Exercise 21 Human Reflex Physiology

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rapid, predictable, involuntary motor responses to stimuli


Five essential components of a reflex arc

receptor, sensory neuron, integration center, motor neuron, effector


What is the importance of reflex testing in a routine physical examination?

It is an important diagnostic tool for assessing the condition of the nervous system.


Reflexes classified as somatic reflexes include

- abdominal reflex

- calcaneal tendon reflex

- corneal reflex

- crossed-extensor reflex

- gag reflex

- patellar reflex

- plantar reflex


Stretch reflexes

- calcaneal tendon reflex

- patellar reflex


Superior cord reflexes

- corneal reflex

- plantar reflex


Reflexes classified as autonomic reflexes

- ciliospinal reflex

- pupillary light reflex


Two spinal cord-mediated reflexes

- patellar reflex

- cross-extensor reflex


Two somatic reflexes in which the higher brain centers participate

- pupillary light reflexes

- superficial cord relexes


Can the stretch reflex be elicited in a pithed animal (that is, an animal in which the brain has been destroyed)?

Yes. Even without the brain, a stretch reflex only needs an afferent control center and motor fibers to be elicited. These components still stay intact even if the brain has been destroyed.


Patellar reflex

Hit patellar tendon to excite muscle spindles of quadriceps. (afferent nerve) femoral nerve to (integration centers) l2 - l4 from there it goes to (efferent nerve) femoral back to quadriceps (effector) to make contraction. also sends to hamstring (effector) to give it resistance.


Calcaneal tendon relex

hit tendon nociceptors in tendo-achilles. goes to CNS by sciatic nerve (afferent) then goes to interneurons in spinal cord (integration center) s1 - s2. then to alfa motor n (efferent n) tibial nerve from sciatic nerve to lead to the (effector) gastrocnemius muscle.


What factor increases the excitatory level of the spinal cord?

muscle activity


What factor decreases the excitatory level of the muscles?



What a subject is concentrating on an arithmetic problem, did the change noted in the patellar reflex indicate that brain activity is necessary for the patellar reflex or on it that it may modify it?

no effect, it does not involve the brain


Ciliospinal reflex



Salivary reflex



Pupillary light reflex



Pupillary light reflex protects

to protect and help control the eyes from damage from different light settings


Corneal reflex protects

to protect the eyes from foreign bodies and lights


Crossed-extensor reflex protects

to help protect and maintain balance when a withdraw reflex occurs at another part of the body. Helps so you will not hurt yourself when a reflex occurs.


Was the pupillary consensual response contralateral or ipsilateral?



Why would such a response be of significant value in this particular reflex?

Helps to even out the light rays making it less stressful for the affected eye.


Differentiate the types of activities accomplished by somatic and autonomic reflexes.

somatic reflexes include all pathways that are voluntary actions of the body. and autonomic reflexes include all pathways that result in involuntary actions.


Micturition reflex

Organ involved: Bladder/uterus

Receptors stimulated: stretch receptors

Action: sensation to urinate


Defecation relex

Organ involved: mouth, pharynx, esophagus, small and large intestines, all digestive organs

Receptors stimulated: stretch receptors

Action: stool passage


Carotid sinus relex

Organ involved: carotid, common carotid, arteries, heart, blood, vessels

Receptors stimulated: beroreceptors

Action: control of blood pressure by regulating changes in heart rate


How do intrinsic and learned reflexes differ?

Basic reflexes are inherited - born with them. Learned/acquired reflexes are not inherited - not born with them.


Three factors that may modify reaction time to a stimulus

illness, age, and fatigue


How did the response time for the learned activity performed in the laboratory compare to that for the simple patellar reflex?

learned reflexes are not as fast as basic reflexes


Did the response time without verbal stimuli decrease with practice?

yes, because it is being learned/stored by repetition


Explain why response time increased when the subject had to react to a word stimulus.

because it distracts, it makes the reflexes slow down, the body can't go as fast with two as it can with one

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