Midterm 1 Flashcards
Motor control definition
How fluid and efficient movements are produced, regulated, and coordinated
What are the 8 essential components of motor control?
Volition
Coordination of signals
Proprioception
Postural adjustments
Sensory feedback
Compensation for the physical characteristics of the body
Unconscious processing
Adaptability
Who is Sir Charles Sherrington?
Father of motor control, neurophysiologist
Homonymous definition
Relating to the same muscle
Concentric vs eccentric
Concentric: contraction in the shortened position
Eccentric: contraction in the lengthened position
Main characteristic of a pseudounipolar neuron
A process emerges from the soma and then splits into two
Bipolar neuron characteristics (2)
2 processes directly from soma
Special sense organs
Multipolar neuron characteristics (2)
Single axon from soma
Motor neurons
What are the 3 types of synapses?
Axoaxonic
Axodendritic
Axosomatic
Which ions are found extracellularly and intracellularly?
Extracellular: Na+ and Cl-
Intracellular: K+ and negative ions
At resting membrane potential where is there a higher concentration of negative ions?
Inside the cell
Depolarization and hyperpolarization is directly related to the membrane permeability of which ion?
Na+
What is the threshold potential of a neuron and a muscle cell?
Neuron: -55mV
Muscle cell: - 75mV
Where is there a high density of Na+ channels?
Axon hillock
What does it mean that APs are dynamic?
They can regenerate along the axon for propagation
What characteristics of the neuron influence propagation speed?
Myelination
Diameter of the axon
Temporal summation
Summation from a single synapse in a certain period of time
Spatial summation
Summing the effects of EPSPs from different synapses at the same time
Motor neuron pool definition
All the (alpha) motor neurons that innervate a single skeletal muscle
Where are the cell bodies of alpha motor neurons found?
Ventral horn of the spinal cord
What are the 2 somatotopic arrangements of motor neuron pools?
Longitudinal arrangement: lower vs upper body (whole spinal cord)
Mediolateral arrangement: medial vs lateral section of the spinal cord
medial = axial m. lateral = distal m.
Motor unit definition
An alpha motor neuron and all the muscle fibres it innervates
What is the smallest functional unit of the neuromotor system?
Motor unit
What is the function of the motor unit?
Produces synchronized contraction of the innervates fibres
Motor end plate definition
Region of muscle fibre that receives ACh from NMJ
- produces EPSP that moves along muscle fibre
Motor unit action potential definition
An action potential that occurs within muscle cells to produce action/contraction
What is the prime difference b/w AP and MUAP?
AP is unidirectional and MUAP is bidirectional
Innervation ratio definition
Average number of muscle fibres the alpha motor neuron innervates
What does a smaller innervation ratio mean?
There is a higher degree of control
What are 3 ways that motor units differ?
Size of soma
Diameter of axon
Properties of the muscle fibres innervated
What are the 3 types of motor units?
Fast fatigable (FF) MU
Fast fatigue-resistant (FR) MU
Slow (S) MU
Characteristics of fast fatigable MU 3
Biggest soma
Biggest axon diameter
High force capacity of m. fibres = quickest fatigue
Characteristics of fast fatigue-resistant MU
Mid for everything
Characteristics of slow MU
Smallest everything
Most fatigue-resistant
What are the 4 events that occur in information processing?
Reception
Transduction
Coding
Awareness
Reception definition
Sensory receptors absorbing the physical energy of the stimulus
Transduction definition
Conversion of physical E into electrical E
Coding definition
Matching of stimuli parameters to the neuronal parameters that represent it, leading to awareness/perception
How are sensory receptors classified?
Based on the origin of the stimulation to which they respond
Exteroceptors
Respond to stimuli in the external environment
Proprioceptors
Respond to mechanical stimuli associated with configuration and movement of body and body segments
Interoceptors
Respond to stimuli within the body
(CO2 levels, etc.)
