1. Neurophysiology lecture topics
1. Role of brainstem and reticular formation
2. Ascending and descending tracts
muscle power
3. Maintenance of posture, equilibrium,
coordination
muscle tone
4. Functions of limbic system and basal ganglia

2. Brains stem
• Midbrain
• Pons
• Medulla

3. Role of brainstem
•
•
•
•
•
•
•
•
•
•
Intermediate centre in controlling motor functions
Ascending and descending pathways cross brain stem
Contains vital centres
Contains reticular formation
Plays a vital role in attention, arousal and states of
consciousness
Brainstem injuries easily cause loss of consciousness
Most of the cranial nerves are connected to brainstem
Contain pain pathways
Involved in suprasegmental control of reflexes and muscle tone
Extrapyramodal tracts strats from the brain stme

4. Reticular formation
• Located in the core of the
brainstem
• Network of neurons
• Main centre of ascending
and descending tracts
• Functions:
consciousness, motor
control, pain modulation,
cardiovascular control,
sleep centres

5. Ascending pathways
• Somatosensory pathways
– Dorsal column – medial lemniscus pathway
– Spinothalamic tracts
• Anterior spinothalamic tract
• Lateral spinothalamic tract
– Spinocerebellar tracts
• Dorsal
• Ventral

6. Sensory area
in the brain
Ascending
Sensory pathway
Central Connections
Sensory nerve
Touch stimulus
Receptor
Sensory
modality

7. Two main ascending pathways
• Dorsal column - medial lemniscus
pathway
fast pathway
• Spinothalamic pathway
slow pathway
These two pathways come together at the level of thalamus

8. Spinothalamic pathway
Dorsal column pathway
Lateral
Spinothalamic
tract
Anterior
Spinothalamic
tract

9. Dorsal column pathway
• touch: fine degree
• highly localised touch
sensations
• vibratory sensations
• sensations signalling
movement
• position sense
• pressure: fine degree
Spinothalamic pathway
• Pain
• Thermal sensations
• Crude touch &
pressure
• crude localising
sensations
• tickle & itch
• sexual sensations

10. 3rd
order
neuron
thalamocortical tracts
internal capsule
thalamus
Medial lemniscus
Dorsal column nuclei
2nd
order
neuron
(cuneate & gracile nucleus)
Dorsal column
1st
order
neuron

11. 3rd
order
neuron
thalamocortical tracts
internal capsule
thalamus
Spinothalamic
tracts
2nd
order
neuron
1st
order
neuron

13. Proprioceptive pathways
• Dorsal column – medial lemniscus –
thalamocortical pathway (conscious
proprioception)
• Spinocerebellar pathway
(unconscious proprioception)

14. Main descending pathways
• Motor pathways
• Corticospinal and corticobulbar tracts
• Starts from the motor cortex

15. Motor cortex
• Located in the frontal lobe
• Precentral gyrus

17. Motor homunculus
First discovered
by
Penfield

18. Corticospinal tract (Pyramidal tract)
• Starts from large cortical cells (pyramidal
cells) in the primary motor cortex
• These cells are called Betz cells
• From these cells starts the motor axon
• Divided into
– Lateral corticospinal tract
• Major part of the CST, cross to the opposite side
at the level of medulla
– Medial corticospinal tract (or anterior CST)
• Minor part, uncrossed tract, at the level of spinal
cord cross to the opposite side

19. Course of the corticospinal tract
• Descends through
– internal capsule
– at the medulla
• cross over to the other side
– descends down as the corticospinal tract
– ends in each anterior horn cell
– synapse at the anterior horn cell

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

21. Motor system
• Consists of
– Upper motor neuron
• Corticospinal tract (pyramidal tract)
• Extrapyramidal tracts
– Lower motor neuron
• Alpha motor neuron
• Gamma motor neuron

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

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

24. 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

25. Upper motor neuron
• Consists of
– Corticospinal tract (pyramidal tract)
– Extrapyramidal tracts

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

27. Reticulospinal tract
• Starts from the reticular formation
• Maintain normal postural tone
• Controls mainly gamma motorneurons (lesser extent alpha
motor neurons)
• Inhibit antigravity muscles (extensor)
• End on interneurons
• Inhibited by cerebral influence
• Mainly ipsilateral

28. Reticular formation
• Loosely arranged cell bodies
in the central core of the brain
stem
midbrain
pons
• Pontine reticular area
medulla
• Medullary reticular area
spinal cord

29. Vestibulospinal tract
• Starts from the vestibular nuclei (present in the medullar region)
• Excitatory to alpha motor neurons of antigravity muscles
(extensor)
• End on interneurons
• Regulates posture and balance
• Mainly ipsilateral
• There are inputs from vestibular organs and cerebellum to
vestibular nuclei

30. • Rubrospinal and tectospinal tracts are not
functionally important in human nervous system

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

32. Suprasegmental control of reflexes and
muscle tone
• Alpha motor neuron is the final pathway
• Gamma motor neuron control
• Alpha-gamma coactivation
• Supraspinal control
– Pyramidal tract: activation of alpha
– Extrapyramidal: mixed effects on alpha and gamma
motor neurons
• Net effect: suppression of gamma motor neuron

33. Extrapyramidal
tracts
•Voluntary movement
•Muscle tone
Gamma
motor
neuron
Corticospinal
tract
Alpha motor
neuron
Muscle spindle
•
•
•
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

34. 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

35. 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

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

37. Clinical situations
• Muscle power
– Normal
– Reduced (muscle weakness)
• muscle paralysis
• muscle paresis
• Muscle tone
– Normal
– Reduced
• Hypotonia (Flaccidity)
– Increased
• Hypertonia (Spasticity)

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

39. • Lower motor neuron lesion causes
– flaccid paralysis (flaccid weakness)
• Upper motor neuron lesion causes
– spastic paralysis (spastic weakness)

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

41. Muscle wasting

42. Fasciculations

43. Upper motor neuron lesion
•
•
•
•
•
•
•
•
muscle weakness
spastic paralysis
increased muscle tone (hypertonia)
reflexes: exaggerated
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

44. Clonus
Clasp knife effect

45. Stroke patient walking

46. 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)

47. positive Babinski sign

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

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

50. Conditions which cause increased
muscle tone
• Spasticity
– Stroke
• Rigidity
– Parkinsonism
• Lead pipe rigidity
• Cogwheel rigidity
• Brainstem lesions
– Decerebrate rigidity
– Decorticate rigidity

51. Reticular formation
• A set of network of interconnected
neurons located in the central
core of the brainstem
• It is made up of ascend-ing and
descend-ing fibers
• It plays a big role in fil-ter-ing
incom-ing stim-uli to
dis-crim-i-nate irrel-e-vant
back-ground stim-uli
• There are a large number of
neurons with great degree of
convergence and divergence

52. Functions
• Maintain consciousness, sleep and arousal
• Reticulospinal pathways are part of the
extrapyramidal tracts
• Several nuclei (PAG, NRM) are part of the
descending pain modulatory (inhibitory)
pathway

53. 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
• Purposeful movement

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

55. (Ref. Guyton)

57. basal ganglia
• caudate nucleus
• putamen
• globus pallidus
• subthalamic nuclei
• substantia nigra
corpus striatum
lentiform
nucleus

58. • 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
• They also have a role in cognitive functions.

