Save
Busy. Please wait.
Log in with Clever
or

show password
Forgot Password?

Don't have an account?  Sign up 
Sign up using Clever
or

Username is available taken
show password


Make sure to remember your password. If you forget it there is no way for StudyStack to send you a reset link. You would need to create a new account.
Your email address is only used to allow you to reset your password. See our Privacy Policy and Terms of Service.


Already a StudyStack user? Log In

Reset Password
Enter the associated with your account, and we'll email you a link to reset your password.
focusNode
Didn't know it?
click below
 
Knew it?
click below
Don't Know
Remaining cards (0)
Know
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.

  Normal Size     Small Size show me how

Spinal motor systems

Organisation, muscle fibres, reflexes

TermDefinition
What is contained in the dorsal horn of the spinal cord? Sensory inputs -> A delta and C fibres
What is contained in the intermediate zone grey matter of the spinal cord? Interneurons
What is contained in the ventral horn of the spinal cord? Motor outputs -> A alpha motor neurons
What is a motoneuron pool? 100-500 alpha motoneurons innervating given muscle (motoneuron pool) located together in ventral horn
What is a motor unit? Each alpha motoneuron nnervates multipe muscle fibres distribted throughout muscle belly -> 1 motoneuron stimulated -> all muscle fibres of motor unit contract -> all muscle fibres in one motor unit are of the same type
What is the somatotopic organisation of the ventral horn? Flexor (dorsal), extensor (ventral), proximal (medial), distal (lateral), hand (dorsal) -> wrist -> elbow -> shoulder (medial)
What are examples of motoneuron degeneration? ALS (amyotrophic lateral sclerosis - motoneuron disease) -> death of presynaptic neuron leads to xcs postsynaptic receptors (hypersensitive) -> endogenous ACh produces involuntary twitches (denervation fasciculations), poliomyelitis
What are examples of peripheral nerve damage? Autoimmune demyelinating disease (Guillain-Barre Syndrome) -> hands/feet muscle weakness -> can spread to cranial nerves/breathing muscles -> can change ANS function (dangerous HR/BP)
What are examples of spinal cord damage? Vertebral column dislocation -> weak spinal joints from injury to muscles/ligaments -> abnormal bone mvmt
What are the 3 histochemical profiles of muscle fibres? Slow, fast fatigue resistant, fast fatiguable
What is the anatomy/biochemistry of slow muscle fibres? Small and few fibres / motor unit, highly vascular, rely on oxidative respiration, high myoglobin content -> red meat
What is the physiology/function of slow muscle fibres? Slow twitch fibres, low tension, fatigue resistant, slow axons -> continuous generation of small forces
What is the anatomy/biochemistry of fast fatiguable muscle fibres? Large and many fibres / motor unit, few capillaries, anaerobic (glycolytic) respiration, low myoglobin content -> white meat
What is the physiology/function of fast fatiguable muscle fibres? Fast twitch fibres, high tension, fatiguable, fast axons -> brief generation of large force
What is rate coding? Vary firing rate of motoneurons -> high AP frequency = high force output, limited by tetany -> amount of vesicular neurotransmitter available/exocytosis rate
What is size principle? Vary motoneuron recruitment -> if more force is needed, more motoneurons are recruited from low force (slow twitch) -> next lowest force generating motor unit -> high force (fast twitch) -> allows for smooth muscle mvmt
How do motoneurons show developmental plasticity? Motoneurons w/ low thresholds innervate few muscle fibres -> induced as slow, low force, fatigue resistant fibres, vice versa -> random inputs automatically recruits motoneurons from low to high force -> no need for brain control of motoneurons
What gives inputs to motoneurons? Muscle spindle afferents (muscle spindle), descending fibres (direct pathways from brainstem/cerebral cortical structures in primates), spinal interneurons (sensory/descending pathways from brainstem/cerebral cortex)
What types of reflexes are there? Simple reflex actions -> specific small group of muscles -> stretch reflexes w/ associated reciprocal/recurrent inhibition, complex reflexes -> functional mvmts w/ multiple muscles (nociceptive withdrawal reflex)
