crossed-extensor reflex accompanies
wat type of relfex
Frequently, the crossed-extensor reflex accompanies the flexor reflex when weight bearing limbs are involved because
it is important to maintain balance while avoiding the painful stimulus.
Contralateral reflex arc
what happens when you step on a sharp object
Think about what happens when you step on a sharp object—
the injured limb must be lifted off the tack by flexing the muscles on the ipsilateral side,
however to maintain balance (and get your weight off the injured foot),
the extensor muscles of the opposite leg must contract.
what happens physiologically
Here's what happens: afferent fibers carry information regarding the painful stimulus to the spinal cord.
There, the information is sent via interneurons to several destinations.
on the same side
On the same side as the stimulus,
the interneuron synapses with the motor neurons innervating the hamstrings causing them to contract (excitatory stimulus).
At the same time, the interneuron inhibits the motor neurons going to the quadriceps muscle (extensors) so the leg can be withdrawn from the stimulus.
colateral side action
That's great, but if the contralateral side of the body didn't respond simultaneously with the opposite reaction of flexors and extensors,
then the individual would fall down.
So, the interneuron crosses over to the other side of the spinal cord where it sends excitatory signals to the quadriceps (extensors) and inhibit the hamstrings (the flexors).
this process allows us
This allows us to remove the foot from the painful and harmful stimulus while maintaining our upright posture.
other ex of cross-extensor reflex
This reflex is also stimulated if a stranger suddenly grabs your arm.
The stimulated arm reflexively withdraws via flexion from the stranger's grasp, while to opposite arm extends to push the stranger away from your body.
crossed extensor reflex sum
Motor response is on the side opposite the stimulus
Flexor reflex pulls the foot away from the tack.
Crossed extensor reflex straightens the other leg to support the body weight.
superficial chord reflex: initiation
Superficial cord reflexes, or simply superficial reflexes are initiated by gently stroking the skin, cutaneous stimulation-
why superficial reflexes are important clinically
The reason why superficial reflexes are important clinically is because
they depend on both the proper functioning of upper motor pathways and on cord-level reflex arcs.
the plantar reflex which test the integrity of the spinal cord from L4-S2 and
indirectly tests if the corticospinal tracts are working properly.
Abdominal reflexes are initiated by stroking the skin of the lateral abdomen around the umbilicus.
It is used to check the integrity of the spinal cord from T8-T12.
The cremasteric reflex is obvious in males only;
it checks the integrity of the lumbar plexus via the genitofemoral nerve at levels L1-L2.
The most tested superficial reflexes include
to check plantar reflex, wat u do
To check the plantar reflex,
the examiner draws a blunt object like the end of a reflex hammer across the lateral aspect of the sole of the foot.
normal plantar reflex reaction
Normally, this causes a downward flexion or curling of the toes.
Babinski sign: wat damaged
However, if either the primary motor cortex or the corticospinal tract is damaged,
the plantar reflex is replaced by an abnormal response called the sign of Babinski.
Babinski sign: reaction
In this case, the toes fan out laterally and the hallux (great toe) dorsiflexes.
babinski sign abnormal in
normal adults who are heavily intoxicated.
This reflex is normal in infants until they reach about the age of one year old because
myelination of the fibers of the corticospinal tract is incomplete.
In an infant, the toes spread. This response disappears as descending motor pathways develop.
cremaster reflex elicited by
The cremasteric reflex is elicited by gently stroking the skin of the inner thigh.
cremaster reflex: injury
injury to lower spinal cord and lumbar plexus.
normal cremasteric reflex reaction
This results in the contraction of the cremaster muscle in the spermatic cord of males.
The cremaster is a continuation of part of the internal oblique muscle.
When the inner thigh is stroked, the cremaster contracts resulting in the visible elevation of the scrotum superiorly towards the abdomen.
when cremaster reflex naturally happens
This happens normally when the scrotum is exposed to low external temperatures.
The purpose of this reflex is to help maintain the internal temperature of the testes within the range necessary for optimal sperm production.
abdominal reflex how test
The abdominal reflexes are initiated by gently stroking the skin just above and around the umbilicus.
abdominal reflex normal reaction
This results in the contraction of the abdominal muscles in such as way as to move the umbilicus toward the site of the stimulus.
abdominal reflex absent when
Abdominal reflexes are absent when corticospinal tract lesions are present.
cranial nerve reflexes
Somatic Reflexes Mediated by Cranial nerves
Thus far, we have examined common somatic reflexes mediated by spinal nerves and pathways involving the spinal cord.
We will now look at somatic reflexes that are mediated by cranial nerves.
Recall that 10 of the 12 pairs of cranial nerves come from the brainstem.
Because the brainstem plays a critical role in keeping us alive,
testing its integrity is extremely important in any neurological exam.
