A&P 13: The Peripheral Nervous System & Reflex Activity Flashcards Preview

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Flashcards in A&P 13: The Peripheral Nervous System & Reflex Activity Deck (142)
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1
Q

Peripheral Nervous System (PNS)

A

provides links from and to the world outside our bodies; includes all neural structures outside the brain and spinal cord (sensory receptors, peripheral nerves & associated ganglia, and efferent motor ending

2
Q

Sensory receptors

A

specialized to respond to changes in their environment

3
Q

Stimuli

A

changes in the environment that cause a response in receptors

4
Q

Mechanoreceptors

A

respond to mechanical force (touch, pressure, including BP, vibration, and stretch)

5
Q

Thermoreceptors

A

respond to temperature changes

6
Q

Photoreceptors

A

respond to light (such as those of the retina of the eye)

7
Q

Chemoreceptors

A

respond to chemicals in solution (molecules smelled or tasted) or changed in blood or interstitial fluid chemistry

8
Q

Nociceptors

A

respond to potentially damaging stimuli that result in pain; stimulate subtypes of thermoreceptors, mechanoreceptors, and chemoreceptors

9
Q

Exteroceptors

A

sensitive to stimuli arising outside the body; most are near or at the body surface; include touch, pressure, pain, and temperature receptors in the skin and most receptors of the special senses

10
Q

Interoceptors

A

AKA visceroceptors; respond to stimuli within the body, such as from the internal viscera and blood vessels; monitor a variety of stimuli, including chemical changes, tissue stretch, and temperature; sometimes their activity causes us to feel pain, discomfort, hunger, or thirst (we are usually unaware of their workings)

11
Q

Proprioceptors

A

respond to internal stimuli; location is more restricted than interoceptors; occur in skeletal muscles, tendons, joints, ligaments, and in connective tissue coverings of bones and muscles; constantly advise the brain of our body movements by monitoring how much the organs containing those receptors are stretched

12
Q

General senses

A

overwhelming majority of sensory receptors belong to this class; simply = the modified dendritic endings of sensory neurons; found throughout the body and monitor most types of general sensory info

13
Q

Special senses

A

receptors for vision, hearing, equilibrium, smell, and taste

14
Q

Sense organs

A

receptors for special senses are housed in these complex organs

15
Q

Nonencapsulated (free) nerve endings

A

present nearly everywhere in the body; particularly abundant in epithelia and connective tissues; most are nonmyelinated, small-diameter, group C fibers; their distal endings (sensory terminals) usually have knoblike swellings; respond chiefly to temperature and painful stimuli; some respond to tissue movements caused by pressure as well

16
Q

Tactile (Merkel) discs

A

lie in the deepest layer of the epidermis; function as light touch receptors

17
Q

Hair follicle receptors

A

free nerve endings that wrap basket-like around hair follicles; light touch receptors that detect bending of hairs

18
Q

Encapsulated nerve endings

A

all consist of 1 or more fiber terminals of sensory neurons enclosed in a connective tissue capsule; virtually all are mechanoreceptors, but they vary greatly in shape, size, and distribution in the body; include tactile corpuscles, lamellar corpuscles, bulbous corpuscles, muscle spindles, tendon organs, and joint kinesthetic receptors

19
Q

Tactile corpuscles (Meissner’s corpuscles)

A

small receptors in which a few spiraling sensory terminals are surrounded by Schwann cells and then by a thin egg-shaped connective tissue capsule; found just beneath the epidermis in the dermal papillae; especially numerous in sensitive and hairless skin areas; receptors for discriminative touch & play the same role in sensing light touch in hairless skin that hair follicle receptors do in hairy skin

20
Q

Lamellar corpuscles

A

Pacinian corpuscles; scattered deep in the dermis & in subcutaneous tissue underlying the skin; mechanoreceptors stimulated by deep pressure; respond only when the pressure is 1st applied and thus are best suited to monitoring vibration (“on/off” pressure stimulus); largest corpuscular receptors; resembles a cut onion; its single dendrite is surrounded by a capsule containing up to 60 layers of collagen fibers and flattened supporting cells

