Lecture 11- Descending Tracts Flashcards
1
Q
OVERVIEW
A
OVERVIEW
2
Q
Motor system comprises the _________ portion of a neural loop
A
efferent
3
Q
Somatomotor signals originate in the ________ cortex of the frontal lobe.
A
somatomotor (precentral gyrus)
4
Q
What 5 CNS structures modify motor signals?
A
- Basal nucleus/thalamus
- Cerebellum
- Reticular formation
- Limbic system
- Red nucleus/substantia nigra
5
Q
Motor signals move in _______ tracts.
A
descending
6
Q
Where are the somatomotor neurons located?
A
- spinal cord ventral horn gray matter
- brainstem CN nuclei: CN 3, 4, 6; 5, 7; 9, 10; 11, 12
7
Q
The motor pathway is a __ neuron pathway
A
2
8
Q
The ______ motor neurons connect the precentral gyrus to somatomotor neurons and form descending tracts
A
upper
9
Q
The _______ motor neurons are in CN nuclei of brainstem or spinal cord/ventral horn and are carried in peripheral nerves.
A
lower
10
Q
What are the 2 lower motor neuron types?
A
- alpha motor neurons
- gamma motor neurons
11
Q
Alpha motor neurons are ________ diameter myelinated ____ neurons that synapse with _________ muscle fibers to contract whole muscle.
A
- large
- fast speed
- extrafusal
12
Q
Gamma motor neurons are ________ diameter myelinated _______ neurons that synapse with __________ (muscle spindle) muscle fibers that keep the muscle spindle sensitive during whole muscle contraction.
A
- medium
- medium speed
- intrafusal
13
Q
Lower motor neurons release NT __________ which binds ________ receptors on muscle cell membrane to always depolarize the muscle
A
- acetylcholine
- nicotinic
14
Q
Small diameter (slow conducting) ______ motor neurons innervate _____ twitch (red) muscle fibers
A
- alpha
- slow
15
Q
Larger diameter (fast conducting) _______ motor neurons innervate ______ twitch (white) muscle fibers
A
- alpha
- fast
16
Q
What does Henneman’s size principle state?
A
Typically slow twitch muscle fibers (small diameter) are activated before fast twitch muscle fibers (large diameter) allowing the 2 types of muscle fibers to contract together
17
Q
Muscle contractions can be initiated in what 2 ways?
A
- somatomotor cortex and control centers in brain = VOLUNTARY
- spinal cord/brain stem = REFLEX
18
Q
Descending tracts have specific somatotopic tracts (homonculus) on the precentral gyrus for what 3 things?
A
- postural gross movement tracts
- fine movement
- limb flexion
19
Q
Collateral connections between tracts (motor to motor or motor to sensory) help coordinate movement = _________.
A
context
20
Q
What are the 4 functions of collateral connections?
A
- reciprocal inhibition
- muscle synergism
- proprioception
- stepping pattern generators
21
Q
What is reciprocal inhibition?
A
antagonist inhibition during agonist contraction
22
Q
What is muscle synergism?
A
coordinated muscle action
23
Q
What is proprioception?
A
information of body position in time and space is used to coordinate muscle contraction
24
Q
What is stepping pattern generators?
A
alternate flexion/extension of the lower limbs
25
SKELETAL MUSCLE CONTRACTION REVIEW
SKELETAL MUSCLE CONTRACTION REVIEW
26
What is a motor unit?
a SINGLE somatomotor neuron (axon) and all the muscle fibers it activates
27
What is a motor neuron pool?
group of motor neuron cell bodies (motor units) in ventral horn that innervate a single muscle.
28
How are motor neuron pools arranged somatotopically in the ventral horn?
- flexors dorsal
- extensors ventral
- axial muscles medially
- appendicular muscles laterally
29
REFLEXES
REFLEXES
30
What is a reflex? Can it occur without brain input?
- predictable response to a given stimulus
| - yes, occurs without brain input
31
Reflexes are _______ dependent, meaning the state of the NS will affect the properties of the reflex ie. signals from the brain influence spinal reflexes.
context
32
If you are relaxed the reflex response may be ____ intense than if you are anxious.
less
33
What is the reflex pathway?
- sensor/receptor
- sensory neuron
- INTERNEURON connection in brainstem or spinal cord
- motor neuron
- skeletal muscle
34
Most skeletal muscle movement is NOT reflex movement, it is _________.
voluntary
35
Difference between tonic and phasic stretch reflexes?
- phasic- brief response to stimulus
| - tonic- responds to stimulus for the duration of stimulus
36
What is the phasic pathway?
- quick stretch stimulus
- muscle spindle
- Ia sensory neuron (annulospiral bag and chain)
- DRG
- spinal cord dorsal horn (also dorsal column to postcentral gyrus)
- synapses w/ alpha somatomotor neuron
- skeletal muscle
37
What is a monosynaptic reflex?
Where the sensory neuron synapses directly with motor neuron (no interneuron)
38
Phasic pathways are _______ and involve a _______ spinal cord level.
- uncrossed
| - single
39
Constant tonic reflexes result from lesion of the brain or spinal cord = ___________ lesion
UMN
40
tonic sensory neurons type II sensory neuron (_________/_______) signal when the muscle spindle is stretched but these signals are normally prevented from activating somatomotor neurons by upper motor neuron inhibition; UMN lesion removes the inhibition and allows the constant afferent signal to produce a constant efferent signal = ________________
- flowerspray/chain
| - tonic reflex contraction
41
Cutaneous reflexes are more complex and involve _________ (minimum __ neuron pathway)
- interneurons
| - 3
42
What is the golgi tendon reflex pathway?
- increased tendon stretch
- golgi tendon organ
- Type Ib afferent
- spinal cord INHIBITORY interneuron
- inhibit alpha motor neuron to homolgous muscle
- muscle w/ stretched tendon relaxes
43
Cutaneous reflexes involve _________ spinal cord segments affecting multiple effectors (more than 1 muscle) on the same side.
-multiple
44
What is the flexor withdrawal reflex pathway?
- pain stimulus
- sensory neuron (Type III or IV)
- ascends/descends for several segments via Lissauer's tract
- activates multiple levels of ventral horn alpha motor neurons
- multiple flexor muscles
- withdrawal from pain stimulus
45
Cutaneous reflexes crossover in the _________ = _______________.
- spinal cord
| - crossed flexor withdrawal reflex
46
DESCENDING TRACT
DESCENDING TRACT
47
Descending tracts are __ neuron pathways
2
48
The Medial Motor Tracts are locates in the medial spinal cord _______ matter and function in ______ muscle posture; girdle muscles/stabilizers
- white
| - axial
49
What are the 5 medial motor tracts?
- Tectospinal Tract
- Medial Reticulospinal Tract
- Medial Vestibulospinal Tract
- Lateral Vestibulospinal Tract
- Medial (Anterior) Corticospinal Tract
50
The tectospinal tract has sensory input from ______, auditory, or ___________ (pain, touch)
- visual
| - somatosensory
51
The tectospinal tract starts and has its soma located in the _______________ = tectum of midbrain (superior and inferior colliculi) in the mesencephalon.
-corpora quadrigeminae
52
The tectospinal tract crosses at the ________ and travels in the _______ column of the spinal cord white matter
- midbrain (mesencephalon)
| - anterior
53
The tectospinal tract ventral horn connection is _____ motor neurons of the ventral horn in the ______ region to control ______ muscles.
- medial
- cervical
- axial
54
What is the effect of the tectospinal tract?
head turning
55
The medial reticulospinal tract has sensory input from the ________ system which monitors and filters sensory input through the brain stem.
-reticular
56
The medial reticulospinal tract starts and has its soma in the _______________ of the metencephalon.
pontine reticular formation
57
The medial reticulospinal tract travels in the _________ column.
-anterior
58
Where does the medial reticulospinal tract cross?
It doesn't
59
The medial reticulospinal tract has medial somatomotor neurons along the entire ___________.
spinal cord
60
What is the effect of the medial reticulospinal tract?
prepare postural (axial) and girdle muscles for limb activity; reaching
61
The medial vestibulospinal tract has sensory input from the vestibular apparatus for ______ and _______ equilibrium.
static and dynamic (linear and angular)
62
The medial vestibulospinal tract starts and has its soma in the _____________ nuclei which is a elongated nucleus in the ______ and ____________.
- medial vestibular
| - pons and myelencephalon
63
Where does the medial vestibulospinal tract cross?
myelencephalon (medulla) (bilateral)
64
The medial vestibulospinal has medial somatomotor neurons along the _____ and _______ spinal cord
cervical and thoarcic
65
What is the effect of the medial vestibulospinal tract?
-BALANCE in response to head movement (coordinates with tectospinal tract)
66
The lateral vestibulospinal tract has sensory input from the vestibular apparatus for _________.
center of gravity
67
The lateral vestibulospinal tract starts and has its soma in the ___________ nuclei located in the ___________.
