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Neuro > Sensorimotor System > Flashcards

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.

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2
Q

Types of motor control

A

Voluntary
Goal-directed
Habit
Involuntary

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3
Q

Voluntary motor control examples

A

Walking
Running
Talking

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4
Q

Goal-directed motor control

A

Conscious
Explicit
Controlled

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5
Q

Habit motor control

A

Unconscious
Implicit
Automatic

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6
Q

Examples of involuntary motor control

A

Eye movements
Facial expressions
Jaw
Tongue
Postural muscles
Hand and fingers
Diaphragm
Cardiac
Intercostals
Digestive tract

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7
Q

Lower motor neurones

A

Cell body in brainstem or spinal cord and projects to the muscle

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8
Q

Upper motor neurons

A

Originate in higher centres and project down to meet the lower motor neurones

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9
Q

Smallest muscle

A

Stapedius- found in the inner ear

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10
Q

Largest muscle

A

Gluteus maximus - found in the hip/buttock

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11
Q

Strongest muscle

A

Masseter- jaw

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12
Q

3 types of muscle

A

Cardiac
Smooth
Skeletal

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13
Q

Antagonistic arrangement

A

Combined co-ordinated action

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14
Q

How do we achieve a range of movements and forces

A

Antagonistic arrangement
Recruitment of muscle fibres

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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

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16
Q

Number of muscle fibres

A

Varies across individuals
Changes little with either time or training
Genetically determined

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17
Q

What attaches muscle to bone

A

Tendon

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18
Q

Muscle fasciculus

A

Several muscle fibres

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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

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20
Q

Motor unit

A

Single alpha motor neurone and all the extrafusal skeletal muscle fibres it innervates

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21
Q

Fewer fibres innervated by a motor neurone means

A

Greater movement resolution eg finger tips and tongue

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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

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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

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24
Q

Size principle

A

Units are recruited in order of size (smallest first)
Fine control typically required at lower forces

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25
Q

Lower alpha motor neurons

A

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.

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26
Q

Motor pool

A

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

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27
Q

Cell bodies in the ventral horn are activated by

A

Sensory information from muscle
Descending information from brain

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28
Q

Muscles can be contracted or relaxed to provide movement, but a good control system (the CNS) needs to know two things:

A

how much tension is on the muscle;
what is the length (stretch) of the muscle

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29
Q

What proprioceptor senses stretch

A

Muscle spindles

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30
Q

Which proprioceptors sense tension

A

Golgi tendon organs

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31
Q

Golgi tendon organs

A

Within the tendon
Sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle

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32
Q

Under conditions of extreme tension

A

Golgi tendon organs act to inhibit muscle fibres to prevent damage

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33
Q

Muscle spindles

A

Sense the length of muscles —>amount of stretch

Embedded within most muscles
Composed of intrafusal fibers
Detect stretch regardless of the current muscle length

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34
Q

Most simple reflex

A

Monosynaptic- eg patellar tendon reflex

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35
Q

system to detect stretch regardless the current muscle length

A

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

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36
Q

Muscle spindle feedback

A

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

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37
Q

Reciprocal innervation

A

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

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38
Q

Alpha motor neurons located laterally

A

Control distal muscles

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39
Q

Alpha motor neurones located medially

A

Control proximal muscles

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40
Q

Muscle tone

A

The degree of contraction of a muscle or the proportion of motor units that are active at any one time

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41
Q

High muscle tone

A

Feels firm or rigid
Resists passive stretch

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42
Q

Low muscle tone

A

Feels soft or flaccid
Offers little resistance to passive stretch

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43
Q

Alpha motor neurones

A

Produce clinical signs of LMN syndrome when damaged
Cell bodies originate in laminae VIII and IX of the ventral horn - somatotopically organised

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44
Q

Function of alpha motor neurones

A

Can be voluntary via UMNs
Can also elicit the myotatic stretch reflex

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45
Q

Gamma motor neurones function

A

Regulation of muscle tone and maintaining nonconscious proprioception
Signal length and velocity of a muscle

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46
Q

Which motor neurones are activated during voluntary movement

A

Both Alpha and gamma simultaneously

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47
Q

Signs of LMN damage

A

Hypotonia - reduced or absent muscle tone
Hyporeflexia- decreased or absent reflexes
Flaccid muscle weakness or paralysis
Fasciculations - small involuntary muscle twitches
Muscle atrophy

