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Y2 HNN > Ascending and descending tracts > Flashcards

Ascending and descending tracts Flashcards

1
Q

what are the different type of axon fibres from skin

A

Aa (alpha)
Ab (beta)
Ad (gamma)
C

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2
Q

Describe the diameter, speed, myelination and sensory receptors for Aa fibres

A

Diameter (nanometre): 13-20
Speed (m/sec): 80-120
Myelinated: very fast
Sensory receptors: proprioceptors of skeletal muscle

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3
Q

Describe the diameter, speed, myelination and sensory receptors for Ab fibres

A

Diameter (nanometre): 6-12
Speed (m/sec): 35-75
Myelinated: slower speed than Aa but faster than Ad
Sensory receptors: mechanoreceptors of skin

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4
Q

Describe the diameter, speed, myelination and sensory receptors for Ad fibres

A

Diameter (nanometre): 1-5
Speed (m/sec): 5-30
Myelinated: slower speed than Aa and Ab
Sensory receptors: pain, temperature

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5
Q

Describe the diameter, speed, myelination and sensory receptors for C fibres

A

Diameter (nanometre): 0.2-1.5
Speed (m/sec): 0.5-2
NOT Myelinated: slowest
Sensory receptors: Temperature, pain and itch

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6
Q

what type of neurons are sensory neurons

A

Unipolar neuron

see pic online

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7
Q

Describe the pain fibre input

A
  1. Painful stimulus on skin (needle prick)
  2. AP released that travels along the sensory neuron with Ad or C fibre axon
  3. AP reaches the SUPERFICIAL dorsal horn of the spinal cord
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8
Q

Describe the touch fibre input

A
  1. Touch stimulus on skin (touching dots)
  2. AP released that travels along the sensory neuron with Ab fibre
  3. AP reaches DEEP dorsal horn of the spinal cord
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9
Q

Explain DAVE

A

Dorsal root
Afferent (sensory info arrives into spinal cord)

Ventral root
Efferent (motor info exits out of spinal cord)

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10
Q

what are ascending and descending tracts

A

Tracts of myelinated axons- forms spinal cord white matter
Ascending- carries sensory info from periphery to brain
Descending- carries motor info from brain to spinal cord

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11
Q

what are the two types of ascending tracts

A
  1. Discriminative (fine) touch- feather touching foot
    Dorsal column pathway
  2. Pain
    Spinothalamic pathway
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12
Q

How does the info in sensory pathways travel

A

1st neuron- Primary sensory neuron (periphery-takes info from mechanoreceptors)
2nd neuron- Secondary sensory neuron (spinal cord/brainstem)
3rd neuron- Tertiary sensory neuron (thalamus to cerebral cortex)

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13
Q

what are the 3 types of TOUCH cutaneous and subcutaneous mechanoreceptors (Ab afferents)

A

Meissner’s corpuscle
Merkel disk
Hair follicle receptor

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14
Q

what are the 2 types of PRESSURE cutaneous and subcutaneous mechanoreceptors (Ab afferents)

A

Pacinian corpuscle

Ruffini ending

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15
Q

Describe the dorsal column (descrimininative touch) pathway

A
  1. Touch stimulus on skin (touching dots)
  2. AP released that travels along the sensory neuron with Ab fibre
  3. AP reaches DEEP dorsal horn of the spinal cord
    PRIMARY:
  4. primary afferent signal (same axon) travels in the dorsal column/ funiculus through the lumbar, thoracic and cervical spinal cord.
  5. in the medulla- the primary afferent neuron synpases into dorsal column nuclei and becomes internal arcuate fibres.
    SECONDARY
  6. the internal arcuate fibres cross over to the other side and goes up through the medial lemniscus in the pons and midbrain
  7. from midbrain the signal goes to the VPL (ventral posterolateral nucleus) of the thalamus
    TERTIARY
  8. the signal goes from thalamus to the internal capsule and then to the sensory cortex (info processed here)
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16
Q

