THE NERVOUS SYSTEM Peripheral Nervous System PNS Composed

THE NERVOUS SYSTEM Peripheral Nervous System

PNS � Composed of nerves and ganglia outside the CNS

Nerve Structure � Neuron fibers axons surrounded by endoneurium � Fasicle – group of neuron fibers surrounded by perineurium � Nerve – several fasicles and blood vessels surrounded by epineurium

Nerve Classification � � Based on direction of impulse 1. Afferent or Sensory – toward CNS 2. Efferent or Motor – away from CNS toward effector (muscle or gland) 3. Mixed Nerves – both sensory and motor *ALL spinal nerves are mixed

Cranial Nerves � � 12 pair – 2 forebrain and 10 brainstem Go mostly to head and neck – exception is vagus nerve to abdominal viscera

Cranial Nerves � � � I – olfactory = sensory II – optic = sensory III – oculomotor = motor IV – trochlear = motor V – trigeminal = mixed VI – abducens = motor VII – facial = mixed VIII – vestibuchochlear = sensory IX – glossopharyngeal = mixed X – vagus = mixed XI – accessory = motor XII – hypoglossal = motor

Spinal Nerves � � 31 pairs ALL ARE MIXED Formed by combining of dorsal and ventral roots Approximately ½” long then splits into rami Named for region of spinal cord from which they arise � Cervical � Thoracic � Lumbar � Sacral � Coccyx

PNS Organization

PNS - Autonomic SYMPATHETIC � � Fight or Flight NT= norepinephrine PARASYMPATHETIC � � Resting and Digesting NT= acetylcholine