Motor System Flashcards
1
Q
A
2
Q
2 classes of muscle
A
smooth and striated muscle
3
Q
where is smooth muscle
A
digestive tract, arteries, etc
4
Q
where is striated muscle
A
cardiac and skeletal muscles
5
Q
what type of muscle is the most muscle mass
A
skeletal muscle
6
Q
role of skeletal muscle
A
move bones around joints, move eyes, control facial expressions, enable speech, controls respiration
7
Q
what smaller parts are skeletal muscles made of
A
100’s of muscle fibers
8
Q
how are skeletal muscles innervated
A
axon branch of lower motor neurons connected to muscle fibers
9
Q
tendon
A
structure that connects muscle to bone
10
Q
2 types of motor neurons
A
upper and lower motor neurons
11
Q
upper motor neurons
A
from brain to spinal cord
12
Q
lower motor neurons
A
from spinal cord to muscle
13
Q
lower motor neuron pathway
A
muscle fiber, mixed spinal nerve, ventral root, ventral horn in spinal cord
14
Q
mixed spinal nerve
A
nerve that carries sensory and motor info to spinal cord
15
Q
significance of size of ventral horn
A
larger ventral horn means more lower motor neurons
ex. part of spine dedicated to arm and leg lower motor neurons larger than abdominal lower motor neurons bc more muscle communication needed
16
Q
what segments of spine innervate arm movement
A
segments C3-T1 (cervical 3- thoracic 1)
17
Q
what segments of spine innervate leg muscles
A
segments L1-S3 (lumbar 1- sacral 3)
18
Q
how many segments in the cervical spine
A
C 1-8
19
Q
how many segments in the thoracic spine
A
T 1-12
20
Q
how many segments in the lumbar spine
A
L 1-5
21
Q
how many segments in the sacral spine
A
S 1-5
22
Q
where in the ventral horn are lower motor neurons that innervate flexors (ex. biceps)
A
dorsal
23
Q
where in the ventral horn are lower motor neurons that innervate extensors (ex. triceps)
A
ventral
24
Q
where in the ventral horn are lower motor neurons that innervate axial muscles (closer to center of body)
A
medial
25
where in the ventral horn are lower motor neurons that innervate distal muscles (further from center of body)
lateral
26
2 classes of lower motor neurons
alpha and gamma motor neurons
27
motor unit
alpha motor neurons and all fibers it innervates
28
motor neuron pool
all alpha motor neurons innervating a muscle
29
what do alpha motor neurons innervate few fibers
when more fine control is needed (ex. in fingertips)
30
neuromuscular junction (NMJ)
specialized synapse formed between nerve and skeletal muscles
31
NMJ activation mechansim
alpha motor neuron action potential, acetylcholine release, EPSP, post synaptic action potential
32
what is another name for an EPSP in the NMJ
end plate potential
33
what causes muscle twutch
post synaptic action potential
34
how can muscle twitch be sustained for sustained muscle contraction
*increase firing rate of motor neuron
*recruit more motor units
35
what motor units are recruit first? then which motor units?
smallest motor units recruited first, than largest ones
36
what are the 3 inputs to alpha motor neurons
*upper motor neurons in motor cortex and brainstem (voluntary control)
*dorsal root ganglion cells that innervate muscle spindles (muscle length)
*spinal cord interneurons (spinal motor programs/ reflexes)
37
muscle spindle
stretch receptors that signal the length and changes in length of muscles
38
muscle spindle structure
*specialized muscle fibers in fibrous capsule
*Ia sensory axons are proprioceptors and synapse on motor neurons and interneurons in ventral horn
39
myotatic reflex
stretch reflex; when a muscle is pulled it tends to contract.
