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Neuroscience, Behavior and Social Sciences > Spinal Cord Circuitry and Reflexes > Flashcards

Spinal Cord Circuitry and Reflexes Flashcards

1
Q

Definition of reflexes

A

Stereotyped, involuntary response to a stimulus

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2
Q

Definition of an autonomic reflex

A

Reflexes mediated by the ANS which activates smooth, cardiac muscle and glands

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3
Q

Definition of a somatic reflex

A

Reflexes mediated by the somatic nervous system which activates skeletal muscle

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4
Q

What is a reflex

What characterises an autonomic and somatic reflex

A

Stereotyped involuntary responses to a stimulus

Autonomic

  • Mediated by the ANS
  • Activates smooth, cardiac muscles and glands
  • often bilateral

Somatic reflexes

  • Mediated by the somatic NS
  • Activates skeletal muscle
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5
Q

What are the 4 main properties of any reflex

A

Simplest neural circuit
Fast automatic behaviour
Very old evoluntionary to help us survive
Unconscious

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6
Q

What are the basic steps in any reflex

A 
Receptor
Sensory neurone 
Interpretation center
Motor neurone
Effectot
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7
Q

Describe the monosynaptic reflex pathway in the knee jerk reaction
What could go wrong in this pathway

A

Muscle spindle surrounded by extrafusal fibres
Myelinated Aa, large diameter fibre in peripheral nerve
Cell body in DRG

Synapse in ventral horn with myelinated Aa motor
Transduces electrical => chemical energy onto NMJ => muscle

Myelinated fibres can get demyelinated => decreased conduction velocity
Cell body in DRG can get damaged
NT problem
NT receptor problem
Muscle problems
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8
Q

Describe the structure of a peripheral nerve

A

Whole nerve surrounded by epineurium
Nerve fascicles in perineurium
Individual fibres surrounded by endoneurium

Peripheral nerve contains many afferent and efferent fibres

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9
Q

What is the average speed of a Aa fibre

A

120m/s

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10
Q

What is the 2 functions of a monosynaptic reflex

What is an example of a monosynaptic reflex

A

Controls stretch leg muscles
Maintains upright posture

Muscle spindles in the stretch reflex

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11
Q

What are the 3 properties of a polysynaptic reflex

A 
Have interneurons
More synapses => 0.5ms synaptic delay => slower reflex
Synapse signals can be changed
-Spatial summation => AP
-Temporal summation => AP
-EPSPs, IPSPs => SP
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12
Q

What are the 2 properties of properioceptors in reflexes

  • where are they found
  • what do they do
A

Found in skeletal muscles, tendons, joint capsules, ligaments
Carry sensory input to CNS

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13
Q

Describe the 3 main properties of muscle spindles

  • location
  • stimulus
  • type of synaptic reflex

-pathway of function

A

-Parallel and inbetween extrafusal muscle fibres
-Respond to stretch, prevent over stretching
Tonically active sensory neurones around intrafusal fibres => CNS
-MONOSYNAPTIC

  • Extrafusal loses tone/stretches too much
  • Intrafusal stretched
  • Sensory afferent from sensory neurone => CNS
  • a motor contracts extrafusal muscle
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14
Q

How is the muscle spindle reflex stopped when you want to move voluntarily

A

Descending pathway coactivates
a motor => extrafusal
y motor => intrafusal

Both contract so length change is not detected by the sensory afferent

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15
Q

Describe the 3 main properties of golgi tendon organs

  • location
  • stimulus
  • type of synaptic reflex

-pathway of function

A
  • Series at musculotendinous junction with collagen fibres
  • Responds to tension
  • POLYSYNAPTIC

-Extrafusal muscle contraction stretches golgi tendon organ
-GTO fires => CNS
Interneurone between afferent and efferent inhibits muscle contraction
-Muscle relaxes, load dropped

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16
Q

What is the withdrawal reflex

3 properties

A

Total flexor pattern => retraction of the whole limb from danger
Hardwired in spinal cord
Many interneurons

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17
Q

Why are interneurons important

A

If both flexors and extensors are excited => both contract => rigidity

Inhibitory interneuron onto antagonist => relaxes => movement

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18
Q

Describe the pathway in the reciprocal innervation reflex to move 1 limb

A

Sensory receptor in muscle spindle
Afferent to SC

Excitatory synapse => contract flexor
Inhibitory interneurone => relax extensor

19
Q

Describe the pathway in cross cord reflexes in order to coordinate 2 limbs when painful stimulus detected

A

Sensory receptor in 1 limb (nociceptor)
Afferent of R leg to CS

4 different effects happen at the same time

  • Excitatory interneuron => contract R flexor
  • Inhibitory interneuron => relax R extensor

Decussation from R dorsal => L ventral

  • Excitatory interneuron => contract L extensor
  • Inhibitory interneuron => relax L flexor
20
Q

How would you coordinate the whole limb in a reflex

A

Ascending and descending fibres in the ventral horn of the SC to innervate different segments of the SC

21
Q

What are spinal pattern generators

How is their input changed/stopped

A

Allows for walking via the crossed extensor reflex
No sensory/descending inputs
Precise temporal sequences of muscle contraction => coordinated mv

Can change timing via rhythm generators
Stopped by descending input from cortex

22
Q

What are the 2 types of complex movement and what areas of the nervous system do they involve