21
Q

Bulbous corpuscles

A

Ruffini endings; lie in the dermis, subcutaneous tissue, and joint capsules; contain a spray of receptor endings enclosed by a flattened capsule; bear a striking resemblance to tendon organs (which monitor tendon stretch) and probably play a similar role in other dense connective tissues where they respond to deep and continuous pressure

22
Q

Muscle spindles

A

fusiform (spindle-shaped) propioceptors found throughout the perimysium of a skeletal muscle; each consists of a bundle of modified skeletal fibers (intrafusal fibers), enclosed in a connective tissue capsule; detect muscle stretch and initiate a reflex that resists the stretch

23
Q

Tendon organs

A

proprioceptors located in tendons, close to the skeletal muscle insertion; consist of small bundles of tendon (collagen) fibers enclosed in a layered capsule, with sensory terminals coiling between and around the fibers

24
Q

Joint kinesthetic receptors

A

proprioceptors that monitor stretch in the articular capsules that enclose synovial joints; contains at least 4 receptor types - lamellar corpuscles, bulbous corpuscles, free nerve endings, and receptors resembling tendon organs; together these receptors provide info on joint position and motion (a sensation of which we are highly conscious)

25
Q

Sensation

A

awareness of changes in the internal and external environments

26
Q

Perception

A

conscious interpretation of stimuli

27
Q

Somatosensory system

A

part of the sensory system serving the body wall and limbs; receives inputs from exteroceptors, propioceptors, and interoceptors; transmits info about several different sensory modalities (types of sensation)

28
Q

Transduction

A

process in which the stimulus energy must be converted into the energy of a graded potential

29
Q

Generator potential

A

when the receptor region is part of a sensory neuron (as with free dendrites or the encapsulated receptors of most general sense receptors), the graded potential is called this because it generates action potentials in a sensory neuron

30
Q

Receptor potential

A

when the receptor is a separate cell (as in most special senses), the graded potential is called this because it occurs in a separate receptor cell

31
Q

Adaptation

A

many, but not all, sensory receptors exhibit this change in sensitivity (& nerve impulse generation) in the presence of a constant stimulus

32
Q

Phasic receptors

A

fast adapting receptors, often giving bursts of impulses at the beginning and the end of the stimulus; report changes in the internal or external environment; examples = lamellar and tactile corpuscles

33
Q

Tonic receptors

A

receptors providing a sustained response with little or no adaptation; nociceptors & most propioceptors are this type because of the protective importance of their info

34
Q

Projection

A

phenomenon in which the exact point in the cortex that is activated always refers to the same “where,” regardless of how it is activated

35
Q

Perceptual detection

A

ability to detect a stimulus has occurred; simplest level of perception

36
Q

Magnitude estimation

A

ability to detect how intense the stimulus is; perceived intensity increases as stimulus intensity increases because of frequency coding

37
Q

Spatial discrimination

A

allows us to identify the site or pattern of stimulation

38
Q

Two-point discrimination test

A

a common tool for studying spatial discrimination in the lab; determines how close together 2 points on the skin can be and still be perceived as 2 points rather than as 1; provides a crude map of the density of tactile receptors in the various regions of the skin

39
Q

Feature abstraction

A

mechanism by which a neuron or circuit is tuned to one feature, or property, of a stimulus in preference to others

40
Q

Quality discrimination

A

ability to differentiate the submodalities of a particular sensation

41
Q

Qualities

A

each sensory modality has several of these submodalities; ex taste is a sensory modality with submodalities including sweet and bitter

42
Q

Pattern recognition

A

ability to take in the scene around us and recognize a familiar pattern, an unfamiliar one, or one that has special significance for us

43
Q

Hyperalgesia

A

pain amplification

44
Q

Phantom limb pain

A

pain perceived in tissue that is no longer present (such as after an amputation); an example of hyperalgesia