40
myotatic/ stretch reflex loop
stimuli, contraction reflex, firing in Ia axon, firing in a motor neurons, trigger muscle contraction
41
reciprocal inhibition
contraction of one set of muscles and relation of antagonist; occurs in myotatic reflexes
42
reciprocal inhibition mechanism
Ia axon synapse on interneurons that inhibit alpha motor neurons innervating antagonist muscles
43
gamma motor neurons
Innervate Intrafusal muscle fibers and ends of fibers (contraction of ends of spindle)
44
intrafusal muscle fibers
muscle fibers in spindles; innervated by gamma motor neurons
45
extrafusal muscle fibers
muscle fibers outside spindles forming muscle bulk; innervating by alpha motor neurons
46
gamma motor neuron purpose
to keep muscle spindles responsive; tension in ends of muscle spindle to keep activation/activity in Ia motor neurons
47
golgi tendon organ
measures muscle tesion
48
muscle tnsion
force of muscle contraction
49
where is golgi tendon organ located
between muscle and tendon; innervated by Ib sensory axons
50
Ib sensory neurons
innervate golgi tendon organ; synapse on interneons in ventral horn
51
how do Ib neruons influence alpha motor neurons
via spinal interneurons; with alpha motor neurons that innervate muscle associated with golgi tendon organ
52
reverse myotatic reflex
a reflex that causes a muscle to relax (reduce contraction) when it's under high tension, preventing potential injury
53
reverse myotatic reflex mechanism
?
54
proprioceptors in muscles
sensitive to muscle length and tension
55
proprioceptors in joints
sensitive to joint angle, direction, and movement velocity
56
proprioceptors in muscles and joins combined
together signal joint position
57
2 pain pathways
dorsal column-medial lemniscal pathway and spinothalamic pathway
58
dorsal column-medial lemniscal pathway
dorsal root axon, dorsal column, dorsal column nuclei, medial lemniscus (cross midline), THALAMUS, CORTEX
59
spinothalamic pathway
dorsal root axon (cross midline), lateral spinothalamic tract, spinal cord, medulla, thalamus, cortex
60
what afferent axons are responsible for pain response
A delta and C axons
61
nociceptor
pain receptor
62
nociceptor mechanism
bending of nociceptor membrane opens ion channel, depolarize, action potential in pain axon
63
pain axon connectivity
synapse with interneurons that excite alpha motor neurons innervating flexors -> reflexively activate muscle
64
flexor reflex
activation of flexor muscle and inhibition of extensor muscles
65
crossed extensor reflex
activation of extensor muscles and inhibition of flexor muscles on opposite side of body
66
neural circuit for walking
alternating activity between interneurons that excite flexor and extensor motor neurons
67
sarcomere
the basic contractile unit of muscle fiber made of thin and thick filaments that slide past each other to contract and lengthen muscle
68
what causes muscle contraction on mechanistic level
Ca 2+ influx
69
sarcomere muscle contraction mechanism
troponin on thin filament block binding of thick filament, Ca2+ binds, thick filament binds and bends (sarcomere slides during muscle contraction)
70
sarcomere thin filament
actin
71
sarcomere thick filament
myosin
72
motor cortex brodmann areas
4 and 6
73
where is primary motor cortex (M1)
area 4
74
where re premotor area (PMA) and supplementary motor area (SMA)
area 6
75
what other brain areas connect with area 6 in the motor cortex? why?
frontal and posterior parietal lobe; send info to motor cortex regarding action planning and cognitive control
76
what pathway do most axons in areas 4 and 6 contribute to
corticospinal tract (cortex -> spine info)
77
what does brief stimulation of M1 result in
twitch in specific muscle (somatotopic map) on contralateral side
78
what does more prolonged electric stimulation (500 ms compared to 50 ms) to M1 result in
more complex movements (ex. a reach rather than just a twitch)
79
proof of rough somatotopic map in motor cortex
certain areas of cortex dedicated to actions involving hands, involving mouth, etc.
