lecture 9 Flashcards
mechanisms of neuronal transduction
what happens when sensory fibers enter the spinal cord?
they are transmitted to higher centers or they synapse locally to elicit motor reflexes
where are the motor neurons located?
they are located in the anterior portion of the cord of the cord aka the ventral horn
how much bigger are the motor neurons located in the anterior portion of the cord compared to other motor neurons?
50-100% times bigger
where are the sensory neurons located?
they are located in the dorsal horn and so they receive a stimulus and transmit to the higher centers of the nervous system
]what the two types of anterior motor neurons?
alpha (lower motor neurons) and gamma motor neurons(which work on sensory apparatus called muscle spindles or intrafusal fibers)
what are the alpha motor neurons?
they give rise to large alpha A fiber, upon stimulation they excite extrafusal fibers (collectively called a motor unit) and these neurons go to the muscle cell
what are the gamma motor neurons?
give rise to smaller type A gamma fibers and go to small special skeletal muscle fibers called intrafusal fibers; note that more of these neurons makes the muscle more sensitive
what is important to note about interneurons?
they help us create reflex type movements and comprise the neural circuitry for the motor reflexes
define the Renshaw Cell Inhibitory System
immediately after the anterior motor neuron axon leaves the body of the neuron, collateral branches from the axon pass to adjacent Renshaw cells. These are inhibitory cells that transmit inhibitory signals to the surrounding motor neurons
Renshaw cells are inhibitory cells that transmit inhibitory signals to the surrounding motor neurons, T/F?
T
what are propiospinal fibers?
they travel up and down the cord for 1-2 segments and provide the pathways for multisegmental reflexes, like the registration of pain and temperature
when we initiate voluntary muscle movements, what fibers are we innervating?
the extrafusal fibers
what are the two types of sensory receptors of the muscle?
muscle spindle and golgi tendon organ
what is the muscle spindle?
these sense muscle length and change in length
what is the golgi tendon organ?
these sense tendon tension and change in tension, these consist of sensory nerve endings interwoven among collagen and are type 1b afferent motor neuron
what type of neuron is the golgi tendon organ?
Type 1b afferent motor neuron
what are the signals from the mentioned sensory receptors (muscle spindle and golgi tendon organ) of the muscle for?
intrinsic muscle control
in terms of the the muscle spindle, there are two important endings, what are they?
primary ending and secondary ending
what type of neurons are the primary endings of the muscle spindle? where do these go?
these are Type 1a afferent motor neuron and they go to the bag fiber
how would you describe the shape of the primary ending?
annulospiral ending located in the center of the receptor area and encircles the central portion of each intrafusal fiber
what type of neurons are the secondary endings of the muscle spindle? where do these go?
type II afferent fibers and these innervate the chain fibers
how would you describe the actions of the secondary fibers?
innervate the receptor region on one or both sides of the primary ending and they spread like branches on a bush, hence the word, chain fibers
what are the extrafusal fibers?
alpha motor neurons that give rise to large type A alpha fibers and are collectively called a motor unit and are outside and around the muscle
what are the intrafusal fibers?
these are gamma motor neurons that are small, special skeletal muscle fibers within the muscle spindle
in terms of physiologic function of the muscle spindle, what do we call the simplest manifestation of muscle spindle function?
muscle stretch reflex
what happens when a muscle is stretched suddenly?
excitation of the spindles causes a reflex contraction of the large skeletal muscle fibers of the stretched muscle and also of closely allied synergistic muscles
what is the importance of the coactivation of alpha and gamma motor neurons?
they keep the length of the receptor portion of the muscle spindle from changing during the course of the muscle contraction and so this phenomenon keeps the muscle spindle from opposing the muscle contraction
T/F, coactivation of the alpha and gamma motor neurons maintains the proper damping function of the muscle spindle, regardless of change in muscle length
T
when alpha motor neurons are stimulated by upper centers, what other motor neuron is stimulated?
gamma motor neurons are also stimulated (both extrafusal and intrafusal fibers contract at the same time)
In terms of the role of muscle spindles in voluntary motor activity, what percent of motor nerve fibers to the muscle are small type A gamma efferent fibers?
31%
what is the name of the efferent fibers that make up 31% of the motor nerve fibers to the muscle, this is in terms of the role of muscle spindles in voluntary motor activity.
type A gamma efferent fibers
in terms of the role of muscle spindles in voluntary motor activity when alpha motor neurons are stimulated, what other motor neurons are stimulated? what is this called? what is the effect on extrafusal and intrafusal fibers?
gamma motor neurons; coactivation of alpha and gamma neurons; it causes them to contract at the same time
what is the golgi tendon organ?
these sense tension and change in tension
what so golgi tendon organs consist of?
sensory nerve ending interwoven among collagen
what motor neurons are the golgi tendon organ?
type 1b afferent motor neuron
in terms of coactivation of alpha and gamma motor neurons what happens if gamma motor axons are cut?
the spindle loses activity when muscle contracts
what is maintained during alpha-gamma coactivation?
maintains spindle function when muscle contracts
during active contraction of the muscle, what motor neurons cause the contraction of the extrafusal muscle fibers with consequent relation of intrafusal fibers?
alpha motor neurons
in active contraction are the spindles activated?
no
what is the tension like in active contraction?
tension is slow, no adjustment made to increase resistance
during muscle contraction is the golgi tendon organ activated? effect?
yes; causes relaxation
in active contraction of the muscle, what fibers and motor neurons are involved?
type Ib fibers and alpha motor neurons
what is active contraction with Gamma Coactivation?
