Nervous System Physiology PDF

Nervous System Physiology Introduction Instructor: Assist Prof. Dr. Shaymaa Jasim 2 NERVOUS SYSTEM (SYSTEMA NERVOSUM) Many organ systems defined in the human body alone do not have the opportunity to work independently. For example, skele...

Nervous System Physiology Introduction Instructor: Assist Prof. Dr. Shaymaa Jasim 2 NERVOUS SYSTEM (SYSTEMA NERVOSUM) Many organ systems defined in the human body alone do not have the opportunity to work independently. For example, skeletal muscles in body parts have blood vessels and nerves in order to work in accordance with the needs; For the nerves and vessels to function normally, the nutrients necessary for their metabolism and needs chemicals such as Na, K etc.  The nervous system works together with the endocrine system as the communication and regulation system of the body. The main purpose of these two systems is to enable the body to act, as well as to give appropriate responses to the stimuli coming from the internal or external environment of the body and to maintain the balance of the body's internal environment (homeostasis). Although the nervous system is a whole in terms of function and morphology, it is classified differently topographically and according to the organ groups it affects. ⚫Topographical Classification of CNS: Brain, brainstem and spinal cord external nerves (spinal and cranial nerves), plexuses and ganglia are examined under the title of peripheral nervous system.  Classification according to the organ groups it affects: Nervous system part related to structures such as voluntary skeletal muscles in our body Somatic Nervous System, The part of the nervous system related to structures that work involuntarily such as smooth muscles, heart and external glands are handled under the title of Visceral (Autonomic) Nervous System.  STRUCTURE OF THE NERVOUS SYSTEM Nervous system formations are made of nervous tissue. Nerve tissue has two main structural elements. These are nerve cells (neurons) and various types of glia cells (neuroglia). The main cells of the tissue are neurons. Neuroglia are the cells that support neurons and feed them.  Neurons have two main structural components.  pericarion (cell body)  cell extensions. In the neuron, the mass of cytoplasm around the nucleus together with the nucleus is called the pericaryon (cell body). Pericarions of various neurons are different in shape and size. In the nervous system, there are neurons with shuttle, star, pyramid, and pear-shaped pericarions. ⚫Cell extensions are of two types, axon and dendrite. ⚫Dendrites are short extensions of the pericarion, one in some and many in others, and they receive the impulses from the environment and other neurons and carry them to the pericarion. ⚫The axon is the single and long extension of the pericarion and is functional in transmitting nerve impulses to other nerve cells, muscle tissue or gland cells.  Neurons fall into three groups according to the size, shape and number of their extensions. Bipolar neuron: 1 axon, 1 dendrite Multipolar neuron: 1 axon with multiple dendrites Pseudounipolar neuron: There is only one extension coming out of the body, this extension then splits into two.. Neurons are also grouped according to their functions. Motor (efferent) neurons control glands and muscles. Sensory (afferent)neurons receive sensory impulses from the body's internal and external environments. Another type of neuron is called an intermediate neuron (interneuron). Interneurons make connections between various neurons.  The second of the two main types of cells that make up the nerve tissue are glial cells. The numbers of glia cells in the nervous system are quite high. Unlike neurons, glia cells maintain their mitotic activities. Glial cells support, nourish, protect neurons, form myelin sheath, and are functional in removing damaged neurons from the environment. Neuroglias have several types: astrocyte (astroglia), oligodendrocyte (oligodendroglia), microglia, ependymal cell, satellite cell, Schwann cell.  Astrocytes support neurons and also provide substance exchange between neurons and blood through their vascular legs and play a role in the blood-brain barrier. Oligodendrocytes form the myelin sheath of axons in the central nervous system. Microglia cells are cells that phagocytosis.  Ependymal cells form a selective barrier between the tissues of the brain and spinal cord and the fluid (cerebrospinal fluid) that fills the cavities that they wall. Ependymal cells have cilia on their apical surfaces. Movement of the cerebrospinal fluid is ensured by the movement of these cilia. Schwann cells form the myelin sheath of axons in the peripheral nervous system..  Various types of physical stimulation outside the body in the nervous system; heat, light, mechanical stimulation, sound waves, It is converted into electrical stimulation and evaluated. This translation process is initiated by the receptors in the organs. All the impulses transmitted to the brain and spinal cord are electrical..  