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S&F 1 > Spinal Mechanisms of Gait- Wilson > Flashcards

Spinal Mechanisms of Gait- Wilson Flashcards

1
Q

How do we apply eccentric contraction to sitting in chair? What is the prime mover for sitting (what is controlling the action of sitting)? Which muscle controls sitting?

A

body weight is heavier than the force generated by the muscle= eccentric contraction
weight =mg (physics)

-what is causing the person to sit?

  • gravity begins the lowering of the body to sit but
  • major extensor of the hip: gluteus maximus, which is an antagonist to gravity, pushes against the gravity to allow you to sit slowly.

-iliopsoas does flexion (major) at the hip joint but is NOT the one that allows you to sit

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2
Q

What is concentric action?

A

muscle shortens because load is less than contraction force

-insertion gets closer to the origin

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3
Q

What is isometric action?

A

muscle length remains the same because load equals contraction force

  • muscle contracts but there is no movement
  • often occurs around joint where agonist and antagonist muscles contract at the same time
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4
Q

What is eccentric action?

A

muscle lengthens because the load is greater than contraction force

-muscle is contracting but the amount of force the muscle can generate is less than the load so the muscle is being stretched

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5
Q

Describe the gait cycle.

A

is from heel strike to heel strike (begins with a heel strike)

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6
Q

How does the musculoskeletal system work?

A

contract (shortening of distance of origin and insertion)

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7
Q

What are the 3 contractions skeletal muscle?

A
  • concentric
  • isometric
  • eccentric
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8
Q

What muscle overcomes gravity to allow you to sit lower?

A

gluteus maximus: which is the major extensor the hip and undergoes eccentric contraction

it is the antagonist to gravity

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9
Q

What accounts for 60% and 40% of the gait cycle?

A

stance phase: (reference limb on the ground) –>60%
1. Heel strike - dorsiflexion of foot - deceleration/braking
2. Foot fat - plantar flexion of foot - Loading/hamstrings and flexor hallucinating longus compressed
3. Midstance - both limbs in the middle of the body - neutral/isometric
4. Push off - getting ready for swing - unload and acceleration/propulsion
swing phase: reference limb off the ground –> 40%

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10
Q

Within the stance phase what accounts 40% and 10% on opposite ends?

A

single support: 40% - only one limb on the ground

double support: 10% on opposite sides (both limbs are on the ground)

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11
Q

What is the segmental motor and sensory innervation of the lower limb?

A

both skeletal muscle and dermis is derived from somite which has segmental organization
-each somite is innervated by a particular section of the neural tube that will become the SC

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12
Q

Sensory innervation to skin has a segmental organization called what?

A

dermatome

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13
Q

The segmental innervation to the muscles of the lower limb is organized how?

A

proximal-distal gradient

  • higher segments of SC innervate proximal structures
  • lower segments of SC innervates distal structures
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14
Q

Describe the swing phase of walking.

A
  • flexion of hip
  • extension of knee
  • extension of ankle (dorsiflexion)

during the swing phase the opposite leg is in the stance phase which ends with “push off “with toes

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15
Q

What parts of the SC control flexing hip, extending knee, and extending ankle?

A
  • flexion of the hip: L2, L3
  • extension of the knee: L3, L4
  • extension of the ankle (dorsiflexion): L4, L5
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16
Q

Describe the stance phase of walking.

A
  • extension of hip
  • flexion of knee
  • flexion of ankle (plantar flexion)
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17
Q

What parts of the SC control extending hip, flexing knee, and flexing ankle?

A
  • extension of hip: L5, S1
  • flexion of knee: L5, S1
  • flexion of ankle: S1, S2
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18
Q

Describe gait in general.

A
  • cyclic and repetitive
  • largely autonomic
  • stereotypic (one step is like the next)
  • alternating, reciprocal activity between the limbs
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19
Q

What study did Dr. Wilson use in class to support his hypothesis?

Hypotheisis: The study of gait reveals the fundamental structure, organization and function of the CNS (spinal cord).

A

Cats can still walk a treadmill following spinal cord transection.

A lesion was placed proximal to the nerves supporting the hind limbs.

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20
Q

Why is the spinal cord called the pattern generator?

A

The only thing connected to the lower limb is the SC.

  • the basic circuits of gait (alternating the limb back and forth making gait possible) are found in the SC
  • you don’t need higher upper parts of your brain to say “move”
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21
Q

Describe the reflex that occurs when an individual steps on a the nail.

A
  • flex the thigh and leg of the limb that stepped on nail
  • extend the other limb to help you keep balanced

-The flexor withdrawal reflex (cross extensor reflex with the flexor reflex) is a basic circuit underlying alternating movements of the limbs.

When the extensors are active in one limb but the flexors are quiet in the other limb. Vice versa.

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22
Q

SC contains pattern generators for gait.

A

you don’t need higher upper parts of your brain to say “move”

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23
Q

What are the simplest types of movements?

