism that relays information from the binding of a signal molecule to a receptor in a target cell's plasma membrane which results in the initiation of an intracellular response. This type of mechanism has a couple different advantages. The first messenger molecule can effect a change inside of the cells, some with the help of second messengers. In addition, a variety of effects can occur due to a variety of intracellular proteins like enzymes, motors, and channels that can be phosphorylated. This process has multiple steps so the signal is amplified

Describe how one hormone can act on many cells and have different effects on the same cell

Specific receptors and the nature of the phosphorylated or synthesized proteins help determine the cell's response to a given hormone. 1 hormone can have different effects in different types of tissues. 1 cell can respond to 2 hormones by having 2 different types of receptors. 1 cell can also have 2 responses to 1 hormone by having 2 receptors linked to 2 different 2nd messenger schemes mediating 2 unique effects

Differentiate the action and effect of steroid hormones and protein hormones

Steroids consist of lipids and cholesterol derivatives, like estrogen or testosterone. Steroids and thyroxine are lipid soluble and act inside of the cell; they are classified as a lipophilic hormones. Steroid diffuses through the membrane of the target cell, then will bind to a specific receptor in the cytosol or the nucleus. This action initiates DNA transcription and making of new proteins. The new proteins are then able to be structural or functional. The proteins include: receptors and enzymes used for growth and development. Proteins and peptides are hormones that are species specific; they act at the cell surface and are classified as a hydrophilic hormone. The hydrophilic mechanism involves signal transduction and often second messenger systems. This process starts with the binding of the hormone, which is the first messenger, with the surface of the cell or the membrane bound receptor. The receptor could be linked to a second messenger, which would act in the cytosol for the non-penetrating hormones. If a second messenger is present, it activates or phosphorylates effector proteins that carry out the hormone's "message".

Define, describe, and explain every aspect of a graded potential

The change in membrane permeability due to a stimulus altering the permeability and making them permeable to ions that diffuse in or out of the cell. The stimulus can be a physical, chemical, or electrical event that gates an ion channels causing the change in permeability of the membrane. The essential protein in this process is chemically gated channels. The size of the stimulus reflects the size of the graded potential, so it is graded in magnitude.The event of graded potential occurs in sensory receptors, dendrites, and soma. || Graded potentials are initiated by the opening of the gated ion channels to have the current flow spread passively. This event is useful for signaling over short distances only because no regeneration occurs. Our bodies a use graded potentials to initiate information flow in sensory cells, to conduct information from dendrites to axons, to represent the entire information transfer in neurons with short axons, and to initiate APs in cardiac muscle cells.|| GPS initiate APs; there are 3 kinds of GPS—receptor potentials, postsynaptic potentials, and pacemaker potentials. A receptor potential is generated by a sensory stimuli. A postsynaptic potential is generated by dendrites and soma by NTs, and can be either excitatory or inhibitory to cause depolarization or hyperpolarization of the cell. A pacemaker potential triggers APs in the heart due to spontaneous oscillations in the membrane potentials. Graded potentials are able to be summed because this is the only way that they can reach threshold potential. Temporal and spatial summation can occur. Temporal summation is when a stimuli is continuously repeated over a certain amount of time so that larger graded potentials can occur. Spatial summation occurs when many sites in a neuron initiate multiple GPs; this too causes larger GPs.

Describe the anatomy and function of the golgi tendon and muscle spindle organs

The golgi tendon organ performs as the muscle tension monitor. It checks how much tension that is being exerted on or by a muscle from either contracting or external stretching. The golgi tendon organ acts as a receptor; the afferent nerve endings that are wrapped around collagen bundles in tendons fire when the tendon is pulled. This central nervous system is informed and if there is excessive tension then the organ will over-ride its excitatory commands, inhibit its contracting muscle, and activate the antagonist. This is done to prevent damage to the tendon. On the other hand, the muscle spindle organ functions as the muscle length monitor. The sensory receptors are muscle stretch receptors that work to detect the passive stretch of muscles. The muscle spindle organ contains intrafusal fibers and mechanosensitive afferent neurons. The afferent sensory neurons detect stretch in the middle non-contractile portion of the spindle and the detected information is then used in spinal reflexes and send to the brain. This muscle sensory system is used to maintain posture, position, and to prevent muscle damage

Name the parameters regulated by homeostatic feedback mechanisms that are controlled by the endocrine system—for each one, name the hormone that regulates this parameter and the gland that secretes the hormone

There are 5 parameters that are regulated by homeostatic feedback mechanisms controlled by the endocrine system; they include: glucose, calcium, sodium, water, and temperature. The pancreas secretes both insulin and glucagon which regulates glucose. Cortisol is secreted by the adrenal cortex and is also used to regulate glucose in the body. Parathyroid hormone is found in the parathyroid and is used to help regulate calcium. In addition, calcitonin is secreted by the thyroid and also contributes to the regulation of calcium levels. The adrenal cortex can also secrete the hormone aldosterone, which regulates sodium. ADH hormone is secreted by the posterior pituitary and regulates water. Lastly, the thyroid also secretes thyroxine in addition to calcitonin and thyroxine regulates temperature inside the body.