What do proprioceptors do? Provide info on body state (kinaesthesia) -> joint position/mvmt, muscle force
What are proprioceptive afferent inputs? Proprioceptors, cutaneous sensation, visual information, vestiblar systems
What types of proprioceptors are there? Muscle spindle afferents (muscle stretch receptors), Golgi tendon organ (muscle tension receptors), joint receptors (Pacinian corpuscles/joint position/mvmt extremes before snapping)
How many spindles are in a muscle? Typical muscle has 20-100 spindles
What is the structure of a muscle spindle? Encapsulated purple bundle of small specialised intrafusal muscle fibres -> 6-12 intrafusal muscle fibres in each spindle, 3 axons to 1 spindle, striated ends (small compared to extrafusal force-generating fibres)
What is the purpose of muscle spindles? Intrafusal contractions don't generate tendon tension but affect spindle sensory nerve ending sensitivity -> contribute to proprioception rather than mvmt
What are the types of intrafusal fibre? Bag fibres -> swollen central region w/ multi-layered nuclei, contractile viscoelastic end regions and non-contractile elastic bag, chain fibres -> uniform diameter w/ single chain of nuclei, uniformly contractile, several of each type in one spindle
What are the sensory afferents/locations from muscle spindles? Primary -> Ia spindle afferents -> large/fast conducting axons (A-alpha) -> terminal branches coil around intrafusal central nuclei, secondary -> II spindle afferents -> small/slow conducting axons (A-beta) -> terminal branches coil adj to central nuclei
What happens to bag fibres when the spindle is stretched? Central bag elongates -> Ia afferent coil tightens/activates -> viscous contractile ends relax to even out length change -> central bag no longer elongated -> Ia afferent adaptation -> large dynamic response (change), small static response (length)
What happens to chain fibres when the spindle is stretched? Uniformly contractile -> uniform stretch along fibre -> small dynamic response (change), large static response (length) -> no adaptation of II afferents
What is the dynamic response? Receptor informs changes in length -> increase/decrease in AP frequency -> fast type Ia afferents for moving stimulus
What is the static response? Receptor informs absolute length -> slow type II afferents
What are the motor efferents to muscle spindles? A gamma motoneuron axons -> cause intrafusal muscle fibre contraction -> dynamic gamma motoneurons to chain fibres, static gamma motoneurons to bag fibres
What motor efferent signals are sent when the muscle contracts? Spindle centre contracts -> afferent fibre coil too slack to signal -> no Ia/II afferent AP -> A gamma signals -> spindle ends contract to compensate -> centre returns to original length -> afferent coil tightens to normal -> restore sensitivity
What motor efferent signals are sent when the muscle is stretched? Spindle centre stretched -> afferent fibre coil too tight -> saturated AP -> A gamma signals -> spindle ends relax to compensate -> centre returns to original length -> afferent coil relaxes to normal -> restore sensitivity
What is the purpose of the motor efferents to muscle spindles? Adjust sensory afferent sensitivity by changing tension of coil around intrafusal muscle fibre centre compensating for changes in length -> prevents signal saturation when muscle too/not stretched
What causes muscle spindle afferents to fire? Changes in muscle stretch, altered gamma motoneuron activity
How does the brain interpret muscle spindle afferent signals? Efference copy from gamma motoneuron to remove spindle afferent ambiguity -> knows that it was due to gamma motoneuron rather than changes in muscle stretch
When are Golgi tendon organs activated? Active tendon tension in collagen fibres due to extrafusal muscle fibre contraction generating force -> passive muscle (no AP) -> passive muscle under load (no AP) -> stimulated alpha motoneurons contract muscle (Golgi AP frequency proportional to load)
What is special about the muscle stretch reflex? Monosynaptic -> muscle spindle afferents directly synapse w/ alpha motoneurons (no interneurons) -> all muscles xcp extraocular (constant eyeball rotation w/out changes in load)
What are the targets for muscle spindles? Muscles of spindle afferents (adjust length), muscles of synergist spindle afferents (adjust length around joint)