Photoreceptors
Respond to light
Mechanoreceptors
Respond to mechanical energy (touch, vestibular)
Chemoreceptors
Respond to chemical substances (gustatory and olfaction)
What is proprioception vs kinesthesia?
Proprioception: static positions, awareness of joint position
Kinesthesia: dynamic position sense
What are 4 attributes that form sensation together?
Modality: what is it
Intensity: amount of stimuli
Duration: start to end of stimuli
Location: where in body
What are the 2 types of adapting receptors?
Phasic responders (rapid): silent when a stimulus is maintained
Tonic responders (slow): continue to fire when stimulus is maintained
Where is the sensory cortex?
Post-central gyrus
What is two-point discrimination?
Ability to distinguish between closely spaced stimuli
What are the 2 reasons why there is a variance in tactile discrimination?
Varying receptor density throughout the body
Regional differences in receptive field size
Receptive field definition
Total area of the skin surface within which a correct stimulus will evoke a response in the afferent fibre
What do Meissner corpuscles respond to?
Pressure
What do Merkel disk receptive fields respond to?
Vertical pressure
What do Pacinian corpuscle receptors respond to?
Vibration
Where does the pseudounipolar neurons (sensory info) convey info to?
Dorsal root ganglion (outside of spinal cord)
What are the 2 branches of the pseudounipolar neuron?
Peripheral and central
Which branch of the pseudounipolar neuron has the sensory receptor?
Terminal of peripheral branch
Which branch of the pseudounipolar neuron leads to the spinal cord?
Central branch
What is the easiest way to identify ascending sensory motor tracts?
Begin with spino- because they start at the spine and ascend
Function of the 1st order neuron
From sensory receptor to the spinal cord
Function of the 2nd order neuron
Decussates in the spinal cord, ascends
Function of the 3rd order neuron
From thalamus to primary somatosensory cortex
What are the 3 sources of sensory feedback receptors that contribute to kinesthetic sense?
Articular receptors (joint capsule)
Muscle
Cutaneous
- all mechanoreceptors
What did the study by Adachi et al. show about the mechanoreceptors in the ACL?
Proprioceptive function of the ACL is related to the number of mechanoreceptors
- important surgical considerations
What are the 2 types of muscle proprioceptors?
Golgi tendon organs
Muscle spindles
What is the function of Golgi tendon organs?
Sense a change in tension/force due to their location in the tendon
What type of neuron innervates Golgi tendon organs?
1B afferents; large diameter & myelinated = fast
What occurs to the 1B afferent when muscle force occurs?
It is compressed and is then depolarize to produce AP
What is the relationship between muscle force and AP firing of 1B afferents?
When there is an increase in muscle force, there is also an increase in AP firing from the 1B afferents
How is muscle force increased? 2
Eccentric and concentric contraction
Does eccentric or concentric contraction have a bigger AP firing frequency of the 1B afferents?
Concentric
What are muscle spindles?
Muscle stretch detectors
What are the 3 main components of a muscle spindle?
Intrafusal fibres
Sensory innervation
Motor innervation
What are the 2 main types of intrafusal fibres found in muscle spindles?
Nuclear bag
Nuclear chain
What are the 2 main sections of all intrafusal fibres? Which section is the contractile region?
Equatorial and polar
Polar is contractile region
What are the 2 subcategories of nuclear bag intrafusal fibres?
Static nuclear bag
Dynamic nuclear bag
What intrafusal fibre type do Ia afferents innervate? What fibre type do Ia and II innervate?
Ia innervates all intrafusal fibres
II (also Ia) innervates only nuclear chain and static bag
In which region does the Ia afferent innervate on all intrafusal fibres?
The central/equatorial region
Where does the II afferents innervate on the static nuclear bag and nuclear chain intrafusal fibres?
At the junction b/w the polar and equatorial/central region
Does muscle stretch result in spindle loading or unloading?
What occurs to the intrafusal fibres when the muscle is stretched?
Spindle loading
If the muscle stretches the spindle stretches (it is within the muscle) and therefore loads the spindle
What occurs to the AP firing frequency when spindle loading occurs?
