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Physiological aspects of Human Nervous System
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- 3. • The brainreceives, processes, and stores sensory input; generates thoughts; and determines the reactions that the body should perform in response to this input. • The spinal cord is important in processing reflexes. • The third component of the nervous system is the motor division. Appropriate signals are transmitted from the CNS to various body parts or effector tissues by way of efferent neuronal pathways.These effector tissues, which include organs, muscles, and glands, carry out the appropriate physiological responses to bring the variable back to within its normal limits.
- 4. • Diseases aregenerally divided into two categories: 1. Those in which the pathophysiology involves internal failure of some normal physiological process and 2. Those that originate from some external source such as bacterial or viral infection. In either case, one or more variables in the internal environment will be disrupted. Therefore, many of the medications currently in use are designed to assist the body in the maintenance of homeostasis when its own regulatory mechanisms fail to do so.
- 5. INTRODUCTION It consists ofliterally billions of neurons interconnected in a highly organized manner to form circuits. The number of neurons and the manner in which they are interconnected in a given circuit distinguishes one region of the brain from another and the brain of one individual from that of another.
- 7. • The nervoussystem is divided into two anatomically distinct regions: 1. Central nervous system 1. Brain 2. Spinal Cord 2. Peripheral nervous system 1. 12 pairs of cranial nerves that arise from the brainstem and 2. 31 pairs of spinal nerves arising from the spinal cord.These peripheral nerves carry information between the CNS and the tissues of the body. 1. The PNS consists of two divisions: • Afferent division • Efferent division
- 8. • The afferentdivision carries sensory information toward the CNS and the efferent division carries motor information away from the CNS toward the effector tissues (muscles and glands). • The efferent division is further divided into two components: • (1) the somatic nervous system, which consists of motor neurons that innervate skeletal muscle; and • (2) the autonomic nervous system that innervates cardiac muscle, smooth muscle, and glands.
- 10. • The humannervous system has three functional classes of neurons: 1. Afferent neurons: lie predominantly in the PNS 2. Efferent neurons: lie predominantly in the PNS. 3. Interneurons: lie entirely within the CNS. Interneurons lie between afferent and efferent neurons and are responsible for integrating sensory input. CLASSES OF NEURONS
- 14. NEUROTRANSMITTER • Neurotransmitters areoften referred to as the body’s chemical messengers. They are the molecules used by the nervous system to transmit messages between neurons, or from neurons to muscles. • Communication between two neurons happens in the synaptic cleft (the small gap between the synapses of neurons). Here, electrical signals that have travelled along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron.
- 15. • A neurotransmitterinfluences a neuron in one of three ways: 1. Excitatory, 2. Inhibitory or 3. Modulatory. An excitatory transmitter promotes the generation of an electrical signal called an action potential in the receiving neuron, while an inhibitory transmitter prevents it. Whether a neurotransmitter is excitatory or inhibitory depends on the receptor it binds to.
- 16. • The firstneurotransmitter to be discovered was a small molecule called acetylcholine. • Glutamate and its derivative GABA • Glycine • Dopamine • Noradrenaline • Serotonin • Histamine
- 18. ION CHANNELS &NEUROTRANSMITTER RECEPTORS • The membranes of nerve cells contain two types of channels defined on the basis of the mechanisms controlling their gating (opening and closing): 1. Voltage-gated: Sodium Channel, Potassium Channel and Calcium Channel 2. Ligand-gated channels: Nicotinic Ach receptors, GABA receptor
- 21. THE SYNAPSE &SYNAPTIC POTENTIALS • The communication between neurons in the CNS occurs through chemical synapses in the majority of cases. • When a microelectrode enters a cell, there is a sudden change in the potential recorded by the electrode, which is typically about –70 mV.This is the resting membrane potential of the neuron. • Two types of pathways - excitatory and inhibitory - impinge on the motor neuron. When an excitatory pathway is stimulated, a small depolarization or excitatory postsynaptic potential (EPSP) is recorded.
- 22. THE SYNAPSE &SYNAPTIC POTENTIALS • Two types of pathways – • Excitatory and • Inhibitory - impinge on the motor neuron. • When an excitatory pathway is stimulated, a small depolarization or excitatory postsynaptic potential (EPSP) is recorded.
- 24. • When aninhibitory pathway is stimulated, the postsynaptic membrane is hyperpolarized owing to the selective opening of chloride channels, producing an inhibitory postsynaptic potential (IPSP). • A second type of inhibition is presynaptic inhibition. It was first described for sensory fibers entering the spinal cord,
- 25. SITES OF DRUGACTION • Virtually all the drugs that act in the CNS produce their effects by modifying some step in chemical synaptic transmission. • These transmitter-dependent actions can be divided into presynaptic and postsynaptic categories. • Drugs acting on the synthesis, storage, metabolism, and release of neurotransmitters fall into the presynaptic category.
- 26. • Synaptic transmissioncan be depressed by blockade of transmitter synthesis or storage. • Blockade of transmitter catabolism inside the nerve terminal can increase transmitter concentrations and has been reported to increase the amount of transmitter released per impulse. Drugs can also alter the release of transmitters. • After a transmitter has been released into the synaptic cleft, its action is terminated either by uptake or by degradation. For most neurotransmitters, there are uptake mechanisms into the synaptic terminal and also into surrounding neuroglia.
- 27. • In thepostsynaptic region, the transmitter receptor provides the primary site of drug action. • Drugs can act either as neurotransmitter agonists, such as the opioids, which mimic the action of enkephalin, or they can block receptor function. Receptor antagonism is a common mechanism of action for CNS drugs.
- 28. BLOOD–BRAIN BARRIER • Themovement of substances between the blood and the extracellular fluid surrounding the cells in most tissues of the body occurs very readily. • Many substances found in the blood are potentially harmful to the CNS. Therefore, the brain and spinal cord are protected from these substances by the blood–brain barrier. • In the capillaries of the brain and spinal cord, there are no pores between the endothelial cells; instead, tight junctions fuse the cells together.As a result, exchange between blood and the extracellular fluid of the brain is altered.
- 29. BLOOD–BRAIN BARRIER In thecapillaries of the brain and spinal cord, there are no pores between the endothelial cells; instead, tight junctions fuse the cells. As a result, the exchange between blood and the extracellular fluid of the brain is altered.
- 30. SUMMARY The physiological aspectsof the nervous system involve its role in regulating and coordinating bodily functions through a complex network of neurons and supporting cells. It facilitates communication between different body parts via electrical and chemical signals, ensuring responses to internal and external stimuli. The nervous system is divided into the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), which includes sensory and motor nerves. Key processes include sensory input, signal transmission, and motor output, which collectively maintain homeostasis, enable voluntary actions, and support cognitive functions such as memory, learning, and decision-making.
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