Chapter 4Organization of the nervous systemDiagram of the peripheral nerves, depicting the extensive nature of the nervous systemFunctional divisions of the nervous systemCells of the nervous systemCells of the nervous system (cont.)The neuron and its componentsThe spinal reflexThe myotatic reflexDiagram of a two-neuron reflex, from a spindle in a muscle back to the muscle fibers of the same muscleThe flexion reflexDiagram illustrating how impulses from a cutaneous receptor reach an effector (skeletal muscle by a three-neuron arc at the level of entranceProprioceptionThe vestibular system consists ofStructural relations of innervation of the human labyrinthKinesthesisMuscle spindleGolgi tendon organVoluntary control of muscular activityThe pyramidal systemMotor cortex (area 4)Important differences between the pyramidal and extrapyramidal systemsThe role of the cerebellum in the proprioceptive-cerebellar systemThe areas of the human cerebral cortexPostureBalanceAnalysis of neural activity in a simple voluntary movementAnalysis of neural activity in a simple voluntary movement (cont.)Neurological disorders and injuriesChapter 4The Nervous SystemOrganization of the nervous system•Anatomical organization:–Central nervous system–Peripheral nervous system•Functional organization: –Autonomic nervous system»Sympathetic»Parasympathetic–Somatic nervous systemVisit The Autonomic Nervous System at www.ndrf.org/ans.htmDiagram of the peripheral nerves, depicting the extensive nature of the nervous systemFunctional divisions of the nervous systemCells of the nervous systemA neuron (a single nerve cell) is made up of:•Dendrites—receive nerve impulses and conduct them to the cell body•Cell body•Axon—conducts impulses away from the cell bodyCells of the nervous system (cont.)•Afferent (sensory) neurons conduct sensory impulses from the periphery to the central nervous system•Efferent (motor) neurons conduct impulses from the central nervous system to the musclesThe neuron and its componentsThe spinal reflexInvolves a minimum of two neuronsThe myotatic reflex•A simple, two-neuron reflex•An example is the knee jerk response.Diagram of a two-neuron reflex, from a spindle in a muscle back to the muscle fibers of the same muscleThe flexion reflex•A simple reflex involving an internuncial neuron•Moving your hand away from a hot surface is an exampleDiagram illustrating how impulses from a cutaneous receptor reach an effector (skeletal muscle by a three-neuron arc at the level of entranceProprioceptionThe feedback of sensory informationabout movement and body positionTwo types of receptors are involved:•Vestibular receptors in the semicircular canals of the inner ear•Vestibular receptors in the utricleThe vestibular system consists of •Vestibular receptors–found in the nonauditory labyrinths of the inner ear•Vestibule–found in each labyrinth endolymph–fluid within the canals•Sacule–involved in sensory perception of vibration•Utricle–contains the otolith organ, which is the source of data that informs us of our posture in spaceStructural relations of innervation of the human labyrinthAnterior semicircular canalPosterior semicircular canalLateral semicircular canalUtricle (otoliths are within the utricle)SacculeCochleaAuditory nerveVestibular nerveKinesthesisThe sense of movement and position ofthe body parts in spaceMain receptors involved are:•Muscle spindles found in the muscle tissue•Golgi tendon organs found at junction between muscle and tendonMuscle spindleGolgi tendon organVoluntary control of muscular activity•Pyramidal system•Extrapyramidal system•Proprioceptive-cerebellar systemThe pyramidal system•System originates in Area 4 in large nerve cells shaped like pyramids•Axons from cells form large descending motor pathways (pyramidal tracts) to synapses with the motor neurons in the ventral horn of the spinal column•85 percent of nerve fibers of pyramidal tract cross from one side to the otherMotor cortex (area 4)•Area of cortex devoted to a body part is–Not proportional to amount of tissue served–Proportional to complexity of movement potential (e.g., hands have disproportionate share of motor neurons)•Motor cortex oriented by movement not muscle–Stimulation results not in twitch of one muscle, but in smooth, synergistic movement of a group of musclesImportant differences between the pyramidal and extrapyramidal systems•Electrical stimulation of the pyramidal system (area 4, or motor cortex) produces specific movements, so it is thought that learning a new skill involves this area.•Stimulation of the extrapyramidal system (area 6, or premotor cortex) produces large, general movement patterns. As skill increases, it is thought that the origin of the movement shifts to this area.The role of the cerebellum in the proprioceptive-cerebellar system•Receives sensory information regarding position, balance, and movement from receptors in muscles, joints, tendons, and skin as well as from visual, auditory, and vestibular organs.•Modifies muscular activity during movement.The areas of the human cerebral cortexPosture•Upright posture mainly brought about through reflexes, particularly the myotatic reflex•Postural reflexes depend on effects of the extrapyramidal systemBalance•Coordination of otolith system and muscle and tendon receptors provide the perception of the body’s orientation and position of the body parts in space•Righting reflex is an exampleAnalysis of neural activity in a simple voluntary movementExample of right arm bringing right indexfingertip to the end of the nose1. Neural activity originates in the arm section of area 4 of the motor cortex2. Proceeds by way of the pyramidal tracts to synapse with the lower motor neuron in the cord and3. Out to the appropriate muscles by way of the brachial plexus 4. To the network of nerves in the axillaAnalysis of neural activity in a simple voluntary movement (cont.)5. At the same time, kinesthetic impulses traverse the afferent pathways to the cerebellum to bring about proper control and coordination6. Kinesthetic impulses act reflexively to relax the antagonists through reciprocal inhibition7. Gamma efferent system is busy all the while innervating the muscle spindles to feed constant measurements of the movement’s progress8. As movement accelerates, more motor units are activated9. Movement has to decelerate in reverse fashion.Neurological