<span>Ptosis refers to drooping of an upper eyelid of one or both eyes. The droop may be hardly visible, or the lid can move down over the entire pupil. Ptosis can affect both children and adults, however more often than not happens for the reason that of aging. In some cases, droopy eyelid is caused by additional grim circumstances, such as a stroke, brain tumor, or cancer of the nerves or muscles. Neurological disorders that affect the nerves or muscles of the eyes , such as myasthenia gravis can also lead to ptosis.</span>
The information from a signal molecule present outside the cell elicits intercellular response when the G protein coupled receptors interact with the wide variety of molecules on the outer surface of the cells.
G Proteins are the specialized proteins having the ability to bind GTP and GDP and is of three units called Alpha, Beta and Gamma subunits which together formed G proteins.
When G protein is activated it will bind GTP and each receptor binds in lock and key method and binding result into conformational change which will trigger a complex chain of events influencing different cell function.
Features exhibited by Signal Transduction System are:
1. Specificity- Signal molecules fits binding site on its complementary receptor. Other signal do not fit
2. Amplification- When enzymes activates enzymes, the number of affected molecules increases.
3. Desensitization- Receptor activation triggers a feedback circuit that shuts off the receptor or removes it from the cell surface.
4. Integration - When two signals have opposite effects on a metabolic characteristics outcome results from the integrated input from both the receptor.
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C. Redox reactions transfer electrons. Oxidation removes electrons and reduction adds electrons.
Answer:
The autonomic nervous system is in charge of controlling visceral effectors. Traditionally, it is described by its peripheral nervous components (ganglia, nerves and plexuses) and two divisions are distinguished: the sympathetic and the parasympathetic. Transmission of the excitatory stimulus through the synaptic cleft occurs by release of neurotransmitters; the neurotransmitters of the sympathetic and parasympathetic nervous system are mainly norepinephrine (NA) and acetylcholine (AC). The NA-secreting fibers are called adrenergic and those that secrete AC, cholinergic. All preganglionic neurons, both those of the sympathetic nervous system and those of the parasympathetic nervous system, are cholinergic. The neuron that releases the neurotransmitter is called a presynaptic neuron. The signal receptor neuron is called a postsynaptic neuron. Depending on the type of neurotransmitter released, postsynaptic neurons are either stimulated (excited) or de-stimulated (inhibited).
Explanation:
The autonomic nervous system is the part of the central and peripheral nervous system that is responsible for the regulation of the involuntary functions of the organism, the maintenance of internal homeostasis and the adaptive responses to variations in the external and internal environment and two divisions are distinguished: the sympathetic and the parasympathetic. Acetylcholine is the preganglionic neurotransmitter of both divisions of the S.N.A. (sympathetic and parasympathetic) and also of the postganglionic neurons of the parasympathetic. The nerves at whose endings acetylcholine are released are called cholinergic. Norepinephrine is the neurotransmitter of postganglionic sympathetic neurons. The nerves into which norepinephrine is released are called adrenergic. Within the efferent sympathetic impulses, the postganglionic neurons that innervate the eccrine sweat glands and some blood vessels that supply the skeletal muscles are of the cholinergic type. Both acetylcholine and norepinephrine act on the different organs to produce the corresponding parasympathetic or sympathetic effects. The peripheral nerve endings of the sympathetic form a reticulum or plexus from which the terminal fibers come in contact with the effector cells. All the norepinephrine in peripheral tissues is found in the sympathetic endings in which it accumulates in subcellular particles analogous to the chromaffin granulations of the adrenal medulla. The release of norepinephrine at nerve endings occurs in response to action potentials that travel through nerve endings. The receptor, when stimulated by catecholamines, sets in motion a series of membrane changes that are followed by a cascade of intracellular phenomena that culminate in a measurable response. There are two classes of adrenergic receptors known as alpha and beta. These two classes are again subdivided into others that have different functions and that can be stimulated or blocked separately. Norepinephrine primarily excites alpha receptors and beta receptors to a small extent. The neurotransmitter acetylcholine is synthesized at the axonal terminal and deposited in synaptic vesicles. Acetylcholine activates two different types of receptors, called muscarinic and nicotinic receptors. Acetylcholine (AC) synthesis takes place at presynaptic termination by acetylation of choline with acetyl-coenzyme A, a reaction catalyzed by acetylcholinetransferase. The energy required for the release of a neurotransmitter is generated in the mitochondria of the presynaptic terminal. Binding of neurotransmitters to postsynaptic membrane receptors produces changes in membrane permeability. The nature of the neurotransmitter and the receptor molecule determines whether the effect produced will be one of excitation or inhibition of the postsynaptic neuron.
The fluid-mosaic model describes the plasma membrane of
animal cells. The plasma membrane that surrounds these cells has two
layers (a bilayer) of phospholipids (fats with phosphorous
attached), which at body temperature are like vegetable oil (fluid).
And the structure of the plasma membrane supports the old saying, “Oil
and water don’t mix.”
Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic
= fearing). Both layers of the plasma membrane have the hydrophilic
heads pointing toward the outside; the hydrophobic tails form the inside
of the bilayer.
Because cells reside in a watery solution (extracellular
fluid), and they contain a watery solution inside of them (cytoplasm),
the plasma membrane forms a circle around each cell so that the
water-loving heads are in contact with the fluid, and the water-fearing
tails are protected on the inside.