Electrical Properties of Nerve Cell There is an ionic difference between inside and outside the cell in all body cells. In other words, the amount of ions in the intracellular and extracellular environment are different. Since ions are charged substances, this different distribution creates a potential difference between intracellular and extracellular. This difference between inside and outside of the cell varies in various types of cells. For example, this difference in nerve cells was measured as approximately -90 mV. It is intracellular negatively charged dueto protein anions that cannot pass the membrane inside the cell. The main ions involved in the electrical potential difference between inside and outside the cell are sodium, potassium and chlorine anions. Sodium is present in excess outside the cell, potassium inside the cell. Since ions are charged, they cannot easily pass through the membrane. The passage of ions across the membrane occurs through their own channels. In a state of rest, in a cell without excitation, the entrance and exit of ions into the cell are in equilibrium, so that the negative intracellular potential is kept constant in the state of equilibrium.  Ionic Equilibrium: Electrochemical Potentials of Ions Ions inside and outside the cell are at certain concentrations at rest. The passage of ions from one medium to another depends on the permeability of the cell membrane and the type of electrical charge in the medium it will pass through. The cell membrane has different permeability properties to each ion. For this reason, even if an ion is too much on one side of the cell membrane, it passes towards the lesser side according to the permeability of the membrane.  Ions diffuse from the high side to the lesser side. Therefore, both electrical and chemical potential play a role in the movement of an ion. Both are called electrochemical potentials. The flow of an ion from one chamber to the other is from where the electrochemical potential of the ion is high to the lower direction. When the ion flow stops between both compartments, the ion has reached electrochemical equilibrium.  Resting membrane Potential If electrodes are inserted into and out of the cell in a nerve cell and these electrodes are connected to a potentiometer, there is a potential difference of -90 mV at rest. This potential difference arises from the different distribution of ions on both sides. It is an intracellular negative potential due to protein anions that cannot pass the membrane inside the cell. The nerve cell is not completely permeable to either potassium or sodium. For this reason, potassium inside the cell and sodium outside the cell are high. Since there is little permeability to both ions, the ions have a transition in both directions due to the chemical potential difference. However, in a cell at rest, the amount of sodium and potassium ions inside and outside of the cell is kept constant. Apart from the different permeability of this membrane to both ions, it is the result of the activity of the sodium potassium pump in the cell membrane. The pump located in the cell membrane brings out the sodium entering the cell and takes potassium in. Here, the activity of the pump is controlled by the number of ions inside and outside the cell. Increase in sodium ions inside the cell or increase in potassium ions outside the cell have both consequences, that is, the pump becomes active. This pump is an enzyme and works in the presence of ATP. By means of this pump, two potassium ions are transported for every three sodium ions, so that both ions are kept in different amounts in and outside the cell. Cell Stimulation Stimulationof a cell in all body cells occurs when the balance potential within the cell changes in the opposite direction. Secretion release as a result of the stimulation in secretory cells, contraction of muscle cells causes the transmitter substance to be released from the axon end of the nerve in the nerve cells. During the excitation:  first, the permeability to sodium ions increases.  Sodium channels open as a result of stimulation by a transmitter substance and sodium begins to rapidly pass into the cell. As the passage of sodium into the cell increases, the electrical potential inside the cell starts to shift from negative to positive. It is known that there are various types of channels in the membrane for each ion. The first of these are channels that are stimulated by chemical substances. The second type is channels sensitive to voltage changes. In the nerve cell, this second type of intracellular potential is activated as it changes from negative to positive.  Depolarization A potential change within the cell from negative to positiveis called depolarization. This happens when sodium ions begin to pass into the cell.  