Questions and Answers
Define a reflex and explain how reflexes differ from voluntary movement.
A reflex is a fast, involuntary, and predictable sequence of actions by glands or muscles in response to a particular stimulus. Reflexes differ from voluntary movement as they do not involve the brain, rely on lower motor neurons, and are stereotyped, while voluntary movements are under our control, can be slow or fast, use higher and lower motor neurons, and are variable.
List and describe the general components of a typical reflex arc.
The components of a typical reflex arc include: 1. Sensory receptor (detects stimulus), 2. Sensory neuron (carries information to the spinal cord), 3. Integrating center (synaptic contact in grey matter), 4. Motor neuron (carries impulses to muscles), 5. Effector (muscle that executes the response).
Describe the structure and explain the function of muscle spindles.
Muscle spindles are stress receptors embedded in skeletal muscles. They contain intrafusal muscle fibers that monitor muscle length and the rate of length change. Sensory neurons provide feedback on muscle length, while gamma motor neurons maintain spindle sensitivity.
Explain and illustrate how the stretch reflex functions using the patellar tendon reflex as an example.
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Explain how the Golgi tendon reflex functions.
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Study Notes
Definition of Reflexes
- Reflexes are fast, involuntary responses triggered by specific stimuli.
- Involvement of spinal cord grey matter leads to spinal reflexes; brain stem involvement results in cranial reflexes.
- Somatic reflexes target skeletal muscles; autonomic reflexes affect smooth muscle, cardiac muscle, or glands.
- Voluntary movements are controlled, variable, and use both higher and lower motor neurons.
Components of a Reflex Arc
- Sensory Receptors: Located in skin, muscle, or tendons; they detect stimuli and start the reflex.
- Sensory Neuron: Transmits signals from receptors to the spinal cord or brainstem.
- Integrating Centre: Interneuron that connects sensory and motor neurons within the spinal cord or brainstem.
- Motor Neuron: Carries impulses from the spinal cord to skeletal muscles.
- Effector: Muscles that execute the reflex action; in somatic reflexes, these are always skeletal muscles.
Muscle Spindles
- Composed of extrafusal fibres (contractile muscle fibres) and intrafusal fibres (modified muscle cells within spindles).
- Act as stretch receptors, monitoring muscle length and rate of change in length.
- Innervated by primary afferent fibres (fast sensory neurons) and secondary afferent fibres (slower sensory neurons).
- Gamma motor neurons regulate spindle sensitivity for stretch detection during muscle contraction.
Stretch Reflex (Patellar Tendon Reflex)
- Involves automatic muscle contraction when the muscle is stretched; maintains tone and posture.
- Example: Tapping of the patellar tendon initiates the knee-jerk reflex.
- Stretching increases spindle activity, leading to reflex contraction that maintains normal muscle tension.
- Monosynaptic pathway: Direct synapse between sensory and motor neurons allows for quick response.
- Utilizes reciprocal inhibition to coordinate muscle action; agonist muscles contract while antagonist muscles relax.
Golgi Tendon Reflex
- Monitors muscle tension in tendons during contraction.
- Activated by sensory neurons that connect to inhibitory interneurons, which inhibit alpha motoneurons.
- Prevents excessive muscle contractions and protects from injury.
- Functions oppositely to the stretch reflex: inhibits agonist muscles while promoting relaxation.
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Description
Test your understanding of somatic reflexes and their distinctions from voluntary movements. This quiz will cover definitions, mechanisms, and examples of reflex actions, focusing on their neural pathways and responses. Prepare to explore how reflexes operate independently of the brain.
