Chapter 13: The PNS and Reflexes

Question 1

Sensory Receptors:

Answer 1

Specialized to respond to changes in the environment called Stimuli.

Question 2

What Sensory Receptors are Classified by:

Answer 2

o 1) Type of Stimulus they detect

o 2) Body Location

o 3) Structural Complexity

Question 3

Classification of Sensory Receptors by Stimulus Type:

Mechanoreceptors

Answer 3

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

Question 4

Classification of Sensory Receptors by Stimulus Type:

Thermoreceptors

Answer 4

Respond to temperature changes.

Question 5

Classification of Sensory Receptors by Stimulus Type:

Photoreceptors

Answer 5

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

Question 6

Classification of Sensory Receptors by Stimulus Type:

Chemoreceptors

Answer 6

Respond to chemicals in solution.

Question 7

Classification of Sensory Receptors by Stimulus Type:

Nociceptors

Answer 7

Respond to potentially damaging stimuli that result in pain.

Question 8

Classification of Sensory Receptors by Location:

Exteroceptors

Answer 8

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.

Question 9

Classification of Sensory Receptors by Location:

Interoceptors

Answer 9

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.

Question 10

Classification of Sensory Receptors by Location:

Proprioceptors

Answer 10

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.

Question 11

The 2 Classifications of Receptors by Structure:

Answer 11

o	Nonencapsulated (Free)
o	Encapsulated

Question 12

Types and Aspects of Nonencapsulated (Free) Receptors:

Answer 12

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.

Question 13

Other Types of Nonencapsulated (Free) Receptors:

Tactile (Merkel) Discs

Answer 13

• 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.

Question 14

Other Types of Nonencapsulated (Free) Receptors:

Hair Follicle Receptors

Answer 14

• Free nerve endings that wrap around hair follicles.

- Light touch receptors that detect bending of hairs.

Question 15

Encapsulated Receptors:

Answer 15

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.

Question 16

Types of Encapsulated Receptors:

Tactile Corpuscles

Answer 16

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.

Question 17

Types of Encapsulated Receptors:

Lamellar Corpuscles

Answer 17

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.

Question 18

Types of Encapsulated Receptors:

Bulbous Corpuscles

Answer 18

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.

Question 19

Types of Encapsulated Receptors:

Muscle Spindles

Answer 19

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.

Question 20

Types of Encapsulated Receptors:

Tendon Organs

Answer 20

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.

Question 21

Types of Encapsulated Receptors:

Joint Kinesthetic Receptors

Answer 21

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.

Question 22

Sensation:

Answer 22

Awareness of changes in the internal and external environments.

Question 23

Perception:

Answer 23

Conscious interpretation of those stimuli.

Question 24

The Somatosensory System:

Answer 24

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

Question 25

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

Answer 25

o Receptor Level: Sensory receptors. o Circuit Level: Processing in ascending pathways. o Perceptual Level: Processing in cortical sensory areas.

Question 26

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

Answer 26

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.

Question 27

Adaptation:

Answer 27

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

Question 28

Phasic Receptors:

Answer 28

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

Question 29

Tonic Receptors:

Answer 29

- Provide a sustained response and never adapt. | - Nociceptors and Proprioceptors fit into this category.

Question 30

Processing at the Circuit Level:

Answer 30

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

Question 31

Processing at the Perceptual Level:

Answer 31

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.

Question 32

Perceptual Detection:

Answer 32

- 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.

Question 33

Magnitude Estimation:

Answer 33

- The ability to detect how intense the stimulus is. | - Perceived intensity increases as stimulus intensity increases because of frequency coding.

Question 34

Spatial Discrimination:

Answer 34

- 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.

Question 35

Feature Abstraction:

Answer 35

- 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.

Question 36

Quality Discrimination:

Answer 36

- The ability to differentiate the submodalities of a particular sensation. - Each sensory modality has several qualities, or submodalities.

Question 37

Pattern Recognition:

Answer 37

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.

Question 38

Perception of pain:

Answer 38

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.

Question 39

Pain Tolerance:

Answer 39

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.

Question 40

Hyperalgesia:

Answer 40

Pain amplification.

