55 terms

Peripheral Nervous System Exam 2


Terms in this set (...)

collection of axons (neurons)
Peripheral Nerves
1. Cranial Nerves
2. Spinal nerves
3. Peripheral Nerves
Types of Nerves
1. Sensory (afferent) nerves
2. Motor (efferent) nerves
3. Mixed (most) nerves
Sensory (afferent) nerves
impulses TOWARD central nervous system
Motor (efferent) nerves
impulses AWAY central nervous system
Mixed Nerves
BOTH sensory and motor
impulses BOTH to and from CNS

spinal nerves are mixed nerves
Regeneration of Nerve Fibers
Mature neurons are mostly AMITOTIC (don't divide and reproduce)

if cell body of damaged nerve is intact peripheral axon may REGENERATE

greater distance between severed ends equal less chance of regeneration
collection of neuron cell bodies association with nerves in PNS
-association with afferent nerve fibers contain cell bodies of sensory neurons
(Dorsal Root Ganglion)
Regeneration of a nerve fiber in PNS
1. axon becomes fragmented at injury site
2. Macrophages clean out the dead axon distal to the injury (clear a pathway)
3. Axon sprouts grow through a regeneration tube formed by Shwann cells
4. Axon regenerates and a new myelin sheath is formed (regenerate @ 1.5mm/day)
Most CNS fibers NEVER regenerate
1. CNS oligodendrocytes have growth-inhibiting proteins that prevent CNS fiber regeneration
2. Astrocytes (blood brain barrier) @ injury site form scar tissue that blocks axonal regrowth
Sensory Receptors
specialized to respond to changes in environment (stimuli)

activation causes production of a graded potential that triggers an AP to CNS
Classifications based on Sensory Receptors
1. types of stimuli they detect
2. structural complexity
Classification by Stimulus Type
Nociceptors-sensitive to pain- causing stimuli

extreme heat or cold
excessive pressure

Noci (inflammatory chemicals)
respond to stretch in skeletal muscles, tendons, joints, and ligaments

position of your limb

inform brain of one's movements
respond to light energy
respond to chemicals: smell, taste, changes in blood chemistry
respond to a mechanical force
pressure, touch, stretch (free nerve endings)
Classification by Receptor Structure
Receptors for
1. General Senses
-simple receptors modified dendritic endings of sensory neurons
2. Special Senses
-complex sense organs
-vision, hearing, equilibrium, smell, and taste
-found in the head
Simple Receptors of the General Senses
Nonencapsulated (free) nerve endings

respond to
-temperature and pain
-pressure-induced tissue movement
Types of Nonencapsulated Dendritic Endings
Light Touch Receptors
-Tactile (Merkel) discs
-Hair Follicle Receptors
Types of Encapsulated Dendritic Endings
1. Tactile (Meissner's ) Corpuscle
2. Lamellar (Pacinian) Corpuscle
3. Ruffini Endings
Tactile (Meissner's) Corpusle
in dermal papilla

discriminative touch (where you're being touched)
Lamellar (Pacinian) Corpuscle
deep pressure and vibration (deep in dermis)
Ruffini Endings
deep CONTINUOUS pressure (in dermis, lack adaptation)
Encapsulated Dendritic Endings
Muscle spindles
Detect Muscle Stretch
Tendon Organs-stretch in tendons

Free Nerve Ending
pain and temperature most superficial

Tactile Corpuscle
fine touch/dermal papilla-eyelids fingertips

Ruffini Corpuscle
pressure and distortion/ skin (lack of adaptation)

Lamellated Corpuscle
deep press and vibration/ deep dermis, joint capsule
Stimulus energy converted into a graded potential (GP)
Receptor Region is Part of a Sensory Neuron
1. Stimulus
2. Generator Potential (GP) in Afferent Neuron
3. Action Potential

4. free nerve endings
Receptor is a Separate Cell
1. Stimulus
2. GP=Receptor Potential
3. affect amount of NT released
4. NTs generate GP in sensory neuron
Referred Pain
Pain from one body region perceived from different region
Visceral and somatic pain fibers travel in same nerves
Brain assumes stimulus from somatic region
Olfactory (I)
Odor detection
Optic (II)
Sight (vision)
Oculomotor (III)
Trochlear (IV)
Abducens (VI)
Movement of eye
Trigeminal (V)
SENSORY: from the face (*3 branches)
MOTOR: chewing
Facial (VII)
SENSORY: from anterior 2/3 of tongue (taste)
MOTOR: to face
Vestibulocochlear (VIII)
Hearing and Balance
Glossopharyngeal (IV)
SENSORY: from posterior 1/3 of tongue (taste)
MOTOR: pharynx elevation
Vagus (X)
SENSORY: visceral
MOTOR: pharynx and larynx

Parasympathetic Motor-visceral smooth muscle, heart, and lungs

ONLY CN to extend beyond head and neck to thorax and abdomen
Accessory (XI)
Neck and Upper Back
Hypoglassal (XII)
Tongue (stick out tongue)
Spinal Nerves: Ventral Roots
Contain motor (efferent) fibers from ventral horn motor neurons
Fibers innervate skeletal muscles
Spinal Nerves: Dorsal Roots
Contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors
Dorsal and Ventral Roots unite to form spinal cords
Rapid predictable response to a stimulus
Occur over specific neural paths (REFLEX ARC)
5 components of Reflex Arc
1. Receptor
2. Sensory Neuron
3. Integration Center
4. Motor Neuron
5. Effector
Stretch Reflex
Maintains muscle tone in large postural muscles and adjusts it reflexively
-causes muscle contraction in response to increased muscle length (stretch)

Monosynaptic and Ipsilateral
Same side
Muscle Fibers
Unstretched Muscle
AP are generated at a constant rate in associated sensory fiber
Stretched Muscle
Stretching activates the muscle spindle, increasing the rate of APs
Stretch Reflex (Patellar Reflex)
1. Tap patellar ligament
2. Stretches the quadriceps
3. Excites its muscles spindles

4. Afferent Impulses
5. To the Spinal Cord
6. Synapses with motor neurons + interneurons

7. The motor neurons sends impulses to the quadriceps
8. Contraction
9. Extension of the knee

10. The interneurons make inhibitory synapses with ventral horn neurons that prevent the hamstrings from resisting the contraction of the quadriceps
Reflex Reactions Indicate
Sensory and motor connections between muscle and spinal cord intact

If NO response, something is wrong in 1 of these areas or ALL.