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Neuroanatomy Exam 2 > Anatomy Descending Tracts > Flashcards

Anatomy Descending Tracts Flashcards

1
Q

Where do somatomotor signals originate?

A

Somatomotor cortex of precentral gyrus of frontal lobe

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2
Q

What CNS structures will modify somatomotor signals?

A
  1. Basal nucleus/thalamus
  2. Cerebellum
  3. Reticular formation
  4. Limbic system
  5. Red nucleus/substantia nigra
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3
Q

somatomotor neuron is found in:
Spinal cord -
Braistem CN nuclei -

A
  1. Spinal cord - ventral horn gray matter

2. Brainstem CN nuclei 3,4,5,6,7,9,10,11,12

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4
Q

What is the effector of a somatomotor signals?

A

Skeletal Muscle

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5
Q

How many neurons in somatomotor pathway?

A

2

  1. Upper
  2. Lower
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6
Q

The upper motor neuron of the somatomotor pathway connect what? Their axons form what type of tracts?

A
  1. Connect precentral gyrus to somatomotor neurons

2. Axons form descending tracts

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7
Q

The lower motor neurons of the somatomotor pathway are found where?

A

CN nuclei of brainstem or spinal cord/ventral horn

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8
Q

What are the two type of lower motor neurons, efferent axons carried in peripheral nerves?

A
  1. alpha motor neurons

2. Gamma motor neurons

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9
Q

What are alpha motor neurons?

A

Large diameter myelinated (fast) neurons that synapse with extrafusal muscle fibers to contract whole muscle

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10
Q

What are gamme motor neurons?

A

Medium diameter myelinated (medium speed) neurons that synapse with intrafusal (muscle spindle) muscle fibers that keep muscle spindles sensitive during whole muscle contraction

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11
Q

Lower motor neurons release what NT that binds to what receptors where?

A

Release ACh that binds nicotinic receptors on muscle cell membrane to always depolarize (stimulate) the muscle

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12
Q

Small diameter (slow conducting) alpha motor neurons innervate what type of muscle fibers?

A

Slow twitch (red) muscle ribers

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13
Q

Larger diameter (fast conducting) alpha motor neurons innervate what type of muscle fibers?

A

Fast twitch (white) muscle fibers

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14
Q

What is Henneman’s Size Principle?

A

Typically slow twitch muscle fibers (small dia motor neurons) are activated before fast twitch muscle fibers (large dia motor neurons) allowing the 2 types of muscle fibers to contract together

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15
Q

What two ways can muscle contraction be initiated?

A
  1. Somatomotor cortex and control centers in the brain (voluntary UMN - precentral gyrus)
  2. Spinal cord/brain stem (reflex LMN - bypass UMN)
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16
Q

T/F Descending tracts have only nonspecific upper motor neuron tracts

A

False, have both

  1. nonspecific upper motor neuron tracts
  2. Specific somatotopic tracts (homunculus) for postural gross movement, fine movement, and limb flexion
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17
Q

Collateral connections between tracts help with what?

A

Help coordinate movement (context)

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18
Q

What is reciprocal inhibition?

A

Antagonist inhibition during agonist contraction

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19
Q

What is muscle synergism?

A

Coordinated muscle action

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20
Q

What is proprioception?

A

Information of body position in time and space is used to coordinate muscle contraction

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21
Q

What is stepping pattern generators?

A

Alternate flexion/extension of lower limbs

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22
Q

What is a motor unit?

A

A single somatomotor neuron (axon) and all the muscle fibers it activates

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23
Q

What is a motor neuron pool?

A

Group of motor neuron cell bodies (motor units) in ventral horn that innervate a single muscle

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24
Q

T/F Motor neuron pools are not arrange somatotopically

A

False, they ARE

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25
Q 
What part of ventral horn are these arranged in:
Flexors - 
Extensors - 
Axial Muscles - 
Appendicular muscles -
A

Flexors - dorsal
Extensors - ventral
Axial Muscles - medial
Appendicular muscles - lateral

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26
Q

What is a reflex?

A

Predictable response to a given stimulus

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27
Q

T/F reflex can occur without brain input

A

True, no UMN

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28
Q

Reflexes are context dependent. What does that mean?

A

State of nervous system will affect the properties of reflex, signals from brain influence spinal reflexes
Example: If you are relaxed, the reflex response may be less intense that if you are anxious

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29
Q

Describe reflex pathway starting with sensor/receptor ->

A
  1. Sensor receptor
  2. Sensory neuron
  3. Interneuron connection in brainstem or spinal cord
  4. Motor neuron
  5. Skeletal muscle
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30
Q

T/F Most skeletal movement is reflex movement

A

False, most is voluntary

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31
Q

Describe a phasic stretch reflex and give examples

A
  • Myotatic reflex, muscle stretch reflex, and deep tendon reflex
  • Brief response to stimulus
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32
Q

Describe pathway of phasic stretch reflex starting with quick stretch stimulus ->

A
  1. Quick stretch stimulus
  2. Muscle spindle
  3. Ia sensory neuron (annulospiral/bag and chain)
  4. DRG
  5. Spinal cord dorsal horn (and dorsal column to brain postcentral gyrus)
  6. Synapse with alpha somatomotor neuron
  7. Skeletal muscle
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33
Q

Is a phasic stretch reflex monosynaptic?