Threshold Value The potential change that occurs within the cell as a result of depolarization may not spread to the whole cell. If the potential change resulting from depolarization reaches the threshold potential for the cell, the stimulus spreads throughout the cell. Each cell has a threshold potential. This potential usually covers a change from -90mV to - 65mV. In other words, the potential change in the cell towards - 25mV plus causes the opening of all sodium channels in the cell membrane and the cell is fully stimulated.  Repolarization Depolarization in the cell ends with the potassium ions starting to go out. After the depolarization reaches its peak, the cell begins to decay again with the loss of positive ions from the cell. The return of the inside of the cell from positive to negative is called the repolarization of the cell. At the end of repolarization, potassium in the cell has been replaced by sodium. Although the cell reaches its equilibrium potential, the location of the ions is reversed. The potassium that goes outside the cell is expelled from the inside and the sodium entering out, and thus the ions are displaced by the Na-K ATPase pump.  Action Potential The impulse wave transmitted along the axon of the nerve cell is called an action potential. Action potential is a stimulus that occurs as a result of the full stimulation of the cell and spreads along the axon. It can als be considered as a depolarization with an action potential above the threshold value.  As a result of the action potential, the transmitter substance is released from the axon end of the nerve cell. As a result of such stimulation in the muscle cell or secretory cell, contraction or release of secretion occurs. If the nerve cell is stimulated with a stimulus below the threshold value, no action potential will occur. Stimuli below the threshold value do not generate a response in the nerve cell.  Transmission of Action Potential The main function of a nerve cell is to transmit action potential and sensory or motor impulses. In the central nervous system, that is, the brain and spinal cord, impulses are transmitted from one nerve to another.  The impulse transmission between two neurons occurs through special junction areas. The stimulus starts from the cell body of a neuron and is transmitted along the neuron's axon, creating electrical potential changes in the cell body of the other neuron.  In the motor nerve cells that come out of the spinal cord, the stimulus is transmitted directly to the muscle cell and ultimately the muscle cell is stimulated. The stimulation mechanism and action potential formation in muscle cells are the same as in the nerve cell. In the nerve cell, the impulses usually come to the dendrites, the short appendages that emerge from the body of the cell. When there is a potential change in the cell body above the threshold value, the stimulus is transmitted along the axon. Stimulation of another neuron or cell occurs when the transmitter substance released from the axon end binds to the membrane of the other neuron. The transmission of the stimulus along the axon is like electric current flowing through a cable. The conduction speed of the stimulus depends on whether the axon is myelinated or not. Impulse transmission is faster in nerve cells with myelin sheath on the axon. The myelin sheath is like the insulating sheath made of plastic around the copper in electrical cables. This environment propagation of electric current is prevented by the sheath.  Myelin sheath occurs when the Schwann cell membrane coils around the axon several times. Throughout the axon, there is a knuckle at certain intervals in the myelin sheath. These knuckles are called Ranvier knuckles or node of Ranvier.  Synaptic Transmission The synapse is the special junction area where a stimulus passes from one neuron to another. There are two types of synapses; 1. Electrical synapse, 2. Chemical synapse In electrical synapses, electrical impulses are transmitted directly from one cell to another. This is also called electronic synapse.  When the action potential reaches the presynaptic axon tip at the chemical synapse, it causes the release of the neurotransmitter substance from there. The transmitter material diffuses into the synaptic space and binds to the receptor material in the postsynaptic neuron membrane. There are receptors specific to the transmitter substance in the post synaptic membrane. With this binding, sodium channels open in the membranes of the postsynaptic neuron and the cell depolarizes. Nerve Muscle Junction Each skeletal muscle cell is associated with a nerve cell extension. Such a nerve extension is the extension of a motor neuron emanating from the brain or spinal cord. Generally, skeletal muscles contract only when stimulated by the action of a motor neuron.  