Topic 101 - The reflexes and movement patterns

Question 1

Words to include the reflexes

Answer 1

• Reflex action
  
  • Involuntary
  • Instataneous movement
  • Stimulus
• Receptor cell
• Afferent neuron
  
  • Axon
  • Afferent fiber
• Central processing unit
• Efferent neuron
  
  • Axon
  • Efferent fiber
• Effector cell
• Spinal cord
• Upper CNS
• Somatic reflex arches
• Monosynaptic reflex arches
• Polysynaptic reflex arches
• Receptor
• Effector
• Flexor = nocioceptive = withdrawl
• Proprioceptive reflexes
• Own reflexes
• Stretch
• Spinal reflexes
• Types:
  
  • Myotatic (stretch) reflex
    
    • Intrafusal fiber
    • Nuclear bag receptor
    • Nucelar chain receptor
    • Grey matter
    • Alpha motorneuron
    • Extrafusal fiber
    • Afferent AP frequency
    • Fusimotor unit
    • Antigravitional musculature
    • Reflectorial contraction
    • Extensor reflex
  • Inverse myotatic reflex
    
    • Passive stretching
    • Fusimotor system
    • Myotatic reflex
    • Golgi tendon organs
      
      • Inhibitory interneurons
      • Alpha motor neuron
      • Skeletal muscle fiber
      • Clasp-Knife effect
        
        • Sudden lengthening
  • Stretch evoked flexor reflex
    
    • Type II. afferent
    • Flower-spray fusimotor receptor
    • Inhibitory interneurons
  • Extensor thrust
    
    • Myotatic stretch reflex
    • Interosseus muscles
• Muscle spindle
• Ia (A alpha) fiber
• Reciprocal innervation
• Exteroceptive reflex
• Reflex arch
• Outside effector organ
  
  • Foreign reflex
• Receptor
  
  • Skin
• Effector
  
  • Muscle
• Averting
• Nociceptive
• Thermoreceptive
• Pain avoiding behavior
• Group II (type A delta)
• Group IV (type C)
• Afferent fibers
• Grey matter
• Spinal ganglia
• Afferent activation
  
  • Ipsiatera extensor muscle
    
    • Inhibitory interneurons
  • Ipsiatera flexor muscle
    
    • Excitatory interneurons
• Ipsilateral muscles
• Contralateral musculature
• Alpha motor neurons
  
  • Extensors
    
    • Excited
  • Flexors
    
    • Inhibited
• Adequate interneurons
• Control
  
  • Upper levels
    
    • Lateral corticospinal tract
    • Descending motor pathways
• Babinski sign
  
  • Lesion
  • Corticospinal tracts (upper levels)

Question 2

Words to include in movement patterns

Answer 2

• Automatic movement
  
  • Walking
  • Scratching
• Spnal cord
• Upper cerebral functions (ø)
• Characteristics
  
  • Stereotype
  • Extend to more segments
  • Rhytmical repated
• Adaptation
  
  • Excitatory effects
• Spontaneous release
  
  • Inhibitory effects
• Stimulus
• Sensory ganglion
• Excitatory interneurons
• Extensor motorneurons
• Flexor motorneurons
• Collataral
• Inhibitory interneurons
• Adaptation
  
  • AP frequcency (↓)
• Extensor motorneuron
• Flexor motorneuron
• Reverber

Question 3

Topics to include in the essay

Answer 3

1. The reflexes
   
   • Reflex of the spinal cord
   • Proprioceptive reflex
     
     • Myotatic reflex
     • Inverse myotatic reflex
     • Flexor stretch reflex
     • Extensor thrust
   • Exteroceptive reflexes
2. Movement patterns

Question 4

The reflexes

Define reflex

Answer 4

Reflex action: Involuntarly and instantaneous movement in response to a stimulus

Question 5

The reflexes

Give the main components of the reflex

Answer 5

1. Receptor cell (tissue, organ)
2. Afferent neuron and its axon, the afferent fiber
3. Central processing unit
4. Effector neuron and its axon, the efferent fiber
5. Effector cell (tissue, organ)

Question 6

The reflexes

Name the different type of reflexes

Answer 6

1. Proprioceptive reflex
   
   1. ​Myotatic (stretch) reflex
   2. Inverse myotatic reflex
   3. Flexor stretch reflex
   4. Extensor thrust
2. Exteroceptive reflexs

Question 7

The reflexes

Give the common features of proprioceptive reflexe

Answer 7

1. Local response: it extends over the area where the stimulus originates
2. The intensity of the response is proportional to the intensity of the stimulus
3. Reciprocal innervation is typical: activation of the ipsilateral extensor is accompanied by inhibition of the ipsilateral flexor and conversely
4. Higher brain levels modulate the reflex

Question 8

The reflexes

Proprioceptive reflex, general

Answer 8

• Receptor is found in the same organ (muscle) as the effector (muscle)
• Monosynaptic reflex arch
• Proprioceptive reflex differs from the exteroceptive reflex in that:
  
  1. Adequate stimulus is the stretching of the muscle
  2. Receptor is in the muscle spindle, its afferent nerve is a fast Ia (A alpha) fiber
  3. Reflex arch is monosynaptic
     
     • ​​Reflex does not fatigue
  4. Alomst no latency
  5. Response is carried out immediately and lasts no longer than the stimulus
• Main types:
  
