Descending Tracts Flashcards
1
Q
Where do somatomotor signals originate?
A
somatomotor cortex (precentral gyrus)
2
Q
what CNS structures modify somatomotor signals?
A
- basal nucleus/thalamus
- cerebellum
- reticular formation
- limbic system
- red nucleus/substantia nigra
3
Q
where are somatomotor neurons located?
A
- spinal cord ventral horn gray matter
- brainstem CN nuclei
- 3, 4, 5, 6, 7, 9, 10, 11, 12
4
Q
where are LMN located?
A
somatomotor neurons in CN nuclei of brainstem
OR
spinal cord/ventral horn
5
Q
where are the efferent axons of LMN?
A
they are carried in peripheral nerves
6
Q
efferent neurons from LMN release what NT?
A
acetylcholine
always depolarizing (excitatory) the muscle never hyperpolarize
7
Q
what types of neuron innervates slow twitch (red) muscle fibers?
A
small diameter (slow conducting) alpha motor neurons
8
Q
what types of neurons innervate fast twitch (white) muscle fibers?
A
large diameter (fast conducting) alpha motor neurons
9
Q
What is the Henneman’s Size principle?
A
slow twich muscle fibers are recruited and activated before fast twitch fibers
this allows 2 fiber types to contract together
10
Q
what are the 2 ways muscle contractions can be initiated?
A
- order comes from somatomotor cortex (voluntary)
- order comes from the spinal cord (reflex)
11
Q
T/F: a reflex does not require an UMN for integration
A
TRUE
the LMN acts as the integrator
However, an UMN can be invovled in modulating the respones to the reflex
12
Q
T/F: all cardiac and smooth muscle activity are reflexive?
A
TRUE
13
Q
what is the role of collateral connections between tracts?
A
helps to coordinate movement and provide context
14
Q
Collateral connections can include what type of coordinating activity?
A
- reciprocal inhibition
- muscle synergism
- proprioception
- stepping pattern generators
15
Q
What are the 2 types of descending tracts?
A
- specific somatotopic tracts
- nonspecific upper motor neuron tracts
16
Q
Specific somatotopic tracts can include what types of tracts?
A
- postural gross movement tracts
- tracts that carry info for fine movement
- tracts for limb flexion
17
Q
T/F: motor unit and motor neuron pools are the same thing
A
FALSE
motor unit = single somatomotor neuron and all muscle fibers it activates
motor neuron pool = group of motor neuron cell bodies in a ventral horn that innervate a single muscle
18
Q
how are motor neuron pools organized within the ventral horn?
A
- flexors are dorsal
- extensors are ventral
- axial muscles are medial
- appendicular muscles are lateral
19
Q
Define reflex
A
a predictable response to a given stimulus
occur w/o brain input (similar to a neural loop)
20
Q
reflexes are _______ dependent
A
content
21
Q
what does the phrase “reflexes are content dependent” mean?
A
the state of the nervous system will affect the properties of the reflex
(if you are relaxed the response may be less intense than if you were anxious)
22
Q
what are the 2 broad categories for reflexes?
A
- Stretch reflexes
- Cutaneous reflexes
23
Q
A stretch reflex that is a result of an UMN lesion will be ______
A
tonic
it will respond to the stimulus for the duration of the stimulus
24
Q
What is a phasic stretch reflex?
A
a reflex that responses briefly to the stimulus
25
what is a monosynaptic reflex?
a reflex when the sensory neuron synapses directly with the motor neuron
\*there is no interneuron
26
Briefly describe the pathway of a stretch reflex
quick stretch stimulus → muscle spindle → Ia sensory neuron (annulospiral/bag and chain) → DRG → spinal cord dorsal horn → synapses w/alpha somatomotor neuron → skeletal muscle
27
what is an uncrossed reflex?
a reflex that involves a single spinal cord level
28
what normally prevents tonic stretch reflexes?
UMN inhibition
29
what is a tonic reflex contraction?
UMN lesion removal of the inhibition of a tonic reflex
it will allow the constant afferent signals to produce a constant efferent signal
30
what are 3 characteristics of a cutaneous reflex?