45
Q

Referred pain

A

phenomenon in which stimuli arising in 1 part of the body are perceived as coming from another part

46
Q

Nerve

A

cordlike organ that is part of the PNS; vary in size, but every one consists of parallel bundles of peripheral axons (some myelinated, some not) enclosed by successive wrappings of connective tissue

47
Q

Endoneurium

A

each axon is surrounded by this delicate layer of loose connective tissue that also encloses the fiber’s associated Schwann cells

48
Q

Perineurium

A

a coarser connective tissue wrapping that binds groups of fibers into bundles (fascicles)

49
Q

Fascicles

A

bundles of fibers

50
Q

Epineurium

A

a tough, fibrous sheath which encloses all the fascicles to form the nerve

51
Q

Mixed nerves

A

contain both sensory and motor fibers and transmit impulses both to and from the central nervous system; most nerves fall into this category

52
Q

Sensory (afferent) nerves

A

carry impulses only toward the CNS

53
Q

Motor (efferent) nerves

A

carry impulses only away from the CNS

54
Q

Ganglia

A

collections of neuron cell bodies associated with nerves in the PNS

55
Q

Wallerian degeneration

A

a process of disintegration of an axon that occurs when it is crushed or severed and cannot receive nutrients from the cell body

56
Q

Cranial nerves

A

12 pairs of these are associated with the brain; 1st 2 attach to the forebrain; the rest are associated with the brain stem

57
Q

Olfactory

A

cranial nerve I; tiny sensory nerves/filaments of smell; run from the nasal mucosa to synapse with the olfactory bulbs

58
Q

Optic

A

CN II; sensory nerve of vision; develops as an outgrowth of the brain so really a brain tract

59
Q

Oculomotor

A

CN III; “eye mover”; supplies 4 of the 6 extrinsic muscles that move the eyeball in the orbit

60
Q

Trochlear

A

CN IV; “pulley”; innervates an extrinsic eye muscle that loops through a pulley-shaped ligament in the orbit

61
Q

Trigeminal

A

CN V; 3 branches springs from this, the largest cranial nerve; supplies sensory fibers from the face and motor fibers to the chewing muscles

62
Q

Abducens

A

CN VI; controls the extrinsic eye muscle that ABDUCTS the eyeball (turns it laterally)

63
Q

Facial

A

CN VII; a large nerve that innervates muscles of FACIAL expression

64
Q

Vestibulocochlear

A

CN VIII; mostly sensory nerve for hearing and balance; formerly called the auditory nerve

65
Q

Glossopharyngeal

A

CN IX; “tongue & pharynx,” structures that this nerve helps innervate

66
Q

Vagus

A

CN X; “wanderer” or “vagabond;” only cranial nerve to extend beyond the head and neck to the thorax and abdomen

67
Q

Accessory

A

CN XI; considered an accessory part of the vagus nerve; formerly called the spinal accessory nerve

68
Q

Hypoglossal

A

CN XII; “under the tongue;” runs inferior to the tongue and innervates the tongue muscles

69
Q

Cranial sensory ganglia

A

in sensory neurons contributing to cranial nerves (V, VII, IX, & X), the cell bodies are located in these clusters just outside the brain

70
Q

Spinal nerves

A

31 pairs, each containing thousands of nerve fibers, arise from the spinal cord and supply all parts of the body except the head and some areas of the neck; all are mixed nerves

71
Q

Rootlets

A

each dorsal and ventral root forms from a series of these that attach along the length of the corresponding spinal cord segment

72
Q

Ventral roots

A

contain motor (efferent) fibers that arise from ventral horn motor neurons and extend to an innervate the skeletal muscles

73
Q

Dorsal roots

A

contain sensory (afferent) fibers that arise from sensory neurons in the dorsal root ganglia and conduct impulses from peripheral receptors to the spinal cord

74
Q

Dorsal ramus

A

small branch of a spinal nerve almost immediately after emerging from its foramen

