Week 2: Spinal Control of Movement/Locomotion

Questions and Answers

What characterizes a spinal reflex?

It is an involuntary response mediated through spinal pathways. (correct)

It is the same as a conditioned reflex.

It is a voluntary action requiring higher brain involvement.

It always involves multiple sensory modalities.

Which type of muscle afferent reflex pathway is associated with proprioceptive feedback?

II pathway

Ib pathway

III pathway

Ia pathway (correct)

What role do central pattern generators (CPGs) play in movement?

They solely control fine motor skills.

They only function during voluntary movements.

They generate rhythmic movements independent of sensory feedback. (correct)

They completely replace the need for sensory input.

What is a key characteristic of muscle receptors involved in motor control?

They provide information about muscle length and tension. Signup and view all the answers

How are reflexes modulated in accordance with the task?

They adjust based on environmental and task-specific demands. Signup and view all the answers

Which type of muscle afferent is primarily responsible for detecting muscle tension?

Ib afferents Signup and view all the answers

What has the perception of a 'reflex' traditionally been considered?

A hard-wired response that is fixed in nature. Signup and view all the answers

Which component is NOT typically associated with the spinal reflex arc?

Central processing unit in the brain Signup and view all the answers

What is the current view on reflex responses in terms of adaptability?

Reflex responses are highly modifiable and context-dependent. Signup and view all the answers

Which statement accurately describes proprioception?

It pertains to the perception of body parts' relative positions and movements. Signup and view all the answers

What are the types of proprioceptors involved in sensing body position?

Muscle spindles, Golgi tendon organs, and joint receptors. Signup and view all the answers

How do extrafusal muscle fibers differ from intrafusal muscle fibers?

Extrafusal fibers are true force-producing fibers in muscles. Signup and view all the answers

What determines the sensitivity of muscle spindles to changes in stretch?

The constant stretching of intrafusal fibers. Signup and view all the answers

What role do visual systems play in proprioception?

They calibrate the proprioceptive system by providing spatial awareness. Signup and view all the answers

Which type of afferent fibers provide rapid responses to changes in muscle length?

Group Ia afferents. Signup and view all the answers

What is a critical aspect of reflex modulation?

It integrates reflex actions with voluntary motor commands. Signup and view all the answers

What is the primary biological function of the stretch reflex?

To maintain muscle at a desired length Signup and view all the answers

Which components are involved in detecting deviations from the desired muscle length?

Muscle spindles Signup and view all the answers

What role do gamma-motor neurons play in the stretch reflex?

They regulate the sensitivity of muscle spindles Signup and view all the answers

The gain of the myotatic reflex refers to what aspect of muscle response?

The amount of muscle force generated in response to stretch Signup and view all the answers

During neurological testing, which afferent input is predominantly used?

Ia muscle spindle afferents Signup and view all the answers

How is muscle tone maintained in muscles?

By maintaining a reflex arc mediated by group II muscle spindle afferents Signup and view all the answers

What role does the central pattern generator (CPG) primarily serve in the locomotion of animals?

It produces rhythmic patterned outputs without requiring sensory feedback. Signup and view all the answers

What is the significance of the γ-bias in the stretch reflex mechanism?

It directly influences muscle spindles' sensitivity and excitability Signup and view all the answers

Which of the following statements is true regarding the activation of CPGs in humans?

There has been no success in activating CPGs for continuous natural walking patterns in humans. Signup and view all the answers

What functional role does the stretch reflex serve in muscle activity during contractions?

It contributes to muscle activity during slow contractions Signup and view all the answers

What happens when the dorsal roots are transected in spinal cord research?

Locomotion can still be triggered by L-DOPA injections. Signup and view all the answers

How does CPG activity adjust to different locomotion speeds in animals?

The speed of CPG-generated locomotion is linked to the speed of the treadmill. Signup and view all the answers

What type of drive activates central pattern generators in intact animals?

Non-rhythmic tonic descending drive from the brain. Signup and view all the answers

What additional functions are central pattern generators thought to control beyond locomotion?

Respiratory and swallowing patterns. Signup and view all the answers

Why is the spinal cord circuitry essential for locomotion?

