Somatosensory system

Question 1

What are the 5 modalities of the somatosensory system and what are its stimuli and receptors

Answer 1

Touch
Stimuli-skin deformation and motion
Receptor-skin
Proprioception
Stimuli-muscle length, muscle force, joint angle
Receptor-muscle spindles and joint capsules
Pain
Stimuli-Noxious stimuli (thermal, mechanical, chemical)
Receptor-all tissues except CNS
Itch
Stimuli-histamine
Receptor-skin
Visceral (not painful)
Stimuli-Thermal, mechanical, chemical
Receptor-gastrointestinal tract, urinary bladder and lungs

Question 2

What are the 4 steps for the physiological mechanism of sensation

Answer 2

transduction->transmission->perception (doesn’t always occur because of anaesthesia)modulation

Question 3

What neurones are the submodalities of somatic sensations mediated by and what do they do

Answer 3

dorsal root ganglion, trigeminal sensory neurones
Function: transduce/encode stimuli into electrical signals
transmit those signals to CNS

Question 4

What 4 properties of a stimulus do receptors respond to

Answer 4

Modality: diff. receptors activated by diff. type of stimuli (receptor specificity)
Intensity: encoded by firing freq (and number of receptors activated;also different receptors have different thresholds of activation)
Duration: encoded by duration of firing
Location: related to relevant receptive fields

Question 5

What do receptor sensitivity, specificity and receptive field mean

Answer 5

Receptor sensitivity:
Receptor specificity: sensory receptors are specialised to transduce particular type of stimulus energy into electrical signals
Receptive field: spatial domain where stimulation excited or inhibits the neurone

Question 6

Give types of proprioceptors and examples of each

Answer 6

Joint receptors: 1) sensory receptors in the joint 2) joint capsule receptros (transduce tension in the joint capsule while perceptioon of angle achieved via afferent signals from muscle spindles and efferent motor commands)
Muscle receptors: 1) Muscle spindle regulate motor control in muscle length, control rate change of length and prevents overstretching. contribute to sense of limb position 2) golgi tendon organ lie in seriees with main muscle ffibres and are sensitive to changes in muscle tension

Question 7

What types of fibres are cold sensitive fibres and warm sensitive fibres

Answer 7

Cold: small myellinated Adelta axons
warm: small unmeylinated C axons

Question 8

What are the 4 main modalities of nociceptors

Answer 8

Thermal (A delta ffibres), mechaanical, polymodall (C fibres), silent (mechanicaly responsive so something not painful before can feel painful)

Question 9

Describe the route taken and the funcitons of the dorsal column medial lemniscus system as wwell as the contralateral antereolateral system

Answer 9

Dorsal column medial lemniscus system=ascends ipsilaterally in spinal cord and conveys mechanosensory info from limbs and trunks to cortex via Ventral Posterior Lateral thalamus
Contralateral antereolateral system=spinoreticular, spinomesencephalic and sspinothalamic tracts cross the midline of the spinal cord and transmits itch, temperature and visceral info to cortex via brainstem and thalamus

Question 10

What are the divisions of the somatic sensory cortex and label them

Answer 10

S1 (primary)-can be subdivided into 4 cytoarchitectonic regions, broadmann’s areas 3a, 3b, 1 and 2. Somatotopic map can be displayed on here (discontinuous+distorted)
S2 (secondary)
Posterior parietal

Question 11

How are sensory information of different modalities processed in somatic sensory cortex and how are inputs procesed for broadmann’s areas from the thalamuss

Answer 11

Diff modalities=parallel processing

Broaadmann’=serially