A

reflexive responses such as monosynaptic movements

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24
Q

What are the basic movement types?

A
  • reflexive responses: simplest type of movement; limited in what it can do (i.e. patellar reflex)
  • rhythmic motor patterns such as walking, running, and chewing: make these movements largely using reflexive responses but you START these movements voluntarily and modify them voluntarily; combine reflexive and voluntary movements

voluntary movements: purposeful and goal directed (i.e. playing the piano, sitting in a chair)

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25
Q

Describe reflexive movements.

A
  • automatic
  • stereotypic
  • fast
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26
Q

What is the simplest circuit for modeling how the brain works?

A

monosynaptic reflex: input output

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27
Q

What makes something a voluntary movement?

A
  • goal directed and purposeful
  • unique motor patterns
  • precise
  • slow
  • clumsy until learned
  • ARE ASSEMBLED FROM BASIC REFLEX CIRCUITS
28
Q

Tension length diagram for a sacromere

SKIP

A
  • at the highest peak there is 100% overlap of myosin heads with actin
  • maximum excursion during contraction
29
Q

What is another term for LMN?

A

final common pathway

30
Q

Any motor signal regardless of where it comes from (cortex or brain stem) cannot directly cause contraction of a muscle. It has to converge where?

A

at the lower motor neuron AKA final common pathway

  • Convergence* onto the Final Common Pathway
  • muscle spindle–>excitatory output to sensory neuron (peripheral afferents)–>interneurons–> to motor neuron
31
Q

General ideas regarding brain and SC.

A

Interneurons and its connection to everything ultimately is what allows us to do a lot of things.

32
Q

Upper motor neurons comes from cortex and brain stem.

A

-they don’t have direct access to muscles but relay their info to interneurons (reflex circuits) then to lower motor neuron to perform the action

33
Q

Converging motor inputs to the final common pathway has what kind of organization?

A

a hierarchical organization (from lowest to highest)

  • SC is the lowest: pattern generator
  • brainstem is higher: posture, rhythmic and stereotyped movements
  • cerebral cortex is the highest: voluntary control; able to perform novel movements
34
Q

What is another term for SC?

A

pattern generator (fundamental circuits or reflexes

35
Q

What is the brain stem responsible for?

A
  • posture
  • rhythmic and stereotyped movements
  • integration of sensory signals to modulate SC networks controlling posture and gait
36
Q

What is the cerebral cortex responsible for?

A

-voluntary control

to be able to do things that have never been done before; takes a lot of practice

37
Q

What are the two types of lower motor neurons?

A

gamma: controls contraction of intrafusal fibers and muscle spindles

alpha motor neurons: contract the extrafusal fibers of the muscle; are directly responsible for initiating their contraction

38
Q

What are upper motor neurons?

A

neurons in cortex (synapses with brain stem and spinal cord) and brain stem (synapse with spinal cord)
(descending motor pathways)

-basal ganglia and cerebellum are other motor neurons that send signal to the cortex via thalamus

39
Q

Why is the basal ganglia imporant in controlling movement?

A

selects what motor behaviors to do and not to do

40
Q

What is the cerebellum responsible for?

A

coordination

41
Q

Hierarchical organization allows higher centers to give GENERAL commands, leaving the DETAILS to lower centers.

A

FACTS

42
Q

What is the advantage of the hierarchial organization?

A

you leave the detail to the SC or lower centers

-hierarchical organization allows higher centers to give general commands, leaving the details to lower centers

43
Q

What is the first level organization of movements?

A

myotatic units

44
Q

Why is Divergence so important?

A

Divergence allows a sensory neuron to affect the activity of many groups of neurons thus producing integration and coordination

IT’s NOT A 1:1 communication (axons split or have collaterals) influencing many SC segments.

Divergence of an afferent affecting all joint of the limb (ipsilateral and contralateral).
-Ia afferents for example have 500 or more branches terminating in the gray matter at several different spinal cord levels.

45
Q

Most sensory inputs go to where? What is important for going to antagonist muscles????

A
  • they may synapse not only on motor neuron but also interneurons
  • Interneurons may synapse of antagonist motor neurons
  • excitatory input to the agonist muscle
  • inhibitory input to interneurons for antagonist muscle (can be excitatory; this prevents clonus or inappropriate movement???
46
Q

The more interneurons there are, the more complex movements can be. True or false?

A

True

47
Q

DIVERGENCE allows coordination of the muscles around a joint!!!

A

This is why he said MYOTATIC UNIT is the first level of organization of movement.

Divergent connections of spindle afferents establish LINKAGES of muscles acting around a joint so that muscles do not act independently of one another.

48
Q

What are the two types of interneurons?

A

-intrasegmental (segmental): most

common type is the Renshaw cells which are inhibitory of motor neurons; prevents motor neurons from firing excessively; helps modulate excitation. Feedback directly onto motor neurons and other motor neurons

T1 and S2??????

