The Physiologic Basis Of Surgery; Chapter 21: Basic Neuroscience


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A review of the Basic Neuroscience Chapter I presented for the Basic Science Junior Residents Lecture

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  • Unipolar neurons have a single process arising from the soma that gives rise to both the dendrite and the axon. The dorsal root ganglion cell, which brings somatic sensation to the CNS is the prototype of this neuronal type.
  • Are found in special sensory systems such as the retina and vestibule.
  • Elaboration of the dendritic tree allows for a greatly increased surface area for synaptic contact. A single Purkinje cell in the cerebellum may receive 150,000 synapses, allowing for extremely fine modulation of cell activity.
  • Are characterized by extensive processes that completely encase the neurons, isolating them from each other except at synapses. They also separate the neuron from direct contact with the capillary. Although they are polarized at -90mV internally, they are not electrically excitable and cannot propagate an action potential. Astrocytes may play a role in regulating the extracellular ionic environment, especially potassium that is liberated during neuronal depolarization. They also respond to ischemia and injury, initially with swelling, and subsequently with proliferation to form scarring in the brain. They also give rise to most of the primary brain tumors.
  • Smaller than astrocytes and are more concentrated in white matter. These cells form the myelin that electrically insulates the axons and greatly increases the rate of nerve impulse propagation.
  • Line the cerebral ventricles. They are a single layer of cuboidal epithelial cells that exhibit secretory and absorptive functions and provide a cell layer between the CSF in the ventricle and the extracellular space of the brain.
  • Represent the reticuloendothelial cells of the CNS and are derived from outside the brain and spinal cord.
  • Microglial proliferation occurs and is thought to represent a major part of an inflammatory response in the CNS. Whether microglial cells are truly resident in the brain tissue or derived only from blood elements is still unclear.
  • The anterior fossa is formed by the orbital roofs, cribiform plate, and lesser wing of the sphenoid. The middle fossa is formed by the greater wing of the sphenoid and petrous portion of the temporal bone on each side, and the posterior fossa by the clivus of the sphenoid and occipital bones and the petrous portions of the temporal bones.
  • The tentorium cerebelli is a dural fold extending from the clinoid processes of the sella turcica and the petrous ridges of the temporal bones to the occipital bone, separates the posterior fossa or infratentorial compartment from the supratentorial compartment. The tentorial notch separates the two sides of the middle fossa and allows passage of the brainstem from the supra- to the infratentorial compartment. The falx cerebri, extends from the crista galli of the cribriform plate to the tentorium and separates the cerebral hemispheres.
  • Includes 7 cervicala vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, a sacrum of 5 fused sacral vertebrae and a coccyx of 2 to 5 vertebrae.
  • The first cervical vertebrae forms a ring to support the cranium and allow rotation. The second cervical vertebra incorporates the body of C1 as the odontoid process, or dens, through the ring of the atlas.
  • The remainder of the cervical, thoracic, and lumbar vertebrae are composed of a body anteriorly and a dorsal arch attached to the body by pedicles and formed by the facet joints (articulating processes), laminae, and spinous processes. The sacral bones are fused into a single triangular-shaped bone, but maintain formina for the exit of sacral nerve roots.
  • Anterior and posterior longitudinal ligaments run the length of the spine, and the intersegmental ligamenta flavus between the lamina and inerspinous ligaments between the spinous processes add additional strength to the spinal column.
  • The posterior columns convey vibration, touch, and joint position. The lateral columns contain the corticospinal (motor) and lateral spinothalamic (pain and temperature), and anterior columns convey touch sensation.
  • The brain weights approximately 1,400 to 1,600 grams in the adult and can be divided in the the cerebral hemispheres, diencephalon, the brainstem (midbrain, pons, & medulla) and the cerebellum.
  • Frontal lobe is anterior to the central sulcus of Rolando and superior and medial to the sylvian fissure. The cortex of the frontal lobe is subdivided into the precentral gyrus (primary motor cortex) just anterior to the central sulcus and premotor cortex. The inferior frontal gyrus, usually on the left side, contains the primary motor speech area.
  • Dr. Penfield's experiments in stimulating the cortex enabled him to develop a complete map of the motor cortex, known as the motor homunculus (there are also other kinds, such as the sensory homunculus). The most striking aspect of this map is that the areas assigned to various body parts on the cortex are proportional not to their size, but rather to the complexity of the movements that they can perform. Hence, the areas for the hand and face are especially large compared with those for the rest of the body. This is no surprise, because the speed and dexterity of human hand and mouth movements are precisely what give us two of our most distinctly human faculties: the ability to use tools and the ability to speak.
  • Deep to the sylvian fissure is the insular cortex covering the basal ganglia.
  • The temporal lobe lies inferior to the sylvian fissure. It is separated from the parietal lobe by a line running from the posterior edge of the sylvian fissure inferiorly to the preoccipital notch and on its inferomedial surface by a line from the splenium of the corpus callosum to the preoccipital notch.
  • The hippocampus is located in the temporal lobe. It is responsible for short-term memory as well as spatial memories.
  • The amygdala, a structure located in the most anterior section of the temporal lobe, is involved primarily in the processing of emotion.
  • Primary auditory cortex is located in the transverse gyri of Heschl.