59. Cortex
Thalamus
Putamen
globus
pallidus

60. Functions
• eg.
– writing letters of alphabet,
– cutting papers with scissors,
– hammering nails,
– passing a football,
– Vocalisation
– Cognitive control of movement

61. • 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

62. 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

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

64. Functions of Basal Ganglia
•
•
•
•
•
Motor control
Learning
Sensorimotor integration
Reward
Cognition

65. Basal Ganglia disorders
• Basal ganglia disorders are also called
extrapyramidal disorders
• Classical disorder is ―Parkinsonism‖
• Other disorders: Athetosis, Chorea,
Hemiballismus

66. 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

67. – 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

69. Physiology of
Posture
Prof. Vajira Weerasinghe
Dept of Physiology

71. Dynamic vs static nature of motor
control
• Static stability
– is dependent on the position of the centre of gravity
with respect to the base of support
• whereas dynamic stability
– is dependent more on the moment of inertia of the
body

72. Adult vs child
• In normal standing, a tall adult will have
a much larger moment of inertia than a
toddler
• Once the centre of gravity moves
outside the base of support the body
will begin to fall
– The adult with the large moment of inertia
will fall much more slowly and will therefore
have a longer time to react to prevent the
fall
– This is one of the reasons that young
children fall more often than adults.

73. Postural control
• Maintaining static nature of the body

74. maintenance of posture
• mainly to maintain the static
posture
• necessary for the stability of
movements
• involve a set of reflexes
• integrated at spinal cord, brain
stem and cortical level

75. normal postural control
• three inputs are required
– Vision
– Proprioception (joint position sense)
– Vestibular Mechanism (balance mechanisms)
– Cutaneous sensations

77. Postural reflexes
• Spinal cord reflexes
–
–
–
–
stretch reflex
positive supporting reaction (magnet reaction)
negative supporting reaction
mass reflex
• Brainstem refelxes
–
–
–
–
–
–
tonic labyrinthine reflex (vestibular)
tonic neck reflexes
labyrinthine righting reflex
neck righting reflex
body-on-head righting reflex
body-on-body righting reflex
• Cortical reflexes
– optical righting reflex
– placing reactions
– hopping reaction

78. • these reflexes are under higher centre inhibition
• transection of spinal cord or brain stem at
different levels release this inhibition
• then the relevant reflexes are seen

79. Retina
Occulomotor system
vestibular nuclei
cerebellum
complex pathways
vestibular
system
neck
receptors
pressure
& other
receptors
postural adjustments

80. cerebellum
• centre of motor coordination
• cerebellar disorders cause
–incoordination or ataxia

85. structure
• Cerebellum is divided into 3 lobes by 2
transverse fissures
– anterior lobe
– posterior lobe
– flocculonodular lobe

87. structure
– anterior lobe (paleocerebellum)
– large posterior lobe (neocerebellum)
– flocculonodular lobe (archicerebellum is the
oldest lobe)

88. • Anterior cerebellum and part of posterior
cerebellum
– receives information from the spinal cord
• Rest of the posterior cerebellum
– receives information from the cortex
• Flocculonodular lobe
– involved in controlling the balance through
vestibular apparatus

89. • Functionally cerebellum is divided into 3
areas medial to lateral
– lateral zone
– intermediate zone
– vermis

91. Inputs
•Corticopontocerebellar (cortical input)
•Olivocerebellar
•Vestibulocerebellar (balance, muscle tone, posture)
•Reticulocerebellar (muscle tone, posture)
•Spinocerebellar
Cerebellum
•(proprioception)
Outputs
Through deep cerebellar nuclei
Brain stem (extrapyramidal pathways)
Thalamus -> Cortex
Basal ganglia

92. Neuronal circuitry of the cerebellum
• Main cortical cells in cerebellum are known
as Purkinje Cells (large cells).
• There are about 30 million such cells.
• These cells constitute a unit which repeats
along the cerebellar cortex.

