Chapter 13: The Peripheral Nervous System and Reflex Activity

Question 1

5 sensory receptors classified by stimulus type

Answer 1

1. Mechanoreceptors
2. Thermoreceptors
3. Photoreceptors
4. Chemoreceptors
5. Nociceptors

Question 2

Mechanoreceptors

Answer 2

respond to touch, pressure, vibration, and stretch

Question 3

Thermoreceptors

Answer 3

sensitive to changes in temperature

Question 4

Photoreceptors

Answer 4

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

Question 5

Chemoreceptors

Answer 5

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

Question 6

Nociceptors

Answer 6

sensitive to paint-causing stimuli (e.g., extreme heat or cold, excessive pressure, inflammatory chemicals)

Question 7

1st step in regeneration of a PNS axon

Answer 7

• the axon fragments
• cut axon ends seal themselves off
• axon transport interrupted, causing cut ends to swell
• without access to cell body, axon and its myelin sheath begins to disintegrate distal to the injury
• degeneration of distal end of cut axon, called Wallerian degeneration, spreads down axon

Question 8

2nd step in regeneration of a PNS axon

Answer 8

• Schwann cells and macrophages clean out dead axon distal to injury
• surviving Schwann cells engulf myelin fragments and secrete chemicals that recruit macrophages
• macrophages help dispose of debris and release chemicals that stimulate Schwann cells to divide

Question 9

3rd step in regeneration of a PNS axon

Answer 9

• axon filaments grow through a regeneration tube
• Schwann cells release growth factors and express cell adhesion molecules (CAMs) that encourage axon growth
• Schwann cells line up along the tube of remaining endoneurium, forming a regeneration tube that guides the regenerating axon “sprouts” across the gap to their original contact

Question 10

4th step in regeneration of a PNS axon

Answer 10

• the axon regenerates and a new myelin sheath forms
• Schwann cells protect and support the regeneration axon and ultimately produce a new myelin sheath

Question 11

Cranial nerves (I-XII)

Answer 11

I. Olfactory
II. Optic
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Vestibulocochlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal

Question 12

Sensory cranial nerves

Answer 12

I. Olfactory: smell
II. Optic: vision
VIII. hearing and balance: cochlea (hearing receptors) and vestibule of inner ear (equilibrium receptors)

Question 13

Motor cranial nerves

Answer 13

III. Oculomotor
IV. Trochlear
VI. Abducens
XI. Accessory
XII. Hypoglossal

Question 14

Motor cranial nerves: motor nerves for eye movement

Answer 14

III. Oculomotor: innervates 4/6 extrinsic eye muscles: inferior oblique, superior rectus, inferior rectus, medial rectus
IV. Trochlear: innervates 1/6 extrinsic eye muscles: superior oblique muscle
VI. Abducens: innervates 1/6 extrinsic eye muscles: lateral rectus muscle

Question 15

Other motor cranial nerves

Answer 15

XI. Accessory: move head and neck innervates sternocleidomastoid and trapezius
XII. Hypoglossal: swallowing and speech; innervates all extrinsic and intrinsic muscles of tongue except palatoglossus

Question 16

Sensory and motor cranial nerves

Answer 16

V. Trigeminal- sensory: general sensation; motor: mandibular branch, muscle of mastication (chewing)
VII. Facial- sensory: taste; motor: chief motor nerve of face- facial expression, lacrimal glands, salivary glands
IX. Glossopharyngeal- sensory: taste; motor: tongue and pharynx for swallowing, parotid salivary glands
X. Vagus- sensory: taste; motor: heart, lung and abdominal vescera (regulate heart rate, breathing, digestive system activity), pharynx and larynx (swallowing)

Question 17

Largest cranial nerve

Answer 17

Trigeminal (V): actually 3 nerves

Question 18

2 cranial nerves with multiple branches and names of the branches

Answer 18

Facial (VII): 5 branches- temporal, zygomatic, buccal, mandibular, and cervical
Trigeminal (V): 3 branches- ophthalmic, maxillary, and mandibular

