The Peripheral Nervous System Chapter 13-14

Nervous System Structural Overview

Peripheral Nervous System All neural structures outside of the brain and spinal cord. Includes sensory receptors, peripheral nerves, ganglia, and efferent motor endings.

Sensory Receptors Respond to specific changes in their environment called stimuli General Sensory Receptors: Free nerve endings Tactile (Merkel) discs Hair follicle receptors Tactile (meissner’s) Corpuscles Lamellar (pacinian) corpuscles Ruffini Endings Muscle Spindles Tendon organs

Somatosensory Neural Integration Three main levels of neural integration in the sensory system Receptor Level Circuit Level Perceptual Level

Processing at the Receptor Level Step 1: Stimulus excites receptor and action potentials reach the CNS Stimulus must match the specificity of the receptor stimulus must be applied within the receptor field stimulus must be converted into a graded potential (transduction) Adaptation

Processing at the Circuit Level Step 2: Impulses must be delivered to the appropriate region of the cortex for localization and perception of the stimulus.

Processing at the Perceptual Level Step 3: Sensory input is interpreted in the cerebral cortex

Perception of Pain Activated by extremes of pressure or temperature Sharp, then aching/burning. A delta, c fibers Based on situation Pain threshold versus pain tolerance

Nerves Cord-like organs composed of bundles of axons. Connective tissue wrappings: endoneurium, perineurium (fascicles), epineurium. Nerves classified by transmission direction: Sensory nerves, motor nerve, mixed nerves.

Peripheral Motor Endings The Neuromuscular Junction

Motor Integration Levels of Motor Control: The Segmental Level (reflexes, CPG’s) The Projection Level (initiate voluntary movement, oversee the segmental level). The Precommand Level (Cerebellum, basal nuclei: coordination, timing, start/stop)

Reflex Activity The Reflex Arc inborn or learned

Components of a Reflex Arc Receptor Sensory Neuron Integration Center Motor Neuron Effector Can be either somatic or autonomic

Spinal Reflexes Stretch Reflex

Spinal Reflexes The Tendon Reflex

Spinal Reflexes The Flexor and Crossed Extensor Reflexes

Superficial Reflexes

The Autonomic Nervous System

ANS Divisions and Roles Parasympathetic Division Rest and Digest Division Keeps body energy as low as possible Sympathetic Nervous System Fight or Flight System Prepares body for emergency situations

Comparison of Somatic NS and ANS

ANS Anatomy Dual Innervation Sites of Origin Relative lengths of their fibers Location of their ganglia

ANS Anatomy Parasympathetic (craniosacral) Division Cranial part Occulomotor N. Facial N. Glossopharyngeal N. Vagus N. (Multiple Plexi) Sacral Part Pelvic Splanchic n. Inferior hypogastric plexus

ANS Anatomy Sympathetic (Thoracolumbar division) Preganglionic fibers arise from Lateral Horns of segments T1-L2

ANS Anatomy Sympathetic trunks and pathways

3 Pathways of Synaptic Innervation Synapse at the Same Level

3 Pathways of Synaptic Innervation Synapse at a higher or lower level

3 Pathways of Synaptic Innervation Synapse in a distant collateral ganglion anterior to the vertebral column

ANS Physiology Neurotransmitters and Receptors Acetylcholine Released by all ANS Preganglionic axons and all parasympathetic postganglionic axons (cholinergic fibers) Norepinephrine Most sympathetic postganglionic axons (adrenergic fibers)

Cholinergic Receptors Nicotinic Receptors Found on sarcolemma of skeletal fibers, all postganglionic neurons, adrenal medulla Muscarinic Receptors Parasympathetic target organs

Adrenergic Receptors alpha and beta receptors alpha 1, 2, Beta 1, 2, 3. can be either excitatory or inhibitory

Pharmacological Effects Atropine (anticholinergic) Neostigmine (anticholinesterase) B2 activators (dilate airways) Beta Blockers (slow heart rate, lower BP)

Interactions of the Autonomic Divisions Dual Innervation Antagonistic Interactions Sympathetic and Parasympathetic Tone Unique roles of the Sympathetic Division thermoregulatory response to heat, renin release, metabolic effects Localized Versus diffuse effects

Control of Autonomic Function Brain Stem and Spinal Cord controls Hypothalamic Controls Cortical Controls