Lecture 13 - Somatic Sensation

Question 1

where is the primary afferent neuron present in?

Answer 1

present in the spinal cord

Question 2

where does the primary afferent neuron synapse on?

Answer 2

synapses on the secondary neurons in the CNS

Question 3

where is the cell body of the primary afferent neuron?

Answer 3

its cell body is located in the dorsal root ganglion

Question 4

where are the dorsal root ganglion part?

Answer 4

considered to be part of the central process

Question 5

what makes up the axons in the PNS in terms of processes?

Answer 5

both the central process and the peripheral make up the axons in the PNS

Question 6

what is the receptive field at the end of the primary afferent neuron composed of?

Answer 6

composed of sensory endings of an axon that contains sensory receptors

Question 7

what is a receptive field?

Answer 7

an area of the skin that a particular axon is responsible for

Question 8

what are the two pathways in the spinal cord used to relay somatic sensation?

Answer 8

anterolateral pathway

dorsal column pathway

Question 9

what is the anterolateral pathway?

Answer 9

begins directly after entering the dorsal root ganglion through the dorsal root in the spinal cord. The anterolateral fibres pass to the front of the spinal cord and cross to the other side up to the nucleus within the brainstem

Question 10

what information does the anterolateral pathway carry?

Answer 10

carries poorly resided stimuli that doesn’t need to be precisely located at the body surface

Question 11

what is examples of the stimuli the anterolateral pathway detects?

Answer 11

includes pain and temperature as they are general sensations from wider areas of the body

Question 12

what is the dorsal column pathway?

Answer 12

enters at the dorsal root and stays at the dorsal side at the back of the spinal cord. It goes up on the same side it comes in and then crosses over at a higher level

Question 13

what is the dorsal column pathway for?

Answer 13

it is for fine touch and proprioception

Question 14

what is the reticular activating system (RAS)?

Answer 14

alerts that something is happening in the environment acting as an alert system
- for integrated/expected vs actual outcomes and proprioception

Question 15

where does the reticular activating system branch into to?

Answer 15

branches into the brainstem

Question 16

what do sensory receptors of the skin convert?

Answer 16

sensory receptors of the skin convert physical stimuli into AP’s in the primary sensory neuron by transduction

Question 17

what is transduction?

Answer 17

transduction is the conversion of energy from one form to another

Question 18

what are proprioreceptors?

Answer 18

skin mechanoreceptors that measure the position of limbs though muscle spindles, Golgi tendon organs and joint capsules

Question 19

what are touch receptors?

Answer 19

mechanoreceptors that are sensitive to mechanical deformation

Question 20

what are nociceptors for pain?

Answer 20

receptors that respond to extreme mechanical temperatures and/or chemical stimuli

Question 21

what are hair receptors?

Answer 21

receptors that detect airflow past the body surface

Question 22

what is a pacinian corpuscle?

Answer 22

a skin touch receptor that detects pressure and vibration and associated with myelinated fibres for precise detection

Question 23

what are the 4 ways sensory information is coded?

Answer 23

modality
intensity
location
duration

Question 24

what is modality?

Answer 24

the specificity of receptors

e.g specific for touch or temp

Question 25

what is intensity in terms of sensory information?

Answer 25

the frequency of AP’s in each axon or the number of axons activated

Question 26

what is location in terms of sensory information?

Answer 26

the mapping of receptive fields of individual primary afferents to specific corticol locations

Question 27

why does location of sensory information vary?

Answer 27

varies due to somatotopic representation in the somatosensory cortex

Question 28

what is duration in terms of sensory information?

Answer 28

detects movement and changing pressure

Question 29

how do rapidly adapting receptors respond?

Answer 29

respond briefly even if the stimulus is sustained

Question 30

how do slowly adapting receptors respond?

Answer 30

can signal the true duration of a stimulus as they fire though-out the whole duration of a stimulus

Question 31

what are the two skin receptors that allow us to distinguish the direction skin is being stretched?

Answer 31

ruffini’s endings and pacinian corpuscles

Question 32

what is lateral inhibition?

Answer 32

a fundamental mechanism to increase the accuracy of sensory information

Question 33

what is lateral inhibition mediated by?

Answer 33

mediated by inhibitory interneurons

Question 34

when is lateral inhibition used?

Answer 34

used wherever an accurate location of a stimulus is required or where a pattern of input needs to be discriminated
e.g vision, smell etc

Question 35

what does lateral inhibition result in?

Answer 35

results in centre-surround inhibition

Question 36

what is the relationship between somatic sensation and lateral inhibition?

Answer 36

in somatic sensation lateral inhibition is a localised sensation to a restricted area of the skin