This document summarizes the motor system, including reflexes, the basal ganglia, and motor functions. It describes the stretch reflex and its components like muscle spindles. It discusses the roles of alpha and gamma motor neurons and how they relate to voluntary and involuntary muscle contractions. Clinical tests of reflexes are used to locate lesions in the motor system.

1. Motor system
Reflexes
Basal ganglia
Prof. Vajira Weerasinghe
Professor of Physiology
Faculty of Medicine

2. Motor Functions
• 1. Voluntary Functions
– Voluntary movement
• 2. Involuntary Functions
– Reflexes

3. What is a reflex?
• Response to a stimulus
• Involuntary, without significant involvement of
the brain
• Stimulus Response
• Modified by descending pathways

4. What is a reflex?
Stimulus
Effector organ
Response
Central
connections
Efferent nerve
Afferent nerveReceptor
Higher centre
control

5. Stretch reflex
• This is a basic reflex present in the spinal cord
• Stimulus: muscle stretch
• Response: contraction of the muscle
• Receptors: stretch receptors located in the
muscle spindle

6. Muscle spindle

7. Skeletal muscle
• Two types of muscle fibres
– extrafusal
• normally contracting fibres
– Intrafusal
• fibres present inside the muscle spindle
• lie parallel to extrafusal fibres
• either end of the fibre contractile
• central part contains
stretch receptors

8. Extrafusal
fibre
Intrafusal
fibre
Skeletal muscle

9. Contractile
areas Stretch
receptor
Skeletal muscle

10. Nerve supply
Sensory to intrafusal fibre:
Ia afferent
II afferent
Motor:
to extrafusal fibre
A motor neuron
to intrafusal fibre
A motor neuron

11. Ia afferent nerve
 motor neuron
one
synapse
muscle
stretchmuscle
contraction
Stretch reflex

12. • When a muscle is stretched
• stretch receptors in the intrafusal fibres are stimulated
• via type Ia afferent impulse is transmitted to the spinal
cord
•  motor neuron is stimulated
• muscle is contracted
• Monosynaptic
• Neurotransmitter is glutamate
Stretch reflex

13. Stretch
Reflex

14. Stretch Reflex - Knee Jerk

15. – nuclear bag fibre
• primary (Ia) afferent
– supplies annulospiral ending in the centre
– provide information on muscle length and velocity (phasic
response) fast stretch reflex
– nuclear chain fibre
• primary (Ia) and secondary (II) afferent
– supplies flower spray ending
– monitor the length of the muscle (tonic response) – slow stretch
reflex
Two types of intrafusal fibres

16. Ia afferent fibre
II afferent fibre
nuclear bag fibre
nuclear chain fibre
 motor
neuron
 motor
neuron
Two types of intrafusal fibres

17. Importance of stretch reflex
• detects muscle length and changes in muscle
length

18. • Phasic stretch reflex
– Stretching the quadriceps muscle quickly (e.g. by tapping
the patellar tendon) evokes a discharge in the primary
afferent (Ia) fibres
– These form monosynaptic excitatory connections with motor
neurons supplying physiological extensors of the knee,
which contract briefly
• Tonic stretch reflex
– Passive bending of the joint elicits a discharge from the
group II afferents that increases the tone of physiological
extensor (antigravity) muscles
– Tonic stretch reflex is important for maintaining erect body
posture
Two types of stretch reflexes

19.  motor neuron
• cell body is located in the anterior horn
• motor neuron travels through the motor nerve
• supplies the intrafusal fibres (contractile
elements at either end)
• About 30% of neurons are gamma type

20.  motor neuron
 motor
neuron
 motor neuron

21. • When  motor neuron is active
– extrafusal fibres are contracted
– muscle contracts
• when  motor neuron is active
– intrafusal fibres are contracted
– stretch receptors are stimulated
– Increase the sensitivity of stretch receptors
 motor neuron

22. at rest
muscle
stretched
active  motor
neuron
Ia
Ia

Ia afferents are stimulated
stretch reflex is initiated
 motor neuron

24.  motor neuron activity
• Maintain the sensitivity of the muscle spindle to stretch
• Modified by the descending pathways
• Cerebellum increases gamma activity
• Descending excitatory and inhibitory influences
• Sum effect is generally inhibitory in nature

