TA: Flavia Filimon

107BSection6

Today:

1) Attention

2) Somatosensory system

1) Attention

- for a review, see R. Desimone and J. Duncan (1995) (Annu. Rev. Neurosci. 18 )

- attention typically enhances activity/ responses to stimuli – attention per se isn’t recorded – just the effects of attention on the response to a stimulus.

- Moran and Desimone (1985) findings:

(Basic findings)

· good stimulus à large response, bad stimulus à small response

· if both good and bad stimuli presented in receptive field à response somewhat diminished; however, if attention is focused on good stimulus, then attentional effects cancel the effects of the bad stimulus à large response (as large as, or slightly larger than, response to passive good stimulus alone)

· if both good and bad stimuli are presented in visual field, and the bad stimulus is attended, the response is suppressed.

à response to good stimulus is suppressed when bad stimulus is attended

à the early parts of the suppressed response (when bad stim. is attended) look like the early parts of the response to the passive good stimulus. Passive bad stimulus response is slowed down

àattentional effects are visible only 40-60 ms after response onset.

2) Somatosensory system

Receptors:

Many different receptors; the range of information coming into the somatosensory system is much greater than in the visual system. In contrast to the visual system, the end of the receptors is connected directly to the nervous system – spinal cord; receptors and ganglion cell are the same.

Unencapsulated receptors:

Pain receptors:

Pain receptors only respond to pain, and not to touch.

1) Transient pain receptors: rapidly adapting – “Y-like” – respond to changes in pain

2) Sustained pain receptors: slowly adapting – “X-like” – respond to sustained pain

The two types of receptors transmit signals via different pathways to the brain.

+ hot and cold receptors – are morphologically distinct.

Encapsulated receptors

Touch receptors:

Touch receptors do not respond differently to touch versus pain.

1) sustained touch receptors: a) Merkel disk receptors (à pressure, texture); superficial;

b) Ruffini ending (receptors) (à skin stretch); deeper in skin

2) transient touch receptors: a) Meissner’s corpuscles (à stroking, fluttering) – in ridges of finger prints.

b) Pacinian corpuscles (à vibration) – deeper.

Muscle and skeletal meachanoreceptors:

- Muscle spindles: Ia – transient à detect change in muscle length

II - sustained à detect muscle length

Both types of spindles are exclusively “ON” receptors – they only detect stretch, no contraction of muscle. We detect where our bodies are (in terms of positions) by the length of our muscles.

- muscle receptors are in the muscle.

- α motor neurons: innervate the muscle; γ motor neurons: innervate the muscle spindle muscle.

- Golgi tendon organs: detect contraction, and the force exerted on the muscles

- on tendons.

BE ABLE TO REPRODUCE A BASIC DIAGRAM OF THE ARM AND ITS DIFFERENT RECEPTORS