  • The parietal lobe extends from just behind the central sulcus, which separates it from the frontal lobe, to the parieto-occipital sulcus on the mesial cerebral hemisphere, separating it from the occipital lobe. A line from the parieto-occipital sulcus to the posterior sylvian fissure to the preoccipital notch divides the parietal lobe from the temporal and occipital lobes on the surface of the hemisphere.
  • The postcentral gyrus immediately behind the central sulcus is the primary sensory cortex.
  • The supramarginal and angular gyri on the dominant hemisphere are concerned with speech reception, reading, writing, and calculation. Body organization and spatial relations are important on non-dominant parietal lobe functions.
  • The occipital lobe is the cortex posterior to the parietal and occipital lobes.
  • The occipital lobe contains the visual cortex.
  • The visual pathway can be followed from the stump of the optic nerves through the chiasm and optic tract to the lateral geniculate nucleus and then through the optic radiations to the primary visual cortex in the occipital lobe. Thalamic radiations also contain reciprocal connections from the cortex to the thalamus.
  • The limbic system wraps around the brain stem and is beneath the cerebral cortex. It is a major center for emotion formation and processing, for learning, and for memory. The limbic system contains many parts, including the cingulate gyrus, a band of cortex that runs from the front of the brain to the back, the parahippocampal gyrus, the dentate gyrus, and most notably, the hippocampus and amygdala. The hippocampus is involved in memory storage and formation. It is also involved in complex cognitive processing. The amygdala is associated with forming complex emotional responses, particularly involving aggression. The limbic structures are also connected with other major structures such as the cortex, hypothalamus, thalamus, and basal ganglia.
  • White matter tracts are divided into Association fibers that connect cortical neurons within the same hemisphereCommissural fibers that connect corresponding areas of cortex in opposite hemispheres
  • 3) Projection fibers that run from the cerebral hemispheres to the brainstem and spinal cord.
  • Connects Wernicke’s area to Broca’s area, thus the arcuate fasciculus is thus essential for normal speech and language function. It also includes optic radiations that radiate from the thalamus to the occipital cortex.
  • Connect the cerebral hemispheres.
  • Corpus Callosum
  • Is in the diencephalon and connects the pretectal nuclei concerned with eye movements.
  • The white matter of the cerebral hemisphere is called the centrum semiovale above the basal ganglia
  • And the internal capsule as it passes through the basal ganglia and thalamus to the brainstem.
  • Deep nuclei of the cerebral hemispheres. Caudate, putamen, globus pallidus, subthalamic nuclei and the substantia nigra. The corpus striatum (caudate + putamen + globus pallidus), or the lenticular nucleus (putamen + globus pallidus). The caudate maintains rhythm of movement. The lenticular nucleus controls muscle tone and body positions. They are believed to modulate motor function but also seem to be concerned with behavior, affect , and ideation.
  • The neostriatum is the principle input structure of the basal ganglia and receives excitatory glutamatergic input from the many areas of the cortex. The outflow of the striatum proceeds along with 2 distinct routes, identified as direct and indirect pathways. The direct pathway is formed as neurons in the stratum that project directly to the output stages of the basal ganglia, substantia nigra pas reticulata (SNpr) and the medial globus pallidus (MGP); this in turn relay to the ventro-anterior and ventro-lateral thalamus, which provides excitatory input to the cortex. The neurotransmitter of both links of the direct pathway of GABA, which is inhibitory, so that net effect of stimulation of direct pathway at the level of striatum is to increase the excitatory outflow from the thalamus to the cortex. The indirect pathway is composed of the strital neurons that project to the lateral globus pallidus (LGP). This structure in turn innervates the subthalamic nucleus (STN), which provides outflow to the SNpr and MGP output stage. As in the direct pathway, 1st two links – projection from the striatum to the LGP and LGP to STN – use the inhibitory transmitter GABA; however the final link – the projection from to SNpr and MGP- is excitatory glutametrgic pathway. Thus the net effect of stimulating the indirect pathway at the level of striatum is to reduce the excitatory outflow from the thalamus to the cerebral pathway. The key feature of this model of basal ganglia function, which accounts for the symptoms observed in PD as results of loss of dopaminergic neurons, is the differtial effect of dopamine on direct and indirect pathway. The dopaminergic neuron of the SNpc innervates all the parts of striatum; however the target striatal neurons express distinct types of dopamine receptors. The striatal neurons giving rise to the direct pathway express primarily the excitatory D1 dopamine receptor protein, while the striatal neurons forming the indirect pathway express primarily the inhibitory D2 type. Thus dopaminergic in the striatum tends to increase the activity of the direct pathway and reduce the activity of indirect pathway, where as the depletion that occurs in PD has the opposite effect. The net effect of reduced dopaminergic input in PD is to increase markedly the inhibitory outflow from the SNpr and MGP to the thalamus and reduce excitation of the motor cortex.
  • Includes the paired thalami, the hypothalmus, the pineal gland, the habenular nuclei, and the subthalamus.
  • The pineal gland which secretes melatonin and plays a part in circadian rhythms. It is located in the roof of the third ventricle.
  • Except for olfaction, all sensory information coming into the cerebral hemispheres is relayed through the thalamus. The thalamus maintains reciprocal connections with all areas of cerebral cortex and has been considered the key to understanding brain function. It is the final relay station for ascending sensory information and because specific ascending sensory pathways and the ARAS converge in the thalamus, the thalamus is considered to bring sensory information into awareness. The ventral nuclei convey sensation of pain, touch, vibration, position, and temperature to the primary sensory cortex. The ventral nuclei also modulate motor activity. The lateral and medial geniculate bodies subserve vision and hearing, respectively. Anterior and dorsal nuclei are related to the limbic system concerned with the emotional and affective processing of information. The intralaminar nuclei are thought to be involved in general arousal responses and central control of pain. The thalami abut the ventricular system, forming the floor of the lateral ventricles and the medial walls of the third ventricle.
