- serious because AMITOTIC (don't divide) - if soma is intact, can be repaired - macrophages: remove debris - Schwann cells: regeneration tube, secrete growth factors - axons: regenerate damaged part

Chapter 13: Peripheral Nervous System and Reflexes Flashcards by Elizabeth Weiss

PNS

-Sensory receptors, peripheral nerves, associated ganglia, motor endings

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Sensory receptors

-activation results in depolarizations –> impulses to the CNS

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Sensory receptors by stimulus type

–mechanoreceptors (touch, pressure, vibration, stretch, itch
–thermoreceptors: temp
–photoreceptors: light
–chemoreceptors: chem (smell, taste, blood)
–nocioeptors: pain

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sensory receptors by location

Exteroceptors:
-touch, pressure, pain, temp
-include special sense
-stimuli arising outside body
Interoceptors
-within body
-internal viscera, blood vessels
-chem changes, stretch, temp
Proprioceptors:
-respond to degree of stretch
-where one is

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Sensory receptors by complexity

Simple:
-unencapsulated: free nerve endings (nocioreceptors, most proprioreceptors)
-encapsulated: specialized structures for particular sensing stimulus (exteroreceptors, most mechanoreceptors, corpuscles)
Complex:
-Special sense organs

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Sensation

awareness of changes

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Perception

Conscious interpretation of stimuli

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Somatosensory system

Receptor level: sensor receptors
Circuit level: ascending pathways
Perceptual level: neuronal circuits in cerebral corex

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Receptor-level processing

receptive field stimulated
Stimulus energy converted into graded potential
must reach generator potential (threshold) for action potential
Adaptation: unchanging stimulus (pain receptors and proprioceptors do not adapt)

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Circuit level processing

-conducting sensory impulses toward brain
First-order Neurons:
-sensory neurons themselves
-dorsal root/cranial ganglia to spinal cord/brain stem
Second order neurons
-dorsal horn of spinal cord/medullary nuclei to thalamus/cerebellum
Third order Neurons
-thalmus to somatosensory cortex of cerebrum

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Sensory perception

Perceptual detection: detecting that stimulus has occurred, summation
Magnitude estimation
Spacial discrimination: site/pattern
Feature abstraction: texture, shape
Quality discrimination: submodalities of sensation (sour/sweet)
Pattern recognition (like melody, familiar face)

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Nerve

-PNS axon enclosed by connective tissue
-Connective tissue coverings include:
Endoneurium (loose, surrounds axon)
Perineurium (course, bundles fibers into fascicles)
Epineurium (tough, fibrous sheath around nerve)

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Classification of nerves

Sensory: afferent, to CNS
Motor: efferent, from CNS
-Mixed: most common, contains both fibers

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Nerve fiber damage

serious because AMITOTIC (don’t divide)
if soma is intact, can be repaired
macrophages: remove debris
Schwann cells: regeneration tube, secrete growth factors
axons: regenerate damaged part

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Parasympathetic autonomic nervous system; parasympathetic ANS

4 of the 12 cranial nerves

- serve internal organs and glands

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Cranial nerve 1: olfactory

terminate in primary olfactory cortex

- carries afferent impulses for sense of smell

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Cranial nerve 2: optic

from retina
converge at optic chiasm
synapse at visual cortex
carries afferent impulses for vision

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Cranial nerve 3: oculomotor

from ventral midbrain to extrinsic eye muscles

- raising eyelid, directing eyeball, constricting iris, controlling lens shape

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cranial nerve 4: trochlear nerve

from dorsal midbrain to superior oblique muscle
motor nerve
directs eyeball

Cranial nerve 5: trigerminal

-sensory impulses from face to motor fibers for mastication (chewing)

Cranial nerve 6: abducens

inferior pons to orbit
motor nerve
lateral rectus muscle of eye

Cranial nerve 7: facial nerve

facial expression
lacrimal (eye, tears) and salivary glands
taste
mixed nerve

Cranial nerve 8: vestibulocochlear

inner ear
cochlear (hearing) and vestibular (balance, equilibrium)
solely sensory

Cranial nerve 9: glossopharyngeal

mixed nerve
motor: tongue, pharynx, parotid salivary gland
sensory: taste, general sensory impulses from tongue and pharynx

Cranial nerve 10: vagus nerve

- only cranial nerve that extends beyond head and neck - mixed nerve - most motor=parasympathetic to heart, lungs, and visceral organs - sensory: taste

Cranial nerve 11: accessory nerve

- motor nerve - fibers to larynx, pharynx, soft palate - innervates trapezius, sternocleidomastoid (move head and neck)

Cranial nerve 12: hypoglossal nerve

- extrinsic and intrinsic muscles of the tongue | - swallowing and speech

about spinal nerves

31 mixed nerves Each connects to spinal cord with two medial roots --ventral roots: from anterior horn, contain motor (efferent) fibers --dorsal roots: from dorsal root ganglion, contain sensory (afferent) fibers

the different types of spinal nerves

``` Named by where they leave vertebral column: 8 Cervical: C1-C8 12 Thoracic: T1-T12 (intercostal nerves) 5 Lumbar: L1-L5 5 Sacral: S1-15 1 Coccygeal: C0 ```

Rami of spinal nerves

- short spinal nerves branch into 3 or 4 mixed rami - small dorsal ramus - larger ventral ramus - tiny meningeal branh - Rami communicantes at base of ventral rami in thoracic (ANS fibers)

Nerve plexi

- all ventral rami except T2-T12 - damage to single spinal segment does not completely paralyze a muscle because muscle receives nerve fibers from more than one

intercostal nerves

supply muscles of the ribs, anterolateral thorax, and abdominal wall

Cervical plexus

- most important nerve is the phrenic nerve: major motor and sensory nerve of diaphragm - Ventral rami of C1-C4

Brachial plexus

- C5-C8 and T1 | - nerves that innervate upper limbs

Lumbar plexus

- L1-L4 - innervates thigh, abdominal wall, psoas muscle - major nerves: femoral and obturator - lumbarsacral plexus: many fibers of lumbar contribute to sacral plexus

Sacral plexus

L4-S4 - major nerve is sciatic: longest and thickest - Sciatic is composed of two nerves: tibial and fibular

Dermatomes

map constructed out of sensations: corresponding to origins of nerve fibers

reflex

-rapid, predictable motor response to stimulus -inborn (intrinsic) or learned (acquired) CNS a. brain b. spinal cord ---> REFLEX ACTIONS

Reflex arc (circuit)

1. receptor: site of stimulus 2. sensory neuron: transmits afferent impulse to CNS 3. integration center 4. motor neuron: conducts efferent impulses from to effector 5. effector: muscle fiber or gland corresponding to efferent impulse

Golgi tendon organs

- skeletal muscles - proprioceptors - level of tension

Muscle spindles

- skeletal muscles - length of muscles - made of intrafusal fibers (do not have myofilaments, no force generation, stretch receptors) - primary sensory endings: type Ia fibers OR - secondary sensory endings: type II fibers

muscle spindle operation

- activated by stretching - increased rate of action potential output from Ia fibers - shortening (contracting) muscles reduces tension (gamma motor nerve fibers)

stretch reflex

- activates muscle spindles | - ex: patellar reflex (quadriceps contract, antagonistic hamstrings relax)

flexor/crossed extensor reflex

- stimulated side is withdrawn | - contralateral side is extended

plantar reflex

- a superficial reflex - stimulating lateral aspect of sole of foot - normal response, downward flexion of toes - indirectly tests for proper coritcospinal tract functioning - Babinski's sign: abnormal, damage where great toe dorsiflexes and smaller toes fan laterally