Question 19

Tic Douloureux - cause & cranial nerve associated

Answer 19

Cause: compression of trigeminal nerve near brain stem
What is it: inflammation of trigeminal nerve, produces excruciating pain
* treated with meds, if unresponsive –> surgery to relieve compression or destroy nerve –> loss of sensation on side of face with destroyed nerve

Question 20

Bell’s palsy: cause & cranial nerve associated

Answer 20

cause: inflamed, swollen facial nerve, possibly due to herpes simplex 1 viral infection
What is it: paralysis of facial muscles on affected side with partial loss of taste
* treatment w/ corticosteroids

Question 21

Nerve Plexuses

Answer 21

• interweaving network of nerves formed by branching and interconnection of ventral rami
• each branch contains fibers from several different spinal nerves

Question 22

What is the benefit of arranging nerves in plexuses

Answer 22

• damage to one branch does not cause paralysis because there are other branches involved in the plexus
• allows for a more organized distribution of nerve signals to different body parts

Question 23

How might the major nerve of the sacral plexus be damaged

Answer 23

• sciatica: stabbing pain in sciatic nerve
• causes: fall, disc herniation, improperly placed injection buttocks
• if nerve cut leg nearly useless- cannot flex leg, foot drop (plantar flexion bc foot and ankle cannot move)
• recovery from sciatic nerve injury is slow and incomplete (deficits remain)

Question 24

Nerve plexuses and their major nerves

Answer 24

• cervical; major nerve: phrenic
• brachial; major nerves: axillary, musculocutaneous, median, radial, ulnar
• lumbar; major nerves: femoral, obturator
• sacral; major nerves: sciatic (composed of tibial and common fibular)

Question 25

Brachial plexus- how subdivisions are oriented from medial to lateral (4)

Answer 25

1. Roots: five ventral rami (C5 to T1 which unite to form... 2. Trunks: upper, middle, and lower, which unite to form... 3. Divisions: anterior and posterior, which unite to form... 4. Cords: lateral, medial, and posterior

Question 26

Intrinsic (inborn) reflexes

Answer 26

* rapid, predictable, involuntary motor movements in response to some stimuli * not learned, not premeditated, subconscious (happen without thinking) * regulated by brain stem and spinal cord * ex. posture, control of visceral activities

Question 27

Learned (acquired) reflexes

Answer 27

* acquired, result from practice or repetitions * ex. riding a bike, driving a car * with practice these activities become largely automatic bc we have put a lot of time and effort into developing the skill

Question 28

Dermatomes - what are they

Answer 28

* area of skin innervated by cutaneous branches of a single spinal nerve (all spinal nerves except C1) * areas of skin that send signals to the brain through spinal nerves

Question 29

Dermatomes - how are they useful to clinicians

Answer 29

* can help healthcare provider detect and diagnose conditions or problems affecting spine, spinal cord, or spinal nerves * extent of spinal cord injuries ascertained by affected dermatomes

Question 30

Stretch reflexes (4)

Answer 30

* plantar * crossed extensor * knee-jerk * tendon reflex

Question 31

Stretch reflexes purpose

Answer 31

* maintain posture and muscle tone in postural muscles * muscles contract if stretched too far

Question 32

Can you artificially trigger any of the stretch reflexes? If so, how would you trigger that stretch reflex to assess it in a clinical setting?

Answer 32

Stretch reflexes can be used for clinical testing, such as by tapping the patellar tendon, to stimulate the knee-jerk reflex, which slightly stretches the quadriceps muscle

Question 33

Babinski's sign- what is it

Answer 33

damage to primary motor cortex or corticospinal tracts causes abnormal response called Babinski's sign- big toe dorsiflexes, smaller toes fan out laterally * normal response: downward curling (flexion) of toes

Question 34

What reflex is this associated with

Answer 34

plantar (babinski) reflex

Question 35

When is it normal vs abnormal to see babinski's sign

Answer 35

normal: infants (1-1.5 years old) due to incomplete myelination of nerve fibers abnormal: children older than 2