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48
Q

Which neurotransmitter is commonly involved with UMN

A

Glutamate

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49
Q

Damage to a UMN

A

Causes weakness or paralysis of movement for the group of muscles it innervates

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50
Q

Signs of UMN damage

A

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

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51
Q

Common cause of UMN signs

A

Stroke when it affects the cerebral cortex of internal capsule

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52
Q

Types of stretch receptors

A

Nuclear chain fibres
Nuclear bag fibres

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53
Q

Nuclear chain fibres

A

Respond to how much the muscle is stretched

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54
Q

Nuclear bag fibres

A

Respond to both magnitude of stretch and the speed it occurs at

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55
Q

What innervates the ends of the intrafusal fibres

A

Gamma motor neurons
Keep the fibres at a set length —> optimises muscle stretch detection

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56
Q

How is the muscle spindle composed

A

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)

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57
Q

Upper motor neuron lesions

A

Everything is going up

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58
Q

What is the middle third of the spindle associated with

A

Fast type 1a Afferent sensory nerves

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59
Q

What are the inferior and superior thirds of the spindle associated with

A

Type 2 afferent sensory nerves

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60
Q

How are muscle spindles connected

A

Attached by connective tissue in parallel to extrafusal fibres

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61
Q

Alpha-gamma co-activation

A

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

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62
Q

What slows the rate of firing in the stretch receptor

A

Contraction of extrafusal fibres —> shortening of the muscle removed tension on the spindle

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63
Q

Muscle spindle

A

Receptors have peripheral endings of afferent nerve fibres
Wrap around modified muscle fibres. = intrafusal fibres

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64
Q

What does tension depend on

A

Muscle length
Load on the muscle
Degree of muscle fatigue

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65
Q

Golgi tendon organs

A

Measure the force developed by the muscles and any resultant change in length

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66
Q

Golgi tendon organs structure

A

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

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67
Q

Which afferent fibres lead from GTO to spinal cord

A

1b fibres
Run to anterior hirn

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68
Q

Output of Golgi tendon organ

A

Output is proportional to muscle tension

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69
Q

Do muscle spindles or Golgi tendon organs have slower afferent fibres

A

GTOs

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70
Q

What do Golgi tendon organs stimulate

A

Motor neurones of antagonistic muscle

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71
Q

Inverse stretch reflex

A

1b fibres inhibit muscle contraction via inhibiting alpha motor neurones
Synergy between this and interneurones regulates muscle tension and prevents overload

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72
Q

How do 1b fibres inhibit muscle contraction

A

Inhibit alpha motor neurones

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73
Q

Stretch reflex

A

Afferent fibres activate excitatory synapses directly on motor neurones which return to the muscle
Monosynaptic arc
Important in posture

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74
Q

Knee jerk reflex

A

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

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75
Q

Polysynaptic reflex arc

A

At least one interneuron between the afferent and efferent neurones

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76
Q

Polysynaptic reflex example

A

Motor neurons of synergistic muscle are activated

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77
Q

Reciprocal innervation

A

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

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78
Q

Withdrawal reflex

A

Activates flexor muscles
Inhibits extensor muscles
When legs affected= crossed-extensor reflex occurs simultaneously to allow shift of weight into other foot

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79
Q

Crossed-extensor reflex

A

Motor neurones to contralateral extensors activated and flexors inhibited to shift weight when pick up foot

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80
Q

Motor cortex

A

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
Q

Upper motor neurones

A

Motor command originates in motor cortex pyramidal cells (in layer 5-6, grey matter).
•These are the upper motor neurons.

82
Q

Pyramidal cell axons

A

project directly or indirectly (e.g. via brainstem) to spinal cord, where they synapse with lower motor neurons.

83
Q

Pyramidal tract

A

axons of these upper motor (pyramidal) neurons form the pyramidal tract

84
Q

Most cortical projections innervate …

A

Contralateral motor units

85
Q

The homunculus

A

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
Q

Descending projections from motor cortex

A

Dorsolateral tracts
Ventromedial tracts

87
Q

Dorsolateral tracts

A

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
Q

Ventromedial tracts

A

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
Q

What do the Dorsolateral tracts project to

A

Distal muscles eg fingers

90
Q

What do the ventromedial tracts project to

A

Proximal muscles of trunk and limbs

91
Q

Brainstem nuclei involved with Dorsolateral tracts

A

Red nucleus

92
Q

Brainstem nuclei involved with ventromedial tracts

A

Tectum
Vestibular nuclei
Reticular formation
Cranial nerve nuclei

93
Q

Basal ganglia

A

A group of structures beneath the cortex that act as a ‘gate-keeper’ for control of the motor system (muscles)

94
Q

Basal ganglia receives input from

A

Many areas of cortex (glutamate)

95
Q

Neurotransmitter involved with excitatory input to basal ganglia

A

Glutamate

96
Q

Output of basal ganglia

A

Back to cortex via thalamus
Mainly inhibitory (GABA)

