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GBE > NBSS (neuroscience) - spinal cord and reflexes > Flashcards

NBSS (neuroscience) - spinal cord and reflexes Flashcards

1
Q

What is the definition of a reflex?

A
  • It is involuntary.
  • It is a response to stimulus.
  • It is not subject to conscious control.
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2
Q

What do the autonomic reflexes activate and how are they mediated?

A
  • Mediated by the autonomic nervous system
  • Activates:
    • Smooth muscle
    • Cardiac muscle
    • Glands
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3
Q

What do the somatic reflexes activate and how are they mediated?

A
  • Mediated by the somatic nervous system.
  • Stimulates skeletal muscle.
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4
Q

What are the 3 steps of a reflex?

A
  • Sensory input
  • Information processing
  • Motor output
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5
Q

What are the 5 components of reflexes?

A
  1. Receptor
  2. Sensory neurone
    • afferent pathway to CNS
  3. Interpretation centre
    • one or more synapse in CNS
  4. Motor neurone
    • efferent pathway from CNS
  5. Effector
    • e.g. muscle contracts / gland secretes
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6
Q

What are the 5 components of a monosynaptic reflex?

A
  1. Receptor - A. muscle spindle
  2. Sensory neurone:
    - B. mylenated, large diameter, 1A (alpha) afferent axon.
    - C. peripheral nerve
    - D. dorsal root ganglion
  3. Interpretation centre
    - E. spinal cord
  4. Alpha motor neurone - myelinated large diameter
  5. Effector
    - F. Muscle extrafusal fibres - neuromuscular junction
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7
Q

What are most reflexes?

A

Most reflexes are polysynaptic - they include interneurones.

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8
Q

why are polysnapses slower?

A
  • As there are more synapses - there is a greater synaptic delay.
  • One synapse = 0.5msec.
  • Interneurones can be either excitatory or inhibitory and pass this message on, on the second synapse.
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9
Q

What are the proprioreceptors?

A
  • Proprioceptors carry input from the sensory neurons to CNS
  • CNS integrates input signal
  • Somatic motor neurons carry output signal – Alpha motor neurons
  • Effectors - contractile skeletal muscle fibers
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10
Q

Where are proprioreceptors located?

A

skeletal muscle, tendons, joint capsules, and ligaments

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11
Q

where are muscle spindles and Golgi tendon organs found?

A

sensory muscle receptors

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12
Q

how can muscle spindle be described?

A
  • muscle spindle in parallel to muscle fibres
  • poles of intrafusal fibres have contractile filaments
  • tonically active - continuously giving information to CNS
  • muscle spindle contracts in parallel to main muscle fibres
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13
Q

how can golgi tendon organ be described?

A
  • golgi tendon organ at muscular-tension junction in series with main muscle fibres
  • sensory receptor intertwined with collagen fibres
  • only afferent neurone
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14
Q

what do muscle spindles do?

A
  • monitor muscle length
  • monitor rate change of length
  • prevent overstretching
  • healthy muscles are never fully relaxed, always tone as sensory neuron is tonically active
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15
Q

why do we need reflexes?

A

prevent muscular damage

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16
Q

whats the difference in reaction to a heavy load in the muscle spindle and golgi tendon reflex?

A

In the muscle spindle reflex - the addition of a load stretches the muscle and spindles, creating a reflex contraction.
- Add load to muscle.
- Muscle and muscle spindle stretch as the arm falls
- Reflex contraction is initiated by muscle spindle which restores the arms position.

In the golgi tendon reflex - an inhibitory interneurone is added. This blocks the muscle from firing.
- Add load to muscle.
- Muscle contraction stretches Golgi tendon organ.
- Neuron from golgi tendon organ fires.
- Motor neuron is inhibited.
- Muscle relaxes.
- If the excessive load is placed on the muscle, golgi tendon reflex causes relaxation, thereby protecting muscle.

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17
Q

what is a total flexor pattern?

A

withdrawal reflex of finger, wrist, elbow and shoulder

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18
Q

What is reciprocal innervation?

A

excitation of one muscle group and inhibition of their antagonists around a joint

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19
Q

what are cross cord reflexes?

