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Neurophysiology lecture topics
1. Role of brainstem and reticular formation
2. Ascending and descending tracts
muscle powe...
Brains stem
• Midbrain
• Pons
• Medulla
Role of brainstem
•
•
•
•
•

•
•
•
•
•

Intermediate centre in controlling motor functions
Ascending and descending pathwa...
Reticular formation
• Located in the core of the
brainstem
• Network of neurons
• Main centre of ascending
and descending ...
Ascending pathways
• Somatosensory pathways
– Dorsal column – medial lemniscus pathway
– Spinothalamic tracts
• Anterior s...
Sensory area
in the brain

Ascending
Sensory pathway

Central Connections
Sensory nerve

Touch stimulus
Receptor
Sensory
m...
Two main ascending pathways
• Dorsal column - medial lemniscus
pathway
fast pathway

• Spinothalamic pathway
slow pathway
...
Spinothalamic pathway
Dorsal column pathway

Lateral
Spinothalamic
tract
Anterior
Spinothalamic
tract
Dorsal column pathway
• touch: fine degree
• highly localised touch
sensations
• vibratory sensations
• sensations signall...
3rd
order
neuron

thalamocortical tracts
internal capsule
thalamus
Medial lemniscus
Dorsal column nuclei

2nd
order
neuron...
3rd
order
neuron

thalamocortical tracts
internal capsule
thalamus

Spinothalamic
tracts

2nd
order
neuron

1st
order
neur...
Proprioceptive pathways
• Dorsal column – medial lemniscus –
thalamocortical pathway (conscious
proprioception)

• Spinoce...
Main descending pathways
• Motor pathways
• Corticospinal and corticobulbar tracts

• Starts from the motor cortex
Motor cortex
• Located in the frontal lobe
• Precentral gyrus
Motor homunculus
First discovered
by
Penfield
Corticospinal tract (Pyramidal tract)
• Starts from large cortical cells (pyramidal
cells) in the primary motor cortex
• T...
Course of the corticospinal tract
• Descends through
– internal capsule
– at the medulla
• cross over to the other side

–...
internal capsule

Upper
motor
neuron

Medulla

anterior horn cell

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

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

gamma motor neuron

alpha moto...
Arrangement at the
anterior horn cell

gamma motor neuron

alpha motor neuron

corticospinal tract
alpha motor neuron
• this is also called the final common pathway
• Contraction of the muscle occurs through this
whether
...
Upper motor neuron
• Consists of
– Corticospinal tract (pyramidal tract)
– Extrapyramidal tracts
Extrapyramidal tracts
• starts at the brain stem
• descends down either ipsilaterally or
contralaterally
• ends at the ant...
Reticulospinal tract
• Starts from the reticular formation

• Maintain normal postural tone
• Controls mainly gamma motorn...
Reticular formation
• Loosely arranged cell bodies
in the central core of the brain
stem

midbrain

pons

• Pontine reticu...
Vestibulospinal tract
• Starts from the vestibular nuclei (present in the medullar region)

• Excitatory to alpha motor ne...
• Rubrospinal and tectospinal tracts are not
functionally important in human nervous system
pyramidal tracts
extrapyramidal tracts

Upper
motor
neuron

alpha motor neurone
gamma motor neurone

Lower
motor
neuron
Suprasegmental control of reflexes and
muscle tone
• Alpha motor neuron is the final pathway
• Gamma motor neuron control
...
Extrapyramidal
tracts

•Voluntary movement
•Muscle tone

Gamma
motor
neuron

Corticospinal
tract

Alpha motor
neuron

Musc...
Clinical Importance of the motor system
examination
• Tests of motor function:
– Muscle power
• Ability to contract a grou...
Basis of tests
• Muscle power
– Test the integrity of motor cortex, corticospinal tract
and lower motor neuron

• Muscle t...
Muscle tone
• Resistance against passive movement
– Gamma motor neuron activate the spindles
– Stretching the muscle will ...
Clinical situations
• Muscle power
– Normal
– Reduced (muscle weakness)
• muscle paralysis
• muscle paresis

• Muscle tone...
Main abnormalities
• Muscle Weakness / paralysis
– Reduced muscle power

• Flaccidity
– Reduced muscle tone

• Spasticity
...
• Lower motor neuron lesion causes
– flaccid paralysis (flaccid weakness)

• Upper motor neuron lesion causes
– spastic pa...
Lower motor neuron lesion
•
•
•
•
•
•

muscle weakness
flaccid paralysis
muscle wasting (disuse atrophy)
reduced muscle to...
Muscle wasting
Fasciculations
Upper motor neuron lesion
•
•
•
•
•
•
•
•

muscle weakness
spastic paralysis
increased muscle tone (hypertonia)
reflexes: ...
Clonus
Clasp knife effect
Stroke patient walking
Babinski sign
• when outer border of the sole of the foot is
scratched
• upward movement of big toe
• fanning out of other...
positive Babinski sign
Site of lesions
Cortex

