11/6 Reflexes

Question 1

What is a spinal cord reflex?

Answer 1

a rapid involuntary predictable motor response to a stimulus. it is unlearned, unpremeditatied and involuntary.

Question 2

what is the role of reflexes?

Answer 2

to aid in posture, and to help prevent injury

Question 3

Why would we use reflexes clinically?

Answer 3

to localize and characterize a neurologic leasion.

Question 4

what is an arrangment of neurons and their synaptic connections in a region of the brain?

Answer 4

local circuit.

Question 5

how can we break down the organization of the brain to individual “modules”

Answer 5

Local circuits that are interconnected and nearly modular, and composed of microcircuits that are then made up of individual synapses, memebranes, and molecules, ions and the genes that encode and control the system’s molecularbiology

Question 6

what war the three elements of most local circuits?

Answer 6

input axons, interneurons (both excitatory and inhibitory), and projection or output neurons.

Question 7

What are the components of a reflex arc?

Answer 7

1. Receptor; 2. Sensory neurons; 3. Integration center (interneuron); 4. Motor neuron; 5. Effector

Question 8

What is a stretch reflex?

Answer 8

a skeletal muscle is stretched passively, and the reflex is to contract the same muscle and relax the antagonist.

Question 9

Examples of stretch reflexes

Answer 9

Myotactic reflex, tendon reflex, patellar reflex, knee-jerk reflex

Question 10

what is a myotatix reflex?

Answer 10

a reflex that is characterized by only one synapse between a sensory cell and motor neuron: the most basic reflex!

Question 11

Why would we even have stretch reflexes?

Answer 11

they provide the NCS with motor control postural control and muscle tone info. detect muscle lenght and rate of change, oppose stretch, etc.

Question 12

what is a motor unit?

Answer 12

a single motor (alpha) neuron and the muscle cells that it synapes.

Question 13

contrast the size of motor units and the function of muslce

Answer 13

the smaller finer control muscles are composed of smaller motor units this can vary from a few to thousands of muscle fibers.

Question 14

what is the point at which neurons connect to muscle fibers called?

Answer 14

the neuromuscular junction.

Question 15

what are the two types of motor neurons?

Answer 15

Alpha and Gama

Question 16

what are alpha motor neurons?

Answer 16

they innervate the main force-generating muscle fibers (the extrafusal fibers)

Question 17

what are gama motor neurons?

Answer 17

they innervate only the fibers of the muscle spindles (intrafusal fibers)

Question 18

what is the major method of increasing the strength of contration of skeletal muscles>

Answer 18

it is recruitment (of more muscle units).

Question 19

what is a muscle spindle?

Answer 19

it is a small spindle-shaped emcapsulated structure oriented parallel to muscle fibers and scattered throughout muscle.

Question 20

what is the purpose of muscle spindles?

Answer 20

they are mechanosensitive propriceptors. or they sense the relative position of neighboring parts of the body and strength of effort involved in movement.

Question 21

what happens physically to a spindle when the muscle moves?

Answer 21

the muscle spindle is stretched when the muscle is stretched: the spindles are about 20% of the length of the fibers and 20 to 100s per muscle.

Question 22

where could we find the greatest number of muscle spindles?

Answer 22

in fine control muscles (hands etc.)

Question 23

what are the motor and sensory nerve fibers to the muscle spindles (intrafusal muscles fibers)

Answer 23

The motor: Gamma efferent motor fibes; Sensory: Secondary sensory endings (type II fibers), and Primary sensory endings (type Ia fibers)

Question 24

What is the function of the two types of muscle spindle sensory fibers?

Answer 24

Secondary sensory: detect amount of stretch; Primary sensory: Detect rate and amount of stretch

Question 25

describe the appearence of the sensory fibers on the muscle spindles:

Answer 25

the secondary sensory ending are nerve fibers that simple synapse at both ends of the muscle spindle (sense the stretch by measuring the change in that distance); The primary sensory endings are wrapped around and around the spindle from the top to the bottom. (sense the stretch and rate by sensing the thickness of the spindle)

Question 26

How does the primary or 1a sensory fiber detect the length and rate of stretch?

Answer 26

they are wrapped around the muscle, and as the muscle stretches, mechanosensitive receptors depolarize sensory endings in response to stretch, and the 1a firing rate is proportional to stretch: High stretch=high firing rate; low stretch= low firing rate

Question 27

how do the gamma neurons and alpha neurons respond to the 1a and type II neurons?

Answer 27

the gamma neurons respond to the Ia fiber firing rate to maintain the length of the spindle fiber in order to maintain the sensitivity of the spindle fiber. The Ia fiber can go to the spinal chord and synapse with inerneruons or directly with alpha neruons to cause alpha neuron action!!

Question 28

what is the mathmatical relationship between 1a sensory fiber firing rate and the stretch of the muscle?

Answer 28

they are directly proportional.

Question 29

what is a myotatic reflex

Answer 29

a stretch reflex that is to the same muscle that is stretched.

Question 30

why would the z bands of a spindle muscle fiber only be at the ends of the fiber?

