LEC-8 Reflexes Flashcards
Alpha motor neurons conduct impulses in the (Aα/Aβ/Aδ) range of conduction velocities.
Aα
Aα fibers typically convey sensory signals for ____________ and ___________.
Propioception and motor
Gamma motor neurons conduct impulses in the (Aα/Aβ/Aδ) range of conduction velocities.
Aδ
Gamma motor neurons innervate the ___________.
Muscle spindle
The intrafusal fibers are composed of _______________ and ____________ fibers.
Nuclear chain; nuclear bag
Skeletal muscle twitches resulting from the contraction of a motor unit are called ________________.
Fasciculations
(T/F) Cardiac, skeletal, and smooth muscles possess motor units.
False. Cardiac and smooth muscle do not possess motor units.
A muscle unit is composed of _______________________.
One alpha motor neuron and all the muscle fibers it innervates
The number of fibers innervated in a motor unit (increases/decreases) as the movements performed by different muscles increase in precision.
Decreases
Most alpha motor neurons innervate between 500-1000 fibers in a motor unit. Intrinsic hand muscles, however, have alpha motor neurons that only innervate between 10-50 muscle fibers.
Type (I/IIA/IIB) are intermediate fibers, fast twitch, and more resistant to fatigue. They possess many mitochondria and make use of oxidative phosphorylation for continued energy.
IIA
Type (I/IIA/IIB) are white, fast twitch fibers that are rapidly fatigued. They are characterized by short contractions with large force. They have few mitochondria and make use of glycolysis and glycogen stores for short intervals of energy.
IIB
Type (I/IIA/IIB) are red, slow twitch fibers that are slowly fatigued. They are characterized by the ability to contract for a long time, albeit with low force.
I
Type (I/IIA/IIB) are the smallest of the fibers.
Type I
The nervous system modifies ____________ and __________ to modulate the force that a muscle produces.
Firing frequency and recruitment of other motor units
All reflexes are under unconscious control via motor pathways originating in the _______ and __________.
Brain and brainstem
Another name for a monosynaptic reflex is a __________________.
Deep tendon reflex (DTR)
Monosynaptic reflexes are carried on type (Ia/II/III) afferent.
Ia
An absent reflex is graded a (0/1/2/3/4/5) on the reflex scale.
0
A clonus is graded a (0/1/2/3/4/5) on the reflex scale.
4
A normal reflex is graded a (0/1/2/3/4/5) on the reflex scale.
2
A diminished (hypoactive) reflex is graded a (0/1/2/3/4/5) on the reflex scale.
1
An increased (hyperactive) reflex is graded a (0/1/2/3/4/5) on the reflex scale.
3
The most important afferent for the stretch reflex is the (primary/secondary/tertiary) spindle afferent, a group (Ia/II/III) nerve fiber. Muscle spindle fibers primarily sense the (length/tension) of a muscle.
Secondary spindle afferent, a group II nerve fiber
Muscle spindle fibers primarily sense the (length/tension) of a muscle.
Length
Golgi tendon organs primarily sense the (length/tension) of a muscle.
Tension
(T/F) Gamma motor neurons may cause contraction of intrafusal muscle fibers, bringing about secondary effects once the change in length is sensed by the muscle spindle.
True.
Abnormal stretch reflexes are most often seen following injures in the ___________ or ____________.
Brain or spinal cord
Firing of gamma motor neurons causes contraction of the _____________.
Muscle spindle
Muscle spindle length during muscular shortening is maintained so that:
The muscle spindle may maintain a length which would allow it to respond to a slight stretch of the whole muscle
The clasp-knife reflex is only seen when the stretch reflex in a muscle is (hyperactive/hypoactive).
Hyperactive
The signals for a clasp-knife reflex are carried on ___ and ___ fiber afferents.
Aδ and C
When the tension in a tendon becomes high enough to damage the muscle or bone, the alpha motor neurons to the muscle are suddenly inhibited via an interneuron and the tension is relieved. This is the (stretch/clasp-knife/flexion) reflex.
Clasp-knife reflex
The (stretch/clasp-knife/flexion) reflex serves to remove a body part from a painful or potentially dangerous stimulus.
Flexion reflex
(T/F) In the flexion reflex, interneurons are activated that excite extensors on the hand or foot following a painful stimulus, while simultaneously inhibiting the flexors of the same body part.
False. Interneurons excite the FLEXORS while inhibiting the EXTENSORS in order to remove the body part from the stimulus.
(T/F) Following a painful stimulus, commissural neurons with axons that cross to the contralateral side of the spinal cord through the anterior white commissure are activated. These neurons serve to activate the extensors and inhibit the flexors of the limb opposite the one injured.
True. This is referred to as the crossed extensor reflex, such as flexing one leg after stepping on a thorn while extending the other to move away from the stimulus.
Following damage to the pyramidal tract, the monosynaptic reflex (or DTR) and the stretch reflex both become (hyperactive/hypoactive).
Hyperactive
(T/F) Following a pyramidal tract lesion, the sign of Babinski appears.
True
Denervation of a muscle fiber may result in its hypersensitivity to acetylcholine from surrounding neuromuscular junctions, producing ____________.
Fibrillations
Descending control fibers for alpha and gamma motor neurons may be found in the _______________ tract.
Lateral corticospinal tract
A lesion in upper motor neurons results in (spastic/flaccid) paralysis.
Spastic
Flaccid paralysis for lower motor neuron lesions
(T/F) Fasciculations are present in upper motor neuron lesions.
False. Fasciculations of motor units are present in lower motor neuron lesions.
What are the primitive reflexes?
Glabellar reflex Snout reflex Rooting reflex Palmomental reflex Grasp reflex - Gegenhalten sign Suck reflex
What part of the brain will end up suppressing the primitive reflexes?
Frontal lobe
What are the developmental reflexes?
Moro reflex Tonic neck reflex Crossed adductor reflex Nick righting reflex Supporting reaction Landau reflex Parachute reflex
What is the afferent and efferent limb of the corneal and blink reflex?
Afferent - CN V
Efferent - Bilateral CN VII
What is the afferent and efferent limb of the pupillary light reflex?
Afferent - CN I (optic)
Efferent - Bilateral CN III
What is the afferent and efferent limb of the gag reflex?
Afferent - CN IX
Efferent - Bilateral CN X
How do you test the corneal reflex?
Hold lower lip down and touch cornea with wisp of cotton
- Should result in contraction of orbicularis oculi m. bilaterally
How do you test the blink reflex?
Stimulate branch of CN V (supraorbital) with electric shock in lab
- First see ipsilateral contraction of orbicularis oculi (10-12ms)
- Then see bilateral contraction of orbicularis oculi (30-35ms)
How do you test the pupillary light reflex?
Shine light through pupil
- Should see contraction of both pupils
- Direct response is the side you stimulate
- Consensual response is the opposite side
How do you test the gag reflex?
Touch cotton swab to soft palate
- Should see an elevation of the palate
