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Nervous System > Nervous System Chapter 13 > Flashcards

Nervous System Chapter 13 Flashcards

1
Q

Peripheral nervous system

A
  • includes all neural structures outside the brain and spinal cord
  • sensory receptors, peripheral nerves and their ganglia, and efferent motor endings
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2
Q

Mechanoreceptors

A
  • respond to mechanical force

- touch, pressure, vibration, stretch

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3
Q

Thermoreceptors

A

-respond to temperature changes

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4
Q

Photoreceptors

A
  • respond to light

- retina

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5
Q

Chemoreceptors

A
  • respond to chemicals in a solution

- molecules smelled or tasted or changes in blood or interstitial fluid chemistry

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6
Q

Nociceptors

A
  • respond to potentially damaging stimuli that result in pain
  • searing heat, extreme cold, excessive pressure, and inflammatory chemicals
  • -they stimulate thermoreceptors, mechanoreceptors, and chemoreceptors
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7
Q

Exteroceptors

A
  • sensitive to stimuli arising outside the body
  • near the body surface
  • touch, pressure, pain, and temperature receptors in the skin and most receptors of the special senses
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8
Q

Interoceptors

A
  • respond to stimuli w/in the body
  • internal viscera and blood vessels
  • monitor chemical changes, tissue stretch, and temperature
  • -sometimes their activity causes us pain, hunger, or thirst
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9
Q

Propreioceptors

A
  • respond to internal stimuli but their location is restricted
  • occur in skeletal muscles, tendons, joints, and 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 these receptors are stretched
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10
Q

General senses

A

-modified dendritic endings of sensory neurons

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11
Q

Special senses

A
  • vision, hearing, equilibrium, smell, and taste

- housed in sense organs ex: eye

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12
Q

Nonencapsulated (free) nerve endings

A
  • nearly everywhere in the body
  • nonmyelinated, small-diameter group C fibers
  • distal endings have small knoblike swellings
  • respond to temperature and painful stimuli–some respond to tissue movements caused by pressure too
  • those that respond to cold are in the superficial dermis
  • those that respond to heat are deeper in the dermis
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13
Q

Tactile discs

A
  • other nonencapsulated nerve endings
  • lie in the deepest layer of epidermis
  • function as light touch receptors
  • they associate w/ enlarged, disc-shaped epidermal cells to form tactile discs
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14
Q

Hair follicle receptors

A
  • other nonencapsulated nerve endings
  • wrap basketlike around hair follicles
  • light touch receptors that detect bending of hairs
    ex: mosquito landing on skin
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15
Q

Encapsulated nerve endings

A
  • have one or more fiber terminals of sensory neurons enclosed in a connective tissue capsule
  • all are mechanoreceptors
  • vary in shape, size, and distribution in the body
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16
Q

Tactile corpuscles

A
  • encapsulated nerve ending
  • spiraling sensory terminals surrounded by schwann cells and then by a thin egg-shaped connective tissue capsule
  • just beneath epidermis in the dermal papillae
  • numerous in sensitive and hairless skin areas (nipples, fingertips, and soles of feet)
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17
Q

Lamellar corpuscles

A
  • encapsulated nerve ending
  • scattered deep in dermis and subcutaneous tissue
  • mechanoreceptors stimulated by deep pressure only when first applied
  • best suited for vibration
  • largest corpuscular receptors
  • in section it resembles a cut onion
  • single dendrite surrounded by a capsule containing up to 60 layers of collagen fibers and flattened supporting cells
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18
Q

Bulbous corpuscles

A
  • encapsulated nerve ending
  • lie in the dermis, subcutaneous tissue, and joint capsules
  • respond to deep and continuous pressure
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19
Q

Muscle Spindles

A
  • encapsulated nerve ending
  • fusiform proprioceptors in the perimysium of skeletal muscle
  • detect muscle stretch and initiate a reflex that resists stretch
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20
Q