Internal capsule
Brain stem

Spinal cord
Anterior horn cell
Motor nerve
Neuromuscular junction
Mus...
Site of lesions

quadriplegia (tetraplegia)
all 4 limbs are affected
cervical cord or brain stem lesion
hemiplegia
one hal...
Conditions which cause increased
muscle tone
• Spasticity
– Stroke

• Rigidity
– Parkinsonism
• Lead pipe rigidity
• Cogwh...
Reticular formation
• A set of network of interconnected
neurons located in the central
core of the brainstem
• It is made...
Functions
• Maintain consciousness, sleep and arousal
• Reticulospinal pathways are part of the
extrapyramidal tracts
• Se...
Basal ganglia
• These are a set of deep nuclei
located in and around the basal
part of the brain that are involved
in moto...
Basal ganglia
• Caudate nucleus
• Putamen
• Globus pallidus
–(internal and external)

• Subthalamic nuclei
• Substantia ni...
(Ref. Guyton)
basal ganglia
• caudate nucleus
• putamen
• globus pallidus
• subthalamic nuclei
• substantia nigra

corpus striatum
lenti...
• Interconnecting circuitry through these nuclei
• These circuits start from the cortex and ends in
the cortex
• These cir...
Cortex

Thalamus
Putamen
globus
pallidus
Functions
• eg.
– writing letters of alphabet,
– cutting papers with scissors,
– hammering nails,
– passing a football,
– ...
• Some of these circuits are excitatory and
some inhibitory
• This depends on the neurotransmitter
involved.

• Inhibitory...
Following pathways are known:

• Dopamine pathway from substantia nigra to
caudate nucleus and putamen
• GABA pathway from...
glutamate

Thalamus
Reticular formation

+

striatum

Cortex
Interneurons: Ach +
Caudate

Putamen

Dopamine
Thalamus

GABA...
Functions of Basal Ganglia
•
•
•
•
•

Motor control
Learning
Sensorimotor integration
Reward
Cognition
Basal Ganglia disorders
• Basal ganglia disorders are also called
extrapyramidal disorders
• Classical disorder is ―Parkin...
Parkinsonism
• due to destruction of dopamine secreting pathways from
substantia nigra to caudate and putamen.
– also call...
– expressionless face
– flexed posture
– soft, rapid, indistinct speech
– slow to start walking
– rapid, small steps, tend...
Physiology of
Posture
Prof. Vajira Weerasinghe
Dept of Physiology
Dynamic vs static nature of motor
control
• Static stability
– is dependent on the position of the centre of gravity
with ...
Adult vs child
• In normal standing, a tall adult will have
a much larger moment of inertia than a
toddler
• Once the cent...
Postural control
• Maintaining static nature of the body
maintenance of posture
• mainly to maintain the static
posture
• necessary for the stability of
movements
• involve a set ...
normal postural control
• three inputs are required
– Vision
– Proprioception (joint position sense)
– Vestibular Mechanis...
Postural reflexes
• Spinal cord reflexes
–
–
–
–

stretch reflex
positive supporting reaction (magnet reaction)
negative s...
• these reflexes are under higher centre inhibition
• transection of spinal cord or brain stem at
different levels release...
Retina

Occulomotor system

vestibular nuclei
cerebellum

complex pathways

vestibular
system

neck
receptors

pressure
& ...
cerebellum
• centre of motor coordination
• cerebellar disorders cause
–incoordination or ataxia
structure
• Cerebellum is divided into 3 lobes by 2
transverse fissures
– anterior lobe
– posterior lobe
– flocculonodular...
structure
– anterior lobe (paleocerebellum)
– large posterior lobe (neocerebellum)
– flocculonodular lobe (archicerebellum...
• Anterior cerebellum and part of posterior
cerebellum
– receives information from the spinal cord

• Rest of the posterio...
• Functionally cerebellum is divided into 3
areas medial to lateral
– lateral zone
– intermediate zone
– vermis
Inputs
•Corticopontocerebellar (cortical input)
•Olivocerebellar
•Vestibulocerebellar (balance, muscle tone, posture)
•Ret...
Neuronal circuitry of the cerebellum
• Main cortical cells in cerebellum are known
as Purkinje Cells (large cells).
• Ther...
Functions of cerebellum
• planning of movements
• timing & sequencing of movements
• particularly during rapid movments su...
Motor Cortex