A

Walking, intersegmental at SC

Turning, intersegmental with the brainstem

23
Q

Describe how cortical control can interfere with reflexes

How can you override this cortical control

A

From cortex =long tracts=> conscious descending inhibition to override reflex

To override this, clench teeth

  • Increases ion movement in CSF
  • Increases membrane excitability => easier to reach AP
24
Q

What is recurrent inhibition
What cell is involved
How does it work

A

Motor neurone is excited, acts on muscle and Renshaw cell

Renshaw cell (inhibitory interneuron) inhibits further excitation of same motor neurone

Allows for self regulation of effectors within SC

25
Q

What are the 2 pyramidal reflexes

Where do they act

A

Corticospinal
-cortex => SC
Corticobulbar
-cortec => brainstem

26
Q

What are the 4 extrapyramidal reflexes

Where do they act

A

Vestibulospinal (maintains balance)
-vestibular nuclei => SC

Tectospinal
-sup colliculus (visual mv) => cervical spine

Reticulospinal
-pons => midbrain

Rubrospinal
-red nucleus in midbrain => SC

27
Q

What are the 2 tracts in the vestibulospinal system
What do they do when you fall
What do they positively and negatively innervate?

A

Lateral VS

  • ipsilateral action
  • controls balance and posture
  • innervates antigravity muscles

When falling
+ve ipsilateral leg extensors (monosynaptic)
-ve ipsilateral leg flexors (monosynaptic)
+ve ipsilateral upper arm flexors (polysynaptic)

Medial VS

  • bilateral action
  • only in the neck and shoulder

When falling
+ve bilateral neck muscles

28
Q

What is the function of the tectospinal tract

A

Coordinates head movements in relation to visual stimuli

29
Q

What is the function of the reticulospinal tract

How does the medial RS and the lateral RS differ

A

Medial RST => increases muscle tone in limbs, excites voluntary movement

Lateral RST => decreases muscle tone in limbs, inhibits voluntary movement

30
Q

What is the function of the rubrospinal tract

A

Output for cerebellum
Contralateral
Role in fine movement

31
Q

Describe the pathway involved in vestibular reflexes when you fall

A

Inner ear receives orientation info via vertical vestibular apparatus
Vestibular nuclei in pons
Spinal motor neurones
Postural reflex body movement

32
Q

Describe the pathway involved in visual reflexes when you fall

A 
Eye sees movement
Lateral geniculate nucleus
Pretectal area in pons
Descending to SC
Spinal motor neurones act to maintain balance
33
Q

Describe pressure receptors in relation to posture

What happens if you damage the peripheral nerves connected to the Pacinian corpuscles in your feet and close your eyes

A

Monitor weight distribution in posture

If you damage peripheral nerves connected to the Pacinian corpuscles in the feet and close your eyes => fall

34
Q

What are the 4 functions of cerebellar reflexes

What tracts do they operate with

A

Integrates sensory info
Body position
Complex movement coordination
Maintains posture

Acts via VST and RST

35
Q

What happens when the reflex response goes wrong
Why are they lost
What can happen as a consequence

A
  • Absent
  • Distorted
  • Exaggerated
  • Change of symmetry

Lost due to

  • degeneration
  • demyelination
  • synaptic problems

Reflexes are lost before weakness

36
Q

What are the 4 potential causes of a weak/absent reflex

A

Damage to nerves outside SC
-Peripheral neuropathy

Damage to motor neurones
-Motor neurone disease

Problems with the NMJ
-Myasthenia gravis

Muscle disease
-Myopathy

37
Q

What are the 2 potential causes of an excessive reflex

A

Spinal cord damage above the level controlling the hyperactive response

Higher CNS damage

38
Q

What are the 2 potential causes of an asymmetric response

A

Early sign of a progressive disease

Localised nerve trauma

39
Q

How would you test for spinal cord injurioes

A

Reflex tests determine area injures

  • Motor neurones above injury => unaffected
  • Motor neurones below injury => absent
40
Q

How would you test for closed head injuries

Why do this test

A

Increased pressure in skull and on the oculomotor nerve

-Changed eye reflex response with the light (oculomotor reflex)

41
Q

Describe the Babinsky reflex in the foot
What is normal
What is patholoigcal/normal for neonates

A

Normal reaction when lateral plantar stroked
-toes curl down

In hemi/paraplegic patients (lost upper motor neurone control) and neonates
-toes curl up

42
Q

What controls the 3 flexor reflexes found in neonates and young infants when they

  • stand
  • walk
  • develop
A

Stand
-flexor reflex controlled by RST

Walk
-flexor synergy with cortex and pattern generator

As they develop, Babinsky reflex is lost

43
Q

Describe how reflexes develop as you develop

  • at birth
  • as CNS matures
A

At birth

  • no voluntary control
  • primitive and developmental reflexes only

As CNS matures

  • higher brain areas override primitive reflexes
  • allows development of mature responses (postural reflex)

Any disinhibitiom is pathological

44
Q

Describe reflexes in patients with cerebral palsy

A

Movements are random and uncontrolled
Higher control development failure
-retain primitive reflexes
-affects sensory mv perception

Neuroscience, Behavior and Social Sciences (50 decks)

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