97
Q

5 principle nuclei of basal ganglia

A

Substantia Nigra (pars compacta & pars reticulata)
Caudate & Putamen (together=striatum)
Globus Pallidus (internal and external segments)
Subthalamic Nucleus

98
Q

Inhibitory neurotransmitter of basal ganglia

A

GABA

99
Q

What forms the striatum

A

Caudate and putamen nuclei of basal ganglia

100
Q

Function of basal ganglia

A

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
Q

Cerebellum

A

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
Q

Cerebellum structure

A

Contains approx half total number of CNS neurons
•Just 10% of total brain weight
•Projects to almost all upper motor neurons

103
Q

Cerebellum function

A

Modulates activity of UMN

104
Q

Types of Inputs to cerebellum

A

Cortical
Spinal
Vestibular

105
Q

Cortical input to cerebellum

A

Mostly from motor cortex (copies of motor commands)
Also somatosensory and visual areas of parietal cortex

106
Q

Spinal input to cerebellum

A

Proprioceptive information about limb position and movement = muscle spindles, Golgi tendon organs

107
Q

Vestibular inputs to cerebellum

A

Rotational and acceleratory head movement (semicircular canals / otoliths in inner ear)

108
Q

Output of cerebellum

A

Thalamus to motor cortex

109
Q

Cerebellar function

A

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
Q

What is precise motor control governed by

A

Size principle
Different types of muscle fibres
Antagonistic arrangement of muscles

111
Q

Final common pathway of motor control

A

Single alpha motor neurone

112
Q

Pyramidal tracts originate

A

In cerebral cortex

113
Q

Role of pyramidal tracts

A

Carry motor fibres to spinal cord and brainstem
Responsible for voluntary control of musculature

114
Q

Where do extrapyramidal tracts originate

A

Brainstem

115
Q

Extrapyramidal tracts function

A

Carry motor fibres to spinal cord
Responsible for involuntary and autonomic control of musculature

116
Q

Which descending tracts are involved in voluntary motor control

A

Pyramidal teacts

117
Q

Which descending tracts are involved in involuntary and autonomic control of musculature

A

Extrapyramidal

118
Q

2 types of pyramidal tracts

A

Corticospinal
Corticobulbar

119
Q

Inputs to corticospinal tracts

A

Primary motor cortex
Premotor cortex
Supplementary cortex

120
Q

Lateral corticospinal tract

A

Decussate and then descends, terminating in ventral horn

121
Q

Pathway of corticospinal tracts

A

Cortex —> descends through internal capsule —> crus cerebri —> pons —> medulla

122
Q

Where does the corticospinal tract divide into 2

A

Caudal part of the medulla

123
Q

Anterior corticospinal tract

A

Remains ipsilateral to the spinal cord, then decussates and terminates in the ventral horn of the upper thoracic levels

124
Q

Where does the corticobulbar tract begin

A

Lateral aspect of primary motor cortex

125
Q

Pathway of corticobulbar tract

A

Cortex —> descend through internal capsule —> crus cerebri —> brainstem —> terminate on motor nuclei of cranial nerves (acting on facial and neck muscles)

126
Q

Hypoglossal nerve

A

Only provides contralateral innervation

127
Q

Facial nerve

A

Has contralateral innervation
Only affects muscles in lower quadrant of the face (below eyes)

128
Q

Where does the facial nerve affect

A

Lower quadrant of face (below eyes)

