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Neuroscience > Sensory Pathways: Touch and Proprioception > Flashcards

Sensory Pathways: Touch and Proprioception Flashcards

1
Q

What receptors are responsible for the sensory modalities of touch and proprioception?

A

Mechanoreceptors

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2
Q

Describe the structure of mechanoreceptors involved in touchand proprioception.

A

The receptor is NOT a separate entity but is actually the peripheral terminal of the peripheral axon of the primary sensory neuron.

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3
Q

Describe the structure of a Pacinian corpuscle and explain how this structure relates to its function.

A

There is an axonal ending in the middle and it is wrapped around several concentric circles of epithelial cells – this allows the receptor to be very sensitive to vibration.

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4
Q

What type of receptors are mechanoreceptors?

A

Mixture of slow and fast adapting receptors

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5
Q

Describe how sensory neurons vary in their properties.

A

They vary in SIZE and CONDUCTION VELOCITY

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6
Q

What are the two classifications of axons?

A

Anatomical = based on axon diameter (labelled using LETTERS)
Physiological = based on conduction velocity (labelled using ROMAN NUMERALS)
As axon diameter and conduction velocity are related, there is a lot of overlap in the classifications

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7
Q

Describe the general structure of sensory neurons that conveytouch and proprioceptive information.

A

They are LARGE and have a FAST conduction velocity

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8
Q

Describe how the receptive fields in the lips and mouth vary from the receptive fields of the upper arm.

A

Lips and Mouth – high-density innervation with very small receptive fields
Upper arm – larger receptive fields and thinner innervation

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9
Q

Describe how neurons can code for the intensity of a stimulus.

A

It is coded by the FREQUENCY of the action potentials going down the sensory fibres

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10
Q

Which part of the spinal cord carries sensory axons for touch and proprioception?

A

Dorsal columns

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11
Q

What are the bundles of axons within the spinal cord that havecome from above and below the waist called? Describe their spatial arrangement within the spinal cord.

A 
Above the waist – Cuneate Fasciculus 
Below the waist – Gracile Fasciculus  
Axons from below the waist are packed more medially in the dorsal column and above the waist are more lateral
Lower = Medial 
Higher = Lateral
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12
Q

Where do these neurons synapse?

A

They synapse in the Cuneate and Gracile Nuclei in the medulla

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13
Q

Describe what happens after these neurons synapse and the tract that they run in.

A

The second order neurons then cross the midline (decussation) and continue up the brainstem in the MEDIAL LEMNISCUS

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14
Q

Which thalamic nucleus is responsible for relaying somatosensory information from the neck down?

A

Ventral Postero-lateral

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15
Q

Describe the passage of the third order sensory neuron.

A

The third order neurone travels from the ventral postero-lateral nucleus in the thalamus to the primary somatosensory cortex

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16
Q

What is the main sensory nerve of the face?

A

Trigeminal Nerve (CN V)

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17
Q

Where does the trigeminal nerve enter the brainstem and where does it synapse with a second order neuron?

A

Pons

It synapses at the trigeminal cranial nucleus

18
Q

Describe the passage of this second order neuron (face- touch and proprioception).

A

The second order neuron crosses the midline (decussation) and joins the medial part of the median lemniscus

19
Q

Which thalamic nucleus is responsible for relaying sensory information from the face?

A

Ventral Postero-medial

20
Q

What is lateral inhibition?

A

Lateral inhibition takes place in the cuneate and gracile nuclei
Each axon has lateral branches that are inhibitory on neighbouringaxons
So each axon will stimulate a second order neuron and inhibit neighboring first order neurons

21
Q

What is the purpose of lateral inhibition?

A

Improves the resolution of localising the stimulus

22
Q

Name the three parts of the somatosensory cortex.

A

Primary Somatosensory Cortex (SI)
Secondary Somatosensory Cortex (SII)
Posterior Parietal Cortex

23
Q

What is the posterior parietal cortex mainly involved in?

