Week 2 - PT 712

Orientation

Ability to maintain an appropriate relationship between the body segments and the environment to complete a task

Stability

Ability to control the COM in relationship to BOS

Center of Mass (COM) vs Center of Pressure (COP) 

Center of Mass: point at center of total body mass

Center of Pressure: center of distribution of total force applied to the supporting surface 

Cerebellum Function 

Control of adaptation; modifies postural muscle amplitude in response to changing task and environmental conditions 

Basal Ganglia Function

Control of postural set; ability to quickly change muscle patterns in response to changing task and environmental conditions

Brainstem Level Functions

Postural tone

Circuits for automatic postural synergies

Vestibular contributions to postural control

Spinal Preparation (SC) Function 

Ground reaction forces for orientation 

Tonically active extensor muscle for antigravity support for postural orientation 

No lateral stability 

Somatosensory contributions to postural control 

Head Righting vs Body Righting

Head righting: aligns the eyes with the horizon and the head with the trunk

Body righting: contributes to movement around the body axis (necessary to assume anti-gravity positions)

Equilibrium Reactions 

Provide balance when the center of gravity is disturbed 

Are righting reactions or equilibrium reactions more mature?

Equilibrium; they include counter-rotation of the head and trunk away from the direction of the displacement and use the extremities

Higher CNS centers have to mature for equilibrium reactions to develop 

Central Set

The state of the nervous system that is influenced or determined by the context of a task

Enables the CNS to optimize postural responses under new task conditions

Clinical Test of Sensory Integration and Balance (CTSIB) 

Tests patient’s ability to maintain standing balance for 30 sec under 6 different sensory conditions that either eliminate input or produce inaccurate visual or surface orientation inputs 

Determines how sensory information is used to maintain vertical orientation 

Adaptive Postural Control

Ability to modify sensory and motor systems in response to changing task and environmental demands

How we maintain postural control while moving through space

An aspect of all 3 types of normal postural control

Steady State Postural Control 

The ability to control the location of the body’s COM within the BOS in predictable, quasi-static conditions 

Anticipatory Postural Control

The ability to generate postural adjustments prior to the onset of and during voluntary movement for the purpose of countering an upcoming disturbance or realigning the body’s COM prior to changing the BOS

Reactive Postural Control

The ability to response to a sensory input that signals a need for a response to ensure successful maintenance of postural control

Need for a response is unexpected and generated externally or secondarily to an internally generated movement

Underlying Determinants of Balance 

• ROM

• Flexibility (joint mobility, muscle length) 

• Muscle performance (strength, power, endurance) 

• Alignment (posture) 

Executive Function

A set of complex cognitive skills including insight, judgement, memory, problem solving, and attention

Responsible for the planning, initiation, sequencing, and monitoring of goal-directed behavior

Arousal vs Alertness 

Arousal: responsiveness to stimuli 

Alertness: a basic arousal process that allows the individual to respond to external stimuli 

Where do righting reactions occur?

At the head/neck

Where do equilibrium reactions occur?

At the trunk and limbs

Where do protective reactions occur? 

In the extremities 

Spinocerebellum Input Source

Spinal cord

Spinocerebellum Division Function

• Movement of distal (paravermis) and proximal (vermis) muscles

• Dynamic control of ongoing movement

• Comparator of planned and executed movements aka error detection

Cerebrocerebellum Input Source 

Cerebral cortex 

Cerebrocerebellum Division Function

• Motor planning, regulation of highly skilled movements

• Uses information about current body position to plan and predict movement aka anticipatory postural control

• Regulates visual guidance of ongoing movement (via higher order visual association areas of cerebral cortex)

Vestibulocerebellum Input Source 

Vestibular nuceli 

Inferior olivary nucleus 

Vestibulocerebellum Division Function

Posture, equilibrium, vestibular-ocular reflex

Which pathway controls conscious proprioception?

Dorsal column-medial lemniscus (DCML)

Which pathway controls unconscious prooprioception?

Spinocerebellar tracts

Conscious vs Unconscious Proprioception 

Conscious: activation of muscles voluntarily according to sensory information

Unconscious: activation of muscles according to sensory information without having to think about the movement

Function of Conscious Proprioception

Awareness of body position and voluntary movement

Function of Unconscious Proprioception

Unconscious motor response to sensory stimulus

Where does the conscious proprioception pathway end up?

Cerebral cortex

Where does the unconscious proprioception pathway end up? 

