Spinal Cord, Brainstem, Cortex, Control of Motor Function Flashcards
1
Q
What are the groups of neurons in the spinal cord?
A
Sensory (afferent)
Anterior motor neurons
Interneurons
2
Q
What do alpha motor neurons give rise to?
A
Aα fibers
3
Q
What neurons is responsible for most of spinal cord integrative function and is capable of spontaneous activity?
A
The interneuron
4
Q
What neuron is 30x as numerous as anterior motor neurons?
A
Interneurons
5
Q
What neuron is small and highly excitable?
A
Interneurons
6
Q
What neurons receive collateral branches from alpha motor neurons
Are inhibitory cells
Transmit inhibitory signals to surrounding motor neurons?
A
Renshaw cells
7
Q
When renshaw cells transmit inhibitory signals to surrounding motor neurons, what does this result in?
A
Results in lateral inhibition
8
Q
Describe the muscle spindle
A
3-10 mm long
consists of 3-12 intrafusal fibers
Central region has no contractile fibers; functions as a sensory receptor
Detects changes in muscle length
9
Q
What are the intrafusal fibers innervated by?
A
Small gamma motor neurons
10
Q
Where do sensory fibers of the muscle spindle originate from?
A
The central region
11
Q
Stretching of the central region of the intrafusal fiber stimulates what?
A
Sensory fibers
12
Q
What are extrafusal fibers?
A
Skeletal muscle fibers
13
Q
What are extrafusal fibers innervated by?
A
Alpha motor neurons
14
Q
Stimulation of sensory fibers from the central region of intrafusal fibers results from what?
A
Lengthening of entire muscle
Contraction of ends of intrafusal fibers
15
Q
What are the types of muscle spindle sensory fibers?
A
Ia (primary fibers)
II (secondary fibers)
16
Q
Describe Ia sensory fibers
A
Forms annulospiral ending
17 um in diameter
Transmits at 70-120 m/sec
17
Q
Describe II sensory fibers
A
Slower than Ia fibers
8 um
18
Q
Describe dynamic stretch reflex
A
Signals transmitted from primary nerve endings
Elicited by rapid stretch or unstretch
Opposes sudden changes to muscle length
19
Q
Describe static reflex
A
Transmitted by both primary and secondary endings
Causes degree of muscle contraction to remain relatively constant.
20
Q
Dynamic stretch reflex and static reflex together prevents what?
A
Jerkiness of body movements (damping)
21
Q
What are nuclear bag fibers?
A
Intrafusal fibers that have nuclei concentrated in “bag” in center of receptor area
22
Q
What are nuclear chain fibers?
A
Intrafusal fibers that have nuclei aligned in chain throughout receptor area
23
Q
Gamma motor neurons hare equal to about _______ the number of alpha motor neurons
A
half
24
Q
Describe Aγ motor neurons
A
5 um
Supply small intrafusal fibers in middle of muscle spindle
25
Describe gamma-dynamic motor neurons
Excite nuclear bag intrafusal fibers
26
Describe gamma-static motor neurons
Excite nuclear chain intrafusal fibers
27
What areas of the brain controls gamma fibers?
Bulboreticular region of brain stem
Cerebellum
Basal nuclei
Cerebral cortex
28
What is the golgi tendon organ?
Encapsulated sensory receptor through which muscle tendon fibers pass
29
How many muscle fibers attach to each Golgi organ?
10-15
30
What is the golgi organ stimulated by?
Contracting or stretching of muscle
31
What does the golgi tendon organ detect?
Muslce tension
32
What is the circuitry of the golgi tendon organ?
Type Ib afferent (16 um dia) -> inhibitory interneuron -> anterior motor neuron
33
The signals generated here cause more COMPLEX patterns of movement than the more discrete pattern generated by the primary motor cortex
Premotor area
34
What part of the premotor cortex develops a "motor image" of the total muscle movement that is to be preformed?
Anterior
35
What part of the premotor cortex does an image excites each successive pattern of muscle activity required to achieve the image?
Posterior
36
What does the posterior motor cortex send signals to?
Primary motor cortex
| Basal nuclei and thalamus->primary motor cortex
37
Review text for mirror neurons.
Be able to describe suggested functions
*source-wiki
A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another.Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting.
