Category Archives: Nervous system

Synaptic Transmission

Ever wondered how sensory and motor functions are accomplished by the nerves? These are carried out by a process called neurotransmission or synaptic transmission between nerve endings. Nerve endings possess vesicles containing neurotransmitters which are signalling molecules released during transmission of signals between nerve endings. To propagate signals for motor or sensory functions the released neurotransmitters bind to the adjoining nerve ending and cause a series of cell changes that result in nerve impulses. These ultimately lead to muscle action, release of bodily secretions and other organ functions.

The orange and blue vesicles in this image captured by scanning electron microscopy contain neurotransmitters that are released from nerve endings (green) during synaptic transmission. (from Brighthub.com – link)

Image source: brighthub.com

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Myelinated Axons SEM

The main purpose of a myelin layer (or sheath) is to increase the speed at which impulsespropagate along the myelinated fiber. Along unmyelinated fibers, impulses move continuously as waves, but in myelinated fibers, they hop or “propagate by saltation.” Myelin decreases capacitance across the cell membrane, and increases electrical resistance. Thus, myelination helps prevent the electrical current from leaving the axon. (from wikipedia)
Image from 2012 National Center for Microscopy and Imaging Research. Image by Thomas Deerinck.

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Thoracolumbar Fracture

A 44-year-old man presented to the emergency department with severe pain after an accident at the gym. He reported he had been doing squats while balancing a 200-kg bar across his trapezius. His knee gave way and he fell to the floor, with the weight landing on his lower back. The patient managed to crawl out from under the weight but did not attempt to walk. On arrival at the emergency department he had full power in both lower limbs and normal sensation to light touch in all dermatomes of the lower limbs. The area over vertebral bodies T11 through L2 was exquisitely tender. Initial frontal and lateral plain films  and an axial computed tomographic study of the area from T12 through L1  showed fracture–dislocation. (Reblogged from NEJM -link)

Image from NEJM   Photo by Laura Jane Evans, MB, BS

The patient was taken to the operating room that night for open reduction and internal fixation of the fracture–dislocation of vertebral bodies T12 through L1. Postoperatively, he had preservation of normal neurologic function, with the exception of mild paresthesia on both sides of his trunk in a T12 dermatomal distribution.

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Neuromuscular Junction TEM

The neuromuscular junction is synapse or junction located at the motor end plate where motor neurons synapse on muscle fibers, also known as a muscle cells. As an action potential reaches the end of a motor neuron, voltage gated calcium channels open allowing calcium to enter the neuron.

Image from Karlsruhe Institute of Technology (link)

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