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
1. Receptor
2. Sensory Neuron
3. Integration
Center
4. Motor Neuron
5. 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