  • Plays a part in emotion, links the CNS with the endocrine system, superior to optic chiasm, its infundibulum connects to pituitary gland.
  • The neuropeptides vasopressing and oxytocin are secreted directly from axons in the posterior lobe of the pituitary, with their cell bodies in the supraoptic and paraventricular nuclei. The hormones of the anterior lobe of the pituitary are regulated by releasing factors from the hypothalamus that are brought to the pituitary gland through the hypophyseal portal system rather than through direct neural connections. These releasing factors regulate growth follicle-stimulating hormone, thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, prolactin, and their target organs through a complicated feedback mechanism. These factors are, in turn, acted on by afferent fibers to the hypothalamus from other brain centers.
  • Characterized by the quadrigeminal plate (superior and inferior colliculi dorsally) and the cerebral peduncles (the corticospinal and corticopontine tracts) ventrally. The Cerebral Aqueduct of Sylvius connects the third and forth ventricles. The tegmentum contains the nuclei of cranial nerves III and IV, the red nuclei, the substantia nigra, the ascending long tracts, including the decussation of the superior cerebellar peduncles; and the reticular formation. CN III exits ventrally.
  • CN IV exits dorsally.
  • Corticospinal and corticobulbar fibers continue caudally.
  • Corticopotine fibers synapse with the pontinue nuclei and project to the cerebellum as the middle cerebellar peducles. The tegmentum of the pons contains the nuclei of CN V with its associated spinal nucleus and tract.
  • The tementum of the pons also contains the nuclei of CNs VI and VII, the ascending tracts, and the reticular formation.
  • The corticospinal tracts form the pyramids on the base of the medulla, and these decussate at this level before entering the spinal cord. The medullary tegmentum contains the nuclei for CNs VIII through XII, the decussation of the posterior columns, the olivary nuclei, the long ascending tracts, and the reticular formation.
  • The cerebellum lies dorsal to the brainstem and is attached to it through the three peduncles: the superior to the mesencephalon, the middle to the pons, and the inferior to the medulla.
  • The cerebellum is composed of a midline vermis and two hemispheres. Anatomically, there are multiple lobes of the cerebellum based on connections between the hemispheres and the vermis. Functionally, the cerebellum may be divided into the flocculonodular lobe (concerned with vestibular function), the anterior lobe (concerned with spinal reflexes), and the posterior lobe (concerned with fine motor activity). The cerebellum functions to coordinate motor activity at an unconscious level and to set postural muscles to allow coordinated voluntary movements. The output of the cerebellum is through the superior cerebellar peduncles to the thalamus and the brainstem nuclei.
  • Oculomotor (CN III), Trochlear (CN IV), and Abducens (CN VI) control the ocular movements. The trochlear nerve innervates the superior oblique muscle to depress and intort the eye. The abduces nerve supplies the lateral rectus muscle that abducts the eye. All other ocular movements including lid elevators and pupillary sphincters are supplied by the oculmotor nerve. The trigeminal nerve, CNV supplies the muscles of mastication as well as sensation for the face. CN VII, the facial nerve supplies the muscles of facial expression. CNVIII hearning and equilibrium. The glossopharyngeal nerve and the vagus nerve supplie the muscles of the pharynx and larynx. The vagus nerve is also involved in autonomic functions. The spinal accessory nerve innervates the trapezius and the SCM muscles. The hypoglossal nerve inervates the tongue.
  • The total brain blood flow of approximately 750 mL/min (15% of cardiac output). Each carotid carries approximately 300 mL/min and the vertebrobasilar system carries 150 mL/min. Unconsciousness ensues in approximately 10 seconds and irreversible in 4-5 minutes. CBF remains constant over a range of systemic ABPs, generally between 60 and 170 mm Hg mean ABP. This is termed autoregulation. The range of autoregulation will be elevated in chronic hypertension.
  • The arterial blood supply to the brain arises from the aortic arch. The right common carotid and subclavian arteries branch from the brachiocephalic artery. The left common carotid artery usually arises directly from the aortic arch.
  • The vertebral arteries are proximal branches of the subclavian arteries. The common carotid arteries bifurcate at about C3-C4 level into ICAs, carrying blood to the brain, external carotid arteries, carrying blood to the neck, face, mouth, jaw, scalp, and meninges.
  • The two ICA systems are interconnected through the anterior communicating artery. The posterior communicating artery connects each ICA to the basilar artery through the posterior cerebral arteries. The system of junctions is called the Circle of Willis.
  • Cerebral veins can be divided into superficial and deep systems. The superficial system drains superiorly and inferiorly from the superficial middle cerebral veins of the sylvian fissure. Superior running veins drain into the superior sagittal sinus. The largest of these is called the Vein of Trolard. Inferiorly running veins drain into the sphenoparietal, petrosal, and transverse (lateral) sinuses. The largest of these is termed the Ven of Labbe.
