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Anatomy 201 > Chapter 13: The PNS and Reflexes > Flashcards

Chapter 13: The PNS and Reflexes Flashcards

1
Q

Sensory Receptors:

A

Specialized to respond to changes in the environment called Stimuli.

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2
Q

What Sensory Receptors are Classified by:

A

o 1) Type of Stimulus they detect

o 2) Body Location

o 3) Structural Complexity

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3
Q

Classification of Sensory Receptors by Stimulus Type:

Mechanoreceptors

A

Respond to mechanical force such as touch, pressure, vibration, and stretch.

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4
Q

Classification of Sensory Receptors by Stimulus Type:

Thermoreceptors

A

Respond to temperature changes.

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5
Q

Classification of Sensory Receptors by Stimulus Type:

Photoreceptors

A

Such as those of the retina of the eye, respond to light.

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6
Q

Classification of Sensory Receptors by Stimulus Type:

Chemoreceptors

A

Respond to chemicals in solution.

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7
Q

Classification of Sensory Receptors by Stimulus Type:

Nociceptors

A

Respond to potentially damaging stimuli that result in pain.

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8
Q

Classification of Sensory Receptors by Location:

Exteroceptors

A

o Sensitive to stimuli arising outside the body.
o Most are near the body’s surface.
o Include touch, pressure, pain, and temperature receptors in the skin and most receptors of special senses.

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9
Q

Classification of Sensory Receptors by Location:

Interoceptors

A

o Called visceroceptors.
o Respond to stimuli within the body.
o Monitor a variety of stimuli including chemical changes, tissue stretch, and temperature.
o Can cause pain, discomfort, hunger, or thirst. But we are usually unaware of their workings.

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10
Q

Classification of Sensory Receptors by Location:

Proprioceptors

A

o Respond to internal stimuli.
o Their location is much more restricted than interoceptors.
o Occur in skeletal muscles, tendons, joints, and ligaments and in connective tissue coverings of bones and muscles.
o Constantly advise the brain of our body movements by monitoring how much our organs containing these receptors are stretched.

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11
Q

The 2 Classifications of Receptors by Structure:

A 
o	Nonencapsulated (Free)
o	Encapsulated
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12
Q

Types and Aspects of Nonencapsulated (Free) Receptors:

A

o Present nearly everywhere in the body, abundant in epithelia and connective tissues.
o Mostly Nonmyelinated, small diameter C-fibers whose distal endings usually have small knoblike swellings.
o Respond chiefly to temperature and painful stimuli, but some respond to tissue movement and pressure as well.
o A key player in detecting painful stimulus is a plasma protein called the vanilloid receptor. Opened by heat, low Ph, and various chemicals.
o Also deals with the itch sensation. The itch receptor has a very thin diameter. Number of chemicals are present in inflamed sites and active these nerve endings.

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13
Q

Other Types of Nonencapsulated (Free) Receptors:

Tactile (Merkel) Discs

A
  • Lie in deepest layer of the epidermis.
  • Function as light touch receptors.
  • Certain free nerve endings associate with enlarged, disc-shaped epidermal cells to form tactile discs.
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14
Q

Other Types of Nonencapsulated (Free) Receptors:

Hair Follicle Receptors

A
  • Free nerve endings that wrap around hair follicles.

- Light touch receptors that detect bending of hairs.

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15
Q

Encapsulated Receptors:

A

o Consist of one or more fiber terminals of sensory neurons enclosed in connective tissue capsule.

o Virtually all are mechanoreceptors, but vary in shape, size, and distribution in the body.

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16
Q

Types of Encapsulated Receptors:

Tactile Corpuscles

A

o Also Called Meissner’s Corpuscles.
o Small receptors with sensory terminals surrounded by Schwann Cells and a thin egg-shaped connective tissue capsule.
o Found just beneath the epidermis in the dermal papillae and are especially numerous in sensitive, hairless skin areas.
o Receptors for discriminative touch, and play a role in sensing light touch in hairless skin.