75
Q

Ventral ramus

A

larger branch of a spinal nerve

76
Q

Meningeal branch

A

tiny branch of a spinal nerve that reenters the vertebral canal to innervate the meninges and blood vessels within

77
Q

Rami communicantes

A

special rami which contain autonomic (visceral) nerve fibers; attach to the base of the ventral rami of the thoracic spinal nerves

78
Q

Nerve plexuses

A

all ventral rami branch and join one another lateral to the vertebral column, forming complicated interlacing nerve networks called this; occur in the cervical, brachial, lumbar, and sacral regions and primarily serve the limbs; ONLY VENTRAL RAMI form these

79
Q

Cervical plexus

A

buried deep in the neck under the sternocleidomastoid muscle, the ventral rami of the 1st 4 cervical nerves form this looping plexus

80
Q

Cutaneous nerves

A

most of the branches of the cervical plexus are these nerves that supply only the skin

81
Q

Phrenic nerve

A

single most important nerve from the cervical plexus; receives fibers from C3, C4, & C5; runs inferiorly through the thorax and supplies both motor and sensory fibers to the diaphragm

82
Q

Brachial plexus

A

large, important plexus situated partly in the neck and partly in the axilla; gives rise to virtually all the nerves the innervate the upper limb; can be palpated in a living person just superior to the clavicle at the lateral border of the sternocleidomastoid

83
Q

Roots of the brachial plexus (5)

A

ventral rami C5-T1; lie deep to the sternocleiodmastoid

84
Q

Upper, middle, & lower trunks

A

at the lateral border of the sternocleiodmastoid

85
Q

Anterior & posterior divisions

A

upper/middle/lower trunks divide almost immediately into these divisions

86
Q

Lateral, medial, and posterior cords

A

the anterior/posterior divisions (indicate which fibers serve the front/back of the limb) pass deep to the clavicle and enter the axilla; there they give rise to these 3 large fiber bundles (named for their relationship to the axillary artery, which runs through the axilla)

87
Q

Axillary nerve

A

branches off the posterior cord and runs posterior to the surgical neck of the humerus; innervates the deltoid and teres minor and the skin & joint capsule of the shoulder

88
Q

Musculocutaneous nerve

A

major end branch of the lateral cord; courses inferiorly in the anterior arm, supplying motor fibers to the biceps brachii, brachialis, and coracobrachialis muscles; distal to the elbow, it provides cutaneous sensation in the lateral forearm

89
Q

Median nerve

A

descends through the arm to the anterior forearm, where it gives off branches to the skin and to most flexor muscles; on reaching the hand, it innervates 5 intrinsic muscles of the lateral palm; activates muscles that pronate the forearm, flex the wrist and fingers, and oppose the thumb

90
Q

Ulnar nerve

A

branches off the medial cord of the brachial plexus; descends along the medial aspect of the arm toward the elbow, swings behind the medial epicondyle, and then follows the ulna along the medial forearm; supplies the flexor carpi ulnaris and the medial part of the flexor digitorum profundus (flexors not supplied by the median nerve); continues into the hand, where it innervates most intrinsic hand muscles and the skin of the medial aspect of the hand; causes the wrist and fingers to flex, and (with the median nerve) adducts and abducts the medial fingers

91
Q

Radial nerve

A

largest branch of the brachial plexus; continuation of the posterior cord; wraps around the humerus (in the radial groove) then runs anteriorly around the lateral epicondyle at the elbow; divides into a superficial branch that follows the lateral edge of the radius to the hand and a deep branch that runs posteriorly; supplies the posterior skin of the limb along its entire course; its motor branches innervate essentially all the extensor muscles of the upper limb; muscles controlled by this nerve extend the elbow, supinate the forearm, extend the wrist/fingers, and abduct the thumb

