Sensorimotor System Flashcards
1
Q
Motor control
A
involves a dynamically changing mix of conscious and unconscious regulation of muscle force, informed by continuous and complex sensory feedback, operating in a framework sculpted by evolutionary pressures.
2
Q
Types of motor control
A
Voluntary
Goal-directed
Habit
Involuntary
3
Q
Voluntary motor control examples
A
Walking
Running
Talking
4
Q
Goal-directed motor control
A
Conscious
Explicit
Controlled
5
Q
Habit motor control
A
Unconscious
Implicit
Automatic
6
Q
Examples of involuntary motor control
A
Eye movements
Facial expressions
Jaw
Tongue
Postural muscles
Hand and fingers
Diaphragm
Cardiac
Intercostals
Digestive tract
7
Q
Lower motor neurones
A
Cell body in brainstem or spinal cord and projects to the muscle
8
Q
Upper motor neurons
A
Originate in higher centres and project down to meet the lower motor neurones
9
Q
Smallest muscle
A
Stapedius- found in the inner ear
10
Q
Largest muscle
A
Gluteus maximus - found in the hip/buttock
11
Q
Strongest muscle
A
Masseter- jaw
12
Q
3 types of muscle
A
Cardiac
Smooth
Skeletal
13
Q
Antagonistic arrangement
A
Combined co-ordinated action
14
Q
How do we achieve a range of movements and forces
A
Antagonistic arrangement
Recruitment of muscle fibres
15
Q
Muscle size and strength is dependent on
A
Cross-sectional area of individual fibres and different proportions of the different types of fibres
16
Q
Number of muscle fibres
A
Varies across individuals
Changes little with either time or training
Genetically determined
17
Q
What attaches muscle to bone
A
Tendon
18
Q
Muscle fasciculus
A
Several muscle fibres
19
Q
Rigor mortis
A
The release of acetylcholine causes a cascade of events resulting in the release of packets of calcium from inside the muscle cell (fibre)
This causes the myosin head to change shape, enabling it to bind with the actin filament
ATP (provides energy for cells) is required to break the bond between the myosin head and the actin filament
ATP is produced by oxidative metabolism, which stops upon death
So the muscle become contracted and remain that way until enzymes begin to disrupt the actin/myosin
20
Q
Motor unit
A
Single alpha motor neurone and all the extrafusal skeletal muscle fibres it innervates
21
Q
Fewer fibres innervated by a motor neurone means
A
Greater movement resolution eg finger tips and tongue
22
Q
Muscle fibres innervated by each motor unit
A
same type of fibre and often distributed through the muscle to provide evenly distributed force (and may help reduce effect of damage)
More motor units fire – more fibres contract – more power
23
Q
Average number of muscle fibres innervated by single motor neuron (a motor unit) varies according to two functional requirements for that muscle:
A
Level of control
Strength
24
Q
Size principle
A
Units are recruited in order of size (smallest first)
Fine control typically required at lower forces
25
Lower alpha motor neurons
Originating in the grey matter of the spinal cord, or in the brainstem, an alpha motor neuron and the muscle fibres it connects to represent the ‘unit of control’ of muscle force.
26
Motor pool
All the lower motor neurones that innervate single muscle
Contains both alpha and gamma motor neurones
Often arranged in a rod like shape within the ventral horn of the spinal cord
27
Cell bodies in the ventral horn are activated by
Sensory information from muscle
Descending information from brain
28
Muscles can be contracted or relaxed to provide movement, but a good control system (the CNS) needs to know two things:
how much tension is on the muscle;
what is the length (stretch) of the muscle
29
What proprioceptor senses stretch
Muscle spindles
30
Which proprioceptors sense tension
Golgi tendon organs
31
Golgi tendon organs
Within the tendon
Sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle
32
Under conditions of extreme tension
Golgi tendon organs act to inhibit muscle fibres to prevent damage
33
Muscle spindles
Sense the length of muscles —>amount of stretch
Embedded within most muscles
Composed of intrafusal fibers
Detect stretch regardless of the current muscle length
34
Most simple reflex
Monosynaptic- eg patellar tendon reflex
35
system to detect stretch regardless the current muscle length
If intrafusal muscle fibre is controlled by same motor neurons as extrafusals, when muscle is slack (or taught), the system won’t be sensitive to slight changes
So, intrafusal fibres are innervated separately, by gamma motor neurons
They keep the intrafusal fibres set at a length that optimises muscle stretch detection
36
Muscle spindle feedback
Sensory fibres are coiled around the intrafusal fibers
Intrafusal fibers are innervated separately, by gamma () motor neurons
They keep the intrafusal fibers set at a length that optimizes muscle stretch detection
37
Reciprocal innervation
Principle described by Sherrington (also called Sherrington’s Law of reciprocal innervation)
Reciprocal innervation of antagonistic muscles explains why the contraction of one muscle induces the relaxation of the other
Permits the execution of smooth movements
38
Alpha motor neurons located laterally
Control distal muscles
39
Alpha motor neurones located medially
Control proximal muscles
40
Muscle tone
The degree of contraction of a muscle or the proportion of motor units that are active at any one time
41
High muscle tone
Feels firm or rigid
Resists passive stretch
42
Low muscle tone
