![]() This figure shows other important features of the spinal cord, many of them related to the spinal cord’s function of relaying information. Below the medullary cone, the vertebral canal contains a bundle of nerve roots called the cauda equina. In an adult, the spinal cord itself terminates at a point called the medullary cone, at approximately the level of the first lumbar vertebrae (L1). Throughout its length, it is enclosed within the spinal column, with the cord passing through the vertebral foramen of the vertebrae. ![]() The spinal cord is a central nervous system structure that extends inferiorly from the brain stem and into the lower back. The structure of the spinal cord aids it in carrying out these relaying and integrative functions. The spinal cord is a nervous system structure dedicated to relaying information from the periphery to the brain and back, as well as carrying out certain levels of integration, such as those found in many reflexes. For example, specialized nerve endings often act as sensors (receptors), information is carried along nerves and/or tracts of the spinal cord, integration occurs within the CNS, and spinal cord tracts and nerves carry the responding information back out to the effectors. In most of these loops, the structures of the nervous system make up more than one component, and carry out more than one function in these loops. It does not store any personal data.The nervous system is critical to many of our homeostatic feedback loops. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. The cookie is used to store the user consent for the cookies in the category "Performance". This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other. The cookies is used to store the user consent for the cookies in the category "Necessary". The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The cookie is used to store the user consent for the cookies in the category "Analytics". These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. ![]() The combination of a LMN and the muscle fibres it innervates is known as a motor unit. Therefore, the cell body of a LMN lies within the central nervous system (CNS). The cell body of a LMN lies within the ventral horn of the spinal cord or the brainstem motor nuclei of the cranial nerves which have motor modalities. In addition, neurons which input to the nuclei of the extrapyramidal tracts (such as the rubrospinal tract) are also UMNs.Ī lower motor neuron (LMN) is a multipolar neuron which connects the UMN to the skeletal muscle it innervates. Therefore neurons which give rise to the various descending motor tracts are all UMNs. The general definition of an UMN is a neuron whose cell body originates in the cerebral cortex or brainstem and terminates within the brainstem or spinal cord. These signs are known collectively as a UMN syndrome. ![]() We will then consider the two broad groups of motor neurons that are found within the nervous system.Īn upper motor neuron (UMN) is a term used to describe what is damaged when a patient displays a variety of neurological signs. The muscle stretch reflex is the most basic reflex pathway in the body and as such, understanding this allows understanding of more complex reflexes. A reflex is defined as an involuntary, unlearned, repeatable, automatic reaction to a specific stimulus which does not require input from the brain. Reflexes are commonly tested as part of an examination of the motor components of the nervous system. The lower motor neurones then directly innervate muscles to produce movement. The motor tracts can be functionally divided into two major groups: pyramidal and extrapyramidal tracts. The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones. The motor system is the components of the central and peripheral nervous system responsible for coordinating motor functions, i.e. ![]()
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