Week 11 - Somatic Senses

Question 1

4 somatic senses

Answer 1

touch, temperature, proprioception, nociception

Question 2

proprioception

Answer 2

awareness of the position of body bards relative to each other

Question 3

nociception

Answer 3

detects tissue damage or the threat of it, and it is perceived as pain or itch

Question 4

Where do receptors for somatic sensation below the chin have their cell bodies

Answer 4

dorsal root ganglia

Question 5

Where do receptors for somatic sensation in the head have their cell bodies

Answer 5

brain

Question 6

Where are the parts of neurons that transduce touch, pressure, etc

Answer 6

nerve endings i.e. in the tips of their fibers, in the skin and viscera

Question 7

what do free nerve endings detect

Answer 7

they detect mechanical stimuli, temperature, and chemicals

Question 8

Merkel receptors

Answer 8

They are mechanoreceptor nerve endings in contact with specialized epithelial cells called Merkel cells

Question 9

encapsulated receptors

Answer 9

Meissner and Pacinian corpuscles are mechanoreceptors sheathed in connective tissue

Question 10

what’s there at the bottom of the epidermis

Answer 10

saucer-shaped Merkle disks
They are very sensitive to deformation of the skin and are more tonic than phasic, i.e. they send a sustained message as long as the deformation persists
they signal contact

Question 11

are most mechanoreceptors tonic or phasic

Answer 11

phasic

Question 12

What is there at the top of the dermis

Answer 12

egg shaped Meissner corpuscles
they are mainly in the tongue and hairless skin- erogenous zones, palms, fingertips, etc
inside each corpuscle, there are many looping endings.

Question 13

what do looping endings in Meissner corpuscles detect

Answer 13

they detect sideways shearing. they are phasic, so they sense changes in shear.

Question 14

whats there deep in the dermis

Answer 14

onion shaped pacinian corpuscles
te nerve endings are heated in many layer. they can sense tiny displacements if the motion is quick. they are phasic. so they respond strongly to vibration and other fast-changing stimuli.

Question 15

where are receptors most densely packed

Answer 15

pals, fingertips and lips

Question 16

test of acuity

Answer 16

2 point discriminatin

Question 17

thermoreceptors

Answer 17

free nerve endings
cold receptors respond maximally at 30 degrees
warm receptors respond most at 45 degrees.
They are both phasic tonic

Above 45 degrees pain receptors are activated

Question 18

paradoxical cold

Answer 18

Cold fibers also
respond briefly to temperatures > 45°C, causing paradoxical cold: a
hot object, touched briefly, may feel cold.

Question 19

nocireceptors

Answer 19

they are free nerve endings that respond to no noxious stimuli
Some respond to damaging mechanical stimuli, others to damaging heat or chemicals
some respond to chemicals released from damaged cells (K+, histamine, prostaglandins) or to serotonin releases by platelets in response to injury

Question 20

small somatosensory afferents

Answer 20

The small fibers, called C and Aδ (A-delta), come mainly from free nerve endings. C fibers are unmyelinated, and conduct spikes at speeds up to 2 m/s. Aδ’s are thicker than C’s, myelinated, and conduct at up to 30 m/s. Different small fibers respond to different adequate stimuli, such
as mechanical stimuli, chemicals, or temperature.

Question 21

large somatosensory afferents

Answer 21

Large fibers, called Aβ (A-beta), come from Merkel disks or
encapsulated mechanoreceptors such as Meissner or Pacinian
corpuscles. They are myelinated, and conduct at 70 m/s

Question 22

how do large fibers project?

Answer 22

Large fibers turn upward on reaching the spinal cord, and run ipsilaterally up to the medulla in tracts called the dorsal columns. In the medulla they synapse on cells whose axons cross the midline.

Question 23

how do small fibers project?

Answer 23

Small fibers synapse directly or via interneurons on motoneurons (for reflex responses) or on dorsal-horn neurons whose axons cross the midline and run in the spinothalamic tracts, in the lateral part of the cord, between the dorsal and ventral horns.

Question 24

large fibers functions

Answer 24

Large fibers provide feedback to the brain, especially to motor
cortex, as it manipulates objects. Their information has to travel a
long way (up to the brain) quickly.

Question 25

functions of small fibers

Answer 25

Small fibers evoke simple responses to specific stimuli: with-
drawing from pain, brushing away a bug, thermoregulatory and sexual responses. Many of these tasks can be handled in the spinal cord,
without immediate input from the brain.

Question 26

how do signals travel thalamus to cortex

Answer 26

Signals from the spinal cord travel via the ventroposterolateral (VPL) nucleus of the thalamus. Signals from the head travel via the ventroposteromedial nucleus (VPM).
Both pass to the primary somatosensory cortex, S1.
Signals travel via thalamus to cortex

Question 27

what is the primary somatosensory cortex

Answer 27

somatotopic
Neighboring areas of skin project to neighboring cells in cortex, so S1 is a map of the contralateral body surface.
The map is distorted, as areas of high sensitivity and acuity (such as hands and lips) get a lot of cortical space, just as the foveas do in the visual system.

Question 28

which lobe is the primary somatosensory cortex in

Answer 28

partietal lobe

Question 29

what enhances spatial differences

Answer 29

lateral inhibition

Question 30

what family do the ion channels of nociceptors belong to

Answer 30

transient receptor potential channels

Question 31

vanilloid receptors

Answer 31

TRPV1 channels
they respond to damaging heat and to chemicals (including capsaicin)
TRPM8 channels response to cold and menthol

Question 32

congenital analgesia

Answer 32

dont feel pain

Question 33

fast pain

Answer 33

carried by A-delta fibers

Question 34

slow pain

Answer 34

carried by C fibres

Question 35

2 responses evoked by pain

Answer 35

quick withdrawal (to get away from the painful thing) and
prolonged immobilization (to promote healing)

Question 36

responses evoked by nociceptive signals

Answer 36

Nociceptive signals trigger withdrawal, e.g. pulling your hand
back from a hot stove. This is a spinal reflex, and so it doesn’t need
immediate input from the brain.
Nociceptive signals also reach the limbic system and hypothalamus, causing emotional distress, nausea, vomiting, and sweating.
Descending pathways through the thalamus can block nociceptive cells in the spinal cord, e.g. in emergencies where survival depends on ignoring pain.

Question 37

referred pain

Answer 37

pain in an internal organ that is felt on the body surface.
Nociceptors from different locations converge on a single ascending tract. So when that tract sends signals to the brain, the brain doesn’t know where the stimulus came from.
As pain is more common in skin than in internal organs, the brain
assumes the problem is on the body surface.

Question 38

liver/gallbladder and heart pain

Answer 38

liver/gallbladder - shoulder
heart - left arm

Question 39

how can pain be gated by A beta activity

Answer 39

In the dorsal horn, C fibers contact secondary neurons. Those
secondaries are inhibited by Aβ fibers via interneurons.
So Aβ’s can block or dampen pain signals, e.g. if you rub a sore
shoulder, it feels better.

Question 40

Acetylsalicylic acid

Answer 40

inhibits prostaglandins and inflam-
mation, and slows transmission of pain signals.

Question 41

opioids

Answer 41

decrease transmitter release from primary sensory neurons and postsynaptically inhibit
secondary sensory neurons.

Question 42

natural painkillers released by the body

Answer 42

endorphins, enkephalins, and dynorphins.