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17
Q

Types of Encapsulated Receptors:

Lamellar Corpuscles

A

o Also called Pacinian corpuscles
o Scattered deep in the dermis, and in subcutaneous tissue underlying the skin.
o Mechanoreceptors stimulated by deep pressure, but respond only when pressure is first applied, and thus are better for monitoring vibration.
o Largest Corpuscle receptors.
o Single Dendrite surrounded by a capsule containing up to 60 layers of collagen fibers and flattened supportive cells.

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18
Q

Types of Encapsulated Receptors:

Bulbous Corpuscles

A

o Also called Ruffini endings.
o Lie in the deris, subcutaneous tissue, and joint capsules.
o Contain receptor endings enclosed by a flattened capsule.
o Respond to deep and continuous tissues.

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19
Q

Types of Encapsulated Receptors:

Muscle Spindles

A

o Fusiform proprioceptors found throughout the perimysium of a skeletal muscle.
o Each spindle consists of a bundle of modified skeletal fibers (intrafusal fibers) enclosed in a connective tissue capsule.
o Spindles detect muscle stretch and initiate a reflex that resists the stretch.

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20
Q

Types of Encapsulated Receptors:

Tendon Organs

A

o Proprioceptors located in tendons close to skeletal muscle insertion.
o Consist of small bundles of tendon fibers enclosed in layered capsule with sensory terminals coiling between and around the fibers.
o Muscle contraction stretches the tendon fibers, resulting in compression of the nerve fibers that activates the tendon organs. A reflex is initiated that causes contracting muscles to relax.

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21
Q

Types of Encapsulated Receptors:

Joint Kinesthetic Receptors

A

o Proprioceptors that monitor stretch in the articular capsules that enclose synovial joints.
o Receptor category contains four receptor types: Lamellar corpuscles, bulbous corpuscles, free nerve endings, and receptors resembling tendon organs.
o Together the receptors provide info. on joint position and motion.

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22
Q

Sensation:

A

Awareness of changes in the internal and external environments.

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23
Q

Perception:

A

Conscious interpretation of those stimuli.

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24
Q

The Somatosensory System:

A
  • The part of the sensory system serving the body walls and limbs.
  • Receives input from exteroceptors, proprioceptors, and interoceptors.
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25
Q

The 3 Main Levels of Neural Integration in the Somatosensory System:

A

o Receptor Level: Sensory receptors.

o Circuit Level: Processing in ascending pathways.

o Perceptual Level: Processing in cortical sensory areas.

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26
Q

For Processing at the Receptor Level to Occur These Things Must Happen:

A

o Stimulus energy must match the specificity of the receptor.
o Stimulus must be applied within a sensory receptor’s receptive field. The smaller the receptive field the greater the ability of the brain to accurately localize the stimulus site.
o Stimulus energy must be converted into the energy of a graded potential, this process is called Transduction. One of two types of Graded potential can be produced at the receptor level: 1) Generator Potential: When the receptor region is part of a sensory neuron. 2) Receptor Potential: When the receptor is a separate cell. The amount of NT release is changed.
o Graded-potentials in the first-order sensory neuron must reach threshold so that voltage-gated sodium channels on the axon are opened and nerve impulses are generated and propagated to the CNS.

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27
Q

Adaptation:

A

A change in sensitivity in the presence of a constant stimulus.

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28
Q

Phasic Receptors:

A
  • Fast-adapting.
  • Five bursts of impulses at the beginning and the end of the stimulus.
  • Report changes in the internal and external environment.
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29
Q

Tonic Receptors:

A
  • Provide a sustained response and never adapt.

- Nociceptors and Proprioceptors fit into this category.

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30
Q

Processing at the Circuit Level:

A

-Main objective for this level is to deliver impulses to the appropriate region of the cerebral cortex for localization and perception of the stimulus.

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31
Q

Processing at the Perceptual Level:

A

o At this level sensory input it interpreted in the cerebral cortex.
o Ability to identify and appreciate sensations depends on location of the target neurons in the sensory cortex, not on the nature of the message.
o The brain always interprets the activity of a specific sensory receptor as a specific sensation, no matter how it’s activated.

