NA and NP (3) - Cranial nerves

Question 1

Which cranial nerves serve only the head and neck structures?

Answer 1

All cranial nerves except the vagus

Question 2

What are the 12 cranial nerves?

Answer 2

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1) Olfactory
2) Optic
3) Occulomotor
4) Trochlea
5) Trigeminal
6) Abducens
7) Facial
8) Vestibulocochlear
9) Glossopharyngeal
10) Vagus
11) Accesory
12) Hypoglossal

Question 3

Which cranial nerves are sensory, motor, or both?

Answer 3

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1- Sensory
2- Sensory
3- Motor
4- Motor
5- Both
6- Motor
7- Both
8- Sensory
9- Both
10- Both
11- Motor
12- Motor

Question 4

What forms as a result of the optic nerve?

Answer 4

The toptic chiasma (fibers partially cross over) and then as optic tracts to the thalamus

Optical radiation to the occiptal cortex

Question 5

Which are the cranial nerves that supply the extrinsic eye muscles? What is the fraction that each nerve supplies?

Answer 5

1; Occulomotor nerves - supply 4/6 extrinsic eye muscles of eyeball, when constracted allows for control of the left and right eye movement

2; Trochlear nerves - innervates 1 pair of extrinsic eye muscles which allows us to see angles, loops through a pulley shaped ligament in orbit

3; Abducens nerve - controls the extrinsic eye muscle tat abducts the eyeball (lateral rectus muscle)

Question 6

What are the different subsections of the 31 spinal nerves?

Answer 6

c1-c8 ; cervical

t1-t12 ; thoracic

L1-L5 ; lumbar

s1-s5 ; sacral

c0 = coccygeal

Question 7

Difference between roots and rami?

Answer 7

Root = one way traffic (to and from spinal cord)

Rami = 2 way traffic (dorsal and ventral with sensory and motor

Question 8

What are the 4 main nerve plexuses and what is their most important nerve within?

Answer 8

1. Cervical plexus and the neck; phrenic nerve controls both motor and sensory fibers to diaphragm
2. Brachial plexus and upper limbs; axillary nerve, musculocutaneous nerve, ulnar nerve, radial nerve, median nerve
3. Lumbar plexus; femoral nerve = anterior thigh muscles to thigh flexors and knee extensors, obturator nerve = medial thigh to adductor muscles
4. Sacral plexus; sciatic nerve diverges into tibial and common fibular nerve. Also superior and inferior gluteal nerves, pudendal nerve.

Question 9

What is a dermatome? What can they be used for clinically?

Answer 9

Area of skin innervated by cutaneous branches of a single spinal nerve

Can be used if a surgeon is going to use local anesthetic to know which nerves or areas to freeze to restrict or suppress pain for a specific region

Question 10

From innermost to outermost, what are the three wrappings found around nerve?

Answer 10

Inner - Endoneurium
= CT that encloses a nerve fiber and associated myelin/neurilemma sheath

Middle - Perineurium
= Coarser CT wrapping around a group of fibers (fascicles)

Outer - Epineurium
= Tough fibrous sheath around all the fascicles to make a nerve

Question 11

What are the types of sensory receptors according to the stimulus detected?

Answer 11

• mechanoreceptors (touch, pressure, BP, vibration, stretch
• thermoreceptors (temperature)
• photoreceptors (light energy found in our eyes)
• chemoreceptors (chemicals in solution such as taste or smell, chemicals in the blood plasma - osmolarity)
• nociceptors (pain or damaging stimuli)

Question 12

What are the sensory receptor types according to their location?

Answer 12

Exteroceptors; surface of the body - stimuli outside the body (touch, pressure, pain, temperature and special senses)

Interoceptors; AKA visceroceptors, stimuli within the body (visceral organs, blood vessels - chemicals, stretch, temperature)

Proprioceptors; skeletal muscle, tendons, joints, ligaments, CT coverings of bone and muscle (monitor stretch)

Question 13

What are the types of sensory receptors according to its structural complexity?

Answer 13

1) Nonencapsulated (free) nerve endings: found in epithelia and CT

• Vanilloid receptor; ion channels are opened by heat, low pH, capsaicin chemicals (spicy foods)
• Itch receptors; in dermis, activated by several inflammatory channels (histamine)
• Epithelial tactile complexes; junction of epidermis and dermis with light pressure receptors (Merkel discs associate with these)
• Hair follicle receptors; light touch receptors detecting hair bending

2) Encapsulated nerve endings: enclosed in a CT capsule and tend to be mechanoreceptors

• Tactile corpuscles (Meissners corpuscles); sensory terminals surrounded by Schwann cells and a thin CT capsule (dermal papillae of nipples, fingertips, soles of feet)
• Lamellar corpuscles (Pacinian corpuscles); single dendrite with capsule of up to 60 collagen fiber layers, activated when pressure is first applied (vibration)
• Bulbous corpuscles (Ruffinis corpuscles); spray of receptor endings enclosed by a flattened capsule, activated during deep and continuous pressure
• Muscle spindles (proprioceptors); associated with muscle fascicles, is modified skeletal muscle fibers (intrafusal fibers) that detect muscle stretch (reflexes to resist stretch)
• Tendon organs (proprioceptors); small bundles of collagen fibers in capsules with sensory terminals (when muscles shorten a reflex causes relaxation)
• Joint kinesthetic receptors (proprioceptors); associated with articular capsules, a combo of everything except muscle spindles (monitors awareness of joint position)