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Intro to Brain and Behavior > Chapter 14: Spinal Cord Control of Movement > Flashcards

Chapter 14: Spinal Cord Control of Movement Flashcards

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The Brain flashcards
1
Q

What are the categories of movement?

A

Reflexive, rhythmic, voluntary

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2
Q

What is reflexive movement?

A

Involuntary coordinated patterns of muscle contraction and relaxation elicited by peripheral stimuli, e.g. knee jerk reflex

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3
Q

What is rhythmic movement?

A

Repetitive motor patterns e.g. breathing, chewing, swallowing, scratching, walking, swimming
Circuits lie in brainstem and spinal cord

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4
Q

What is voluntary movement?

A

Goal-directed
Improve with practice

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5
Q

How are motor systems are organized?

A

Hierarchically
Forebrain
Brainstem
Spinal cord

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6
Q

What does the spinal cord do?

A

Carries motor information from the brain to the periphery
Carries sensory input from the periphery to the brain
Mediates reflexes for body

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7
Q

What is the spinal cord anatomy?

A

Dorsal root are afferents (sensory)
Dorsal root ganglion contains somas of sensory afferents entering the cord
Ventral root are efferents (motor)
Spinal nerves mix of sensory and motor neurons

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8
Q

What is gray matter?

A

Nerve cell bodies, dendrites and axons

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9
Q

What is white matter?

A

Bundles of myelinated axons organized into tracts

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10
Q

How is the spinal gray matter divided?

A

Dorsal horn
Intermediate gray
Ventral horn

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11
Q

What types of neurons are in the dorsal horn?

A

Mainly neurons responding to sensory input

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12
Q

What types of neurons are in the ventral horn?

A

Mainly motor neurons whose axons exit the spinal cord

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13
Q

What types of neurons are in the intermediate gray?

A

Some sensory neurons, some motor neurons, interneurons

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14
Q

What is a motor unit?

A

One alpha motor neuron and all the muscle fiber it innervates

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15
Q

What is a motor neuron pool?

A

The collection of alpha motor neurons that innervate a single muscle

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16
Q

What are the two types of lower motor neurons?

A

Alpha motor neurons
Gamma motor neurons

17
Q

What are alpha motor neurons?

A

They innervate extrafusal muscle
Trigger the generation of force in the muscle

18
Q

What are gamma motor neurons?

A

Innervate intrafusal muscle fibers of the muscle spindle

19
Q

What is the organization of motor neuronal pools in the ventral horn?

A

It is divided like an arm
Axial muscles close to the middle
Extensors at the middle towards the ventral end
Flexors are above extensors
Distal muscles most far away from middle

20
Q

What type of interaction of neurons is needed for voluntary contraction of skeletal muscle?

A

Upper motor neuron goes down the tract synapses to lower motor neuron on spinal nerve to skeletal muscle

21
Q

What are the mechanisms done by lower motor neurons to control the force of a muscle contraction?

A

By varying firing rare of motor units
Recruitment of synergistic motor units

22
Q

What means by varying firing rate of motor units?

A

One AP in the alpha motor neuron causes an endplate potential large enough to generate one postsynaptic AP in the muscle
AP in the muscle causes a muscle twitch
Increasing AP frequency leads to twitch summation and eventually sustained contraction

23
Q

What means by recruitment of synergistic motor unit?

A

Size principle: small motor units are recruited first (slow) then larger motor units (fast)

24
Q

What are large motor units (fast twitch)?

A

Generate more force
Tire easily

25
Q

What are small motor units (slow twitch)?

A

Generate less force
For endurance

26
Q

What are fast-fatigable motor units?

A

Generates the most force but fatigues easily

27
Q

What are fast fatigue-resistant motor units?

A

Generates force but takes less time to fatigue

28
Q

What are slow motor units?

A

Generate low force and lasts a long time

29
Q

How much input does an alpha motor neuron receives?

A

Three sources- interneurons, muscle spindles, upper motor neurons

30
Q

What is a muscle spindle?

A

Proprioceptor (body position)- stretch receptor
detect changes in muscle length
intrafusal muscle in a fibrous capsule inside the extrafusal muscle fiber
Situated in parallel with extrafusal muscle fibers
Ia sensory afferents wrap around intrafusal muscle fibers and inform CNS about muscle length

31
Q

What is the monosynaptic myotatic reflex arc (stretch reflex)?

A

When weight is added to muscle, it will stretch, but then it will contract due to the Ia axons and alpha motor neuron

32
Q

What is the knee-jerk reflex?

A

When you hit the tendon of quadriceps that has a muscle spindle that is wrap around Ia sensory afferent and activates alpha motor neuron causing the muscle to contract

33
Q

What happens when you stretch a muscle?

A

Stretching the muscle stretches the Ia nerve endings and activates alpha motor neuron
Extrafusal muscle contracts and activity in Ia axon stops
Spindle no longer sensitive to stretch
Gamma motor neuron activity resets the length of the spindle by contracting intrafusal muscle fiber.
Ia can continue to inform CNS of changes in length

34
Q

What do gamma motor neurons do for the muscle spindle?

A

Gamma motor neuron activity resets the length of the spindle by contracting intrafusal muscle fiber.
Ia can continue to inform CNS of changes in length
Thus, alpha and gamma co-activation normally

35
Q

What are golgi tendon organs?

A

Proprioceptors
Monitors muscle tension- the force of contraction
Situated in series with muscle fiber
Ib afferents encode muscle tension information

36
Q

What is the reverse myotatic reflex?

A

Ib axon synapse with inhibitory interneuron inhibiting the alpha motor
Reflex protects muscle from being overloaded

37
Q

What is reciprocal inhibition?

A

The contraction of one set of muscles is accompanied by the relaxation of the antagonist muscles.

38
Q

What is the flexor crossed-extensor reflex?

A

Ipsilateral: excite flexors, inhibit extensors
Contralateral: excite extensors, inhibit flexors

39
Q

What are central pattern generators?

A

Circuits that give rise to rhythmic motor activity

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