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MD4001 - Physiology > Ascending Pathways > Flashcards

Ascending Pathways Flashcards

1
Q

What is the modality and features of:

Hair follicle receptors:

A
  • Touch
  • Rapidly adapting
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2
Q

What is the modality and features of:

Merkel endings

A
  • Pressure, low frequency vibration
  • Slowly adapting
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3
Q

What is the modality and features of:

Meissner Corpuscles

A
  • Light touch
  • Rapidly adapting
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4
Q

What is the modality and features of:

Pacinian corpuscle

A
  • Vibration and Joint position sense (JPS)
  • Rapidly adapting
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5
Q

What is the modality and features of:

Ruffini endings

A
  • Skin stretch, pressure and JPS
  • Slowly adapting
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6
Q

What is the modality and features of:

Nocioceptors

A

Pain

Free nerve endings

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7
Q

What is the modality and features of:

Muscle Spindles

A

Muscle length and proprioception

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8
Q

What is the modality and features of:

Golgi Tendon Organ

A

Joint position sense

Slowly adapting

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9
Q

Describe the sensor response in comparison to an action potential

A

Slow

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10
Q

Describe the concept of lateral inhibition

A
  • Each sensory neuron has a receptive field
  • Dendrites are dense at the centre and diffuse at the periphery
  • Stimuli at the centre of the field activate more dendrites than at the periphery and so cause faster firing
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11
Q

What is the main function of lateral inhibition?

A

Sharpens discrimination between two points

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12
Q

How does lateral discrimination translate to sensation?

(draw a diagram)

A
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13
Q

What is the function of the 1st neuron in the sensory pathway?

(take signals from the periphery to the CNS)

A

1st neurons in the ascending pathway “sense” and exit from their cognate dermatome zone then feeds into a chunk of spinal cord that “belongs” to that body segment

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14
Q

Draw a diagram illustrating somatic sensory input

A
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15
Q

Describe the action of spinal cord segements

A

Sensory rootlets come from a dermatome

  • Internally indistinct/functionally important
  • Serves body segment (dermatome/myotome)
  • Lower segments much higher than their level of exit therefore the cauda equina
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16
Q

How many pathways travel to the cerebral cortex for concious sensation

A

Two

Both pathways have 3 neurons, relay in thalamus and cross over to the opposite side of the brain

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17
Q

Do the dorsal and anterolateral pathways cross the spinal cord?

A

Yes

18
Q

What is the function of the dorsal colum (medial lemniscal pathway)?

A

Vibration and conscious position sense - two-point discrimination/fine touch

19
Q

Describe the pathway of a sensory signal coming from the leg to the brain (below T6) travelling in the dorsal column

A
  • 1st neuron – DRG, spinal cord ascends on SAME side to medulla
  • 2nd neuron – medulla, axon crosses and ascends to thalamus
  • 3rd neuron – in thalamus ascend to cerebral cortex (postcentral gyrus)
20
Q

Describe the pathway of a sensory signal coming from the arm to the brain (above T6) travelling in the dorsal column

A
  • Arm fibres more lateral in spinal cord
  • 2nd neuron in separate medulla nucleus to neurons “servicing” the leg
  • 3rd neuron in thalamus and projects to cerebral cortex
21
Q

How is the primary somatosensory cortex arranged?

A
  • Somatotopy in the primary somatosensory cortex
  • Topographical arrangement of the body representation across the sensory cortex
22
Q

Cortical functions of the dorsal column

A
  1. To determine the shape of an object (without sight)
    * Proprioception from the finger joints and fine discriminating touch provides a very accurate model of any object that is handled
  2. To determine the texture of an object (without sight)
  • Texture is determined by vibration and slip (Meissner) receptors as well as fine discriminating touch.
  • Note pleasure can be associated with this pathway

**Requires the somatosensory area association area in the parietal lobe is functioning properly/normally

23
Q

Astereognosis

A

is the inability to identify an object by active touch of the hands without other sensory input, such as visual or sensory information.