  1. Myotatic (stretch) reflex
  2. Inverse myotatic reflex
  3. Flexor stretch reflex
  4. Extensor thrust

Question 9

The reflexes

Proprioceptive reflex: myotatic (stretch) reflex

Answer 9

• Location of receptors: at two sites of the intrafusal fiber
  
  • ​Through the Ia fiber of the nuclear bag receptor and nuclear chain receptor they arrive to the grey matter
  • Here they synapse directly and through excitatory interneurons to the alpha motorneuron of the corresponding extrafusal fibers
  • Stretching of the muscle increases the afferent AP frequency in the fusimotor units, which then increases the corresponding alpha motorneuron activity
  • Response of stretching is contraction
• Alone the effect of the afferent signal following the stretching would be too large. Fine tuning of the effect is done by recurrent inhibition:
  
  • Renshaw cells (inhibitory interneurons) are activated by the collaterals of the excited alpha motorneurons and cause retrograde inhibition on:
    
    • Motorneurons that are activating them
    • Interneurons that inhibit the flexors
  • Result: strong afferent effects are smoothed
• Myotatic reflex is found in antigravitational musculature
  
  • ​Reflectorial contraction
  • Also called extensor reflex due to the importance of the extensor muscles
• Also called stretch reflex
• Myotatic reflex is a muscle contraction in response to a stretching within the muscle.
• A spinal reflex is a fast response that involves a afferent signal into the spinal cord and an efferent signal out to the muscle
• When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases α-motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax. The reflex functions to maintain the muscle at a constant length
• Gamma motoneurons regulate how sensitive the stretch reflex is by tightening or relaxing the fibers within the spindle​

Question 10

The reflexes

Proprioceptive reflex: Inverse myotatic reflex

Answer 10

• At passive stretching the muscle first contracts because of the fusimotor system, but then at further stretching a sudden relaxation occurs
• Golgi tendon organs found in the tendons are activated:
  
  • Clasp-knife effect: They excite inhibitory interneurons and so by inhibiting the alpha motor neuron of the given skeletal muscle fiber they cause sudden lengthening
• Role: modulating, fine tuning role in normal movement execution
• Also called golgi tendon reflex
• inhibitory effect on the muscle resulting from the muscle tension stimulating Golgi tendon organs of the muscle
• The reflex arc is a negative feedback mechanism preventing too much tension on the muscle and tendon. When the tension is extreme, the inhibition can be so great it overcomes the excitatory effects on the muscle’s alpha motoneurons causing the muscle to suddenly relax

Question 11

The reflexes

Proprioceptive reflex: Flexor stretch reflex

Answer 11

• Light stretching may cause extenstion in both extensor and flexor muscles
• Type II. afferent, flower spray fusimotor receptors may play a role
• The inhibitory effect acts through inhibitory interneurons

Question 12

The reflexes

Proprioceptive reflex: Extensor thrust

Answer 12

• Pressing the sole of the foot of an animal causes the extension of the limb
• Reason: myotatic stretch reflex produced through the extension of interosseus muscles
• Role: ensure a reliable support during stepping

Question 13

The reflexes

Exteroceptive reflexes, definition

Answer 13

• Receptor is located in an organ (skin) different from that of the effector (muscle)
  
  • Receptor: skin
  • Effector: muscle
• Polysynaptic reflex arch
• The reflex forms the basis of the averting, nociceptive, pain avoiding behavior

1. From the nociceptive and thermorecepros of the skin group II (typa A delta) and group IV (type C) afferent fibers arrive to the grey matter via spinal ganglia
2. Afferent activation:
   
   • ​Relaxes ipsilateral extensor muscles through inhibitory interneurons
   • Activates ipsilateral reflexor muscles through excitatory interneurons
   • Result: the limb is moved away from the painful stimulation

• Exteroceptive reflex has an effect on:
  
  • Ipsilateral muscles
  • Contralateral musculature
• Alpha motorneurons of the extensors are excited
• Alpha motorneurons of the flexors are inhibited
• Under control of upper levels:
  
  • ​Fibers of lateral corticospinal tract
  • Other decending motor pathways
• Babinski sign: Indicates a lesion of the corticospinal tract (upper levels)

Question 14

Movement patterns

Define movement patterns and give examples

Answer 14

• More automatic movement types are known that require an organization more complicated than simple reflexes but are carried out similarly by the control of the spinal cord independently from upper cerebral functions
• Example:
  
  • Walking
  • Scratching

Question 15

Movement patterns

Characteristics

Answer 15

• Stereotype
• Extend to more segments
• Rhytmically repeated
• Last much longer than the stimulus

Question 16

Movement patterns

What is important in the creation of the rhythm?

Answer 16

• Two characteristics of neurons is important:
  
  1. Adaptation to excitatory effects
  2. Spontaneous release from inhibitory effects

Question 17

Movement patterns

Describe the scratch movement pattern in dog

Answer 17

• Step 0:
  
  • Stimulus arriving from the sensory ganglion
• Step 1 & 2
  
  • Passes through excitatory interneurons
• Step 3
  
  • Running towards the extensor motoneuron
• Step 4
  
  • Running towards the flexor motoneuron
• Step 5 & 6
  
  • The excitatory interneurons send collaterals to inhibitory interneurons, that inhibit the oppositely functioning excitatory interneurons
  • The continuous stimulation causes adaptation (AP frequency is decreased), and from the continuous inhibition neurons are released after a while
• The extensor motorneuron, then the flexor motoneuron dominates
• Rhythmic movement pattern occurs
• The demonstrated neural circuit is completed by a reverber