Proprioception and motor control Flashcards
proprioceptors, structure and function of muscle, golgi tendon organs, proprioceptive diseases
exteroception
perception of external/enironmental stimuli acting on the body e.g. touch, sound, smell
What is proprioception?
The perception of joint and body movement, as well as position of the body or body segments in space.
Defined by Lord Sherrington and opposed to exteroception.
mechanical basis of proprioception
Nobel prize to ardem patapoutin: Piezo 1 & 2
What are the key organs of proprioception?
- Muscle spindles
- Golgi tendon organs
- Joint capsule receptors
What are PIEZO-1 and PIEZO-2?
Non-selective cation channels in the cell membrane that are sensitive to mechanical stimulation
PIEZO2 in proprioception
- hghly expressed in proprioceptive peripheral endings (muscle spindles and golgi tendon organs)
Piezo2 and motor coordination
conditional KO mice with no piezo2 in dorsal root ganglion proprioceptive neurons have impaired limb coordination (piezo2 necessary in motor coordination)
What type of fibers are muscle composed of?
muscle spindles as key organ in proprioception
- Intrafusal fibers
- Extrafusal fibers
what do extrafusal fibres do
- provide force to muscles
- stimulated by alpha motor neurons in sc
what do infrusal fibres do
- parallel to EF fibres, no force
- stimulated by gamma motor neurons
muscle spindles: sensory feedback
- made of IF
- central regions non-contractile
- contratile sides of IF to adjust length
3 types of IF fibres
- dynamic nuclear fiber
- static nuclear fiber
- nuclear chain fiber
what are IF fibers innervated by
- Ia afferents
- II afferents
What do type 1a afferents sense?
Both velocity and muscle length.
What do type 2 afferents sense?
Muscle length.
gamma motor neurons that innervate IF fibers
- dynamic and static
How do Golgi tendon organs differ from muscle spindles?
Golgi tendon organs are located in series with muscles, while muscle spindles are in parallel.
what are golgi tendon organs innervated by
type Ib axons intertwined with collagen fibres
- when muscle contracts, collagen compressed, generates Ib signalling
what do GTOs do
signal force in muscle
joint capsule receptors
important organ in proprioception
provide brain with information about joint position, movement and location
What are the two types of nerve endings found in joint capsule receptors?
- Ruffini type endings (type I)
- Pacini type endings (type II)
summary of proprioceptor afferents
What is gain in the context of motor control?
The relationship between output from and input to a given system
In the example of a shower, what does turning the handle represent?
The controller adjusting the INPUT to reach a desired temperature which is OUTPUT. GAIN is sensed temprature (output back to input to adjust)
What is an isometric exercise?
An exercise aimed at maintaining a constant muscle length against a constant load with a constant contraction
What role do gamma fibers play in proprioception?
They stimulate muscle spindles to contract and help control GAIN and keep muscle spindle signals within a working range.
high gain = increase in muscle length
gain control by gamma fibers in muscle spindles
MS signal changes in muscle length during contract which provides sensory feedback for motor control. Gamma motor neurons adjust MS length to maintain this feedback
when is sensory GAIN at 0
when muscle length changes are no accompanied by MS length changes as this breaks MS signalling
GAIN control y static and dynamic gamma fibres
MS signal both muscle length (static) and changes in muscles length (dynamic)
what do static gamma fibers do
increaase the fain of static sensory response (higher baseline)
what do dynamic gamma fibers do to gain
increase the gain of dynamic sensory response
Fill in the blank: PIZO-2 is important for _______.
motor coordination.
True or False: Muscle spindles generate force.
False.
What happens to the firing rate of primary sensory neurons associated with Golgi tendon organs when muscle force increases?
The firing rate increases.
What do dynamic nuclear fibers and static nuclear bag fibers do?
They are types of intrafusal fibers innervated by different types of gamma motor neurons.
What is the significance of the configuration of PIZO proteins at rest?
They are invaginated in the cell membrane and closed, preventing ion flux.
What is the primary function of muscle spindles?
To provide feedback on muscle length.
What is the function of muscle spindles?
Muscle spindles provide sensory feedback about changes in muscle length and the rate of those changes.
They are essential for proprioception, helping the nervous system monitor muscle stretch and tension.
What happens to muscle spindle signaling during muscle contraction?
During muscle contraction, muscle spindle signaling decreases as the spindle also shortens, leading to a drop in sensory feedback gain.
This occurs even when the muscle is electrically stimulated.
What are gamma fibers and their role?
Gamma fibers are motor neurons that innervate muscle spindles, allowing them to maintain sensitivity during muscle contraction.
They help keep muscle spindles within a signaling range.
What are the two types of gamma fibers?
Static gamma fibers and dynamic gamma fibers.
Each type modulates muscle spindle responses differently.
What is the difference between static and dynamic responses of muscle spindles?
Static responses signal the muscle length, while dynamic responses signal the change in muscle length.
Both responses can be modulated independently.
How can the gain of proprioceptive feedback be adjusted?
The gain of proprioceptive feedback can be adjusted by stimulating either static or dynamic gamma fibers.
This allows for different feedback based on behavioral states.
In what situations are static gamma fibers more active?
Static gamma fibers are more active during static postures, such as standing or sitting or slow movements
They provide necessary feedback in those conditions.
When is dynamic feedback more critical?
Dynamic feedback is critical during fast movements or unpredictable or complex actions, such as running or grabbing an object unexpectedly.
It allows for quick adjustments in response to changes.
What did the experiment with the monkey and joystick demonstrate?
It demonstrated how the gain of tactile and proprioceptive signaling changes dynamically across different behavioral states.
- relevant feedbacks amplified (proprioceptive during movement)
- less relevant suppressed (tactile during movement)
Proprioceptive feedback becomes more important as the monkey becomes active.
What happens to proprioceptive signaling in mutant mice lacking muscle spindles?
- Erg3 Mutant mice have less sensory feedback
- show impaired coordination and less regular locomotion patterns due to lack of proprioceptive feedback
- feedback from muscle spindles affect movement
Basic patterns may be preserved, but fine motor control is severely affected.
What challenges do mutant mice face on complex tasks like navigating a ladder?
Mutant mice struggle significantly with precision tasks, often missing targets, indicating the importance of proprioception for FINE MOTOR CONTROL
Control animals perform these tasks regularly without issue.
Who is Ian Waterman and what condition did he experience?
Ian Waterman contracted a sensory neuropathy that resulted in complete loss of proprioception below the neck.
He requires visual feedback for all movements and took years to partially recover functional movement.
True or False: Muscle spindles are not involved in sensory feedback during muscle contraction.
False.
Muscle spindles provide critical feedback, but their signaling decreases during contraction.
Fill in the blank: The two components of muscle spindle response are _______ and _______.
dynamic component, steady component.
Each component provides different types of sensory feedback.
