L6: NC Reflexes

Sensory receptors

• What do they respond to?

• What are the two parent categories?

Respond to different stimuli.

Interreceptor: senses information from within the body such as: temperature, pain, and pressure

Exteroceptors: Near the body surface, responds to external stimuli.

What are proprioceptors?

Synonymous with sensory receptors.

Respond to stimuli that informs the degree the body segment is changing, direction, and rate

What are the various muscle receptors?

Muscle spindles and Golgi Tendon Organ (GTO)

What is a muscle spindle

• Location

• Senses

MS is a tiny capsule filled with fluid and specialized fibers.

They are located predominantly in the muscle belly, situated in parallel with fibers direction.

Senses when the muscle is stretched.

Where are a great amount of muscle spindles located?

Are located in the muscles that control fine motor skills.

Muscle spindle anatomy

• Fiber types

• Nerve endings

Extrafusal fibers: normal muscle fibers

Intrafusal fibers: muscle fibers within the spindle

• non-contractile center portion

• the ENDS contract

Type I ending: Primary/Annulospiral ending: coiled around the middle noncontractile section

Type II ending: Flower-spray endings: coiled around the ends of noncontractile midsection

Type I ending: Primary/Annulospiral ending

• sensitive to

• Phasic info.

Sensitive to the velocity of change/ rate of change in length (fast or slow)

Speed in which the muscle is changing length.

Type II ending: Flower-spray endings

• Sensitive to

Sensitive to static (tonic) muscle length

• change of length of the muscle NOT the speed at which it changed.

How does the CNS differentiate between annulospiral n. endings and flower-spray n. endings?

The difference in the frequency of the impulse between phasic and tonic information.

What type of motor neuron interfuses the fibers of muscle spindles?

Extrafusal fibers are innervated by alpha motor neurons

Intrafusal fibers are innervated by gamma motor neurons

How is the Golgi Tendon Organ (GTO)/ Tendon Organ situated?

• what does it monitor? explain

• Purpose?

Is embedded “in series” in the tendon at the MTJ (weakest length)

It monitors tension. As tension increases and becomes too much for the GTO → the GTO sends information via a sensory n to CNS → causes an inhibitory response → motor n to muscle, inhibiting and relaxing it.

Protective mechanism

What are the joint and skin proprioceptors?

Pacinian Corpuscles, Ruffini endings, and cutaneous receptors.

Pacinian Corpuscles

• Location

• Detect

• Transmits

• Purpose

L: In regions around the joint capsules, ligaments, skin, and tendon sheaths

D: Rapid joint angle changes (rapid) and pressure

T: impulses to CNS for rapid changes in joint angles and pressures for brief periods of time (not continuous)

P: Predicts where body joint segment will end in space at current rate.

• and appropriate readjustment in position can be anticipated and effected

Ruffini Endings

• Location

• Detect

L: in deep layers of skin and joint capsule

D: Continuous states of pressure in joints and skin

• senses joint position and changes in joint angle, activated by mechanical deformation

Cutaneous receptors

• what are the two types

Meissner corpuscles: sensation of touch

Free nerve endings: sensation of pain

Serve as proprioceptors when they show sensitivity to texture, hardness, softness, and shape, and participate in reflexes.

What are the labyrinthine and neck proprioceptors?

semicircular canals and neck proprioceptors

Semicircular canals

• Located

• Filled with

• How is motion detected

• Responsible for

L: located at perfect right angles to each other.

It is filled with endolymph and hair cells.

Hair cells detect the motion of fluid as the head moves. Information is then sent to the CNS → gives a sense of head movement and overall balance.

Responsible only for the orientation and movement of the head.

Neck proprioceptors

• what are they?

• Sensitive to?

• Which muscles have the highest density?

Are a collection of all proprioceptors.

Sensitive to change of angle between the body and head through the neck.

Deep neck muscles have the highest density of spindles compared to other muscles

• important in the maintaining balance.