Feels soft or flaccid
Offers little resistance to passive stretch
43
Alpha motor neurones
Produce clinical signs of LMN syndrome when damaged
Cell bodies originate in laminae VIII and IX of the ventral horn - somatotopically organised
44
Function of alpha motor neurones
Can be voluntary via UMNs
Can also elicit the myotatic stretch reflex
45
Gamma motor neurones function
Regulation of muscle tone and maintaining nonconscious proprioception
Signal length and velocity of a muscle
46
Which motor neurones are activated during voluntary movement
Both Alpha and gamma simultaneously
47
Signs of LMN damage
Hypotonia - reduced or absent muscle tone
Hyporeflexia- decreased or absent reflexes
Flaccid muscle weakness or paralysis
Fasciculations - small involuntary muscle twitches
Muscle atrophy
48
Which neurotransmitter is commonly involved with UMN
Glutamate
49
Damage to a UMN
Causes weakness or paralysis of movement for the group of muscles it innervates
50
Signs of UMN damage
Hypertonia - abnormally high level of muscle tone due to loss of descending inhibition
Hyperreflexia - brisk reflexes
Spasticity - muscle is tight and stiff on passive movement
Positive babinski sign- large toe extends in response to a blunt object stroked on the plantar surface (instead of flexes)
Clonus- where a muscle is suddenly stretched and held there
Clasp knife reflex- rapid decrease in resistance when flexing a joint
51
Common cause of UMN signs
Stroke when it affects the cerebral cortex of internal capsule
52
Types of stretch receptors
Nuclear chain fibres
Nuclear bag fibres
53
Nuclear chain fibres
Respond to how much the muscle is stretched
54
Nuclear bag fibres
Respond to both magnitude of stretch and the speed it occurs at
55
What innervates the ends of the intrafusal fibres
Gamma motor neurons
Keep the fibres at a set length —> optimises muscle stretch detection
56
How is the muscle spindle composed
2 ends are contractile
Centre is non-contractile
Middle 1/3 is associated with fast type 1a Afferent sensory nerves
inferior and superior thirds are associated with type 2 afferent sensory nerves (slower conducting)
57
Upper motor neuron lesions
Everything is going up
58
What is the middle third of the spindle associated with
Fast type 1a Afferent sensory nerves
59
What are the inferior and superior thirds of the spindle associated with
Type 2 afferent sensory nerves
60
How are muscle spindles connected
Attached by connective tissue in parallel to extrafusal fibres
61
Alpha-gamma co-activation
Prevents loss of sensory information by preventing the central region of the muscle spindle from going slack during a shortening muscle contraction
Ensures information about muscle length will be continuously available
62
What slows the rate of firing in the stretch receptor
Contraction of extrafusal fibres —> shortening of the muscle removed tension on the spindle
63
Muscle spindle
Receptors have peripheral endings of afferent nerve fibres
Wrap around modified muscle fibres. = intrafusal fibres
64
What does tension depend on
Muscle length
Load on the muscle
Degree of muscle fatigue
65
Golgi tendon organs
Measure the force developed by the muscles and any resultant change in length
66
Golgi tendon organs structure
Endings of afferent fibres that wrap around collagen bundles in the tendons
1b fibres —> run to anterior horn
Posses slower afferent fibres than muscle spindles
67
Which afferent fibres lead from GTO to spinal cord
1b fibres
Run to anterior hirn
68
Output of Golgi tendon organ
Output is proportional to muscle tension
69
Do muscle spindles or Golgi tendon organs have slower afferent fibres
GTOs
70
What do Golgi tendon organs stimulate
Motor neurones of antagonistic muscle
71
Inverse stretch reflex
1b fibres inhibit muscle contraction via inhibiting alpha motor neurones
Synergy between this and interneurones regulates muscle tension and prevents overload
72
How do 1b fibres inhibit muscle contraction
Inhibit alpha motor neurones
73
Stretch reflex
Afferent fibres activate excitatory synapses directly on motor neurones which return to the muscle
Monosynaptic arc
Important in posture
74
Knee jerk reflex
Patellar tendon is tapped
Thigh muscles are stretched
Stretch receptors activated
Afferent nerve fibres activated—> activate excitatory synapses on the motor neurones that control this muscle
Stimulation of motor units
Contraction of muscle
Extension of lower leg
75
Polysynaptic reflex arc
At least one interneuron between the afferent and efferent neurones
76
Polysynaptic reflex example
Motor neurons of synergistic muscle are activated
77
Reciprocal innervation
Polysynaptic
Afferent nerve fibres end in inhibitory interneurons
When activated, inhibit motor neurones of the antagonistic muscle whose interaction would interfere with the reflex response
78
Withdrawal reflex
Activates flexor muscles
Inhibits extensor muscles
When legs affected= crossed-extensor reflex occurs simultaneously to allow shift of weight into other foot
79
Crossed-extensor reflex
Motor neurones to contralateral extensors activated and flexors inhibited to shift weight when pick up foot
80
Motor cortex
Primary motor cortex exerts quite direct, top down control over muscular activity, with as few as one synapse (in the spine) between a cortical neuron and innervation of muscle cells
81
Upper motor neurones
Motor command originates in motor cortex pyramidal cells (in layer 5-6, grey matter).