Spindle loading, due to muscle stretch, results in increased AP firing frequency
What is the difference in AP firing frequency between muscle spindles and Golgi tendon organs in response to muscle stretch?
Muscle spindles have a more robust (higher AP firing freq) than Golgi tendon organs
In response to stretch, and therefore spindle loading, which afferent fibre (Ia or II) will have a more robust response and why?
Ia will have a more robust response.
Majority of stretching occurs in the equatorial region which is where the Ia afferents are
What type of contraction (eccentric vs concentric) results in spindle unloading?
Concentric contraction, the muscle shortens
What is observed in the AP firing frequency during spindle unloading and why?
There is decreased AP firing frequency, occurs because when the spindle is compressed the afferents that wrap around it are slacked and stimulated less
What is the difference between a muscle spindle and Golgi tendon organ in response to concentric contraction?
Muscle spindle is unloaded, compressed, and therefore has decreased AP firing frequency
GTO is compressed within the tendon and has an increased AP firing frequency
In spindle unloading, which afferent shows a greater decrease in AP firing frequency and why?
Ia afferent has a bigger decrease because of it’s location, slackened more when around the equatorial region
What influence do the static and dynamic phases of muscle length have on Ia and II afferents firing frequency?
Static phase: Ia and II reach a similar steady firing rate
Dynamic phase: Ia has a more robust response than in the static phase and compared to II afferents. II afferents increase firing frequency slightly
How does the velocity of stretch impact the AP firing frequency of Ia afferents?
Higher velocity of stretch increases the AP firing frequency
What information do Ia afferents in muscle spindles provide? 3
- static length (position)
- dynamic length (movement)
- rate of length change (velocity)
What kind of motor neurons innervate muscle spindles and where do they innervate?
Gamma motor neurons; innervate at the polar regions
What is the function of the gamma motor system in muscle spindles?
Regulate the sensitivity of muscle spindles for detecting stretch
What are the 2 types of gamma motor neurons?
Static and dynamic
Of the 2 types, what gamma motor neuron increases steady-state firing?
Static gamma motor neuron
Of the 2 types of gamma motor neurons, which type increases firing rate during dynamic phase of stretch?
Dynamic gamma motor neurons
What type of intrafusal fibre do dynamic gamma MN and static gamma MN innervate?
Dynamic gamma MN: innervates dynamic nuclear bag
Static gamma MN: innervates static nuclear bag and nuclear chain
In muscle spindle unloading (concentric) the afferents do not produce an AP, how does the CNS get information on muscle length and rate of change?
Activation of gamma MNs; fusimotor system
How does the muscle spindle remain taut to respond to muscle length change?
Alpha - gamma co-activation
Gamma activation leads to shortening of polar regions and stretching of equatorial region = taut spindle
What is required for Ia afferents to fire during concentric contraction?
The firing of gamma MNs to keep the muscle spindle taut
If gamma MNs activate before alpha MNs (in muscle spindle) what does it do to the intrafusal fibre?
It prestretches the equatorial region and alters their sensitivity
What type of MN regulates the muscle spindle’s sensitivity to stretch?
Gamma MNs
What type of gamma MN is activated in slow and predictable change in muscle length?
Static gamma MN
What type of gamma MN is activated in rapid and unpredictable change in muscle length?
Dynamic MNs
What type of MN (alpha or gamma) activity is increased as requirements for stretch sensitivity increases?
I.e Walking on ice
Gamma MN
How is gamma MN bias adjusted to prime the spindles for impending stretch?
Upper motor neurons
Lower motor neurons
Rootlets
Collection of axons entering or exiting the spinal cord
Roots
Collection of 8-12 rootlets
What forms a spinal nerve?
Anterior and posterior roots
What type(s) of fibres (afferent, efferent) make up a spinal nerve?
Both, it is mixed
What does the spinal nerve divide into?
