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Introduction to Physiology of the Nervous System Dr Fawzia Alrouq Physiology Department , College of Medicine , King Saud University , Riyadh 1 Objectives At the end of this lecture the student should : understand that the nervous system can be classified in more than one way , depending on the purpose of the study undertaken . appreciate that animal experiments are essential for advancement of knowledge about nervous system functions understand that , under strict ethical considerations , human studies are also carried out to understand neurophysiology . know that much of human physiology can be learned from observing the consequences of human lesions & diseases . be able to explain what is meant by telencephalon , diencephalon ,brainstem , basal ganglia , cerebellum and spinal cord ; & outline their function . 2 Nervous system organization fig 6-37 Classification of the Nervous System • The nervous system ( NS) can be classified in more than one way : (I) Central & Peripheral NS (A) Central Nervous System (CNS) : consisting of the brain and spinal cord , and (B) Peripheral Nervous System (PNS ) : Fibers outside the CNS (II) Sensory & Motor NS (A) Sensory : includes (i) sensory ( afferent ) fibers , ascending ( sensory ) pathways , & brain sensory centers (B) Motor : includes brain motor centers , descending (motor ) pathways & motor ( efferent ) fibers . (III) Somatic & Autonomic NS (A) Somatic ( Voluntary) Nervous System (B) Autonomic ( Inovluntary) Nervous System 4 Methods of Studying Physiology of the Nervous System 5 • Understanding anatomy : Since very old times in the history of medicine , it was appreciated that understanding anatomy (what structures make up the human body & how arranged ) has been essential for understanding physiology ( how the body functions) . • Learning from animals : • Making lesions or injecting chemicals in brain & then studying their effects onneuronal behavior & structure , & on animal behavior . • Recording ( with or without stimulation ) of electrical activity from nerves , muscles , brain or spinal cord in animals . • Learning from humans ( under strict ethical laws ) : • Studying effects of lesions ( disease , trauma etc ) and chemicals ( drugs or toxins ; taken accidentally or administered intentionally) on human wellness , function and behavior . • Recording spontaneous and evoked nerve activity , muscle electrical activity , and brain waves . • Functional radiological methods 6 The Human Brain Phineas Gage Phineas Gage • In 1848 in Vermont, had a 3.5-foot-long, 13 lb. metal rod blown into his skull, through his brain, and out of the top of his head. Gage survived. In fact, he never even lost consciousness. • Friends reported a complete change in his personality after the incident. He lost all impulse control. The Human Brain • Composed of wrinkled, pinkish gray tissue • Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem • Ranges from 750 cc to 2100 cc • Contains almost 98% of the body’s neural tissue • Average weight ~3 lb • 1010 to 1011 neurons • Trillions of connections • men = larger • Women = better connected Basic Pattern of the Central Nervous System • Spinal Cord – Central cavity surrounded by a gray matter core – External to which is white matter composed of myelinated fiber tracts • Brain – Similar to spinal cord but with additional areas of gray matter – Cerebellum has gray matter in nuclei – Cerebrum has nuclei and additional gray matter in the cortex Figure 12.4 Overview of the Brain 12 Components of The Brain • A/ Telencephalon (1) Cerebrum and (2) Basal Ganglia ( collection of grey matter situated inside the cerebral hemispheres ) • B/ Diencephalon • Mainly : (1) Thalamus ( mainly a relay station for sensory pathways in their way to the cerebral cortex ) (2) Hypothalamus ( contains cesnter for autonomic and endocrine control ) 13 • C/ Brainstem (1) Midbrain (2) Pons (3) Medulla • E/ Cerebellum The Brainstem • The term “ brainstem ” is actually an anatomic rather than physiologic term , because it is easier , in terms of anatomy , to group “ all CNS structures that hang between the cerebrum and spinal cord “ together . • However , in terms of Physiology , the situation is more complicated , because brainstem structures are involved in many diverse & different bodily functions . These functions include (1) regulation of Consciousness , Wakefulness & Sleep , (2) Respiratory , Cardiovascular and Gastrintestinal control , (3) Balance ( Vestibular nuclei ) . (4) Moreover , it contain several Cranial Nerve nuclei . 