A

Yes, sensory neuron synapse directly with motor neuron (no interneuron)

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34
Q

Is phasic stretch reflex crossed or uncrossed?

A

Uncrossed

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35
Q

T/F Phasic stretch reflex involves many spinal cord segments

A

False, only single spinal cord level

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36
Q

What is a tonic stretch reflex?

A

Respond to stimulus for duration of stimulus

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37
Q

Tonic stretch reflex results from what?

A

Lesion of brain or spinal cord (UMN lesion)

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38
Q

Tonic reflex contraction -

A
  • Normal = tonic sensory neurons type II sensory neuron (flowerspray/chain) signal when muscle spindle is stretch but normally prevented from activating somatomotor neurons by UMN inhibition.
  • UMN lesion removes inhibition and allows the constant afferent signal to produce a constant efferent signal
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39
Q

How many neurons in cutaneous reflex pathway?

A

Minimum of 3

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40
Q

Golgi tendon reflex - start with increased tendon stretch

A

increased tendon stretch -> golgi tendon organ -> type Ib afferent -> spinal cord inhibitory interneuron -> inhibit alpha motor neuron to homolgous muscle -> muscle with stretched tendon relaxes

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41
Q

How many spinal cord segments affected by flexor withdrawal reflex?

A

Multiple affecting multiple effectors (more than 1 muscle) on same side

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42
Q

Flexor withdrawal reflex - start with pain stimulus

A

pain stimulus -> sensory neuron (Type III or IV) -> ascends/descends for several segments in Lissauer’s tract -> activates multiple levels of ventral horn alpha motor neurons -> multiple flexor muscles -> withdrawal from painful stimulus

43
Q

Is flexor withdrawal reflex crossed or uncrossed?

A

Crossed in spinal cord

Ex: crossed flexor withdrawal reflex

44
Q

How many neurons in descending tract?

A

2 neuron pathway

45
Q

Where are the medial motor tracts located and what do they function in?

A

Located in medial spinal cord white matter

Function in axial muscle/posture; girdle muscles/stabilizers; contextual

46
Q

What sensory input found in tectospinal tract?

A
  1. Visual
  2. Auditory
  3. Somatosensory (pain, touch)
47
Q

Where does the tectospinal tract begin?

A

Soma located in corpora quadrigeminae (tectum of midbrain - superior/inferior colliculi) in mesencephalon

48
Q

Where does tectospinal tract crossover?

A

At level of mesencephalon

49
Q

Where does the tectospinal tract travel in spinal cord and what do you find in descending tract?

A

Anterior column of spinal cord white matter Ventral horn (somatomotor) connection - recall medial motor neurons of ventral horn in cervical region control axial muscles

50
Q

Effect of the tectospinal tract?

A

Head turning

51
Q

What sensory input found in medial reticulospinal tract?

A

Reticular system monitors and filters sensory input through the brain stem into the diencephalon (pretty much everything)

52
Q

Where does the medial reticulospinal tract start?

A

Soma located in pontine reticular formation of metencephalon

53
Q

Where does medial reticulospinal tract travel in spinal cord?

A

In spinal cord anterior column

54
Q

Is the medial reticulospinal tract crossed or uncrossed?

55
Q

T/F the medial reticulospinal tract travels in the ventral horn along the entire spinal cord

56
Q

What are the 2 effects of the medial reticulospinal tract?

A

Effect: prepare postural (axial) and girdle muscles for limb activity; reaching

57
Q

What sensory input in the medial vestibulospinal tract?

A
  1. Vestibular apparatus (static and dynamic equilibrium)
58
Q

Where does the medial vestibulospinal tract start?

A

Soma located in medial vestibular nuclei - elongate nucleus in metencephalon (pons) and myelencephalon (medulla)

59
Q

Where does the medial vestibulospinal tract travel in spinal cord?

A

Anterior column

60
Q

Does the medial vestibulospinal tract cross?

A

Crosses at level of myelencephalon (medulla)

61
Q

What two areas of spinal cord does the medial vestibulospinal tract travel along?

A

Cervical and thoracic spinal cord

62
Q

What is the effect of the medial vestibulospinal tract?

A

Balance in response to head movement (coordinate with tectospinal tract to maintain balance with head turning)

63
Q

What sensory input in the lateral vestibulospinal tract?

A
  1. Vestibular apparatus (center of gravity)
64
Q

Where does the lateral vestibulospinal tract start?

A

Soma located in lateral vestibular nuclei located in metencephalon (pons)

65
Q

Where does the lateral vestibulospinal tract travel in spinal cord?

A

Anterior column

66
Q

Does the lateral vestibulospinal tract cross?

67
Q

What areas of spinal cord does the lateral vestibulospinal tract travel along?

A

The entire spinal cord

68
Q

What is the effect of the lateral vestibulospinal tract?