The place where the nerve extension and muscle fiber meet, and fuse is called the muscle-nerve junction (myneuronal junction). The membrane of the muscle cell in this junction area undergoes a change, forming a structure called the motor endplate. The last parts of the motor nerve extension are branched. The ends of these branches enter the synaptic clefts located on the muscle sarcolemma. Nerve extension terminations contain many synaptic vesicles that store chemical transmission substances called neurotransmitters. ⚫As soon as a nerve impulse from the brain and spinal cord reaches the end of the motor nerve extension, it causes acetylcholine, a neurotransmitter substance, to be released from the synaptic vesicles in this area. This neurotransmitter is exocytosed into the space between the muscle fiber motor endplate and the end of the nerve. ⚫Acetylcholine in the synaptic space combines with acetylcholine receptors in muscle fiber sarcolemma, increasing the permeability of the membrane to sodium ions. ⚫Na ion entry creates an action potential and depolarizes the membrane.This action potential leads to the release of calcium ions from the sarcoplasmic reticulum to the cytosol by moving through the sarcolemma to the T tubules and then into the cell. Thus, muscle contraction is initiated.  CENTRAL NERVOUS SYSTEM The central nervous system has two parts as the spinal cord (medulla spinalis) and the brain (encephalon). SPINAL CORD (medulla spinalis) ⚫ The spinal cord lies within the spinal canal (canalis vertebralis). ⚫It is the continuation of the brain stem.The 1st cervical vertebra starts at the top of the atlas. 1.-2. ⚫It extends to the lumbar vertebra. ⚫The lower end of the spinal cord is like a cone (conus medullaris). ⚫The cone extends to the coccyx with a rope- like extension called the phylum terminale. The spinal cord, which has a transversally segmental structure, has 31 segments. A pair of spinal nerves arise from each segment. Spinal cord sections and the numbers of segmental spinal nerves emerging from these are as follows;  Cervical section 8 pairs thoracic 12 section). pairs Lumbar section (waist 5 pairs section) sacral section) 5 pairs coccygeal 1 pair section ⚫If a transverse section is taken from the medulla spinalis, which is made of nerve tissue, and examined, the H-shaped or butterfly- shaped substantia grisea (gray matter) in the inner part and the substantia alba (white matter) around it are distinguished. ⚫Gray matter is mainly made up of nerve cell bodies.  Within the gray matter are assemblages of nerve cell bodies (nucleus) to carry out specific functions. In the central part of the gray matter is canalis centralis (central canal). Single-store ependymal cellscover the wall of the channel. This channel contains CSF (cerebrospinal fluid). White matter is made up of myelinated axons (nerve fibers) and neuroglia. The spinal cord has three basic functions: reflex activities, and the transmission of motor and sensory impulses. A reflex is a simple, fast, and automatic response. For example, hitting the patellar ligament with a reflex hammer creates an involuntary and rapid extension of the leg. Here, a receptor that receives the sensation, the afferent neuron that takes the sensation to the relevant segment of the spinal cord, the intermediate neuron that transfers the impulse of the afferent neuron to the motor neuron, a motor neuron and the muscles that respond to the stimulus play a role. 58 İstinye Üniversitesi Uzaktan Eğitim Merkezi 59 İstinye Üniversitesi Uzaktan Eğitim Merkezi 60 İstinye Üniversitesi Uzaktan Eğitim Merkezi 61 İstinye Üniversitesi Uzaktan Eğitim Merkezi 62 İstinye Üniversitesi Uzaktan Eğitim Merkezi 63 İstinye Üniversitesi Uzaktan Eğitim Merkezi In addition to transmitting sensations such as pain, heat, pressure, and tension from different parts of our body to the relevant parts of the central nervous system, most of the motor commands received from the motor units of the central nervous system are transmitted by the spinal cord.  BRAIN (encephalon, whole brain) The brain (encephalon), which is the largest part of the central nervous system and is in the skull; cerebrum (brain hemispheres), diencephalon (intermediate brain), truncus cerebri (brain stem) and the cerebellum (cerebellum) It is examined by dividing into four major sub- sections. Generally, the word "brain" should mean the whole brain. Cerebrum (brain hemispheres, telencephalon): The cerebrum consists of two cerebral hemispheres (hemispherium cerebri) separated by a deep cleft with a longitudinal course. The intermediate structure called the corpus callosum connects the two hemispheres and consists of nerve wires extending between the two hemispheres.  The brain is two hemispheres! Each hemisphere controls the opposite side of the body. The right side of the body is represented on the left side of the brain, as the sensory nerves in the body cross before they reach the brain. For example, the pain sensation of the left leg is perceived from the somatic sensory field of the right hemisphere. Likewise, the right motor cortex controls the motor movement of the left side of the body. Therefore, bleeding in one hemisphere of the brain and any damage due to other reasons cause paralysis and sensory loss on the other side of the body. The surface of the cerebrum is not flat, there are many bumps. Each hemisphere consists of four lobes: lobus frontalis, lobus temporalis, lobus parietalis and lobus occipitalis. In the cerebrum, pericarions are in the outer cortex layer. In the inner medulla layer there are nerve wires and neuroglia.  