25. Alpha gamma co-activation
• Gamma motoneurons are activated in parallel with
alpha motoneurons to maintain the firing of spindle
afferents when the extrafusal muscles shorten
• Activity from brain centres often causes simultaneous
contraction of both extra- and intrafusal fibres, thereby
ensuring that the spindle is sensitive to stretch at all
muscle lengths

27. Inverse stretch reflex
• When the muscle is strongly stretched ->
muscle is relaxed
• Golgi tendon organs are stimulated
• Via type Ib afferents impulse is transmitted to
the spinal cord
• inhibitory interneuron is stimulated
•  motor neuron is inhibited
• muscle is relaxed

28.  motor neuron
Undue stretch
Golgi tendon organ
muscle
relaxation
Ib afferent nerve
inhibitory
interneuron
Inverse stretch reflex

29.  motor neuron
Undue stretch
Golgi tendon organ
muscle
relaxation
Ib afferent nerve
inhibitory
interneuron
Inverse stretch reflex

30. Inverse stretch reflex

31. Importance of inverse stretch
reflex
• detects muscle tension

32. Deep tendon reflexes (DTR)
• Biceps jerk
• Triceps jerk
• Supinator jerk
• Knee jerk
• Ankle jerk
• Jaw jerk

33. • reflex level
• biceps jerk C56
• supinator jerk C56
• triceps jerk C78
• knee jerk L34
• ankle jerk S12
Spinal cord level of stretch reflexes
(tendon jerks)

34. Superficial reflexes
• Withdrawal reflex
• Superficial abdominal reflex
• Flexor plantar reflex

35. Withdrawal Reflex
• Stimulus:
– cutaneous stimulation (usually noxious)
• Response:
– withdrawal of the hand
• Polysynaptic reflex

36. Withdrawal Reflex

37. muscle
contraction
cutaneous
receptors
polysynaptic

38. muscle
contraction
cutaneous
receptors

39. Withdrawal Reflex

40. Agonist – antagonist movements
• Elbow flexion, extension
• Wrist flexion, extension
• Forearm supination, pronation
• Shoulder adduction, abduction
• Hip flexion, extension
• Thigh adduction, abduction
• Knee flexion, extension
• Ankle dorsiflexion, plantar flexion

41. Reciprocal innervation
• inside the spinal cord
– Agonist and antagonistic muscles are reciprocally
innervated
– stimulation of flexor muscles
– inhibition of extensor muscles
– excitatory neurotransmitter is glutamate
– inhibitory neurotransmitter is glycine
flexor
extensor
+++
----

42. Reciprocal Innervation

43. Crossed extensor reflex
• In withdrawal reflex
• When one hand is stimulated by a noxious
stimulus
– Ipsilateral hand: flexor response
– Contralateral hand: extensor response
• When one leg is stimulated by a noxious
stimulus
– Ipsilateral leg: flexor response
– Contralateral leg: extensor response

44. Withdrawal Reflex with the Crossed extensor
reflex of the hand
44

45. Withdrawal Reflex with the Crossed extensor
reflex of the leg
45

46. Superficial abdominal reflexes
• light scratch of the abdominal skin
• brisk unilateral contraction of the abdominal wall

47. Flexor plantar reflex
• Scratching the sole of foot
• Plantar flexion
• Normal response

48. Clinical Importance of reflexes
(tendon jerks)
• Locate a lesion in the motor system
• To differentiate upper motor neuron lesion from
a lower motor neuron lesion

49. Motor System
• Starts at the motor cortex
• Motor cortex is located at the frontal lobe
– precentral cortex

50. 50

51. 51

52. Motor homunculus
First discovered
by
Penfield
52

53. Brodmann areas Primary motor cortex
Area 4
53

54. Motor cortex
• different areas of the body are
represented in different cortical areas in
the motor cortex
• Motor homunculus
– somatotopic representation
– not proportionate to structures but
proportionate to function
– distorted map
– upside down map

55. Motor cortical areas
• primary motor cortex
(MI)
– precentral gyrus
• Movements are executed
• secondary motor cortex
(MII)
– premotor cortex
– supplementary motor
area (SMA)
• Movements are planned
together with cerebellum,
basal ganglia and other
cortical areas