Many studies link mirror neurons to understanding goals and intentions
facilitation of learning
involved in empathy
may provide the neurological basis of human self-awareness
38
How does damage to broca's area affect speech?
Damage to a discrete part of a the brain in the left frontal lobe (Broca's area) of the language-dominant hemisphere has been shown to significantly affect use of spontaneous speech and motor speech control.
39
How is Broca's area related to associated respiratory and voluntary eye movement fields?
Frontal eye field - anterior to the premotor cortex and superior to Broca's area
Look in text
40
Cells in motor cortex are organized into _____ columns.
Vertical
41
Each column of the motor cortex stimulates what?
a group of synergistic muscles or even a single muscle
42
Each column of the motor cortex has how many distinct layers?
6
43
Where are pyramidal cells in the columns of the motor cortex?
The 5th layer
44
Where do input signals enter in the columns of the motor cortex?
2-4
45
What layer are neurons of the motor cortex that communicate with other regions of the cerebral cortex?
6th layer
46
Typical descending pathway consists of a series of what two motor neurons?
What is not taken into consideration?
Upper motor neurons (UMNs)
Lower motor neurons (LMNs)
Does not take into consideration the assocation neurons between UMNs and LMNs
47
Where are upper motor neurons?
Entirely within the CNS
48
Where do upper motor neurons originate in?
Cerebral cortex
Cerebellum
Brainstem
49
What do upper motor neurons form?
Descending tracts
50
Where do lower motor neurons begin?
In the CNS
From anterior horns of spinal cord
From brainstem cranial nerve nuclei
51
What are lower motor neurons made up of?
Alpha motor neurons (A-α)
52
What do lower motor neurons make up?
Spinal and cranial nerves
53
The upper motor neurons of the pyramidal system originate where?
In the motor cortices
54
75-85% of the upper motor neurons decussate in pyramids and form what?
Lateral corticospinal tracts
55
15-25% of upper motor neurons decussate near what?
Near synapse with lower motor neurons and form anterior corticospinal tracts
56
Upper motor neurons of the pyramidal system synapse with what?
Association neurons in spinal cord central gray
57
What are the components of the pyramidal system?
Corticospinal tract
| Corticobulbar tract
58
The lateral corticospinal tract is made up of what?
Corticospinal fibers that have crossed in medulla
59
The lateral corticospinal tract supply what?
all levels of spinal cord
60
The anterior corticospinal tract is made up of what?
Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs
61
The anterior corticospinal tract supply what?
Neck and upper limbs
62
What is the corticospinal tract also referred to as?
The pyramidal tract
63
What is the origin of the corticospinal tract?
Primary motor cortex
Premotor cortex
Somatosensory area
64
What is the pathway of the corticospinal tract?
Site of origin->internal capsule->medullary pyramids (forms these structures) cross in lower medulla (most fibers)->lateral columns of spinal cord (lateral corticospinal tract
65
In the corticospinal tract pathway, + the fibers that do not cross continue down how?
Ipsilaterally in ventral corticospinal tract
66
Where are giant pyramidal (Betz) cells located?
In motor cortex
67
Describe giant pyramidal (Betz) cells
```
Large cell (60 um)
Large fibers (16 um)
Transmit at 70m/sec
Make up about 3% (34,000) of fibers in the tract
Send collaterals back to cortex
```
68
Other fibers from cortex of the corticospinal tract pass to:
Into caudate nucleus and putamen
Pass to red nucleus
Pass to reticular substance and vestibular nuclei
Large numbers of fibers pass to pontine nuclei
69
What are the corticospinal tract functions?
Adds speed and agility to conscious movements: especially movements of hands
Provides a high degree of motor control: i.e movement of individual fingers
70
What are the symptoms of corticospinal tract lesions?
Reduced muscle tine
Clumsiness
Weakness
Not complete paralysis
71
What does complete paralysis results from?
If both pyramidal and extrapyramidal systems are involved (as is often the case)
72
What does the corticobulbar tract innervate?
The head
73
Where do most fibers of the corticobulbar tract terminate?
In reticular formation near cranial nerve nuclei
74
The association neurons of the corticobulbar tract leave ______ _______ and synapse in cranial nerve nuclei
Reticular formation
75
What do the association neurons of the corticobulbar tract synapse with?