Tendon organs

A
  • encapsulated nerve ending
  • proprioceptors in the tendons close to the skeletal muscle insertion
  • muscle contraction stretches the tendon fibers and the resulting compression on the nerve fiber activates the tendon organ
  • initiates a reflex that causes the contracting muscle to relax
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21
Q

Joint kinesthetic receptors

A
  • encapsulated nerve ending
  • proprioceptors that monitor stretch in the articular capsules that enclose synovial joints
  • contain lamellar corpuscles, bulbous corpuscles, free nerve endings, and receptors resembling tendon organs
  • provide info on joint position and motion
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22
Q

Somatosensory system

A
  • part of sensory system serving the body wall and limbs
  • receives input from exteroceptors, protrioceptors, and interoceptors
  • 3 levels: receptor, circuit, and perceptual
  • sensory input is relayed toward the head and processed along the way
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23
Q

Processing at Receptor Level

A
  • stimulus energy must match the specificity of the receptor (touch receptor isn’t sensitive to light)
  • stimulus must be applied within a sensory receptor’s receptive field
  • stimulus energy must be converted into energy of a graded potential=transduction
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24
Q

Generator potential (type of graded potential)

A

-when receptor region is part of a sensory neuron

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25
Q

Receptor potential (type of graded potential)

A

-when the receptor is a separate cell

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26
Q

Phasic receptors

A
  • fast adapting–report changes in the internal or external environment
    ex: lamellar and tactile corpuscles
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27
Q

Tonic receptors

A
  • provide a sustained response w/ little or no adaptation

ex: nociceptors and proprioceptors

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28
Q

Processing at circuit level

A

-deliver impulses to the appropriate region of the cerebral cortex for localization and perception of the stimulus

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29
Q

Processing at the perceptual level

A
  • sensory input is interpreted in the cerebral cortex
  • the ability to identify and appreciate sensations depends on the location of the target neurons in the sensory cortex, not the nature of the message
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30
Q

Perceptual detection

A

-ability to detect that a stimulus has occured

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31
Q

Magnitude estimation

A

-ability to detect how intense the stimulus is

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32
Q

Spatial discrimination

A
  • identify the site or pattern of stimulation
  • two-point discrimination test: determines how close together 2 points on the skin can be and still be perceived as two points rather than one
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33
Q

Feature abstraction

A
  • a neuron or circuit is tuned to one feature or property of a stimulus in preference to others
    ex: touch tells us that velvet is warm, compressible, and smooth but not completely continuous
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34
Q

Quality discrimination

A
  • ability to differentiate the submodalities of a sensation

ex: taste is a sensory modality and its submodalities include sweet and bitter

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35
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
    ex: can look at dots and recognize a pattern of a face
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36
Q

Hyperalgesia

A

-pain amplification/increased sensitivity to pain

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37
Q

Visceral pain

A
  • results form noxious stimulation of receptors in the organs of the thorax and abdominal cavity
  • usually dull aching, gnawing, or burning
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38
Q

Referred pain

A
  • pain stimuli arising from one part of the body are perceived as coming from another part
    ex: heart attack–pain in the left arm
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39
Q

Endoneurium

A
  • surrounds axon

- delicate layer of loose connective tissue that encloses the fibers associated w/ Schwann cells

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40
Q

Perineurium

A

-coarser connective tissue wrapping–binds groups of fibers into bundles called fascicles

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41
Q

Epineurium

A

-encloses all the fascicles to form the nerve

42
Q

Mixed nerves

A
  • contain both sensory and motor fibers and transmit impulses to and from the CNS
  • most nerves are mixed
43
Q

Sensory (afferent) nerves

A

-carry impulses toward the CNS

44
Q

Motor (efferent) nerves

A

-carry impulses away from the CNS

45
Q

Ganglia

A
  • collections of neuron cell bodies associated w/ nerves in the PNS
  • if associated w/ afferent fibers, the cell bodies are from sensory neurons (dorsal root ganglia)
  • if associated w/ efferent nerve fibers, mostly contain cell bodies of autonomic motor neurons
46
Q

Nuclei

A

-collections of neuron cell bodies in the CNS

47
Q

What happens if a peripheral axon is severed or crushed?