Cerebellum

Which is the largest of the cerebellar peduncles?

Middle cerebellar peduncle

What are the input pathways of the cerebellum?

Cerebral cortex via pontine nuclei from the middle cerebellar peduncle 

Vestibular nuclei complex

Spinal cord via spinocerebellar tracts

Inferior olivary nucleus

Inputs to the inferior cerebellar peduncle

What are the output pathways of the cerebellum?

Deep cerebellar nuclei to the cerebral cortex via the superior cerebellar peduncle 

Vestibular complex to the vestibulospinal tracts and vestibulo-ocular pathways through the inferior cerebellar peduncle

Climbing Fibers

Afferent fibers coming from the inferior olive going to the cerebellar cortex 

Mossy Fibers

Afferent fibers going to the cerebellum 

Purkinje Fibers

Efferent fibers from the cerebral cortex to the cerebral nuclei

All output from the CB cortex is via purkinje cells

Why does the vestibular complex move directly via the inferior cerebellar peduncle (and bypass the deep nuclei)? 

So that we can access vestibulo-ocular reflexes more quickly and maintain balance

Do we expect hypertonia or hypotonia with cerebellar damage?

Hypotonia

True or False: The cerebellum communicates with LMNs directly.

False

Consequences of Cerebellar Damage

• Persistent errors in movement, lack of coordination (ataxia)

• Errors on the same side as the cerebellar lesion

• Hypotonia

• Impaired oculomotor control

• Difficulties in motor learning

• Difficulties with adaptation, learning new skills

Dyssynergia/Ataxia 

Breakdown of normal coordinated voluntary movement 

Inability to correctly sequence intersegmental movements 

Disordered contraction of agonist and antagonistic muscles resulting in lack of coordinated movement 

Dysarthria

Impaired ability to control muscles used for speech

Impairments in slurred speech, difficulty speaking

Dysmetria

Impaired ability to control distance and speed of movement

Results in undershooting or overshooting movements

Can affect limbs, speech, eye movements

Dysdiadochokinesia  

Impaired ability to perform rapid, alternating movements 

Intention Tremor

Involuntary oscillating movement occurring with action

Sensory Ataxia

Loss of sensory input (DCML disruption)

Impaired conscious proprioception

CL ataxia if lesion in thalamus, thalamic radiation, somatosensory cortex

Ipsilateral ataxia if due to lesions of dorsal columns or peripheral nerves

Cerebellar Ataxia 

Result of damage to the cerebellum 

No primary sensory impairment 

Only minimally worse with eyes closed (unstable with eyes open) 

Ipsilateral ataxia 

What areas would a posterior lobe lesion impact?

Cognition

Emotion/limbic

Autonomic function

Cerebellar cognitive affective syndrome

What is the order of the deep cerebellar nuclei (lateral to medial)?

Dentate → Interposed (Emboliform → Globose) → Fastigial

Role of Cerebellum in Motor Control

• Balance

• Equilibrium

• Muscle tone

• Coordination

• Motor learning

Are afferent pathway fibers inhibitory or excitatory? 

Excitatory 

Are efferent pathway fibers inhibitory or excitatory?

Inhibitory

Does coordinated movement involve distal or proximal fixation?

Proximal fixation to allow for distal mobilization (proximal stability allows for distal mobility)

Dexterity 

Skillful use of fingers during fine motor tasks 

Agility

Ability to rapidly and smoothly initiate, stop, modify movement while maintaining postural control

What needs to be screened prior to completing a coordination examination?

• ROM

• Muscle performance

• Sensory integrity (sensation)

Coordination Impairments 

Related to the location of CNS lesions, often associated with restrictions in activity and participation

What are the two key areas of the CNS that act together with the cortex to produce coordinated movement? 

Cerebellum & Basal Ganglia 

Intra-limb vs Inter-limb Coordination Exam

Intra-limb: examines each UE or LE at once (self-selected and fast speeds)

Inter-limb: examines both UEs or LEs simultaneously (self-selected and fast speeds)

Which cranial nerves are at the level of the midbrain?

III, IV

Which cranial nerves are at the level of the pons?

V, VI, VII, VIII

Which cranial nerves are at the level of the medulla?

IX, X, XII

Which cranial nerves are at the level of the spinal cord?

XI

Solitary Nucleus (Autonomic) CNs

VII, IX, X

Nucleus Ambiguous CNs

IX, X, XI

Spinal Trigeminal Nucleus CNs

V, IX, X