Nervous System Physiology Essentials 1 PDF - 2024-2025

Nervous System Physiology Essentials 1 Physiology Chapter 3  Nervous system The nervous system consists of neurons that transmit signals and neuroglia that provide support to neurons. The main function of the nervous system is to receive information, organize it appropriately, devel...

Nervous System Physiology Essentials 1 Physiology Chapter 3  Nervous system The nervous system consists of neurons that transmit signals and neuroglia that provide support to neurons. The main function of the nervous system is to receive information, organize it appropriately, develop it and transmit it. It is divided into 2: central nervous sytem, peripheral nervous system. Central nervous system (CNS): brain and medulla spinalis Peripheral nervous system (PNS): 12 pairs of cranial nerves, 31 pairs of spinal nerves and their ganglia. The peripheral nervous system basically provides the flow of information between the CNS and other body parts. PNS consists of afferent-efferent neurons. Receptor -- afferent (sensory neuron) -- CNS--- efferent (motor neuron) --- muscle or gland (effector organ)  Central nervous system The central nervous system (CNS) is the most basic information processing center of the body, encompassing our brain and spinal cord. The CNS is the region where all neural activities of the body are managed and coordinated. The brain and spinal cord receive sensory information from the body and the environment, process it, and organize appropriate responses. Brain manages cognitive functions such as thinking, perception, learning, memory, and emotion. Spinal cord enables the transmission of signals between the body and the brain. The CNS consists of neurons and glial cells. While neurons provide the transmission of signals, glial cells support, nourish, and protect neurons.  Peripheral nervous system The peripheral nervous system (PNS) covers all the nerve structures outside the CNS. It provides communication between the CNS and the rest of the body. The PNS carries out information exchange between the body's organs, muscles, skin and other structures and the CNS through nerve fibers originating from the brain and spinal cord. The PNS is divided into 2 main sections: Somatic Nervous System: It contains the nerves that control our voluntary movements. It contains the motor nerves that enable the movement of the muscles and the sensory nerves that carry sensory information to the brain and spinal cord. sensations such as touch, temperature and pain are perceived and voluntary muscle movements are controlled. Autonomic Nervous System: It consists of nerves that regulate and control involuntary functions. This system regulates functions that are not under conscious control, such as heartbeat, respiration, digestion and sweating.  Autonomic nervous system: Sympathetic- Parasympathetic The autonomic nervous system is also divided into two sub-sections: Sympathetic Nervous System: Triggers the “fight or flight” response prepares the body for stress situations. Speeds up the heart rate, increases blood pressure, slows down digestion. Parasympathetic Nervous System: Rest and digest Enables the body to return to normal during rest and relaxation. Slows down the heart rate, speeds up digestion, and saves energy. Autonomic nervous system: Sympathetic- Parasympathetic Ganglion is a nerve node where the many bodies of neurons come together and nerve signals are transmitted. There are two types of neurons in the autonomic nervous system: preganglion and postganglion neurons. Preganglion and postganglion neurons provides signal transmission between the CNS and target organs. Preganglion neurons leave the CNS and proceed to the ganglia. Postganglion neurons start from the ganglia and carry signals to the target organ.  Autonomic nervous system: Sympathetic- Parasympathetic The sympathetic nervous system is called thoracolumbar. It originates from the thoracic and lumbar regions of the spinal cord and its ganglia are arranged in the sympathetic chain close to the spinal cord. Therefore, sympathetic preganglia are short because the ganglia are close to the spinal cord. However, a longer distance is required to reach the target organ, so sympathetic postganglia are long. The parasympathetic nervous system is called cranio-sacral. Parasympathetic preganglia originate from the cranial and sacral regions and go near the organs without passing through the sympathetic chain. They synapse with postganglionic parasympathetic fibers near the organ. Therefore, parasympathetic preganglia are long and postganglia are short.  