Lecture 6: Motor Functions of Spinal Cord and Reflexes Flashcards
what are the 3 neurons part of Neuronal Organization of the Spinal Cord
sensory neurons
motor neurons
interneurons
Where do you find the sensort neurons in the spinal cord
dorsal root ganglion
where do you find the motor neurons in the spinal cord
anterior horn
What is the function of sensory neurons in the spinal cord
transmit signals to higher centers
what is the function of motor neurons in the spinal cord
directly innervate skeletal muscle fibers
Where do sensory neurons synapse and why
Synapse at the spinal cord level to elicit motor reflexes
what are the 2 types of motor neurons of the spinal crod
Alpha MNs
Gamma MNs
What is the fucntion of Alpha MN? Gamma MN?
excite extrafusal muscle fibers (motor units), muscle contraction
A-gamma axons) excite intrafusal (spindles) fibers (muscle sensory receptors)
Which motor neuron excites intrafusal msucle fibers
gamma MN
Which motor neurons excites extrafusual muscle fibers
alpha
What is the “typical muscle fiber”
alhpa
What are interneurons and what are the two types
Local neurons that have connections with sensory & motor neurons
They can be inhibitory or excitatory
true or false: Interneurons are only excitatory
false, theyre excitatory and inhibitor
What kind of receptors are sensory receptors of the muscle?
MECANORECEPTORS (i.e. stimulated by mechanical displacement of the muscle)
What are the two sensory receptors (mecanoreceptors) of the msucle>
MUSCLE SPINDLES
GOLGI TENDON ORGANS
Where are muscle spindles located
Are distributed throughout the muscle belly (midportion of intrafusal fibers)
What do muscle spindles sense
Sense muscle length (stretched, relaxed, contracted) and rate of change of length
Sensory signals in the muscle spendles are transmitte through what type of fibers?
1a (primary sensory ending) fibers
II (secondary sensory ending) fibers
Whree are golgi tendon organs lcocated?
in the muscle tendon
what do golgi tendons sense?
Sense tendon tension and rate of change of tension.
what are the Sensory signals of the golgi tendon transitted through
1b fibers
be able to locate the primary sensory endings, secondary sensory endings and 1b fibers
/
rank by 1a, 1b and II by conduction velocity
Ia, Ib, II
What is thje function of the msucle s[indles
Function: To provide info on the position of body parts (proprioception)
Where do the Primary sensory endings of the muscle spindle (type Ia fibers) terminate?
Terminate on nuclear bag and nuclear chain fibers
true or false: muscle spindles respond to both dynamic and static changes in the muscle length and stretch
true!! `
explain how muscle spindle fibers respond to dynamic and statoic
Respond to the rate of change in muscle length (dynamic) and to the degree of stretch of the muscle (static)
type 1a and type 2
where do sSecondary sensory endings of the muscle spindle (type II fibers) terminate and what do they respond to ?
Terminate on nuclear chain fibers
Respond mostly to the degree of stretch of the muscle (static response)
understand the diagram of passive muscle strecth vs primary and secondary endings
.
When there is a dynamic change in muscle strentch BLANK are very good at detecting and sending out the signal
primary sensory endings
WHat is the function of Alpha-Gamma Coactivation
causes the tension on the muscle spindles to be maintained as the muscle shortens; thus sensitivity to stretch is maintained
true or false: to send signals to the CNS, muscle spindles MUST be stretched
true
explain the steps to how alpha-gamma coactivation works in extension
Elbow is extended = extrafusal and intrafusal fibers are stretched = muscle spindles are responding by sending signals to the CNS
explain what would happen wihtout the alpha gamma coactivation if we contracted our muscles
During biceps curl, alpha motorneurons (Mns) are activated to contract muscle fibers → muscle spindles get shorten and can no longer send signals to the CNS (doesn’t exist in reality)
explain what happens in reality to allow muscle spiindles to be strecthed during flexion/ contraction
as alphas are activated to contract extrafusal, gamma are activated to contract intrafusal fibers → muscle spindles get stretched and respond by sending signals to the CNS= COACTIVATION
TRUE OR FALSE: GTO are Encapsulated sensory receptor through which muscle tendon fibers pass
true
when are golgi tendons stimulated?
“Tensed” by the contraction or stretching of the muscle (sensitive to muscle tension)
Golgi tendons have a static response, dyanmic, or both?
both
explain how golgi tendons have a static and dynamic resoonse
GTOs react intensively when muscle tension suddenly increases (dynamic) or settles down rapidly to a lower level of steady state tension (static)
what type of fibers are golgi tendon signals transmitted by?