1. involves interneurons (minimum 3 neuron pathway)
2. involved multiple spinal cord segments
3. crossover in the spinal cord = crossed flexor withdrawl reflex
31
a golgi tendon reflex is what type of reflex?
cutaneous reflex
32
Descending tracts can be divided into what 4 categories?
1. Medial Motor Tracts
2. Lateral Motor Tracts
3. Corticobulbar Tracts
4. Nonspecific Upper Motor Tracts
33
What tracts are included in the Medial Motor Tracts?
1. Tectospinal tract
2. Medial Reticulospinal Tract
3. Medial Vestibulospinal Tract
4. Lateral Vestibulospinal Tract
5. Medial (Anterior) Corticospinal tract
34
What is the sensory input to the tectospinal tract?
visual, auditory, or somatosensory (pain and touch)
35
where does the Tectospinal tract start?
Soma = corpa quadrigemina
36
where does the Tectospinal tract crossover?
at the level of the mesencephalon
37
after crossing over, where does the tectospinal tract descend/travel?
tectospinal tract in anterior column of spinal cord white matter
38
Where does the tectospinal tract terminate/end/connect?
medial motor neurons of the ventral horn in the cervical region
these control axial muscles
39
what supplies sensory input to the Medial Reticulospinal Tract?
reticular system
40
where does the Medial Reticulospinal tract begin?
soma = pontine reticular formation of metencephalon
41
where is the medial reticulospinal tract located?
anterior column of spinal cord descending from metencephalon
42
where does the medial reticulospinal tract cross?
it doesn't
it remains uncrossed
43
what is the destination/end point of the medial reticulospinal tract?
medial somatomotor neurons along the entire spinal cord
44
what is the role of the medial reticulospinal tract?
prepare postural (axial) and girdle muscles for limb activity (reaching)
45
what supplies sensory input to the medial vestibulospinal tract?
vestibular apparatus/static and dynamic equilibrium
46
where does the medial vestibulospinal tract begin?
soma = medial vestibular nuclei
| (elongate nucleus in pons and medulla)
47
where does the medial vestibulospinal tract travel?
anterior column of spinal cord
48
where does the medial vestibulospinal tract cross?
at the medulla
49
what is the destination/end point of the medial vestibulospinal tract?
medial somatomotor neurons along the cervical and thoracic spinal cord (brachial plexus)
50
what is the role of the medial vestibulospinal tract?
effect = balance in response to head movement (coordinate with tectospinal tract to maintain balance with head turning)
51
what provides sensory input to the lateral vestibulospinal tract?
vestibular apparatus/center of gravity
52
where does the lateral vestibulospinal tract begin?
soma located in lateral vestibular nuclei located in pons
53
where does the lateral vestibulospinal tract travel?
anterior column of spinal cord
54
where does the lateral vestibulospinal tract cross?
it doesn't
it remains uncrossed
55
what is the destination/end point of the lateral vestibulospinal tract?
medial somatomotor neurons along entire spinal cord
56
what is the role of the lateral vestibulospinal tract?
effect = upright posture/balance: stimulates axial extensors, and inhibits axial flexors when a person is standing upright
57
what provides input to the medial (anterior) corticospinal tract?
diverse associative input from pre-motor and parietal cortex of frontal lobe
58
where does the medial (anterior) corticospinal tract begin?
soma = somatomotor cortex (pre-central gyrus of frontal lobe)
59
describe the pathway of the medial (anterior) corticospinal tract
leaves the precentral gyrus and descends to the medulla through the internal capsule then the crus cerebrii and then the pons until it reaches the pyramids
60
where does the medial (anterior) corticospinal tract cross?
it doesn't
it is the 10% that remains uncrossed at the pyramids
61
what is the destination/end point of the medial (anterior) corticospinal tract?
medial somatomotor neurons in the cervical and thoracic spinal cord
62
what is the role/effect of the medial (anterior) corticospinal tract?
balance to prepare postural muscles for voluntary movements
63
where are all medial motor tracts located in the spine?
medial spinal cord white matter
64
what is the general function of all medial motor tracts?
function in axial muscle/posture
girdle muscles/stabilizers
contextual info
65
which medial motor tracts do **_not_** cross?
medial reticulospinal tract
lateral vestibulospinal tract
medial (anterior) corticospinal tract
66
which medial motor tracts cross (2)?
tectospinal tract
medial vestibulospinal tract
67
What tracts are included in the Lateral Motor Tracts?