Answer 30

the ends are the only part that contract, therefore the contraction of the muscle (gamma neurons) also causes the stretch of the fiber and can cause greater sensitivity of the spindle fiber to stretch!

Question 31

how does a stretch reflex work…..?

Answer 31

stretching the muscle stimulates the spindle afferents, i.e. the 1a axon. In the spinal cord the 1a axons terminate monosynaptically onto the alpha motor neurons that innervate the same muscle, thus stretching of a muscle causes rapid feedback excitation of the same muscle through the minimum possible circuit: one sensory neuron, one synapse, and one motor neuron. (there is no interneuron=only one synapse), at the same type through a interneuron the antagonist muscle is also inhibited. (reciprocal innervation)

Question 32

Why do we even have these reflexes?

Answer 32

important for maintain muscle tone and adjusting reflexively and important for maintaing posture!

Question 33

How can we excite a muscle spinde?

Answer 33

Two ways: 1. stretch the muscle: extra and intrafusal muscle lengthing due to relaaxation of muscle or contraction in antagoistic muscle. 2. Gamma fiber signaling: evoked intrafusal stretch (this occurs during voluntary contraction and loading of the muscle!!

Question 34

how can the brain use the spindles to control the tone of muscles and smoothness of contraction in a wide variety of different situations?

Answer 34

Gama fibers allow for the contraction of the spindle fibers and this will increase or decrease the sensitivity of the unit to stretch and therefore provide control in a variety of situations!

Question 35

what if I lose either the efferent or and afferent nerves to the muscle spindles?

Answer 35

then the muscle is immediately flaccid – loses its tone!

Question 36

how can we contract the muscle and maintain sensitivity on the muscle spindle?

Answer 36

the alpha and the gamma fibers are activated at the same time and this will shorten the muscle spindles and lead to shortening of the muscle spindle and make it more sensitive to the shortened length of the muscle.

Question 37

Why would we need to maintain the sensitivity of the musle spindles through the use of the Gamma fibers?

Answer 37

to maintain a good control and posture in contraction situations!

Question 38

what is a golgi tendon reflex?

Answer 38

The golgi tendon reflex is a counter reflex to the stetch reflex – it will act to loosen the muscle under stetch in order to prevent damage to the muscle!

Question 39

what is a golgi tendon organs?

Answer 39

they are in the ends of the tendon, where there are encapsulated sense organs in series with the muscle fibers, about 10 to 15 muslce fibers connected to each golgi tendon organ. they have 1b afferent neurons that send info on the stretch of the tendon and the muscles connected to it!

Question 40

what is the purpose of the golgi tendon organs?

Answer 40

they sense the load or the stretch on the muscles and send inhibitory signals to stop the over stretch of the muscle: protect the muscle! It can therefore control the group of muscle to make sure that it is evenly being contracted as well.

Question 41

contrast the stretch and golgi reflex

Answer 41

it is the opposite of the stretch reflex! opposes muscle contraction through inhibition of motro nerons causing relaxation. golgi is anti alpha neurons and stretch is pro alph!

Question 42

Besides preventing the tearing of muscle fibers what else do golgi fibers seem to do?

Answer 42

they can balance a muscle load by balancing the stretch between different groups of muscle fibers.

Question 43

Describe the circuit of nerves for the Golgi reflex

Answer 43

the gogli tendon organ senses stetch and sends signal down Ib neuron that goes to dorsal root and the spinal chord to synapse with interneurons that then synapse with alpha motor neurons to inhibit the contracting muscle and activate the non-contracting muscle.

Question 44

what the what…golgi and stretch oppose each other how can we get anything done?

Answer 44

the amplitude and sensitivity of the relfexes is extensively modulated by descending input form the upper motor neurons. the two reflexes send signals to the higher motor control centers, an help provide smooth muscle movement.

Question 45

What is the Flexor-withdrawl/flexor and crossed-extensor/flexor reflex?

Answer 45

occurs with pain, tactile or noxious stimulus. cause withdrawl of affected side and extension of the opposite side (i.e. step on a tack)

Question 46

describe the circutei for a flexor and crossed extensor reflex

Answer 46

the afferent fiber neuron will synapse with interneurons on both sides of spinal chord to lead to withdrawl of body on one side and extension on the other.

Question 47

Waht are superficial reflexes?

Answer 47

they are triggered by gentle cutaneous stimulation of the skinn or mucous membranes.

Question 48

waht is the plantar reflex?

Answer 48

normal response to L4-S2 stimulation on the foot is to flex toes, the abnormal is to extend toes (babinski relfex)

Question 49

when a muscle is suddenly stretched, a signal is transmitted over 1a sensory fibers from muscle spindles. describe the response elicited by these spindle afferent signals

Answer 49

Contraction of the muscle in shich the ative spindles are located. When a muscle is stretched, signals traveling over Ia sensory fibers will lead to contraction of the muscle in which the ative spindles are located. at the same time, the antagonist muscles will be inactivated. the intrafusal fibers in the spindle do not go slack due to the tonic activation of gamma motor neurons by supraspinal system.