How does the labyrinthine system and neck proprioceptors work independently and together.

LS detects when head movement and sends signals for the head to straighten out and align with the neck/body.

NP can override the signaling of the LS to the CNS to prevent reflexes when in control of movement (balanced).

What is a reflex movement?

→ How does it travel?

Is a specific pattern of movement without violation (voluntary intervention) from the cerebrum

Stimulus → Receptor → sensory neuron → spinal cord→ motor neuron → muscle → response

What are the two categories of neural pathways?

Monosynaptic: sensory neuron synapses to motor neuron directly

Polysynaptic: interneurons are involved

What are the proprioceptive reflexes?

Phasic reflexes

• knee-jerk reflex

Tonic reflexes

• Golgi tendon reflex

• Asymmetrical TNR

• Symmetrical TNR

• Labyrinthine reflex symmetrical

• Labyrinthine righting reflex

• 
  

Phasic stretch reflex

• Associated with..

• Generally happens when…

  • Gives a…

Associated with annulospiral ending of the muscle spindle

Generally happens when a muscle is eccentrically lengthened and quickly (no pause) concentrically contracts.

• “Neuromuscular bump” in which the muscle spindle sends an impulse for the muscle to contract in addition to a cognitive (voluntary) contraction.

Knee-jerk reflex

• what type of reflex

• explain both synapses

Phasic Stretch Reflex

Monosynaptic

• Stimulus→ patellar tendon is hit

• Receptor→ muscle spindle

• Sensory neuron→ sends info to spinal cord

  • Spinal cord→ sensory neuron synapses and sends an excitatory stimulus motor neuron to quadriceps

• Motor neuron→ delivers motor input to quadriceps

• Muscles→ quadriceps contract, extending the knee

Polysynaptic

• Stimulus→ patellar tendon is hit

• Receptor→ muscle spindle

• Sensory neuron→ sends info to spinal cord

• Spinal cord→ sensory neuron synapses with interneuron which synapses to motor neuron that innervates the hamstrings sending an inhibitory stimulus

• Motor neuron→ inhibitory stimulus increases threshold

• Muscles → hamstrings relax

What is a tonic stretch reflex?

• Associated with…

• What is the neurological response…

• It gives us a sense of…

Associated with the flower spray ending

The static (maintained stretched length) or slow stretching of muscle is met with a neurological response to contract, producing a longer lasting tonic contraction.

• Muscles tries to contract when being stretched out and continues even after released.

TSR gives us a sense of muscle tone

What is muscle tone?

Is the state of contraction the muscle maintains/the resting length of the muscle spindles.

• muscle spindles adjust to a certain level of tone (resting length) and try to maintain it → response by the muscle to want to contract back to its tone during and after the contraction is released.

Asymmetrical Tonic Neck Reflex

• what type of reflex?

• what is detected?

  • explain…

• Reflex mainly occurs

  • reason for reflex?

Tonic stretch reflex

Right or left rotation of the head/neck is detected by joint proprioceptors of the neck.

• When the head is turned to the right → joint proprioceptors detect a change in joint angle → information is sent via sensory neurons → CNS→ motor neuron of the right arm is stimulated, and contracts abductors and extensors/motor neuron of left arm is stimulated and contracts adductors and flexors.

  • and vice-versa

Reflex mainly occurs in babies, not adults

• Believed to be a protective reflex for them to not roll face down before proper motor control.

Symmetrical Tonic Neck Reflex

• What is it?

• What happens → Response

• What is it believed to facilitate?

Flexion or extension of the head/neck and how the arms respond accordingly.

When a baby does flexion/extension, proprioceptors of the neck send information to the spinal cord

• Neck extension → extension of arms

• Neck flexion→ flexion of arms

Believed to facilitate locomotion (crawling) in babies

What is the labyrinthine reflex symmetrical?

• Correlated to?