56. Primary motor cortex
• Corticospinal tract (pyramidal tract)
originates from the primary motor cortex
• Corticobulbar tract also originates from
the motor cortex and supplies brainstem
and the cranial nerves
• Cell bodies of the corticospinal tracts are
called Betz cells (large pyramidal shaped
cells)
• Corticospinal tract descends down the
internal capsule

57. Course of the corticospinal
tract• Descends through
– internal capsule
– at the medulla
• cross over to the other side
• uncrossed tracts
– descends down as the corticospinal
tract
– ends in each anterior horn cell
– synapse at the anterior horn cell
(directly or through interneurons)

58. Medulla
internal capsule
Upper
motor
neuron
Lower
motor
neuron
anterior horn cell
58

59. Primary and secondary
cortical areas
• Primary areas are primarily
connected with the peripheral
organs/structures
– Primary motor cortex (area 4)
• Secondary areas are inter-
connected to each other by
cortico-cortical pathways and
perform complex processing
– Premotor cortex (area 6)
– Supplementary motor area
(superomedial part of area 6)

60. Functional role of primary and
secondary motor areas
• SMA (Supplementary motor area)
assembles global instructions for
movements
• It issues these instructions to the
Premotor cortex (PMC)
• Premotor cortex works out the
details of smaller components
• And then activates specific Primary
motor cortex (MI)
• Primary motor cortex through
Corticospinal tracts (CST) activate
specific motor units
SMA
PMC
MI
CST
Motor units
60

61. Complex nature of Cortical
Control of Movement
8.6161

62. idea
•premotor area
•supplementary
motor area
(SMA)
•Prefrontal
cortex (PFC)
Primary
motor cortex
movement
basal ganglia
cerebellum cerebellum
plan execute
memory, emotions 62

63. Motor system
• Consists of
– Upper motor neuron
– Lower motor neuron

64. Lower motor neuron
• consists of mainly
• alpha motor neuron
– and also gamma motor neuron
alpha motor neuron
gamma motor neuron

65. alpha motor neuron
gamma motor neuron
corticospinal tract
Arrangement at the
anterior horn cell
65

66. alpha motor neuron
• this is also called the final common
pathway
• Contraction of the muscle occurs
through this whether
– voluntary contraction through corticospinal
tract
or
– involuntary contraction through gamma
motor neuron - stretch reflex - Ia afferent

67. motor unit
• muscle contraction occurs in terms of motor units
rather than by single muscle fibres
• a motor unit is defined as
– anterior horn cell
– motor neuron
– muscle fibres supplied by the neuron
• Muscle power/strength is obtained by the principle of
“Recruitment of motor units”

68. motor unit
• Innervation ratio
– motor neuron:number of muscle
fibres
• in eye muscles
– 1:23 offers a fine degree of
control
• in calf muscles
– 1:1000 more strength

69. Upper motor neuron
• Consists of
– Corticospinal tract (pyramidal tract)
– Extrapyramidal tracts
• Start from the brainstem
• Ipsilateral/contralateral
• Cortical pathways can excite/inhibit these tracts
• Modify the movement that is initiated by the CST
• Influence (+/-) gamma motor neuron, stretch reflex, muscle tone
• Important for postural control
• Cerebellar and basal ganglia influence on the lower motor neuron will
be through extrapyramidal tracts

70. Extrapyramidal tracts
• starts at the brain stem
• descends down either ipsilaterally or
contralaterally
• ends at the anterior horn cell
• modifies the motor functions

71. Extrapyramidal tracts
• there are 4 tracts
– reticulospinal tracts
– vestibulospinal tracts
– rubrospinal tracts
– tectospinal tracts

72. reticulospinal tract
• relay station for descending motor
impulses except pyramidal tracts
• receives & modifies motor commands
to the proximal & axial muscles
• maintain normal postural tone
• excitatory to alpha & gamma
motorneurons
• end on interneurons too
• this effect is inhibited by cerebral
influence
• mainly ipsilateral
midbrain
pons
medulla
spinal cord

73. Reticular formation
• A set of network of interconnected
neurons located in the central
core of the brainstem
• It is made up of ascending and
descending fibers
• It plays a big role in filtering
incoming stimuli to discriminate
irrelevant background stimuli
• There are a large number of
neurons with great degree of
convergence and divergence