Question 41

Phantom Limb Pain:

Answer 41

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

Question 42

Visceral Pain:

Answer 42

- 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.

Question 43

Referred Pain:

Answer 43

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

Question 44

Nerves and the 3 Successive Wrappings of Nerves:

Answer 44

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.

Question 45

Classifications of Nerves Based on the Direction they Transmit Impulses:

Answer 45

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.

Question 46

The 4 Steps of Regeneration of Nerve Fibers in PNS:

Answer 46

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.

Question 47

Regeneration of Nerve Fibers in CNS:

Answer 47

o CNS fibers never regenerate. | o Damage to brain or spinal cord is irreversible.

Question 48

The 12 Cranial Nerves: I. Olfactory

Answer 48

- Tiny sensory nerves of smell. - Run from nasal mucosa to synapse with the olfactory bulbs. - SENSORY.

Question 49

The 12 Cranial Nerves: II. Optic

Answer 49

- Brain tract involved in vision. | - SENSORY.

Question 50

The 12 Cranial Nerves: III. Oculomotor

Answer 50

- Eye Mover. - Supplies 4 of the 6 extrinsic muscles that move the eyeball in orbit. - MOTOR.

Question 51

The 12 Cranial Nerves: IV. Trochlear

Answer 51

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

Question 52

The 12 Cranial Nerves: V. Trigeminal

Answer 52

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

Question 53

The 12 Cranial Nerves: VI. Abducens

Answer 53

- The nerve that controls the extrinsic eye muscle that abducts the eyeball. - MOTOR.

Question 54

The 12 Cranial Nerves: VII. Facial

Answer 54

- Large nerve that innervates the muscles of facial expression. - BOTH.

Question 55

The 12 Cranial Nerves: VIII. Vestibulocochlear

Answer 55

- Mostly sensory nerve for hearing and balance. - Formerly called “auditory nerve”. - BOTH.

Question 56

The 12 Cranial Nerves: IX. Glossopharyngeal

Answer 56

- Means “tongue and pharynx”, structures that this nerve helps to innervate. - BOTH.

Question 57

The 12 Cranial Nerves: X. Vagus

Answer 57

- The only cranial nerve to extend beyond the head and neck to the thorax and abdomen. - BOTH.

Question 58

The 12 Cranial Nerves: XI. Accessory

Answer 58

- Considered an accessory part of the vagus nerve, formerly called spinal accessory nerve. - MOTOR.

Question 59

The 12 Cranial Nerves: XII. Hypoglossal

Answer 59

- Under the tongue. - Runs inferior to the tongue and innervates the tongue muscles. - MOTOR.

Question 60

Spinal Nerves:

