The nervous system is a very complex system which is vital to the functioning of the human body. It monitors the body and takes actions as necessary. Moreover, the nervous system is responsible for conscious and unconscious muscle coactions, and for the regulation of activities involving internal organs. It also consists of structures that transmit electrical and chemical signals between the brain and the body’s organs and tissues.
The nervous system is comprised of the central nervous system (CNS) and peripheral nervous system (PNS). The CNS is comprised of the brain and spinal cord. And the spinal and cranial nerves comprise the PNS. The somatic system and the autonomic system make up the peripheral nervous system. Furthermore, the autonomic system divides into the parasympathetic branch and the sympathetic branch.
This article will look at the structures of the nervous system. Also, it will look at some basic functioning of the nervous system. These are 11 Facts About the Nervous System Every Nursing Student Should Know.
Fact #1 The Nervous System Contains Two Types of Tissue.
The nervous system contains two types of tissue. First, there are the neurons or nerve cells. Additionally, there are cells that support the neurons called the glial cells (neuroglia) and the Schwann cells. However, the neurons are the primary cell of the nervous system. The glial cells are the most abundant support cells in the central nervous system. And, the Schwann cells are primarily in the peripheral nervous system.
The main function of a neuron is to receive information and transmit messages from one cell to another, throughout the body. Neurons control all the functions of the nervous system. Moreover, neurons can be classified by their appearance, their structure or by their function.
Structurally, a neuron can be bipolar, multipolar and unipolar. Firstly, a bipolar neuron has one axon and one dendrite. Secondly, a multipolar neuron has one axon and many dendrites. And finally, a unipolar neuron has one process that splits into a central and the peripheral projection.
Functionally, neurons classified by the function are afferent and efferent neurons. Afferent neurons (also called sensory neurons or input neurons) carry impulses from the peripheral receptors (skin and sensory organs) to the central nervous system (spinal cord and the brain). Efferent neurons (also called motor neurons or output neurons) carry and transmit impulses from the central nervous system (brain and spinal cord) to muscles and glands (effectors). Interneurons (also called association neurons) carry information between neurons.
The glial cells (neuroglia) are specialized cells of the nervous tissue. These cells are the support cells of the nervous system. Therefore, they line, cover, support and protect the structures of the nervous tissue. These cells cannot measure the environment or send orders like the neurons, but, they allow for the nervous system to perform its function.
Fact #2 There are Three Components of a Nerve Cell.
The neurons of the nervous system detect environmental changes and initiate body responses to maintain homeostasis. The neurons or nerve cells vary in their shape however, they all have three basic components; the cell body, the dendrites, and the axon. Also, each component of the neuron has a specific function.
The bigger portion of the neuron is the cell body. Each cell body contains a nucleus. The cell body controls the function of the cell which includes cell metabolism. Each cell body has dendrites which receive information from the environment. Also, these dendrites receive information from other cells and carry that information to the cell body.
The dendrites are the thin branch-like fibers of the cell. The dendrites receive neurotransmitters released from other neurons. Then, they convert those chemical signals into electrical impulses. And finally, they carry those nerve impulses toward the cell body.
Each neuron has an axon. Axons are the long projections of the cell body that carry the nerve impulses away from the cell body. Each neuron has just one axon.
Moreover, each axon is covered with a layer of lipid material containing segments called myelin. The myelin insulates the axon and assists with the proliferation of impulses. This entire membrane is the myelin sheath.
Additionally, the axon has gaps at regular intervals along the nerve fibers. The gaps are the nodes of Ranvier. The nerve impulse travels down the nerve fiber hopping from node to node. Therefore, this allows the impulse to travel faster.
So, the impulse leaves the cell body and travels down the axon. The impulse then arrives at the axon terminal. Additionally, this is where the axon connects to the receiving cells. And this area between the axon terminal and the receiving cells is the synapse.
Fact #3 Neurons are Excitable Cells.