Before we get into brain structures and functions, let's look at how the brain is built.  At the lower level (above the spinal cord cord), there is the brainstem consisting of midbrain, pons and medulla oblongata  The cerebellum sits behind the brain stem 2 thalamus are placed on the brain stem. The hypothalamus is just below the thalamus. The thalamus and hypothalamus make up the diencephalon. The forebrain has begun from this area. The hippocampus that hangs over and between the thalamus nuclei on both sides. Above these, the ventricles are located. Part of the 3rd ventricle is between the thalamus. The 4th ventricle is in the brain stem. Basal ganglia nuclei begin to settle. The amygdala is located adjacent to the tip of the hippocampus on both sides. Above these are white matter formed by axons. There is a cortex at the outermost, its curved structure is noticeable.  Theoutermost layer of the brain that we call the cortex has a protruding structure. These indentations are called sulcus. The curved regions between the indentations take the name gyrus. Unlikethe medulla spinalis, the outermost layer of the brain (ie cortex) is made up of gray matter. This means that the cortex is made up of neuron bodies. There are also gray matter groups in the inner part of the brain. As mentioned earlier, these regions are called nuclei.  The brain is divided into4 lobes on both sides. Frontal, parietal, temporal and occipital lobes. The frontal and parietal lobes separate the central sulcus. The temporal lobe separates the lateral sulcus from other lobes. Occipital lobe located behind the parietal lobe.. FRONTAL LOBE The frontal lobe plays a fundamental role in the planning and execution of movement. It includes prefrontal, premotor and motor areas. Prefrontal cortex: associated with higher levels of thinking, decision making, and planning. It has a significant inhibitory role on impulses and actions. Impulsivity and behavioral changes occur in its injury. Premotor and motor cortex: processes and transmits information about body movements.  PARIETAL LOBE: It is separated from the frontal lobe by the central sulcus. It contains the primary sensory cortex. It plays a role in spatial orientation and information processing. TEMPORAL LO B E I t s l o c a te d u n d e r t h e f ro n t a l a n d p a r i e t a l l o b e. I t i s a s s o c i a te d w i t h a u d i to r y p ro c e s s e s a n d m e m o r y  OCCIPITAL LOBE Visual information is processed in this lobe. LIMBIC SYSTEM Some of the subcortical structures have formed a functional union around the intermediate brain that surrounds it like a ring. This structure is specifically called the Limbic system(Latin: limbus = ring, border). Structures such as the hippocampus, amygdala, fornix, mammillary body, septum, cingulat cortex (limbic cortex) in the limbic system carry out emotional and basic mental functions. For example, the amygdala is a region involved in feelings of fear and aggression. The hippocampus allows us to memorize anything we have learned. BASAL GANGLIA Basal ganglia are a group of nuclei located under the cortex (caudate nucleus, putamen, globus pallidus). all functions of the basal ganglia are NOT fully known. Itis accepted that the basal ganglia play an important role in the automatic continuation of many movements whose known functions are initiated voluntarily. Responsible for sequential movements with the right timing and sequence. Inbasal ganglia diseases, irregular contraction of skeletal muscles, tremors in the arms and legs, irregular movements are seen. Parkinson's disease is the most common disease of the basal ganglia. View of the basal ganglia from a different angle  Diencephalon : It is located between two hemispheres. This is called the intermediate brain. the intermediate brain include: thalamus, hypothalamus, subthalamus, metathalamus, epithalamus. The intermediate brain has important functions in humans. The coordination of the senses, and the autonomic system are managed from here.  Thethalamus contains the subcortical junctions of pain, sense of heat, sight and sense of smell. Hypothalamus includes centers for temperature regulation, circulation, water metabolism, sleep, and wakefulness. pineal body, which is an important structure contained in Epithalamus, secretes melatonin in response to ambient light. brain stem The brain stem is examined in three parts. 1.Medulla oblongata (spinal bulb, bulbus), 2.pons (bridge) 3.mesencephalon (midbrain). These three parts together are called the brainstem. Medulla oblongata (spinal bulb, bulbus): ⚫The lowest part of the entire brain. It is located above the spinal cord, at the base of the skull. The continuation is the spinal cord. ⚫The centers for respiration and metabolism are here. There are centers dealing with swallowing, vomiting and coughing reflexes.  