Question

Describe the parts of the brain neuron including; the axon ; the dendrite ; what are neurotransmitters? ;what are vesicles? ; describe the Synapse ; what is the function of receptors; what is the Action Potential; and explain synaptic reuptake

Answer 1

Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between.While neurons have a lot in common with other types of cells, they’re structurally and functionally unique.

Parts of a neuron

Neurons vary in size, shape, and structure depending on their role and location. However, nearly all neurons have three essential parts: a cell body, an axon, and dendrites.

Axon

An axon is a long, tail-like structure which joins the cell body at a specialized junction called the axon hillock. Many axons are insulated with a fatty substance called myelin. Myelin helps axons to conduct an electrical signal. Neurons generally have one main axon.

Dendrites

Dendrites are fibrous roots that branch out from the cell body. Like antennae, dendrites receive and process signals from the axons of other neurons. Neurons can have more than one set of dendrites, known as dendritic trees. How many they have generally depends on their role.For instance, Purkinje cells are a special type of neuron found in the cerebellum. These cells have highly developed dendritic trees which allow them to receive thousands of signals.

Neurotransmitters

Neurotransmitters are often referred to as the body’s chemical messengers. They are the molecules used by the nervous system to transmit messages between neurons, or from neurons to muscles.

Communication between two neurons happens in the synaptic cleft (the small gap between the synapses of neurons). Here, electrical signals that have travelled along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron.A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory.An excitatory transmitter promotes the generation of an electrical signal called an action potential in the receiving neuron, while an inhibitory transmitter prevents it. Whether a neurotransmitter is excitatory or inhibitory depends on the receptor it binds to.Neuromodulators are a bit different, as they are not restricted to the synaptic cleft between two neurons, and so can affect large numbers of neurons at once. Neuromodulators therefore regulate populations of neurons, while also operating over a slower time course than excitatory and inhibitory transmitters.Most neurotransmitters are either small amine molecules, amino acids, or neuropeptides. There are about a dozen known small-molecule neurotransmitters and more than 100 different neuropeptides, and neuroscientists are still discovering more about these chemical messengers. These chemicals and their interactions are involved in countless functions of the nervous system as well as controlling bodily functions.

Vesicle

A vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes (not to be confused with lysosomes). If there is only one phospholipid bilayer, they are called unilamellar liposome vesicles; otherwise they are called multilamellar. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.

Vesicles are parts of cells that serve a variety of different functions. The function of vesicles are organelles, and the small enclosed sacs that comprise them can transport and store substances within a cell from one cell to another. They have a lipid bilayer, which separates the contents of the vesicle from the rest of the cell, from the cytoplasm and its contents.Vesicles can hold many different compounds, in either liquid or gas forms. Some of the functions of vesicles include secreting hormones, degrading worn-out cell parts, and regulating buoyancy.Vesicles are found in different kinds of cells, like archaea, bacteria, and plant and animal cells. The vesicles found in these different cells have different functions, and one cell can have various types of vesicles, which have different roles.Some of the different forms of vesicles that animal and plant cells can have include vacuoles, transport vesicles, lysosomes, and secretory vesicles.

Synapse

Synapse, also called neuronal junction, the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction.

When a nerve signal reaches the end of the neuron, it cannot simply continue to the next cell. Instead, it must trigger the release of neurotransmitters which can then carry the impulse across the synapse to the next neuron.Once a nerve impulse has triggered the release of neurotransmitters, these chemical messengers cross the tiny synaptic gap and are taken up by receptors on the surface of the next cell. These receptors act much like a lock, while the neurotransmitters function much like keys. Neurotransmitters may excite the neuron they bind to or inhibit it.

The Parts of the Synapse

Synapses are composed of three main parts:

• The presynaptic ending that contains neurotransmitters
• The synaptic cleft between the two nerve cells
• The postsynaptic ending that contains receptor sites

Function of receptors

Receptors are present in our all parts of the body for example in skin, eye, nose tongue etc. They detect the signals and then send them to brain in the form of electrical signals.
Receptors can become dysfunctional temporarily or sometimes permanently depending upon the level of exposure to a certain stimulus. For ex- laser beam entering directly into the eyes can burn the retinal cells and can make a person temporarily or permanently blind, depending upon the length of period for which the exposure sustains. Similar is the case of burns. A mild burn can desensitize the skin for some time but a significant burn can cause a permanent loss of sensation in the burnt area.
The associated problem includes loss of stimulus from that particular receptor, which is certainly not good for the coordination in the body.

Action Potential

An action potential (AP) is the mode through which a neuron transports electrical signals. It is defined as a brief change in the voltage across the membrane due to the flow of certain ions into and out of the neuron. In this article we will discuss how an action potential is generated and how conduction of an action potential occurs.An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern. Sufficient current is required to initiate a voltage response in a cell membrane; if the current is insufficient to depolarize the membrane to the threshold level, an action potential will not fire. Examples of cells that signal via action potentials are neurons and muscle cells.

Reuptake

Reuptake is the reabsorption of a neurotransmitter by a neurotransmitter transporter located along the plasma membrane of an axon terminal (i.e., the pre-synaptic neuron at a synapse) or glial cell after it has performed its function of transmitting a neural impulse.

Reuptake is necessary for normal synaptic physiology because it allows for the recycling of neurotransmitters and regulates the level of neurotransmitter present in the synapse, thereby controlling how long a signal resulting from neurotransmitter release lasts. Because neurotransmitters are too large and hydrophilic to diffuse through the membrane, specific transport proteins are necessary for the reabsorption of neurotransmitters. Much research, both biochemical and structural, has been performed to obtain clues about the mechanism of reuptake.