A neuron is an excitable cell because they can generate and conduct an impulse to other parts of the cell. This occurs after the neuron has been stimulated. So, anytime a neuron generates a nerve impulse there is the generation of an action potential. When an action potential is generated there is a change in the membrane potential of the neuron’s cell membrane. Therefore, the action potential is the change in the membrane potential and charge across a cell membrane. Then, the action potential travels along the axon to the end of the nerve cell. The generation of an action potential involves polarization, depolarization, and repolarization.
A cell in a resting state or polarized state is not stimulated. Therefore, this cell carries a negative charge. This means the cell has a more negative charge inside the cell than outside. Also, this means there is a higher concentration of sodium ion outside the cell and a higher concentration of potassium ions inside the cell. Potassium and sodium ions are both positively charged. However, there are enough negative ions inside the cell to make the inside more negative than the outside of the cell. Additionally, a difference between the electrical charge of the inside of the cell and the outside of the cell is the resting membrane potential.
Therefore, when a stimulus occurs strong enough to change the membrane potential, an action potential is produced. Remember an action potential is the change in the membrane potential and charge across a cell membrane.
So, when an action potential is initiated, the cell membrane becomes more permeable to sodium and the sodium gates open. Then, this allows sodium ions to move across the cell membrane into the cell. These sodium ions are positively charged. When these positively charged sodium ions enter into the cell, it becomes more positive. Therefore, there is a change in the charge of the cell from negative to positive. This change is depolarization.
Next, the sodium ion gates close and the gates for the potassium ions open. Potassium is also positive. So, these positively charged potassium ions leave the cell and take their positive charge with them. Consequently, the inside of the cell becomes negative again and returns to its resting state. This process is repolarization. Following repolarization, the cell is in a resting state or polarized.
Fact #4 Communication Between Neurons Occur At The Synapse.
Neurons communicate by transmitting impulses to each other. The area between two neurons is the synapse. The synapse is the location at which nerve impulses are transmitted from one neuron to another. Also, impulses transmit from one neuron to a muscle or a gland. The structure of the synapse includes a presynaptic terminal, a postsynaptic cell, a synaptic cleft, and a receptor.
Firstly, impulses are transmitted via chemical or electrical conduction. This means there are chemical and electrical synapses. The action potential moves from neuron to neuron in an electrical synapse by allowing an electrical current to flow between neurons. In a chemical synapse, the action potential reaches the axon terminal or presynaptic terminal and causes the release of chemical substances called neurotransmitters. The neurotransmitters cross the synaptic cleft and attach to receptor sites on the postsynaptic cell.
The neurons are named depending on whether they relay messages away for the synapse or toward the synapse. Presynaptic neurons conduct nerve impulses toward the synapse. Conversely, postsynaptic neurons relay nerve impulses away from the synapse.
Fact #5 Neurotransmitters are the Chemical Messengers.
Neurotransmitters are chemical messengers. They carry a signal from one neuron across the synaptic cleft to the next neuron. The neurotransmitters are contained in sacs called vesicles.
Calcium ions cause these vesicles to release the neurotransmitters. Firstly, when a nerve impulse is transmitted and reaches the axon terminal, it depolarizes the terminal. Remember depolarization is a change in the charge of the cell. Depolarization causes calcium gates to open. Therefore, more calcium flows in causing more depolarization. When calcium flows in neurotransmitters are released.
Then, the neurotransmitters move towards and connect to the receptor cell. Finally, the binding of the neurotransmitter changes the permeability of the postsynaptic neuron cell membrane. Some neurotransmitters excite the receiving cell and some calm the receiving cell down. A postsynaptic neuron may be excited or inhibited.
Substances such as norepinephrine, acetylcholine, dopamine, histamine, and serotonin are all considered neurotransmitters. Many of these neurotransmitters have more than one function.
Fact #6 The Central Nervous System Includes the Brain and Spinal Cord.