1b
what is a fcuntion of the 1b in the golgi tendons?
Ib fibers inhibit indirectly (through interneurons) alpha motor neuron at the spinal cord to allow the muscle to relax and thus to relieve the tension on the tendon.
What type of mecanism is the spinal crod reflexes
Mechanism by which sensory impulses are automatically converted into a motor effect
true or false: spinal relfexes are voluntary
false
What are spinal reflexes
Involuntary and rapid reactions controlled by the spinal cord integration centers
are spinal reflexes a protective mecanism or destructive?
Protective mechanism to the body (e.g. prevent an over stretch (or contraction) of the muscle, withdrawal from a painful stimulus…)
From a human physiology perspective, can we say that the goaltender has good or bad reflexes?
no
are the strecth reflex and golgi tendon reflex the same?
NO COMPLETELY DIFF
is the strectch reflex associated with the msucle spindles or the golgi tendons
msucle spindles
how is the strectn reflex activated
Sudden stretch of the muscle activates the muscle spindles (of the same muscle)
what are they Associated sensory fibers for stretch reflex?
(Ia & II)
true or false: Type Ia and II fibers synapse directly with alpha motor neurons causing the muscle to contract
true
what type of reflex is the strecth reflex?
monosynaptic
what is the fucntion of the strectn reflex
Function of the stretch reflex is to oppose sudden changes in muscle length (stretching)
explain the neuronal circuit of the stretch reflex
Sudden stretch of muscle
muscle spindles sends signal to spinal through: afferent signal via primary (Ia) and secondary (II) sensory endings
There is a synapse in spinal cord with α-motor neurons
alpha motor neurons send back signal for muscle contraction results to oppose stretch
Reciprocal innvervation: Collateral 1a synapses inhibitory interneurons
Inhibitory interneuron sends efferent signal to antagonist
(Relaxation of antagonist muscle)
Does the strecth reflex have only an afferent signal>
no , it also has a efferent singal (Inhibitory)
If there is a sudden stretch in my quad muscle, what will happen
msucle spindles will feel the stretch and send signal up through 1a and 2 to the spinal cord
signal synapses with alpha motor neurons which signal contracttion of the quad muscle to oppose the stretch
AT THE SAME TIME, collaterol 1a synapses with inhibiotry interneurons to send an inhibitory signal to the hamstreing
Where does the 1a signal synpase with in the stretch reflex?
synapses with alpha motor neurons for contraction
synapses with inhibitory interneurons to stop hamstring
what is the function of the golgi tendon reflex
: to relieve excess tension on the tendon
true or false: Contracting of a muscle creates a tension on the tendon attached to the same muscle and thus activates the Golgi tendon organs
treue
explain the neuronal circuit for the golgi tendon reflex
1) increased tension at the tendon
2) - Sensory neurons synapse with interneurons that inhibit alpha motor neurons and cause the muscle to relax
3) collateral: - Sensory neurons synapse with interneurons that excite alpha motor neurons of antagonist muscles and cause muscle to contract (reciprocal activation)
true or false: Afferent impulses from golgi tendon are also transmitted to the cerebellum where it is used to adjust muscle tension.
true
know the graph of golgi tendon response to muscle contraction vs stretch
.
Extrafusal fibers are acitviated by which neurons
ALPHA MOTOR NEURONS
what is another name for the flexion refle x/
withdrawal reflex
what is The flexion reflex initiated by
a painful stimulus that causes automatic WITHDRAWAL of the threatened body part
explain the senseory neuron synapse for the flexion reflex
Sensory neurons synapse with interneurons that:
Excite motor neurons of the flexor muscle (e.g. Biceps) and cause muscle to contract
Inhibit motor neurons of the extensor muscle (e.g. Triceps) and cause the muscle to relax
explain the flexion and cross extensor reflex?
1) painful stimuli detected by nociceptor
2) signal is sent to aplha motor neurons to stimulate excitatory neurons to contract the agonist
3) same time: inhibiroty neurons inhibit the antagonist msucle
on the other leg!!!
EXTENSORS CONTRACT while flexors inhbit to allow leg to stand on the ground
knwo the graphs for stretch Reflexes between Controls and SCI subjects
;
why do SCI have so much more reflexes
SCI HAVE TOO MUCH EXCITATORY ACITIVTY AT THE SPINAL CORD