•These are the upper motor neurons.
82
Pyramidal cell axons
project directly or indirectly (e.g. via brainstem) to spinal cord, where they synapse with lower motor neurons.
83
Pyramidal tract
axons of these upper motor (pyramidal) neurons form the pyramidal tract
84
Most cortical projections innervate …
Contralateral motor units
85
The homunculus
reasonable representation, but an oversimplification: damage to a single finger area doesn’t mean loss of voluntary control of that finger.
•Representations are more complex and overlapping
•After all, few motor commands require isolated activation of a single motor unit
86
Descending projections from motor cortex
Dorsolateral tracts
Ventromedial tracts
87
Dorsolateral tracts
Contain a direct corticospinal route
Contain a indirect route via brainstem nuclei = red nuclei
Innervate contralateral side of one segment of spinal cord
Sometimes project directly to alpha motor neuron
Project to distal muscles, e.g. fingers
88
Ventromedial tracts
Contain a direct corticospinal route
Contain an indirect route via brainstem nuclei = tectum, vestibular nuclei, reticular formation and cranial nerve nuclei
Diffuse innervation projecting to both sides and multiple segments of spinal cord
Project to proximal muscles of trunk and limbs
89
What do the Dorsolateral tracts project to
Distal muscles eg fingers
90
What do the ventromedial tracts project to
Proximal muscles of trunk and limbs
91
Brainstem nuclei involved with Dorsolateral tracts
Red nucleus
92
Brainstem nuclei involved with ventromedial tracts
Tectum
Vestibular nuclei
Reticular formation
Cranial nerve nuclei
93
Basal ganglia
A group of structures beneath the cortex that act as a ‘gate-keeper’ for control of the motor system (muscles)
94
Basal ganglia receives input from
Many areas of cortex (glutamate)
95
Neurotransmitter involved with excitatory input to basal ganglia
Glutamate
96
Output of basal ganglia
Back to cortex via thalamus
Mainly inhibitory (GABA)
97
5 principle nuclei of basal ganglia
Substantia Nigra (pars compacta & pars reticulata)
Caudate & Putamen (together=striatum)
Globus Pallidus (internal and external segments)
Subthalamic Nucleus
98
Inhibitory neurotransmitter of basal ganglia
GABA
99
What forms the striatum
Caudate and putamen nuclei of basal ganglia
100
Function of basal ganglia
Disinhibitiry gating of motor cortex output
Multiple command systems
•Spatially distributed
•Processing in parallel
•All act through final common motor path
•[Cannot do more then one thing (well) at a time]
101
Cerebellum
large brain structure that acts as a ‘parallel processor’, enabling smooth, co-ordinated movements. It may also be very important in a range of cognitive tasks.
102
Cerebellum structure
Contains approx half total number of CNS neurons
•Just 10% of total brain weight
•Projects to almost all upper motor neurons
103
Cerebellum function
Modulates activity of UMN
104
Types of Inputs to cerebellum
Cortical
Spinal
Vestibular
105
Cortical input to cerebellum
Mostly from motor cortex (copies of motor commands)
Also somatosensory and visual areas of parietal cortex
106
Spinal input to cerebellum
Proprioceptive information about limb position and movement = muscle spindles, Golgi tendon organs
107
Vestibular inputs to cerebellum
Rotational and acceleratory head movement (semicircular canals / otoliths in inner ear)
108
Output of cerebellum
Thalamus to motor cortex
109
Cerebellar function
It knows what the current motor command is
It knows about actual body position and movement —> projects back to motor cortex
Computes motor error and adjusts cortical motor commands accordingly
Not just motor control, but motor learning too, in collaboration with basal ganglia and cortical circuits.