Intrafusal and extrafusal fibers contract; spindles activated, reinforcing contraction stimulus via 1a fibers in accord with resistance
in active contraction with Gamma Coactivation, is the golgi tendon organ activated? effect?
Tendon organ is activated, causing relaxation if load is too big
in the damping mechanism in smoothing muscle contraction what happens when the spindle is not working properly?
the muscle contraction is jerky
in neuronal circuitry of the stretch reflex, what is the monosynaptic pathway?
pathway allows a reflex signal to return with the shortest time delay to the muscle after excitation of the spindle
in the neuronal circuitry of the stretch reflex, what is the monosynaptic stretch?
a single synapse between the afferent and efferent neurons
what does the monosynaptic reflex oppose?
sudden changes in muscle length
what is the purpose in the clinical application of the stretch reflex?
To determine how much background excitation or tone the brain is sending to the spinal cord
what is being tested in the clinical application of the stretch reflex?
the facilitation of gamma efferents
what is the effect of cortical lesions in the clinical application of the stretch reflex?
increase muscle stretch reflexes
what is the name of the reflex tested in the clinical setting?
knee jerk reflex
what is spinal reflex circuit?
when a skeletal muscle is abruptly stretched and a reflexive contraction of the same muscle occurs, increasing muscle tension and opposing the stretch.
for what is the spinal reflex circuit strong? what is this reflex also called?
in physiological extensor muscles; myotatic reflex
what is the knee jerk reflex?
A light tap on the patellar tendon deflects the tendon, which then pulls on and stretches the quadriceps femoris muscle
what neurons are affected in the knee jerk reflex?
type 1a sensory neurons
what happens physiologically to the body when we use the knee jerk reflex?
Passive stretching a skeletal muscle causes a reflexive contraction of that same muscle and relaxation of the antagonist muscle
what is stimulated in the reflexive contraction of the knee jerk response?
The reflex stimulates in the spinal cord → the motor neurons to the extensor muscles → inhibits the motor neurons to the flexor muscle
what does the stretch reflex depend on?
the nervous system and requires sensory feedback from the muscle
what abolishes the stretch reflex?
Cutting the dorsal (sensory) roots to the lumbar spinal cord
what is the effect of the knee jerk reflex?
the stretch reflex in the quad
so in the knee jerk reflex, we see reciprocal innervation. What is this?
As the knee jerk reflex causes contraction of the quadriceps muscle → there is an antagonist relaxation during contraction (semitendinosus muscle antagonist to knee jerk reflex)
what neuron are affected in reciprocal innervation?
Branches of the group Ia sensory axons excite specific interneurons that inhibit the α motor neurons of the antagonists
what is the reflex the inverse myotatic reflex is also called?
golgi tendon reflex
in the inverse myotatic reflex, what is the effect of the golgi tendon organs?
they become aligned in series with the muscle and super sensitive to the tension of a tendon and respond to force generated by muscle
what sensory axons are involved in the Golgi tendon reflex?
group 1b sensory axons and these excite both the excitatory and inhibitory interneurons within the spinal cord
This circuit inhibits the muscle in which tension has increased and excites the antagonist muscle (opposite of stretch reflex)
what does the inverse myotatic reflex inhibit?
the motor neurons to the extensor muscle and stimulates the motor neurons to the flexor muscle
T/F, the inverse myotatic reflex uses more of the golgi tendon organ then it uses the sensory type 1b neuron?
T
why does the golgi tendon want to equalize the force among muscle fibers?
to prevent too much tension on the muscle
what is the inhibitory nature of the tendon reflex?
if the tension on the muscle and tendon is too high than inhibitory effect occurs providing relaxation of the entire muscle (lengthening reaction)
what is the purpose of the protective mechanism in the golgi tendon reflex?
prevents tearing of the muscle or avulsion of the tendon from its attachments to the bones
what type of reflex happens when you touch a hot pan?
reflexive
what are the neurons that stimulate the flexor reflex?
from fast pain afferent neurons in the skin
how is the flexor reflex different from a simple stretch reflex?
Unlike simple stretch reflexes, coordinate movement from entire limb or even pairs of limbs
so in a leg that feels pain, what does the reflex inhibit? what about the opposite leg?
the motor neurons to the extensor muscle and stimulates the motor neurons to the flexor muscle; In the opposite leg, the reflex stimulates the motor neurons to the extensor muscle and inhibits the motor neurons to the flexor muscle (supports the body weight when the other leg flexes)
how do reflexes affect movement?
it affects coordination of several muscle groups
Reflexive Movement
- Spinal integration, input to the brain
Postural reflexes
- Cerebral integration, maintains balance, input to cortex
