sensory receptor pathways

Question 1

what are the 3 main types of sensory receptors based on structure or stimulus?

Answer 1

• sensory receptors
  -somatic receptors
  -special senses receptors

Question 2

describe somatosensory receptors - location, where do they send signals to, what inputs?

Answer 2

-located peripherally in skin, internal organs, muscle etc
-relay info to the somatosensory cortex via spinal cord
-relay info on lots of things eg touch, temperature, pain can all be felt on the finger tips and perceived in the somatosensory cortex

Question 3

describe special senses receptors

Answer 3

-located and fount in the special sense organs of the head and face eg eye, ears nose and tongue
-relay info to their respective brain region in the sensory cortex, eg visual cortex, auditory cortex etc

Question 4

what are the different types of somatic sensory receptors of the skin?

Answer 4

-merkels disc
-meissners corpuscle
-ruffini endings
-pacinian corpuscle
-hair receptor

Question 5

describe hair receptors

Answer 5

• simple cutaneous mechanoreceptor which is abundant in hairy skin
  -rapidly acting and have small receptive field
  -detect velocity and direction of mvt across the skin

Question 6

describe Merkel’s disc-neurite complex

Answer 6

• mechanoreceptor found in the basal epidermis
  -abundant in non hair skin eg lips & fingertips
  -slowly adapting receptors w/ small receptive field
  -sensitive to the detection of light touch

Question 7

describe pacinian capsule

Answer 7

-complex receptors - found in the sub-cutaneous and deep dermal layer of hairless skin
-compression leads to opening of ion channels and depolarisation
-rapidly adapting and have large receptive fields

Question 8

describe Ruffini endings

Answer 8

-complex receptors in dermal layer
-slowly adapting skin stretch receptors with large receptive fields
-detect stretch, skin and joint deformation

Question 9

describe meissners corpuscles

Answer 9

• encapsulated mechanoreceptors
• rapidly adapting w/ small receptive fields
  -densely found in the fingertips, and other locations
  -fine touch and low freq vibrations

Question 10

what structure do all somatosensory pathways pass through before they project to their region of the primary somatosensory cortex?

Answer 10

the thalamus

Question 11

what are the 1st order neuron’s of the somatosensory pathways ?

Answer 11

the somatosensory neurons

Question 12

describe the dorsal column medical lemniscal pathway

Answer 12

-relays info to the somatosensory cortex on fine touch, and proprtioception
-3 order neuron system
-1st order neurons ascend in the dorsal column of the spinal cord
-2 dorsal column tracts - fascislus gracilis and fascicles cuneatus

Question 13

describe the order of neurons in the DCML pathway

Answer 13

-1st order neurons ascend into the dorsal column of the spinal cord
-then they synapse with the 2nd order neuron in the ipsilateral nuclei gracicilis (lower limb) or the cuneatus (upper limb) of the medulla
-2nd order neurons decussate in the medulla to form contralateral medical lemniscus tract
-synapse with the 3rd order neurons in the thalamus and then project to the somatosensory cortex

Question 14

describe the spinothalamic pathway

Answer 14

-carries info to brain about pain, temperature and crude touch
-1st order neurons synapse with 2nd order in dorsal horn
-2nd order neurons ascend in the anterior and lateral fasciculi of the spinal cord
-2nd order synapses with the 3rd order which projects info to the thalamus

Question 15

describe the spinocerebellar pathway

Answer 15

-provides info from the muscle spindles, Golgi tendon organs and other sensory proprioceptors
-there is a posterior and anterior spinocerebellar tract

Question 16

what does the anterior vs the posterior spinocerebellar tract carry info about?

Answer 16

-anterior - carries info about movements of the limb as a whole
-posterior - carries info about the fine co-ordination of muscles controlling posture and movements of individual muscles

Question 17

describe the posterior spinocerebellar pathway

Answer 17

-1st order neurons ascend into spinal cord to the upper lumbar segment
-synapse with 2nd order neurons in Clarkes column
-2nd order neutrons form the ipsilateral posterior spinocerebellar tract & ascend to the cerebellum

Question 18

describe the anterior spinocerebellar pathway

Answer 18

-1st order neuron projects to and synapses with the 2nd order neurons in the lumbar and sacral regions of spinal cord
-2nd order neurons decussate and ascend in the contralateral anterior spinocerebellear tract
-they then decussate again to terminate in the ipsilateral cerebellum

Question 19

what is lateral inhibition?

Answer 19

the capacity of an excited neuron to reduce the activity of its neighbours

Question 20

what is adaption?

Answer 20

the reduction of the receptor potential over a period of time despite the continued presence of a stimulus at a constant magnitude

Question 21

what pathway is affected with posterior cord syndrome?

Answer 21

the DC-ML pathway

Question 22

what pathway would anterior cord syndrome affect?

Answer 22

the spinothalamic pathway