NBSS (neuroscience) - spinal cord and reflexes

Question 1

What is the definition of a reflex?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

• Mediated by the somatic nervous system.
• Stimulates skeletal muscle.

Question 4

What are the 3 steps of a reflex?

Answer 4

• Sensory input
• Information processing
• Motor output

Question 5

What are the 5 components of reflexes?

Answer 5

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

Question 6

What are the 5 components of a monosynaptic reflex?

Answer 6

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

Question 7

What are most reflexes?

Answer 7

Most reflexes are polysynaptic - they include interneurones.

Question 8

why are polysnapses slower?

Answer 8

• 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.

Question 9

What are the proprioreceptors?

Answer 9

• 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

Question 10

Where are proprioreceptors located?

Answer 10

skeletal muscle, tendons, joint capsules, and ligaments

Question 11

where are muscle spindles and Golgi tendon organs found?

Answer 11

sensory muscle receptors

Question 12

how can muscle spindle be described?

Answer 12

• 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

Question 13

how can golgi tendon organ be described?

Answer 13

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

Question 14

what do muscle spindles do?

Answer 14

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

Question 15

why do we need reflexes?

Answer 15

prevent muscular damage

Question 16

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

Answer 16

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.

Question 17

what is a total flexor pattern?

Answer 17

withdrawal reflex of finger, wrist, elbow and shoulder

Question 18

What is reciprocal innervation?

Answer 18

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

Question 19

what are cross cord reflexes?

Answer 19

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

Question 20

difference between ipsilateral and contralateral

Answer 20

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

Question 21

what are intersegmental reflexes ?

Answer 21

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

Question 22

What is the building block for walking?

Answer 22

Crossed extensor reflex.

Question 23

What are central pattern generators?

Answer 23

They control rhythmic movements

Question 24

What is descending control?

Answer 24

Change motor neurone pool excitability

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

Question 25

how is descending control seen clinically?

Answer 25

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)

Question 26

What is the function of Renshaw cells?

Answer 26

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.

Question 27

what is in the pyramidal pathway?

Answer 27

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

Question 28

what is in the extrapyramidal pathway?

Answer 28

- 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

Question 29

What is the function of vestibulospinal control?

Answer 29

control balance and posture innervating antigravity muscles

Question 30

what is the tectospinal extrapyramidal pathway for?

Answer 30

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

Question 31

what is the reticulospinal extrapyramidal pathway for?

Answer 31

MRST pons: increase muscle tone - exciting vol LSRT medulla: inhibit muscle tone - inhibit vol

Question 32

what is the rubrospinal extrapyramidal pathway for?

Answer 32

fine movements

Question 33

what are the supra spinal reflexes?

Answer 33

- postural reflexes (whole body - center of gravity remains ) - vestibular reflexes - brain stem reflexes

Question 34

what is the labyrinthine righting reflex

Answer 34

labyrinthine righting reflex (vestibular) - FALL PREVENTION - lean off balance - stimulates semicircular canals - motor response of neck and limbs - maintenance of upright posture

Question 35

where do we detect labyrinthine righting reflex?

Answer 35

labyrinth in inner ear - vestibular apparatus detecting movement and position Inner ear → vestibular nuclei → spinal motor neurones Postural reflex body movements

Question 36

where is the reflex centre?

Answer 36

cerebellum

Question 37

what does reflex centre in cerebellum do?

Answer 37

- integrate sensory information - position of the body - coordinates complex movements - maintains posture

Question 38

what does possible nerve damages outside spinal cord indicate

Answer 38

peripheral neuropathy

Question 39

what does damage to motor neruons indicate

Answer 39

motor neruon disease

Question 40

what does damage to neuromuscular junction indicate

Answer 40

myasthenia gravis

Question 41

what is a muscle disease

Answer 41

myopathy

Question 42

what does an excessive response suggest?

Answer 42

- spinal cord damage **ABOVE** level controlling hyperactive response - higher CNS damage - **disinhibition**

Question 43

what does an asymmetric response suggest?

Answer 43

- early progressive disease onset - localised nerve damage : trauma

Question 44

What is the Babinski reflex?

Answer 44

- 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.

Question 45

how is cerebral palsy related to developmental issues?

Answer 45

- 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