A
  1. axon fragments–axon and myelin sheath next to the injury disintegrate from lack of nutrients
  2. macrophages clean out the dead axon–they release chemicals that stimulate Schwann cells to divide
  3. axon filaments grow through a regeneration tube–surviving Schwann cells proliferate–they release CAMs that encourage axonal growth–form a regeneration tube which is a system of cellular cords that guide the regenerating axon spouts across the gap to their original contacts
  4. axon regenerates and a new myelin sheath forms
48
Q

Olfactory nerve

A
  • olfactory nerve fibers arise form olfactory sensory neurons located in olfactory epithelium of nasal cavity and pass through the cribiform plate to synapse in olfactory bulb
  • the fibers extend posteriorly as olfactory tract
  • purely sensory
  • carry afferent impulses for sense of smell
49
Q

Optic nerve

A
  • fibers arise from retina of eye
  • the nerves pass through the optic canal of orbit
  • optic nerves converge to form the optic chiasma where fibers partially cross over, continue as optic tract, enter thalamus, and synapse there
  • thalamic fibers run to occipital cortex where visual interpretation occurs
  • purely sensory
  • carry afferent impulses for vision
50
Q

Oculomotor nerve

A
  • fibers extend from ventral midbrain and pass through bony orbit, via superior orbital fissure to the eye
  • chiefly motor nerves, few proprioceptive afferents
  • each nerve includes: somatic motor fibers to 4 of 6 extrinsic eye muscles that help direct the eyeball and to levator palpebrae which raises the upper eyelid ; parasympathetic motor fibers to sphincter pupillae (causes pupil to constrict) and ciliary muscle (controlling lens shape for visual focusing) ; sensory afferents which run from same four extrinsic eye muscles to the midbrain
51
Q

Trochlear nerve

A
  • fibers emerge from dorsal midbrain and course ventrally around midbrain to enter orbit through superior orbital fissure along w/ oculomotor nerves
  • primarily motor nerves–supply somatic motor fibers to the superior oblique muscle which passes through the pulley-shaped trochlea
52
Q

Trigeminal nerve

A
  • largest–fibers extend from pons to face and form 3 divisions: opthalmic, maxillary, and mandibular
  • -opthalmic: fibers from face to pons via superior orbital fissue–conveys sensory impulses from skin of anterior scalp, upper eyelid, and nose, and from nasal cavity mucosa, cornea, and lacrimal gland
  • -maxillary: fibers from face to pons via foramen rotundum–conveys sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek, upper lip and lower eye lid
  • -mandibular: fibers pass through skill via foreman ovale–conveys sensory impulses from anterior tongue, lower teeth, skin of chin, temporal region of scalp–supplies motor fibers to and carries proprioceptor fibers from muscles of mastication
53
Q

Abducens nerve

A
  • fibers leave inferior pons and enter orbit via superior orbital fissure to run to eye
  • primarily motor–supply somatic motor fibers to lateral rectus muscle an extrinsic muscle of the eye
  • convey proprioceptor impulses from same muscle to brain
54
Q

Facial nerve

A
  • fibers issue from pons, lateral to abducens, enter temporal bone via internal acoustic meatus and run w/in bone before emerging through stylomastoid foreman
  • mixed nerves that are chief motor nerves for the face
  • five branches: temporal, zygomatic, buccal, mandibular, and cervical
  • convey muscle impulses to skeletal muscles of the face (except mastication) and transmit proprioceptor impulses from same muscles to pons
  • transmit parasympathetic motor impulses to lacrimal glands, nasal and palatine glands, and submandibular and sublingual salivary glands
  • convey sensory impulses from taste buds of anterior 2/3 of tongue
55
Q

Vestibulocochlear nerve

A
  • fibers from hearing and equilibrium apparatus located within inner ear of temporal bone and pass through internal acoustic meatus to enter brain stem at pons-medulla border
  • cochlear division: afferent fibers from hearing receptors in cochlea
  • vestibular division: equilibrium receptors in semicircular canals and vestibule
  • -together they make the vestibulocochlear
  • mostly sensory-
  • vestibular: transmits afferent impulses for sense of equilibrium and
  • cochlear: afferent impulses for sense of hearing
56
Q