The central nervous system controls all the functions of the body. Also, this system responds to any changes inside and outside the body. The central nervous system consists of the brain and spinal cord, motor pathways, protective structures, and blood supply.
The brain is responsible for a person’s intelligence, personality, reasoning, and their mood. It also allows a person to interact with their environment. The components of the brain are the cerebrum, cerebellum, and brainstem.
The cerebrum is the largest part of the brain. The longitudinal fissure divides the brain into the right and left hemispheres. Likewise, the transverse fissure separates the cerebrum from the cerebellum. The surface of the cerebrum contains ridges called gyri. It also contains grooves called sulci. Because of the gyri and sulci, the surface area of the cerebrum is increased.
The brain contains sections called lobes. The lobes of the brain have the name of the skull bones that cover them. These lobes occur in pairs. There is one in each hemisphere of the brain. The brain has two hemispheres – right and left. The most anterior lobes are the frontal lobes. And, behind the frontal lobes are the parietal lobes. Additionally, behind the parietal lobes are the occipital lobes. As well as, the temporal lobes which are the most inferior lobes.
The cerebellum is posterior to the brainstem and plays an important role in sensory and motor coordination and also balance. Its surface is also convoluted like that of the cerebrum. From its appearance, the cerebellum has been known as the “little brain.”
The brainstem is a stalk-like structure that is below and partially covered by the cerebrum. The brainstem divides into three sections. These sections are the medulla oblongata, the pons, and the midbrain. The medulla oblongata is continuous with the spinal cord. It is the lowest portion of the brainstem. Then, there is the pons which is just above to the medulla oblongata and connects the medulla oblongata and the cerebellum to the upper portions of the brain. Finally, the midbrain is the most superior portion of the brainstem.
The reticular system is a network of nerve cell bodies in the brainstem. This system is essentially responsible for maintaining a wakeful state. Also, this system is vital for maintaining awareness of your environment. Your reticular system is what wakes you up in the morning from your sleeping state. The reticular system also controls cardiovascular and respiratory function.
The Spinal Cord
The spinal cord is located in a cylindrical structure that is inside the vertebral column. The vertebral column surrounds and protects the spinal cord. The spinal cord extends from the medulla oblongata down the length of the vertebral column. It allows nerve impulses to travel to and from the brain. Also, the spinal cord controls many reflexes of the body.
There are 31 pairs of spinal nerves that arise from the spinal cord. Each segment of the spinal cord contains the name of the corresponding vertebrae. Likewise, each spinal nerve contains the names of the corresponding vertebrae. The spinal nerves include eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal.
The actual spinal cord ends at around the second lumbar vertebrae. The end of the spinal cord tapers into a cone-shaped area called the conus medullaris. Then, the spinal nerves continue from the end of the spinal cord and form a bundle of nerve roots called the cauda equina. Finally, a filament of the pia mater that surrounds the brain and spinal cord continues to the coccyx and anchors the spinal cord there. This filament is called the filum terminale
Fact #7 The Meninges Protect the Brain and Spinal Cord.
The meninges are a group of three protective membranes that surrounds the brain and spinal cord. These three membranes are the dura mater, the arachnoid (mater), and the pia mater.
The dura mater is the thick tissue that lines the inside of the skull. This layer is the outermost layer that covers the brain. Then, between the dura mater and the skull and is the epidural space. The epidural space also lies between the dura mater and the vertebral column.
The arachnoid is a delicate middle layer that follows the same contours as the dura mater. This layer resembles a spider web. The arachnoid is comprised of elastic fibers and collagen. Also, between the arachnoid and the pia mater is the subarachnoid space. Cerebrospinal fluid fills the subarachnoid space. This layer also has arachnoid villi which are fingerlike projections that allow outflow of cerebrospinal fluid into the venous circulation. The subdural space is between the dura mater and the arachnoid mater. This layer can be open due to trauma, sometimes causing a subdural hematoma.
