Somatosensory Processing

Question 1

______ is the sense of oneself

Answer 1

Proprioception

-Receptors in the skeletal muscle joint capsules, and the skin provide information about the posture and movements of our own body

Question 2

______ – the sense of direct interaction with the external world

Answer 2

-Exteroception

-Receptors embedded under the skin convey sensations of contact, pressure, stroking, motion, vibration, temperature, pain

Question 3

______ the sense of the function of the major organ systems of the body and its internal state

Answer 3

-Interoception –

-Receptors in the viscera convey non-conscious sensations involved in regulation autonomic functions: the cardiovascular, respiratory, digestive, and renal systems

Question 4

Explain this image

Answer 4

4 types of sensory nerve fibers

Conduction velocity of myelinated peripheral nerve fibers is approximately six times the fiber of the diameter, smaller = faster conduction

Question 5

How does proprioception work in limb position sense?

Answer 5

Muscle spindles: intrafusal fibers

• Aligned and parallel with muscle
• Enclosed within a capsule
• Detect muscle stretch
• Signal limb positioned (signaled by the mean rate of discharge in the muscle spindles) & change in position (the response of the primary ending increases in the direct t proportion of the rate of length change)

Question 6

What is located between skeletal muscle and tendon, enclosed within a capsule that detects muscle tension and force?

Answer 6

Golgi tendon organs

Question 7

Explain this image?

Answer 7

Spindles encode muscle stretch, only on triceps muscle

What is the point?

Our sense of where our body is is encoded jointly by an ensemble activity from many receptors and nerves to understand where our body is

Question 8

What are the 4 types of exteroception: tactile perception receptors

Answer 8

Pacinian corpuscles, Merkel disc, Meissner corpuscles, Free nerve endings, Ruffini endings,

Question 9

What are the characteristic s of Meissner’s corpuscle?

Answer 9

ØMost numerous

ØLocated close to skin surface

ØSensitive to dynamic skin deformation of relatively high frequency (~5–50 Hz)

ØDetect changes in texture (activated by lateral motion)

ØFA1: fast adapting

Question 10

What are the characteristics of Merkel disc/cell?

Answer 10

ØLocated at the tip of epidermal sweat edges

ØSensitive to low-frequency dynamic skin deformations (<~5 Hz)

ØDetect sustained touch and pressure (activated by edge, points): important for detecting surface features, eg reading Braille

ØSA1: slowly adapting firing proportional to pressure

Question 11

What are the characteristics of pacinian corpuscles?

Answer 11

ØLocated in dermis deep tissue

ØImportant for using tools (activated by vibration)

ØFA2: fast adapting

ØRespond to high frequencies

Question 12

What are the characteristics of Ruffini endings?

Answer 12

ØLocated in dermis

ØDetect tension (activated by skin stretch, eg when manipulating large objects

ØSA2: Slowly adapting

Question 13

Explain this image

Answer 13

Receptive fields on human hadn are smallest in fingertips

Question 14

Explain this image

Answer 14

Results of an experiment measuring the minimal (threshold) amplitude of vibration at the fingertip that people can detect, as a function of the vibratory frequency

Threshold amplitude of vibration at different frequencies

Question 15

What is the point of this image?

Answer 15

Responses of touch receptors to braille dots scanned by the fingers

• Receptors code different features to help us perform tasks, ie, SA1 is the best here

Question 16

Explain this image

Answer 16

Sensory information from the hand during grasping in lifting

all 4 receptors are working throughout this task, RA2 would be good for the prediction

Question 17

Explain this pathway

Answer 17

Dorsal Column-Medial Lemniscus Pathway: -> transmits touch & position sense (kinesthesis)

Question 18

Explain this pathway

Answer 18

Anterolateral path -> transmits temperature, pain and itch

Question 19

What are the 4 sub-areas that makeup S1 in the somatosensory cortex?

