Unit 4: sensory pathways, nociception and plasticity

Question 1

sensory pathways general concept

Answer 1

All types of sensory stimuli are received by peripheral receptors and sent to primary sensory cortices to be processed.

Question 2

how many sensory neurons are needed to carry the sensor info

Answer 2

At least three sensory neurons are needed to carry the sensory information to its corresponding sensory cortex
3rd order neuron: from the thalamus to the somatosensory cortex

2nd order neuron: from the spinal cord or the medulla to the thalamus

1st order neuron: from the sensory receptor to the spinal cord or the medulla

Question 3

what processes sensory info from skin or muscle receptors

Answer 3

the somatosensory cortex

Question 4

what processes the sensory info from the retina, the ears, the olfactory mucosa and the gustatory receptors

Answer 4

the correspondent sensory cortex

Question 5

where does most sensory info come from

Answer 5

Most sensory information comes from anywhere on the right side of the body, crosses the midline and ends up being processed on the left side of the brain. The pathways of the special senses may have some differences

Question 6

optic pathway:

Answer 6

In the optic pathway there are axons that cross at the chiasm (60%) and axons that don’t (40%), the information then reaches the visual area of the thalamus and is processed at the visual cortex (occipital lobe)

Question 7

auditory pathway:

Answer 7

Sound information from ear mechanoreceptor is gathered by the VIII cranial nerve, relays in the olives of the medulla, where it crosses, goes up the inferior colliculus of the midbrain, then the thalamus and lastly primary auditory cortex (parietal lobe)

Question 8

olfactory pathway

Answer 8

The axons that form the olfactory nerve reach the corresponding olfactory bulb without crossing. From here, secondary sensory neurons project through the olfactory tract to the olfactory cortex, skipping the thalamus. There is a direct link between smell, memory and emotion, as the secondary information also searches the limbic system (amygdala, hippocampus)

Question 9

gustatory pathway:

Answer 9

The information from taste buds on the tongue, the palate, the pharynx and the esophagus is transmitted through 3 cranial nerves: VII, IX, X. All three components reach the gustatory nucleus at the medulla, where the information crosses. Then it goes up to the thalamus and the insular cortex.

Question 10

types of receptors: 6

Answer 10

1. Mechanoreceptors: mechanical stimuli: touch, pressure, hearing, balance
2. Thermoreceptors: temperature changes
3. Nociceptors: painful stimuli
4. Photoreceptors: detect light on the retina
5. Chemoreceptors: detect changes in molecule concentrations in mouth, nose and internal liquids
6. Osmoreceptors: changes in osmotic pressure

Question 11

according to their sensitivity receptors can be classified as

Answer 11

1. Slow adapting or tonic receptors:
   They start firing at the onset of the stimulus and continue responding as long as it is present. Parameters that must be monitored continuously
2. Rapidly adapting or phasic receptors:
   They fire at the onset of the stimulus but cease firing if the strength of the stimulus remains constant, allows the body to ignore information

Question 12

according to their location the receptors can be classified as:

Answer 12

1. Interoceptive receptors:
   * Located on organs, blood vessels, etc.
   * Provide info regarding the internal environment (pH, concentration of substances, pressure, O2)
2. Proprioceptive receptors:
   * Located on skeletal muscles, tendons, joints
   * Provide info regarding mechanical changes on the structures
3. Exteroceptive receptors:
   * Located on the skin
   * These information enters the CNS through the sensory branches of the spinal nerves and the trigeminal nerve (V cranial nerve)

Question 13

dermatome:

Answer 13

• Skin area that sends sensory information to the CNS through the same nerve.
• Each nerve innervates a specific skin area
• Dermatomes overlap, so a dorsal root injury does not imply total loss of sensitivity in the area

Question 14

word somatosensory def

Answer 14

that sensory information coming from the skin exteroceptors or from proprioceptors and which is mostly processed in the primary somatosensory cortex

Question 15

different ascending routes of sensory info

Answer 15

1. To the somatosensory cortex: (Gree n)
   a. Medial lemniscus pathway
   b. Spinothalamic pathway
   Conscious information (10% of the efferent information)
   * The dorsal column-medial lemniscus pathway carries information about touch, conscious proprioception and vibration
   * The spinothalamic pathway informs about nociception and temperature
2. to the cerebellum: (yellow)
   a. spinocerebellar pathway
   Non-conscious information (90% of the afferent information)
   Carries postural and proprioceptive information from muscle receptors (golgi receptors, muscle spindles) and joint receptors
   fastest route on the CNS
3. Connections between medullar segments (red)
   Propriospinal system
   Carries information from the motor circuits along the spinal cord
   Activity of the gait central pattern generators (CPGs) at the cervical and lumbar levels

Question 16

The crossing of the ascending information that reaches the somatosensory cortex can occur at two different locations, depending on the type of information

Answer 16

Medulla oblongata (gracilis and cuneatus nuclei)
Spinal cord (anterior white commissure)

Question 17

Spinothalamic pathways:

Answer 17

Axons cross at the white anterior commissure of the spinal cord
2 pathways:
* Lateral: pain, temp
* Anterior: crude touch, pressure tickle, itch

Question 18

how many neurons does proprioceptive info need and why

Answer 18

This nonconscious information does not pass through the thalamus, so it only requires two neurons

Question 19

what does proprioceptive info allow the cerebellum to do

Answer 19

This information allows the cerebellum to regulate muscle tone, coordinate movements and participate in the balance of the body. To do this, the cerebellum also receives visual information and from the vestibular system (balance)