what fibre axons are involved in sensing pain

17
Q

what are the nociceptor peripheral endings that detects pain

A

free nerve endings

18
Q

Describe the spinothalamic pathway

A

PRIMARY
1. Painful stimulus on skin (needle prick)- detected by free nerve endings
2. AP released that travels along the sensory neuron with Ad or C fibre axon
3. AP reaches the SUPERFICIAL dorsal horn of the spinal cord- primary afferent
SECONDARY
4. The primary afferent signal synapses into the secondary afferent signal and crosses over to the ventro-lateral aspect of the spinal cord.
5. The secondary signal travels through lumbar, thoracic and cervical spinal cord - Anterolateral funiculus
6. The secondary afferent signal travels on the same side and travels upwards through the medulla,pons, midbrain and thalamus.
TERTIARY
7. Thalamus- secondary signal synpases into tertiary signal and travels through internal capsule to the sensory cortex- information processed here

19
Q

what are the two types of descending tracts? (motor-voluntary)

A

1) Corticospinal tracts

2) Corticobulbar tracts

20
Q

How does the info in motor (descending) pathways travel

A

From Motor Cortex, Upper motor neuron carries info and synpases to lower motor neuron in brainstem/spinal cord. the lower motor neuron carries info the muscle = movement

21
Q

What is the purpose of corticobulbar pathway

A

motor control of cranial nerves

22
Q

Describe the corticobulbar pathway

A
  1. AP generated in motor cortex
  2. Neurons carry AP down midbrain, pons and medulla
  3. SOme neurons synpase in the trigeminal motor nucleus in pons to become –> Trigeminal NErve
  4. Some neurons synapse in the facial motor nucleus in pons to become –> Facial nerve
  5. Some neurons synapse in the nucleus ambiguous in medulla to become –> Vagus nerve and Hypoglossal nerve
23
Q

Describe the corticospinal pathway

A
  1. Motor cortex generates AP
  2. Neurons travel down Midbrain, pons and medulla and crosses over at pyramidal decussation
  3. 85% cross over are knowsn as lateral corticospinal and 15% stay on the same side and are known as anterior corticospinal
  4. both travel downwards
  5. anterior corticospinal (15%)- stops at mid thoracic level
  6. lateral corticospinal (85%)- continues travelling downwards
24
Q

what are the three types of descending tracts? (motor-tone)

A

Reticulospinal
Tectospinal
Vestibulospinal

25
Q

Describe the 2 tracts in the reticulospinal pathway (name, origin and their function)

A

Reticulopsinal pathways are bilateral projections

1) Pontine Tracts
- Comes from ipsilateral oral and caudal PONTINE reticular nuclei
- controls EXTENSORS

2) Medullary Tracts
- comes from ipsilateral gigantocellular reticular nuclei of the MEDULLA
- controls FLEXORS

26
Q

how does the reticulospinal pathways travel down the spinal cord

A
  • Bilateral projections
  • on the ventral surface of spinal cord
  • pontine tracts are medial in ventral area of spinal cord
  • medullary tracts are lateral in ventral area of spinal cord
  • runs entire lenght of spinal cord
27
Q

Why are reticulospinal pathway important and what does it damage lead to

A
  • Important in maintenace of balance and posture
  • modulates acitivty of alpha-motor neurons (LMN)
  • damage leads to loss of postural control
28
Q

describe the vestibulospinal pathway

A
  • runs medially in ventral area- ventromedial
  • originates from ipsilateral lateral vestibular nucleus in medulla
  • runs entire length of spinal cord
29
Q

describe the tectospinal pathway

A
  • runs ventromedially
  • origin- contralateral superior colliculus in midbrain and crosses
  • runs only to cervical spinal cord only and doesnt to thoracic and lumbar
30
Q

why does the tectospinal pathway project to cervical cord ONLY

A
  • Innervates muscles of the neck ONLY

- modulates activity of both alpha and gamma motor neurons (voluntary and involuntrary)

Y2 HNN (34 decks)

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