Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MD4001 Week 0 > 8. Sensory pathways 1 > Flashcards

8. Sensory pathways 1 Flashcards

1
Q

3 stages to corporal senses?

A
  1. Detection of a stimulus
  2. Transmission of stimulus information to the brain
  3. Recognition (conscious or unconscious) of the nature, location, intensity and duration of the stimulus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What 5 factors do cutaneous receptors detect?

A
  • warmth
  • cold
  • nociception
  • pressure
  • vibration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

From axonal type A-delta, A-beta, A-gamma to C what happens to the following factors:

  • Diameter?
  • Speed?
  • Degree of myelination?
A

Diameter narrows
Speed decreases
Degree of myelination decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q 
What are the sensory receptors for the following axons:
A-delta?
A-beta?
A-gamma?
C?
A

A-delta: Proprioceptors of skeletal muscle
A-beta: Mechanoreceptors of skin
A-gamma: Pain, temperature
C: Temperature, pain, itch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

name the specialised cutaneous receptors?

A

Free nerve endings: Detect pain, slow adapting

Merkel’s disks: Detect static touch and pressure, slow adapting

Meissner’s corpuscles: Detects changes in touch and pressure, rapid adapting

Pacini’s corpuscles: Detects vibrations, rapidly adapting

Hair follicle receptors: Non specialist endings but sensitive to movements of the hair

Ruffini corpuscles: Skin stretch and directions. Slow adaptation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Detection of muscle contraction

A

Muscle spindles measure changes in length of muscle.
It regulates muscle length via the gamma reflex loop.

When intrafusal fibres are stretched (muscle length increases) afferent fibres stimulate the contraction of extrafusal fibres via alpha motor neurons.

Golgi tendon organs detect the tension in the muscle via type 1b sensory nerve endings which innervate a collagen matric in the tendon. As the tendon stretches the endings depolarise and send afferent information to the CNS.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

En route to the cortext all sensory informations passes through the…

A

THALAMUS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the basic thalamic circuitry?

A

The thalamus has reciprocal connections to all cortical regions, and can relay information, receive feedback and modulate cortical activity
Thalamic connections form peduncles to the cortex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the divisions of the white matter in the spinal cord?

A

FASCICULUS GRACILIS carries information from the lower body extremities

FASCICULUS CUNEATUS carries information from the upper body extremities

DORSAL and VENTRAL SPINOCEREBELLAR tracts carry proprioceptive information from muscle spindles (Dorsal) & Golgi organs (ventral)

ANTERIORLATERAL SYSTEM
Spinothalamic tract – pain transmission etc.
Spinomesencephalic
Spinoreticular

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the 4 principal ascending somatosenstory pathways in the spinal cord?

A
  1. Dorsal column medial lemniscus pathway
  2. Anterolateral pathways (system)
  3. Spinocerebellar pathway
  4. (Trigeminalpathway)–thalamus and brainstem
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the medial lemniscal pathway in the dorsal column?

A
  1. Composed of large diameter (fast Aβ fibres)
  2. 1st order neurons ascend ipsilaterally in dorsal columns known as the:
    - Fasciculus gracilis (enters up to T6) and the
    - Fasciculus cuneatus (enters above T6)
  3. At the Gracile and Cuneate nuclei in the brainstem they synapse with 2nd order neurons .
  4. These then decussate (arcuate fibers), form part of the medial lemniscus and project to the ventral posterolateral lobe (VPL) of the thalamus and then to the cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain lateral inhibition

A

Stimuli at the center of the field activate more dendrites (as dendrites are more dense at centre) than at the periphery and so cause faster firing
Hence adjacent neurones with overlapping fields inhibit one another, so that the one with the stimuli closest to it’s centre produces a greater signal, therefore greater inhibition on the adjacent neurone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does lateral inhibition aid discrimination between two points?

A

Lateral inhibition relies on reciprocal inhibition between two adjacent neurons where the extent of inhibition from each one is linked to the stimulus point on the neuronal receptive field overlap

I.e. if the stimulus is close to centre of one neurones receptive field, it will have a high inhibition in adjacent neurone.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Signs of lesions for the dorsal column - medial lemniscal pathway?

A
  1. Lesions of the GRACILE FASCICULUS can cause GAIT ATAXIA, as the brain (cortex and cerebellum) is deprived of information about the position of the feet.
    - Classic sign of gait (or sensory) ataxia is the stamp and stick gait.
    - Patient stamps down feet to enhance sensory input and maintains a broad based stance.
  2. Lesions of the CERVICAL CORD also cause UPPER EXTREMITY ATAXIA
  3. Cause PARAESTHESIA’S in the distal part of extremities. Can result from ECTOPIC DISCHARGE in damaged dorsal column axons and may present symptoms before abnormalities are seen in neuro exam
  4. Excessive swaying (when standing with feet together and eyes closed i.e. Romberg’s sign. However, this symptoms is also present in vestibular disease and cerebellar disorders

** Often patient is able to compensate with vision and thus minimise sensory ataxia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Symptoms of paraesthesias?

A

Tingling
Numbness
Crawling
Deadness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How can dorsal column function impairment be inferred?q

A

by testing the ability to feel changes in the position of toes and fingers or feel a tuning fork vibration without looking
**ALTHOUGH finger/toe proprioception is not lost until about 75 % of posterior column axons have ceased to function

17
Q

What are the CORTICAL FUNCTIONS of the dorsal column- medial lemniscal pathway?
Requirement?

A
  • FINE TACTILE and PROPRIOCEPTIVE information is used* for:
    1. To determine the shape of an object (without sight).
  • Uses proprioception from the finger joints and fine discriminating touch
  1. To determine the texture of an object (without sight)
    - Texture is determined by vibration and slip receptors + fine discriminating touch. (Note this pathway is associated with pleasure)

REQUIRES THE NORMAL FUNCTION SOMATOSENSORY AREAS OF THE PARIETAL LOBE

18
Q

Lesions of one of the somatosensory association cortex areas leads to….

A

Amorphosynthesis:
These patients still have an appreciation of pain and temperature, they are unable to locate with any certainty the location of the source of the stimulus

E.g.

  • Patient unable to recognise complex object by feel on the opposite side to the lesion
  • Patients often only explore one half of an object during testing of object recognition
  • Patients can also neglect the whole of the opposite side of their body such that they overlook motor output on that side.

MD4001 Week 0 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions