Exam 2 Flashcards
Afferent vs Efferent nerve
Afferent nerve carries impulses towards CNS
Efferent nerve carries impulses away from CNS
Ventral vs Dorsal horn
Ventral horn (anterior) efferent motor neurons leave
Dorsal horn (posterior) afferent sensory nerves enter
Contraction vs Contracture
Contraction is physio shortening of the muscle
Contracture is abnormal FIXED shortening
Agonist vs Antagonist
The agonist is the primary muscle responsible for movement
Antagonist is the muscle that opposes the movement
What is the function of the Autonomic Nervous System and what two systems subdivide the ANS?
ANS is the involuntary internal regulating system that controls the moment-to-moment activity of the viscera and the body’s internal response to external stimuli. Composed of the Sympathetic and Parasympathetic Systems
What are the function of each the Sympathetic and Parasympathetic Systems?
The sympathetic responds to stress in a fight or flight reaction.
The parasympathetic controls the internal maintenance (recovery) of the body in its rest + digest states.
Describe the Anatomy of the Sympathetic Systems
Bilateral chains of ganglia from T1 to L2 exit along with somatic motor axons at the ventral roots via the intervertebral foramina. Cervical ganglia control the upper extremities and head while lumbar nerves control lower extremities
Describe the Anatomy of the Parasympathetic Systems
A Cranial-Sacral System that has no role in the EXTRs
CN III, VII, IX provide supply innvervation for the organs of the head
CN X and S2-S4 provide rest of the viscera
What role does ANS play in the skeletal muscles
The skeletal muscles are primarily under voluntary control, however, some processes are automatic. Ventral and Dorsal root are a mix of ANS system
DRG (dorsal root ganglion) = Sensory
Ventral roots = motor
Describe the two types of ventral motor neurons
Alpha motor neurons which innervate the large skeletal muscle fibers (extrafusal fibers).
Gamma motor neurons which innervate small skeletal muscle fibers (intrafusal fibers) and contribute to the muscle spindle apparatus formation.
Describe a motor unit of an alpha motor nueron
Motor unit = a single alpha motor neuron which innervates several hundred skeletal muscle fibers (one muscle)
What two reflex systems modulated muscular activity?
Muscle spindle reflex reacts to changes in muscle length and the rate of change in muscle length.
Golgi tendon reflex reacts to muscle tension and changes in muscle tension.
What composes the Muscle Spindle Reflex?
The muscle spindles are intrafusal mechanoreptors that exist in parallel with the larger extrafusal skeletal fibers. They provide a dampening function to prevent jerkiness in body movement. They are composed of two types of intrafusal fibers nuclear bag fibers (have nuclei bunched in the center) and nuclear chain fibers (nuclei aligned in single file in the center).
Where is the greatest and least contractibility in the nuclear bag and nuclear chain fibers?
Both are intrafusal muscle spindle reflex fibers
Poor central contractility but greater contractility at the ends
What is the difference between the Type 1A vs Type II muscle spindle fibers?
Type 1A are heavily myelinated fibers associated with nuclear bag fibers.
The distal ends of the Type 1A wrap around the central noncontractile region of the intrafusal muscle fibers and aids in excitatory response when stretched.
Type II are associated with nuclear chain fibers and respond to muscle length changes. Type II fibers transmit this signal to the spinal cord.
Explain the Tendon Reflex Effect
The sudden strike of the reflex hammer results in elongation of the muscle spindle fibers.
The stretch results in the increased firing of the Type 1A fibers.
The Type 1A fibers enter the spinal cord and synapse with alpha motor neurons that innervate the quadriceps
This synapse instructs the muscles to contract.
What is the function of the Gamma Loop?
The gamma loop is essential for maintenance of stretch reflexes and muscle tone.
Gamma motor fibers receive supraspinal input from the cerebral cortex which signals contraction of the intrafusal fiber.
The contraction stimulates increased 1A activity → alpha motor activation → extrafusal muscle contraction
Describe the interactions of the Alpha-Gamma Coactivation loop
When the brain signals the alpha motor neurons to initiate extrafusal contraction, parallel impulses are sent to the gamma neurons to signal the intrafusal fibers to also contract
Muscle spindle fibers remain under nearly constant tension