92
Q

Lumbosacral trunk

A

many fibers of the lumbar plexus contribute to the sacral plexus via this

93
Q

Lumbosacral plexus

A

lumbar plexus + sacral plexus; serves mainly the lower limb; also sends some branches to the abdomen, pelvis, and buttock

94
Q

Lumbar plexus

A

arises from spinal nerves L1-L4 & lies within the psoas major muscle; its proximal branches innervate parts of the abdominal wall muscles and the psoas muscle, but its major branches descend to innervate the anterior and medial thigh

95
Q

Femoral nerve

A

largest terminal nerve of the lumbosacral plexus; runs deep to the inguinal ligament to enter the thigh and then divides into several large branches; the motor branches innervate anterior thigh muscles (quads = principle thigh flexors and knee extensors); cutaneous branches serve the skin of the anterior thigh and the medial surface of the leg from knee to foot

96
Q

Obturator nerve

A

enters the medial thigh via the obturator foramen and innervates the adductor muscles

97
Q

Sacral plexus

A

arises from spinal nerves L4-S4; lies immediately caudal to the lumbar plexus; has a dozen named branches; about half serve the buttock and lower limb; the others innervate pelvic structures and the perineum

98
Q

Sciatic nerve

A

the largest branch of the sacral plexus; the thickest and longest nerve in the body; supplies the entire lower limb except the anteromedial thigh

99
Q

Tibial nerve

A

nerve that continues through the popliteal fossa and supplies the posterior compartment muscles of the leg and the skin of the posterior calf and sole of the foot

100
Q

Sural nerve

A

in the vicinity of the knee, the tibial nerve gives off this nerve, which serves the skin of the posterolateral leg

101
Q

Medial/lateral plantar nerves

A

at the ankle, the tibial nerve divides into these 2 nerves, which serve most of the foot

102
Q

Common fibular nerve

A

AKA common peroneal nerve; descends from its point of origin, wraps around the neck of the fibula, and then divides into superficial and deep branches; the branches innervate the knee joint, skin of the anterior and lateral leg and dorsum of the foot, and muscles of the anterolateral leg (extensors that dorsiflex the foot)

103
Q

Superior/inferior gluteal nerves

A

next largest sacral plexus branches; together they innervate the buttock and tensor fasciae latae muscles

104
Q

Pudendal nerve

A

“shameful;” innervates the muscles and skin of the perineum and helps stimulate erection and control urination

105
Q

Intercostal nerves

A

ventral rami of T1-T12 mostly course anteriorly, deep to each rib as these nerves, which supply the intercostal muscles, the muscle and skin of the anterolateral thorax, and most of the abdominal wall; give off cutaneous branches to the skin

106
Q

Subcostal nerve

A

lies inferior to the 12th rib, which makes it this type of nerve

107
Q

Dermatome

A

“skin segment;” area of skin innervated by cutaneous branches of a single spinal nerve; every spinal nerve except C1 innervates these

108
Q

Hilton’s Law

A

any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint

109
Q

Motor endings

A

the PNS elements that activate effectors by releasing neurotransmittesr

110
Q

Neuromuscular junctions

A

terminals of somatic motor fibers that innervate voluntary muscles form elaborate ___ ___ with their effector cells

111
Q

Varicosities

A

an axon serving smooth muscle or a gland (NOT cardiac muscle) has a series of these knoblike swellings containing mitochondria and synaptic vesicles (make it look like a string of beads

112
Q

Segmental level

A

lowest level of the motor hierarchy; consists of reflexes and spinal cord circuits that control automatic movements

113
Q

Central pattern generators

A

circuits that control locomotion and other specific and oft-repeated motor activities

114
Q

Projection level

A

spinal cord is under the direct control of this level of motor control; consists of neurons acting through the direct and indirect motor pathways

115
Q

Precommand areas

A

systems which control the outputs of the cortex and brain stem motor centers and stand at the highest level of the motor hierarchy

116
Q

Cerebellum

A

key center for “online” sensorimotor integration and control; target of ascending proprioceptor, tactile, equilibrium, and visual inputs

