Neurophysiology I

Question 1

describe the four types of mechanoreceptors in the skin and what stimulus they respond to

Answer 1

Mechanoreceptors - specialized sense organs

1) Meissner’s corpuscles
- dendrites encapsulated in connective tissue
- respond to changes in texture and slow vibrations
2) Merkel cells
- expanded dendritic endings
- respond to sustained pressure and touch
3) Ruffini corpuscles
- enlarged dendritic endings with elongated capsules
- respond to sustained pressure and touch
4) Pacinian corpuscles
- unmyelinated dendritic endings of a sensory nerve fiber 2um in diameter- encapsulated by connective tissue
- respond to deep pressure and fast vibration

Question 2

Describe the receptors that mediate the sensation of pain and temperature

Answer 2

Nociceptors - free nerve endings
four types:
1) Mechanical - respond to deep pressure
2) Thermal - respond to extreme temperatures (above 42C or severe cold)
3) Chemically sensitive - respond to various chemicals
4) Polymodial - respond to combination of stimuli

Question 3

Define generator potential

Answer 3

It is the nonpropagated depolarizing potential resembling an excitatory postsynaptic potential recorded when a small amount of pressure is applied to the pacinian corpuscle

Question 4

What is sensory coding?

Answer 4

the conversion of a stimulus to a recognizable sensation

Question 5

What are the four attributes of a stimulus?

Answer 5

Modality - it is the type of energy transmitted by the stimulus
Location - it is the site on the body or space where the stimulus originated
Intensity - it is the signaled response amplitude or frequency of action potential generation
Duration - it is the time from start to end of a response in the receptor

Question 6

Describe a)sensory unit and b)receptive field

Answer 6

a) a single sensory axon and all of its peripheral branches

b) the spatial distribution from which a stimulus produces a response in that unit

Question 7

What is lateral inhibition and what is the advantage of it?

Answer 7

information from sensory neurons whose receptors are at the edge of the stimulus are inhibited compared to those at the center of stimulus.
It enhances contrast and makes a stimulus easier to perceive…increases ability of brain to localize sensory input

Question 8

What does two-point discrimination vary with?

Answer 8

the size of the secondary field. if all the receptors at each point go back to a single secondary sensory neuron the brain perceives it as one point. if it goes back to two, the brain perceives two separate points

Question 9

differentiate between a)pain and b)nociception

Answer 9

a) an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or as described in terms of such damage
b) the unconsious activity induced by the harmful stimulus applied to sense receptors

Question 10

differentiate between a)first pain and b)second pain

Answer 10

a) from activation of thinly myelinated A-delta fibers - release glutamate - rapid, sharp pain
b) activation of unmyelinated C fibers - release glutamate and substance P - dully achy pain

Question 11

differentiate between a)acute and b)chronic pain

Answer 11

a) has sudden onset and recedes during the healing process - can be regarded as “good pain” - serves important protection mechanism
b) “bad pain” - it persists long after recovery from an injury and often refractory to common analgesic agents.

Question 12

why does chronic pain happen?

Answer 12

can result from nerve injury, toxic-induced nerve damage, and ischemia.

Question 13

differentiate between a)hyperalagesia and b)allodynia

Answer 13

• pain is often accompanied by both of these
• both signify increased sensitivity of nociceptive afferent fibers
  a) an exaggerated response to noxious stimulus
  b) a sensation of pain in response to a normally innocuous stimulus (eg. the painful sensation from a warm shower when the skin is damaged by sunburn)

Question 14

describe and explain visceral pain

Answer 14

Dull, poorly localized pain
Often accompanied by nausea, perspiration, increased BP and muscle spasms
Radiates or refers to other areas

Question 15

describe and explain reffered pain

Answer 15

Pain felt in a somatic structure due to some irritation of a visceral organ.
**look at slide #30 for a visual

Question 16

Compare the pathway that a)mediates sensory input from touch, proprioceptive, and vibratory senses to the b)mediating information from nociceptors and thermoreceptors

Answer 16

a) Fibers mediating these sensations asend via the dorsal column/medial lemniscal system. The fibers ascend ipsilaterally in the dorsal columns of the spinal cord to the medulla, where they synapse in the gracilus and cuneate nuclei. the second-order neurons from these nuclei cross the midline and ascend in the medial lemniscus to end in the contralateral ventral posterior lateral nucleus and related specific sensory realy nuclei of the thalamus.
b) Fibers mediating these sensations asend via the ventrolateral tract. Fibers synapse on the neurons in the dorsal horn of the spinal cord. Their axons cross the midline and ascend in the ventrolateral quadrant of the spinal cord to the VPL and then to the primary somatosensory cortex.

Question 17

Describe the process involved in modulation of transmission in pain pathways

Answer 17

transmission of nociceptive pathways can be interupted by actions within the dorsal horn of the spinal cord. simultaneous activation of innocuous cutaneous mechanoreceptors whose afferents emit collaterals that terminate in tht dorsal horn may alleviate pain - eg. shaking or rubbing of and injury can allevieate pain. The activity of the cutaneous mechanoreceptors may reduce the responsiveness of the dorsal horn to the nociceptors.
This is calle gate-control mechanism

Question 18

List some botanicals and nutrients that have been used for pain relief and give the rational for their use and their clinical effectiveness.

Pain relief?

Answer 18

…didn’t really cover this…?

Pani relief...
Medications:
Analgesics, NSAIDS, Opiods
Natural Modalites:
Diet, herbs, enzymes, phenylalanine, acupuncture, physical medicine and manipulation

Question 19

describe innocuous cold/cool receptors; location; active when

Answer 19

on dendritic endings of A-delta and C fibers
inactive at 40C, steadily increase firing rate as skin temp falls to 24C, then decrease firing rate as it continues to fall to 10C. below 10C they are inactive

about 4-10 times as many cold-sensitive spots compared to heat-sensative spots

Question 20

describe innocuous warm receptors; location; active when

Answer 20

on C fibers

threshold of activation 30C and increase firing rate up to 46C

Question 21

What is the sclera?

Answer 21

The outer protective layer of the eye

Question 22

What is the cornea?

Answer 22

The anterior part of the sclera. The sclera is modified anteriorly to form this transparent structure that allows light rays to enter the eye

Question 23

What is the choroid?

Answer 23

A layer inside the sclera that contains many blood vessels that nourish the structures in the eyeball

Question 24

What is the retina?

Answer 24

The neural tissue containing receptors. It lines the posterior two thirds of the choroid.

Question 25

What is the crystalline lens? and what holds it in place?

Answer 25

A transparent structure held in place by a circular lens ligament, the zonule

Question 26

What structure does the zonule attach to?

Answer 26

The zonule holds the crystalline lens in place and attaches to the thickened anterior part of the choroid, which is called the ciliary body.

Question 27

Describe the ciliary body

Answer 27

It contains circular muscle fibers and longitudinal muscle fibers that attach near the corneoscleral junction.

Question 28

Describe the iris

Answer 28

it is the pigmented and opaque structure in front of the lens. it contains circular muscle fibers that constrict and radial muscle fibers that dilate the pupil