Glossopharyngeal nerve

A
  • fibers emerge from medulla and leave skull via jugular foramen to run to throat
  • mixed nerves–innervate part of tongue and pharynx
  • somatic motor fibers to and proprioceptors from muscle that elevates pharynx in swallowing
  • parasympathetic motor fibers to parotid salivary glands
57
Q

Vagus nerve

A
  • only cranial nerves to extend beyond head and neck region
  • fibers emerge from medulla, pass through skull via jugular foramen and descend through neck region into thorax and abdomen
  • mixed nerves–almost all motor fibers are autonomic parasympathetic fibers–motor efferents to and sensory fibers from the pharynx, larynx, and visceral organs of the thoracic and abdominal cavities
58
Q

Accessory nerve

A
  • arise as spinal rootlets from cervical spinal cord and enter the foramen magnum
  • primarily motor–supply somatic efferents to the traps and sternocleidomastoid and carry proprioceptor afferents from the same muscles
59
Q

Hypoglossal nerve

A
  • fibers arise from series of roots from the medulla and exit the skull via hypoglossal canal to travel to tongue
  • primarily motor
60
Q

Spinal nerves

A
  • 31 pairs
  • arise form spinal cord and supply all parts of the body except the head and some areas of the neck
  • all are mixed nerves
  • 8 cervial; 12 thoracic; 5 lumbar; 5 sacral; 1 pair of tiny coccygeal
  • go through intervertebral foreman
  • very short–divide into dorsal and ventral ramus
61
Q

Ventral roots

A

-contain motor fibers that innervate skeletal muscles

62
Q

Dorsal roots

A

-contain sensory fibers that conduct impulses from peripheral receptors to the spinal cord

63
Q

Rami communicantes

A
  • contain autonomic nerve fibers

- attach to base of the ventral rami of the thoracic spinal nerves

64
Q

Dorsal rami

A
  • supply posterior body trunk

- each dorsal ramus innervates the narrow strip of muscle and skin in line with where it emerges from the spinal column

65
Q

Ventral rami

A

-supply anterior trunk and the limbs

66
Q

Nerve plexuses

A
  • except for T2-T12, all ventral (not dorsal) rami branch and join one another lateral to the vertebral colum, forming nerve plexuses
  • occur in cervical, brachial, lumbar, and sacral regions and primarily serve the limbs
  • fibers from ventral rami criss cross one another– each resulting branch of the plexus contains fibers from several spinal nerves and fibers from each ventral ramus travel to the body periphery via several routes
  • therefore, each muscles receives it’s nerve supply from more than one spinal nerve–advantage: damage to one spinal segment or root can’t completely paralyze any limb muscle
67
Q

Cervical plexus

A
  • C1-C4
  • innervates muscles and skin of neck and shoulder
  • the phrenic nerve serves the diaphram
68
Q

Brachial plexus

A
  • C5-T1
  • serves the shoulder, some thorax muscles, and the upper limb
  • proximal to distal it has roots, trunks, divisions, and cords (really tired? drink coffe.)
  • main nerves arising from cords are axillary, musculotaneous, median, radial, and ulnar nerves
69
Q

Lumbar plexus

A
  • L1-L4
  • provides motor supply to the anterior and medial thigh and part of the leg
  • chief nerves are femoral and obturator
70
Q

Sacral plexus

A
  • L4-S4
  • supplies posterior muscles and skin of lower limb
  • principle nerve is the large sciatic nerve composed of the tibial and common fibular nerves
71
Q

Axillary nerve of brachial plexus

A

-innervates deltoid and teres minor and the skin and joint capsule of the shoulder

72
Q

Musculocutaneous nerve of brachial plexus

A
  • supplies motor fibers to the biceps brachii, brachialis, and coracobrachialis
  • provides cutaneous sensation in the lateral forearm
73
Q

