Paul McMenamin; Week 7 MED1011; Anatomy
Epineurium, perineurium and endoneurium travel in bundles with supporting elements. Motor horns are ventral to spinal cord, sensory dorsal. Rootlets are straight out of the spinal cord and only have one derivative (sensory or motor), roots are dorsal and ventral, then they combine to the mixed spinal nerve proper and then the rami. Grey and white rami communicantes connect to the sympathetic chain. Roots, Trunks, Divisions, Cords, Branches. Skin sensation has 5 modalities, fine touch, vibration, light touch, temperature, pain. Sensory stretch receptors in muscles outline how stretched the muscle is via muscle spindles which contain intrafusal fibres. Numbers of fibres vary in different muscles, abundant in muscles that work against gravity eg the back. Joints have rich proprioception and pain receptors. Sympathetics and parasympathetics may have complentary actions, independant actions or opposite actions. Second order neurons get to their destination by spinal nerves, cranial nerves, splanchic nerves, blood vessels. Nerves have a blood supply, especially bigger ones (vasa nervorum).
Carpal tunnel and tarsal tunnel entrapments can occur. Nerve injuries occur by severence. Cranial nerves have I and II from the forebrain, III and IV from the midbrain, V and VI from the pons and the rest from the medulla. Not present in spinal nerves are the visceral efferents (branchiomotor) which supply striated muscles from the pharyngeal/branchial arches; and special somatic afferents such as vestibulocochlear which controls hearing and balance and taste/smell.