The pia mater is the innermost layer. So, this layer covers the surface of the brain and spinal cord. The pia mater is thin and very closely covers the contour of the brain. The pia mater contains blood vessels that supply the brain and spinal cord.
Fact #8 The Brain and Spinal Cord Float in Cerebrospinal Fluid.
The cerebrospinal fluid is a clear fluid that bathes the brain and spinal cord. The cerebrospinal fluid also acts as a shock absorber protecting the structures from blows. It also carries nutrients as it moves back and forth between the cranial cavity and the spinal cavity. The cerebrospinal fluid is produced by the choroid plexus within structures of the brain called ventricles.
There are four ventricles in the brain. Firstly, there are two lateral ventricles in the cerebrum. Then, there is the third ventricle between the cerebrum and the brain stem. Finally, the fourth ventricle is between the medulla oblongata and the cerebellum. As the cerebrospinal fluid circulates through the ventricles, the arachnoid villi absorb the cerebrospinal fluid back into the subarachnoid space.
Fact #9 The Peripheral Nervous System Includes all the Nerves Outside the Central Nervous System.
The peripheral nervous system contains the cranial nerves and spinal nerves. There are 12 pairs of cranial nerves that receive information from the head and neck. And, there are 31 pairs of spinal nerves that supply the rest of the body. For more information on the spinal and cranial nerves, read the article on spinal and cranial nerves.
The components of the peripheral nervous system include the peripheral nerves that carry information from the central nervous system to the rest of the body. Also, it contains sensory receptors which receive information such as pain, touch, and temperature. Additionally, it contains the motor nerve endings which cause the muscle and organs to respond.
Fact #10 The Somatic and Autonomic Nervous System are Divisions of the Peripheral Nervous System.
The peripheral nervous system further divides into the somatic nervous system and the autonomic nervous system. The somatic nervous system regulates voluntary motor control and provides sensory input for your nervous system. Somatic sensation allows you to feel the world around you. These sensations include fine touch, crude touch, vibration, pain, temperature, and body position.
The autonomic nervous system provides the nerves to the parts of the body that is involuntary and not under conscious control. The autonomic nervous system is also responsible for maintaining a stable internal environment. It regulates cardiac muscle, smooth muscle, and the glands of the body. This system is an involuntary system because these functions are not under conscious control. The autonomic nervous system divides into the sympathetic branches and parasympathetic branches of the nervous system.
Fact #11 The Autonomic Nervous System is Divided into the Sympathetic and Parasympathetic Branches.
The autonomic nervous system divides into two branches; the parasympathetic and the sympathetic. These branches supply the same systems but just have opposite effects. The parasympathetic branch often deals with normal body functions and conserves the body’s energy. Conversely, the sympathetic branch is the body’s alert system commonly known as the “fight or flight” response. This system responds to stress and prepares the body to defend itself.
Sympathetic Nervous System
The sympathetic branch of the autonomic nervous system controls the fight-or-flight response. When the body is in danger the effects of the sympathetic nervous system increase the heart rate, increase blood pressure, decrease digestion, and causes sweating and a dry mouth. The response of the sympathetic nervous system also causes the pupils to dilate.
Parasympathetic Nervous System
The parasympathetic branch of the autonomic nervous system has the opposite effect of the sympathetic branch. So, the parasympathetic branch is responsible for the conservation and restoration of energy stores. It also helps the body return back to normal from a sympathetic response. In contrast, the parasympathetic effects include a decrease in heart rate, decrease in respiration, a decrease in blood pressure and an increase in digestive activity.
The nervous system is a wondrous network of complex structures that facilitate the operations of other systems of the body. This article contains 11 Facts About the Nervous System Every Nursing Student Should Know that will help you understand a bit more about the structures and functions of the nervous system.
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Lewis S., Bucher l., Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 10th ed, St Louis, MO: Elsevier Inc. 2017.
Mosby’s Medical Dictionary (2017). 10th ed. St Louis, MO. Elsevier Inc.
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