Research Paper: Neuroscience and Human Development

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[. . .] In contrast, motor neurons transmit action potentials from the central nervous system toward the periphery (Seeley et al., 2005).

Neurons and their Electrical Activity

The nervous system is composed of millions of nerve cells called neurons. Neurons are the parenchyma of the nervous system which performs every function of the nervous system from simple sensory functions to complex thinking and analysis. Neurons, upon receipt of stimuli, transmit responsive signals to other neurons or to effector organs. Clark (2005) observes that the anatomy of a neuron is composed of four main parts; the cell body, the dendrites, the axon, and the nerve fibers. Given the importance of each of the neuron components, it is important to discuss how each work separately and in tandem to achieve efficient and appropriate responses in the human body.

Varying in diameter and containing a single nucleus, the cell body is the primary component of the neuron. The nucleus of the neuron provides information for protein synthesis and contains most of the organelles of the neuron. Seeley et al., (2005) write that the cell body contains large numbers of mitochondria because of its high metabolic function and also abundant rough endoplasmic reticulum's which referred to as Nissl bodies.

The dendrites of a neuron are cytoplasmic extensions that reach out from the cell body like arms and contain a full array of cellular organelles, such as mitochondria, chromatophilic substance, and ribosomes. The most important feature of a dendrite is its electrical activity. Dendrites receive information from other neurons and transmit them toward the cell body, then produce electrical impulses referred to as graded potentials. Graded potentials can have varying degrees of depolarization or hyperpolarization. These graded potentials arise in the dendrites or in the cell body as a result of various stimuli and are important in initiating action potentials in neurons. As the graded potential passes through a cell body, it may initiate an action potential at the base of another cytoplasmic projection which is the axon (Clark, 2005).

An axon is a long cell process extending from the neuron cell body. Each neuron contains only one axon. The axon has a plasma membrane which is called the axolemma, and a cytoplasm which is called the axoplasm. Unlike dendrites, there are no chromatophilic substances found in axons. Axons may branch distally into axon terminals called telodendria. These end in sacs called synaptic end bulbs. Synaptic end bulbs are parts of synapses or neuroeffector junctions. Axons also play an important role in the electrical impulse activities of neurons. They carry action potentials away from the perikaryon toward the synaptic end bulbs, and these action potentials require the axolemma to have many volt-gaged ion channels. The releases of neurotransmitters from synaptic vesicles into the synaptic cleft are caused by these action potentials. A mechanism of active movement in the axon is called axonal transport. It expends energy to move substances in both directions in the axoplasm approximately 300 mm per day. This mechanism involves the cytoskeleton, and is used to deliver organelles and wastes back to the cell body (Clark, 2005).

Nerve fibers are collections of axons or dendrites, and may have myelin; surrounding additional layers for insulation. Axons are surrounded by cell processed of oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelin sheaths are repeatedly wrapped around axon segments to form tightly wrapped cell membranes. Myelin sheaths prevent almost all electrical current flow through the cell membrane. Gaps exist between the myelin sheaths known as the nodes of Ranvier. It can be seen about every millimeter between the oligodendrocyte segments or between individual Schwann cells. Current flows easily between the extracellular fluid and the axon at the nodes of Ranvier, and action potentials can develop (Seeley et al., 2005).

The Central Nervous System

The central nervous system consists of the brain and the spinal cord. The brain is contained within the cranial cavity while the spinal cord is inside of the vertebral column. The peripheral part of the brain is comprised of grey matter while the inside of the brain, the medulla, is comprised of white matter. Both the brain and the spinal cord are completely surrounded by three meninges or membranes which lay between the skull and the brain. Meninges are connective tissue membranes that serve to protect the brain and the spinal cord from injuries. The function of the meninges is to cushion the tissues of the brain and the spinal cord should some physical trauma occur. Bhise and Yadav (2008) note that the three protective meninges are: the dura mater, arachnoid mater, and the pia mater.

