Neuroscience

The Spinal Cord (Organization of the Central Nervous System) Part 4

Corticospinal Tract This tract is involved in the control of fine movements. It is the largest and perhaps the most important descending tract in the human CNS. A schematic representation of the course of this tract is shown in Figure 9-12. It arises from the cerebral cortex, passes through the medullary pyramids, and terminates in […]

The Spinal Cord (Organization of the Central Nervous System) Part 5

Lesions of the Spinal Cord Spinal Cord Transection A complete transection of the spinal cord results in loss of muscle tone, motor function, reflex activity, visceral sensation, and somatic sensation below the level of the transection. Immediately after the spinal cord damage, there is a period during which all spinal reflexes below the level of […]

The Spinal Cord (Organization of the Central Nervous System) Part 6

Flexion (Withdrawal) Reflex Receptors The flexion reflex is primarily mediated by pain receptors (nociceptors) consisting of free nerve endings. Noxious stimuli activate these receptors. Circuitry and Mechanism A schematic representation of the circuitry involved in the flexion reflex is shown in Figure 9-18. When a noxious stimulus is applied to the skin or deeper structures, […]

Brainstem I: The Medulla (Organization of the Central Nervous System) Part 1

Gross Anatomical View and Internal Organization Gross Anatomical View The purpose of this topic is to begin to develop an understanding of the organization of the brainstem by considering the neuroanatomy of the medulla. Knowledge of the anatomy of the principal neural cell groups and pathways of the medulla is essential in acquiring an appreciation […]

Brainstem I: The Medulla (Organization of the Central Nervous System) Part 2

Internal Nuclei of the Brainstem Reticular Formation. The internal core of the entire brain-stem contains mainly a complex set of neuronal groups (coupled with related fiber bundles) that are collectively referred to as the reticular formation.In brief, it appears to be involved in such processes as modulation of sensory transmission to the cortex, regulation of […]

Brainstem I: The Medulla (Organization of the Central Nervous System) Part 3

Clinical Considerations Typically, damage to a part of the brainstem results from a vascular lesion. As a general rule, there are certain deficits that are common to lesions of the lateral aspect of the brainstem. Likewise, there are several deficits that are common to lesions of the medial aspect. Lateral Medullary Syndrome The lateral medullary […]

Brainstem II: Pons and Cerebellum Part 1

In the previous topic, we examined the organization of the medulla. In this topic, a parallel analysis will be made with respect to the pons and cerebellum. Similar to the medulla, the pons consists of different kinds of nuclear groups belonging to cranial nerves as well as other groups that are unrelated to cranial nerves. […]

Brainstem II: Pons and Cerebellum Part 2

Major Cell Groups Figures 11-3 through 11-6 depict major nuclear cell groups. Caudal Pons A number of important nuclei, associated in part with cranial nerves, are present in the caudal pons. These include the motor nuclei of the facial (cranial nerve [CN] VII) and abducens (CN VI) nerves, the spinal nucleus of the trigeminal CN […]

Brainstem II: Pons and Cerebellum Part 3

Caudal Basal Pontine Syndrome Caudal basal pontine syndrome, which is associated mainly with the paramedian branches of the basilar artery, affects mainly the descending corticospinal tract and root fibers of CN VI if the lesion extends far enough medially. The effects of such a lesion would typically produce contralateral hemiplegia and signs of paralysis of […]

Brainstem III: The Midbrain (Organization of the Central Nervous System) Part 1

The midbrain lies between the pons and the forebrain (Figs. 12-1 and 12-2). When viewed in cross section at either rostral or caudal levels of the midbrain, it is customary to divide this region of the brainstem into three anatomically distinct components (Fig. 12-3). (1) The most dorsal part is called the tectum. It is […]

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