lab 7 // powerlab 2- reflexes & reaction times

reflexes

a response reaction

learned reflexes

results from repetition

inborn reflex

a rapid, predictable, involuntary, and unlearned motor response to a stimulus

myotatic reflex

the stretch reflex

what are the five parts of a reflex arc?

1. receptor
2. sensory neuron
3. integration center
4. motor neuron
5. effector

spinal reflexes

reflexes that do not involve higher brain centers for the arc to function

stretch and tendon reflexes

helps coordinate smooth movements of skeletal muscle groups

muscle spindles

spindles in skeletal muscle that convey information about muscle length or the amount of stretch

golgi tendon organs

convey information about tendon tension to inform the CNS for the regulation of these reflexes

what are muscle spindles & golgi tendon organs examples of?

proprioceptors

intrafusal muscle fibers

3-10 modified skeletal small (1/4th regular size) muscle fibers that make up muscle spindles

sensory component center of the intrafusal fibers

non-contractile because they lack myofilaments

ends of intrafusal fibers

do contain myofilaments and do contract!

extrafusal muscle fibers

the regular muscle fibers surrounding a muscle spindle

anulospiral endings

endings of large axons that wrap around the center of the muscle spindle

what are anulospiral endings stimulated by?

the degree of stretch & the rate of stretch

flower spray endings

smaller axons that supply the ends of the muscle spindles and are only stimulated in response to the amount of stretch

gamma efferent fibers

- innervates the contractile ends of the intrafusal fibers to stimulate them to contract as the rest of the muscle contracts
- maintains tension in the intrafusal fibers so they do not slack as the muscle contracts and thus lose sensitivity

efferent fibers (aka alpha efferent fibers)

stimulate contraction in the extrafusal fibers

external stretch

the muscle spindle is stretched when the muscle lengthens

internal stretch

gamma motor neurons that cause the intrafusal fiber ends to contract, which will stretch the spindle's middle --> causes the anulospiral and flower spray endings to fire at an increased rate ↑

alpha-gamma coactivation

occurs as descending motor pathway fibers synapse with alpha & gamma motor neurons to cause the extrafusal fibers and intrafusal fibers ends to simultaneously contract --> maintains the aforementioned tension in the muscle spindle to maintain sensitivity

the brain can stimulate gamma neurons to do what?

1. cause the spindle to stretch and become more sensitive
2. can inhibit gamma neurons to cause the spindle to loosen & become insensitive

reciprocal inhibition

the sensory axon synapses in the spinal cord with an inhibitory interneuron --> in turn synapses with an alpha motor neuron that conducts impulses to the antagonist muscle (hamstrings in this case) --> inhibits contraction --> allowing contraction of the stretched muscle

all stretch reflexes are?

1. ipsilateral
2. monosynaptic

ipsilateral

involves motor activity on the same side of the body

monosynaptic

involves one synapse

polysynaptic

the inhibitory portion of the pathway in the reflex arc

the patellar knee-jerk reflex

tested to determine if motor & sensory communications between the spinal cord and thigh muscles are functioning

exaggerated reflex

could indicate damage in the brain or spinal cord
ex: a stroke

absent reflex

could indicate damage of peripheral nerves
ex: from neurosyphilis or chronic diabetes mellitus

tendon reflex

- polysynaptic
- has the OPPOSITE response of causing muscles to relax in circumstances of high tendon tension
- aids in preventing tendons & muscles from tearing when excess stretching force is applied
ex: trying to lift a load that is too heavy

tendon organs

- have a high threshold of activation
- are activated when a muscle strongly contracts or is passively stretched

afferent sensory fibers

synapse in the spinal cord with interneurons that both send signals to higher brain centers, and synapse with motor neurons in the spinal cord

reciprocal activation

1. the efferent motor neuron to the contracting muscle with the stretched tendon is inhibited
2. the efferent motor neuron to the antagonist muscle is activated so it will contract
--> relieves tension on the tendon!

"direct light" or pupillary reflex

involves 4 neurons that connect the retina to the midbrain then conveys information back to the ciliary muscle

consensual light reflex

- when light is focused upon the eye, the pupillary sphincter muscle in the iris constricts, reducing the aperture (diameter) of the pupil
- at the same time, the pupillary sphincter muscle of the other eye constricts too

miosis

pupillary constriction

mydriasis

pupillary dilation

flexion withdrawal reflex

mediates the withdrawal of a limb from a painful stimulus
ex: a pinprick or the heat of a flame

crossed extension reflex

- the reaction of the stimulated limb is often accompanied by an opposite reaction in the opposite limb
- serves to enhance postural support during withdrawal of the affected limb from the painful stimulus

what reflexes does the crossed extension reflex include?

consists of an ipsilateral withdrawn reflex + a contralateral extensor reflex in the opposite limb

superficial reflexes

- stimulated by gentle stroking of the skin in specific locations
- clinically, these are used to test spinal cord-level reflex arcs and upper motor pathways

plantar reflex

elicited by running a blunt object down the lateral aspect of the sole of the foot --> toes should flex

what two things does the plantar reflex assay?

1. indirectly assays the functionality of the corticospinal tracts
2. directly assays spinal cord integrity from L4 to S2

babinski's sign

- an abnormal reflex where instead of the toes flexing, the great toe dorsiflexes and the other toes laterally fan
- occurs if the corticospinal tract or primary motor cortex is impaired
- seen in babies until they are 1 yr old

abdominal reflexes

elicited by stroking the lateral skin of the abdomen on any side of the umbilicus

what does the abdominal reflex assay?

tests spinal cord integrity from T8-T12

corticospinal tract lesion

absence of the abdominal reflex

voluntary reactions

more complicated than reflexes since they require higher brain functions rather than relying on low-level neuronal circuitry

light (photonic) stimuli reaction time

190 ms

sound stimuli reaction time

150 ms

touch reaction time

155 ms

visual stimuli reaction time

20-40 ms

auditory stimuli reaction time

8-10 ms

age

+/-
for both males and females, reaction time shortens from infancy to late 20's → slowly increases until your 50's and 60's → then lengthens faster as you are 70+ years

arousal

+/-
- reaction time is fastest with an intermediate level of arousal
- deteriorates when the subject is either too relaxed or too tense

distraction

+
increases reaction time significantly, especially in younger individuals

gender

+/-
males generally have faster reaction times than females

practice

-
practice at a task decreases reaction time

errors

+
when a volunteer makes an error (ex: pressing the button before the stimulus is presented), subsequent reaction times are slower likely due to the subject being more cautious

fatigue

+
reaction time is deteriorated when the task is complicated compared to when it's simple
Ex: mental fatigue (sleep) has the greatest effect

punishment

-
shocking a subject when he reacts slowly shortens reaction time

drugs

+/-
- stimulants tend to decrease reaction times to a point
- depressants often increase reaction times

warnings

-
reaction times are faster when the subject has been warned that a stimulus will arrive soon