1. lateral corticospinal tract
2. Rubrospinal tract
3. Lateral (medullary) reticulospinal tract
68
where are all the lateral motor tracts located in the spinal cord?
lateral spinal cord white matter
69
what is the general function of all the lateral motor tracts?
function in fine movements of face, and extremities
70
what supplies input to the lateral corticospinal tract?
pre-frontal cortex and motor associative cortex
71
where does the lateral corticospinal tract begin?
soma located in somatomotor cortex (pre-central gyrus) of the frontal lobe = UMN
72
how does the lateral corticospinal tract descend from the frontal lobe?
descends to medulla → corticospinal tracts through internal capsule → crus cerebri → pons → pyramids
73
where does the lateral corticospinal tract cross?
decussation of the pyramids in caudal closed medulla
74
what is the lateral corticospinal tract's destination/end point and how does it get there?
lateral somatomotor neurons in ventral horn (LMN) in brachial plexus and lumbosacral plexus regions of spinal cord
gets there via the lateral spinal column (lateral corticospinal tract)
75
what is the effect of the lateral corticospinal tract?
fine movements of extremities
fractionation of movement
76
what does fractionation of movement mean?
the activation of individual muscles independent of other hand muscles innervated by lateral somatomotor neurons at the same level
77
what supplies input to the rubrospinal tract?
motor cortex
78
where does the rubrospinal tract begin?
soma = red nucleus of mesencephalon
79
where does the rubrospinal tract cross and descend?
crosses at mesencephalon
descends in pons → medulla → spinal cord lateral column
80
what is the destination of the rubrospinal tract?
lateral somatomotor neurons in brachial plexus region of spinal cord
81
what is the effect of the rubrospinal tract?
activates wrist hand extensor muscles
82
what supplies input to the lateral (medullary) reticulospinal tracts?
motor cortex
83
where does the lateral (medullary) reticulospinal tract begin?
reticular nuclei of the medulla
84
where does the lateral (medullary) reticulospinal tract cross and how does it descend?
it doesn't cross
descends in the lateral spinal column
85
what is the destination of the lateral (medullary) reticulospinal tract?
lateral somatomotor neurons in the brachial and lumbosacral plexus of spinal cord
86
what is the effect of the lateral (medullary) reticulospinal tract?
prepare postural (axial) and girdle muscles for limb activity; reaching
87
the corticobulbar tracts is also known as what?
Corticobrainstem Tract
88
what supplies input to the corticobrainstem tract?
associative cortex = premotor cortex
89
where does the corticobrainstem tract begin?
pre-central gyrus of frontal lobe (somatomotor cortex)
90
Describe how the corticobrainstem descends and where it heads
descends to cranial nerve nuclei in pons, medulla, and cervical spinal cord via internal capsule and cerebral peduncles
91
where are the LMN for the corticobrainstem tract?
somatomotor neurons in cranial nerve nuclei
92
where does the corticobrainstem tract cross?
in brainstem pons and medulla
(muscles of upper face = controlled by bilateral cerebral hemispheres CN 7)
(muscles of lower face = controlled by contralateral hemisphere of CN 7)
93
what are the effects of the corticobrainstem tract?
1. CN 5 controls muscles of mastication
2. CN 7 controls muscles of facial expression
3. CN 9, 10 control pharynx and larynx muscles
4. CN 11 controls traps and SCM
5. CN 12 controls tongue muscles
94
what tracts make up the nonspecific upper motor tracts?
1. cerulospinal tract
2. raphespinal tract
95
what activates the nonspecific upper motor tracts and what is their role?
both are activated by the limbic system (emotions) and provide context to affect other descending tracts
96
how does the cerulospinal tract work?
mediates it effects by release of NE from locus ceruleus
97
how does the raphespinal tract work?
mediates its effects by release of serotonin form raphe nucleus