24
Q

Stereognosis

A

the mental perception of depth or three-dimensionality by the senses, usually in reference to the ability to perceive the form of solid objects by touch.

25
Q

What are the two types of pain and fibres in the anterolateral pathway?

A
  • Discriminative “localising pain” – well localised and brief via A delta fibres (Small myelinated fibres (pain location perception – post central gyrus)
  • Affective “suffering pain” less localised and longer lasting via unmyelinated C fibres (->centres for emotion/memory, physiological reactions and planning avoidance)
26
Q

What is another name for the anterolateral pathway?

A

spinothalamic tract

27
Q

What senses are carried in the anterolateral pathway?

A

pain and temperature

28
Q

Draw a digram of the pathway of the anterolateral pathway

A
  • 1st neuron in DRG
  • 2nd neuron in posterior horn (crosses to ooposite side close to same level in white commissure and ascends to thalamus)
  • 3rd neuron in thalamus
29
Q

Draw a diagram showing the pathway of the neurons in a discriminative pain pathway

A

FAST pathway

Neospinothalamic

30
Q

Draw a diagram showing the pathway of affective pain in the spinothalamic tract

A

SLOW pathway

Paleospinothalmic tract

31
Q

Summarise the pain function/connections of the anterolateral system

A
  • Prolonged stimulation of the paleo-spinothalamic pathways (c fibres and slow pain) is said to be on the hardest pains to bear and can affect mood and outlook (amygdala and cingulate gyrus)
  • Synapse with brainstem nuclei to increase arousal – pain prevents sleep (thalamus)
  • Stimulates (indirectly) autonomic circuitry – pain makes you sweat and feel sick (hypothalamus)
  • These pathways provide us with the pain basis for avoidance behaviours that protect us from harm (insula)
  • They are linked to a strong memory forming circuit (hippocampus and amygdala)
  • Positively associated with limbic system – emotional component (amygdala)
32
Q

What is this area of the brain for?

A

Discriminitive pain

33
Q

What is this area of the brain for?

A

Affective pain

34
Q

What is the function of this area of the brain?

A

Integrates discriminitive and affective pain

(coordinates avoidance)

35
Q

What is the thalamus and what are its main functions?

A
  • A collection of nuclei on diverse pathways to the cerebral cortex
  • Mainly for:
    • Conscious sensation relay and processing o Motor circuits
    • Emotion/memory
    • Special sense hearing and vision
36
Q

How are the thalamus and the cortex connected?

A

White matter bundles

Most info passes to the cortex (relay) but there are some reciprocal connections from all cortical to regulate thalamus activity/processing

37
Q

What is the effect of lesions of the anterolateral tract?

A

Lesions in the anterolateral tract cause decreased perception of pain and temperature on the contralateral side of the body, always one or two dermatomes below the level of the lesion

38
Q

What conditions can affect the dorsal spinal cord?

A
  • Vitamin B12 deficiency (SCDC)
  • HIV myelopathy
  • Tabes Dorsalis (syphilis)
  • Multiple Sclerosis
39
Q

What are the spinocerebellar pathways?

A

The cerebellum functions to gather information about the movements of the body and compare them with planned and active movements of the body. It then issues real time correctional information to achieve smooth accurate movements – Error based learning

40
Q

Highlight the function of each ascending pathway of the spinal cord

A
  • Fasciculus gracilis carries information from the lower body extremities (touch, vibration, conscious proprioception)
  • Fasciculus cuneatus carries information from the upper body extremities (touch vibration, conscious proprioception)
  • Dorsal and ventral spinocerebellar tracts (proprioceptive information from muscle spindles (dorsal_ & Golgi organs (ventral)
  • Anterolateral (spinothalamic) tract (touch, pain, temperature, itch etc.)

MD4001 - Physiology (11 decks)

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