Peripheral Nervous System

Question 1

What are the 31 Pairs of Spinal Nerves?

Answer 1

*Cervical: 8
*Thoracic: 12
*Lumbar: 5
*Sacral: 5
*Coccygeal: 1

Question 2

What are Dermatomes?

Answer 2

*Map showing the relationship between sensory receptors of the skin and the spinal nerves
*Useful in clinical setting when trying to determine if there has been spinal cord or spinal nerve damage

Question 3

What is Paraplegia?

Answer 3

Paraplegia
* Damage between T1 →L2
* Loss of feeling/motor functions of legs

Question 4

What is Quadriplegia?

Answer 4

Quadriplegia
* Damage above T1
* Loss of feeling/motor functions of all 4 limbs
* May be partial or full loss of upper limbs
* If damage occurs above C4, diaphragm is impacted
* Loss of ability to breathe without help

Question 5

What is Shingles?

Answer 5

*Varicella-zoster virus resides in single dorsal
root ganglion
- From previous chicken pox infection
*If immune system is weakened (due to
illness or age), virus can multiply, travel
along peripheral sensory nerves, and cause
painful skin lesions
*The lesions are located within a dermatome
*A vaccination is available to prevent
outbreak

Question 6

What is Structural Organization
of PNS?

Answer 6

*Sensory receptors →sensory neurons
- Respond to stimulus and initiate action potentials
- (Some sensory neurons are able to respond to stimuli without a receptor)
*→Motor neurons
*→Effector(s)

Question 7

What ar sensory receptors?

Answer 7

Can be simple
* Ex. Free nerve ending (dendrite) of sensory neuron
Can be complex
* Ex. Specialized cell (Pacinian corpuscle)
Functional classification of receptors
* Mechanoreceptors: respond to mechanical forces
* Thermoreceptors: temperature changes
* Chemoreceptors: chemicals
* Photoreceptors: light
* Nociceptors: pain

Question 8

What is Specialized Sensory Processing?

Answer 8

Echolocation
Magnetoreception

Question 9

What is Echolocation?

Answer 9

Echolocation
* Not just for bats!
* Humans can train themselves to use
echoes to help with navigation
(especially those without sight)

Question 10

What is Magnetoreception?

Answer 10

Magnetoreception
* Are humans innately able to respond to
magnetic forces/ sense magnetic fields?
* A magnetosensitive protein (cryptochrome-
2) has been found in the human eye

Question 11

What is Mechanoreceptors: Meissner’s Corpuscle?

Answer 11

*Mechanoreceptors respond to distortion caused by pressure changes, vibration, etc.
*An example is the Miessner’s(tactile) corpuscle
- Responds to light, discriminative touch
- Located in dermal papillae of hairless skin

Question 12

What is Mechanoreceptors: Pacinian Corpuscle?

Answer 12

Pacinian (lamellar) corpuscle
* Responds to deep pressure
* Located in dermis and hypodermis
* Adapt rapidly, so good at on/off processing or
rapid vibration

Question 13

What is Mechanoreceptors: Ruffini Endings?

Answer 13

Ruffini endings (bulbous corpuscle)
* Located in dermis and hypodermis
* Respond to deep pressure, stretch
* Adapt slowly so are able to monitor continuous pressure

Question 14

What are Mechanoreceptors: Proprioceptors?

Answer 14

*Proprioceptors are encapsulated nerve endings that monitor stretch in their locomotory organs (muscles, tendons, etc.)
- Examples: muscle spindle, (golgi) tendon organ
*Offer awareness of movement
*Cerebellum uses information to determine where our body parts are in space

Question 15

What are Mechanoreceptors: Root Hair Plexus?

Answer 15

Root hair plexus
* Free nerve endings wrapped around hair follicle
* Respond to movement (deflection) of the hair

Question 16

What are Thermoreceptors?

Answer 16

*Free nerve endings that respond to temperature changes
*Found throughout the body

Question 17

What are Nociceptors?

Answer 17

*Free nerve endings that respond to mechanical, thermal, or chemical stimuli
- Examples: excessive pressure, extreme temperatures, chemical released from damaged cells
*Pain is the emotional way our brain interprets the stimulus

Question 18

What are Itch Receptors?

Answer 18

*Itch receptors are recently discovered free nerve endings
- Scientists used to believe nociceptors responded to the itch stimulus
*Itch receptors respond to inflammatory chemicals (ex. Histamine)
*A major difference between nociception and itch:
- Pain elicits a withdrawal reflex
- Itch elicits a scratch reflex

Question 19

What are Chemoreceptors: Taste?

Answer 19

*Chemoreceptors respond to certain chemicals
- Taste, olfaction, blood chemistry
*Taste buds have chemoreceptors that respond to chemicals of food
*Gustatory pathway:
- Chemoreceptor of taste bud →spinal cord →thalamus →gustatory cortex in insula

Question 20

What are Photoreceptors: Eye?

Answer 20

*Photoreceptors respond to light
* found in retina of eye
- (melanocytes have now been found to be photoreceptive)

Question 21

What are Peripheral Nerves?

Answer 21

*Include cranial nerves and spinal nerves
* All cranial nerves except the Vagus (X) are involved with functions of the head and neck
* 31 pairs of spinal nerves form nerve plexuses

Question 22

What are the Divisions of a Spinal Nerve?

Answer 22

*Spinal nerves split into a dorsal ramus and a ventral ramus
*The ventral rami form the nerve plexuses
- Except in the thoracic region
– Ventral rami innervate the thoracic cage

Question 23

What is the Nerve Plexuses?

Answer 23

*A plexus is a network of nerves that supply specific regions of the body
*Made of ventral rami of all spinal nerves except T2-T12
*Nerve plexuses:
- Cervical
- Brachial
- Lumbar
- Sacral

Question 24

What is the Cervical Plexus?

Answer 24

*Formed from ventral rami C1-C5
*Innervates back of neck and diaphragm
- Damage to phrenic nerve can impair breathing

Question 25

What is Brachial Plexus?

Answer 25

*Formed from ventral rami C5-T1
*Innervates upper limb

Question 26

What is Lumbar Plexus?

Answer 26

*Formed from ventral rami L1-L4
*Innervates anterior region of lower limb

Question 27

What is Sacral Plexus?

Answer 27

*Formed from ventral rami L4-S4
*Innervates posterior region of lower limb

Question 28

What is Sciatic Nerve formed from?

Answer 28

*Formed from sacral plexus

Question 29

What is Polio?

Answer 29

*Virus that in some individuals targets motor neurons
*Epidemic in mid-1900s
- Vaccine was developed in 1955
*Level of paralysis determined by which motor neurons infected
* Many infected recovered completely
- However, 30 years later have weakness, muscle wasting, called postpolio syndrome
*Iron lungs helped those whose respiratory muscles were paralyzed (image on right)

Question 30

Is polio still present?

Answer 30

• The U.S. has been successful at eradicating polio, but not all countries have
  (Afghanistan, Pakistan, Nigeria still have the virus)

Question 31

What is the Innervation of Skeletal Muscle?

Answer 31

*Motor neurons innervate skeletal muscle

Question 32

What is Postpolio Syndrome?

Answer 32

*During infection with poliovirus, motor neuron is invaded
*That neuron is destroyed, but neighboring motor neuron is not
*After recovery, surviving neurons extend axonal branches to muscle missing innervation
*These benevolent neurons over-exert and lose function