Peripheral somatic nerves consists generally of somatic-motor, autonomic-motor and sensible fibres.
The cell bodys of somatomotor fibres for the striated musculature are always lying in the brainstem (12 pare cerebral nerves) or the fore horn of the whole spinal medulla. The stimulus runs from central to peripheral (efferent). The lateral cutaneous femoral nerve consists of sensible fibres and no motor fibres. The shiatic nerve consists of 20% motor fibres, 30% sensible, and 50% sympathetic fibres. The gluteal nerves consist of pure motor fibres, sympathetic fibres and no sensible fibres. 1,2
The autonomic-motor fibres for the smooth muscles of the blood and lymphatic vessels are of sympathetic origin. Venes are not innervated. They function by the musculare pump system and in some cases by valves. The cells bodies of the autonomic-motor fibres are situated in the lateral horn between C8-L2. They are termed: the centro-ganglionar neurons. All motor neurons, situated in the spinal medulla go via the fore horn to the peripheral nerve. It must be mentioned that all smooth muscles can contract without external innervation (for example: heart, gut). This is due to the intrinsic nerve system with is influenced by the sympathetic and parasympathetic nervous system. 3-5
The sensible fibres for somatic structures originate from muscles, tendons, capsules, joints, ligaments and bones. Their cell bodies are lying in the spinal ganglions of the corresponding nerve (= afferent). 2,6
The cell bodies of the sensible fibres for autonomic structures are situated in the spinal ganglions of the segments where the sympathetic neurons start (SI-joint: T11-L1). The peripheral autonomic nerve contains generally autonomic-motor and sensible fibres and serves for the innervation of organs. Glands are always dubble innervated (sympathetic and parasympathetic), except for the adrenals. 2 Examples:
– The femoral arterie contains sensible fibres which go to the spinal ganglions and arrive in the dorsal horn where connections exist, via intercalar neurons, with the origins of the sympathethic fibres of the levels T10-T11.
– Knee joint: is sensible innervated via the sciatic nerve (posterior side of the knee), but in the knee capsule, sensible fibres exist which connect via the femoral arterie the levels T10-T12.
Peripheral autonomic nerves consist of autonomic-motor and sensible fibres. They innervate organs and glands.
The cell bodies of viscero-sensible nerve fibres are situated in the spinal ganglions of those segments from where the sympathetic and parasympathetic neurons start. Example: the pelvis organs: S2-S4 and/or TLJ (= thoracolumbar junction). The TLJ receives a lot of information.
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