-propriospinal (intersegmental): axons project to different SC levels are longer

49
Q

What are the types of ) propriospinal (intersegmental) interneurons?

A
  • short: control the appendicular structures of a single limb; connects limb (lateral) motor nuclei; connects neighboring segments or myotactic units; projections are ipsilateral
  • long: responsible for controlling axial muscles like your erector spinae, abdominal muscles, intercostal muscles; control posture; connects widely separate spinal segments; connects axial (medial) motor nuclei (controlling posture; shift of balance need to shift muscle tone on both sides so BILATERAL)
50
Q

Lamina IX is where you find lower motor neurons. Lamina IX is not a continuous but isolated in “islands”. It is organized into two groups: the medial group and lateral group which control what and are receive input from where?

A

medial group: controls axial musculature and receives input from long propriospinal interneurons

lateral group: controls appendicular structures and will receive input from short propriospinal interneurons

-extensors located more ventrally and flexors located more dorsally in the ventral horn where Lamina IX is located

51
Q

Lateral motor group develop from where and receive what input?

A

-brachial and lumbosacral plexus which control the upper and lower limbs

-receive input from short propriospinal
interneurons

52
Q

What is fasciculus proprius?

A

The fasciculus proprius (FP), the collective term for tract fibers that run from one spinal cord segment to another, is immediately adjacent to gray matter.

-pathway where the long and short propriospinal
interneurons are connecting different segments of the SC

53
Q

Improper modulation of the short propriospinal

interneurons displays what during a test for cerebellar lesion?

A

-poor connection between myotatic units; the activity of the short propriospinal interneurons are not being controlled by the cerebellum and thus movements are not coordinated

-guy raising leg to touch facilitator fingers is “segmental”
(movements of the lower limb are fragmented)

54
Q

What coordinates the hip and shoulder rotating in opposite directions?

A

long propriospinal interneurons

The hip and shoulder rotate in opposite directions:

  • is reminiscent of quadrupedal locomotion
  • is necessary to maintain balance
  • requires reflexive coordination (connections) of limbs regions of the SC
  • is impaired in certain neurological disorders (Parkinson’s Disease)
55
Q

Improper modulation of the long propriospinal

interneurons displays what?

A
  • Parkinson’s disease
  • no alteration of the hip and shoulders going in the opposite direction
  • guy not walking right
56
Q

Depending on circumstances, reflexes respond in opposite ways. Same stimulus different responses show what?

A

plasticity

UMN can change or turn on or off motor system depending on what situation a person finds themselves in

57
Q

What is rigidity?

A
  • too much muscle tone

- increased sensitivity of tonic stretch reflex

58
Q

Most of the descending input controlling movement from the brainstem and motor cortex go to where?

A

interneurons where you can modulate or change reflexes

59
Q

Reflex circuits of the spinal cord can be turned on/off or modulated by what?

A

directly by brain stem and cortex and indirectly by the basal ganglia and cerebellum (supra spinal pathways from brainstem to cortex)

dependent on the circumstance

60
Q

Stroking the plantar surface of a baby’s foot evokes an _______of the great toe.

A

extension of digits

which is an enhanced withdrawal reflex to a noxious stimulus (stroking)

61
Q

After the first year of life, the extension plantar response is inhibited. Thus, stroking the plantar surface evokes _________of toes. What may occur to this response with a CNS lesion?

A
  • flexion
  • A CNS lesion may release the inhibition of the normal interneuron circuit (performed by the CST) resulting in return of the extension plantar response (a positive Babinski sign)

-extension plantar response is being suppressed so we can be able to walk

62
Q

What are the four mechanisms by which spinal cord circuits are modulated?

A
  • postsynaptic which can be inhibitory (disexcitation) or excitatory (disinhibition)
  • presynaptic which can be inhibitory or excitatory
63
Q

The RMP of neurons are highly negative. Excitatory inputs make the MP more positive. If you generate an action potential you get a muscle contraction. What occurs with inhibitory inputs?

A

the MP becomes more negative thus the neuron is far away from the threshold potential so no AP, no contraction of muscles

64
Q

Explain gating by interneurons.

A

Synaptic gating is the ability of neural circuits to gate inputs by either suppressing or facilitating specific synaptic activity.

Gating can occur by shunting inhibition in which inhibitory interneurons change the membrane conductance of an excitatory target axon, thereby diffusing its excitatory signal. A gating signal from the gatekeeper triggers these inhibitory interneurons in order to prevent one set of neurons from firing even when stimulated by another set. I

65
Q

Locomotor patterns are generated by intrinsic circuits in the __________.
Descending signals from the brain stem and cortex can (de)activate or modulate these circuits.

A

spinal cord

-Descending pathways orchestrate spinal reflexes

66
Q

descending pathways orchestrate what?

A

spinal reflexes

S&F 1 (25 decks)

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