Neuroanatomy L8: Control of posture Flashcards
Postural control is the maintenance of _______ and ______ of body segments
body orientation; stability (balance)
What is the definition of postural orientation?
the relationship of body segments to each other, to the task, and to the environment
Postural control is the maintenance of ______ or center of mass within base of support while standing or sitting still, when the base of support does not change
postural stability
Postural control is the ability to regain postural _____ after external stimulus or perturbation, with or without a change in _____
stability; base of support
Postural control is the ability to maintain and regain postural stability after ________ movements, like moving limbs relative to the body.
self-initiated
Normal erect posture characterized by ____ (large/small) anterior posterior, and medial lateral oscillations over a fixed base of support. What is this due to?
small
Due to small bursts of electrical activity in the muscles.
A bodies centre of mass (COM - represents the _______ of the matter in a body or system) is typically just anterior to the S1 vertebrae
mean position
What does a body’s centre of mass (COm) represent? Where is it usually?
The mean position of the matter in a body or system
Is typically just anterior to the S1 vertebrae
In quiet erect standing, the body’s COM passes very close to the ____, slightly anterior to the _____, close to the ______, slightly anterior to the ______, and anterior to the _______.
ear; acromion process of the scapula; greater trochanter; knee joint; ankle joint
What are the 5 important structures that the body’s COM passes through in quiet erect standing?
- very close to the ear
- slightly anterior to the acromion process of the scapula
- close to the greater trochanter
- slightly anterior to the knee joint
- anterior to the ankle joint
A body’s _________ represents a single point on a surface through which the resultant force passes. This is within the _____ during quiet stance.
centre of pressure (COP); “foot print”
What does a body’s centre of pressure (COP) represent?
a single point on a surface through which the resultant force passes
____ fluctuates during quiet standing with our body sway. Explain this with a 20 year old, healthy individual. Be specific with A-P and M-L direction and the mm displacement.
COP
Fluctuations are greater in the A-P direction, and there is only a small M-L change. 10mm displacement of AP
How does postural sway change between age (eg. 86 year old and 20 year old)?
Postural sway is increases with age
Increased AP and ML sway in 86 year old
There is some association with _____increase and occurrence of retrospective falls and prospective falls. In fact, ______ is greater in people who have fallen before, and who are likely to fall in the near future.
COP; Postural sway
Why is postural sway is greater in older people?
Altered ability to interpret or detect sensory information (ie. impaired vision) and activate muscles to respond efficiently (reduced strength and muscle atrophy with age).
Changes in sensory information (input), and motor ability (output)
What are 3 sensory inputs to the postural control system?
- Visual
- Vestibular
- Somatosensory
How does visual input connect to the postural control system?
Lighting; movement of self or environment
How does vestibular input connect to the postural control system?
Gravity; Linear & Angular Head and Eye Movement
How does somatosensory input connect to the postural control system?
Proprioception and tactile (eg. muscle spindles)/(Also skin sensation (ie. how much stretch can be felt in the skin indicates joint position).). Surface changes & irregularities; Base of support changes
___ input is affected with age.
vestibular
CNS selects and weights inputs based upon: _______, ________, ______ to task
Availability; Accuracy; Value
What are 3 factors the CNS uses to select and weight inputs? Give an example of this concept when it is dark (loss of visual input)
- Availability
- Accuracy
- Value
ie. if it is dark, the nervous system will place more emphasis on information from the vestibular and somatosensory systems to control balance.
These multisensory (visual, vestibular and somatosensory) inputs can elicit quick changes in _____. Particularly when the brain predicts sensory inputs, but received _____ information. The _____ compares descending motor plan with _______ to make adjustments to the motor plan to _____ to a situation.
posture; different; cerebellum; sensory input; adapt
CNS corrects the body’s motion based on the error between the predicted and actual sensory inputs. Why? Fast processing power…Also long term adaptations
adapt to plan on the run to keep “us” stable
Based on a study done COP, what did 2 repetitions of 30s with a participant with “Foam Eyes Closed” show? Why?
5cm AP displacement, 4-6cm ML displacement
Loss of visual input impairs the ability to modulate the motor output, and results in increased sway.
With firm eyes open (control), firm eyes closed, foam eyes open and foam eyes opened, rate the order of least to most postural sway?