Lower motor neurons
76
Fibers from primary motor cortex (corticorubral pathway) and branches from corticospinal tract synapse in what?
magnocellular portion of red nucleus
77
Large neurons from magnocellular region of red nucleus gives rise to what?
Rubrospinal tract which decussates in lower brain stem
78
What has a somatotopic respresentation of all the muscles of the body?
The magnocellular region
79
What system includes pathways that contributes to motor control but that are not part of the corticospinal system?
Extrapyramidal system
80
What does the extrapyramidal system include?
Descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts
81
What tracts are included in the extrapyramidal system?
Rubrospinal tracts
Vestibulospinal tracts
Reticulospinal tracts
82
Where does the rubrospinal tract begin?
In the red nucleus
83
Where does the rubrospinal tract decussate?
In the midbrain
84
The rubrospinal tract descends in _______
Lateral funiculus (column)
85
The rubrospinal tract function is closely related to what?
cerebellar function
86
Lesions of the rubrospinal tract leads to:
```
Impairment of distal arm and hand movement
Intention tremors (similar to cerebellar lesions)
```
87
The vestibulospinal tract originates in what?
Vestibular nuclei
88
The vestibulospinal tract receives major input from what?
vestibular nerve (CNVIII)
89
The vestibulospinal tract descends in what?
Anterior funiculus (column)
90
The vestibulospinal tract synapses with what? What is it primarily involved in?
LMNs to extensor muscles
| Primarily involved in maintenance of upright posture
91
The reticulospinal tract originates in ______ regions of reticular formation
Various
92
The reticulospinal tract descends where?
In anterior portion of lateral funiculus
93
What is the function of the reticulospinal tract?
Thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs
94
The pontine reticular nuclei excite what?
Antigravity (axial) muscles (support body against gravity)
95
The pontine reticular nuclei fibers make up what?
Pontine reticulospinal tract (anterior column)
96
The medullary reticular nuceli relaxes what?
Antigravity muscles
97
The medullary reticular nuclei fibers make up what?
The medullary reticulospinal tract (lateral column)
98
What are the vestibular apparatus components?
Utricle
Saccule
Semicircular canals
99
The macula of the utricle is located where?
On horizontal plane
100
What does the macula of the utricle play a role in?
Determining orientation of head when head is upright
101
What is the macula of the saccule located in?
Vertical plane
102
What does the macula of the saccule play a role in?
Signals head orientation when person is lying down
103
What is each macula covered by?
Gelatinous layer
104
THe macula contains large numbers of embedded small _____ ______ _______
Calcium carbonate cyrstals (statoconia)
105
The macula contains thousands of hair cells which do what?
project cilia into the gelatinous layer
106
The weight of the statoconia bends what?
Cilia in the direction of gravitation pull
107
In the macula, each hair cell has how many small cilia?
50-70 (stereocilia)
108
The macula hair cell has ___ large cilium(s)
1
Off set to one side
(kinocilium)
109
Tips of stereocilia are connected to what?
Together and to kinocilium
110
Bending of cilia opens what?
Hundreds of cation channels causing receptor membrane depolarization
111
Bending of cilia in opposite direction closes what?
Channels and hyperpolarizes receptor membrane
112
Hair cells are oriented such that bending the head in different directions causes what?
Different groups of hair cells to depolarize
113
When head is bent forward 30* lateral ducts are what?
horizontal
114
When the head is bent foward 30*, anterior ducts are:
In vertical planes projecting forward and 45* outward
115
When head is bent forward 30*, posterior ducts are:
In vertical planes projecting backward and 45* outward
116
The ampulla has an enlargement where?
At one end of each duct
117
What is the ampulla filled with?
(along the duct) with endolymph
118
Define crista ampullaris
Small crest within each ampulla
119
Define cupul
Loose mass of gelatinous tissue on top of crista
120
When head begins to rotate in any direction, describe what happens to the fluid in the semicircular canals
Inertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head
121
In semicircular canals, fluid flows from the duct and through what?
The ampulla and causes the cupula to bend to one side
122
Hundreds of hair cells within each cupula detect what?
Bending and send signals via the vestibular nerve