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32
Q

Perceptual Detection:

A
  • The ability to detect that a stimulus has occurred.
  • Simplest level of perception.
  • Inputs from several receptors must be summed for perceptual detection to occur.
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33
Q

Magnitude Estimation:

A
  • The ability to detect how intense the stimulus is.

- Perceived intensity increases as stimulus intensity increases because of frequency coding.

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34
Q

Spatial Discrimination:

A
  • Allows us to identify the site or pattern of stimulation.
  • Common tool for studying this quality is the two-point discrimination test which determines how close together two points on the skin can be and still be perceived as two points rather than as one.
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35
Q

Feature Abstraction:

A
  • The mechanism by which a neuron or circuit is tuned to one feature, or property, of a stimulus in preference to others.
  • Sensation usually involves an interplay of several stimulus features.
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36
Q

Quality Discrimination:

A
  • The ability to differentiate the submodalities of a particular sensation.
  • Each sensory modality has several qualities, or submodalities.
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37
Q

Pattern Recognition:

A

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

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38
Q

Perception of pain:

A

o Pain receptors activated by extremes of pressure, temperature, and a group of chemicals released from injured tissue.

o Sharp pain carried by smallest of myelinated sensory fibers, group A delta fibers. While the pain is carried slower than small nonmyelinated group C fibers both release the NTs glutamate and substance P, and activate second-order sensory neurons.

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39
Q

Pain Tolerance:

A

o Everybody has the same pain threshold, meaning we all perceive pain at roughly the same stimulus intensity. BUT we all have different tolerances to pain.

o Genes help determine a person’s pain tolerance and response to pain medications.

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40
Q

Hyperalgesia:

A

Pain amplification.

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41
Q

Phantom Limb Pain:

A

When somebody feels pain in a limb that is no longer present.

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42
Q

Visceral Pain:

A
  • Results from noxious stimulation of receptors in the organs of the thorax and abdominal cavity.
  • Dull aching, gnawing or burning in the deep tissue of the body.
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43
Q

Referred Pain:

A

Pain stimuli arising in one part of the body are perceived as coming from another part.

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44
Q

Nerves and the 3 Successive Wrappings of Nerves:

A

A cordlike organ that’s part of the peripheral nervous system. Vary in size but all consist of bundles of peripheral axons.

o Endoneurium: Delicate layer of loose connective tissue that also encloses the fiber’s associated Schwann cells.
o Perineurium: Coarser connective tissue wrapping, binds groups of fibers into fascicles.
o Epineurium: Encloses all fascicles to form the nerve.

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45
Q

Classifications of Nerves Based on the Direction they Transmit Impulses:

A

o Mixed Nerves: Contain both sensory and motor fibers and transmit impulses both to and from the CNS. Most nerves are in this category.

o Sensory (Afferent) Nerves: Carry impulses only toward the CNS.

o Motor (Efferent) Nerves: Carry impulses only away from the CNS.

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46
Q

The 4 Steps of Regeneration of Nerve Fibers in PNS:

A

o 1) The axon fragments.
o 2) Macrophages clean out the dead axon.
o 3) Axon filaments grow through a regeneration tube.
o 4) The axon regenerates and a new myelin sheath forms.

47
Q

Regeneration of Nerve Fibers in CNS:

A

o CNS fibers never regenerate.

o Damage to brain or spinal cord is irreversible.

48
Q

The 12 Cranial Nerves:

I. Olfactory

A
  • Tiny sensory nerves of smell.
  • Run from nasal mucosa to synapse with the olfactory bulbs.
  • SENSORY.
49
Q

The 12 Cranial Nerves:

II. Optic

A
  • Brain tract involved in vision.

- SENSORY.

