The Somatic Nervous System Introduction and structure Jennifer Carbrey Ph.D. Department of Cell Biology Somatic Nervous System Review of general principles Spinal cord structure Define motor unit Neuromuscular junction Control of Movement Types of lower motor neurons Types of muscle sensory receptors Reflexes Locomotion Nervous System Organization Somatic Nervous System sympathetic NS CNS organs acetylcholine, norepi, nicotinic AChR adrenergic adrenal gland CNS epinephrine released into blood organs acetylcholine, epinephrine, nicotinic AChR adrenergic parasympathetic NS CNS organs acetylcholine, acetylcholine, nicotinic AChR muscarinic AChR somatic NS skeletal Somatic motor programs serve essential needs CNS muscle (i.e., locomotion, posture, breathing) and range acetylcholine, from involuntary actions (withdrawal reflexes) to nicotinic AChR complex voluntary activities. Spinal Cord Structure image by Ruth Lawson Otago Polytechnic (modified), Creative Commons Attribution 3.0 Unported license http://commons.wikimedia.org/wiki/File:Anatomy_and_physiology_of_animals_Relation_btw_sensory,_relay_%26_motor_neurons.jpg, Motor Unit one neuron can control from 3-1000 fibers, all will be in the same muscle, usually spread out a muscle fiber is usually innervated by a single neuron A MOTOR UNIT consists of a motor neuron and all of the muscle fibers it controls. image by OCAL (modified), http://www.clker.com/profile-1068.html, public domain Neuromuscular Junction action axon terminal potential voltage- Ca2+ gated 2+ Ca 2+ channels Ca Acetylcholine released by somatic motor neuron postsynaptic cell Muscle motor end plate contains nicotinic AChR Sarcolemma (muscle PM) contains voltage-gated channels image by OCAL (modified), http://www.clker.com/clipart-26784.html, public domain Key Concepts Somatic nervous system controls locomotion, fine movements, body posture, and equilibrium by acting on motor neurons in the spinal cord that innervate skeletal muscles. A motor neuron and the muscle fibers that it innervates constitute a motor unit. Motor neurons have cell bodies located in grey matter of the ventral horn of the spinal cord. The spinal cord contains interneurons which play a role in coordinating the responses of antagonistic and synergistic muscles to carry out intended movements as well as reflexive movements initiated by sensory receptors. .