Chapter 13- The Peripheral Nervous System

Front 1

Peripheral Nervous System (PNS) includes what?

Back 1

all neural structures outside the brain and spinal cord

Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings

Provides links to and from the external environment

Front 2

Sensory Receptors

Back 2

Structures specialized to respond to stimuli

The realization of these stimuli, sensation and perception, occur in the brain

Front 3

The activation of sensory receptors results in:

Back 3

depolarizations that trigger impulses to the CNS

Front 4

Receptor Classification by Stimulus TYPE

Back 4

Mechanoreceptors
Thermoreceptors
Photoreceptors
Chemoreceptors
Nociceptors

Front 5

Mechanoreceptors

Back 5

respond to touch, pressure, vibration, stretch, and itch

Front 6

Thermoreceptors

Back 6

sensitive to changes in temperature

Front 7

Photoreceptors

Back 7

respond to light energy (e.g., retina)

Front 8

Chemoreceptors

Back 8

respond to chemicals (e.g., smell, taste, changes in blood chemistry)

Front 9

Nociceptors

Back 9

sensitive to pain-causing stimuli

Front 10

Receptor Class by Location: Exteroceptors

Back 10

-Respond to stimuli arising outside the body
-Found near the body surface
-Sensitive to touch, pressure, pain, and temperature
-Include the special sense organs

Front 11

Receptor Class by Location: Interoceptors

Back 11

Respond to stimuli arising within the body

Found in internal viscera and blood vessels

Sensitive to chemical changes, stretch, and temperature changes

Front 12

Receptor Class by Location: Proprioceptors

Back 12

Respond to degree of stretch of the organs they occupy

Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and
muscles

Constantly “advise” the brain of one’s movements

Front 13

Receptor Classification by Structural Complexity

Back 13

Receptors are structurally classified as either simple or complex

Most receptors are simple and include encapsulated and unencapsulated varieties

Complex receptors are special sense organs

Front 14

Free dendritic nerve endings

Back 14

Simple Receptors: Unencapsulated

Respond chiefly to temperature and pain

Front 15

Merkel (tactile) discs

Back 15

Simple Receptors: Unencapsulated

Front 16

Hair follicle receptors

Back 16

Simple Receptors: Unencapsulated

Front 17

Meissner’s corpuscles (tactile corpuscles)

Back 17

Simple Receptors: Encapsulated

Front 18

Pacinian corpuscles (lamellated corpuscles)

Back 18

Simple Receptors: Encapsulated

Front 19

Ruffini’s corpuscles

Back 19

Simple Receptors: Encapsulated

Front 20

Sensation & Perception

Back 20

Survival depends on both

Front 21

Sensation is:

Back 21

the awareness of changes in the internal and external environment

Front 22

Perception is:

Back 22

the conscious interpretation of those stimuli

Front 23

Organization of the Somatosensory System

Back 23

Input comes from exteroceptors, proprioceptors, and interoceptors

outside, inside or where your body is in space

Front 24

The three main levels of neural integration in the somatosensory system are:

Back 24

Receptor level – the sensory receptors

Circuit level – ascending pathways

Perceptual level – neuronal circuits in the cerebral cortex

Front 25

Processing at the Receptor Lever

Back 25

The receptor must have specificity for the stimulus energy

The receptor’s receptive field must be stimulated

Stimulus energy must be converted into a graded potential

A generator potential in the associated sensory neuron must reach threshold

Front 26

Adaptation of Sensory Receptors

Back 26

Adaptation occurs when sensory receptors are subjected to an unchanging stimulus-

*Receptor membranes become less responsive

*Receptor potentials decline in frequency or stop

Front 27

Adaptation of Sensory Receptors

Back 27

Receptors responding to pressure, touch, and smell adapt quickly

Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood

Pain receptors and proprioceptors do not exhibit adaptation

Front 28

Processing at the Circuit Level

Back 28

Chains of three neurons conduct sensory impulses upward to the brain

Front 29

First-order neurons

Back 29

conduct impulses from the skin to the spinal cord or brain stem

Front 30

Second-order neurons

Back 30

transmit impulses to the thalamus or cerebellum

Front 31

Third-order neurons

Back 31

conduct impulses to the somatosensory cortex of the cerebrum

Front 32

Main Aspects of Sensory Perception:
Perceptual detection

Back 32

detecting that a stimulus has occurred from several receptors

Front 33

Main Aspects of Sensory Perception:
Magnitude estimation

Back 33

how intense the stimulus is

Front 34

Main Aspects of Sensory Perception:
Spatial discrimination

Back 34

identifying the site or pattern of the stimulus (two point discrimination)

Front 35

Main Aspects of Sensory Perception:
Feature abstraction

Back 35

used to identify a substance that has specific texture or shape

Front 36

Main Aspects of Sensory Perception:
Quality discrimination

Back 36

the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)

Front 37

Main Aspects of Sensory Perception:
Pattern recognition

Back 37

ability to recognize patterns in stimuli (e.g., melody, familiar face)

Front 38

Classification of Nerves

Back 38

Sensory and motor divisions

Sensory (afferent) – carry impulse to the CNS

Motor (efferent) – carry impulses from CNS

Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve

Front 39

Number of Cranial Nerves?