Median nerve of brachial plexus

A
  • descends to anterior forearm and gives off branches to skin and most flexor muscles
  • innervates 5 intrinsic muscles of the lateral palm
  • activates muscles that pronate the forearm, flex the wrist and fingers, and oppose the thumb
74
Q

Ulnar nerve of the brachial plexus

A
  • descends to medial aspect of arm toward the elbow, goes behind medial epicondyle and then follows ulna along the medial forearm
  • continues to the hand where it innervates most intrinsic hand muscles and the skin of the medial aspect of the hand
  • causes wrists and fingers to flex and adducts and abducts the medial fingers
75
Q

Radial nerve of the brachial plexus

A
  • largest branch
  • wraps around humerus (in radial groove) and runs anteriorly around the lateral epicondyle at the elbow
  • it divides into superficial branch that follows the lateral edge of the radius to the hand and a deep branch that runs posteriorly
  • supplies skin of limb along its entire course
  • motor branches innervate all extensor muscles of upper limb
  • muscles controlled by it extend the elbow, supinate the forearm, extend the wrist and fingers and abduct the thumb
76
Q

Femoral nerve of lumbar plexus

A
  • skin of anterior and medial thigh
  • skin of medial leg and foot, hip and knee joints
  • motor to anterior muscles of thigh and to pectineus and iliacus
77
Q

Obturator nerve of lumbar plexus

A
  • motor to adductor magnus, longus, and brevis muscles, gracilis muscl of medial thigh, obturator externus
  • sensory for skin of medial thigh and for hip and knee joints
78
Q

Sciatic nerve of sacral plexus

A
  • tibial and common fibular

- supplies entire lower limb, except anteromedial thigh

79
Q

Tibial nerve of sacral plexus

A
  • continues through popliteal fossa

- supplies posterior compartment muscles of the leg and the skin of the posterior calf and sole of the foot

80
Q

Common fibular nerve of sacral plexus

A
  • wraps around neck of fibula and divides into superficial and deep branches
  • innervate knee joint, skin of the anterior and lateral leg and dorsum of the foot and muscles of the anterolateral leg (the extensors that dorsiflex the foot)
81
Q

Intercostal nerves

A
  • ventral rami of T1-T12 course anteriorly, deep to each rib
  • supply intercostal muscles, the muscle and skin of the anterolateral thorax, and most of the abdominal wall
  • give off cutaneous branches to the skin
82
Q

Dermatomes

A
  • area of skin innervated by cutaneous branches of a single spinal nerve
  • C1 doesn’t innervate dermatomes
83
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

84
Q

Motor endings

A

-PNS elements that activate effectors by releasing neurotransmitters

85
Q

Neuromuscular junctions

A
  • formed by somatic motor fibers that innervate voluntary muscles
  • axon terminals contain synaptic vesicles filled w/ acetylcholine which signal the muscle cell to contract
  • the synaptic cleft has glycoprotein-rich basal lamina (not seen at other synapses)–contains enzyme that breaks down ACh
86
Q

Variscosities

A
  • junctions b/t autonomic motor endings and their effectors (smooth and cardiac muscle and glands)
  • knoblike swellings containing mitochondria and synaptic vesicles
  • innervate smooth muscle and glands
  • don’t form specialized neuromuscular junctions and the motor responses elicited are generally slower
87
Q

Segmental level

A
  • lowest level of motor heirarchy
  • consists of reflexes and spinal cord circuits that control automatic movements
  • activates ventral horn motor neurons to stimulate the muscles
  • consists of reflexes and central pattern generators which are segmental circuits controlling locomotion
88
Q

Projection level

A
  • this directly controls the spinal cord
  • consists of descending fibers that project to and control the segmental level
  • fibers from the brain stem motor areas (indirect system) and cortical motor areas (direct system)
  • neurons in the brain stem appear to turn central pattern generators on and off, or to modulate them
89
Q