A

Upright posture/balance - stimulate axial extensors and inhibit axial flexors when person is standing upright

69
Q

What input in the medial (anterior) corticospinal tract?

A

Diverse associative input from pre motor and parietal cortex of frontal lobe

70
Q

Where does the medial (anterior) corticospinal tract start?

A

Soma located in somatomotor cortex ( pre central gyrus of frontal lobe - trunk of homunculus)

71
Q

Pathway of the medial (anterior) corticospinal tract from precentral gyrus to pyramids?

A

Precentral gyrus -> internal capsule -> crus cerebri -> pons -> pyramids

72
Q

Where does the medial (anterior) corticospinal tract travel in spinal cord?

A

Anterior column

73
Q

Is the medial (anterior) corticospinal tract crossed or uncrossed?

74
Q

What areas of spinal cord does the medial (anterior) corticospinal tract travel along?

A

Cervical and thoracic

75
Q

What is the effect of the medial (anterior) corticospinal tract?

A

Balance to prepare postural muscles for voluntary movements

76
Q

Where are the lateral motor tracts located and what are their function?

A

Located in lateral spinal cord white matter

Function in fine movements of face and extrimities

77
Q

What is the input to the lateral corticospinal tract?

A

Pre-frontal cortex and motor associative cortex

78
Q

Where does the lateral corticospinal tract start?

A

Soma located in somatomotor cortex (pre-central gyrus) of the frontal lobe (UMN)

79
Q

Describe pathway of the lateral corticospinal tract from pre central gyrus to medulla?

A

Internal capsule -> crus cerebri -> pons -> pyramids

80
Q

Where does the lateral corticospinal tract cross?

A

Cross at decussation of pyramids

81
Q

Descend down spinal cord in what part?

A

Lateral column spinal cord (corticospinal)

82
Q

What regions of spinal cord does the lateral corticospinal tract travel to?

A

Lateral somatomotor neurons in ventral horn (LMN) in brachial and lumbosacral plexus regions of spinal cord

83
Q

What is the effect of the lateral corticospinal tract?

A
  1. Fine movements of extremities
  2. Fractionation of movement - activated individual muscles independent of other hand muscles innervated by lateral somatomotor neurons at the same level
84
Q

What is the input of the rubrospinal tracts?

A

Motor cortex

85
Q

Where do the rubrospinal tracts start?

A

Soma located in red nucleus of mesencephalon

86
Q

Where do the rubrospinal tracts cross?

A

Cross at mesencephalon

87
Q

Describe pathway of the rubrospinal tracts to spinal cord?

A

Pons -> medulla -> spinal cord lateral column

88
Q

What region of the spinal cord do the rubrospinal tracts go to?

A

Brachial plexus region

89
Q

What is the effect of the rubrospinal tracts?

A

Activate wrist and hand extensors

90
Q

What is the input into the lateral (medullary) reticulospinal tracts?

A

Motor cortex

91
Q

Where do the lateral (medullary) reticulospinal tracts start?

A

Reticular nuclei of the medulla

92
Q

In what column does the lateral (medullary) reticulospinal tracts descend?

A

Lateral column

93
Q

Is the lateral (medullary) reticulospinal tracts crossed or uncrossed?

94
Q

What regions of spinal cord do the lateral (medullary) reticulospinal tracts go to?

A

Medial somatomotor neurons brachial and lumbosacral plexus of spinal cord

95
Q

What are the 2 effects of the lateral (medullary) reticulospinal tracts?

A

Effect: prepare postural (axial) and girdle muscles for limb activity; reaching

96
Q

What is the input to the corticobalbar tracts?

A

Associative cortex = premotor cortex

97
Q

Where do the corticobalbar tracts start?

A

Pre-central gyrus of frontal lobe = somatomotor cortex

98
Q

The corticobalbar tracts descend where via the pons, medulla, and cervical spinal cord?

A 
CN nuclei 
3,4,6 ->eye movement
5,7 -> face movement
9,10 -> pharynx and larynx
11 -> Trap 
12 -> tongue
99
Q

Where do the corticobalbar tracts cross?

Describe differences of upper/lower face muscles

A

Cross in brainstem pons and medulla:

  1. Muscles of upper face are controlled bilaterally by both cerebral hemispheres CN 7
  2. Muscles of lower face are controlled contralateral hemi CN 7
100
Q

What are the effect of the corticobalbar tracts?

A 
CN 5 - muscles mastication
CN 7 - facial expression
CN 9,10 - pharynx/larynx muscles
CN 11 - Trap, SCM
CN 12 - Tongue muscles
101
Q

What are nonspecific upper motor tracts?

A

Both tracts activated by limbic system (emotions) ad provide context to affect other descending tractd

102
Q

What is the nonspecific upper motor tract ceruleospinal tract?

A

Mediates its effects by release of NEpi from locus ceruleus

103
Q

What is the nonspecific upper motor tract raphespinal tract?

A

Mediates its effects by release of Serotonin from raphe nucleus

Neuroanatomy Exam 2 (7 decks)

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