Lecture 9 Flashcards
(105 cards)
1
Q
List the groups of neurons in the spinal cord.
A
Sensory (afferent), anterior motor (efferent), interneurons, Renshaw cells
2
Q
What is a motor unit composed of?
A
Single motor neuron and the muscle fibers it innervates
3
Q
What is a motor neuron pool?
A
Group of motor neurons that innervate fibers within the same muscle
4
Q
What do efferents give rise to?
A
A alpha fibers
5
Q
T or F: Interneurons are small and highly excitable.
A
True.
6
Q
Describe interneurons.
A
Capable of spontaneous activity, responsible for most of spinal cord integrative function
7
Q
How numerous are interneurons?
A
30x as numerous as anterior motor neurons
8
Q
What are Renshaw cells?
A
Inhibitory cells in anterior horns of spinal cord
9
Q
Where do Renshaw cells receive collateral branches from?
A
Alpha motor neurons
10
Q
What do Renshaw cells transmit inhibitor signals to? What does this result in?
A
Surrounding motor neurons which results in lateral inhibition and enhances fluidity of limb movement; Same motor neurons which results in recurrent inhibition
11
Q
Where is the cell body of efferents?
A
In motor cortex, brainstem, or spinal cord
12
Q
Where do the axons of efferents project to?
A
SC or effector organ/muscle
13
Q
Where and to what do upper motor neurons synapse?
A
Synapse onto interneurons or lower motor neuron in SC
14
Q
Regarding efferents, where does the lower motor neuron go?
A
From spinal cord to effector
15
Q
What is the neurotransmitter of UMN to LMN?
A
Glutamate
16
Q
Where are lower motor neurons found?
A
Anterior gray portion of SC or cranial nerve nuclei of brainstem
17
Q
Where do lower motor neurons terminate? What is the neurotransmitter?
A
Terminate at effector; Acteylcholine
18
Q
Regarding a motor unit, what does recruitment refer to?
A
Increase in tension of muscle contractions by activation of additional motor units
19
Q
How many muscle fibers do small vs. large motor units innervate?
A
Small = a few Large = many
20
Q
Which motor neurons fire last and generate the largest force?
A
Large motor neurons
21
Q
Which motor neurons have the lowest threshold?
A
Small motor neurons
22
Q
T or F: Small motor neurons are capable of spontaneous activity.
A
False. Interneurons are capable of spontaneous activity.
23
Q
Most interneurons are inhibitory and use ___ as the neurotransmitter, but some are excitatory and use ___ as the neurotransmitter.
A
GABA; Glutamate
24
Q
Which neurotransmitter does Renshaw cells use?
A
Glycine
25
T or F: Renshaw cells may be supplied by more than 1 alpha motor neuron and may synapse on multiple motor neurons.
True.
26
When Renshaw cells transmit inhibitory signals to the same motor neuron, which type of feedback is being utilized?
Negative
27
What do Ia inhibitory interneurons do?
Inhibit antagonistic muscle, signal from muscle spindle, avoid spasticity
28
What do Ib inhibitory interneurons do?
Autogenic inhibition reflex, responsible for smooth contraction and protects muscle from tears
29
The Golgi tendon is activated with ___.
Stretch
30
What connects with Ib interneurons to inhibit the same muscle?
Golgi tendon
31
What are excitatory interneurons involved in?
Spinal reflex to remove extremity from damaging stimulus
32
What sends a signal to excitatory interneurons that send ipsilateral and contralateral signals?
Sensory group III afferents
33
List the various muscle sensors.
Muscle spindle, Golgi tendon, Pacinian corpuscles, free nerve endings
34
What does the muscle spindle (group Ia and II afferents) detect?
Detects both dynamic and static changes in muscle length
35
How is the muscle spindle (group Ia and II afferents) arranged?
Arranged in parallel with extrafusal fibers
36
How is the Golgi tendon organ (group Ib afferents) arranged?
In series with extrafusal fibers
37
What does the Golgi tendon organ (group Ib afferents) detect?
Muscle tension
38
What do Pacinian corpuscles (group II afferents) detect?
Vibration
39
What do free nerve endings (groups III and IV afferents) detect?
Noxious stimuli
40
T or F: Group IV nerve fibers are myelinated.
False. Groups I, II, and III are myelinated, group IV is not.
41
Quickly refresh what A fibers are. What are the different types?
Somatic, myelinated; Alpha (largest), beta, gamma, delta (smallest)
42
Quickly refresh what B fibers are.
Lightly myelinated, preganglionic fibers of ANS
43
Quickly refresh what C fibers are.
Unmyelinated, found in somatic and ANS, type IV fibers
44
What are the 3 types of fibers that sensory fibers can be?
A alpha or A beta, A delta, C
45
What is the conduction rate of A alpha or A beta fibers?
30-120 m/sec
46
What is the conduction rate of A delta fibers?
4-30 m/sec
47
What is the conduction rate of C fibers?
Less than 2.5 m/sec
48
T or F: Nociceptors and thermoreceptors are related to C fibers or A delta fibers.
True.
49
How long is a muscle spindle?
3-10 mm
50
What does a muscle spindle consist of?
3-12 intrafusal fibers (innervated by small gamma motor neurons, encapsulated within a sheath to form muscle spindle, run parallel to extrafusal fibers)
51
With finer movements, the number of muscle spindles required ___.
Increases
52
What are muscle spindles innervated by?
Small gamma motor neurons
53
What does the central region of a muscle spindle function as?
Sensory receptor (no contractile fibers)
54
Where do sensory fibers originate from in a muscle spindle?
Central region
55
In a muscle spindle, what stimulates sensory fibers?
Stretching of central region of intrafusal fibers
56
What are the 2 types of intrafusal fibers?