74. Functions
• Maintain consciousness, sleep and arousal
• Motor functions (postural and muscle tone
control)
– Reticulospinal pathways are part of the
extrapyramidal tracts
• Pain modulation (inhibition)
– Several nuclei (PAG, NRM) are part of the
descending pain modulatory (inhibitory) pathway

75. vestibular nuclei & tracts
• responsible for maintaining tone
in antigravity muscles & for
coordinating the postural
adjustments in limbs & eyes
• connections with vestibular
receptors (otolith organs) &
cerebellum
• mainly ipsilateral
• supplies extensors
midbrain
pons
medulla
spinal cord

76. red nucleus
• present in the midbrain
• rubrospinal tract originates from the red
nucleus
• ends on interneurons
• control the distal muscles of limbs
• excite limb flexors & inhibit extensors
• higher centre influence (cerebral cortex)
• mainly contralateral
• supplies flexors
• Functionally this tract is not important in
human motor system
midbrain
pons
medulla
spinal cord

77. tectospinal tract
• tectospinal tract originates from
the tectum of the midbrain
• ends on interneurons
• mainly contralateral
• supplies cervical segments only
• Functionally this tract is not
important in human motor system
midbrain
pons
medulla
spinal cord

78. inferior olivary nucleus
• present in the medulla
• function:
– motor coordination
• via projections to the cerebellum
• sole source of climbing fibres to the cerebellum
– motor learning
– Functionally this nucleus is not important in human
motor system

79. Upper
motor
neuron
Lower
motor
neuron
extrapyramidal tracts
pyramidal tracts
alpha motor neurone
gamma motor neurone
79

80. Clinical Importance of the motor system
examination
• Tests of motor function:
– Muscle power
• Ability to contract a group of muscles in order to make an
active movement
– Muscle tone
• Resistance against passive movement

81. Basis of tests
• Muscle power
– Test the integrity of motor cortex, corticospinal tract
and lower motor neuron
• Muscle tone
– Test the integrity of stretch reflex, gamma motor
neuron and the descending control of the stretch
reflex

82. Muscle tone
• Resistance against passive movement
– Gamma motor neuron maintains the sensitivity of spindles
– Stretching the muscle will activate the stretch reflex
– Muscle will contract involuntarily
– Gamma activity is under higher centre inhibition

83. • There is a complex effect of corticospinal and extrapyramidal tracts on the alpha and
gamma motor neurons (in addition to the effect by muscle spindle)
• There are both excitatory and inhibitory effects
• Sum effect
– excitatory on alpha motor neuron
– Inhibitory on gamma motor neuron
Corticospinal
tract
Extrapyramidal
tracts
Alpha motor
neuron
Gamma
motor
neuron•Voluntary movement
•Muscle tone
Muscle spindle

84. Clinical situations
• Muscle power
– Normal
– Reduced (muscle weakness)
• Paralysis, paresis, plegia
• MRC grades
0 - no movement
1 - flicker is perceptible in the muscle
2 - movement only if gravity eliminated
3 - can move limb against gravity
4 - can move against gravity & some resistance exerted by examiner
5 - normal power
• Muscle tone
– Normal
– Reduced
• Hypotonia (Flaccidity)
– Increased
• Hypertonia (Spasticity)

85. Main abnormalities
• Muscle Weakness / paralysis
– Reduced muscle power
• Flaccidity
– Reduced muscle tone
• Spasticity
– Increased muscle tone

86. Upper and lower motor neurons
• Lower motor neuron lesion causes
– flaccid paralysis (flaccid weakness)
• Upper motor neuron lesion causes
– spastic paralysis (spastic weakness)

87. Lower motor neuron lesion
• muscle weakness
• flaccid paralysis
• muscle wasting (disuse atrophy)
• reduced muscle tone (hypotonia)
• reflexes: reduced or absent (hyporeflexia or
areflexia)
• spontaneous muscle contractions
(fasciculations)
• plantar reflex: flexor
• superficial abdominal reflexes: present

88. Muscle wasting
88

89. Fasciculations
89

90. Upper motor neuron lesion
• muscle weakness
• spastic paralysis
• increased muscle tone (hypertonia)
• reflexes: exaggerated (hyperreflexia)
• Babinski sign: positive
• superficial abdominal reflexes: absent
• muscle wasting is very rare
• clonus can be seen:
– rhythmical series of contractions in response to sudden stretch
• clasp knife effect can be seen
– passive stretch causing initial increased resistance which is released
later
• eg. Stroke 90