50
Q

The 12 Cranial Nerves:

III. Oculomotor

A
  • Eye Mover.
  • Supplies 4 of the 6 extrinsic muscles that move the eyeball in orbit.
  • MOTOR.
51
Q

The 12 Cranial Nerves:

IV. Trochlear

A
  • Means “pulley” and innervates an extrinsic eye muscle that loops through a pulley-shaped ligament in the eyes orbit.
  • MOTOR.
52
Q

The 12 Cranial Nerves:

V. Trigeminal

A
  • Three branches spring from this, the largest cranial nerve.
  • Supplies sensory fibers to the face and motor fibers to the chewing muscles.
  • BOTH.
53
Q

The 12 Cranial Nerves:

VI. Abducens

A
  • The nerve that controls the extrinsic eye muscle that abducts the eyeball.
  • MOTOR.
54
Q

The 12 Cranial Nerves:

VII. Facial

A
  • Large nerve that innervates the muscles of facial expression.
  • BOTH.
55
Q

The 12 Cranial Nerves:

VIII. Vestibulocochlear

A
  • Mostly sensory nerve for hearing and balance.
  • Formerly called “auditory nerve”.
  • BOTH.
56
Q

The 12 Cranial Nerves:

IX. Glossopharyngeal

A
  • Means “tongue and pharynx”, structures that this nerve helps to innervate.
  • BOTH.
57
Q

The 12 Cranial Nerves:

X. Vagus

A
  • The only cranial nerve to extend beyond the head and neck to the thorax and abdomen.
  • BOTH.
58
Q

The 12 Cranial Nerves:

XI. Accessory

A
  • Considered an accessory part of the vagus nerve, formerly called spinal accessory nerve.
  • MOTOR.
59
Q

The 12 Cranial Nerves:

XII. Hypoglossal

A
  • Under the tongue.
  • Runs inferior to the tongue and innervates the tongue muscles.
  • MOTOR.
60
Q

Spinal Nerves:

A 
o	8 pairs of Cervical Spinal Nerves (C1-C8)
o	12 pairs of Thoracic Nerves (T1-T12)
o	5 pairs of Lumbar Nerves (L1-L5)
o	5 pairs of Sacral Nerves (S1-S5)
o	1 pair of Coccygeal Nerves (Co1)
61
Q

Rootlets:

A
  • What spinal roots are composed of.

- Attach along the length of the corresponding spinal cord segment.

62
Q

Ventral Roots:

A

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

63
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.

64
Q

The 3 Parts a Spinal Nerve Divides into After Emerging from the Foramen:

A

o Dorsal Ramus
o Ventral Ramus
o Meningeal Branch

65
Q

Rami Communicantes:

A

Special rami that contain autonomic (visceral) nerve fibers, attach to the base of the ventral rami of the thoracic spinal nerves.

66
Q

Nerve Plexuses:

A

Complicated, interlacing nerve networks formed by ventral ramis branching and joining together into one, lateral to the vertebral column.
o Occur in the cervical, brachial, lumbar, and sacral regions. NOT THORACIC!
o In these plexuses, fibers from various ventral rami criss-cross and redistribute so 1) each resulting branch of the plexus contains fibers from several spinal nerves. 2) Fibers from each ventral ramus travel to the body periphery via several routes.

67
Q

Cervical Plexuses:

A

o Under the sternocleidomastoid muscle, the ventral rami of the first four cervical nerves form it.
o Most of it’s branches are cutaneous nerves that supply only the skin.
o Transmit sensory impulses from the skin of the neck, ear, back of the head, and shoulder. Also they innervate the muscles of the anterior neck.
o Phrenic Nerve: Single most important nerve from this plexus. Recieves fibers from C3-C5. Runs inferiorly through the thorax and supplied both motor and sensory fibers to the diaphragm(Chief muscle for breathing movements).

68
Q

Nerves of the Brachial Plexus and Upper Limb:

Musculocutaneous

A
  • Muscular branches: flexor muscles in anterior arm.

- Cutaneous Branches: skin or lateral forearm

69
Q

Nerves of the Brachial Plexus and Upper Limb:

Median

A
  • Muscular branches in flexor group of anterior forearm; intrinsic muscles of lateral palm and digital branches of the fingers.
  • Cutaneous Branches: skin of lateral two-thirds of hand on ventral side and dorsum of fingers 2 and 3.
70
Q

Nerves of the Brachial Plexus and Upper Limb:

Ulnar

A
  • Muscular Branches: flexor muscles in anterior forearm; most intrinsic muscles of hand.
  • Cutaneous Branches: Skin of medial third of hand, both anterior and posterior aspects.
71
Q

Nerves of the Brachial Plexus and Upper Limb:

Radial

A
  • Muscular Branches: Posterior muscles of arm and forearm.