A

more than one limb, opposite limb affected and effects reversed

  • same side/ipsilateral : excitation of flexor and inhibition of extensors
  • opposite side/contralateral: inhibition of flexor and excitation of extensor
20
Q

difference between ipsilateral and contralateral

A
  • Ipsi for withdrawal - flex to remove
  • Contra for stability - straight leg for support
21
Q

what are intersegmental reflexes ?

A

reflexes travelling different levels of spinal cord to enable different muscles to be affected - enables full withdrawal

22
Q

What is the building block for walking?

A

Crossed extensor reflex.

23
Q

What are central pattern generators?

A

They control rhythmic movements

24
Q

What is descending control?

A

Change motor neurone pool excitability

can be pyramidal (from motor cortex) and extra pyramidal (vestibular nuclei)

25
Q

how is descending control seen clinically?

A

patients overriding knee-jerk reflex, can be determined whether they are overriding or if there is a neural issue via Jendrassik manoeuvre (patient holds hands together before them and squeezes simultaneously as knee-jerk happens)

26
Q

What is the function of Renshaw cells?

A

you dont want continuous excitation to motor neurone so Renshaw cells act as inhibitory interneurons that inhibits itself (feedback mechanism of control) regulating spinal motor neruones

Essentially act as a negative feed back loop to stop excessive excitation.

27
Q

what is in the pyramidal pathway?

A
  • corticospinal - from cortex to spine; descending = motor pathway
  • coritcobulbar - from cortex to pons/brain stem
28
Q

what is in the extrapyramidal pathway?

A
  • vestibulospinal - vestibular nucleus to spinal cord
  • tectospinal - from superior colliculus - midbrain to spinal cord
  • reticulospinal - from reticulum in brainstem; MRST-pons or LRST-medulla to spinal cord
  • rubrospinal - from red nucleus to midbrain
29
Q

What is the function of vestibulospinal control?

A

control balance and posture innervating antigravity muscles

30
Q

what is the tectospinal extrapyramidal pathway for?

A

coordination of head movements in relation to visual/auditory stimuli; ringing bells behind baby heads

31
Q

what is the reticulospinal extrapyramidal pathway for?

A

MRST pons: increase muscle tone - exciting vol

LSRT medulla: inhibit muscle tone - inhibit vol

32
Q

what is the rubrospinal extrapyramidal pathway for?

A

fine movements

33
Q

what are the supra spinal reflexes?

A
  • postural reflexes (whole body - center of gravity remains )
  • vestibular reflexes
  • brain stem reflexes
34
Q

what is the labyrinthine righting reflex

A

labyrinthine righting reflex (vestibular) - FALL PREVENTION

  • lean off balance
  • stimulates semicircular canals
  • motor response of neck and limbs
  • maintenance of upright posture
35
Q

where do we detect labyrinthine righting reflex?

A

labyrinth in inner ear - vestibular apparatus detecting movement and position

Inner ear → vestibular nuclei → spinal motor neurones
Postural reflex body movements

36
Q

where is the reflex centre?

A

cerebellum

37
Q

what does reflex centre in cerebellum do?

A
  • integrate sensory information
  • position of the body
  • coordinates complex movements
  • maintains posture
38
Q

what does possible nerve damages outside spinal cord indicate

A

peripheral neuropathy

39
Q

what does damage to motor neruons indicate

A

motor neruon disease

40
Q

what does damage to neuromuscular junction indicate

A

myasthenia gravis

41
Q

what is a muscle disease

A

myopathy

42
Q

what does an excessive response suggest?

A
  • spinal cord damage ABOVE level controlling hyperactive response
  • higher CNS damage
  • disinhibition
43
Q

what does an asymmetric response suggest?

A
  • early progressive disease onset
  • localised nerve damage : trauma
44
Q

What is the Babinski reflex?

A
  • Stroke the lateral aspect of the sole of the foot
  • The reaction = extension in the first two toes in hemiplegic and paraparetic patients and neonates.
45
Q

how is cerebral palsy related to developmental issues?

A
  • children unable to make transition to inhibit survival patterns - disinhibition
  • movement random and uncontrolled
  • failed development higher control
  • spectra of disorders retaining prmitive reflexes affecting sensory perception of movement
  • limbs, eyes, balance and hearing uncontrolled via disinhibit due to no descending control

GBE (58 decks)

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