12/13 – Sensory Pathways

Question 1

All spinal pathways involve a:

Answer 1

-sequence of neurons
>excitability is transmitted from one neuron to the next in the sequence

Question 2

Pathways can be either:

Answer 2

-ascending
-descending

Question 3

Ascending pathways:

Answer 3

-carrying info from receptors (periphery) to the brain
-SENSORY

Question 4

Descending pathways:

Answer 4

-conveying info from brain to SC neurons
-MOTOR

Question 5

What are examples of somatic sensations:

Answer 5

-proprioception
-exteroception
-nociception

Question 6

What is proprioception?

Answer 6

-sense of location and movement of the body segments in space
>position sense, kinesthesia
*very important for an animal to have
*without it=animal has uncoordinated gait=ATAXIA

Question 7

Ataxia:

Answer 7

-inappropriate or uncoordinated gait

Question 8

Why is proprioception important clinically?

Answer 8

-can be the earliest indicator of disease or damage in the spinal cord

Question 9

What are the receptors involved in proprioception?

Answer 9

-muscle spindles (1a fibers): muscle stretch
-Golgi tendon organs (1b fibers): muscle force
-joint capsule stretch receptors

Question 10

What are the brain regions involved in proprioception?

Answer 10

-conscious proprioception
-subconscious proprioception

Question 11

Conscious proprioception:

Answer 11

-awareness of body movements in space
>generally what we are testing in an exam
-CEREBRAL CORTEX

Question 12

Conscious proprioception spinal pathways:

Answer 12

-collateral branch goes in an ascending pathway up to the brain stem
>travel in a white matter tract, myelinated axon
>dorsal funiculus on same side

Question 13

What happens when the ascending pathway reaches the brain?

Answer 13

-at level of brain stem will synapse onto nucleus and info will go to opposite side (‘crossing over’)
>medulla
>thalamus
>to somatosensory cortex

Question 14

If you see sensory deficits to left side of animal, damage could be on the:

Answer 14

-left side of animal or brainstem
OR
-right side of the brain

Question 15

Funiculus:

Answer 15

-area within the SC that various tracts are going to run through
>dorsal: sensory only
>lateral and ventral: mix of motor and sensory that are moving in that area
*paired (see diagram)
*NOT TRACTS

Question 16

Subconscious proprioception:

Answer 16

-“involuntary” control of proprioception -> not conscious/aware
-CEREBELLUM
-harder to test clinically

Question 17

Subconscious proprioception spinal pathways:

Answer 17

-lateral branches on either side

Question 18

What are the dorsal funiculi for conscious proprioception?

Answer 18

-fasciculus gracilis (medial) -> info from pelvic limbs
-fasciculus cuneatus (lateral) ->info from thorax limbs

Question 19

Conscious proprioception: spinal pathway

Answer 19

-sensory input originates from one side of the body (ipsilateral), but crosses over (decussates) in the medulla
>pathway continues on the contralateral side to the thalamus and the somatosensory cortex

Question 20

Subconscious proprioception: spinal pathway

Answer 20

-dorsal spinocerebellar tract (lateral funiculus): ipsilateral side (uncrossed)
-ventral spinocerebellar tract (lateral funiculus): contralateral side (*crossed pathway at the level of the SC)

Question 21

Tracts of the conscious and subconscious pathway:

Answer 21

-located superficially in the white matter (myelinated axons)
*most likely to be damaged due to compressed force, mass, subdural hemorrhages, etc.
>can be an early indicator of disease or problems

Question 22

What are the steps for assessing proprioception?

Answer 22

1. Examine the gait
2. Challenge their proprioception
3. Test postural reactions/responses

Question 23

Examine the gait:

Answer 23

-incoordination -> ATAXIA
-VERY IMPORTANT: what is normal?

Question 24

Challenge their proprioception:

Answer 24

-circling
-stepping up onto/over obstacles

Question 25

Test postural reactions/responses:

Answer 25

-knuckling
-hopping:
-wheelbarrowing
-hemi-walking: 2 limbs on one side of the body and they must walk sideways
*must be done weight bearing

Question 26

Hopping:

Answer 26

-lift 3 limbs up and push the animal laterally towards the limb that is still on the ground
>’asking them to catch themselves’

Question 27

Hemi-walking:

Answer 27

-2 limbs on one side of the body and they must walk sideways
>coordination between forelimb and hindlimb

Question 28

Exteroception:

Answer 28

-detection of sensations from OUTSIDE the body (external stimulus)
>not detecting painful stimuli

Question 29

Enteroception:

Answer 29

-detection of stimuli from WITHIN the body
-uses the same pathways as exteroception but, receptors are different

Question 30

Why is exteroception important in animals?

Answer 30

-detect their external environment
-sense potential dangers

Question 31

What are the receptors of exteroception (exteroceptors)?

Answer 31

*mostly located in skin
-pressure receptors
-light touch receptors
-vibration receptors
-temperature receptors
-hair receptors (more numerous in most animals)
-tylotrich receptors (vibrissae, ‘whisker’s) ->not present in humans

Question 32

Dermatomes:

Answer 32

-spatial areas that are innervated by specific spinal nerves
>can help you localize a lesion

Question 33

What are the brain regions of exteroception?

Answer 33

-cerebral cortex to the somatosensory cortex

Question 34

What is the spinal pathway for exteroception?

Answer 34

-similar to conscious proprioception
-SC to medulla (cross over) to thalamus to somatosensory cortex
-travel via the same tracts (x2 dorsal)