- Firm eyes open
- Foam eyes open
- Firm eyes closed
- Foam eyes closed
What happens in firm eyes open?
The firm surface provides more reliable sensory information, and allows the motor output to be modulated more effectively - resulting in less postural sway to maintain balance.
What happens in firm eyes closed?
proprioceptive input- maintain posture
visual input disrupted- eyes closed
What happens in foam eyes open?
visual input- helped to maintain posture
proprioceptive input disruptuve- from base of feet
What happens in foam eyes closed?
Both visual and proprioceptive input are both disrupted
Postures are maintained by a combination of _______ and _______ structures. Give examples of both.
active (muscle contraction); passive (primarily connective tissue including within musculotendinous units)
What are 2 factors that the postural control system must respond to (or prepare for)?
- Externally generated stimuli/perturbations
- Internally generated (self initiated) stimuli/perturbations
What are externally generated stimuli/perturbations and how must the postural control system respond to (or prepare for) it? List 2 factors.
- Constant (or longer term) environmental forces:
- e.g. Gravity, merry-go-round! (not constant (changing) but long term- must adapt)
- Occasional environmentally generated forces:
- e.g. Ground reaction forces, being pushed / support being removed, catching/hitting a ball.
What are internally generated stimuli/perturbations and how must the postural control system respond to (or prepare for) it?
- Rhythmical internally generated forces
- e.g. Breathing (When a muscle contracts, or when we breath, the balance is perturbed (ie. the centre of mass is disturbed by the internal forces), and the nervous system must account for this), gait
- Occasional internally generated forces
- e.g. Coughing/laughing, preparing to catch a ball
We learn through ______ how to prepare and respond to ______ and __________ perturbations
exposure; external; internal
What are the function of the motor areas of the the cerebral cortex?
Planning and initiation of voluntary movement, including postural components of voluntary movement
What are the function of the cerebellum?
Sensory motor integration & learning
What are the function of the brainstem?
Basic movement and posture
What are the function of the spinal cord?
Reflex activity (involuntary movements
The cerebellum contributes to ______, _______, ______ and _______ movement.
coordination; precision; timing; refining
The cerebellum receives and integrates ______ input, and _______ input (the motor plan), and fine-tunes _____ activity.
cortical; motor
What are 2 disorders that cerebellar damage is associated with?
- Voluntary movements
- Postural control
How are voluntary movements associated with cerebellar damage? Short and long term.
Short term: Errors in force, direction, speed of movement
Longer term: “Motor learning”, refining movement over time
How are postural control associated with cerebellar damage?
- Balance
- Gait pattern
- wide stance
- Hypotonia (decreased muscle tone)
How is wide stance associated with cerebellar damage?
Wide stance is an adaptation to increase the base of support (esp. with no cerebellar correction)
The _____ and the ______ tracts begin in the brainstem, and receive collaterals from the pyramidal tracts.
Corticospinal; Corticobulbar
Upper motor nuerons begin in the ____, and descend to the ______.
cerebral cortex; spinal cord
Upper motor neurons (UMNs) refer to all motoneurons that arise from ____ and the _____ that influence the activity of __________.
cortex; brainstem; lower motoneurons (LMN).
What do upper motor neurons (UMNs) refer to?
all motoneurons that arise from cortex and brainstem that influence the activity of lower motoneurons (LMN)
UMN within the ______ tract connect to ______, and control movement of the _____, _______ and the ______.
corticospinal; LMN’s; torso; upper; lower limbs
UMN from the corticospinal tract divide into those from the _____ and ______corticospinal tracts.
lateral; anterior
What are 2 corticospinal tracts that the UMN are divided into?
- Lateral
- Anterior
UMN from the lateral corticospinal tract transmit the neural signal to produce ______ movements of the ______.
voluntary; distal extremities
UMN from the anterior corticospinal tract are responsible for _______ that occur to compensate for
postural adjustments; voluntary movements
Corticobulbar UMN primarily originate in the _____.
primary motor cortex
The corticobulbar UMN have indirect connections (polysynaptic) between ______ and ______ via the ______, cerebellum and _____.
cortex; LMN; basal ganglia; brainstem nuclei
Interaction with sensory information, refines the _____ signal for the corticalbulbar tract.
descending
Other UMN (eg from the vestibulospinal tracts) initiate _______ in response to changes in balance
postural adjustments
What is the function of the corticobulbar tract?