Two rami (arms)
What are the 2 rami that a spinal nerve divides into and what do they innervate?
Dorsal (posterior) ramus: deep muscles of back
Ventral (anterior): lateral & anterior torso, upper and lower limbs
What is found in the grey matter of the spinal cord?
Cell bodies, dendrites, and unmyelinated axons
What is found in the white matter of the spinal cord?
Myelinated axons - ascending and descending tracts
What type of tract (ascending/descending) is the posterior funiculus? Therefore what kind of information (sensory/motor) is carried in this tract?
Ascending; sensory
In which funiculus (posterior/lateral/anterior) is the dorsal column medial lemniscus pathway found?
Posterior
What type of tract (ascending/descending) is found in the lateral funiculus?
Both, mixed
What type of tract (ascending/descending) is the anterior funiculus? Does it carry sensory or motor info?
Descending; motor
What structure connects the R and L grey matter of the spinal cord?
Grey commissure
Where are the sensory nuclei found in the spinal cord? (Anterior/posterior/lateral horn)
Posterior horn of grey matter
Where are the motor nuclei found in the grey matter of the spinal cord? (Anterior/posterior/lateral horn)
Anterior horn of grey matter
What type of nuclei does the lateral grey horn of the spinal cord house?
Autonomic or visceral motor nuclei
What are the 2 subsections of the posterior funiculus?
Fasciculus gracilis
Fasciculus cuneatus
Where does the fasciculus gracilis carry info from?
Lower limbs (T6 or lower) to higher areas
Where does the fasciculus cuneatus carry info from?
From upper limbs to higher areas
What pathway are the fasciculus gracilis and cuneatus apart of?
Dorsal column medial lemniscus (DCML) pathway
What are the 4 systems that contribute to motor output?
- spinal cord & brainstem
- descending systems
- basal ganglia
- cerebellum
What is reciprocal inhibition?
Simultaneous contraction of the agonist relaxation of the antagonist muscles
How can excitatory inputs be modulated to be less effective/strong? 2
Presynaptic inhibition
Postsynaptic inhibition
What is presynaptic inhibition?
An inhibitory IN acts (GABA) on the presynaptic axon and dampens its response
What occurs in postsynaptic inhibition?
Membrane hyperpolarization leads to less sensitivity to excitatory input
Reflex definition
Rapid, involuntary and stereotyped motor response to a sensory stimulus
Spinal reflex definition
Neural circuitry for motor response contained in the spinal cord
How were spinal reflexes discovered?
Sherrington’s cats; decerebrate preparations
What does decerebrate mean?
Lesions at the brainstem so the brain and spinal cord do not talk
Reflex arc definition
Neural pathway involved in a reflex action
What are the 3 components of a reflex arc?
Afferent neuron; central processing unit; efferent neuron
How can reflex circuitry be categorized?
Based on the number of synapses; monosynaptic, oligosynaptic, polysynaptic
Where are interneurons found in the spinal cord?
Dorsal and ventral horns, intermediate areas
What is reflex latency?
The time delay between stimulus and reaction
What are the 3 components of reflex latency?
Δta: time of afferent conduction
Δte: time of efferent conduction
∆tc: central delay
What impacts the time of efferent conduction? 3
Neuron type
Length of fibre
Health of neuron
What impacts the time of central delay?
Number of synapses
What is the function of the monosynaptic stretch reflex?
Maintain muscle length at a desired set of values
What locations in the body is the monosynaptic stretch reflex seen in?
Ankle, jaw, biceps, triceps, knee
What are the components of the monosynaptic stretch reflex? 5
Homonymous muscle
Muscle spindle
Sensory cell body of pseudounipolar neuron
Synapse
Alpha MN
What muscle is excited an inhibited in the MSR?
Homonymous and synergistic muscle is excited
Antagonist is inhibited
How many collaterals does the Ia afferent axon split into in the spinal cord for the MSR? What does each do?
3 collaterals
2 excite the agonist and Synergist
1 inhibits the antagonist
What is the reflex latency value of the MSR?
