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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 activityalpha motor activationextrafusal 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


What are the Golgi Tendon organs?

Golgi tendon organs are mechanoreceptors within the collagen tissue fibers at the musculotendinous junctions. 


They provide a connection between the tendon and the extrafusal muscle


What is the function of the Golgi Tendon Reflex?

When force is applied to the Golgi tendon, the sensory fiber is stretched which activates Type 1B nerve fibers and cause an inhibitory effect on the alpha motor neurons causing the muscles to relax (extend).


Golgi Tendon reflex is opposite of muscle spindle reflex 


What is the crossed extensor reflex?

The crossed extensor reflex is a primitive protective reflex that when an agonist is stimulated so is the antagonist


What is reciprocal inhibition?

When a contraction is initiated in the agonist muscle, there is a reflex relaxation in the antagonist



What is the Viscerosomatic Reflex?

When there is a disruption to an internal organ or tissue the results is a reflex dysfunction of a segmentally related musculoskeletal region


What is Facilitation?

Facilitation indicates that an area has developed a lower threshold for dysfunction


These low-threshold segments show hyperexcitability, hyperirritable and hyper-responsiveness


What is nociception?

Nociception is the detection of tissue damage (Mechanical, Thermal, or Chemical). 


Signals initiate protective reflexes (facilitation) and initiation of the neurogenic inflammatory response


What are the two types of Nociceptors?

Aδ Mechanical Nociceptors

•Thinly myelinated fibers

•Respond to mechanical injury and tissue damage

•Small sensitive spots scattered over an area


C-polymodal Nociceptors

Unmyelinated fibers

•Respond to mechanical, thermal, and chemical stimuli

•Sensitive spots covering an area


What tissues lack nociceptive fibers?

Articular cartilages

Hyaline cartilages

Nucleus pulposus

CNS parenchymal tissue



Primary hyperalgesia

When primary afferent nociceptors become more sensitive to low thresholds after repeated stimulation



The tissue is so sensitive that non-noxious stimuli can elicit pain


Secondary hyperalgesia

When pain develops outside the area of stimulation