• Stimulus, receptors, response

• Mainly seen

During TNR, neck proprioceptors also stimulate the lower extremities

Stimulus: is head/neck flexion or extension

Receptors: joint receptors in the neck

Response: lower extremity appropriate response to stimulus

• TNR Extension → lower extremities extend

  • TNR Flexion → lower extremities flex

Labyrinthine Righting Reflex

• What is the LS attempting to maintain?

• What is the receptor?

• Difference between babies and adults

  • controlled vs. uncontrolled

The LS tries to maintain the head in an upright position with gravity.

The receptor is the utricle

• functions to sense when the head is not in line and stimulates the CNS to bring the head back up and in line with the neck.

In babies, their LS does not allow them to fall with their body. In every position, the head remains upright.

In adults, the LRR can be overridden, and the person’s head can follow their body when in control.

• However, if a person is falling, there is a neurological response for the upper and lower extremities to contract and get themselves upright with gravity.

LRR when spinning

• What causes dizziness? What is the body’s response?

Fluid in the semicircular canals is in motion as a person spins. When the person stops spinning, the fluid continues to move, causing dizziness.

• Body/extremities try to restore balance by thrusting about arms, because the LS is signalling to the brain that the person is still out of balance.

What are the exteroceptive reflexes?

Flexor reflex, extensor thrust reflex, and flexor and crossed extensor reflex.

Flexor reflex

• Stimulus

• Receptor

• Response

S: Pain

Receptor: free nerve endings

→ information is sent to the CNS→ faciliatory response to flexors close to the source of pain

Response: quick withdraw from source of pain

Extensor thrust reflex

• Receptor

• Explain how it works when walking/running

R: Pacinian corpuscle (at balls of feet)

When weight is shifted during walking/running on the balls of our feet, there is an increase in pressure detected. Information is sent to the CNS (spine) via a sensory neuron → synapses occur to the extensors of the hip, knee, and ankle (plantarflexors) and they contract → person thrusts themselves forward and upwards

Flexor and Crosses Extensor Reflex

• Receptor

• What happens to each leg

This is a reflex that mainly occurs in the lower extremities.

1) Free nerve ending detects painful stimulus

2) Sensory neuron sends info to spinal cord

3b) The leg that received the pain stimulus

• Motor neuron to flexors gets facilitatory activation

  • Dorsiflexors, knee flexors, and hip flexors contract

• Motor neurons to extensors are inhibited

• Result: Leg is withdrawn from source of pain

However, to readjust weight, the flexor reflex occurs simultaneously with the extensor reflex

3c) Sensory neurons via interneurons synapse to motor neurons of opposite leg

• Motor neurons of the extensors are stimulated and muscles contract

• Flexors are inhibited

• Result: Body weight is shifted and we stay upright with gravity

What is kinesthetic awareness?

• When would we not have controlled movements?

• Kinesthetic proprioception is like? Serves as a foundation to?

The conscious awareness of body position (or joint position) and the amount & rate of

• without rapid transmission of sensory→ integrative→ and motor commands we would not have controlled movements.

  • Kinesthetic proprioception is like muscle memory, which serves as the foundation of voluntary motor skill learning and movement overall.

What is reciprocal inhibition?

• Is it automatic? When is it not?

Agonists are stimulated by motor neurons to contract, and the antagonists are simultaneously and reciprocally inhibited.

• This is automatic in reflexes and familiar movements. However, when learning a new skill or when a skill is complex, it is consciously controlled to achieve more skilled performance.

What is coactivation/reciprocal activation?

• When does it happen (2)? What is happening?

When the opposite muscle group is stimulated to contract.

• May happen when an unfamiliar motor task is performed, so more muscle than necessary contracts (requiring more energy).

  • May also happen to maintain joint stiffness, either for a movement or injury.

When does coactivation decrease?

Coactivation decreases as person learns to do reciprocal inhibition. The persons movements get more efficient (requiring less energy).