129
Q

Which cranial nerves are exceptions to innervating motor neurones bilaterally

A

Facial
Hypoglossal

130
Q

Corticobulbar fibres innervate

A

Innervate motor neurones bilaterally

131
Q

Where do the corticobulbar tracts terminate

A

Motor nuclei of cranial nerves acting on facial and neck muscles

132
Q

Number of extrapyramidal tracts

A

4

133
Q

Where do extrapyramidal tracts originate

A

Brainstem

134
Q

Which extrapyramidal tracts decussate

A

Rubrospinal
Tectospinal

135
Q

What are the 4 extrapyramidal tracts

A

Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal

136
Q

Vestibulospinal tracts arise from

A

Vestibular nuclei

137
Q

Vestibulospinal tracts supply

A

Ipsilateral information

138
Q

Vestibulospinal tracts control

A

Balance and posture

139
Q

Vestibulospinal tracts - types

A

Medial and lateral tracts

140
Q

Medial Reticulospinal tracts arise from

A

Pons

141
Q

Lateral Reticulospinal tracts arise from

A

Medulla

142
Q

Medial Reticulospinal tracts function

A

Facilitates voluntary movements
Increases muscle tone

143
Q

Lateral Reticulospinal tracts function

A

Inhibits voluntary movement
Reduces movement tone

144
Q

Rubrospinal tracts arise from

A

Red nucleus

145
Q

Rubrospinal tracts function

A

Fine control of hand movement

146
Q

Tectospinal tracts arise from

A

Superior colliculus

147
Q

Tectospinal tracts function

A

Coordinates movement of the head in relation to vision stimuli

148
Q

Where does the lateral corticospinal tract decussate

A

Caudal medulla

149
Q

Where does the anterior corticospinal tract decussate

A

Uncrossed
Some cross in spinal cord

150
Q

Where does the rubrospinal tract decussate

A

Level of origin in midbrain

151
Q

Where does the medial vestibulospinal tract decussate

A

Bilateral from origin
Does not extend beyond cervical region

152
Q

Where does the pontine Reticulospinal tract decussate

A

Uncrossed

153
Q

Where does the medullary Reticulospinal tract decussate

A

Partially

154
Q

Target of the lateral corticospinal tracts

A

Alpha motor neurones related to hand and digits or interneurones

155
Q

Target of the anterior corticospinal tract

A

Motor neurones related to the trunk muscles
Input is bilateral

156
Q

Target of the rubrospinal tract

A

Alpha motor neurones of proximal muscles especially flexors

157
Q

Target of the medial vestibulospinal tracts

A

Alpha and gamma motor neurones for extensor muscles

158
Q

Target of the Reticulospinal tracts

A

Cervical and lumbosacral pattern generatirs

159
Q

Target of the MLF ascending

A

Links vestibular and nuclei related to moving eye

160
Q

Function of lateral corticospinal tracts

A

Initiation of movement

161
Q

Function of the anterior corticospinal tracts

A

Initiation of movement in trunk muscles

162
Q

Function of the rubrospinal tract

A

Supraspinal control of flexor motor neurones and proximal limb muscles

163
Q

Function of the medial vestibulospinal tracts

A

Supraspinal control of extensor muscles

164
Q

Function of the Reticulospinal tracts

A

Locomotion
Posture

165
Q

Function of the MLF - ascending

A

Coordinates head and eye movements

166
Q

Muscles of the lower limbs are represented where in the motor cortex

A

Medially

167
Q

Muscles of the face are represented where in the motor cortex

A

Laterally

168
Q

Where are axons of upper motor neurons mainly located

A

Lateral white matter of the spinal cord

169
Q

The anterior corticospinal tract mainly supplies the

A

Contralateral side of the body

170
Q

How are fibres of the corticospinal tract organised

A

Somatotopically

171
Q

Alternative name for primary motor cortex

A

Brodmann’s area 4

172
Q

What produces an abnormal rhythmical output in Parkinson’s disease

A

Basal ganglia

173
Q

At what level do the lateral corticospinal tracts decussate

A

Level of medullary pyramids

174
Q

Where are the cell bodies of LMN located

A

Ventral horn of spinal cord

175
Q

What is a motor unit

A

Motor neuron and all MMUs it innervates

176
Q

Where do the LMN leave the spinal cord

A

Anteriorly (ventrally)

177
Q

Where does the lateral corticospinal tract decussate

A

In medullary pyramids

178
Q

What percentage of the corticospinal tract is anterior

A

15%

179
Q

Where is the anterior corticospinal tract located in relation to the anterior horn of grey matter

A

Antero-medially

180
Q

Which corticospinal tracts contains more fibres

A

Lateral (85% vs 15%)

181
Q

Which motor neurones innervate extrafusal muscle fibres

A

Alpha motor neurons

182
Q

Which motor neurons innervate intrafusal muscle fibres

A

Gamma motor neurones

183
Q

Function of extrafusal muscle fibres

A

Muscle contraction

184
Q

Function of intrafusal muscle fibres

A

Body position
Proprioception

185
Q

Somatotopical organisation of corticospinal tract

A

Lower extremity fibres located laterally
Upper extremity and head fibres located medially

186
Q

Direct pathway function

A

Increase movement

187
Q

Direct pathway

A

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
Q

Function of indirect pathway

A

Decreases or stop movement

189
Q

Indirect pathway

A

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
Q

Knee jerk reflex

A
  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
Q

Overview of movement pathway

A

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
Q

Where are primary motor neurones located

A

Primary motor cortex

193
Q

Where do the axons from the primary motor cortex travel through

A

Projections through internal capsule to brainstem and then spinal cord

194
Q

Where do the UMN synapse

A

Anterior horn cells of spinal cord

195
Q

Rhyme to remember nerve roots

A

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
Q

A reflex is an automatic, involuntary reaction to a stimulus.

Which group of spinal nerves innervates the biceps reflex?

A

C5/C6

197
Q

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.

A

Corticospinal

198
Q

A reflex is an automatic, involuntary reaction to a stimulus.

Which group of spinal nerves innervates the ankle reflex?

A

S1/S2

Neuro (22 decks)

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