  • The superior sagittal and straight sinuses converge at the torcula and continue as the paired transverse sinuses. These are joined by the superior petrosal sinuses behind the mastoid processes and descend as the sigmoid sinus, which form the jugular bulbas the jugular foramen, and continue into the neck as the internal jugular veins. Connections between the sigmoid, petrosal, and cavernous sinuses and the pterygoid plexus all for collateral drainage when the internal jugular veins are blocked.
  • CSF is contained in the ventricles and the cerebral and spinal subarachnoid spaces, and is continuous with the brain extracellular space. These spaces contain approximately 150 mL CSF in the young adult, of which 25 mL is in the ventricles, 50 mL is in the spinal subarachnoid space and 75 mL is in the cerebral subarachnoid space and cisterns. Approximately 70% of the CSF is generated by the choroid plexus, the other 30% from brain capillaries and metabolic water. CSF production is approximately 500 mL/d. Therefore, the entire CSF volume turns over three to four times each 24 hours. CSF is absorbed at the archnoid villi, clusters of arahnoid cells that project into the dural sinuses.
  • The Glasgow coma scale is commonly used to grade levels of consciousness in patients with head injuries and gives a score from 15 (fully awake) to 3 (comatose) based on best verbal response, best motor response, and eye opening.
  • The pressure-volume relation describes a curve that is relatively flat to pressure increases over additions of volume until a point at which the curve rapidly steepens to become almost vertical. The flat area of the curve is presumed to demonstrate compensatory mechanisms such as movement of blood or CSF out of the cranial cavity, and the steep portion represents exhaustion of these compensatory mechanisms.
  • With generalized increase in ICP, CBF is maintained until CPP drops below 50 mm Hg.
  • The most important consequence of increased ICP is brain herniation. Two dural folds, the falx cerebri and the tentorium cerebelli, divide the intracranial space into compartments. The falx separates the two hemispheres as deep as the corpus callosum, and the tentorium separates he cerebrum from the cerebellum withan opening.
  • The tentorial notch or hiatus, allows the brainstem to pass through. At the foramen magnum, the medulla passes through to the spinal cord. Because these structures are unyielding, pressure effects will cause the brain to move through these openings, creating pressure and vascular effects on vital structures.
  • Bilateral temporal lobe herniation: begins as agitation, decreasing LOC, small reactive pupils, bilateral increased tone, Babinski sign, and Cheyne-Stokes respirations.
  • If herniation cannot be reversed rapidly, hemorrhages appear in the brainstem, leading to a poor prognosis, even if pressure is subsequently relieved.
  • The most common glial tumors in adults
  • Brain tumors are the second most common form of neoplasia in children and are usually malignant, whereas some cystic astrocytomas in the cerebellum are compatible with decades of survival. Primitive embryonic cells give rise to a variety of tumors—medulloblastoma, germinoma, neuroblastoma, and others in this age group. In children tumors arise most commonly in the posterior fossa and around the ventricular system, although in adults they are more common in the cerebral hemispheres, basal ganglia, and thalamus.
  • (Sphenoid Wing Meningioma( Examples include meningioma, acoustic neuroma, and epidermoid tumors, and rarely do they invade brain tissue. Pituitary tumors are also included in this group because they grow into the intracranial cavity. Despite the histologically benign nature of these extra-axial tumors, their typical location at the base of the skull, around the brainstem, from CNs, and along the dural sinuses can pose considerable problems for removal.
  • Malignant tumors outside the nervous system commonly metastasize to the brain, in both the supratentorial and infratentorial compartments. Lung and breast tumors are the most common metastaic lesions, followed by kidney, melanom, and GI malignancies. Lesions commly present aqt the gray-white matter junction. Although multiplicity is common, solitary metastases occur and may be the first presenting symptoms of the disease.
  • Brain trauma includes a spectrum of pathophysiologic consequences: synaptic impairment, neuronal disruption, ischemia, increased ICP, edema, bleeding, and herniation syndromes.
  • A contusion may develop beneath the site of impact (coup contusion) but more commonly develops where the brain has struck the internal aspect of the skull on the contralateral side (contrecoup contusion).
  • Epidural hematoma usually is associated with skull fracture and bleeding from the meningeal arteries or sinuses.
  • Epidural hematomas are typically temporoparietal but may occur anywhere, including the posterior fossa.
  • Subdural hematoma results from shearing of bridging veins and is extending from front to occiput. Skull fractures are present in approximately 50% of subdural hemotomas.
  • Some patients with severe closed head injury will show no abnormalities on imaging studies and are considered to have diffuse axonal shearing injuries. Some of these patient make remarkable recoveries, but others are left in a permanent vegetative state. This man is s/p a fall who stayed in a coma for 3 weeks prior to dying from pneumonia. You can see petechiae on the corpus callosum as well as bruising in the pontine tegmentum.
  • Approximately half of spinal injuries are cervical and half are thoracolumbar. In addition, approximately half of spinal cord injuries are complete and half are incomplete.
  • Central cord syndrome describes an injury for which weakness in the arms is out of proportion to leg weakness, and sensory functions are preserved partially or completely.
  • Hemisection of the cord causes ipsilateral paralysis and position/vibration sense loss, and contralateral pain and temperature loss. Ipsilateral segmental sensory loss completes the syndrome.
  • Loss of motor, pain, and temperature sensation bilaterally with preservation of position and vibration sense.
