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An Overview of the Brainstem

The term brainstem (sometimes written brain stem ) can mean either the portion of the brain that consists of the medulla oblongata, pons, and midbrain or the portion that consists of these structures plus the diencephalon. This book follows the former convention. For our purposes, therefore, the brainstem consists of the rhombencephalon, comprising the myelencephalon and metencephalon (but excluding the cerebellum ), and the mesencephalon. These…

The Spinal Cord

Although small in diameter, the spinal cord is the most important conduit between the body and the brain. Recall that many cranial nerves contain sensory fibers that receive information from, and motor fibers that project to, diverse body areas; these bypass the spinal cord. The spinal cord conveys sensory input from the upper limbs, trunk, lower limbs, and most of the viscera and contains fibers and…

A Survey of the Cerebrovascular System

About 50% of the problems that occur inside the cranial cavity and result in neurologic deficits are vascular in origin. Consequently, a detailed understanding of cerebrovascular patterns is absolutely essential to establish an accurate diagnosis of the neurologically compromised patient. The brain is a voracious consumer of oxygen and therefore requires a great deal of oxygenated blood. Although it makes up only about 2% of total…

The Meninges

The human nervous system is extremely delicate and lacks the internal connective tissue framework seen in most organs. For protection, the brain and spinal cord are each encased in a bony shell, enveloped by a fibrous coat, and delicately suspended within a fluid compartment. In the living state, the nervous system has a gelatinous consistency, but when treated with fixatives, it becomes firm and easy to…

The Ventricles, Choroid Plexus, and Cerebrospinal Fluid

The ventricular spaces of the brain are the adult elaborations of the neural canal of early developmental stages. These spaces, the choroid plexuses in them, and the cerebrospinal fluid (CSF) produced by the choroid plexus are essential elements in the normal function of the brain. In many situations, CSF may be used in the diagnosis of a variety of clinical disorders. Overview By about the third…

Chemical Signaling in the Nervous System

The adult brain averages 86 billion (∼10 11 ) neurons plus an equal number of nonneuronal support cells according to recent estimates. Each neuron can make thousands of terminal contacts, meaning that there are 10 14 to 10 15 connections within the brain, with still more in the periphery. We can bring some order to this massive system by understanding the chemistry used to coordinate specific…

The Electrochemical Basis of Nerve Function

Membranes composed of a lipid bilayer enclose all cells in the body as well as all the organelles within those cells. Being lipid, these membranes are impermeant to small ions and macromolecules alike. A variety of transport proteins, selected from among hundreds available in the genome ( Table 3.1 ), are inserted into the lipid bilayer to bring specific functions to one cell type or another.…

The Cell Biology of Neurons and Glia

The number of cells in the adult human central nervous system (CNS) has been estimated at 100 billion. All arise from a relatively small population of precursors, yet a diversity of cell types is seen in the adult. Their most basic classification is as neurons and glia (glial cells). Overview Nerve cells ( neurons ) manipulate information. Doing so involves changes in the bioelectrical or biochemical…

Orientation to the Structure and Imaging of the Central Nervous System

Our nervous system makes us what we are. Personality, outlook, intellect, coordination, and the many other characteristics are the result of complex interactions within our nervous system. Information is received from the environment and transmitted into the brain or spinal cord. Once this sensory information is processed and integrated, an appropriate motor response is initiated. The nervous system can be viewed as a scale of structural…

Cerebrovascular Disease

Study Guidelines 1. Review the blood supply of the central nervous system and the relevance of the circle of Willis (circulus arteriosus) in limiting the deficit from a cerebral artery occlusion (see Chapter 4 ). 2. Define stroke, transient ischaemic attack, and subarachnoid haemorrhage. 3. Describe the clinical features expected with a stroke within the anterior, middle, and posterior cerebral artery. 4. Describe the clinical features…

Pituitary and Hypothalamus

Study Guidelines 1. The pituitary gland (hypophysis cerebri) is in the hypophyseal fossa of the sphenoid bone and is intimately linked to the hypothalamus. It is composed of two parts: the adenohypophysis and the neurohypophysis. 2. Hypothalamic neuroendocrine cells fulfil the basic criteria both for neurons and for endocrine cells. Small neuroendocrine cells control release of hormones by the purely endocrine cells of the anterior pituitary…

Olfactory and Limbic Systems

Study Guidelines Olfactory System In most vertebrates, the olfactory system is altogether more important than it is in humans. Although damage to the olfactory pathway on one side is associated with anosmia on that side, olfactory deficits are often found in neurodegenerative disorders. Limbic System Cortical and subcortical limbic areas are prominent features of the brain in primitive mammals where they are intimately concerned with mechanisms…

Hemispheric Asymmetries

Study Guidelines 1. List the different cognitive domains and their individual roles. 2. Describe and contrast the clinical outcome of injuries to the Broca and Wernicke areas. 3. Describe the ‘steps’ performed when reading in relation to areas of the brain involved. 4. Discuss the different clinical manifestations of frontal lobe injuries. 5. Discuss the different clinical manifestations of right parietal lobe injuries. The two cerebral…

Visual Pathways

Study Guidelines 1. Define the layers of the retina and the cell types located in each. 2. Contrast a rod versus a cone cell with respect to structure, function, and localisation within the retina. 3. Be able to trace the pathway from retina to occipital cortex and distinguish between the function of those optic nerve fibres that will end in the midbrain and those that project…

Evoked Potentials

Study Guidelines 1. Describe the general methodology performed to record sensory evoked potentials, the sensory modalities assessed, and an example of clinical disorders and expected abnormality. 2. Contrast the performance of a motor evoked potential versus a motor nerve conduction study. 3. Provide an example of how motor evoked potentials can be used to detect physiologic changes in the motor cortex. 4. Provide an example of…

Electroencephalography

Study Guidelines 1. Be able to describe the origin of the recorded EEG, underlying rationale for the 10–20 recording system, and the significance of the letter/number combinations used to define electrode placements. 2. Contrast the patterns that typify the waking EEG from that associated with sleep, both REM and NREM sleep. 3. Discuss why the phenomenon of phase reversal is useful in the interpretation of an…

Cerebral Cortex

Study Guidelines 1. The cerebral cortex is the part of the body that makes us truly human. Its structure is enormously complex, and assignment of functions to different parts is made difficult, and often unrealistic, by the multiplicity of interconnections. 2. Sensory, motor, and cognitive areas of the cortex are taken in turn. 3. Although damage often leads to permanent disability, the plasticity of the cortex…

Cerebellum

Study Guidelines 1. Describe the functional organisation of the cerebellum and the relationship to the deep cerebellar nuclei. 2. Classify the microscopic organisation of the cerebellar cortex and the cell types found in each layer. 3. Contrast the two types of afferents to the cerebellar cortex with respect to origin, termination, and neurotransmitters. 4. Characterise the origin of output from the cerebellum, the neurotransmitter released, and…

Basal Ganglia

Study Guidelines 1. Identify basal ganglia nuclei in brain sections. 2. List the four different basal ganglia circuits (or loops) and describe their function. 3. Summarise the major neurotransmitters involved in the basal ganglia circuits and their function (excitatory or inhibitory): cortical input, globus pallidus, striatum, substantia nigra, subthalamic nucleus, and thalamus. 4. Draw the direct and indirect basal ganglia pathways and predict the outcome of…