- lateral vestibular
| - pons
68
The lateral vestibulospinal tract travels in the ________ column.
anterior
69
Where does the lateral vestibulospinal tract cross?
It doesn't
70
The lateral vestibulospinal tract has medial somatomotor neurons along the entire ___________.
spinal cord
71
What are the effects of the lateral vestibulospinal tract?
- upright posture/balance
| - stimulates axial extensors, and inhibits axial flexors when a person is standing upright
72
The medial (anterior) corticospinal tract has diverse associative input from the ______ and __________ cortex.
premotor and parietal
73
The medial (anterior) corticospinal tract starts and has its soma in the _________ cortex
somatomotor cortex
74
How does the medial corticospinal tract descend from the somatomotor cortex (order)?
- internal capsule
- crus cerebri
- pons
- pyramids
- medial corticospinal tract in anterior column
75
Where does the medial (anterior) corticospinal tract cross?
It doesn't
76
The medial (anterior) corticospinal tract has medial somatomotor neurons in the _______ and ________ spinal cord.
cervical and thoracic
77
What are the effects of the medial (anterior) corticospinal tract?
balance to prepare postural muscles for voluntary movements
78
The Lateral Motor Tracts are located in the lateral spinal cord _______ matter and function in fine movements of _____ and __________
- white
| - face and extremities
79
What are the 3 Lateral Motor Tracts?
- lateral corticospinal tract
- rubrospinal tract
- lateral (medullary) reticulospinal tract
80
The lateral corticospinal tract has input from the ______ and _______ cortex
prefrontal and motor associative cortex
81
The lateral corticospinal tract starts and has its soma in the _________ cortex = UMN
somatomotor
82
How does the lateral corticospinal tract descend from the somatomotor cortex (order)?
- internal capsule
- crus cerebri
- pons
- pyramids
83
Where does the lateral corticospinal tract cross?
decussation of pyramids
84
The lateral corticospinal tract is located in the _______ ventral horn and has somatomotor neuron in ventral horn = LMN in ________ and __________ plexus regions of spinal cord
- lateral
| - brachial and lumbosacral
85
What are the effects of the lateral corticospinal tract?
- fine movements of extremities
| - fractionation of movement
86
What is fractionation of movement?
activate individual muscles independent of other hand muscles innervated by lateral somatomotor neurons at the same level.
87
The rubrospinal tract has input from the ______ cortex
motor
88
The rubrospinal tract starts and has its soma in the ____________ of the mesencephalon.
red nucleus
89
Where does the rubrospinal tract cross?
mesencephalon
90
The rubrospinal tract descends from the pons to the medulla to the spinal cord ________ column.
lateral
91
The rubrospinal tract has lateral somatomotor neurons in _________ plexus region of spinal cord
brachial
92
What are the effects of the rubrospinal tract?
activate wrist and hand extensor muscles
93
The lateral (medullary) reticulospinal tract recives input from the _____ cortex.
motor
94
The lateral (medullary) reticulospinal tract starts and has its soma in the ______________ of the medulla.
reticular nuclei
95
The lateral (medullary) reticulospinal tract descends the spinal cord in the _________ column.
medial (?)
96
Where does the lateral (medullary) reticulospinal tract cross?
It doesn't
97
The lateral (medullary) reticulospinal tract has lateral somatomotor neurons in ______ and __________ plexus of spinal cord.
brachial and lumbosacral
98
What are the effects of the lateral (medullary) reticulospinal tract?
prepare postural (axial) and girdle muscles for limb activity; reaching
99
Corticobulbar tracts receive input from the ________ cortex
premotor
100
Corticobulbar tracts descend to ___________ nuclei in pons, medulla, and cervical spinal cord
cranial nerve
101
Muscles of the upper face are controlled __________ by CN7
bilaterally
102
Muscles of the lower face are controlled by the ___________ hemisphere
contralateral
103
Corticobulbar tracts involve what cranial nerves and function?
```
CN5= muscles of mastication
CN7= muscles of facial expression
CN9,10= pharynx and larynx
CN11= neck muscles
CN12= tongue muscles
```
104
What are the 2 nonspecific upper motor tracts that are activated by the limbic system and provide context to affect other descending tracts?
- ceruleospinal tract
| - raphespinal tract
105
The ceruleospinal tract mediates its effects by releasing ________ from the ___________.
- NEpi
| - locus ceruleus
106
The raphespinal tract mediates its effects by release of ________ from __________
- serotonin
| - raphe nuc.