91. Clasp knife effect
Clonus 91

92. Stroke patient walking

93. Babinski sign
• when outer border of the sole of the foot is
scratched
• upward movement of big toe
• fanning out of other toes
• feature of upper motor neuron lesion
• extensor plantar reflex
• seen in infants during 1st year of life (because
of immature corticospinal tract)

94. positive Babinski sign
94

95. Site of lesions
Cortex
Internal capsule
Brain stem
Spinal cord
Anterior horn cell
Motor nerve
Neuromuscular junction
Muscle

96. Neurological diseases
Disease Involvement
• Stroke UMN
• Peripheral neuropathy LMN
– Mononeuropathy
– Polyneuropathy
• Plexopathy LMN
• Radiculopathy LMN
• Myelopathy LMN, UMN
• Motor neuron disease LMN, UMN
• Monoplegia (monoparesis)
• Hemiplegia (hemiparesis)
• Paraplegia (paraparesis)
• Quadriplegia (quadriparesis)

97. Site of lesions
monoplegia
only 1 limb is affected either UL or LL,
lower motor neuron lesion
hemiplegia
one half of the body including
UL and LL
lesion in the Internal capsule
paraplegia
both lower limbs
thoracic cord lesion
quadriplegia (tetraplegia)
all 4 limbs are affected
cervical cord or brain stem lesion

98. Some common neurological
diseases
98

99. Stroke
• Cerebrovascular accident (CVA)
• A serious neurological disease
• 2nd main cause of deaths in the world
• Two types
– cerebrovascular ischaemia causing infarction
– haemorrhage
• Sudden onset hemiplegia
• Hypertension, diabetes, obesity are risk factors

100. Peripheral neuropathies
• Mononeuropathies
– Carpal tunnel syndrome (CTS)
– Ulnar neuropathy - claw hand
– Saturday night palsy (radial nerve lesion) – wrist drop
– Common peroneal nerve lesion – foot drop
– Posterior tibial nerve lesion – tarsal tunnel syndrome
– Sciatic nerve lesion
– Facial nerve lesion – Bell’s palsy
• Polyneuropathies
– Diabetic, vitamin deficiency, toxic

101. Median nerve compression
(Carpal tunnel syndrome)

102. Ulnar nerve lesion
(Ulnar tunnel syndrome)
Clawing of the hand

103. Radial nerve lesion
(Saturday night palsy)
Wrist drop
Wrist guard

104. Common peroneal nerve
lesion
Foot drop
Ankle guard

105. Posterior tibial nerve lesion
(Tarsal tunnel syndrome)

106. Sciatic nerve lesion

107. Facial nerve lesion
(Facial palsy or Bell’s
palsy)

108. Brachial plexopathy
(Erb’s palsy)

109. Cervical spondylosis

110. Sciatica

111. Cervical or thoracic
myelopathy
Paraplegia
Quadriplegia

112. Motor neuron disease (MND)
• Both upper and lower motor neurons are affected
• In lower motor neurons, anterior horn cell disease
are affected
• Also called “Amyotrophic lateral sclerosis” (ALS)
• Weakness of lower limbs, upper limbs
• Speech defect: dysarthria
• Difficulty in swallowing: dysphagia

113. Motor neuron disease
Stephen Hawking

114. Basal ganglia
• These are a set of deep nuclei located
in and around the basal part of the
brain that are involved in motor
control, action selection, and some
forms of learning

115. Basal ganglia
• Caudate nucleus
• Putamen
• Globus pallidus
–(internal and external)
• Subthalamic nuclei
• Substantia nigra
International Basal Ganglia Society

116. (Ref. Guyton)116

117. thalamus
globus pallidus
putamen
caudate
117

118. 118

119. Basal ganglia
• caudate nucleus
• putamen
• globus pallidus
• subthalamic nuclei
• substantia nigra
corpus striatum
lentiform
nucleus

120. Basal ganglia
• Interconnecting circuitry through these
nuclei
• These circuits start from the cortex and
ends in the cortex
• These circuits are very complex
• Their effect is excitatory or inhibitory on
motor functions (depending on the
neurotransmitter involved)
• They also have a role in cognitive
functions

