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Flashcards in Chapter 54 Deck (26):

What do Alpha motor neurons give rise to?

give rise to large type Aα motor neurons, these are located in the anterior horn of the spinal cord


1 Alpha motor neuron stimulates 3-100's of skeletal muscle fibers. Which process is this?

Motor unit


What is the role of the gamma motor neurons?

Transmit impulses through small type Aγ motor fibers which go to small skeletal muscle fibers called intrafusal fibers


What is the role of interneurons?

They display many interconnections with each other and they synapse on anterior motor neurons; essential for the integrative function of the spinal cord


What is the role of Renshaw cells?

these inhibitory cells transmit inhibitory signals to surrounding motor neurons (lateral inhibition); this focuses the signal and suppresses its lateral spread


What is the role of the central portion of the intrafusal muscle fiber?

no actin or myosin; functions as a sensory receptor (afferent)


What are the 2 ways to excite the central portion of the intrafusal muscle fiber?

Lengthening the muscles --> stretches the receptor

Even if the length of the muscle does not change, contraction of the end portions --> stretches the receptor


What are the roles of the end portions of the intrafusal muscle fiber?

contract; excited by small γ motor neurons which originate from small type A gamma motor neurons (aka gamma efferent fibers) in the anterior horn


Which type of neurons innervate the extrafusal fibers?

Aα nerve fibers


What is the pirmary ending of the muscle spindle?

large sensory nerve fibers that encircle the central portion of each intrafusal fiber (center of receptor area); type Ia fiber


What is the secondary ending of the muscle spindle?

innervate the receptor region on one or both sides of the primary ending ; type II fiber


What is the static response to muscle stretch from the intrafusal fibers?

When the sensory receptor of the intrafusal muscle fiber gets stretched slowly, the number of impulses transmitted from both the primary and the secondary endings increases almost directly in proportion to the degree of stretching and the endings continue to transmit these impulses for several minutes.


What is the dynamic response to rapid change in intrafusal length?

If the spindle receptor increases in length suddenly, then the primary ending is stimulated powerfully while the secondary ending is not.

Essentially, the primary ending is highly responsive to rapid rate of change in spindle length. Only active while the length is actually increasing


What is coactivation?

whenever signals are transmitted from the brain to the alpha motor neurons the gamma motor neurons are stimulated also


What is the role of coactivation of alpha and gammaMN's?

This causes both the extrafusal skeletal muscle fibers and muscle spindle intrafusal muscle fibers to contract at the same time.
Keeps the length of the receptor portion of the muscle spindle from changing during contraction and from opposing the muscle contraction
Maintains proper damping function of the muscle spindle regardless of change in length


Hyperreflexia on the knee jerk reflex is indicative of what type of lesion?



Hyporeflexia on the knee jerk reflex is indicative of what type of lesion?



What do golgi tendon organs detect?

detects muscle tension (tensed by contracting or stretching muscles) as reflected by the tension in itself


What is the role of the golgi tendon reflex?

Golgi tendon reflex is stimulated by increased tension in the connecting muscle
This reflex is inhibitory and it prevents the development of too much tension on the muscle


What is the flexor reflex?

cutaneous sensory stimulus from a limb causes flexor muscles of the limb to contract --> withdrawing the limb from the stimulating object.


What is the crossed-extensor reflex?

about .2-.5 seconds after a stimulus elicits a flexor reflex in one limb the opposite limb begins to extend; many interneurons are involved in the circuit between the incoming sensory neuron and the motor neuron of the opposite side of the cord responsible for the crossed extension


What is the main cause of local muscle pain?

Muscle spasm


What is the mass reflex for the spinal cord?

when the spinal cord suddenly becomes excessively active this may cause massive discharge in large portions/entire of the spinal cord.

(btw, it's spinal "cord" as a "cord" is a cylindrical object. A "chord" is a musical tone. just fyi to everyone because that bugs the shit outta me).


What are the 4 effects of the mass reflex?

Major portion of the body’s skeletal muscles goes into strong flexor spasm
Colon and bladder are likely to evacuate
Arterial pressure often rises to maximal values (systolic 200 mmHg)
Large areas of the body break out into profuse sweating


What are the immediate effects of spinal cord tansection?

All cord functions (inc. reflexes) immediately become depressed (total silence) --> spinal shock
Non communication between higher centers and cord neurons via reticulospinal tracts, vestibulospinal tracts, and corticospinal tracts


What are the long term effects of spinal cord transections?

In human it typically results in hyperexcitability of some or all cord functions
Blood pressure (Drop to 40 mmHg initially  normal w/in days)