1625915643-5d53d156c9525bd62bd0d3434ecdc231 (843955), страница 16
Текст из файла (страница 16)
Four lobes are discernable from the surface; the fifth lobe, theinsula, can be viewed by retracting the outer cortex at the lateral fissure. The cerebral cortex is the highestcenter of the brain and is involved in learning, memory, and reasoning, as well as motor and sensory controland integration.DiencephalonThe diencephalon, consisting of the thalamus and hypothalamus, is located between the cerebral hemispheres andthe brainstem and is part of the limbic system (see Fig.
4.6).The thalamus processes sensory input and relays it to thecerebral cortex and processes motor signals leaving thecerebral cortex. The hypothalamus has a central role inthe regulation of body temperature, the reproductive system,hunger and thirst, salt and water balance, circadian rhythms,the autonomic nervous system, and endocrine function(Table 4.2).CerebellumThe cerebellum is located between the cerebral cortex andthe spinal cord and in close proximity to the brainstem (seeFig. 4.1). It integrates sensory and motor information as wellas information from the inner ear and has an important rolein proprioception (unconscious perception of posture, spatial54The Nervous System and MuscleGenu of corpus callosumHead of caudate nucleusColumns of fornixBody of fornixThalamusUncusBody of fornixCrura of fornixColumns of fornixFimbria of hippocampusCommissureof fornixCrura of fornixHippocampusCommissure of fornixSplenium of corpus callosumLateral ventricleMamillary bodiesBAHippocampuswith fimbriaAmygdaloid bodiesFigure 4.6 The Limbic System The limbic system consists of the hypothalamus and several structures forming a border or ring (limbus) around the diencephalon.
It includes the cingulate, parahippocampal,and subcallosal gyri, and the amygdala, hypothalamus, hippocampi, and mamillary bodies. A, Cerebralcortical and white matter have been removed, as well as the corpus callosum and part of the thalamusand caudate nucleus. B, The fornix consists of curved bundles of fibers connecting the mamillary bodiesand hippocampi. The limbic system has an important role in emotion and the linking of emotion with memory,as well as endocrine and autonomic function.orientation, and movement). Proprioception is based oninput from proprioceptors within muscles, joints, tendons,and the inner ear.BrainstemThe brainstem is the lowest portion of the brain, consistingof the midbrain, pons, and medulla oblongata (medulla). Themedulla, which is anatomically continuous with the spinalcord, contains centers that regulate autonomic functions.This includes centers involved in the regulation and integration of cardiovascular and respiratory functions, and swallowing, vomiting, and coughing reflexes.
The pons, situated above(rostral to) the medulla, is also involved in regulation ofbreathing, and relays sensory information from the cerebrumto the cerebellum. The midbrain, also known as the mesencephalon, is the most rostral portion of the brainstem. It isinvolved in eye movement and transmission of visual andauditory information. It is also the location of the substantianigra, which, in association with the basal ganglia, has a rolein regulation of motor activity. Cranial nerves III-XII (CNIII-XII) originate from the brainstem.The Spinal CordThe spinal cord originates at the medulla at the base of theskull and extends within the vertebral column from themedulla oblongata to the lumbar region (Fig.
4.7). It consistsof neural tissues covered by three meninges (membranes) thatare continuous with those of the brain:■■■the inner pia materthe middle arachnoid membranethe outer dura materCerebrospinal fluid is found between the arachnoid membrane and pia mater. The spinal cord gives rise to 31 pairs ofspinal nerves, organized into three plexuses:Organization and General Functions of the Nervous System55Base of skullC1 vertebra (atlas)C1 spinal nerveCervical plexusC8 spinal nerveBrachial plexusT1 spinal nerveSpinal dura mater1st ribFilaments of spinal nerveroots (T7 and T8)Intercostal nervesT12 spinal nerveL1 vertebra12th ribConus medullarisLumbar plexusL1 spinal nerveL5 vertebraCauda equinaS1 spinal nerveSacral plexusSacrum (cut away)Termination of dural sacSciatic nerveCoccygeal nerveCoccyxFigure 4.7 Spinal Cord and Ventral Rami In Situ The 31 pairs of spinal nerves originating fromthe spinal cord are organized into the cervical, brachial, and lumbosacral plexuses.
