Exteroception

Question 1

Somatosensory system

Answer 1

collection of receptors whose endings transduce information about the body surface, the skin, although deeper tissues reported as well

Question 2

2 major subdivisions of somatosensory system

Answer 2

dorsal column (posterior column) or lemniscal system (fine, discriminative, touch perception, limb prioprioception)
2) antero-lateral system (pain/temperature/crude touch)

Question 3

type s of skin sensory receptors

Answer 3

• cell bodies in DRG

- Merkel’s disk, Pacinian corpuscle, Meisner’s corpuscle, free nerve endings (Ruffini’s endings, hair follicles)

Question 4

Rapidly adapting receptors

Answer 4

when stimulated with steady touch fire a few APs then stop firing even though sin still pressed

Question 5

slowly adapting receptors

Answer 5

when stimulated with steady touch, will keep firing throughout time the skin is pressed

Question 6

Receptive field for skin receptor

Answer 6

area of skin in which a mechanical stimulus elicits a response from the cell

Question 7

how are somatosensory receptors classified

Answer 7

according to slow vs rapidly adapting, size of receptive field (small fields/sharp borders vs large, poorly defined fields)
- Large - covers entire finger/greater part of palm

Question 8

Meissner’s corpuscles

Answer 8

correspond to rapidly-adapting, afferents with small receptive fields

Question 9

Merkel’s discs

Answer 9

afferents innervating these have small fields and slow adapting

Question 10

Pacinian corpuscles

Answer 10

afferents with large reeptive fields lie deep in dermis and subcutaneous tissues; rapidly adapting

Question 11

Ruffini endings (free nerve endings)

Answer 11

afferents with slowly adapting, large receptive fields

Question 12

Small receptive field afferents

Answer 12

• support fine, tactile sense of fingertips

- higher density of Corpuscles/Merkel’s discs

Question 13

Large receptive field size afferents

Answer 13

• hgih sensitivity to skin deformation over wide area
• Pacinian corpuscles, (vibration)
• Ruffini’s ending (stretch)

Question 14

Rapid adapting sensory receptors

Answer 14

Meissner’s Corpuscle, Pacinian corpuscle

Question 15

Slow-adapting sensory receptors

Answer 15

Merkel’s disk, Ruffini’s endings

Question 16

Hair follicle receptors

Answer 16

dermal tissue around each follicle penetrated by several myelinated axons that produce several unmyelinated branches; some run up/down follicle and others spiral around
- bending of hair shaft activates terminals –> rapidly adapting

Question 17

Types of axons for mechanoreceptors

Answer 17

large, myelinated axons (Aβ) but smaller/slower than proprioceptors in skeletal muscle

Question 18

Types of axons for proprioceptors of skeletal muscle

Answer 18

Aα (larger/faster than mechanoreceptors in skin)

Question 19

Locaiton of cell bodies of mechanoreceptors from skin/proprioceptors

Answer 19

DRG; centrally projecting processes in dorsal root enter spinal cord– bifurcate–local branches prject to dorsal horn for spinal reflexes adn ascending branches enter dorsal column toascend spinal cord

• those from lower limbs– ftravel in fasciculus gracilus
• those from upper body/limbs run in fasciculus cuneatus

Question 20

where is the synapse onto second order cells in lemniscal system

Answer 20

medulla; axons then cross medulla to form medial lemniscus –> ascend to synapse in ventro-basal complex of the thalamus in the ventra-posterior-lateral nucleus

Question 21

where does the second synapse ocur in the lemniscal system

Answer 21

Thalamus!

• trunk and limbs represented by cells in ventral-posterior-lateral nucleus
• head represented by cells in ventral-posterior -medial nucleus
• together VPM and VPL form ventrobasal complex

Question 22

Where do from ventrobasal complex asons project

Answer 22

areas 3, 1, and 2 on posterior bank of central sulcus

Question 23

Where do axons go from ventrobasal complex

Answer 23

(this is in thalamus) and the axons go to the primary motor cortex

Question 24

areas richly innervated by primary afferents…

Answer 24

have relatively larger areas of cortical surface devoted to them (homonculus has larger hands and face, esp lips, and relatively small trunk and proximal limbs)

Question 25

How are functionally related cells organized

Answer 25

columnar organization of cortex in virtually all areas; interconnections– imply cortical columns serve as computational modules that transform information received from the thalamus and redistribute to other regions of the brain

Question 26

where do different layers of cortex project/receive from

Answer 26

VI: to thalamus
V: projects to other subcortical structures
IV: from thalamus
III: project to other areas of somatosensory cortex
II: to other areas of somatosensory cortex

(II/III- to ipsilateral SII, contralateral SI, posterior parietal cortex, and motor cortex)

Question 27

Brodmann’s areas 1/2

Answer 27

respond to more complex stimuli (direction-, orientation-0, shape-sensitive

Question 28

Brodmann’s areas 3a 3b

Answer 28

simple punctate stimulation

• 3a= proprioception
• 3b = touch

Question 29

Brodmann areas corresponding to somatosensory cortex

Answer 29

1, 2, 3

Question 30

Somatosensory area II

Answer 30

posterior/inferior to Somatosensory Area I – tend to have more complex stimulus requirements than those in SI

Question 31

Trigeminal ganglion

Answer 31

“DRG for the head”

Question 32

afferent fibers from trigeminal ganglion run..

Answer 32

peripherally through 3 branches of trigeminal nerve (opthalmic, maxillary, mandibular)

Question 33

What senses carreid by trigeminal nerve

Answer 33

discriminative touch (lemniscal) proprioceptive and pain and temperature, some motor and autonomic neurons

Question 34

soma of mechanoreceptors located where?

Answer 34

trigeminal ganglion; these terminate in different nuclei corresponding to connections of analogous spinal cord brethren

Question 35

Where are cell bodies of proprioceptive afferents (incl muscle stretch receptors) that run in trigeminal

Answer 35

Centrally located cell bodies (only ones in adult CNS) that make up trigeminal mesencephalic nucleus
(cell bodies for muscles of mastication in motor trigeminal nucleus)

Question 36

Barrels

Answer 36

group of vertical cells in cortex with similar function