  • The spinal nerves contain motor, sensory, and visceral elements. Motor (ventral) and sensory (dorsal) roots form the spinal nerve at each level. Visceral fibers travel with the ventral root. In the cervical and lumbar areas, the spinal nerves form plexuses, where redistribution of axons takes place to form the peripheral nerves. The peripheral nerves are invested in a connective tissue sheath, the epineurium. Within the nerve the axons are arranged in fascicles bound by perineurium. The perineurium is the first level of a blood-nerve barrier. A regrouping of axons into different fascicles occurs along the course of a nerve such that when a segment of nerve is removed, the fascicles no longer precisely match. Connective tissue within the fascicle invests each axon as the endoneurium. Finally the axon is surrounded by myelin.
  • The cervical plexus is formed from the first four cervical segments. C2, with its dorsal ramus, supplies the occipitalis muscle and the skin of the scalp as the occipital nerves. C2-C4 supply the hyoid muscles, through the ansa cervicalis, and the diaphragm, through the phrenic nerve.
  • The brachial plexus is formed by the spinal nerves of C5 through T1. These form upper (C5, C6), middle (C7), and lower (C8,T1) trunks. The trunks form anterior and posterior divisions that give rise to three cords names for their relation to the axillary artery. The lateral cord is formed by the anterior division of the upper and middle trunks (C5-C7), the medical cord by the anterior division of the lower trunk (C8, T1), and the posterior cord from the posterior division of all three thrunks (C5-C8). The cords then give rise to the major peripheral nerves.
  • The first three and the upper portion of the fourth lumbar nerves form the lumbar plexus.
  • Arises from spinal nerves L4 to S3. The principal nerves formed by this plexus are the sciatic (L4-S3), the gluteals (L4-S1), and the pudendal (S2-S4). The Sciatic nerve is a composite nerve of two divisions, the peroneal and the tibial.
  • With axonotmetic and neurotmetic injuries, wallerian degeneration occurs. The axon degenerates toward the motor endplate, and Schwann cells form tubules to receive regenerating axons, but scar tissue can inhibit this process. Lack of clinical recovery 16 weeks after nerve injury usually indicates a grade 3 or higher injury. Most muscles are subject to a 24 month limit of denervation, after which no useful motor recovery is expected from reconnection.
  • Grade 1 is disruption of the myelin sheath, which manifests as a conduction block. Grade 2 is the loss of axon continuity with preservation of all layers of connective framework. (The endoneurial, perineurial, and epineuiral layers all remain intact. Grade 3 is loss of axon continuity with loss of endoneuiral integrity. In this setting, internal endoneurial scarring can prevent reinnervation, and disruption of the endoneurial sheath may allow mismatched reinnervation as regenerating axons stray from their proper endoneurial sheaths. Grade 4 is loss of perineural integrity and therby disruption of the fascicle. This is associated with more intraneural scarring and consequently less-effective nerve regeneration. Grade 5 is loss of eipneurial continuity and thereby transection of the nerve.
  • Up to 20% of suspected transection injuries actually leave the nerve in continuity, and some of these recover without surgery. However, most laceration injuries are Grade 4 or 5 and will require surgical intervention.
  • Usually neuropraxic and/or axonotmetic, but on occasion, endoneurail damage does occur. The recovery time is the major indicator of degree of injury. Motor fibers are the most susceptible to compression. They are the first to fail and the last to recover, and in mild injuries may be the only ones that suffer.
  • Nerve injury proceeds starting at Grade 1 and progresses by grade until the upper 30% limit is reached. At this time the perineurium and then the epineurium give way and the nerve ruptures.
  • Seizures result from excessive and/or hypersynchronous, usually self-limited abnormal activity of neurons. A seizure may occur in the normal human brain from a variety of noxious stimuli depending on individual thresholds. In some, mild sleep deprivation, alcohol withdrawal, and in children, fever, can provoke a seizure. Epilepsy is a condition wherein the disturbance of the brain either microscopic or macroscopic is responsible for the seizure and for repetitive events. Seizures occurring in childhood and adolescence often have no radiologic abnormalities and may have a genetic basis, whereas seizures in adults are more likely to have associated structural abnormalities.
  • Drugs such as phenytoin, carbamazepin, and valproate bind to activated sodium channels from the inside of the cell membrane and maintain the channel in an inactive form temporarily. Its short duration of blockage will impede the rapid repetitive firing of neurons characteristic of a seizure.
  • The chloride channel complex is regulated by GABA, a major inhibitory neurotransmitter of the brain. Opening of the chloride channel by GABA allows chloride ions to enter the neuron and hyperpolarize the cell, thereby making the neuron more difficult to fire. Chloride channel activity can be enhanced by three mechanismsProlonging the channel’s opening time (Barbituates)By increasing the opening frequency (Benzodiazepines)By increasing the channel’s conductance.
  • Ancillary tests include an isoelectric (flat) EEG and absence of CBF on angiography or radioisotope scan. When ancillary testing is used as an adjunct to clinical examination, brain death may not be declared until the adjunctive test fully supports the clinical diagnosis. Appropriate periods between two examinations range from 6 to 24 hours, and some hospitals require examinations by two independent examiners, especially in cases of transplantation. The time of death is generally considered when cardiac arrest occurs in cases for which life support is withdrawn. Time of death is at the time of brain death determination in cases of transplantation.
  • The report fo the President’s Commission outlines criteria valid in children older than 5 years of age. The supposition of increased resistance to injury in the child’s brain is controversial land lacks good clinical support. As a consequence, a task force of pediatricians and neurologists developed guidelines to deal with the problem of pediatric brain death.
