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Neuroscience > Spinal Reflexes and Muscle Tone > Flashcards

Spinal Reflexes and Muscle Tone Flashcards

1
Q

what are the key components of a reflex?

A

afferent fibers bring action potential to the great matter- where it synapses on the cell body of a motor neuron (efferent) which then sends a signal back out to the muscles

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2
Q

what root do afferent sensory fibers enter the spinal cord through?

A

through the dorsal root

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3
Q

Aalpha axons innervate what?

A

skeletal muscle

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4
Q

gamma motor neurons axons innervate what?

A

intrafusal fibers

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5
Q

dorsal roots innervate what?

A

sensory information

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6
Q

ventral roots of the spinal nerve innervate what?

A

motor

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7
Q

what are the five components of the reflex arch?

A
  1. stimulus to receptor
  2. sensory/afferent neuron
  3. integration center in spinal cord
  4. motor/efferent neuron
  5. effector muscle
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8
Q

what are the three types of sensory receptors?

A

Exteroceptors (skin/sense organs) = respond to external stimuli- information about temp. pressure etc

proprioceptors (muscles tendons joints) = send information about your position in space

interoceptors (internal organs)= send information about pain/stretching of internal organs

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9
Q

does every reflex involve interneurons?

A

no, but the majority do

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10
Q

what are the effector organs in the somatic vs. autonomic system?

A

somatic = skeletal muscles

autonomic = cardiac muscle, smooth muscle, and gland cells

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11
Q

what do internuerons do?

A

they are responsible for the distribution of sensory information and coordination of commands within the CNS - they allow for complexity

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12
Q

what is the difference between monosynaptic and polysynaptic reflexes?

A

Monosynaptic

–Only one synapse between afferent and efferent neurons

–The only monosynaptic reflexes which occur in the body are the stretch (myotatic) reflexes

•Polysynaptic

–From 2 to 100s of synapses between afferent and efferent neurons

–e.g. withdrawal reflex

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13
Q

why are muscles always at least partially contracted?

A

Why? If muscles relaxed completely (no resting tone), they would overlengthen, and too much time would be required to take up slack when a contraction was called for.

On the other hand, too much tone would not allow for sufficient rest and recovery.

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14
Q

muscles and their tendons have what two main sensory receptors?

A

(both are types of proprioceptor)

  • Muscle spindles (length/rate of change in length)
  • Golgi tendon organs (tension/rate of change of tension
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15
Q

what are the principle regulators of muscle tone?

A

muscle spindles

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16
Q

what are the components of the stretch reflex

A

Components of the stretch reflex

  • Sensory receptor: Muscle spindles
  • Area for integration: Spinal cord
  • Effector: Skeletal muscle that is stretched
17
Q

what motoneurons maintain proper tension while muscles are relaxed?

A

gamma motoneurons - which supply the muscle spindles

18
Q

which part of the brain is continually informed of even slight changes in muscle tone?

A

The cerebellum

19
Q

decreased muscle tone is indicative of what?

A

motor neuron, cerebellum, acute stroke or cord lesion

20
Q

increased muscle tone is due to what?

A
21
Q

the knee jerk reflex is what kind of reflex?

A

it is a stretch reflex - which is informative about the integrity of the CNS

22
Q

describe the sequence of events in the knee jerk reflex

A
23
Q

what causes hyporeflexia?

A

results if any part of the reflex pathway from the spindle back to the muscle is damaged= diminished stretch reflex response

•Examples of conditions associated with hyporeflexia:

–Poliomyelitis (virus damages lower motor neurons)

–Lower motor neuron lesions (e.g. those serving foot)

–Muscular dystrophy (degenerative disease of skeletal muscle)

24
Q

what is the term for apparent loss of tendon relfexes?

A

areflexia

•Causes

–Can be due to lack of clinical experience!

–Any lesion of the reflex arc (e.g. root lesion or peripheral neuropathy)

25
Q

what is hyperreflexia - what are its cuases?

A

•Hyperreflexia results following damage to motor pathways from brain to the spinal cord

–Certain stretch reflexes become exaggerated (e.g. elbow)

•Causes

–Upper motor neuron lesion (UMNL)

–Greatly exaggerated muscle jerk response can occur after stroke or brain tumour

–Damage to motor areas of cerebral cortex (e.g. loss of inhibitory inputs from higher areas to some motor neurons)

26
Q

where is the golgi tendon organ located?

A

in the muscle tendon - detects muscle tension =

27
Q

describe the golgi tendon organ pathway

A

increased muscle tension is detected by the golgi tendon organ - which transmits signals to the spinal cord to inhibit motor neuron - this prevents too much tension on muscle, controls force within muscles and stiffness of particualar joints

28
Q

does the golgi tendon organ pathway initiate reflexes?

A

no - not directly

29
Q

somatic reflexes result in what?

A

limb movement

30
Q

what is the ‘protagonist’ and the ‘antagonist’ in reflexes?

A

when a specific muscle contracts = protagonist

opposing muscles that relax to allow movement = antagonist

31
Q

what must occur in antagonist muscles to allow the protagonist to move?

A

relaxation in the antagonist must occur = this is called reciprocal innervation

32
Q

describe reciprocal innervation as it pertains to the knee jerk reflex

A

when you hit the knee tendon, the monosynaptic path starts to contract the quadricepts- allong the same path however, the antagonist muscle (the hamstrings) relaxes

33
Q

withdrawal reflexes are an example of what kind of reflex?

A

polysynaptic reflexes - they move a part of the body away from painful stimulation = protective

34
Q

describe the pathway in a flexor withdrawal reflex

A
  1. touch hot plate
  2. synapses on excitatory neuron which contracts biceps
  3. at the same time it inhibits contraciton of the triceps -
35
Q

strength of the reflex is related to what?

A

to the intensity of the stimulus

36
Q

what is the ‘crossed extensor reflex’?

A
  • Not all spinal reflex action is limited to motor responses on the side of the body to which the stimulus is applied
  • example) . Why do you not fall over when the foot is lifted away from the sharp object?

–Withdrawal reflex is accompanied by the crossed extensor reflex

37
Q

What is a learned reflex?

A

may involve overriding basic reflexes and is learned by repetition

ex) muscle memory - you know how to throw a ball, or catch a ball after practicing

Neuroscience (44 decks)

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