The nervous system comprises of different parts, all of which play a vital role in maintaining body functions. The peripheral nervous system includes the skin, muscles, and internal organs. Each of these parts connects by a system of afferents, which carry information into and away from the central nervous system.
Neurons
When nerve impulses travel through neurons, the cells emit an electrical charge known as an action potential. An action potential produces when the number of positively charged ions in the segment of the neuron exceeds the number of negatively charged ions. This results in a temporary positive charge of the segment.
Neurons are the building blocks of the nervous system, and they are responsible for the transmission of information throughout the body. They contain three major parts: the nucleus, the dendrite (which collects information from other cells), and the axon, which transmits signals away from the cell body.
Neurons can be further classified based on their functions and their chemical communication. For example, one type of neuron is called a multipolar neuron, which has one axon and multiple dendrites.
Myelin sheath
In the nervous system, the myelin sheath form by the accumulation of myelin cells. The structure of myelin varies depending on the area of the nervous system it is located in. In the PNS, the myelin sheath form by Schwann cells while in the CNS, it forms by oligodendrocytes.
One example of a myelinated nerve fiber is located in the primary visual cortex. This neuron contains a dense undercoating and paranodes, or points where myelin lamellae terminate in a helical fashion. The inner and outer tongues of the sheath gradually separate, and a spiraled tunnel of cytoplasm extends between them.
The myelin sheath consists of a lipid bilayer and proteins. This structure provides a stable framework for myelin synthesis and maintenance. It has several key components, including the myelin basic protein (MBP), which positively charges and hydrophobic.
Spinal cord
The spinal cord is sheath in three layers, the arachnoid, the pia, and the dura. The arachnoid forms the outer layer, the pia is underneath, and the dura attach to the spinal cord by lateral denticulate ligaments that arise from the pial folds. The dura is located at the level of the second sacral vertebra.
The spinal cord consists of 31 pairs of nerves. Each spinal nerve has a separate root. In the cervical spine, each pair of spinal nerves leaves the vertebral column at its corresponding level, the first one exits at the C1 vertebra, the second between the C2-C3 segment, and the eighth one leaves between the C7 vertebra and the first thoracic vertebra.
The spinal cord transmits sensory and motor commands from the brain to the body. It also coordinates reflexes. The 31 spinal nerves form a segmental network. Injury to the spinal cord disrupts this conduit between the brain and the body. This can lead to deficits in movement, sensation, and autonomic regulation. In some cases, spinal cord injuries can even lead to death.
Cranium
The cranium is the outermost part of the human brain. It contains a network of specialized nerves that carry information from the brain to other parts of the body. The cranium contains between 15 and 33 billion neurons, each of which connects to thousands of other neurons. It also contains the olfactory nerve, which governs smell.
Cranial nerves control the motor functions of the body, as well as the sensations we experience. Some of these nerves also control motor activities in the heart. The remaining 10 cranial nerves emerge from the brainstem. The brainstem is made up of three different parts: the cerebrum, the pons, and the brainstem.
The cranium contains many small holes to allow blood vessels and nerves to enter and exit the skull. The biggest hole is at the base of the cranium, where the spinal cord travels. The occipital bones are also located, articulating with the first vertebra in the spine.
Somatic and visceral parts of the nervous system
The somatic and visceral parts of the nervous systems connect by nerves called dorsal root ganglia (DRG). These neurons receive a variety of noxious stimuli and produce sympathetically mediated responses that can cause pain or increased blood pressure.
The SRG is made up of cranial and spinal nerves that transmit sensory information to the central nervous system (CNS) and motor neurons that transmit movement messages to muscles. Without these nerves, animals would not be able to process information about their environment or control their movements.
The SRG contains connections in all 31 spinal nerves, which branch out to form nerves that extend throughout the body. These nerves carry sensory information from the eyes and ears to the brain. Once in the CNS, these nerves branch out to form thousands of association nerves that integrate sensory input with motor output. These nerves control the heart rate, digestion, respiration, and salivation.
The SRG, made up of two branches: the voluntary part, which contains the motor neurons, and the involuntary part, which regulates visceral functions. The SRG further divides into two subsystems, the somatic nervous system and the autonomic nervous system. The somatic nervous system controls voluntary body movements, while the autonomic part controls involuntary functions.
Chemical barriers
Chemical barriers in the nervous system (CNS) can be a major obstacle in treating neurodegenerative disorders. Nevertheless, small molecule CNS-targeting drugs can overcome these barriers. The development of these agents requires a clear understanding of the physiological and physiochemical characteristics of BBB.
The BBB compose of many different cell types, including neurons, pericytes, and the cerebral endothelium. It serves as a structural roadblock for microorganisms that travel through the bloodstream. It also serves to protect the microenvironment of the brain by regulating the entry of harmful molecules.
A classic series of experiments was conducted by Ehrlich in 1885 in which a blue dye was injected intravenously into a rat’s brain. Ehrlich erroneously, surmised that the brain was made of tissue that could not adhere to the dye. A second experiment, carried out in 1913 by Goldmann, found that the CSF constituted a selective barrier between blood and brain.
The blood-brain barrier is an interface between the blood and the brain, and it serves protective functions by preventing passive passage of ions, proteins, and hydrophilic substances. This barrier also prevents the accumulation of circulating blood cells and proteins in the brain, thereby interfering with water homeostasis.
Muscle cells
The nervous system controls the movement of muscle cells. Skeletal muscle is the most common type of muscle and makes up about 40% of the body’s mass. Its contractions cause bones to move. Skeletal muscles control by the cerebral cortex. Each muscle cell is called a myoblast and develops from a group of smaller cells during embryonic development. Muscle cells categorize into three types based on their structure and function.
Nerve cells are made of neurons and produce electrical impulses that travel along the membranes of muscle cells. These impulses then cause the muscle to contract. Understanding the structure of nerve cells and muscle cells will help you understand how they work. Here is a brief explanation of the different types of muscle cells and their function.
Muscle cells have two kinds of cell membranes. The innermost layer is called the sarcoplasm, while the outer layer is the cytoplasm. The sarcoplasm composes of thick and thin myofilaments. Smooth muscle cells do not have sarcomeres. The thin filaments of smooth muscle do not contain troponin. Myosin and actin interact with calcium and calmodulin to trigger contraction.
Reflex circuits
The nervous system has groups of neurons called reflex circuits that send and receive information. Reflexes are the simplest type of circuit, because they are an automatic reaction to a specific stimulus. The stimulus initiates an action by sending a message to a motor neuron, which then sends a signal to a muscle, causing it to contract.
Reflex arcs, made up of sensory neurons and motor neurons. A sensory neuron carries a signal to the motor neuron, which then fires a muscle or bone. These circuits have several components, and they are all interconnected. For example, when a dog bites another dog, the motor neuron triggers the action by sending a signal to the nerves, and the muscle moves the bone.
Another example of a reflex circuit is the one that governs organ homeostasis. The principle of reflex control is well established and has been studied extensively in organs that are relatively accessible. This includes the gastrointestinal tract, skeletal muscle, and neuroendocrine systems. Recent advances in the field have led to the identification of similar fundamental units of reflex neural action.