Somatic nervous system The somatic nervous system (SNS) controls the body's voluntary muscle movements Somatic nerves originating from the brain and spinal cord send signals to the muscles, allowing them to move, Transmit sensory information from the external environment (such as touch, temperature, pain) to the CNS. The SNS consists of2 main types of nerve fibers: Sensory Nerves: Transmit sensory information from the skin, muscles, and joints to the brain and spinal cord. Motor Nerves: Send signals from the brain and spinal cord to the muscles, allowing the muscles to move. Conscious movements such as walking, writing, and speaking can be performed. Since the SNS operates under voluntary control, it can change the body's movement and position depending on the person's will.  Enteric nervous system (ENS) Located in the wall of the digestive system that allows the intestines to function on their own. The ENS regulates the contraction of the stomach and intestines, the secretion of digestive enzymes, the movement of food through the digestive tract, and the blood flow of the intestines. The ENS is divided into two main nerve networks, the myenteric and submucosal plexuses: Myenteric plexus: Controls intestinal movements. MOTOR MOVEMENTS OF THE DIGESTION SYSTEM Submucosal plexus: Regulates the secretion of digestive juices and blood flow. SECRETIONS OF HORMONES AND ENZYMES There is a constant flow of information from the ENS to the CNS. NEURONS The neuron is the nerve cell, which is the basic functional unit of the nervous system. Neurons transmit signals and provide information communication. It consists of three main parts: soma (cell body), dendrites and axon. Soma (Cell Body): The central part that contains the neuron's nucleus and other organelles allows the neuron to maintain its vital functions collects signals from the dendrites. Dendrites: Branched structures around the soma receive electrical signals from other neurons. transmit these signals via the soma to the axon. Axon: A long, thin extension that allows the neuron to communicate with other cells. It enables signals to be transmitted from the cell body to distant regions. At the end of the axon are synaptic nodes that enable signals to be transmitted to other neurons. Axon hillock The axon hillock is the area where the soma meets the axon. The axon hillock is where the electrical signal (action potential) is first initiated in the neuron. This area contains many ion channels and acts as a “threshold” area that decides whether the neuron will transmit the signal or not.  Types of Connections Between Neurons There are different types of connections between neurons. These connections determine the direction and effect of signal transmission: Axo-dendritic Connection: A connection type where the axon connects to the dendrite of another neuron. It is the most common /// signals are usually transmitted this way. Axo-somatic Connection: A connection between the axon of one neuron and the soma of another neuron. It allows signals to be transmitted directly to the cell body. Axo-axonal Connection: A connection between the axon of one neuron and the axon of another neuron. It plays a role in modulating or regulating the signal.  AXON The neuron axon is wrapped in a myelin sheath, The myelin sheath surrounds the axon and is lipid-protein structured. It provides isolation of the neuron and prevents electrical signal loss. There are 1 micrometer gaps between the myelin sheath, these are nodes of Ranvier. The conduction speed is slow in unmyelinated axons. The myelin sheath increases the conduction speed. The conduction speed increases as the axon diameter increases. In the peripheral nervous system, Schwann cells form the myelin sheath of a myelinated axon. In the central nervous system, oligodendrocyte cells form the myelin sheath.  Central Nervous System (CNS) Myelin Sheath Diseases Multiple Sclerosis (MS): (Autoimmune) One of the most common myelin sheath diseases. The immune system can disrupt signal transmission by attacking the myelin sheath formed by oligodendrocytes in the central nervous system. Symptoms include fatigue, loss of balance and muscle weakness. Neuromyelitis Optica (Devic's Disease): (Autoimmune) An autoimmune disease that affects the optic nerve and spinal cord. By targeting the myelin sheath, problems related to blindness and spinal cord damage can occur. Acute Disseminated Encephalomyelitis (ADEM): (Inflammatory) A widespread inflammation of the CNS, more common in children. It usually occurs following a viral infection or vaccination and causes myelin loss. Peripheral Nervous System (PNS) Myelin Sheath Diseases Guillain-Barré Syndrome (GBS): (Autoimmune) Develops as a result of the immune system attacking the myelin sheath of peripheral nerves. It is typically characterized by muscle weakness and rapidly progressive paralysis. Charcot-Marie-Tooth Disease: (Genetically inherited) A genetic disease that causes the myelin sheaths in peripheral nerves to deteriorate. Symptoms include muscle weakness, loss of sensation, and deformities. Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): (Autoimmune) An autoimmune disease that is similar to GBS but progresses more slowly. Muscle weakness and loss of sensation develop due to myelin loss.  Neuroglial cells Neuroglia cells are auxiliary cells that support, nourish and protect neurons in the central and peripheral nervous systems. They undertake critical functions for the healthy functioning of the nervous system.  Types of Neuroglia and Their Functions Central nervous system’s neuroglial cells: Astrocytes: They protect the blood-brain barrier, provide nutrients to neurons, regulate ion balance and contribute to the formation of scar tissue in the event of damage. Microglia: They act as immune cells in the CNS (macrophages) They phagocyte the damaged cells and waste in the event of infection or injury. Oligodendrocytes: They cover the axons of neurons in the CNS with myelin, accelerating signal transmission. Ependymal Cells: They cover the brain ventricles and spinal canal, regulating the circulation of cerebrospinal fluid.  Types of Neuroglia and Their Functions Peripheral nervous system neuroglial cells: Schwann Cells: They provide myelin to the axons of neurons in the peripheral nervous system, accelerating signal transmission. They also help heal peripheral nerve injuries. Satellite cells: They surround neuron cell bodies in ganglia in the peripheral nervous system, providing support, nourishment and contributing to healing in case of damage. Classification of neurons: Classified according to structure and function. Functional classification of neurons: 1- Afferent 2- İnterneuron 3- Efferent Structural classification of neurons Unipolar: A single-pole neuron, a single branch called a neurite extends from the soma. The neurite then forms dendritic and axonal. It is mostly found in the ear and cerebellar cells. Bipolar: It has 2 axons. It is especially found in the retina. Multipolar: It has many dendrites and axons. It is abundant in the CNS. The most common type is pyramidal neurons. Pyramidal neurons are found in the cerebral cortex, hippocampus, and amygdala. It is the largest neuron in the CNS. Pseudounipolar: A single neck emerges from a single soma and that neck splits into 2 separate ends. Sensory neurons are structured in this shape. It resembles the letter T. One end of the T receives the stimulus and the other end transmits the received stimulus to the spinal cord or other synapses. The arm that receives the stimulus is the dendrite, and the arm that transmits the stimulus is the axon.  Nerve fiber types: These different types of fibers transmit signals at varying speeds according to the needs of the nervous system Classified according to diameter and conduction speed. As the diameter of the nerve fiber increases, the conduction speed increases. Large fibers are related to motor functions, proprioceptive senses, conscious touch, pressure; Small fibers are related to pain, heat, and autonomic functions. Group A and B fibers are myelinated, group C is unmyelinated.  1. Type A Nerve Fibers Diameter: They are the widest (5-20 µm) fibers. Conduction Velocity: They have the fastest conduction velocity (up to 120 m/s). Subtypes: Aα: Motor nerve fibers control muscle movements. Aβ: They carry sensory stimuli such as touch and pressure. Aγ: They regulate the sensitivity of muscle spindles. Aδ: They transmit sharp, rapid pain (such as a cut) and temperature sensations. Type A a, y fibers are alpha motor neurons - gamma motor neurons. Alpha motor neuron: ends in extrafusal muscle fibers. Gamma motor neuron: innervates intrafusal muscle fibers. They are myelinated and are responsible for motor and sensory functions that require rapid response.  2. Type B Nerve Fibers Diameter: They are medium-sized (1-3 µm). Conduction Velocity: They conduct at medium speed (3-15 m/s). Features: They are myelinated and are usually found in preganglionic nerve fibers in the autonomic nervous system. They are used for involuntary control of organs.  3. Type C Nerve Fibers Diameter: The thinnest (0.5-1.5 µm). Conduction Velocity: Has the slowest transmission velocity (less than 2 m/s). Features: Unmyelinated and functions in sensory stimuli that require a slow response. Carries sensations that need to be transmitted slowly, such as constant, burning pain and temperature. Thank you