Pons (bridge): It is the middle part of the brain stem and is in front of the cerebellum, between mesencephalon and medulla oblongata. The nerve wires that travel between the cerebrum, cerebellum and medulla oblongata pass through here. That is why it is called a bridge. Mesencephalon (midbrain): Above the Pons and the smallest part of the whole brain parts. Aquaductus cerebri passes through the mesencephalon. CSF is in it.  Cerebellum: It is located behind the medulla oblongata and pons. It is the second largest division of the entire division. The outer surface of the cerebellum contains many parallel grooves and plica protrusions bounded by them. ⚫In the cerebellum, the substantia grisea (gray matter) is outside, and the substantia alba (white matter) is inside. ⚫The cerebellum is called arbor vitae (tree of life) because of this arbor-like appearance, as the white matter extends into the gray matter like tree branches. ⚫The cerebellum provides muscle tone and balance, and the harmony of the muscles. ⚫Balance and proper posture are achieved with the senses coming from the muscles, joints and hemisphere tracts.  Brain Cavities (ventriculus cerebri) There are four cavities filled with cerebrospinal fluid (CSF) within the entire brain compartments. These spaces, called ventricles), are lined with ependymal cells and are in contact with each other. Lateral Ventriculus (ventriculus I, ventriculus II): These two lateral ventricles are within the cerebral 2 hemispheres. The terms ventriculus I for the space in the right cerebral hemisphere and ventriculusII for the space within the left cerebral hemisphere can be used. Third Ventricle (III): It is the part of the ventricular system located in the diencephalon. It relates to Ventriculus I and II by one hole each. Fourth Ventricle (ventriculus IV): Ventriculus tertius opens here. From the lower corner of the ventriculus quartus it continues with the canalis centralis of the spinal cord. On the walls of the brain cavities, there are formations lined with cubic epithelium called plexus choroideus. Plexus choroideus, responsible for the secretion of liquor cerebrospinalis (cerebrospinal fluid is found in all ventricles. CSF is found in all cavities and canalis centralis. The CSF acts as a protective cushion against mechanical trauma between the central nervous system and the surrounding bones. CSF is responsible for, nutrition in the central nervous system, * removal of metabolites and * Some hormones secreted from the hypothalamus also have functions such as transporting them to the pituitary gland. Most of the CSF produced around 500-750 ml per day in humans is secreted from the ventriculus lateralis. There is very little protein in the CSF.  Ifthe flow of CSF in the ventricles is obstructed, the ventricles expand. In the period when the skull bones are not closed yet, a condition called hydrocephalus occurs in babies. Inadults, the expanding ventricle puts pressure on the brain tissue as the skull cannot expand. Cerebrospinal membranes (meninges) The brain and spinal cord are surrounded externally by three membranes. These are called meninges. Outside to inside: dura mater, arachnoidea mater piamater.  Dura mater: This layer is a thick membrane made of irregular tight connective tissue that is located outside of the membranes surrounding the brain and medulla spinalis and does not stretch. The part of the dura mater that surrounds the brain is called the dura mater cranialis, and the part that surrounds the medulla spinalis is called the dura mater spinalis.  It is firmly attached to the periosteum of the skull bones in the tumor. In the spinal cord there is a space (spatium epidurale) between vertebral periosteum A gap called s u b d u r a l s p a c e ( spatium subdurale) is formed between the dura mater and the arachnoidea mater. Arachnoidea mater: It is a thin but non-permeable membrane in the appearance of a spider web, which surrounds the brain and medulla spinalis and is located between the dura mater and the pia mater. Between the pia mater andthe arachnoidea mater is the spatium subarachnoidea and circulates in it cerebrospinal fluid.  Pia mater: Pia mater is a membrane made of thin, loose connective tissue that tightly surrounds the brain and spinal cord of the medulla. It nourishes the brain tissue with the abundant vascular network it carries and enters the brain tissue around the vessels.  PERIPHERAL NERVOUS SYSTEM The part of the nervous system outside the brain and spinal cord is considered as the peripheral nervous system (Systema Nervosum Periphericum). The nerves examined in the peripheral nervous system provide the connection between the central nervous system and the body parts and organs in the periphery. Through these links, they work for the same purpose in accordance many organs in the body. The peripheral nervous system is examined in two parts as the somatic (cerebrospinal) and autonomic nervous system. While the somatic system ensures the harmony of the body with the outside world, the autonomic system creates and maintains the internal balance.  