Answer 19

S1 – comprised of sub-areas

3a – proprioceptive inputs

3b – cutaneous

1 – cutaneous – larger RFs

2 – cutaneous (complex touch) / proprioceptive

Question 20

Know the receptor fields

Answer 20

3a muscle tissue (deep)

3b (SA1, RA1 skin)

1 (RA1, RA2 skin)

2 (proprioception deep, complex touch skin)

5 (active touch skin)

Question 21

Explain this image

Answer 21

Columnar organization of the somatosensory cortex

• Organized in columns
• Separate body maps in each subregion of S1
• Feedforward signals from thalamus – layer IV
• Feedback: recurrent signals from other SS areas, as well as PPC, motor, limbic and medial temporal cortex: sensory gating

Question 22

Explain 3 characteristics of area 1

Answer 22

• RFs ­ compared to area 3b
• ~ 10% respond to stimuli in 1 direction only
• involved in sensing the details of surface texture

Question 23

Explain the characteristics of area 2

Answer 23

• large RFs
• integration of cutaneous & proprioceptive inputs
• convergence of inputs from areas 3a, 1 and thalamus
• cells respond to moving stimuli in preferred directions
• cutaneous responses may be conditional on proprioceptive cue

Question 24

What are the characteristics of the secondary somatosensory area (S-II)

Answer 24

• large, bilateral RFs
• emphasis on discrimination of texture, and size
• processing modulated by attention

Question 25

Explain Diagram

Answer 25

Attention enhances the response of a neuron in the S-II A: Dual-task, tactile task, ask to indicate whether the orientation of bars was the same or different. The visual task, detect a change in brightness of square displayed B: Mean firing rate was higher when animal attended to the tactile task than when the stimulus was ignored by the visual task C. Stimulus stronger in tactile task

Question 26

What make of the posterior parietal cortex (PPC)

Answer 26

Area 5, Area 7

Question 27

What are the 3 characteristics of area 5?

Answer 27

* bilateral RFs * respond to combinations of joint manipulations through different angles * posture specific

Question 28

What happens during lesions of area 5?

Answer 28

•clumsy movements • •movements of contralateral limbs made imprecise • •may produce perceptual loss of the affected parts

Question 29

What are the characteristics of area 7?

Answer 29

•somatosensory information integrated with visual information • •aligns body schema with visual scene • •neurons may respond to stroking a particular body region or if an observed object passes over it without touching • •Processing modulated by attention • •Lesions: misguidance of limb movement in space (optic ataxia)

Question 30

•SS input controlled by pre- & post-synaptic inhib. at each\_\_\_\_\_\_

Answer 30

synaptic junction

Question 31

True or False: in DC-ML pathway – axons from SI & motor cortex can block information at the DCN or thalamus

Answer 31

True

Question 32

How does movement-related gating occur in regards to SS information?

Answer 32

* Psychophysical thresholds for detecting tactile stimulation are different during movement * No attenuation… * Somatosensory-evoked potentials in human cerebral cortex are also modulated during movement * Greater attenuation during self motion

Question 33

Answer 33

Air puffs were applied to the center of the receptive field (ulnar forearm in this case) either at a variable delay or with the animal at rest (right, control trial). The evoked potential traces are averages of 38 trials, aligned on the onset of the air puff stimulus (negative up). The corresponding displacement traces and EMG were averaged either on the onset of displacement (left), to show where the air puffs were applied relative to the motor task, or on the onset of the trial (right). F, flexion; X, extension.

Question 34

Explain this image

Answer 34

•How can you tell the difference between u moving and something move you? comparison between predicted sensory feedback and actual sensory feedback

Question 35

How does pre-synaptic inhibition work?

Answer 35

* Axo-axonic synapses * 1 mechanism – ↑ Cl- permeability * Shunts depolarizing current of AP * ↓ Influx of Ca2+ into presynaptic terminal * ↓ Neurotransmitter release