Peter J. Hand, V.M.D.,Ph.D.Professor Emeritus of AnatomyDepartment of Animal BiologySchool of Veterinary MedicineUniversity of PennsylvaniaGROSS ANATOMY LECTURE 4Peripheral Nervous System Somatic Division

Peripheral Nervous System (PNS)What is the Pattern of Spinal Nerve Branching? Branches of the Segmental-type of Spinal Nerve (Thoracic level)

Somitogenesis Pairs of somites forming along side the neural tube in a developing embryo give rise to the structures of a single body segmentWhat is the Pattern of Spinal Nerve Branching? Branches of the Segmental-type of Spinal Nerve (Thoracic level)Spinal Nerves and Their Attachment to the Spinal Cord Cat Cervical Spinal Nerves

Neurocytology

What histological components of a nerve cell are present in a peripheral nerve?

Cross Section of a Typical Peripheral Nerve

Neurocytology

What neurons look like - their processes Motor neurons Sensory neurons

Conventions in Depicting Neurons

Sensory Neurons Carry Information to the CNS

What is the Pattern of Spinal Nerve Branching? Branches of the Segmental-type of Spinal Nerve (Thoracic level)Branches of a Spinal Nerve: Fiber (meaning axons) types (or neuron types) that are in spinal nerves and their branches

Brachial Plexus Formed by Interconnections Among Ventral Rami of Spinal Nerves

Sensory Innervation of the Axial Body Parts

Each Spinal cord segment innervates a particular skin zone called a dermatome. Or, all the skin sensory neurons entering a single spinal cord segment via its dorsal root innervate a single band of skin referred to as a dermatome. Dermatomes are vertically oriented bands and occur along the trunk in the same order as the spinal cord segments innervating them. There is overlap.*** Dermatomes are more difficult to plot on the limbs but roughly go down the cranial surface and up the caudal surface with a fair amount of overlap