4: Physiology - Primary sensory neurons and their modalitiies 2

Question 1

Starting at slide 10:

Where is the primary somatosensory area of the brain?

Answer 1

Post-central gyrus

Parietal lobe, just after the central sulcus

Question 2

Which body parts are found at the medial and lateral ends of the sensory strip?

Answer 2

Medially - peripheries i.e upper and lower limbs

Laterally - face, pharynx, abdominal organs

Question 3

What is the sensory homunculus?

Answer 3

Visual representation of how much cortex is devoted to each body part’s sensation

i.e massive hands big lips

Question 4

How many layers of cells does the somatosensory area have?

Answer 4

Six

Question 5

In the somatosensory area, neurons corresponding to different parts of the body are arranged into what?

Answer 5

Columns

e.g columns for each finger

Question 6

What happens to the columns of somatosensory cortex corresponding to an area of the body if that area of the body is amputated?

Answer 6

They process info from the adjacent areas of the body instead

i.e other sensory areas take over

Question 7

What happens to the contralateral somatosensory cortex if a part of the body receives more sensory input?

Answer 7

It enlarges

Question 8

Sensory info from one side of the body is processed on the (ipsilateral / contralateral) side of the brain.

Answer 8

contralateral

Question 9

Which somatosensory cortex integrates sensory, visual and auditory information?

Answer 9

S2

just posterior to S1

Question 10

Where is the S2 somatosensory cortex?

What is its function?

Answer 10

Posterior parietal cortex

Integrates information from S1 so you know what an object is without having to analyse it

Question 11

What are the two main sensory pathways we need to know about?

Answer 11

Dorsal column / medial lemniscus pathway

Spinothalamic tract

Question 12

Where do sensory nerve fibres decussate (cross over) in the DC/ML pathway?

Answer 12

Pyramids of the medulla

Question 13

Where do sensory nerve fibres decussate in the spinothalamic tract?

Answer 13

Immediately at the spinal cord level they entered at

Question 14

What structures are connected by the

a) 1st

b) 2nd

c) 3rd order neurons of the DC/ML pathway?

Answer 14

a) Spinal cord to medulla

b) Medulla to thalamus

c) Thalamus to post-central gyrus

Question 15

What structures are connected by the

a) 1st

b) 2nd

c) 3rd-order neurons of the spinothalamic tract?

Answer 15

a) Sensory neuron to spinal cord

b) Spinal cord to thalamus

c) Thalamus to post-central gyrus

Question 16

What is the medial tract of the DC/ML pathway called?

Answer 16

Fasciculus gracilis

Question 17

What is the lateral tract of the DC/ML pathway called?

Answer 17

Fasciculus cuneatus

Question 18

The fasciculus cuneatus runs in the ___ aspect of the dorsal column.

The fasciculus gracilis runs in the ___ aspect of the dorsal column.

Answer 18

fasciculus cuneatus - lateral dorsal column

fasciculus gracilis - medial dorsal column

Question 19

Sensory fibres from which parts of the body run in the fasciculus cuneatus?

Answer 19

Upper trunk

Arms

Question 20

Sensory fibres from which parts of the body run in the fasciculus gracilis?

Answer 20

Lower trunk

Legs

Question 21

Sensory information from which spinal levels is carried in the fasciculus gracilis?

Answer 21

T6 and below

Question 22

Sensory information from which spinal levels is carried in the fasciulus cuneatus?

Answer 22

T5 and above

Question 23

The DC/ML pathway is the main route by which sensory fibres reach the brain.

Which cranial nerve is the exception and which part of the body does it supply?

Answer 23

CN V

Anterior head

Question 24

Where do fibres synapse at the end of the

a) fasciculus cuneatus

b) fasciculus gracilis?

Answer 24

a) Cuneate nucleus

b) Gracile nucleus

Question 25

Where do fibres from the **DC/ML pathway** decussate?

Answer 25

**Medulla**

Question 26

Sensory information regarding fine touch, proprioception and vibration from the **right side** of the body is processed on the **left side** of the brain. Why?

Answer 26

**100% ​decussation at medulla**

Question 27

After decussating at the medulla, how do DC/ML fibres reach the thalamus?

Answer 27

**Medial lemniscus** hence the name

Question 28

How do **sensory fibres** from the DC/ML pathway travel from the **thalamus** to the **primary somatosensory area****?**

Answer 28

**Internal capsule**

Question 29

Which **senses** are provided by the **DC/ML pathway**?

Answer 29

**Fine touch** **Vibration** **Proprioception**

Question 30

What is **stereognosis**?

Answer 30

**Ability to recognise an object using fine touch**

Question 31

What is **lateral inhibition**? Which **cells** are involved?

Answer 31

**The ability for an activated neuron to inhibit the neurons around it** **Interneurons** (release inhibitory neurotransmitters)

Question 32

What is the term used to describe the ability of activated neurons to inhibit the neurons around them?

Answer 32

**Lateral inhibition**

Question 33

What is the point of **lateral inhibition**?

Answer 33

**Supposedly sharpens senses by turning off irrelevant signals around the activated sensory neuron**

Question 34

Which **cranial nerve** is responsible for somatic sensory innervation of the face?

Answer 34

**CN V** ## Footnote **Trigeminal nerve and its three divisions**

Question 35

Where do **somatic** **sensory fibres** from the **trigeminal nerve** synapse first?

Answer 35

**Trigeminal ganglia**