Peripheral nerves are divided into : cranial nerves and spinal nerves. Cranial Nerves (nervi craniales, pairs of heads) The nerves that come out of the brain and go to the environment are called cranial nerves. 12 pairs of cranial nerves emerge from the brain. These cranial nerves bring the information they receive from sensory receptors to the brain. This information is then transmitted from the central nervous system to the muscles and glands. Cranial nerves are referred to by their names as wellas Roman numerals according to the order they exit from the brain.  Some pairs of cranial nerves are only sensory nerves, some are only motor fiber and some are mixed nerves.  Cranial nerves are: I.Olfactory nerve: It is a purely sensory cranial nerve that receives olfactory impulses. It starts from the axons of bipolar cells in the mucosa in the nasal cavity and ends in the cerebrum. II.N. optic nerve: It is the nerve of vision. The axons of the ganglion cells in the retinal layer of the eye n. forms the opticus, carries it to the occipital lobe of the brain. III.N. oculomotor nerve: Carries motor fibers to the eye muscles, starting from the mesencephalon and ending in the eye muscles. IV.N. trochlearis: Carries motor fibers to the eye muscles, starting from mesencephalon and ending in eye muscles. V.N. trigeminus: It has three major branches. These branches go to the teeth, lip skin, lower eyelid, palate, chewing muscles and nasal cavity. It contains sensitive and motor branches. VI.N. abducent nerve: Carries motor fibers to the eye muscles, starting from the pons, ending in the eye muscles. VII.N. facial nerve: innervate facial muscles, sublingual and sub- maxillofacial salivary glands. contains motor and sensory nerve fibers.  VIII.N. vestibulocochlear nerve: It is the hearing and balance nerve. The nerve wires of sensitive cells that receive the senses of hearing and balance in the ear make It is the only pair of heads that cannot come out of the head. IX.N. glossopharyngeal nerve The tongue and the pharynx nerve. It affects the pharyngeal muscles and the parotid gland. It contains sensory and motor nerve fibers. X.Vagal nerve: It gives branches to the internal organs in the chest and abdomen. It is responsible for hunger, pain, respiratory reflexes, swallowing, and movements of internal organs. It contains sensory and motor nerve fibers. XI.Spinal accessory nerve: Affects neck and neck muscles, contains motor nerve fibers only. XII.Hypoglossal nerve: Affects tongue muscles and sublingual muscles. Contains motor nerve fibers only. Spinal Nerves (Nervi spinales) Spinal nerves are formed by the union of the posterior root (dorsal radicles) and spinal roots called the anterior root (ventral radicles). There are 31 pairs of spinal nerves, one pair from each spinal cord segment. 8 pairs in the neck area, 12 pairs in the chest area, 5 pair lumbar (waist area) 5 pairs of sacral and 1 pair is also found in the coccyx area.  In the medulla of spinal cord (medulla spinalis), anterior roots are formed from the axons of the motor cells in the anterior horn of the gray matter. The dorsal roots are the extensions of the cells in the spinal ganglion. These fibers carry the senses they receive from the periphery, sensory receptors, to the spinal medulla. A spinal nerve immediately divides into anterior (ventral) and posterior (dorsal) branches after existing through the intervertebral foramen.  The anterior branches of many spinal nerves do not directly go and innervate the structures in the trunk, the anterior branches of the spinal nerves combine to form a nerve network, this is called the plexus. Nerves originating from the plexuses have a special name. They innervate the trunk and extremities. Major plexuses; Plexus cervicalis (cervical plexus, neck plexus): It is formed by the union of the anterior branches of the first four neck spinal nerves. It innervates neck and shoulder skin and superficial tissues, anterior neck muscles, and diaphragm. Brachial plexus, (arm plexus): It is a nerve network that provides the innervation of the free upper part of the shoulder girdle and is formed by the last four neck (C5-C8) spinal nerves and the anterior branches of the first thoracic (T1) spinal nerve.  Plexus lumbalis (lumbal plexus, waist plexus): Lumbal plexus is formed by the front branches of the first three lumbars (L1-2-3) and the majority of the anterior branch of L4. The anterior and lateral walls of the abdomen, external genital organs and nerves that provide the innervation of the thigh emerge from the lumbar plexus. Plexus sacralis (sacral plexus): The sacral plexus is formed by the junction of the fifth lumbal nerve (L5) and the first four sacral nerves (S1- 4). It innervates the posterior aspect of the upper part of the leg and almost the entire leg below the knee.  Somatic senses  Somatic senses are touch, vibration, pressure, position-movement, temperature and pain sensation. The receptors of the somatic system are the specialized end regions of the afferent neurons.  