Fibers from the plexusesare distributed, respectively, to the neck, upper limbs, and pelvis and lower limbs. Efferent fibers innervateskeletal muscle, whereas afferent fibers carry sensory information from the skin, muscle, and joints to theCNS.■■■The cervical plexus, which forms nerves distributed tothe back of the head and the neck.The brachial plexus, which forms nerves distributed tothe upper limbs.The lumbosacral plexus, which forms nerves distributedto the pelvis and lower limbs.The anatomy of spinal membranes and nerve roots is illustrated in Figure 4.8.THE PERIPHERAL NERVOUS SYSTEMThe peripheral nervous system is the portion of the nervoussystem that lies beyond the brain and spinal cord. It consists of:■■Motor neurons that convey impulses from the CNS toeffector tissues or organs.Sensory neurons that convey impulses from peripheralsensory receptors to the CNS.56The Nervous System and MusclePosterior viewVentral root of spinal nerveDorsal root of spinal nerveSpinal sensory (dorsal root) ganglionVentral ramus of spinal nerveDorsal ramus of spinal nerveDura materArachnoid materSubarachnoid spacePia mater overlying spinal cordFilaments of dorsal rootMembranes removed: anterior view(greatly magnified)Gray matterWhite matterFilaments of dorsal rootDorsal root of spinal nerveFilaments of ventral rootSpinal sensory (dorsal root) ganglionDorsal ramus of spinal nerveVentral ramus of spinal nerveVentral root of spinal nerveSpinal nerveGray and white rami communicantesFigure 4.8 Spinal Membranes and Nerve Roots Motor fibers and sensory fibers pass through 31pairs of spinal nerves.
The outer dura mater, arachnoid mater, and inner pia mater are the three coveringsof the spinal cord, with CSF circulating in the subarachnoid space.The peripheral nervous system is subdivided into somaticand autonomic components. In the somatic portion of theperipheral nervous system, motor fibers of the spinal nervesinnervate skeletal muscles; sensory information from receptors in the skeletal muscles, joints, and skin is transmittedthrough sensory fibers to the CNS (Fig. 4.9). The autonomiccomponent of the peripheral nervous system is composed ofmotor and sensory fibers involved in the involuntary controlof homeostatic mechanisms through actions on visceralorgans.
The autonomic nervous system and its sympatheticand parasympathetic divisions are discussed further inChapter 7.Organization and General Functions of the Nervous SystemPosterior hornDorsal root ganglionSensory neuron cell bodyDorsal rootAnterior hornMotor neuron cell bodyVentral rootPeripheral nerveAxonMyelin sheathMotor neuronSensory neuronNeuromuscularjunctionSkinMuscleFigure 4.9 Somatic Component of the Peripheral Nervous System The peripheral nervoussystem can be subdivided into somatic and autonomic components. The somatic nervous system containsmotor nerves and sensory nerves innervating skin and muscle.
The soma (cell bodies) of motor nerves andsensory nerves are located in the gray matter of the anterior horn of the spinal cord and in the dorsal rootganglia, respectively.5758The Nervous System and MuscleCLINICAL CORRELATESpinal Cord InjuryInjury to the spinal cord results in deficits in motor and sensoryfunction below the point of injury.
The most common cause ofspinal cord injury is trauma; other causes include neurodegenerative diseases as well as tumors and vascular diseases affecting thespine. Spinal cord injury is classified as complete, when no neurological function is retained beyond the point of damage, orincomplete, when some sensory or motor function remains.Effects of spinal cord damage correspond to the level of injury,with increasing severity at higher levels:■ Sacral and lumbar injuries are associated with problems insexual, bladder, and bowel function, as well as motor andsensory deficits in the lower limbs.■ Thoracic injuries are associated with paraplegia (paralysis of thelower body).■ Cervical injuries result in some degree of quadriplegia (paralysis below the neck), depending on the level of injury.
Patientswith injuries at spinal cord level C3 or above require mechanical ventilation.FunctionMusclesSegmentsInspirationDiaphragmC3, 4, 5Shoulder abductionDeltoidC5Elbow flexionExtensor carpiradialis longusand brevisC5, 6WristextensionBiceps brachiiBrachialisC6, 7Elbow extensionTriceps brachiiC7, 8FingerflexionFlexor digitorumsuperficialis andprofundusC8Finger abductionand adductionInterosseiL2, 3Thigh adductionAdductor longusand brevisL3, 4Knee extensionQuadricepsL4, 5Ankle dorsiflexionTibialis anteriorL4, 5Great toeextensionExtensor hallucislongusL5, S1Ankleplantar flexionGastrocnemiusSoleusS1, 2Anal contractionSphincter aniexternusS2, 3, 4Motor Impairment Related to Level of Spinal Injury59CHAPTER5Sensory PhysiologySensory systems allow us to maintain homeostasis and respondto the external environment in an adaptive manner.
Much ofthe awake brain is devoted to transducing, encoding, sensing,and eventually perceiving and reacting to or trying to makesense of both our external and internal environments. Animportant task of the brain is to filter out the large amountsof incoming information to prevent information overload.During sleep, the incoming sensory information is drasticallyreduced as the brain continues to try to make sense of thestored information and “reset” itself for the next day’s influxof sensory inputs.SENSORY RECEPTORSSpecialized receptors detect stimuli of various types, includingvisual, olfactory, gustatory (taste), auditory, and somatosensory (mechanical, thermal, and painful) stimuli.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