Functional brain imaging studies have demonstrated that the cerebellum is involved in a wide variety of non-motor tasks
110
What is precise motor control governed by
Size principle
Different types of muscle fibres
Antagonistic arrangement of muscles
111
Final common pathway of motor control
Single alpha motor neurone
112
Pyramidal tracts originate
In cerebral cortex
113
Role of pyramidal tracts
Carry motor fibres to spinal cord and brainstem
Responsible for voluntary control of musculature
114
Where do extrapyramidal tracts originate
Brainstem
115
Extrapyramidal tracts function
Carry motor fibres to spinal cord
Responsible for involuntary and autonomic control of musculature
116
Which descending tracts are involved in voluntary motor control
Pyramidal teacts
117
Which descending tracts are involved in involuntary and autonomic control of musculature
Extrapyramidal
118
2 types of pyramidal tracts
Corticospinal
Corticobulbar
119
Inputs to corticospinal tracts
Primary motor cortex
Premotor cortex
Supplementary cortex
120
Lateral corticospinal tract
Decussate and then descends, terminating in ventral horn
121
Pathway of corticospinal tracts
Cortex —> descends through internal capsule —> crus cerebri —> pons —> medulla
122
Where does the corticospinal tract divide into 2
Caudal part of the medulla
123
Anterior corticospinal tract
Remains ipsilateral to the spinal cord, then decussates and terminates in the ventral horn of the upper thoracic levels
124
Where does the corticobulbar tract begin
Lateral aspect of primary motor cortex
125
Pathway of corticobulbar tract
Cortex —> descend through internal capsule —> crus cerebri —> brainstem —> terminate on motor nuclei of cranial nerves (acting on facial and neck muscles)
126
Hypoglossal nerve
Only provides contralateral innervation
127
Facial nerve
Has contralateral innervation
Only affects muscles in lower quadrant of the face (below eyes)
128
Where does the facial nerve affect
Lower quadrant of face (below eyes)
129
Which cranial nerves are exceptions to innervating motor neurones bilaterally
Facial
Hypoglossal
130
Corticobulbar fibres innervate
Innervate motor neurones bilaterally
131
Where do the corticobulbar tracts terminate
Motor nuclei of cranial nerves acting on facial and neck muscles
132
Number of extrapyramidal tracts
4
133
Where do extrapyramidal tracts originate
Brainstem
134
Which extrapyramidal tracts decussate
Rubrospinal
Tectospinal
135
What are the 4 extrapyramidal tracts
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal
136
Vestibulospinal tracts arise from
Vestibular nuclei
137
Vestibulospinal tracts supply
Ipsilateral information
138
Vestibulospinal tracts control
Balance and posture
139
Vestibulospinal tracts - types
Medial and lateral tracts
140
Medial Reticulospinal tracts arise from
Pons
141
Lateral Reticulospinal tracts arise from
Medulla
142
Medial Reticulospinal tracts function
Facilitates voluntary movements
Increases muscle tone
143
Lateral Reticulospinal tracts function
Inhibits voluntary movement
Reduces movement tone
144
Rubrospinal tracts arise from
Red nucleus
145
Rubrospinal tracts function
Fine control of hand movement
146
Tectospinal tracts arise from
Superior colliculus
147
Tectospinal tracts function
Coordinates movement of the head in relation to vision stimuli
148
Where does the lateral corticospinal tract decussate
Caudal medulla
149
Where does the anterior corticospinal tract decussate
Uncrossed
Some cross in spinal cord
150
Where does the rubrospinal tract decussate
Level of origin in midbrain
151
Where does the medial vestibulospinal tract decussate
Bilateral from origin
Does not extend beyond cervical region
152
Where does the pontine Reticulospinal tract decussate
Uncrossed
153
Where does the medullary Reticulospinal tract decussate
Partially
154
Target of the lateral corticospinal tracts
Alpha motor neurones related to hand and digits or interneurones
155
Target of the anterior corticospinal tract
Motor neurones related to the trunk muscles
Input is bilateral
156
Target of the rubrospinal tract
Alpha motor neurones of proximal muscles especially flexors
157
Target of the medial vestibulospinal tracts
Alpha and gamma motor neurones for extensor muscles
158
Target of the Reticulospinal tracts
Cervical and lumbosacral pattern generatirs
159
Target of the MLF ascending
Links vestibular and nuclei related to moving eye
160
Function of lateral corticospinal tracts
Initiation of movement
161
Function of the anterior corticospinal tracts