Receptors exist in different ways, they are found in skin, joints, muscle spindles, tendons. Different types of receptors in the skin. Each one has a different sensation The stimulus received from the receptors in the skin is carried to the spinal cord by afferent nerves. As the intensity of the stimulus increases, the frequency of the action potential increases.  Somatic sensory neurons (afferent neurons) enter the medulla spinalis from the posterior root, then pass to the opposite side and go up in special ways. It reaches the somatosensory cortex in the parietal lobe after passing through the thalamus. There is a representative map of the body in the somatosensory cortex. -The areas where the body is represented are differentfrom the actual body measurements. As you can see, while the hands, lips, tongue and face occupy a lot of space in the cortex, the rest of the body occupies less space. This is because more nerve cells from these areas reach the cortex. Thus, the sensory sensitivity of areas such as lips and hands is more.  DERMATOM Afferent nerves coming from different parts of the body enter the medulla spinalis at different levels. The area of skin stimulated by these nerves is called dermatome. Dermatomes are in the form of belts on the trunk and strips on the extremities. Nerve jumps from the upper and lower segments to the skin segment (dermatoma) stimulated by a spinal nerve. Thus, if a single peripheral nerve is cut. There is no loss of sensations in the skin segment of that nerve. Sensory loss occurs if several spinal nerves in neighboring segments are cut. ,  Visceral sensations:  The senses that comes from internal organs are called visceral sensations.  The nerves that transmit the visceral senses enter the medulla of spinal cord from the posterior root, just like the somatic nerves.  Visceral senses unlike somatic senses cannot be localized well (poor localization).  Referred pain Referred pain is pain perceived at a location other than the site of the painful stimulus/ origin. It is the result of a network of interconnecting sensory nerves, that supplies many different tissues. When there is an injury at one site in the network it is possible that when the signal is interpreted in the brain signals are experienced in the surrounding nervous tissue. Nerve fibers of higher region sensory inputs such as the skin and nerve fibers of lower sensory inputs such as the stomach converge at the same level of the spinal cord. This can result in confusion on where the sensation/pain is coming from so that stimulus of the lower sensory inputs to the brain can interpreted as coming from the higher regions, resulting in the the pain sensation being located along the related dermatome of the same spinal segment. Somatic areas where internal organ pain is felt AUTONOMOUS NERVOUS SYSTEM The autonomic nervous system is a part of the peripheral nervous system and works independently, continuously and involuntarily. This system controls the contraction of smooth muscles, the secretion of glands and the regulation of heart rhythms. The function of this system is to adjust in some activities of the body in order to keep the indoor environment constant. The autonomous system shows its effect in 3 basic structures. These are heart muscle, smooth muscles of internal organs and glands. By controlling smooth muscles, it keepsthe digestive,respiratory, circulatory, excretory and reproductive systems under control. In short, the term autonomous includes all neural elements related to internal organ functions. The first neuron of the autonomic chain is in the central nervous system. Its axon synapses with the second neuron in the chain. The second neuron is in a ganglion of the peripheral autonomic system. The nerve wire (axon) of the first neuron is called the preganglionic wire. The axons of the second neuron leading to effector organs such as muscle and gland are called postganglionic wires. The autonomic nervous system consists of two anatomically and functionally different parts: the sympathetic system and the parasympathetic system.  The neurons of the sympathetic system are found in the thoracic (T1-T12) and lumbar segments (L1-L3) in the spinal cord. The preganglionic wires coming out of the neurons here come to the truncus sympathicus, which lies like a chain on both sides of the spine. Some of the wires that come to these ganglia synapse with the neurons here, and some go to the organs. The wires leading to the organs synapse with the neurons in the ganglia within the organ. Postganglionic wires coming out of the ganglions go to the organs.  The neurons of the parasympathetic system are in two places. In the gray matter in the brain stem and the gray matter in the sacral part of the spinal cord. The nerve wires coming out of here come to the ganglia and synapse with the neurons there. Parasympathetic ganglia are located close to or within the walls of the organs. 139 İstinye Üniversitesi Uzaktan Eğitim Merkezi Sympathetic activation Parasympathetic activation Thank you