Nerve Impingement

Hubner et al. 2000 Kayser et al. 2003). In specific settings, US is an efficient means to detect interposition of soft tissues within the fracture line that can interfere with healing, as well as to identify nerve impingement between fracture fragments or inside a callus (see Chapters 4, 7) (Sooner et al. 1999,2001 Tukenmez et al. 2006). 

There is now evidence that the mammalian central nervous system contains several dozen neurotransmitters such as acetylcholine, noradrenaline, dopamine and 5-hydroxytryptamine (5-HT), together with many more co-transmitters, which are mainly small peptides such as met-enkephalin and neuromodulators such as the prostaglandins. It is well established that any one nerve cell may be influenced by more than one of these transmitters at any time. If, for example, the inhibitory amino acids (GABA or glycine) activate a cell membrane then the activity of the membrane will be depressed, whereas if the excitatory amino acid glutamate activates the nerve membrane, activity will be increased. The final response of the nerve cell that receives all this information will thus depend on the balance between the various stimuli that impinge upon it. 

When you look at a circle moving in Flatland, your 2-D retina captures a circular pattern impinging on the nerve cells. Each point in the circle corresponds to a light ray from the circle to a single point in your retina. If you are looking from above, each ray goes up to your eye. If a 4-... 

Skeletal muscle spasms are used to describe the increased tension often seen in skeletal muscle after certain musculoskeletal injuries and inflammation (muscle strains, nerve root impingements, etc.) occur.20,96 This tension is involuntary, so the patient is unable to relax the muscle. Spasms differ from spasticity because spasms typically arise from an orthopedic injury to a musculoskeletal structure or peripheral nerve root rather than an injury to the CNS. Likewise, muscle spasms are often a continuous, tonic contraction of specific muscles rather than the velocity-dependent increase in stretch reflex activity commonly associated with spasticity. The exact reasons for muscle spasms are poorly understood. According to some authorities, muscle spasms occur because a vicious cycle is created when the initial injury causes muscular pain and spasm, which increases afferent nociceptive input to the spinal cord, further exciting the alpha motor neuron to cause more spasms, and so on.61,96 Other experts believe that muscle spasms occur because of a complex protective mechanism, whereby muscular contractions are intended to support an injured vertebral structure or peripheral joint.96 Regardless of the exact reason, tonic contraction of the affected muscle is often quite painful because of the buildup of pain-mediating metabolites (e.g., lactate). 

When a sound pressure wave impinges on the ear, it is amplified by the external auditory meatus and causes the tympanic membrane to vibrate in a characteristic manner. This vibration is transformed by the auditory ossicles of the middle ear into movements of the stapedial footplate. These movements create pressure waves in the fluids of the inner ear which displace the basilar membrane of the cochlear duct and cause the hair cells located on the top of the basilar membrane to generate electrical potentials. This potential elicits impulses in the auditory nerve. After the auditory nerve, the nerve impulses are transmitted through the cochlear nuclei, the trapezoid body, the... 

The nerve axon in figure 7-F impinges back on itself and releases its neurotransmitter norepinephrine (also called noradrenaline, hence the term "noradrenergic hypothesis"). The neurotransmitter typically stimulates inhibitory receptors on the... 

The po.ssible existence of a junction between muscle and nerve was suggested as early as 1856, when Claude Bernard ob.servcd that the site of action of curare was neither the nerve nor the muscle. Since that lime, it has been agreed that ACh mediates transmission at the neuromuscular junction by a sequence of events described above in this chapter. The neuromuscular junction consists of the axon impinging onto a specialised area of the mu.scle known as the muscle end plate. The axon is covered with a myelin sheath, containing the nodes of Ranvier, but is bare at the ending. The nerve terminal is separated from the end plate by a gap of 200 A. The subsynaptic membrane of the end plate contains the cholincigic receptor, the ion-conducting channels (which are opened under the influence of ACh), and AChE. 

Certain other substances (tetanus toxin) reach nerve cells directly via distal axonal entry. Tetanus toxin is transported to the spinal anterior horn cell, subsequently translocates and binds to presynaptic inhibitory (glycinergic) nerve terminals impinging on the motor nerve cell, and thereby suppresses the inhibition of motor neuron activity leading to hyperexcitation. Violent and sustained muscle contraction (tetany) results in response to external stimulation. Another example of peripheral entry to the CNS is the transport and delivery of metals (manganese, aluminum) from the nose along olfactory neurons to the brain of laboratory animals. 

Still other integral membrane proteins, most common in the cell membrane of nerve cells, contain transmembrane channels that open with the proper stimuli, letting sodium ions rush in (depolarizing the membrane) as an excitatory action that activates neural networks required for thought processes. Additionally, nerve cell processes impinging on muscle cells depolarize and in turn activate channel... 

In addition, other elements such as epineuriem and supportive fet may be directly affected by protruded disc and in turn directly affect the contents of the intervertebral foramina. Besides the segmental nerve, arteries and veins may likewise be compressed, bringing about vascular stasis. The loss of shock absorption, inflammation, and edema may lead to back pain. Impingement on a nerve root may lead to a radiculopathy into an extremity. 

When examining the elbow, it may be appropriate to test the deep tendon reflexes at the elbow and forearm. This is most commonly performed to rule out the compression/impinge-ment of the nerves exiting from the foramina of the cervical spine. 

These two tunnels in particular are significant in that each contains a major nerve to the hand, which has a small diameter space through which the nerve passes. Tendons of the wrist and fingers occupy the greater part of that space. This makes impingement of the nerve a possibility when the diameter is narrowed by swelling, displacement of a bone, fibrous bands, or scar tissue. 

This case is a good example of multiple impingement syndromes. Besides the obvious carpal tunnel, A.M. had some additional impingement of the median nerve as it passes by the pronator teres. The tension in the soft tissues at the thoracic inlet impinged the nerves of the brachial plexus as they passed through the costoclavicular space. It is important to remember that when there is a fall on the rigid arm, the force is transmitted all the way to the neck. In A.M. s case,... 

Impingement neuropathies occur when surrounding tissues entrap a nerve, causing mechanical irritation or injury to the nerve. The most common ones occur to nerves of the upper or lower extremity and are discussed in those sections of this book. 

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