Exam (elaborations) BSC 2346 (BSC2346) BSC 2346 Module 08 Lab Worksheet: Peripheral Nervous System

BSC 2346 Module 08 Lab Worksheet: Peripheral Nervous System. Introduction This week’s lab will focus on the peripheral nervous system, the cranial nerves and testing these components of the nervous system. Objectives Objectives for this week’s lab include: 1) Identify the components of the peripheral nervous system, 2) Identify the cranial nerves, and 3) Differentiate upper versus lower motor neurons and lesions. Overview The peripheral nervous system (PNS) consists of all the neural structures outside of the central nervous system (CNS) including the peripheral nerves, sensory receptors, ganglia and efferent motor endings. The PNS is divided into a sensory (also referred to as afferent) division and a motor (also referred to as efferent) division. The sensory division transmits neural information from the body, including the internal organs, to the CNS and the motor division transmits neural information from the CNS to the body. A peripheral nerve is a bundle of individual axons of neurons. One peripheral nerve can literally have hundreds and even thousands of axons of sensory and motor neurons. Peripheral nerves originate from one of the 31 pairs of spinal nerves and form nerve plexuses- a complex network of spinal nerves joining together. Nerve plexuses occur in the cervical, brachial, lumbar and sacral regions of the body. The 12 pairs of cranial nerves (CN) originate from the brain and brain stem, unlike the 31 pairs of spinal nerves which originate from the spinal cord. The cranial nerves are considered a portion of the PNS due to the fact their axons extend beyond the brain. The only exception is with cranial nerve II (optic nerve), it is technically considered part of the diencephalon. The CN have specific functions within the body, mainly in the head region such as movement of the eyes, muscles of the face, the tongue and so forth but CN X (vagus nerve) has strong parasympathetic stimulation throughout the majority of organs in the thoracic and abdominal cavities. Part of the neurological testing within this lab will assess the CN. A dermatome refers to a specific area of skin that is innervated by a branch of a single spinal nerve. A dermatome map of the body is demonstrated in “Appendix A”. You can determine the area of damage to the spinal cord and/or specific spinal nerve by testing the dermatomes. Reflexes can be classified as inborn or learned but both are developed to help maintain homeostasis to varying degrees. Inborn or intrinsic reflexes are extremely fast, controlled and predictable motor responses to a stimulus. Intrinsic reflexes have very specific neural pathways called reflex arcs and technically have five components to them. Reflexes will create an expected response upon a specific stimulus and is executed prior to conscious perception. Upper motor neurons (UMN) are neurons that originate in the cerebral cortex or brainstem and travel to the body via a few different motor spinal tracts. These motor neurons ultimately stimulate skeletal muscle movement. Lower motor neurons (LMN) connect the UMN to the skeletal muscles and are found outside of the CNS. A lesion, or damage, to either a UMN or LMN will cause specific characteristics to muscle tone, reflexes, muscle strength and voluntary/involuntary muscle movements. Please see “Appendix C” regarding these characteristic differences. Performing a neurological test will help differentiate between an UMN lesion and a LMN lesion.