  • The Physiologic Basis Of Surgery; Chapter 21: Basic Neuroscience

    1. 1. The Physiologic Basis of Surgery Chapter 21: Basic Neuroscience Leslie Hutchins, MD April 9, 2009 Basic Science Lecture
    2. 2. Cellular Morphology: Unipolar Neuron (c) Dorling Kindersley
    3. 3. Cellular Morphology: Bipolar Neuron (c) Dorling Kindersley
    4. 4. Cellular Morphology: Multipolar Neuron (c) Dorling Kindersley
    5. 5. Glial Cells Astrocytes  Oligodendrocytes  Ependymal cells  Microglia 
    6. 6. Astrocytes
    7. 7. Oligodendrocytes
    8. 8. Schwann Cell Figure 21.1: Concentric layers of the Schwann cell membrane encase a peripheral nerve axon as myelin. The Physiologic Basis of Surgery
    9. 9. Ependymal cells
    10. 10. Microglial Cells
    11. 11. Voltage Gated Channels and the Action Potential
    12. 12. Nerve Action Potential
    13. 13. Chemical Synapse
    14. 14. Skull
    15. 15. The Spine
    16. 16. Atlas & Axis
    17. 17. Vertebrae
    18. 18. Ligaments
    19. 19. Spinal Cord Anatomy Begins  Foramen Magnum as a  continuation of the Medulla Oblongata Terminates  Conus Medullaris  Adult: Lower Border of L1  Young Child: Upper Border  of L3 Filum Terminale  Prolongation of the  piamater Attaches to the spinal  cord at the coccyx Dural Sac  Ends at the level of the  second sacral vertebra
    20. 20. Spinal Cord Anatomy Gray Matter   Ventral (motor) Horns  Dorsal (sensory) Horns White Matter   Anterior Columns  Lateral Columns  Posterior Columns D .E . H aines, Neuroanatomy: An Atlas of Structures, Sections, and Systems, 3rd ed. (1991), U rban & Schwarzenberg E ncyclopedia Britannica, I nc.
    21. 21. Spinal Cord Cross Section: Fiber Tracts
    22. 22. Cerebral Hemispheres Figure 21.3: Lobes of the right hemisphere. The Physiologic Basis of Surgery
    23. 23. The Brain
    24. 24. Frontal Lobe
    25. 25. Motor Homunculus
    26. 26. Frontal Lobe
    27. 27. Temporal Lobe Figure 21.3: Lobes of the right hemisphere. The Physiologic Basis of Surgery
    28. 28. Temporal Lobe
    29. 29. Temporal Lobe
    30. 30. Temporal Lobe
    31. 31.
    32. 32. Parietal Lobe Figure 21.3: Lobes of the right hemisphere. The Physiologic Basis of Surgery
    33. 33. Parietal Lobe
    34. 34. Parietal Lobe
    35. 35. Occipital Lobe Figure 21.3: Lobes of the right hemisphere. The Physiologic Basis of Surgery
    36. 36. Occipital Lobe
    37. 37. Visual Radiations
    38. 38. Visual Pathway
    39. 39. Limbic Lobe
    40. 40. White Matter Tracts
    41. 41. White Matter Tracts
    42. 42. Arcuate Fasciculus
    43. 43. Corpus Callosum & Anterior Commissure
    44. 44.
    45. 45. Posterior Commissure
    46. 46.
    47. 47. Centrum Semiovale
    48. 48. Internal Capsule
    49. 49. Basal Ganglia
    50. 50. Yin et al. Nature Reviews Neuroscience 7, 464–476 (June 2006) | doi:10.1038/nrn1919
    51. 51. Dystonia  /0504-learning_to_walk_again.htm
    52. 52. Diencephalon
    53. 53. Pineal Gland
    54. 54. Thalamus
    55. 55. Hypothalamus
    56. 56. Hypophyseal Portal System
    57. 57. Brainstem The Physiologic Basis of Surgery
    58. 58. Upper Mesencephalon
    59. 59. Lower Mesencephalon
    60. 60. Lower Mesencephalon
    61. 61. Upper Pons
    62. 62. Upper Pons
    63. 63. Middle Pons
    64. 64. Pons
    65. 65. Medulla
    66. 66. Medulla
    67. 67. Medulla
    68. 68. Medulla
    69. 69. Cerebellum
    70. 70. Cerebellum
    71. 71. Cranial Nerves Cranial Nerves By Functional Grouping: •I, II, and VIII primarily effect sensory functions •IV, VI, XI, and XII primarily effect motor functions •III, V, VII, IX and X have mixed sensory, motor, and parasympathetic functions
    72. 72. Cerebrovascular Physiology Figure 21.15: Graphic relation of cerebral blood flow (CBF) to arterial blood pressure (ABP) with progressive vasoconstriction being responsible for the flat portion of the curve (autoregulation). Note that the curve is shifted to the right in hypertension The Physiologic Basis of Surgery
    73. 73. Cerebrovascular Anatomy
    74. 74. Cerebrovascular Anatomy
    75. 75. Cerebrovascular Anatomy
    76. 76. Cerebral Veins
    77. 77. Cerebral Veins
    78. 78. Cerebrospinal Fluid
    79. 79. Neural basis of Consciousness A state of awareness of self  and surrounding.