70ms
What is reciprocal innervation?
Innervation of the agonist and antagonist comes from the same neuron source
What is monosynaptic reflex gain?
The magnitude of motor response relative to the magnitude of sensory stimulus
What is high gain vs low gain?
For the same input, high gain has a more effective reflex pathway that creates a stronger output than low gain
What mechanisms are thought to account for reflex gain? 3
Fusimotor activity
Presynaptic modulation
Postsynaptic modulation
What are 3 potential contributing factors to a hypoactive MSR?
- disorder of reflex circuit
- higher order issue
- peripheral disorder (spindle)
What is a possible explanation for hyperactive MSR?
- higher order issue (lesions); no descending inhibition
What is the purpose of the Hoffmann reflex?
It eliminates peripheral input (muscle spindle) and assesses the resulting motor response
What occurs at low stimulus intensity in the Hoffmann reflex?
Large fibre axons are activated (Ia) which leads to a reflex-based motor response
What is the reflex latency speed of the Hoffmann reflex?
30ms, eliminates the time from the muscle spindle
What occurs as stimulus intensity increases in the Hoffmann reflex?
As stimulus intensity increases the recruitments of small neurons (alpha MN) occurs
In increased stimulus intensity, what does the subsequent recruitment/activation of alpha MNs result in?
Hoffmann reflex
Causes a direct stimulation of muscle fibres
What is the M-wave representative of?
Alpha MN recruitment
As stimulus intensity increases, what occurs to the M-wave and H-reflex amplitude?
M-wave amplitude increases until all alpha MNs are recruited
H-reflex amplitude decreases due to electrical blockade
Explain what the neuron types are involved in the electrical blockade
Antidromic (opposite) propagation of the efferent MN blocks the orthodromic propagation of the Ia axon and blocks AP
What can the M-wave amplitude tell us?
There is an increase in stimulation intensity due to more alpha MNs recruited
If M-wave (stimulus intensity) is constant, but there is a change in H-wave (increase or decrease), what causes this?
Change in reflex gain
Reflex modulation
What is the H-reflex a clinical test of?
Integrity of central mechanisms in altering the excitability of an alpha MN pool
What is modulation of reflex gain based on?
The functional demands of the task
What is the effect of taping along the muscle fibres of the triceps surae?
Reduces motor neuron excitability; decrease in reflex gain
What is the effect of taping across the muscle fibres of the triceps surae?
Had no effect on motor neuron excitability
What are renshaw cells?
They are inhibitory interneurons in the grey matter of the spinal cord
What does co-contraction allow for? 4
Direction reversals (flexion to extension)
Increase in joint stiffness
Precise movements
Joint stabilization
Where do renshaw cells receive their input from?
Alpha motor neurons and descending commands
What is the relationship between a renshaw cell and the alpha motor neuron it innervates?
What is this relationship called?
Renshaw receives excitatory info from alpha MN
Same alpha MN receives the same renshaw cell’s inhibitory inputs
Recurrent collateral
Renshaw mediated co-contraction definition
Decreasing alpha MN agonist output and (inhibition) and increasing antagonist alpha MN output (disinhibition) via renshaw neuron
Why is the decrease in alpha MN output via renshaw activation needed?
There needs to be periods of decreased MN output to allow for a change in direction
What type of interneurons mediates the inverse stretch reflex?
Ib inhibitory interneurons
How is the flexor reflex classified?
It is an interjoint multi-segmental reflex
What is the outcome of the flexor reflex?
Elevation of the limb due to a noxious stimuli
Which muscles are excited and inhibited on the ipsilateral side in response to the flexor reflex?
Flexors are excited
Extensors are inhibited
What is the flexor/crossed extensor reflex?
Same as the flexor reflex, but it involves both sides; contralateral
What muscles are excited and inhibited on the contralateral side during the flexor/crossed extensor reflex?
The extensors are excited
The flexors are inhibited
- allows for the planting of the foot