96. Functions of cerebellum
• planning of movements
• timing & sequencing of movements
• particularly during rapid movments such as
during walking, running
• from the peripheral feedback & motor cortical
impulses, cerebellum calculates when does a
movement should begin and stop

97. Motor Cortex
Thalamus
Cerebellum
brain
stem
nuclei
proprioceptive
tactile
feedback
Muscles

98. ‘Error correction’
• cerebellum receives two types of information
– intended plan of movement
• direct information from the motor cortex
– what actual movements result
• feedback from periphery
– these two are compared: an error is calculated
– corrective output signals goes to
• motor cortex via thalamus
• brain stem nuclei and then down to the anterior horn cell
through extrapyramidal tracts

99. • ‘Prevention of overshoot’
– Soon after a movement has been initiated
– cerebellum send signals to stop the movement at
the intended point (otherwise overshooting occurs)
• Ballistic movements
– rapid movements of the body, eg. finger movements
during typing, rapid eye movements (saccadic eye
movements)
– movements are so rapid it is difficult to decide on
feedback
– therefore the movement is preplanned
• Cerebellum perform motor learning (memory)

100. planning of movements
• mainly performed by lateral zones
• sequencing & timing
– lateral zones communicate with premotor areas,
sensory cortex & basal ganglia to receive the plan
– next sequential movement is planned
– predicting the timings of each movement

101. features of cerebellar disorders
• ataxia
– incoordination of movements
– ataxic gait
• broad based gait
• leaning towards side of the lesion
• dysmetria
– cannot plan movements
• past pointing & overshoot
• decomposition of movements
• intentional tremor

102. features of cerebellar disorders
• Dysdiadochokinesis (adiadochokinesis)
– unable to perform rapidly alternating movements
• dysarthria
– slurring of speech
• nystagmus
– oscillatory movements of the eye

103. features of cerebellar disorders
• hypotonia
– reduction in tone
• due to reduction in excitatory influence on gamma motor
neurons by cerebellum (through vestibulospinal tracts)
• decreased reflexes
• head tremor
• head tilt
• In unilateral cerebellar lesions, incoordination
occurs in the ipsilateral side

104. • But what finally drives us to action???
•perhaps motivation
•motivation is controlled by limbic
system and hypothalamus

105. Limbic system

107. limbic system
• nuclei
–
–
–
–
amygdala
septal nuclei
mammillary body
hypothalamus
• cortical areas
–
–
–
–
hippocampal gyrus
cingulate gyrus
dentate gyrus
entorhinal, amygdaloid cortex
• paralimbic structures
• orbital gyrus, insula, nucelus accumbens, thalamic
nuclei, superior temporal gyrus,
• fibre tracts: fornix, medial forebrain bundle

108. limbic cortex
• consist of 3 layered cortex (in contrast to 6
layered cortex of the neocortex)

109. • Limbic system is a link between the
brain stem and neocortex
• Limbic structures are connected to
each other and with the association
cortex and the brain stem

110. • Medial forebrain bundle is a major efferent
connection of the limbic system:
• projected to the hypothalamus, reticular formation. Influence on
autonomic and endocrine activity
• Amygdala receives inputs from olfactory pathways
• Connections with the neocortex provide a
synthesis of emotional and rational thought

111. Functions
Limbic system is also referred to as the
‘emotional brain’
• Emotional (include motor activity)
• Behavioural (Motivations, Drives: appetite,
thirst, sexual behaviour, Reward system)
• Memory
– Utilizes the hypothalamus to effect the physical manifestations
associated with emotions, etc.

112. Complex role of the limbic system
• as an intermediary between
– external events (carried to the CNS via afferents)
– our processing of those events (involving cortical
and subcortical brain areas)
– our responses to those events (both behavioral and
autonomic)

113. Role in memory storage
• Working memory—short term
– cortical phenomenon
• Explicit (declarative)—factual knowledge
– temporal events, stored in hippocampus
• Examples: what innervates biceps femoris m.?
• Implicit (procedural)—learned skills
– unconsciously recalled—includes emotional
responses—stored in amygdala (at least in part)
• Examples: writing, playing a musical instrument

114. Hippocampus
• is a part of the brain located
inside the temporal lobe
• plays a major role memory
consolidation
• responsible for spatial memory
• might act as a cognitive map —
a neural representation of the
layout of the environment.
• In Alzheimer's disease, the
hippocampus becomes one of
the first regions of the brain to
suffer damage