Anatomy Descending Tracts Flashcards
1
Q
Where do somatomotor signals originate?
A
Somatomotor cortex of precentral gyrus of frontal lobe
2
Q
What CNS structures will modify somatomotor signals?
A
- Basal nucleus/thalamus
- Cerebellum
- Reticular formation
- Limbic system
- Red nucleus/substantia nigra
3
Q
somatomotor neuron is found in:
Spinal cord -
Braistem CN nuclei -
A
- Spinal cord - ventral horn gray matter
2. Brainstem CN nuclei 3,4,5,6,7,9,10,11,12
4
Q
What is the effector of a somatomotor signals?
A
Skeletal Muscle
5
Q
How many neurons in somatomotor pathway?
A
2
- Upper
- Lower
6
Q
The upper motor neuron of the somatomotor pathway connect what? Their axons form what type of tracts?
A
- Connect precentral gyrus to somatomotor neurons
2. Axons form descending tracts
7
Q
The lower motor neurons of the somatomotor pathway are found where?
A
CN nuclei of brainstem or spinal cord/ventral horn
8
Q
What are the two type of lower motor neurons, efferent axons carried in peripheral nerves?
A
- alpha motor neurons
2. Gamma motor neurons
9
Q
What are alpha motor neurons?
A
Large diameter myelinated (fast) neurons that synapse with extrafusal muscle fibers to contract whole muscle
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
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
12
Q
Small diameter (slow conducting) alpha motor neurons innervate what type of muscle fibers?
A
Slow twitch (red) muscle ribers
13
Q
Larger diameter (fast conducting) alpha motor neurons innervate what type of muscle fibers?
A
Fast twitch (white) muscle fibers
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
15
Q
What two ways can muscle contraction be initiated?
A
- Somatomotor cortex and control centers in the brain (voluntary UMN - precentral gyrus)
- Spinal cord/brain stem (reflex LMN - bypass UMN)
16
Q
T/F Descending tracts have only nonspecific upper motor neuron tracts
A
False, have both
- nonspecific upper motor neuron tracts
- Specific somatotopic tracts (homunculus) for postural gross movement, fine movement, and limb flexion
17
Q
Collateral connections between tracts help with what?
A
Help coordinate movement (context)
18
Q
What is reciprocal inhibition?
A
Antagonist inhibition during agonist contraction
19
Q
What is muscle synergism?
A
Coordinated muscle action
20
Q
What is proprioception?
A
Information of body position in time and space is used to coordinate muscle contraction
21
Q
What is stepping pattern generators?
A
Alternate flexion/extension of lower limbs
22
Q
What is a motor unit?
A
A single somatomotor neuron (axon) and all the muscle fibers it activates
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
24
Q
T/F Motor neuron pools are not arrange somatotopically
A
False, they ARE
25
```
What part of ventral horn are these arranged in:
Flexors -
Extensors -
Axial Muscles -
Appendicular muscles -
```
Flexors - dorsal
Extensors - ventral
Axial Muscles - medial
Appendicular muscles - lateral
26
What is a reflex?
Predictable response to a given stimulus
27
T/F reflex can occur without brain input
True, no UMN
28
Reflexes are context dependent. What does that mean?
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
29
Describe reflex pathway starting with sensor/receptor ->
1. Sensor receptor
2. Sensory neuron
3. Interneuron connection in brainstem or spinal cord
4. Motor neuron
5. Skeletal muscle
30
T/F Most skeletal movement is reflex movement
False, most is voluntary
31
Describe a phasic stretch reflex and give examples
- Myotatic reflex, muscle stretch reflex, and deep tendon reflex
- Brief response to stimulus
32
Describe pathway of phasic stretch reflex starting with quick stretch stimulus ->
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
33
Is a phasic stretch reflex monosynaptic?
Yes, sensory neuron synapse directly with motor neuron (no interneuron)
34
Is phasic stretch reflex crossed or uncrossed?
Uncrossed
35
T/F Phasic stretch reflex involves many spinal cord segments
False, only single spinal cord level
36
What is a tonic stretch reflex?
Respond to stimulus for duration of stimulus
37
Tonic stretch reflex results from what?
Lesion of brain or spinal cord (UMN lesion)
38
Tonic reflex contraction -
- 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
39
How many neurons in cutaneous reflex pathway?
Minimum of 3
40
Golgi tendon reflex - start with increased tendon stretch
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
41
How many spinal cord segments affected by flexor withdrawal reflex?
Multiple affecting multiple effectors (more than 1 muscle) on same side
42
Flexor withdrawal reflex - start with pain stimulus
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
Is flexor withdrawal reflex crossed or uncrossed?
Crossed in spinal cord
| Ex: crossed flexor withdrawal reflex
44
How many neurons in descending tract?
2 neuron pathway
45
Where are the medial motor tracts located and what do they function in?
Located in medial spinal cord white matter
| Function in axial muscle/posture; girdle muscles/stabilizers; contextual
46
What sensory input found in tectospinal tract?
1. Visual
2. Auditory
3. Somatosensory (pain, touch)
47
Where does the tectospinal tract begin?
Soma located in corpora quadrigeminae (tectum of midbrain - superior/inferior colliculi) in mesencephalon
48
Where does tectospinal tract crossover?
At level of mesencephalon
49
Where does the tectospinal tract travel in spinal cord and what do you find in descending tract?
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
Effect of the tectospinal tract?
Head turning
51
What sensory input found in medial reticulospinal tract?
Reticular system monitors and filters sensory input through the brain stem into the diencephalon (pretty much everything)
52
Where does the medial reticulospinal tract start?
Soma located in pontine reticular formation of metencephalon
53
Where does medial reticulospinal tract travel in spinal cord?
In spinal cord anterior column
54
Is the medial reticulospinal tract crossed or uncrossed?
