Section 5, Exam 2 Flashcards
A specialized proprioceptor that sends information to the CNS about muscle length and the velocity of stretch (mm/s)
Muscle spindle
Muscle spindles are oriented in ______ to extrafusal muscle fibers throughout the fleshy part of skeletal muscle
Parallel
What type (motor or sensory) of innervation does the muscle spindle receive?
Both motor and sensory (group Ia and group II)
What is the only receptor that receives both sensory and motor innervation?
The muscle spindle
What are muscle spindles enclosed in?
A fusiform shaped connective tissue capsule
Skeletal muscle fibers outside the capsule are termed ________.
Extrafusal muscle fibers
Term used to refer to structures inside the fusiform shaped connective tissue capsule
intrafusal
On average, about how many nuclear bag fibers do muscle spindles have? Nuclear chain fibers?
2; 4-6
When A gamma efferent axons stimulate muscle fibers, what will happen to the middle of the muscle spindle?
It will stretch due to contraction in the polar region in the m. spindle
The property that makes material resistant to a change in form, shape, or structure
Viscosity
The equatorial region of both the nuclear bag and chain fibers are ______ viscous comparison to the polar regions
Less viscous
The polar regions of both the nuclear bag and chain fibers are _____ sensitive to stretch or length change
Less
What region of the muscle spindle contains more contractile proteins?
Polar regions
Polar regions are more resistant to change its form or structure because of ___________ between protein molecules.
Electrostatic attraction
The equatorial regions of both the nuclear bag and chain intrafusal muscle fibers are innervated by?
Ia (A alpha) afferent axons
What does the “a” indicate in the Ia axon classification?
Innervation of the annulospiral nerve
What are annulospiral nerve endings also known as?
The primary endings
In most cases, what type of intrafusal muscle fiber does Group II afferent axons innervate?
Nuclear chain fibers (sometimes nuclear bag, but significantly less instances)
Where in the muscle spindle do Group II axons innervate?
Polar region
True or False:
Group II has a slower AP conduction velocity than the Ia axons.
True; they also have smaller sensory axons
What are group II nerve endings also known as?
The secondary endings or the flower spray endings
Where do A gamma motor neurons connect?
ONLY the polar regions of the nuclear bag and nuclear chain fibers
What does the contracting of the polar myofibrils in the muscle spindle cause?
A stretch of the spindle’s equatorial region (due to both ends of intrafusal muscle fibers being pulled)
What does activation of the gamma motor neurons prevent while extrafusal muscle contracts?
Prevents the muscle spindle from becoming slack
Why does the muscle spindle need to remain taught even during muscle contraction?
To maintain sensitivity so the sensory receptors can send information to the CNS
True or false:
Activation of A gamma axons causes activation of muscle contraction.
False; A gamma only sensitizes the equatorial region of the muscle spindle. There is not enough of a pull (or stretch) on the equatorial region to cause a muscle contraction
The discharge of nerve action potentials at any constant or fixed muscle length
The static response
With the static response, a greater length give you ________.
A greater frequency of action potentials
What afferent neuron(s) have a static response?
Group Ia and Group II (primarily)
The discharge of APs during the stretch or muscle length change.
The dynamic response
What afferent neuron(s) are velocity sensitive?
Group Ia
Static response signals of fixed length to the CNS:
Longer muscle length —> ______
Shorter muscle length —> ______
Greater AP (impulse) frequency; Lower AP (impulse) frequency
Dynamic Response signals of velocity of length change to CNS:
Greater stretch velocity –> _____
Slower stretch velocity –> _____
Greater AP (impulse) frequency; Lower AP (impulse) frequency
Physical properties innervated by _____ are low viscosity stretch sensitive equatorial region
Ia
Physical properties innervated by _____ are high viscosity stretch resistant polar region
II
Conduction properties of the axons of ____ are larger in diameter causing greater impulse conduction velocity with faster response.
Ia
Conduction properties of the axons of ____ are smaller in diameter causing lower conduction velocity with slower response.
II
A specialized proprioceptor that sends information to the CNS about muscle contraction (or shortening force) and muscle stretch (or lengthening force)
GTO
GTO’s are oriented in ____ to 15-20 extrafusal muscle fibers in the musculotendinous junction of skeletal muscle
Series
The GTO is composed of a network of _______________ arranged in series with 15-20 extrafusal muscle fibers.
Small unmyelinated nerve fibers
True or False:
The nerve fibers of the GTO are enclosed in a capsule.
True
The nerve fibers are branches of _______.
A single Ib myelinated primary afferent axon
True or False:
The GTO has no motor nerve connection or innervation.
True
What stimulates the GTO?
Muscle tension developed during a muscle contraction
GTOs send a ____ frequency of APs to the CNS during muscle contraction and a ______ frequency of APs during muscle stretch.
Greater; lower
Do muscle spindles send action potentials during muscle contraction?
No, because they are slack