Answer 60

``` 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) ```

Question 61

Rootlets:

Answer 61

- What spinal roots are composed of. | - Attach along the length of the corresponding spinal cord segment.

Question 62

Ventral Roots:

Answer 62

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

Question 63

Dorsal Roots:

Answer 63

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

Question 64

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

Answer 64

o Dorsal Ramus o Ventral Ramus o Meningeal Branch

Question 65

Rami Communicantes:

Answer 65

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

Question 66

Nerve Plexuses:

Answer 66

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.

Question 67

Cervical Plexuses:

Answer 67

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).

Question 68

Nerves of the Brachial Plexus and Upper Limb: Musculocutaneous

Answer 68

- Muscular branches: flexor muscles in anterior arm. | - Cutaneous Branches: skin or lateral forearm

Question 69

Nerves of the Brachial Plexus and Upper Limb: Median

Answer 69

- 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.

Question 70

Nerves of the Brachial Plexus and Upper Limb: Ulnar

Answer 70

- 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.

Question 71

Nerves of the Brachial Plexus and Upper Limb: Radial

Answer 71

- Muscular Branches: Posterior muscles of arm and forearm. | - Cutaneous branches: Skin of posterolateral surface of entire limb.

Question 72

Nerves of the Brachial Plexus and Upper Limb: Axillary

Answer 72

- Muscular Branches: Deltoid and teres minor muscles. | - Cutaneous Branches: Some skin of the shoulder region.

Question 73

Nerves of the Brachial Plexus and Upper Limb: Dorsal Scapular

Answer 73

Rhomboid muscles and levator scapulae.

Question 74

Nerves of the Brachial Plexus and Upper Limb: Long Thoracic

Answer 74

Serratus anterior muscle.

Question 75

Nerves of the Brachial Plexus and Upper Limb: Subscapular

Answer 75

Teres major and subscapularis muscles.

Question 76

Nerves of the Brachial Plexus and Upper Limb: Suprascapular

Answer 76

Shoulder joint; supraspinatus and infraspinatus muscles.

Question 77

Nerves of the Brachial Plexus and Upper Limb: Pectoral

Answer 77

Pectoralis major and minor muscles.

Question 78

Nerves of the Branches of the Lumbar Plexus: Femoral

Answer 78

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.

Question 79

Nerves of the Branches of the Lumbar Plexus: Obturator

Answer 79

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.

Question 80

Nerves of the Branches of the Lumbar Plexus: Lateral Femoral Cutaneous

Answer 80

Skin of lateral thigh; some sensory branches to peritoneum.

Question 81

Nerves of the Branches of the Lumbar Plexus: Iliohypogastric

Answer 81

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

Question 82

Nerves of the Branches of the Lumbar Plexus: Ilioinguinal

Answer 82

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

Question 83

Nerves of the Branches of the Lumbar Plexus: Genitofemoral

Answer 83

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.

Question 84

Nerves of the Branches of the Sacral Plexus: Sciatic Nerve

Answer 84

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.

Question 85

Nerves of the Branches of the Sacral Plexus: Superior Gluteal

Answer 85

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

Question 86

Nerves of the Branches of the Sacral Plexus: Inferior Gluteal

Answer 86

Motor Branches: to gluteus maximus.

Question 87

Nerves of the Branches of the Sacral Plexus: Posterior Femoral Cutaneous

Answer 87

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

Question 88

Nerves of the Branches of the Sacral Plexus: Pudendal

Answer 88

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

Question 89

Intercostal Nerves:

Answer 89

- 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.

Question 90

Subcostal Nerve:

Answer 90

- The nerve lying inferior to the twelfth rib. | - Very UNUSUAL.

Question 91

Dermatome:

Answer 91

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

Question 92

Hilton's Law:

Answer 92

-Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint.

Question 93

Motor Endings:

Answer 93

-The PNS elements that activate effectors by releasing neurotransmitters.

Question 94

Neuromuscular Junction:

Answer 94

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

Question 95

Varicosities:

Answer 95

Knoblike swellings containing mitochondria and synaptic vesicles.

Question 96

The 3 Levels of Motor Control: 1) Segmental Level

Answer 96

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.

Question 97

The 3 Levels of Motor Control: 2) Projection Level

Answer 97

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.

Question 98

The 3 Levels of Motor Control: Precommand Level

Answer 98

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

Question 99

Inborn (Intrinsic) Reflex:

Answer 99

A rapid, predictable motor response to a stimulus.

Question 100

Learned (acquired) Reflex:

Answer 100

Results from practice or repetition.

Question 101

The 5 Components of a Reflex Arc:

Answer 101

- 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).

Question 102

Somatic Reflexes:

Answer 102

Activate skeletal muscle.

Question 103

Autonomic (Visceral) Reflexes:

Answer 103

Activate visceral effectors.

Question 104

Spinal Reflexes:

Answer 104

- Somatic reflexes that are mediated by the spinal cord. | - Many occur without direct involvement of higher brain centers.

Question 105

Stretch Reflex:

Answer 105

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

Question 106

Monosynaptic and Ipsilateral:

Answer 106

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

Question 107

Tendon Reflexes:

Answer 107

Polysynaptic, muscles relax and lengthen in response to tension.

Question 108

Reciprocal Activation:

Answer 108

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

Question 109

Flexor or Withdrawal Reflex:

Answer 109

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

Question 110

Crossed-Extensor Reflex:

Answer 110

- 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.

Question 111

Superficial Reflexes:

Answer 111

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

Question 112

Plantar Reflex:

Answer 112

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.

Question 113

Abdominal Reflex:

Answer 113

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