A

Spatial relationships

24
Q

Damage to the touch and proprioception pathway will halt sensory information going up to the primary somatosensory cortex. What effects will this have?

A

Anaesthesia (complete cessation of sensation)

Parasthesia (sensation is there but it isn’t normal)

25
Q

What is the most common cause of peripheral neuropathy?

A

Diabetes mellitus

26
Q

Three classifications of sensory neurones?

A

Aβ-fibres: innocuous mechanical stimulation

Aδ-fibres: noxious mechanical and thermal stimulation

C-fibers: noxious mechanical, thermal and chemical stimulation

27
Q

What are the two thermoreceptors? Describe them. Which are heat activated which are cold activated?

A

Aδ- and C-fibres
Free nerve endings
Transient receptor potential (TRP) ion channels

4 heat activated:
TRPV1-4
2 cold activated 
TRPM8
TRPA1
28
Q

Stimulus threshold?

A

’A threshold is the point of intensity at which the person can just detect the presence of a stimulus 50% of the time (absolute threshold)’’

29
Q

What is the link between stimulus strength, NT release and intensity?

A

Increased stimulus strength and duration = increased neurotransmitter release = greater intensity

30
Q

Describe tonic receptors. What do they detect? Give an example

A

-– do not adapt or adapt very slowly

Detect continuous stimulus strength
Continue to transmit impulses to the brain as long the stimulus is present
Keeps the brain constantly informed of the status of the body
e.g. Merkel cells
Slowly adapt allowing for superficial pressure and fine touch to be perceived.

31
Q

Describe phasic receptors. What do they detect Give an example

A

-– adapt quickly
Detect a change in stimulus strength
Transmit an impulse at the start and the end of the stimulus
e.g. when a change is taking place
The pacinian receptor
Sudden pressure excites receptor
Transmits a signal again when pressure is released

32
Q

Receptive field?

A

region on the skin which causes activation of a single sensory neuron when activated’’

33
Q

Two point discrimination?

A

Minimum distance at which two points are perceived as separate
Related to the size of the receptive field

34
Q

Where are the cell bodies: body and face?

A

Cell bodies are in the dorsal root ganglia (body) and trigeminal ganglia (face)

35
Q

What is lateral inhibition?

A

A receptive field can overlap with another receptive field
Difficult to distinguish between 2 stimulus locations
Lateral inhibition prevents the overlap of receptive fields
Facilitates pinpoint accuracy in localisation of the stimulus
Mediated by inhibitory interneurons within dorsal horn of spinal cord
Facilitates enhanced sensory perception (discrimination

36
Q

Dorsal column function? What does the information travel along?

A

Innocuous mechanical stimuli

  • Fine discriminative touch
  • Vibration

Information conveyed from lower limbs and body (below T6) travel ipsilaterally along the gracile tract

37
Q

What is adaptation?

A

-when a continuous sensory stimulus is applied the receptor responds at a high impulse rate at first and then a progressively slower rate until finally the rate of action potentials decreases to very few or none at all

38
Q

How many neurones do all sensory pathways involve?

A

3 orders of neurones

2 in motor

39
Q

Outline Dorsal Columns – Medial Lemniscus pathway

Touch & Proprioception for body

A

Lower limbs to 1order neurone to Gracile fasciculus (medial)
Upper limbs to 1order neurone to Cuneate fasciculus (lateral)
Synapse in Medulla with 2order neurone to decussates in Medulla
2o neurone ascends in “Medial Lemniscus” to Thalamus (VPL)
Synapse in Thalamus with 3order neurone to S1

VPL on Body (Memory aid: Visible Panty Line is found on the body)
Ventral posterolateral nucleus

40
Q

Outline Dorsal Columns – Medial Lemniscus pathway

Touch & Proprioception for face

A

Sensory information from FACE
Face to Trigeminal nerve (1order neurone)
Synapses with 2order neurone in the Pons to decussates in Pons
2order neurone joins Medial Lemniscus to Thalamus (VPM)
Synapse in Thalamus with 3o neurone to S1

VPM to Head
ventral posteromedial nucleus

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