Introduction to CNS Physiology PDF

‫بسم هللا الرحمن الرحيم‬ INTRODUCTION TO NEUROPHYSIOLOGY By Prof. Amani El-Baz Prof. and Head of Physiology dept, MBBS, MSc, PhD, MHPE Faculty of Medicine, Suez Canal University December 2024  OBJECTIVES: By the e...

‫بسم هللا الرحمن الرحيم‬ INTRODUCTION TO NEUROPHYSIOLOGY By Prof. Amani El-Baz Prof. and Head of Physiology dept, MBBS, MSc, PhD, MHPE Faculty of Medicine, Suez Canal University December 2024  OBJECTIVES: By the end of the lecture the student should be able to: Notify the nervous system as the higher most control system Identify the functional division of the nervous system. Name the parts of a neuron and describe their functions List the various nerve fiber types found in the mammalian nervous system and their functions Know the meaning of reflex action and describe components of reflex arc. Outline the functional organization of the sensory system. Outline the functional organization of the motor system. Identify the higher functions of the brain. As a control system: The nervous system (NS) is the higher most body control system. It shares the control function with the endocrine system, but it controls the endocrine system itself. Its functional unit is the neuron which functions in integration and transmission The nervous system is composed of two divisions: Central nervous system (CNS), which includes the brain and the spinal cord, Peripheral nervous system (PNS), which includes sensory receptors, sensory nerves, and ganglia outside the CNS. The CNS and PNS communicate extensively with each other. ANATOMICAL DIVISION OF THE NERVOUS SYSTEM 12 pairs of cranial nerves 31 pairs of spinal nerves Functional division of the NS: The sensory or afferent division brings information into the nervous system, usually beginning with events in sensory receptors in the periphery. These receptors include, visual receptors, auditory receptors, chemoreceptors, and somatosensory (touch) receptors. This afferent information is then transmitted to higher levels of the nervous system and finally to the cerebral cortex. The motor or efferent division carries information out of the nervous system to the periphery. This efferent information results in contraction of skeletal muscle, smooth muscle, and cardiac muscle or secretion by endocrine and exocrine glands.  BASIC TASKS Sensory Receptors: Monitor both external and internal environments. Central Nervous System: Analyze the information and often integrate it with stored information. Peripheral Nervous System: If necessary, signal muscles and other effector organs to make an appropriate response.  INTEGRATION OF SENSORY INFORMATION The central nervous system decodes incoming sensory nerve impulses. Integration of information from several sensory inputs may be required. Integration with information stored in memory may also be required.  SIGNALING EFFECTORS TO RESPOND The central nervous system sends nerve impulses out to effector organs (muscles, glands, other organs) signaling them to make an appropriate response. Sometimes decoding and signaling effector organs involves only a simple spinal reflex. Nerve cells (Neurons) are the structural units of the nervous system. THE 4 FUNCTIONAL DOMAINS WITHIN A NEURON Input region/s for depolarising membrane currents (excitatory synapses or sensory receptor channels) Trigger zone integration of depolarising signals to initiate action potentials or not Propagation region- axon or sensory fibre Chemical release zone- transmitter or hormone release terminal TYPES OF NEURONS: STRUCTURAL CLASSIFICATION TYPES OF NEURONS: FUNCTIONAL CLASSIFICATION The overall structure of the nervous system  TRANSMISSION OF INFORMATION Information must be transmitted within each neuron and between neurons GLIAL CELLS (NEUROGLIA) NON EXCITABLE CELLS IN CNS Are much more numerous than neurons, include: A) Astrocytes (has many processes): Support neurons. Form the blood-brain barrier (BBB). Maintain the chemical environment proper for the generation of nerve impulses B) Oligodendrocytes (has little processes): They are responsible for forming and maintaining the myelin sheath around CNS axons. myelin sheath is a multilayered lipid and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction. C) Microglia cells: They function as phagocytes, that remove cellular debris, microbes, damaged tissue, and neurotransmitters reuptake. IN THE PNS SCHWANN CELLS: These cells encircle PNS axons, forming myelin sheath around it. Schwann cells neurolemma participate in axon regeneration, which is more easily accomplished in the PNS than in the CNS. B) SATELLITE CELLS: They provide structural support for PNS neurons. They regulate the exchanges of materials between neuronal cell bodies and interstitial fluid. WHAT IS A NERVE ? Bundle of axons outside CNS. Types: - Mixed, the most, ex: sciatic nerve. - Sensory, such as some cranial nerves, ex: optic and auditory nerves. CRANIAL AND SPINAL NERVES There are 12 pairs of cranial nerves , the first two connect with the cerebrum and diencephalon, the rest connect with the brain stem There are 31 spinal nerves arising from the different spinal segments 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal Types of Nerve Fibers Nerve fibers are classified according to their conduction velocity, which depends on the size of the fibers and the presence or absence of myelination. The larger the fiber, the higher the conduction velocity. Conduction velocity also is increased by the presence of a myelin sheath around the nerve fiber. Thus large myelinated nerve fibers have the fastest conduction velocities, and small unmyelinated nerve fibers have the slowest conduction velocities. Two classification systems, which are based on differences in conduction velocity, are used. The first system, applies to both sensory (afferent) and motor (efferent) nerve fibers and uses a lettered nomenclature of A, B, and C. The second system, applies only to sensory nerve fibers and uses a Roman numeral nomenclature of I, II, III, and IV. REFLEX ACTION A reflex is the involuntary response to a stimulus. Many of the reflexes are essential for homeostasis. Reflex actions are performed through pathway called reflex arc GENERAL FUNCTIONS OF THE NERVOUS SYSTEM Three basic Functions of the Nervous System A. Sensory function. Sensory receptors detect stimuli (internal or external) and send nerve impulse via cranial/spinal nerves (PNS) to the brain and spinal cord (CNS). B. Integrative function. The Central nervous system analyzes sensory information and accordingly makes decisions for appropriate responses. C. Motor function.The decision taken by integrative part, is sent from CNS as motor orders via cranial/spinal nerves (PNS) to effector organs (muscles and glands). Stimulation of the effectors causes muscles to contract and glands to secrete their secretory substances. SENSORY AND MOTOR SYSTEMS  FUNCTIONAL INTEGRATION OF CNS High intellectual functions External st. Neocortex Neocortex Limbic sys. Behavior & Emotions Hypoth. Paleocortex Vegetative functions Internal st. Primitive Brain Functional organization of the sensory system: Sensory receptors: Receive (detect) sensory informations (energies), transduce them to electrical energy in the sensory pathway associated with them. Sensory pathways: Transmit the sensory informations to areas of perception in the CNS (Sensory cortex). Sensory cortex: Perceives the transmitted sensory informations (electrical energy) as modalities of sensations (Touch, pressure, electromagnetic, warm, cold, pain, … etc). Functional organization of the motor system: Voluntary movements: Orders come from CTX through the descending motor tracts. Muscle tone: This is involuntary activity of skeletal muscles. The basic reflex in muscle tone is the stretch reflex which is spinal reflex. Coordination of voluntary movement & muscle tone: Is the function of cerebellum & basal ganglia. Higher functions of the brain: - - Language & speech. - Perception. - Memory & learning. - Consciousness - Sleep & arousal. - High intellectual functions. - Behavior. References: Lippincott’s Illustrated Reviews: Physiology, 2013. Linda S. Costanzo. Physiology, sixth edition,2018. Thanks