Clinical Case
The following clinical case is intended to illustrate some of the basic neuroanatomical concepts presented in this topic. You are not expected to diagnose the patient’s condition or suggest any therapy or medical steps to be taken. Rather, we hope that this case and those that follow will demonstrate the very real clinical relevance of basic neuroscience information.
History
Saul is a 75-year-old man who recently learned from his internist that he had an irregular heartbeat. He was prescribed medication to regulate his heart rate and asked to return in a few days, but he was too frightened to fill the prescription or return for the appointment. One morning, 3 weeks after seeing his physician, he awoke and, upon attempting to get out of bed, was unable to move his left arm and leg. Using his right hand, he dialed 911. When the operator answered, he attempted to explain his problem, but his speech was so slurred that the operator could not understand him.The operator told him to remain on the line so that the call could be traced. An ambulance arrived shortly afterward, and Saul was taken to the nearest emergency room (ER).
Examination
The ER staff noted Saul’s irregular heartbeat. A neurologist arrived and confirmed that, although Saul’s speech was quite slurred, much like that of an inebriated person, his sentences were grammatically correct and everything he attempted to say made logical sense. His blood alcohol level was 0.0. He could follow three-step commands and repeat statements, despite his slurred speech. When he tried to smile, his mouth drooped on the left side. But when he wrinkled his eyebrows, his forehead remained symmetric. His left arm was completely paralyzed, but he was able to wiggle his left leg minimally.Saul was admitted to the intensive care unit for treatment.
Explanation
Saul’s abnormal heartbeat is called atrial fibrillation, a rhythm characterized by irregularity and, typically, rapidity. It can cause strokes by dislodging small dots from the heart and causing them to travel as emboli to the cerebral blood vessels, causing occlusion.
Saul’s condition is an example of a right frontal lobe cortical stroke involving the precentral gyrus or the primary motor cortex.The motor problems, including the slurred speech and arm and leg weakness, occurred because of involvement of these areas. This region is functionally organized as a homunculus, with representation of each region of the body in specific locations.The effects can be attributed mainly to occlusion of the middle cerebral artery (a branch of the internal carotid artery and a common location for emboli) because this artery subserves most of the affected region. However, the superior portion of this region is partially within the territory of the anterior cerebral artery. Clinically, this is demonstrated by the fact that the patient’s leg is somewhat involved but not as extensively as his arm. Although there is weakness of the lower two thirds of the face, the forehead is not involved because of bilateral cortical innervation of this region. Because the majority of people are right-handed with left-sided cerebral dominance (the side where language originates), Saul’s language disturbance is solely motor, and he is able to follow commands and construct sentences. Saul was transferred from the ER to another section of the hospital. After remaining in the hospital for approximately 4 weeks, he was sent to a nearby rehabilitation facility where he was able to regain most of his basic motor functions, including speech.
SUMMARY TABLE
Overview of the Major Structures of the Brain and Their Functions
Brain Region |
Structure |
General Functions |
Associated Disorder(s) |
Cerebral Cortex |
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Frontal lobe |
Precentral gyrus |
Voluntary movement of muscles of body and head region |
Loss of voluntary movement of body and head region |
Premotor region |
Aids and integrates voluntary movements of body |
Apraxia (loss of ability to carry out complex movements of body and head) |
|
Frontal eye fields |
Controls voluntary horizontal movement of the eyes |
Loss of voluntary control of horizontal eye movement (i.e., eyes cannot deviate to side opposite lesion) |
|
Prefrontal cortex |
Intellectual functions;affective processes |
Intellectual and emotional impairment |
|
Broca’s motor speech area |
Regulates motor aspects of speech |
Motor aphasia |
|
Parietal lobe |
Postcentral gyrus |
Conscious perception of som-esthetic sensation |
Loss of somatosensory perception |
Wernicke’s area |
Receptive integration of speech |
Receptive aphasia |
|
Superior parietal lobule |
Integration of sensory and motor functions; programming mechanism for motor responses |
Posterior parietal syndrome; sensory neglect; apraxia |
|
Temporal lobe |
Superior temporal gyrus |
Auditory perception |
Loss of auditory perception |
Middle temporal gyrus |
Detection of moving objects |
Loss of movement detection |
|
Inferior temporal gyrus |
Recognition of faces |
Loss of facial recognition |
|
Occipital lobe |
Upper and lower banks of calcarine sulcus |
Visual perception |
Partial or total loss of vision of the contralateral visual fields for both eyes, depending upon the extent of the lesion in the visual cortex |
Deep Brain Structures |
::::::::::::::::: |
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Ventricles of the brain |
Lateral, third, and fourth ventricles and cerebral aqueduct |
Flow of CSF throughout the CNS: a source of electrolytes and conduit of neuroactive and metabolic products |
Hydrocephalus |
Basal ganglia |
Caudate nucleus, putamen, globus pallidus, subthalamic nucleus, substantia nigra |
Regulation of motor functions associated with cerebral cortex |
Dyskinesia |
Brain Region |
Structure |
General Functions |
Associated Disorder(s) |
|
Diencephalon |
||
Thalamus |
Thalamic nuclei |
Transmission of signals from other regions of the CNS to the cerebral cortex mediating sensory, motor, cognitive, and affective (emotional) functions |
Disruption and possible loss of sensory, motor, and other functions |
Hypothalamus |
Hypothalamic nuclei |
Visceral (feeding,drinking, autonomic, and endocrine functions and sexual and emotional behavior) |
Disruption, loss, or alterations in visceral and affective functions and processes |
Limbic structures |
Hippocampal formation, amygdala, septal area,cingulate gyrus, prefrontal cortex |
Modulation of hypothalamic functions; regulation of emotional behavior; short-term memory |
Temporal lobe epilepsy; loss of control of emotions and related affective processes; loss of short-term memory |
Cerebellum and Brainstem |
|||
Cerebellum: anterior, posterior, and flocc-ulonodular lobes |
Integration of motor functions related to all regions of the CNS associated with motor and related processes |
Loss of balance; ataxia; hypotonia; loss of coordination; disorders of movement when intentionally attempting to produce a purposeful response |
|
Midbrain |
Transmission and regulation of sensory, motor, and autonomic functions (cranial nerves III and IV) |
Sensory, motor, and autonomic deficits as well as deficits associated with cranial nerves III and IV |
|
Pons |
Transmission and regulation of sensory, motor, and autonomic functions (cranial nerves V, VI, and VII) |
Sensory, motor, and autonomic deficits as well as deficits associated with cranial nerves V,VI,and VII |
|
Medulla |
Transmission and regulation of sensory, motor, and autonomic functions (cranial nerves VIII, IX, X,XII) |
Sensory, motor, and autonomic deficits, including respiration, as well as deficits associated with cranial nerves VIII, IX, X, and XII |
CNS = central nervous system; CFS = cerebrospinal fluid.