14 , Cerebrum 15 The Cerebrum : Composed of 2 Cerebral Hemispheres , each of which controls functions on the opposite half of the body • Each hemisphere is divided by big Sulci ( fissures ) into 4 lobes : • Parietal lobe • Occipital lobe • Temporal lobe • Frontal lobe Sulci that divide the cerebrum into lobes • Central Sulcuds ( Rolandic Fissure ) : separaetes Parietal & Fontal lobes • Lateral Sulcus ( Sylvian Fissure ) separates Parietal & Temporal Lobes • Parieto-Occipital Sulcus : Separates Parietal and Occipital Lobes . • Lobes are further divided by smaller Grooves into ridges called Gyri Most people ( about 90 %) have the left cerebral hemisphere dominant , and are therefore righthanded . The remaining ( around 10 % ) of the population usually have their right hemisphere dominant , and are therefore left-handed . The frontal lobe of the dominant hemisphere contains Broca’s area (the area for production of speech ) . Therefore, if a right-handed person gets a stroke involving his left cerebral hemisphere , he is likely to have right-sided hemiplegia ( paralysis ) and aphasia ( loss of the power of speech). 18 Occiptal Lobe • Contains primary visual Cotrex + • Visual AssociationCortex • Disease : blindness 19 Parietal Lobe Contains (1) Primary Somatosensory in the post-central gyrus to receive general sensations from opposite ( contralateral ) half of the body (2) Sensory Association Cortex ( for integration & association of sensory information ) Parietal lobe is essential for our feeling of touch, warmth/heat , cold, pain , body position and appreciation of shapes of palpated objects . When damaged , the person loses the ability to recognize shapes of complex objects by palpation (palpation = examaination of objects by touch ) . & develops Sensory Inattention on opposite side 20 Temporal Lobe • • • • (1) contain centers for hearing and taste , (2) contribute to smell perception . (3) essential for memory function . (4) lesion may lead to memory impairment & can be associated with temporal lobe epilepsy 21 Frontal Lobe • Responsible for initiation and execution of voluntary movement . • Also contains Broca’s area of speech in the dominnat hemisphere ( i.e., in the left hemisphere in most people ) . • Lesion can cause (1) paralysis on opposite side of the body , (2) aphasia ( loss of ability to speak ) if lesion involves Broca’s area in the dominant hemisphere ) . 22 Basal Ganglia ( BG) • Collection of grey matter situated inside the cerebral hemispheres . • Lesions may cause a variety of conditions that affect movement e.g. • Parkinson’s disease which is associated with rigidity of muscles & difficulty of movement . 23 Cerebellum • Important for ccordination of body movements and balance . • Diseases can result in inccordination of movement and ataxia . 24 Spinal Cord and Spinal Nerves The spinal cord is generally cylindrical in shape From it emerge 31 pairs of spinal nerves: • 8 cervical, • 12 thoracic, • 5 lumbar, • 5 sacral and • 25 1 coccygeal. DRG Spinal Nerve • The spinal arise from the spinal cord with dorsal and ventral roots . • The dorsal root contains afferent ( sensory ) fibers • The afferent fiber is usually a pseudobipolar cell whose cell-body ( soma) is located in the dorsal root ganglion ( DRG) • The ventral root usually contains efferent ( motor ) fibers ( somatic or autonomic) . • The 2 roots unite at or close to the intervertebral foramen to form the spinal nerve . Spinal cord Gray matter: cell bodies & synapses White matter: ascending & descending tracts Ventral root: efferent pathways Dorsal root: afferent pathways Dorsal root ganglion: cell bodies of afferent neurons fig 6-41 The spinal cord , beside carrying sensory ( ascending ) and motor ( descending ) tracts , Also contains the centers of Spinal Reflexes 28 Nervous system organization fig 6-37 Peripheral nervous system: efferent division fig 6-43 Somatic: single neuron, innervates skeletal muscle, voluntary control Autonomic: 2 neuron chain, innervates smooth, cardiac muscle, glands, largely involuntary control THANK YOU 31