It is capable of generating and adjusting rhythmic movements independent of the brain. Signup and view all the answers

What is a significant feature of central pattern generators in relation to sensory input?

They can be initiated without any sensory input. Signup and view all the answers

What is the primary function of the muscle spindle system?

Monitors and maintains muscle length Signup and view all the answers

In a flexion reflex pathway, which action occurs in response to nociceptive stimuli?

Excitation of ipsilateral flexors and inhibition of extensors Signup and view all the answers

What role do Renshaw cells play in motoneurone regulation?

They mediate recurrent inhibition back to homonymous motoneurones. Signup and view all the answers

What is the effect of excitatory input to a Renshaw cell on motoneuronal response?

Decreases motoneuronal responsiveness Signup and view all the answers

Which sensory receptors are primarily involved in triggering the flexion reflex?

Cutaneous nociceptors Signup and view all the answers

What happens to the flexion reflex when descending pathways are damaged?

It can be triggered by various stimuli. Signup and view all the answers

Which of the following best describes the role of supraspinal inputs on Renshaw cells?

They can inhibit or facilitate Renshaw cell activity. Signup and view all the answers

Study Notes

Spinal Control of Movement and Locomotion

Spinal reflex: an involuntary response activated by sensory receptors through spinal pathways, now understood as highly modifiable based on context and task.
Reflex modulation indicates reflex responses depend on the specific task being performed rather than being hard-wired.

Proprioception and Muscle Receptors

Proprioception: the sense of body position, movement, and effort, derived from various specialized mechanoreceptors called proprioceptors.
Key proprioceptors include:
- Muscle spindles: sense changes in muscle length and movement velocity.
- Golgi tendon organs: monitor muscle tension.
- Joint receptors: contribute to proprioceptive feedback.
Integration of proprioceptive information occurs alongside signals from vestibular, cutaneous, and visual systems to accurately determine body position.

Muscle Spindles and the Stretch Reflex

Muscle spindles consist of intrafusal muscle fibers responsible for sensory input, maintaining sensitivity to stretch regardless of muscle length.
Stretch reflex serves as a feedback control mechanism to adjust muscle length based on detected deviations, activating α-motor neurons for appropriate muscle contraction.
Muscle tone, or steady muscle tension, is maintained by group II muscle spindle afferents.

Spinal Reflexes and CNS Integration

The central nervous system utilizes spinal cord organization to minimize processing demands on higher brain centers, integrating gamma drive to influence muscle activity during slow contractions.
Reflex gain is determined by excitability of α-motor neurons and sensitivity of muscle spindles controlled by γ-motor neuron activity.
Ib inhibitory interneurons receive various synaptic inputs, modulating the reflexive response.

Protective Reflexes

Flexion reflex pathways activate due to cutaneous nociceptors, triggering polysynaptic pathways that excite ipsilateral flexors while inhibiting extensors.
Descending pathways can suppress reflex actions; damage can lead to reflex activation by other stimuli.

Recurrent Inhibition and Renshaw Cells

Renshaw cells, identified in the 1940s, inhibit motoneurons via feedback loops, regulating motoneuron firing in response to higher-level inputs from the brain.
Inhibition of Renshaw cells increases motoneuron responsiveness, while excitation decreases it, demonstrating a gain control mechanism.

Rhythmic Movements and Central Pattern Generators (CPGs)

Rhythmic movements (e.g., locomotion, breathing) are managed by central pattern generators situated in the spinal cord.
CPGs can generate oscillating motor patterns independent of sensory input, influenced by supraspinal and peripheral feedback.
Speed of locomotion in animals can adjust based on treadmill speed, illustrating the role of stretch reflexes in spinal motor programs.
CPGs enable coordinated movements even after spinal cord injuries, prompting locomotion in cats and rats.
In intact animals, CPGs are activated by tonic descending drive from the brain, generating foundational rhythmic patterns for movement and respiration.

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Description

This quiz focuses on spinal control of movement and locomotion, including reflexes managed by muscle and cutaneous afferents. Drawing from key chapters in renowned neuroscience texts, students will deepen their understanding of spinal reflex mechanisms.