Thalamus
Cerebellum

brain
stem
nuclei

proprioceptive
tactile
feedback

Muscles
‘Error correction’
• cerebellum receives two types of information
– intended plan of movement
• direct information from th...
• ‘Prevention of overshoot’
– Soon after a movement has been initiated
– cerebellum send signals to stop the movement at
t...
planning of movements
• mainly performed by lateral zones
• sequencing & timing
– lateral zones communicate with premotor ...
features of cerebellar disorders
• ataxia
– incoordination of movements
– ataxic gait
• broad based gait
• leaning towards...
features of cerebellar disorders
• Dysdiadochokinesis (adiadochokinesis)
– unable to perform rapidly alternating movements...
features of cerebellar disorders
• hypotonia
– reduction in tone
• due to reduction in excitatory influence on gamma motor...
• But what finally drives us to action???

•perhaps motivation
•motivation is controlled by limbic
system and hypothalamus
Limbic system
limbic system
• nuclei
–
–
–
–

amygdala
septal nuclei
mammillary body
hypothalamus

• cortical areas
–
–
–
–

hippocampal...
limbic cortex

• consist of 3 layered cortex (in contrast to 6
layered cortex of the neocortex)
• Limbic system is a link between the
brain stem and neocortex
• Limbic structures are connected to
each other and with th...
• Medial forebrain bundle is a major efferent
connection of the limbic system:
• projected to the hypothalamus, reticular ...
Functions
Limbic system is also referred to as the
‘emotional brain’
• Emotional (include motor activity)
• Behavioural (M...
Complex role of the limbic system
• as an intermediary between
– external events (carried to the CNS via afferents)
– our ...
Role in memory storage
• Working memory—short term
– cortical phenomenon

• Explicit (declarative)—factual knowledge
– tem...
Hippocampus
• is a part of the brain located
inside the temporal lobe
• plays a major role memory
consolidation
• responsi...
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
Dental lecture: brain stem, ascending and descending pathways
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Dental lecture: brain stem, ascending and descending pathways

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Transcript of "Dental lecture: brain stem, ascending and descending pathways "