80
premotor area (PMA) cells function
respond to instruction to move and continue resoming until movement takes place; signals upcoming movements and contributes to planning movement
81
M1 neuron functions
respond before and during voluntary movements
82
M1 neurons preference vs broad tuned
M1 neurons have prefered directions but are also broadly tuned (bell curve representation)
83
vector notation of neuron preference
vector points in preferred direction and the longer the vector the stronger preference
84
population vector
average of direction vectors for many M1 cells; way of depicting population coding in vector form
85
relationship between population vector and movement direction
strong correlation
86
where is population vector response sent
down descending tract to skeletal muscles
87
dynamical system
future state can be predicted based on current state
88
how can euron activity before movement be represented
state-space graph
89
state-space graph
a mathematical representation of a dynamic system describing how a system evolves over time
90
state space graph: subspace
corresponds to a particular motor movement, neurons move towards certain subspace for desired movement
91
how does neural activity change from pre-target -> over time post target
pre target: variance in activity
post- target: trajectories diverge
over more time post target: trajectories diverge fully into subspace -> ready to execute movement
92
why would a particular action/ localized body part have more cells dedicated to it in the motor cortex
more cells controlling particular action lead to finer control
93
plasticity of motor cortex
representations of movements can change due to either lesions/ recovery or through learning/ training experiences (more neurons from other areas reported to another area /redistributed)
94
2 descending tracts of spinal tract
lateral and ventromedial pathways
95
lateral pathways
corticospinal tract and rubrospinal tract
96
ventromedial pathways
tectospinal tract, vestibulospinal tract, pontine reticulospinal tract, medullary reticulospinal tract
97
lateral pathway function
control fine movements of arms and fingers; voluntary movement
98
inputs to M1 (in area 4)
premotor cortex (area 6), somatosensory cortex (areas 1,2,3)
ventrolateral thalamus
99
outputs of M1
from M1 layer 5 ->
lower motor neurons in spinal cord, subcortical sites
100
corticospinal tract
motor cortex, midbrain, medullary pyramid, crosses into contralateral on pyramidal tract, ventral horn
101
rubrospinal tract
motor cortex, red nuclei in spinal cord, ventral horn
102
major and minor tracts in lateral pathway
major: corticospinal tract
minor: rubrospinal tract
103
ventromedial pathway function
control proximal and axial muscles
104
vestibulospinal tract function and mech
keeps head and eyes stable:
vestibular nucleus (medulla)-> innervates BOTH ventral horns
105
tectospinal tract function and mech
orients head and eyes to stimuli:
superior colliculus (midbrain)-> innervates cross lateral ventral horn
106
pontine reticulospinal tract function and mech
keeps upright posture:
pontine reticular formation (pons) -> spinal cord same side
107
medullary reticulospinal tract function and mech
counters pontine nuclei (not stand up):
medullary reticular formation (medulla) -> spinal cord same side
108
what controls the reticulospinal tracts
cortex
109
basal ganglia's roles in motor processing
cognitive and motor processing: prefrontal, motor and sensory cortex -> basal ganglia -> thalamus -> cortex
110
how do the basal ganglia direct and indirect pathways work together in motor control
direct pathway: facilitates wanted action (disinhibit thalamus)
indirect pathway: inhibit unwanted actions (inhibit thalmus)
111
cerebellum information input and output
input: pons -> cerebellar cortex
output: deep cerebellar nucleus
112
cerebellum/ cortex pathway
cortex, pons, cerebellum, thalamus, cortex
113
inferior olive role in motor processing
sends error signals to cerebellum (it receives along with the effreces copies from the frontal cortex)
114
what information does cerebellum integrate
motor commands, current states, errors
*** automatic motor command OR sensory prediction
115
how are desired actions from frontal cortex transported into cerebellum
mossy fibers
116
how is information about world/ current state from parietal cortex transported into cerebellum
mossy fibers
117
how is information about actions errors from inferior olive transported into cerebellum
climbing fibers
118
purkinje cells
cells in cerebellum that have extensive dendrite branching all in the same plane (flat)
119
3 layers of cerebellum cortex
molecular layer, purkinje cell layer, granule cell layer