Uncrossed
55
T/F the medial reticulospinal tract travels in the ventral horn along the entire spinal cord
True
56
What are the 2 effects of the medial reticulospinal tract?
Effect: prepare postural (axial) and girdle muscles for limb activity; reaching
57
What sensory input in the medial vestibulospinal tract?
1. Vestibular apparatus (static and dynamic equilibrium)
58
Where does the medial vestibulospinal tract start?
Soma located in medial vestibular nuclei - elongate nucleus in metencephalon (pons) and myelencephalon (medulla)
59
Where does the medial vestibulospinal tract travel in spinal cord?
Anterior column
60
Does the medial vestibulospinal tract cross?
Crosses at level of myelencephalon (medulla)
61
What two areas of spinal cord does the medial vestibulospinal tract travel along?
Cervical and thoracic spinal cord
62
What is the effect of the medial vestibulospinal tract?
Balance in response to head movement (coordinate with tectospinal tract to maintain balance with head turning)
63
What sensory input in the lateral vestibulospinal tract?
1. Vestibular apparatus (center of gravity)
64
Where does the lateral vestibulospinal tract start?
Soma located in lateral vestibular nuclei located in metencephalon (pons)
65
Where does the lateral vestibulospinal tract travel in spinal cord?
Anterior column
66
Does the lateral vestibulospinal tract cross?
Uncrossed
67
What areas of spinal cord does the lateral vestibulospinal tract travel along?
The entire spinal cord
68
What is the effect of the lateral vestibulospinal tract?
Upright posture/balance - stimulate axial extensors and inhibit axial flexors when person is standing upright
69
What input in the medial (anterior) corticospinal tract?
Diverse associative input from pre motor and parietal cortex of frontal lobe
70
Where does the medial (anterior) corticospinal tract start?
Soma located in somatomotor cortex ( pre central gyrus of frontal lobe - trunk of homunculus)
71
Pathway of the medial (anterior) corticospinal tract from precentral gyrus to pyramids?
Precentral gyrus -> internal capsule -> crus cerebri -> pons -> pyramids
72
Where does the medial (anterior) corticospinal tract travel in spinal cord?
Anterior column
73
Is the medial (anterior) corticospinal tract crossed or uncrossed?
Uncrossed
74
What areas of spinal cord does the medial (anterior) corticospinal tract travel along?
Cervical and thoracic
75
What is the effect of the medial (anterior) corticospinal tract?
Balance to prepare postural muscles for voluntary movements
76
Where are the lateral motor tracts located and what are their function?
Located in lateral spinal cord white matter
| Function in fine movements of face and extrimities
77
What is the input to the lateral corticospinal tract?
Pre-frontal cortex and motor associative cortex
78
Where does the lateral corticospinal tract start?
Soma located in somatomotor cortex (pre-central gyrus) of the frontal lobe (UMN)
79
Describe pathway of the lateral corticospinal tract from pre central gyrus to medulla?
Internal capsule -> crus cerebri -> pons -> pyramids
80
Where does the lateral corticospinal tract cross?
Cross at decussation of pyramids
81
Descend down spinal cord in what part?
Lateral column spinal cord (corticospinal)
82
What regions of spinal cord does the lateral corticospinal tract travel to?
Lateral somatomotor neurons in ventral horn (LMN) in brachial and lumbosacral plexus regions of spinal cord
83
What is the effect of the lateral corticospinal tract?
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
What is the input of the rubrospinal tracts?
Motor cortex
85
Where do the rubrospinal tracts start?
Soma located in red nucleus of mesencephalon
86
Where do the rubrospinal tracts cross?
Cross at mesencephalon
87
Describe pathway of the rubrospinal tracts to spinal cord?
Pons -> medulla -> spinal cord lateral column
88
What region of the spinal cord do the rubrospinal tracts go to?
Brachial plexus region
89
What is the effect of the rubrospinal tracts?
Activate wrist and hand extensors
90
What is the input into the lateral (medullary) reticulospinal tracts?
Motor cortex
91
Where do the lateral (medullary) reticulospinal tracts start?
Reticular nuclei of the medulla
92
In what column does the lateral (medullary) reticulospinal tracts descend?
Lateral column
93
Is the lateral (medullary) reticulospinal tracts crossed or uncrossed?
Uncrossed
94
What regions of spinal cord do the lateral (medullary) reticulospinal tracts go to?
Medial somatomotor neurons brachial and lumbosacral plexus of spinal cord
95
What are the 2 effects of the lateral (medullary) reticulospinal tracts?
Effect: prepare postural (axial) and girdle muscles for limb activity; reaching
96
What is the input to the corticobalbar tracts?
Associative cortex = premotor cortex
97
Where do the corticobalbar tracts start?
Pre-central gyrus of frontal lobe = somatomotor cortex
98
The corticobalbar tracts descend where via the pons, medulla, and cervical spinal cord?
```
CN nuclei
3,4,6 ->eye movement
5,7 -> face movement
9,10 -> pharynx and larynx
11 -> Trap
12 -> tongue
```
99
Where do the corticobalbar tracts cross?
| Describe differences of upper/lower face muscles
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
What are the effect of the corticobalbar tracts?
```
CN 5 - muscles mastication
CN 7 - facial expression
CN 9,10 - pharynx/larynx muscles
CN 11 - Trap, SCM
CN 12 - Tongue muscles
```
101
What are nonspecific upper motor tracts?
Both tracts activated by limbic system (emotions) ad provide context to affect other descending tractd
102
What is the nonspecific upper motor tract ceruleospinal tract?
Mediates its effects by release of NEpi from locus ceruleus
103
What is the nonspecific upper motor tract raphespinal tract?
Mediates its effects by release of Serotonin from raphe nucleus