- Cutaneous branches: Skin of posterolateral surface of entire limb.

72
Q

Nerves of the Brachial Plexus and Upper Limb:

Axillary

A
  • Muscular Branches: Deltoid and teres minor muscles.

- Cutaneous Branches: Some skin of the shoulder region.

73
Q

Nerves of the Brachial Plexus and Upper Limb:

Dorsal Scapular

A

Rhomboid muscles and levator scapulae.

74
Q

Nerves of the Brachial Plexus and Upper Limb:

Long Thoracic

A

Serratus anterior muscle.

75
Q

Nerves of the Brachial Plexus and Upper Limb:

Subscapular

A

Teres major and subscapularis muscles.

76
Q

Nerves of the Brachial Plexus and Upper Limb:

Suprascapular

A

Shoulder joint; supraspinatus and infraspinatus muscles.

77
Q

Nerves of the Brachial Plexus and Upper Limb:

Pectoral

A

Pectoralis major and minor muscles.

78
Q

Nerves of the Branches of the Lumbar Plexus:

Femoral

A

Skin of anterior and medial thigh via anterior femoral cutaneous branch; skin of medial leg and foot, hip and knee joints via saphenous branch; motor to anterior muscles of thigh and to pectineus, iliacus.

79
Q

Nerves of the Branches of the Lumbar Plexus:

Obturator

A

Motor to adductor magnus, longus, and brevis muscles, gracilis muscle of medial thigh, obturator externus; sensory for skin of medial thigh and for hip and knee joints.

80
Q

Nerves of the Branches of the Lumbar Plexus:

Lateral Femoral Cutaneous

A

Skin of lateral thigh; some sensory branches to peritoneum.

81
Q

Nerves of the Branches of the Lumbar Plexus:

Iliohypogastric

A

Skin of lower abdomen and hip; muscles of anterolateral abdominal wall.

82
Q

Nerves of the Branches of the Lumbar Plexus:

Ilioinguinal

A

Skin of external genitalia and proximal medial aspect of the thigh; inferior abdominal muscles.

83
Q

Nerves of the Branches of the Lumbar Plexus:

Genitofemoral

A

Skin of scrotum in males, of labia majora in females, and of anterior thigh inferior to middle portion of inguinal region; cremaster muscle in males.

84
Q

Nerves of the Branches of the Sacral Plexus:

Sciatic Nerve

A

o Sciatic Nerve: Composed of two nerves (Tibial and Common Fibular) in a common sheath; they diverge just proximal to the knee.
o Tibial: Cutaneous Branches: to skin of posterior surface of leg and sole of foot. Motor Branches: To muscles of back of thigh, leg and foot.
o Common Fibular: Cutaneous Branches: To skin of anterior and lateral surface of leg and dorsum of foot. Motor branches: to short head of biceps femoris of thigh, fibular muscles of lateral compartment of leg, tibialis anterior, and extensor muscles of toes.

85
Q

Nerves of the Branches of the Sacral Plexus:

Superior Gluteal

A

Motor Branches: To gluteus medius and minimus and tensor fasciae latae.

86
Q

Nerves of the Branches of the Sacral Plexus:

Inferior Gluteal

A

Motor Branches: to gluteus maximus.

87
Q

Nerves of the Branches of the Sacral Plexus:

Posterior Femoral Cutaneous

A

Skin of buttocks, posterior thigh, and popliteal region; length varies; may also innervate part of skin of calf and heel.

88
Q

Nerves of the Branches of the Sacral Plexus:

Pudendal

A

Supplies most of the skin and muscles of perineum; external anal sphincter.

89
Q

Intercostal Nerves:

A
  • These nerves supply the intercostal muscles, the muscle and skin of the anterolateral thorax, and most of the abdominal wall.
  • The nerves also give off cutaneous branches to the skin.
90
Q

Subcostal Nerve:

A
  • The nerve lying inferior to the twelfth rib.

- Very UNUSUAL.