117
Q

Basal nuclei

A

receives inputs from all cortical areas and send their output back mainly to premotor and prefrontal cortical areas via the thalamus; appear to be involved in more complex aspects of motor control; under resting conditions, they inhibit various motor centers of the brain

118
Q

Monosynaptic reflex

A

a single synapse between a sensory neuron and a motor neuron

119
Q

Polysynaptic reflex

A

more complex reflex arc involving multiple synapses with chains of interneurons

120
Q

Somatic reflexes

A

classification of reflexes that activate skeletal muscles

121
Q

Autonomic (visceral) reflexes

A

classification of reflexes that activate visceral effectors (smooth or cardiac muscles or glands)

122
Q

Spinal reflexes

A

somatic reflexes that are mediated by the spinal cord

123
Q

Intrafusal muscle fibers

A

each muscle spindle consists of 3-10 of these modified skeletal muscle fibers enclosed in a connective tissue capsule

124
Q

Extrafusal muscle fibers

A

effector fibers of the muscles

125
Q

Anulospiral endings

A

AKA primary sensory endings; endings of large axons that wrap around the spindle center; stimulated by both the rate and degree of stretch

126
Q

Flower spray endings

A

AKA secondary sensory endings; formed by smaller axons that supply the spindle ends; stimulated only by degree of stretch

127
Q

Gamma efferent fibers

A

the intrafusal muscle fibers have contractile regions at their ends, which are the only areas containing actin and myosin myofilaments; arise from small motor neurons in the ventral horn of the spinal cord; maintain spindle sensitivity

128
Q

Alpha efferent fibers

A

fibers of the large alpha motor neurons

129
Q

Alpha motor neurons

A

stimulate the extrafusal muscle fibers to contract

130
Q

Alpha-gamma coactivation

A

descending fibers of motor pathways synapse with both alpha and gamma motor neurons, and motor impulses are simultaneously sent to the large extrafusal fibers and to muscle spindle intrafusal fibers; stimulating the intrafusal fibers maintains the spindle’s tension (and sensitivity) during muscle contraction, so that the brain continues to be notified of changes in the muscle length

131
Q

Stretch reflex

A

reflex that makes sure the muscle stays at a set length

132
Q

Patellar/knee-jerk reflex

A

stretch reflex that helps keep your knees from buckling when you are standing upright

133
Q

Reciprocal inhibition

A

branches of the afferent fibers synapse with interneurons that inhibit motor neurons controlling antagonistic muscles (parallel processing); resultant inhibition is this

134
Q

Monosynaptic & ipsilateral

A

involving a single synapse and motor activity on the same side of the body

135
Q

Tendon reflexes

A

muscles relax and lengthen in response to tension

136
Q

Reciprocal activation

A

phenomenon in which, simultaneously, motor neurons in spinal cord circuits supplying the contracting muscles are activated; contracting muscle relaxes as its antagonist is activated

137
Q

Flexor (withdrawal) reflex

A

a painful stimulus initiates this reflex; causes automatic withdrawal of the threatened body part from the stimulus

138
Q

Crossed-extensor reflex

A

often accompanies the flexor reflex in weight-bearing limbs and is particularly important in maintaining balance

139
Q

Superficial reflexes

A

elicited by gentle cutaneous stimulation; depend on functional upper motor pathways and on cord-level reflex arcs; best known are plantar and abdominal reflexes

140
Q

Plantar reflex

A

tests the integrity of the spinal cord from L4 to S2; indirectly determines if the corticospinal tracts are functioning properly; normal response = toes curl

141
Q

Babinski’s sign

A

if the primary motor cortex or corticospinal tract is damaged, the plantar reflex is replaced by this abnormal reflex, in which the great toe dorsiflexes and the smaller toes fan laterally

142
Q

Abdominal reflexes

A

check the integrity of the spinal cord and ventral rami from T8 to T12; vary in intensity from one person to another; absence indicates lesions in the corticospinal tract

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