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The C8 nerve contributes to the motor innervation of many of the muscles in the trunk and upper limb. Its primary function is the flexion of the fingers, and this is used as the clinical test for C8 integrity, in conjunction with the finger jerk reflex.
The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5, C6, C7, C8, and T1).This plexus extends from the spinal cord, through the cervicoaxillary canal in the neck, over the first rib, and into the armpit, it supplies afferent and efferent nerve fibers to the chest, shoulder, arm, forearm, and hand.
The test can be performed by tapping the triceps tendon [3] [note 1] with the sharp end of a reflex hammer while the forearm is hanging loose at a right angle to the arm. A sudden contraction of the triceps muscle causes extension, [note 2] and indicates a normal reflex. [4] [5]
This is true for all spinal nerves except for the first spinal nerve pair (C1), which emerges between the occipital bone and the atlas (the first vertebra). [3] Thus the cervical nerves are numbered by the vertebra below, except spinal nerve C8, which exists below vertebra C7 and above vertebra T1.
The cervical spinal nerve 7 (C7) is a spinal nerve of the cervical segment. [1] It originates from the spinal column from above the cervical vertebra 7 (C7). It runs through the interspace between the C6 and C7 vertebrae.
An action potential (or nerve impulse) is a transient alteration of the transmembrane voltage (or membrane potential) across the membrane in an excitable cell generated by the activity of voltage-gated ion channels embedded in the membrane. The best known action potentials are pulse-like waves that travel along the axons of neurons.
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Cutaneous innervation of the upper limbs is the nerve supply to areas of the skin of the upper limbs (including the arm, forearm, and hand) which are supplied by specific cutaneous nerves. Modern texts are in agreement about which areas of the skin are served by which cutaneous nerves, but there are minor variations in some of the details.