Facilitates the maintenance of balance and posture
What are the 4 motor outputs important for the postural control system?
EXAM QUESTION- describe
Voluntary >>> Anticipatory >> Automatic >>> Reflex
What are 6 features of the “voluntary” motor output that affects the postural control system?
- Cortically driven (Highly regulated by the pyramidal tract)
- Self-generated or in response to an external stimuli
- 200+ milliseconds from initiation of signal in the cortex (This is a long time in terms of responding to dangerous stimuli)
- Purposeful activities
- Complex and coordinated with infinite variety
- Output via the corticospinal and corticobulbar tracts
What are 3 features of the “anticipatory” motor output that affects the postural control system?
- Activation of postural muscles before voluntary movement begins (i.e. feedforward) in anticipation of the destabilising forces caused by the movement
- Cortically driven (part of the movement plan) (developed in the cortex)
- Memory-based/learnt movements, can adapt with repetition and change in circumstances (Develop with exposure to the task)
Based on the anticipatory motor output experiment where leg muscle activity is monitored before movement of arm, what would turning off the soleus and turning on the hamstrings do to this persons posture?
Prepares for the arm movement.
Based on the anticipatory motor output experiment where leg muscle activity is monitored before movement of arm why would turning of soleus and hamstrings facilitate this movement?
By turning off the soleus and hamstrings, we get dorsiflexion and knee flexion in response to gravitational forces. This places the COM posteriorly to compensate for anterior weight of the arm swinging forward.
Anticipation of local pain can adapt with a change in ____. Based on an experiment where electrical shocks are sent in the muscles (back and elbow) after auditory stimuli, what happens to the muscles? Be specific with back and elbow.
circumstance
Just anticipating back pain will change the way that the back muscles recruit, resulting in a delay in multifidus and transversus abdominus.
No difference when anticipating elbow pain
What are 6 features of the “automatic” motor output that affects the postural control system?
- Controlled at the level of the brain stem & cortex
- Triggered by external stimuli
- 90 to 100 millisecond latency following external stimuli
- “First line of defense” against perturbations
- Coordinated and highly generalised patterns
- Highly adaptable to conditions
What are 3 autonomic strategies for postural control?
- Ankle
- Hip
- Step
When is the ankle strategy used?
When perturbations are slow and low in amplitude
What are features of the contact surface for the ankle strategy?
Contact surface firm, wide and longer than foot
How are muscles recruited in the ankle strategy?
Distal-to-proximal
Are head movements in phase with hips in the ankle strategy?
Yes
When is the hip strategy used?
Used when perturbation is fast or large amplitude
What are features of the contact surface for the hip strategy?
Surface is unstable, narrow or shorter than feet
How are muscles recruited in the hip strategy?
Muscles recruited proximal-to-distal
Are head movements in phase with hips in the ankle strategy?
No
How is the trunk affected with the hip strategy? Why?
Rapid trunk adjustments to larger amplitude perturbation
When is the step strategy used?
Used to prevent falls
- When perturbations are fast or large amplitude
- When other strategies fail
What is altered in a step strategy?
Alters base of support
What is required in the muscle in the step strategy?
Requires the recruitment of many muscles
When trying to test the ankle strategies, what happens when the physio stands behind the participant?
first time: step strategy –> second time: hip strategy
When trying to test the ankle strategies, what happens when the physio stands in front of the participant?
first time: ankle strategy
Why is the response (for strategies) larger when the physio is standing behind the participant compared to infront of them?
Vision is anterior, and less ability to react when falling backward (we’re adapted to be able to stop ourselves falling forward) thus there is greater danger associated with falling backward.
What are 4 features of the “reflex” motor output that affects the postural control system?
- Controlled at the spinal cord, triggered by external stimuli
- Occur with a latency of ~35 to 40 Milliseconds
- Regulate local muscle contraction only (not generalised, multi-segmental)
- Highly Stereotypical
In the reflex motor output, the simplest neural circuit involves a ___ receptor and its _____ axon and a group of _____ the receive information in the spinal cord
sensory; afferent; motor units
Postural control is modified directly at the ______ by ___, _______ and other sensory inputs etc
spinal cord; pain; voluntary contraction
Describe key features of Voluntary, Anticipatory, Automatic and Reflex Control of Posture
EXAM QUESTION
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