Root avulsion injury can be further divided based on the location of the lesion: pre- and postganglionic lesions. In a preganglionic lesion, the sensory fibre remain attached to the cell body of the sensory ganglion, thus there is no wallerian degeneration of the sensory fibre, thus sensory action potential can still be detected at the distal end of the spinal nerve. However, those who get this type of lesion have sensory loss over the affected nerve roots. In this case, surgical repair of the lesion is not possible because the proximal nerve tissue is too short for stitching to be possible. For postganglionic lesions, the cell body of the sensory ganglion is detached from the spinal nerve, leading to wallerian degeneration of the sensory fibre. Thus, no action potential detected at the distal end of spinal nerve. However, surgical repair is possible because proximal nerve tissue has enough length for stitching. Impact
Heavy impact to the shoulder is the second common mechanism to causing injury to the brachial plexus. Depending on the severity of the impact, lesions can occur at all nerves in the brachial plexus. The location of impact also affects the severity of the injury and depending on the location the nerves of the brachial plexus may be ruptured or avulsed. When passing through between the clavicle and first rib, the brachial plexus may be crushed in the costoclavicular space. This is usually due to direct trauma to the shoulder or neck region as a result of motorvehicular accidents, occupational injuries or sports injuries.
Reflex bradycardia is a bradycardia (decrease in heart rate) in response to the baroreceptor reflex, one of the bodys homeostatic mechanisms for preventing abnormal increases in blood pressure. In the presence of high mean arterial pressure, the baroreceptor reflex produces a reflex bradycardia as a method of decreasing blood pressure by decreasing cardiac output.Blood pressure (BP) is determined by cardiac output (CO) and total peripheral resistance (TPR), as represented by the formula BP = CO x TPR. Cardiac output (CO) is affected by two factors, the heart rate (HR) and the stroke volume (SV), the volume of blood pumped from one ventricle of the heart with each beat (CO = HR x SV, therefore BP = HR x SV x TPR). In reflex bradycardia, blood pressure is reduced by decreasing cardiac output (CO) via a decrease in heart rate (HR).An increase in blood pressure can be caused by increased cardiac output, increased total peripheral resistance, or both. The baroreceptors in the carotid sinus sense this increase in blood pressure and relay the information to the cardiovascular centres in the medulla oblongata. In order to maintain homeostasis, the cardiovascular centres activate the parasympathetic nervous system. Via the vagus nerve, the parasympathetic nervous system stimulates neurons that release the neurotransmitter acetylcholine (ACh) at synapses with cardiac muscle cells.