91
Q

Dermatome:

A
  • An area of skin innervated by the cutaneous branches of a single spinal nerve.
  • Every spinal nerve except C1 innervates dermatomes.
92
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.

93
Q

Motor Endings:

A

-The PNS elements that activate effectors by releasing neurotransmitters.

94
Q

Neuromuscular Junction:

A

Somatic motor fibers that innervate voluntary muscles form them with their effector cells.

95
Q

Varicosities:

A

Knoblike swellings containing mitochondria and synaptic vesicles.

96
Q

The 3 Levels of Motor Control:

1) Segmental Level

A

LOWEST. Consists of reflexes and spinal cord circuits that control automatic movements. Activates network of ventral horn neurons in a group of cord segements, causing them to stimulate specific groups of muscles.
o Central Pattern Generators: Circuits that control locomotion and other specific repeated motor activites.

97
Q

The 3 Levels of Motor Control:

2) Projection Level

A

MIDDLE. Upper motor neurons of the motor cortex initiate the direct (pyramidal) pathways. Axons of direct pathway neurons produce discrete voluntary movements of the skeletal muscles. Brain stem motor nuclei oversee the indirect pathways. Axons of these pathways help control reflex and CPG-controlled motor actions, modifying and controlling the activity of the segmental apparatus.

98
Q

The 3 Levels of Motor Control:

Precommand Level

A

HIGHEST. In the Cerebellum(Sensorimotor integration and control center) and Basal Nuclei(input receptor). Programs and instructions.

99
Q

Inborn (Intrinsic) Reflex:

A

A rapid, predictable motor response to a stimulus.

100
Q

Learned (acquired) Reflex:

A

Results from practice or repetition.

101
Q

The 5 Components of a Reflex Arc:

A
  • 1) Receptor: Site of the stimulus action.
  • 2) Sensory Neuron: Transmits afferent impulses to the CNS.
  • 3) Integration Center: In simple reflex arcs, the integration center may be a single synapse between a sensory neuron and motor neuron (monosynaptic reflex). More complex reflex arcs involve multiple synapses with chains of interneurons (polysynaptic reflex).
  • 4) Motor Neuron: Conducts efferent impulses from the integration center to an effector organ.
  • 5) Effector: Muscle fiber or gland cell that responds to the efferent impulses (by contracting or secreting).
102
Q

Somatic Reflexes:

A

Activate skeletal muscle.

103
Q

Autonomic (Visceral) Reflexes:

A

Activate visceral effectors.

104
Q

Spinal Reflexes:

A
  • Somatic reflexes that are mediated by the spinal cord.

- Many occur without direct involvement of higher brain centers.

105
Q

Stretch Reflex:

A

Makes sure that the muscles stay at a certain set length.

106
Q

Monosynaptic and Ipsilateral:

A

All stretch reflexes involve a single synapse and motor activity on the same side of the body.

107
Q

Tendon Reflexes:

A

Polysynaptic, muscles relax and lengthen in response to tension.

108
Q

Reciprocal Activation:

A

Motor neurons in spinal cord circuits supplying the contracting muscles are inhibited and antagonist muscles are activated.

109
Q

Flexor or Withdrawal Reflex:

A

Causes automatic withdrawal of threatened body part from the painful stimulus.

110
Q

Crossed-Extensor Reflex:

A
  • Often accompanies the flexor reflex in weight-bearing limbs and is important in maintaining balance.
  • For instance if you step on a piece of glass you automatically lift the injured foot a reflex causes your other leg to tense in order to bare your weight.
111
Q

Superficial Reflexes:

A

Elicited by gentle cutaneous sensation such as stroking of the skin with a tongue depressor.

112
Q

Plantar Reflex:

A

Tests integrity of spinal cord from L4-S2. The sole of the foot I poked, a normal response is for the toes to curl, however if the primary motor cortex or corticospinal tract is damaged the big toe will dorsiflex and the smaller toes fan laterally. This is called Babinski’s sign.

113
Q

Abdominal Reflex:

A

Stroking skin of lateral abdomen checks integrity of spinal cord from T8-T12. No response indicates legions in the corticospinal tract.

Anatomy 201 (12 decks)

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