  1. 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. 2. Brains stem • Midbrain • Pons • Medulla
  3. 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. 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. 5. Ascending pathways • Somatosensory pathways – Dorsal column – medial lemniscus pathway – Spinothalamic tracts • Anterior spinothalamic tract • Lateral spinothalamic tract – Spinocerebellar tracts • Dorsal • Ventral
  6. 6. Sensory area in the brain Ascending Sensory pathway Central Connections Sensory nerve Touch stimulus Receptor Sensory modality
  7. 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. 8. Spinothalamic pathway Dorsal column pathway Lateral Spinothalamic tract Anterior Spinothalamic tract
  9. 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. 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. 11. 3rd order neuron thalamocortical tracts internal capsule thalamus Spinothalamic tracts 2nd order neuron 1st order neuron
  12. 12. Proprioceptive pathways • Dorsal column – medial lemniscus – thalamocortical pathway (conscious proprioception) • Spinocerebellar pathway (unconscious proprioception)
  13. 13. Main descending pathways • Motor pathways • Corticospinal and corticobulbar tracts • Starts from the motor cortex
  14. 14. Motor cortex • Located in the frontal lobe • Precentral gyrus
  15. 15. Motor homunculus First discovered by Penfield
  16. 16. 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
  17. 17. 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
  18. 18. internal capsule Upper motor neuron Medulla anterior horn cell Lower motor neuron
  19. 19. Motor system • Consists of – Upper motor neuron • Corticospinal tract (pyramidal tract) • Extrapyramidal tracts – Lower motor neuron • Alpha motor neuron • Gamma motor neuron
  20. 20. Lower motor neuron • consists of mainly • alpha motor neuron – and also gamma motor neuron gamma motor neuron alpha motor neuron
  21. 21. Arrangement at the anterior horn cell gamma motor neuron alpha motor neuron corticospinal tract
  22. 22. 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
  23. 23. Upper motor neuron • Consists of – Corticospinal tract (pyramidal tract) – Extrapyramidal tracts
  24. 24. Extrapyramidal tracts • starts at the brain stem • descends down either ipsilaterally or contralaterally • ends at the anterior horn cell • modifies the motor functions
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. • Rubrospinal and tectospinal tracts are not functionally important in human nervous system
  29. 29. pyramidal tracts extrapyramidal tracts Upper motor neuron alpha motor neurone gamma motor neurone Lower motor neuron
  30. 30. 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
  31. 31. 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
  32. 32. 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
  33. 33. 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
  34. 34. 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
  35. 35. Clinical situations • Muscle power – Normal – Reduced (muscle weakness) • muscle paralysis • muscle paresis • Muscle tone – Normal – Reduced • Hypotonia (Flaccidity) – Increased • Hypertonia (Spasticity)
  36. 36. Main abnormalities • Muscle Weakness / paralysis – Reduced muscle power • Flaccidity – Reduced muscle tone • Spasticity – Increased muscle tone
  37. 37. • Lower motor neuron lesion causes – flaccid paralysis (flaccid weakness) • Upper motor neuron lesion causes – spastic paralysis (spastic weakness)
  38. 38. 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
  39. 39. Muscle wasting
  40. 40. Fasciculations
  41. 41. 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
  42. 42. Clonus Clasp knife effect
  43. 43. Stroke patient walking
  44. 44. 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)
  45. 45. positive Babinski sign
  46. 46. Site of lesions Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle
  47. 47. 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
  48. 48. Conditions which cause increased muscle tone • Spasticity – Stroke • Rigidity – Parkinsonism • Lead pipe rigidity • Cogwheel rigidity • Brainstem lesions – Decerebrate rigidity – Decorticate rigidity
  49. 49. 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
  50. 50. 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
  51. 51. 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
  52. 52. Basal ganglia • Caudate nucleus • Putamen • Globus pallidus –(internal and external) • Subthalamic nuclei • Substantia nigra International Basal Ganglia Society
  53. 53. (Ref. Guyton)
  54. 54. basal ganglia • caudate nucleus • putamen • globus pallidus • subthalamic nuclei • substantia nigra corpus striatum lentiform nucleus
  55. 55. • 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.
  56. 56. Cortex Thalamus Putamen globus pallidus
  57. 57. Functions • eg. – writing letters of alphabet, – cutting papers with scissors, – hammering nails, – passing a football, – Vocalisation – Cognitive control of movement
  58. 58. • 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
  59. 59. 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
  60. 60. glutamate Thalamus Reticular formation + striatum Cortex Interneurons: Ach + Caudate Putamen Dopamine Thalamus GABA globus pallidus Subthalamic nucleus GABA Substantia nigra Reticular formation
  61. 61. Functions of Basal Ganglia • • • • • Motor control Learning Sensorimotor integration Reward Cognition
  62. 62. Basal Ganglia disorders • Basal ganglia disorders are also called extrapyramidal disorders • Classical disorder is ―Parkinsonism‖ • Other disorders: Athetosis, Chorea, Hemiballismus
  63. 63. 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
  64. 64. – 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
  65. 65. Physiology of Posture Prof. Vajira Weerasinghe Dept of Physiology
  66. 66. 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
  67. 67. 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.
  68. 68. Postural control • Maintaining static nature of the body
  69. 69. 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
  70. 70. normal postural control • three inputs are required – Vision – Proprioception (joint position sense) – Vestibular Mechanism (balance mechanisms) – Cutaneous sensations
  71. 71. 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
  72. 72. • 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
  73. 73. Retina Occulomotor system vestibular nuclei cerebellum complex pathways vestibular system neck receptors pressure & other receptors postural adjustments
  74. 74. cerebellum • centre of motor coordination • cerebellar disorders cause –incoordination or ataxia
  75. 75. structure • Cerebellum is divided into 3 lobes by 2 transverse fissures – anterior lobe – posterior lobe – flocculonodular lobe
  76. 76. structure – anterior lobe (paleocerebellum) – large posterior lobe (neocerebellum) – flocculonodular lobe (archicerebellum is the oldest lobe)
  77. 77. • 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
  78. 78. • Functionally cerebellum is divided into 3 areas medial to lateral – lateral zone – intermediate zone – vermis
  79. 79. 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
  80. 80. 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.
  81. 81. 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
  82. 82. Motor Cortex Thalamus Cerebellum brain stem nuclei proprioceptive tactile feedback Muscles
  83. 83. ‘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
  84. 84. • ‘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)
  85. 85. 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
  86. 86. 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
  87. 87. features of cerebellar disorders • Dysdiadochokinesis (adiadochokinesis) – unable to perform rapidly alternating movements • dysarthria – slurring of speech • nystagmus – oscillatory movements of the eye
  88. 88. 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
  89. 89. • But what finally drives us to action??? •perhaps motivation •motivation is controlled by limbic system and hypothalamus
  90. 90. Limbic system
  91. 91. 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
  92. 92. limbic cortex • consist of 3 layered cortex (in contrast to 6 layered cortex of the neocortex)
  93. 93. • 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
  94. 94. • 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
  95. 95. 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.
  96. 96. 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)
  97. 97. 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
  98. 98. 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
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