Lecture 24

Question 1

What is skin?

Answer 1

our heaviest organ and protects us by keeping damaging agents from
penetrating the body

Question 2

What is the epidermis?

Answer 2

outer layer of the skin, which is made up of dead skin cells

Question 3

Describe the dermis

Answer 3

below the epidermis and contains mechanoreceptors that
respond to stimuli such as pressure, stretching, and vibration

Question 4

Describe the Merkel Receptor

Answer 4

(one of two types of)
mechanoreceptors located close to surface of the skin

• Have relatively small cutaneous receptive fields
• They fire continuously while stimulus is present (hence
  ‘slowly adapting’, or ‘SA1’)
• Responsible for sensing fine details

Question 5

Describe the Meissner corpuscle

Answer 5

• Meissner corpuscle are the other kind of
  mechanoreceptor located close to the skin’s surface
  (and also have relatively small cutaneous receptive
  fields)
• These fire only when a stimulus is first applied and
  when it is removed (hence ‘rapidly adapting’, or ‘RA1’)
• Responsible for controlling hand-grip

Question 6

Describe Ruffini cylinder

Answer 6

• Ruffini cylinder are one (of two types of)
  mechanoreceptors located deeper in the skin
• They fires continuously to stimulation (hence ‘SA2’)
• Associated with perceiving stretching of the skin

Question 7

Describe Pacinian corpuscles

Answer 7

• Pacinian corpuscles fire only when a stimulus is first
  applied and when it is removed (hence ‘RA2’)
• Associated with sensing rapid vibrations and fine
  texture

Question 8

Describe a challenge for the cutaneous system

Answer 8

One major challenge for the cutaneous
senses is the distance the signals from
these receptors must travel (to the brain),
as compared to other senses with more
‘localized’ receptors (e.g. the eye, the
ear, etc.)

• Two major pathways for these signals
  exist in the spinal cord (with signals
  entering via the dorsal root)
• These crossover to the opposite side of
  the body and synapse in the thalamus (in
  the ventrolateral nucleus), i.e.
  contralateral wiring

Question 9

What is the medial lemniscal pathway?

Answer 9

The medial lemniscal pathway
consists of large fibres that carry
proprioceptive and touch information,
and send high-speed signals

Question 10

What is the spinothalamic pathway?

Answer 10

The spinothalamic pathway consists
of smaller fibres that carry
temperature and pain information

Question 11

How do somatosensory signals travel?

Answer 11

From the thalamus to parietal lobe, specifically the somatosensory
receiving area (S1) (and possibly directly to the secondary receiving
area, S2)

Question 12

What is the homunculus?

Answer 12

Body map

Question 13

What is somatotopy?

Answer 13

Concept of somatotopy (like
retinotopy and tonotopy)

• Plasticity in neural functioning
  leads to multiple homunculi and
  changes in how cortical cells are
  allocated to body parts

Question 14

What is two point threshold?

Answer 14

minimum separation needed between two points to
perceive them as being separate/distinct

Question 15

What is grating acuity?

Answer 15

placing a grooved stimulus on the skin and asking the
participant to indicate the orientation of the grating

Question 16

What is raised pattern identification?

Answer 16

can also use various raised patterns (like
Braille) to determine the smallest size that can be identified

Question 17

What is a corpuscle?

Answer 17

• The corpuscle (a minute body or cell in an
  organism) structure surrounding Pacinian receptors
  is responsible for the selective response to vibration
• It only transmits repeated pressure (like vibration)
  to the actual receptor, not continuous pressure
• Can be likened to an onion in form
• Consists of a series of layers, with fluid between
  each layer

Question 18

What is surface texture?

Answer 18

the physical surface created by peaks and valleys
on a given material

Question 19

What are spatial cues?

Answer 19

determined by the size, shape, and distribution of surface elements

Question 20

What are temporal cues?

Answer 20

determined by the rate of vibration as skin is moved across finely textured surfaces

Question 21

Describe ventral posterior nucleus

Answer 21

Neurons in the ventral posterior nucleus
have centre-surround receptive fields
(like in the LGN)