As the thickest and most superficial of the three meninges, the dura mater folds extend into the longitudinal fissure between the two cerebral hemispheres as well as between the cerebrum and cerebellum. The dura mater contains spaces called dural venous sinuses within the folds in the dura mater. These sinuses collect blood from the small veins of the brain. The dural venous sinuses empty their collected blood into the internal jugular veins, which then exits the skull. The dura mater is tightly attached to the periosteum of the skull. The dura mater of the spinal cord contains a space between the vertebrae referred to as the epidural space, which is used for the administration of anesthetics during surgery (Seeley et al., 2005). The second meningeal membrane is the arachnoid mater which is composed of thin and wispy connective tissues that cover the brain and the spinal cord. The space between the dura mater and the arachnoid mater is called the subarachnoid space, which generally provides a space containing a very small amount of serous fluid. It is a delicate serous membrane that contains cerebrospinal fluid (Bhise & Yadav, 2008).

The last meningeal membrane is the pia mater. Tightly bound to the surface of the brain and the spinal cord the pia mater is adjacent to the arachnoid mater. The space between the arachnoid mater and the pia mater is called the subarachnoid space, which contains blood vessels and is filled with cerebrospinal fluid. Seely et al. (2005) writes that the function of the pia is to protect the nervous tissue as well as to supply blood and nourishment to the central nervous tissue (Seeley, et al., 2005).

The central nervous system contains fluid-filled cavities called ventricles. These are irregularly shaped cavities that contain cerebrospinal fluid. There are four ventricles in the central nervous system; the right and left lateral ventricles, as well as the third and fourth ventricles. Collectively, these ventricles produce cerebrospinal fluid that serve to nourish and provide protection to the nervous tissues (Seeley et al., 2005). Within the cerebral hemispheres, the lateral ventricles lay on either side of the median plane just below the corpus calosum, separated by a thin membrane called septum lucidum. Blood capillaries are present in the lateral ventricles. It is also lined internally by means of ciliated epithelium called choroid plexus where cerebrospinal fluid is derived (Bhise & Yadav, 2008). As a smaller midline cavity, the third ventricle, located in the center of the diencephalon between the two halves of the thalamus, is filled with cerebrospinal fluid and it is connected by holes to the lateral ventricles known as interventricular foramina (Bhise & Yadav, 2008).

The fourth ventricle, connected to the third ventricle by the cerebral aqueduct, a narrow canal, is located at the base of the cerebellum. This fourth ventricle is present below and behind the third ventricle and between the cerebellum and pons varolii. The fourth ventricle is Connected continuously with the central canal of the spinal cord, the fourth ventricle opens into the subarachnoid space through foramina in its walls and roof (Seeley, et al., 2005).

With an abundant supply of cerebrospinal fluid, the central nervous system contains a cerebrospinal fluid produced by the choroid plexuses. These are specialized structures made of ependymal cells which are located in the ventricles. Cerebrospinal fluid fills the brain ventricles, the central canal of the spinal cord, as well as the subarachnoid space. Flowing from the lateral ventricles into the third ventricle and then through the cerebral aqueduct in the fourth ventricle, the Cerebrospinal fluid incrementally enters the central canal of the spinal cord. Cerebrospinal fluid exits from the fourth ventricle through small openings and enters the subarachnoid space. Arachnoid granulations are masses of arachnoid tissue that penetrate into the superior sagittal sinus, while cerebrospinal fluid passes from the subarachnoid space into the blood through these granulations (Seeley et al., 2005).

One of the main functions of the cerebrospinal fluid is to protect and support the delicate structures of the brain and the spinal cord. Also, the cerebrospinal fluid maintains uniform pressure around the brain structure. The cerebrospinal fluid provides a cushion for the brain and the spinal cord and serves to protect the brain and spinal cord in the event of injury or severe trauma. Lastly, the cerebrospinal fluid keeps the brain and the spinal cord moist as… [END OF PREVIEW]

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Neuroscience and Human Development.  (2010, December 31).  Retrieved March 26, 2019, from https://www.essaytown.com/subjects/paper/neuroscience-human-development-one/6182870

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"Neuroscience and Human Development."  31 December 2010.  Web.  26 March 2019. <https://www.essaytown.com/subjects/paper/neuroscience-human-development-one/6182870>.

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"Neuroscience and Human Development."  Essaytown.com.  December 31, 2010.  Accessed March 26, 2019.
https://www.essaytown.com/subjects/paper/neuroscience-human-development-one/6182870.