    80. 80. Anatomy of Mental Status Ascending reticular activating system (ARAS).  Activating systems in the upper pons and midbrain and  its projections through the nonspecific thalamic nuclei and hypothalamus to the limbic and prefrontal cortex and ultimately to the cerebral hemispheres, especially the left hemisphere. Determines the level of arousal.  Cerebral hemispheres and interaction between  functional areas in cerebral hemispheres. Determines the intellectual and emotional  functioning. Interaction between cerebral hemispheres and  activating systems.
    81. 81. The content of consciousness Sum of patient’s intellectual  (cognitive) functions and emotions (affect). An isolated lesion of one hemisphere  does not impair consciousness, although it may depress affect (content of consciousness). However, structural lesions in the  brain can cause coma if they involve the ARAS and its projections.
    82. 82. Glasgow Coma Scale
    83. 83. Glasgow Coma Scale Individual elements as well as the  sum of the score is important. GCS 9= E2 V4 M3 @ 07:35  Classification:  Severe: GCS≤8  Moderate: GCS 9-12  Minor: GCS≥13 
    84. 84. Raised Intracranial Pressure Figure 21.17: Relation between intracranial volume and intracranial pressure. ICP, intracranial pressure The Physiologic Basis of Surgery
    85. 85. Monro-Kellie Hypothesis ICP is stable as long as volume  added is balanced by volume displaced. Three components:  Brain Tissue (1,500 mL)  Cerebral Blood Volume (200 mL)  Cerebrospinal Fluid (100 mL)  Expansion by any one causes rise in  ICP if volume of other two remains constant.
    86. 86. Cerebral Perfusion Pressure CPP= MAP – ICP  MAP = DBP + 1/3(SBP - DBP)  CPP: 70-100 mm Hg 
    87. 87. Herniation
    88. 88. Herniation
    89. 89. Central Herniation
    90. 90. Lateral Herniation Decreased LOC  Ipsilateral oculomotor paresis, generally beginning  with dilated nonreactive pupil and later involving lid elevation and extraocular movements Parasympathetic fibers, located around the outer  aspect of the third nerve, are compressed by the uncus. This leads to unopposed sympathetic fibers resulting in ipsilateral pupil dilation. Contralateral hemiparesis  Results from compression of ipsilateral cerebral  peduncle. Since the cortical spinal tracts decussate below the midbrain at the level of the pons, the hemiparesis is contralateral. Sustained hyperventilation 
    91. 91. Both syndromes Progress to:  Decreased responsiveness  Decorticate posturing  Decerebrate posturing  Midrange nonreactive pupils  Loss of oculocephalic and  oculovestibular reflexes Loss of corneal reflexes  Ataxic breathing patterns 
    92. 92. Herniation Progression leads to herniation of  the cerbellar tonsils through the foramen magnum with medullary compression, resulting in: Loss of motor tone  Loss of gag and cough reflexes  Apnea  Cardiovascular collapse  Death 
    93. 93. Increase ICP Managed by:  Head elevation  Improves venous return to heart  Hyperventilation  Cerebral vasoconstriction and reduces CBV  Mannitol  Decreases the brain tissue compartment by  shrinking the extracellular and perhaps intracellular space.
    94. 94. Brain Tumors Primary Secondary   Neuroglial tissues Metastic   Astrocytomas  Ependymomas  Oligodendrogliomas  Meninges  Reticuloendothelial  cells Vascular cells  intrinsic to the brain
    95. 95. Glioblastoma Multiforme
    96. 96. Pediatric Brain Tumors
    97. 97. Extrinsic Brain Tumors
    98. 98. Brain Metastasis
    99. 99. Chromosome Tumor Syndrome Typical Tumor Types Location Hereditary cutaneous malignant Dysplastic nevi, melanoma 1p melanoma/dysplastic nevus syndrome von Hippel-Lindau syndrome Hemangioblastoma, 3p pheochromocytoma, renal cell carcinoma Multiple endocrine neoplasia, Pituitary tumor, parathyroid 11p type 1 adenoma, endocrine pancreatic tumors Multiple endocrine neoplasia, Pheochromocytoma, medullary 10 type 2 thyroid carcinoma Familial retinoblastoma Retinoblastoma, osteosarcoma 13q Neurofibromatosis (NF1) Neurofibroma, optic glioma, 17q neurofibrosarcoma Neurofibromatosis (NF2) Vestibular schwannoma, 22q meningioma, spinal nerve root neurofibroma Tuberous sclerosis Subependymal giant cell 16q astrocytomas hamartomas
    100. 100. Neurotrauma Cerebral Contusion:  Transient LOC attributed to traction on  the upper brainstem and reversible synaptic impairment in the reticular- activating system. More severe:  Persistent mild impairment of higher  cortical functions Boxers subjected to repeated  concussion may later show a degenerative-type dementia.