Precommand level

A
  • cerebellum and basal nuclei

- subconsciously integrate mechanisms mediated by the projection level

90
Q

Reflex arc

A
  • receptor—site of stimulus action
  • sensory neuron—transmits afferent impulses to the CNS
  • integration center—either monosynaptic or polysynaptic region within the CNS
  • motor neuron—conducts efferent impulses from the integration center to an effector organ
  • effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
91
Q

Stretch and tendon reflexes

A

For skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary
Muscle spindles inform the nervous system of the length of the muscle
Golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons

92
Q

Muscle spindles

A

-Composed of 3–10 short intrafusal muscle fibers in a connective tissue capsule
Intrafusal fibers
–Noncontractile in their central regions (lack myofilaments)
–Wrapped with two types of afferent endings: primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers
-Contractile end regions are innervated by gamma (γ) efferent fibers that maintain spindle sensitivity
Note: extrafusal fibers (contractile muscle fibers) are innervated by alpha (α) efferent fibers

93
Q

2 ways muscles spindles are excited

A

-External stretch of muscle and muscle spindle
-Internal stretch of muscle spindle:
–Activating the γ motor neurons stimulates the ends to contract, thereby stretching the spindle
-Stretch causes an increased rate of impulses in Ia fibers
-Contracting the muscle reduces tension on the muscle spindle
-Sensitivity would be lost unless the muscle spindle is shortened by impulses in the γ motor neurons
α–γ coactivation maintains the tension and sensitivity of the spindle during muscle contraction

94
Q

Stretch reflex

A

-Maintain muscle tone in large postural muscles
-Cause muscle contraction in response to increased muscle length (stretch)
How a stretch reflex works:
-Stretch activates the muscle spindle
-IIa sensory neurons synapse directly with α motor neurons in the spinal cord
-α motor neurons cause the stretched muscle to contract
-All stretch reflexes are monosynaptic and ipsilateral
-Reciprocal inhibition also occurs—IIa fibers synapse with interneurons that inhibit the α motor neurons of antagonistic muscles
Example: In the patellar reflex, the stretched muscle (quadriceps) contracts and the antagonists (hamstrings) relax

95
Q

Tendon reflex

A

Polysynaptic reflexes

  • Help to prevent damage due to excessive stretch
  • Important for smooth onset and termination of muscle contraction

Produce muscle relaxation (lengthening) in response to tension

  • Contraction or passive stretch activates Golgi tendon organs
  • Afferent impulses are transmitted to spinal cord
  • Contracting muscle relaxes and the antagonist contracts (reciprocal activation)
  • Information transmitted simultaneously to the cerebellum is used to adjust muscle tension
96
Q

Flexor reflex

A
  • Initiated by a painful stimulus
  • Causes automatic withdrawal of the threatened body part
  • Ipsilateral and polysynaptic
97
Q

Crossed-extensor reflex

A
  • Occurs with flexor reflexes in weight-bearing limbs to maintain balance
  • Consists of an ipsilateral flexor reflex and a contralateral extensor reflex
  • The stimulated side is withdrawn (flexed)
  • The contralateral side is extended
98
Q

Superficial reflexes

A

Elicited by gentle cutaneous stimulation

Depend on upper motor pathways and cord-level reflex arcs

99
Q

Plantar reflex (superficial)

A

Stimulus: stroking lateral aspect of the sole of the foot
Response: downward flexion of the toes
Tests for function of corticospinal tracts

100
Q

Babinski’s sign (superficial reflex)

A
  • if primary motor cortex or corticospinal tract is damaged, great toe dorsiflexes and smaller toes fan laterally
  • infants exhibit this b/c their nervous systems are incompletely myelinated
  • in adults indicates corticospinal or motor cortex damage
101
Q

Abdominal reflex (superficial)

A

Cause contraction of abdominal muscles and movement of the umbilicus in response to stroking of the skin
Vary in intensity from one person to another
Absent when corticospinal tract lesions are present

102
Q

Sliding filament model of contraction

A

In the relaxed state, thin and thick filaments overlap only slightly
During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line

Nervous System (2 decks)

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