121. 121

122. 122

123. Basal ganlgia
• Some of these circuits are excitatory
and some inhibitory
• This depends on the neurotransmitter
involved.
• Inhibitory: dopamine and GABA
• Excitatory: Ach
• Others: glutamate (from cortical
projections) enkephalin etc

124. Basal ganglia
Following pathways are known:
• Dopamine pathway from substantia nigra to caudate
nucleus and putamen
• GABA pathway from caudate and putamen to globus
pallidus and substantia nigra
• Ach pathway in the caudate and putamen

125. Cortex
Putamen
globus
pallidus
Thalamus
Caudate
Substantia
nigra
Subthalamic
nucleus
Reticular
formation
Dopamine
Thalamus
Reticular formation
glutamate
GABA
Interneurons: Ach
striatum GABA
+
+
125

126. Functions of Basal Ganglia
• Motor control
• Learning
• Sensorimotor integration
• Reward
• Cognition
• Performs purposeful movement

127. Cortico–Basal Ganglia Motor Loop
• Basal ganglia
receives
information from
cerebral cortex
(frontal, prefronal
and parietal)
• Complex
mechanisms occur
inside basal
ganglia
• Output goes to the
thalamus
• From the thalamus
to the frontal cortex
(premotor and
supplementary
motor areas)
Basal ganglia inhibit muscle tone

128. Basal Ganglia disorders
• Parkinsonism
• Athetosis
• Chorea
• Hemiballismus
• Basal ganglia disorders are also called extrapyramidal
disorders

129. Parkinsonism
• due to destruction of dopamine secreting pathways
from substantia nigra to caudate and putamen.
– also called “paralysis agitans” or “shaking palsy”
– first described by Dr. James Parkinson in 1817.
• In the west, it affects 1% of individuals after 60 yrs
Classical Clinical features:
• Tremor, resting
• Rigidity of all the muscles
• Akinesia (bradykinesia): very slow movements
• Postural instability

130. – expressionless face
– flexed posture
– soft, rapid, indistinct speech
– slow to start walking
– rapid, small steps, tendency to run
– reduced arm swinging
– impaired balance on turning
– resting tremor (3-5 Hz) (pill-rolling tremor)
• diminishes on action
– cogwheel rigidity
– lead pipe rigidity
– impaired fine movements
– impaired repetitive movements
130

131. 131

132. Resting tremor
132

133. Cortex
Putamen
globus
pallidus
Thalamus
Caudate
Substantia
nigra
Subthalamic
nucleus
Reticular
formation
Dopamine
Thalamus
Reticular formation
glutamate
GABA
Interneurons: Ach
striatum GABA
+
+
133

134. Parkinsonism
• this could be caused by
– idiopathic causes (no definite cause)
– drugs
– toxins
– MPTP (1 methyl 4 phenyl tetrahydropyridine)
• experimentally induced parkinsonism
– associated with other disorders

135. Parkinsonism
• Treatment is to
– increase dopamine content by giving dopaminergic
drugs
• Ldopa
– decrease Ach activity by giving anticholinergic drugs

136. Chorea
• Lesions in the caudate
nucleus
• jerky movements of the
hand, face and other parts
• patient is unable to control
them
• may get worse with
anxiety
• disappears in sleep
136

137. Athetosis
• Lesions in
putamen
• spontaneous
slow writhing
movements
(twisting
movements) of
fingers, hands,
toes, feet.

138. Hemiballismus
• Lesions in
subthalamus
• violent, flailing
movements of
arm & leg on
one side of
the body
138

139. Summary of control of motor system
• 1. Cerebral cortex: As a whole is essential for sending analytical command
signal for execution
• Frontal: corticospinal pathways
• Premotor and SMA: sequencing and modulation of all voluntary movements
• Prefrontal cortex (PFC): planning and initiation
• Parietal cortical areas: guidance of movement
• Visual, auditory and somatosensoy association areas: conscious guidance of
movement
• Proprioceptive: unconscious guidance of movement
• 2. Subcortical centres
– Basal ganglia: maintenance of tone and posture
– Cerebellum: coordination
• 3. Brainstem centres
• Major relay station through pontine and medullary nuclei, vestibular: stretch reflex,
posture, repetitive movements
• 4. Spinal cord
• Final common pathway
• Motor unit
• Spinal cord reflexes (stretch reflex, withdrawal reflex)
139