What is the advantage of the stretch reflex? Simplifies mvmt control for unknown/unpredictable loads -> brain determines initial changes in muscle length, spinal cord determines force required
What is the disadvantage of the stretch reflex? Gain is less than 1 (less force of contraction than extent of muscle stretch), feedback system will have delays and generate oscillations
What can result from damage to descending systems? Motor cortex damage (stroke, cerebral palsy) -> spasticity -> hypertonia (continuous contraction), high gain (exaggerated stretch reflex), myoclonus (oscillating muscle contractions)
How is the stretch reflex regulated? Gamma motoneurons reset muscle spindle afferent sensitivity, low mvmt/precision required -> brain sets high gain/spindle sensitivity -> strong stretch reflex -> ballet dancers w/ overlearned mvmts/predictable environment -> dampened stretch reflexes
What is the role of proprioceptors in supraspinal motor systems? Sensory info used for predictive feedforward mvmt (cerebellum/motor cortex) using model systems, prioprioceptor -> spinocerebellar pathway -> cerebellum
What is reciprocal inhibition? Muscle spindle afferents excite glycinergic group Ia inhibitory interneurons associated w/ each motoneuron pool -> synapse w/ antagonist muscles -> prevent further stretch
What is recurrent inhibition? Motoneuron axons have recurrent collateral branches in spinal cord -> innervate inhibitory Renshaw cells -> synapse back on motoneuron cell body in spinal cord ventral horn -> prevent all motoneurons from firing at once (smooth/precise mvmt)
What are the characteristics of spinal reflexes? Activate specific mvmt patterns (specific muscle groups), all have interneurons (xcp stretch), context dependent (same stimuli gives different efferent), multijoint, multisensory (different afferents), controlled by descending motor pathways
What is the pathway of the nocicpetive withdrawal reflex? Noxious stimuli -> nociceptor -> sensory afferent -> substantia gelatinosa -> interneuron -> motoneuron efferent -> excite flexors/inhibit extensors
What are the neonatal reflexes? Grasp reflex, Babinski's sign (plantar reflex) -> stick from heel to toe -> toes extend/leg flexes (adult toes flex to support body weight), reflex stepping (dragging baby has flexed legs like stepping but can't actually support body weight)
What are the characteristics of pathological reflexes? Response to loss of motor cortex control -> normally repressed brainstem takes over spinal reflex control, exaggerated reflexes (spasticity -> stiff uncontrolled muscles w/ strong reflex clonus -ve feedback oscillation), adult -> child Babinski reversion
What happens to locomotion when spinal cord is separated from brain? Intact stepping motor pattern via central pattern generators -> don't need sensory inputs -> intrinsic spinal mechanism responsible
What happens to locomotion when the spinal cord is transected? Loss of functional locomotion -> different infant stepping patterns -> larger cerebral cortex as compensation (encephalisation) -> weaker ability to generate locomotion in spinal cord -> CPG outputs must be adjusted by sensory systems/brain
Created by: vykleung
Popular Neuroscience sets

 

 



Voices

Use these flashcards to help memorize information. Look at the large card and try to recall what is on the other side. Then click the card to flip it. If you knew the answer, click the green Know box. Otherwise, click the red Don't know box.

When you've placed seven or more cards in the Don't know box, click "retry" to try those cards again.

If you've accidentally put the card in the wrong box, just click on the card to take it out of the box.

You can also use your keyboard to move the cards as follows:

If you are logged in to your account, this website will remember which cards you know and don't know so that they are in the same box the next time you log in.

When you need a break, try one of the other activities listed below the flashcards like Matching, Snowman, or Hungry Bug. Although it may feel like you're playing a game, your brain is still making more connections with the information to help you out.

To see how well you know the information, try the Quiz or Test activity.

Pass complete!
"Know" box contains:
Time elapsed:
Retries:
restart all cards