Initiation of movement in trunk muscles
162
Function of the rubrospinal tract
Supraspinal control of flexor motor neurones and proximal limb muscles
163
Function of the medial vestibulospinal tracts
Supraspinal control of extensor muscles
164
Function of the Reticulospinal tracts
Locomotion
Posture
165
Function of the MLF - ascending
Coordinates head and eye movements
166
Muscles of the lower limbs are represented where in the motor cortex
Medially
167
Muscles of the face are represented where in the motor cortex
Laterally
168
Where are axons of upper motor neurons mainly located
Lateral white matter of the spinal cord
169
The anterior corticospinal tract mainly supplies the
Contralateral side of the body
170
How are fibres of the corticospinal tract organised
Somatotopically
171
Alternative name for primary motor cortex
Brodmann’s area 4
172
What produces an abnormal rhythmical output in Parkinson’s disease
Basal ganglia
173
At what level do the lateral corticospinal tracts decussate
Level of medullary pyramids
174
Where are the cell bodies of LMN located
Ventral horn of spinal cord
175
What is a motor unit
Motor neuron and all MMUs it innervates
176
Where do the LMN leave the spinal cord
Anteriorly (ventrally)
177
Where does the lateral corticospinal tract decussate
In medullary pyramids
178
What percentage of the corticospinal tract is anterior
15%
179
Where is the anterior corticospinal tract located in relation to the anterior horn of grey matter
Antero-medially
180
Which corticospinal tracts contains more fibres
Lateral (85% vs 15%)
181
Which motor neurones innervate extrafusal muscle fibres
Alpha motor neurons
182
Which motor neurons innervate intrafusal muscle fibres
Gamma motor neurones
183
Function of extrafusal muscle fibres
Muscle contraction
184
Function of intrafusal muscle fibres
Body position
Proprioception
185
Somatotopical organisation of corticospinal tract
Lower extremity fibres located laterally
Upper extremity and head fibres located medially
186
Direct pathway function
Increase movement
187
Direct pathway
Primary motor cortex —> striatum [excitatory = glutamate]
Striatum —> internal Globus pallidus and pars reticulata [inhibitory= GABA]
—> thalamus and pars compacta [inhibitory = GABA]
Excitatory signals further excite inhibitory pathway via dopamine [D1 receptors]
—> excitatory signals from thalamus to primary motor cortex
188
Function of indirect pathway
Decreases or stop movement
189
Indirect pathway
Primary motor cortex —> Putamen [excitatory= glutamate]
Striatum —> external Globus pallidus [inhibitory = GABA]
Inhibits Globus pallidus so cannot inhibit Subthalamic nucleus
—> excitatory to internal Globus pallidus and pars reticulata [glutamate]
—> inhibitory signals being sent to thalamus [GABA]
190
Knee jerk reflex
1. The muscle spindle is stretched in the quadriceps following stretch of the patellar tendon- caused by the tap stimulus
2. This causes action potentials to be fired by la afferent fibres which then synapse within the spinal cord with alpha-motor neurones which innervate extrafusal fibres
3. The antagonistic muscle is inhibited by inhibitory interneurons and the agonist muscle contracts- quadriceps contract and hamstrings relax
191
Overview of movement pathway
Plan out the motor programme
Voluntarily execute the programme—>
Motor signal relays to the peripheral nervous system to activate the muscles
Signals cross to the muscles via NMJ
Muscles activated
Smoothen the execution- extra pyramidal
Brain receives feedback- muscle spindles/joint position
Co-ordinate the movement
192
Where are primary motor neurones located
Primary motor cortex
193
Where do the axons from the primary motor cortex travel through
Projections through internal capsule to brainstem and then spinal cord
194
Where do the UMN synapse
Anterior horn cells of spinal cord
195
Rhyme to remember nerve roots
S1,2: tie my shoe - ankle reflex.
L3,4: kick the door - knee reflex.
C5,6: pick up sticks - biceps reflex.
C7,8: lay them straight - triceps reflex.
196
A reflex is an automatic, involuntary reaction to a stimulus.
Which group of spinal nerves innervates the biceps reflex?
C5/C6
197
The spinal cord has a variety of tracts each with their own function.
Which descending motor tract originates in the cerebral cortex and synapses in the spinal cord.
Corticospinal
198
A reflex is an automatic, involuntary reaction to a stimulus.
Which group of spinal nerves innervates the ankle reflex?
S1/S2
