Changes

==Sympathetic Nervous System==

==Sympathetic Nervous System==

[[Image:ANS.png|thumb|right|300px|''Autonomic Nervous System Schematic'' (Red = SNS & Blue = PNS), Gray's Anatomy, 1918, WikiMedia Commons]]

[[Image:ANS.png|thumb|right|300px|''Autonomic Nervous System Schematic'' (Red = SNS & Blue = PNS), Gray's Anatomy, 1918, WikiMedia Commons]]

The SNS is activated in stressful or physically demanding situations and can temporarily enhance the physical performance of the body in order to better cope with the stressor. The preganglionic neurons (see Basics section) of the SNS are found within the lateral horns of the spinal cord within the full length of the thoracic vertebrae and the cranial lumbar vertebrae. The number of vertebral segments containing SNS preganglionic neurones has wide variation depending on the species in question; horses have 18 thoracic segments, canines have 13 and humans have 12. In most domestic species, the cranial most 4 to 6 lumbar vertebrae contain SNS segments. These preganglionic segments are located like a string of beads along either side of the spinal cord and are referred to as ''sympathetic chain ganglia''. In most cases the number of sympathetic ganglia exceeds the number of spinal cord vertebrae containing the preganglionic cell bodies. Within the abdominal cavity ventral to the lumbar vertebrae there are three sympathetic ganglia called the ''prevertebral ganglia''.

The SNS is activated in stressful or physically demanding situations and can temporarily enhance the physical performance of the body in order to better cope with the stressor; it is often referred to as the ''fight or flight'' system. The sympathetic division of the ANS has a thoracolumbar outflow from the CNS. The preganglionic neurons (see Basics section) of the SNS are found within the grey matter of the lateral horns of the spinal cord within the full length of the thoracic vertebrae and the cranial lumbar vertebrae. Preganglionic neurones in the SNS are relatively short. The number of vertebral segments containing SNS preganglionic neurones has wide variation depending on the species in question; horses have 18 thoracic segments, canines have 13 and humans have 12. In most domestic species, the cranial most 4 to 6 lumbar vertebrae contain SNS segments. These preganglionic segments are located like a string of beads along either side of the spinal cord and are referred to as ''sympathetic chain ganglia''. In most cases the number of sympathetic ganglia exceeds the number of spinal cord vertebrae containing the preganglionic cell bodies. SNS axones exit the spinal cord via the ventral root allowing the formation of the sympethetic trunk via processes called ''white rami communicantes'' which are heavily myelinated. On entry to the sympathetic trunk, there are three possibilities for the neuron. Firstly the SNS neuron could immediately synapse within the sympathetic trunk itself. Secondly it could run up or down the sympathetic trunk prior to synapsing or finally it could leave the sympathetic trunk without synapsing at all and instead run to ''collateral ganglia''. Within the abdominal cavity ventral to the lumbar vertebrae there are three sympathetic ganglia called the ''prevertebral ganglia'' where this form of specialised synapsing occurs. The prevertebral ganglia are made up of the ''cranial mesenteric'', ''caudal mesenteric'' and ''coeliac''. Postganglionic fibres from these ganglia distribute to abdominal and pelvic organs.

<br />

<br />

<br />

<br />