    101. 101. Contusion
    102. 102. Hematomas
    103. 103. Middle Meningeal Artery
    104. 104. Epidural Hematoma
    105. 105. Subdural Hematoma
    106. 106. Diffuse Axonal Injury
    107. 107. Spinal Cord Injury
    108. 108. Incomplete Lesion Any residual motor or sensory  function more than 3 segments below level of injury. Look for signs of preserved  long-track function. Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    109. 109. Signs of Incomplete Lesion Sensation (including position sense)  or voluntary movements in the lower extremities. “Sacral Sparing” sensation around  anus, voluntary rectal sphincter contraction, or voluntary toe flexion. An injury doesn’t qualify as  incomplete with preserved sacral reflexes alone. Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    110. 110. Types of Incomplete Lesions Central Cord Syndrome 1. Brown-Séquard Syndrome 2. Anterior Cord Syndrome 3. Posterior Cord Syndrome 4. Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    111. 111. Central Cord Syndrome
    112. 112. Brown-Séquard Syndrome
    113. 113. Anterior Cord Syndrome
    114. 114. Complete Lesion No preservation of any motor and/or  sensory function more than 3 segments below the level of injury. Almost 3% of patients with complete  injuries on initial exam will develop some recovery within 24 hours. The persistence of complete spinal cord  injury beyond 24 hours indicates no distal function recovery Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    115. 115. Spinal Shock Hypotension:  Interruption of sympathetics  Loss of vascular tone below level of  injury Leaves parasympathetics relatively  unopposed causing bradycardia. Loss of muscle tone due to skeletal  muscle paralysis below the level of injury results in venous pooling and thus a relative hypovolemia. Blood loss from associated wounds →  true hypovolemia. Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    116. 116. Spinal Shock Transient loss of neurologic  function (including segmental and polysynaptic  reflex activity and autonomic function) below the level of spinal cord injury → flaccid paralysis & areflexia lasting various periods (usually 1-2 weeks, occasionally several months and sometimes permanently), the resolution of which yields the anticipated spasticity below the level of the lesion. Greenberg, M. Handbook of Neurosurgery: Sixth Edition. 2006; 698-713.
    117. 117. Reflex Arcs
    118. 118. A natomy of the Peripheral Nervous S ystem 31 pairs of spinal nerves  (Each formed by 2 roots) The spinal nerves exit through  the intervebral foramen  8 cervical  1st exits through the Occipital Bone and C1  8th exits between C7 & T1  12 thoracic  Distal to T1 each spinal nerve exits below its corresponding vertebra  5 lumbar  5 sacral  1 coccygeal
    119. 119.
    120. 120. Cervical Plexus
    121. 121. Brachial Plexus The Physiologic Basis of Surgery
    122. 122. Lumbar Plexus The Physiologic Basis of Surgery
    123. 123. Lumbosacral Plexus The Physiologic Basis of Surgery
    124. 124. Peripheral Nerve Injury Sunderland Seddon Description Recovery Recovery Rate Surgery Temporary interruption to nerve Neurapraxia I Complete Fast (days-12 wks) None transmission with restoration in weeks quot;Blockedquot; nerve Complete disruption of nerve transmission II (axon) with Complete Slow (3cm/mth) None regeneration and full recovery Disruption of axon and connective tissue III (endoneurium) Varies Slow (3cm/mth) Varies Axonotmesis causing disorganised regeneration Disruption of axon, endoneurium, and inner membrane IV sheath (perineurium), None None Yes with intact outer nerve layer (epineurium) but no regeneration Complete severance Neurotmesis V None None Yes of the nerve Neuroma- Mixture of one or VI more of the above Varies depending on injury incontinuity conditions
    125. 125. Seddon System Neurapraxia  Axon is left in continuity but is focally  demyelinated at site of injury. Positioning palsies  Prolonged periods of immobilization  Axonotmesis  Axonal continuity is lost in addition to  demyelination, but the connective tissue sheath is intact. Recovery is dependent on axonal regeneration  Neurotmesis  Axonotmesis + Disruption of Connective Tissue 
    126. 126. Wallerian Degeneration
    127. 127. Sunderland Classification
    128. 128. Clinical Nerve Injuries Laceration 1. Compression 2. Stretch 3. High-Velocity Missile Injury 4.
    129. 129. Laceration Knife wounds  Shattered glass  Animal bites  Chain Saws  Propeller Blades  Auto Metal 
    130. 130. Acute Compression Injuries Prolonged immobility:  Extreme fatigue  Alcohol Intoxication  Drug-abuse  General anesthesia 
    131. 131. Stretch As a nerve is stretched more  that 6% to 20% of its length, nerve function starts to fail.
    132. 132. High-velocity Nerves directly in the path may  be severed or torn, but most are injured secondarily as the result of sudden stretch, with all grades of injury being observed.
    133. 133. Seizures Generalized: Loss of  consciousness occurs Partial: Consciousness is  preserved
    134. 134. Postictal State A period of drowsiness and  confusion following a seizure that occurs and clears after a few hours.
    135. 135. Todd Paralysis With partial and generalized  seizures, a postictal neurologic deficit, such as hemiparesis, can occur and usually clears over 24 to 48 hours.
    136. 136. Sodium Channels
    137. 137. Chloride Channels
    138. 138. Brain Death ←
    139. 139. Ancillary Exams
    140. 140. Table 21.4 Modification of Brain Death Criteria for Children and Infants Less Than 5 Years Old Infants 7 d to 2 mo Two examinations and two confirmatory EEGs separated by at least 48 h Infants 2 mo to 1 yr Two examinations and EEGs separated by at least 24 h unless CBG studies document no cerebral perfusion Children 1–5 yr When an irreversible cause exists, a 12-h interval between examinations is recommended. In cases of hypoxia- ischemia, a 24-h interval is recommended. If an EEG shows electrical silence or a CBF study demonstrates no cerebral perfusion, the time interval between examinations may be reduced The Physiologic Basis of Surgery