Back 39

12 pairs arise from the brain

Front 40

Characteristics of cranial nerves:

Back 40

They have sensory, motor, or both sensory and motor functions

Each nerve is identified by a number (I through XII) and a name

Four cranial nerves carry parasympathetic fibers that serve muscles and glands

Front 41

Cranial Nerve I

Back 41

Olfactory- SMELL

carrying afferent impulses for the sense of smell

Front 42

Cranial Nerve II

Back 42

Optic- VISION

carrying afferent impulses for vision

Arises from the retina of the eye

Front 43

Cranial Nerve III

Back 43

Oculomotor

Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape

Fibers supply the extrinsic eye muscles

Front 44

Cranial Nerve IV

Back 44

Trochlear

Fibers innervate the superior oblique muscle

Primarily a motor nerve that directs the eyeball

Front 45

Cranial Nerve V

Back 45

Trigeminal

Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

Front 46

3 divisions of Cranial Nerve V: Trigeminal

Back 46

ophthalmic (V1),
maxillary (V2),
mandibular (V3)

Front 47

Cranial Nerve VI

Back 47

Abducuens- ABducts the eye

Primarily a motor nerve innervating the lateral rectus muscle (abducts the eye)

Front 48

Cranial Nerve VII

Back 48

Facial

Mixed nerve with five major branches

Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands

Sensory function is taste from the anterior two-thirds of the tongue

Front 49

Cranial Nerve VIII

Back 49

Vestibulocochlear

*Functions are solely sensory – equilibrium and hearing

Fibers arise from the hearing and equilibrium apparatus of the inner ear

Two divisions – cochlear (hearing) and vestibular (balance)

Front 50

Cranial Nerve IX

Back 50

Glossopharyngeal

Fibers run to the throat

Nerve IX is a mixed nerve with motor and sensory functions

Front 51

Motor function of Cranial Nerve IX

Back 51

innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland

Front 52

Sensory function of Cranial Nerve IX

Back 52

fibers conduct taste and general sensory impulses from the tongue and pharynx

Front 53

Cranial Nerve X

Back 53

Vagus

The only cranial nerve that extends beyond the head and neck

The vagus is a mixed nerve

Front 54

Motor function of Cranial Nerve X

Back 54

Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs

Front 55

Sensory function of Cranial Nerve X

Back 55

Its sensory function is in taste

Front 56

Cranial Nerve XI

Back 56

Accessory

Primarily a motor nerve

-Supplies fibers to the larynx, pharynx, and soft palate

-Innervates the trapezius and sternocleidomastoid, which move the head and neck

Front 57

Cranial Nerve XII

Back 57

Hypoglossal

Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

Front 58

Spinal Nerves

Back 58

Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head

They are named according to their point of issue

Front 59

Cervical Spinal Nerves

Back 59

8 cervical (C1-C8)

Front 60

Thoracic Spinal Nerves

Back 60

12 thoracic (T1-T12)

Front 61

Lumbar Spinal Nerves

Back 61

5 Lumbar (L1-L5)

Front 62

Sacral Spinal Nerves

Back 62

5 Sacral (S1-S5)

Front 63

Coccygeal Spinal Nerves

Back 63

1 Coccygeal (C0)

Front 64

Spinal Nerves: Roots

Back 64

Each spinal nerve connects to the spinal cord via two medial roots

Front 65

Ventral roots contain:

Back 65

motor (efferent) fibers

Front 66

Dorsal roots contain:

Back 66

sensory (afferent) fibers

Front 67

Dermatomes

Back 67

A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve

All spinal nerves except C1 participate in dermatomes

Front 68

Reflexes

Back 68

A reflex is a rapid, predictable motor response to a stimulus

Front 69

Reflexes may:

Back 69

Be inborn (intrinsic) or learned (acquired)

Involve only peripheral nerves and the spinal cord

Involve higher brain centers as well

Front 70

Reflex Arc

Back 70

There are five components of a reflex arc:
-Receptor
-Sensory neuron
-Integration center
-Motor neuron
-Effector

Front 71

Reflex Arc:
Receptor

Back 71

site of stimulus

Front 72

Reflex Arc:
Sensory neuron

Back 72

transmits the afferent impulse to the CNS

Front 73

Reflex Arc:
Integration center

Back 73

either monosynaptic or polysynaptic region within the CNS

Front 74

Reflex Arc:
Motor neuron

Back 74

conducts efferent impulses from the integration center to an effector

Front 75

Reflex Arc:
Effector

Back 75

muscle fiber or gland that responds to the efferent impulse

Front 76

For skeletal muscles to perform normally:

Back 76

The Golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of the muscle

Stretch reflexes initiated by muscle spindles must maintain healthy muscle tone

Front 77

Muscle Spindles are wrapped with 2 types of Afferent endings:

Back 77

primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers

These regions are innervated by gamma (γ) efferent fibers

Front 78

Stretching the muscles activates the muscle spindle

Back 78

There is an INCREASED rate of action potential in Ia fibers

Front 79

Contracting the muscle reduces tension on the muscle spindle

Back 79

There is a DECREASED rate of action potential on Ia fibers

Front 80

Excited γ motor neurons of the spindle cause the stretched muscle to ____

Back 80

contract

Front 81

Afferent impulses from the spindle result in

Back 81

inhibition of the antagonist
(ex: tapping patellar tendon)

Front 82

What is the Golgi Tendon Reflex?

Back 82

The opposite of the stretch reflex

Contracting the muscle activates the Golgi tendon organs

Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated

As a result, the contracting muscle relaxes and the antagonist contracts

Front 83

The flexor reflex is:

Back 83

initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part

Front 84

The crossed extensor reflex has two parts

Back 84

The stimulated side is withdrawn

The contralateral side is extended