Nuclear bag and nuclear chain
57
What do nuclear bag fibers detect?
Rate of change in muscle length
58
What are nuclear bag fibers innervated by?
Group Ia afferents and dynamic gamma efferents
59
What is the structure of nuclear bag fibers?
Multiple nuclei located in a central bag-like configuration
60
What are nuclear chain fibers innervated by?
Group II afferents and static gamma efferents
61
What do nuclear chain fibers detect?
Static change in muscle length
62
T or F: Nuclear bag fibers are more numerous than nuclear chain fibers.
False. Nuclear chain fibers are more numerous than nuclear bag fibers.
63
How are nuclear chain fibers arranged?
In a single row
64
Which neurotransmitter do alpha and gamma motor neurons use?
Acetylcholine
65
What do alpha motor neurons innervate?
Effector (skeletal muscle)
66
What do gamma motor neurons innervate?
Intrafusal muscle fibers
67
What is the purpose of gamma motor neurons?
Keep muscle spindles taut
68
What does stimulation of sensory fibers form the central region of an intrafusal fiber result from?
Lengthening of an entire muscle or contraction of the ends of the intrafusal fiber
69
The number of gamma motor neurons is equal to about ___ the number of alpha motor neurons.
Half
70
What are the 3 types of gamma motor neurons?
A, gamma-dynamic, and gamma-static
71
Describe A gamma motor neurons.
5 um diameter, supply small intrafusal fibers in the middle of the muscle spindle
72
What do gamma-dynamic motor neurons excite?
Nuclear bag intrafusal fibers
73
What do gamma-static motor neurons excite?
Nuclear chain intrafusal fibers
74
List the brain areas controlling gamma fibers.
Bulboreticular region of brain stem, cerebellum, basal nuclei, cerebral cortex
75
Describe the dynamic stretch reflex.
Signals transmitted from primary nerve endings, elicited by rapid stretch or unstretch, opposes sudden changes to muscle length
76
Describe the static reflex.
Transmitted by both primary and secondary endings, causes degree of muscle contraction to remain relatively constant
77
Outline the stretch reflex.
Stretching of muscle stretches group Ia afferent fibers → Ia fibers synapse directly on alpha motor neurons of same muscle → muscle contracts and decreases tension on muscle spindle → synergistic muscles are activated and antagonistic muscles are inhibited
78
T or F: The Golgi tendon reflex is opposite the stretch reflex.
True.
79
Describe the structure, function, and circuitry of the Golgi tendon organ.
```
Structure = arranged in series with extrafusal fibers, 10-15 muscle fibers attached to each Golgi organ, no motor component, encapsulated
Function = detects muscle tension (stimulated by contracting or stretching of muscle
Circuitry = Type Ib afferent (16 um diameter) → (+) → inhibitory interneuron → (-) → anterior motor neuron
```
80
What is the function of the premotor and supplementary motor areas?
Generate plan for movement (transfer plan to primary motor cortex)
81
Describe the signals generated by the premotor and supplementary motor areas as compared to the primary motor cortex.
More complex patterns of movement than the more discrete pattern generated by the primary motor cortex
82
What does the anterior part of the premotor cortex develop?
Motor image of total muscle movement that is to be performed
83
Which motor cortex programs complex motor sequences and is responsible for mental rehearsal for a movement?
Supplementary motor cortex
84
Describe how the image in the posterior motor cortex excites each successive pattern of muscle activity required to achieve an image.
Posterior motor cortex → primary motor cortex → basal nuclei and thalamus → primary motor cortex
85
Describe the cellular organization of a motor cortex.
Organized into vertical columns, where each column stimulates a group of synergistic muscles or even a single muscle
86
How many layers does each motor cortex column have?
6
87
Which layers are pyramidal cells in the motor cortex column?
5
88
Where do input signals enter in the motor cortex?
2-4
89
Neurons arising in which layer communicate with other regions of the cerebral cortex?
6
90
A typical descending pathway consists of a series of which 2 motor neurons?
Upper and lower
91
T or F: Upper motor neurons being in the CNS but eventually extend into the PNS.
False. Upper motor neurons are entirely within the CNS.
92
Where do upper motor neurons originate?
Cerebral cortex, cerebellum, brainstem
93
What do upper motor neurons form?
Descending tracts
94
Where do lower motor neurons begin?
In CNS from anterior horns of SC or brainstem cranial nerve nuclei
95
What are lower motor neurons made up of?
Alpha motor neurons
96
What do lower motor neurons make up?
Spinal and cranial nerves
97
How are upper motor neurons classified?
According to where they synapse in the ventral horn
98
What does the medial activation system innervate?
Postural and girdle muscles
99
What is lateral activation system associated with?
Distally located muscles used for fine movements
100
What does the nonspecific activating system facilitate?
Local reflex arcs
101
What is the difference between the dynamic and static stretch reflexes?
Dynamic stretch reflex is over within a fraction of a second after the muscle has been stretched (or unstretched) to its new length, but then weaker static stretch reflex continues for a prolonged period
102
Where does the output from the posterior motor cortex go?
Areas of frontal motor cortex
103
How does damage to Broca’s area affect speech?
Makes it impossible for the person to speak whole words rather than uncoordinated utterances
104
How is Broca’s area related to associated respiratory and voluntary eye movement fields?
Cortical area closely associated to Broca’s area causes appropriate respiratory function, so respiratory activation of the vocal cords can occur simultaneously with the movements of the mouth and tongue during speech
Premotor area directly above Broca’s area is a locus for controlling voluntary eye movements
105
Describe mirror neurons.
Become active when a person performs a specific motor task or when he or she observes the same task performed by others; Neurophysiologists believe that mirror neurons may be important for understanding the actions of other people and for learning new skills by imitation