The two cranial nerve reflexes most commonly tested are the corneal reflex and the gag reflex.
cornea reflex mediated thru
The corneal reflex is mediated through the trigeminal nerve (cranial nerve V).
how to test corneal reflex
To test this reflex, the cotton on the end of a large swab (Q-tip) is drawn out into a fine wisp of fibers.
The patient is then asked to look away from the examiner (toward the opposite wall) at a distant object.
The examiner quickly but gently touches the subject's cornea with the wisp of cotton.
normal corneal reflex reaction
If everything is normal, the subject will blink their eye.
fn corneal reflex
This reflex is protective in that it protects the eye from harmful, foreign debris that might interfere with vision.
corneal reflex tests
Cranial nerves V and VII have their nuclei (neuron cell bodies) in the pons of the brainstem.
Tests trigeminal nerve (sensory input) and integrity of brainstem.
Motor output from cranial nerve VII (facial).
Absence of this reflex often indicates serious damage to the brainstem resulting from compression of the brain or other trauma.
cough reflex tests
The gag or cough reflex tests the somatic motor responses of cranial nerves IX and X.
how to test cough reflex
The reflex is initiated by holding the tongue down with a tongue depressor,
having the subject say "Ahhh", and
then touching the mucosa alternately on each side of the uvula.
normal response cough reflex
The mucosa (pharynx) of the posterior pharyngeal walls should rise equally and evenly simultaneously on both sides.
Patient will gag
fn cough reflex
The gag reflex is important in preventing solid material to pass into our airways.
autonomic reflexes: def
There are three, easy to elicit visceral reflexes that also test the integrity of the brainstem since
they are mediated through the autonomic fibers that travel in certain cranial nerves.
Visceral reflexes mediated through the autonomic nervous system that we are usually not aware of.
autonomic reflex: list, mediated thru
1. These are the pupillary reflexes mediated through the parasympathetic division of the autonomic nervous system;
2. the ciliospinal reflex which tests pupillary responses mediated through the sympathetic division of the autonomic nervous system, and
3. the salivary reflex which is also parasympathetic.
types of pupilary reflexes: list
There are several types of pupillary reflexes—
the pupillary light reflex,
the consensual reflex,
accomodation for near vision and the
types of response to pupillary reflexes
Consensual pupillary reflex
pupillary light reflex and the consensual reflex similarities
In the both the pupillary light reflex and the consensual reflex,
light is used as a stimulus.
The retina of the eye is the receptor,
the optic nerve contains the afferent fibers and
conducts the stimulus to the brainstem,
the parasympathetic fibers in the oculomotor nerve carry the efferent impulses to the
smooth muscle of the iris which is the effector.
why pupillary light reflex n clinicians
Pupillary light reflex is a safety feature of the visual system.
Also is one of the body's vital signs, so it is of diagnostic value to clinicians.
how to test pupillary reflex
The pupillary reflex results when light is directed into the pupil of one eye.
normal pupillary reflex response
"Pupils equal and responsive" , is a common phrase used in various emergency or hospital television series.
The pupil should respond by getting smaller caused by the contraction of the constrictor muscles in the iris.
abnormal pupillary reflex means
If this doesn't happen, it could mean that either the retina or optic nerve is damaged,
or the visceromotor output pathway from the oculomotor nerve is not working.
This type of response indicates ipsilateral issues.
normal 2 eyes response to pupillary reflex
Normally, when light strikes the retina of one eye,
both pupils constrict equally.
This is the consensual light reflex
consensual reflexes: def
(consensual reflexes of any type are observed on one side of the body when the other side is stimulated).
explain why response happens puppilary response
The reason for the consensual light reflex is because nerve fibers project bilaterally to
an oculomotor complex that sends efferent fibers to join with both oculomotor nerves.
If both pupils fail to constrict equally, damage
If both pupils fail to constrict equally when the light is directed into one eye, then there is damage to the oculomotor complex in the midbrain.
fn pupillary reflex
The pupillary light reflexes function to protect the retina (part of the CNS) from damage resulting from excessively bright light.
ciliospinal reflex examines - wat response
The ciliospinal reflex is another way in which pupillary responses can be examined.
ciliospinal reflex mediated by, at work when
Unlike the light reflexes, the ciliospinal reflex is mediated via the sympathetic division of the autonomic nervous system.
The sympathetic stimulation of pupillary dilator muscles is at work when we are in dim light, or during the flight versus fright reaction.
ciliospinal reflex involves
The ciliospinal reflex is kind of bizarre in that the sensory receptors do not involve any structures in the eye.
how to test ciliospinal reflex
This reflex is initiated by gently stroking the skin at the hair line on the back of one side of the subject's neck.
normal response ciliospinal reflex
This results in the dilation of the pupil on the ipsilateral side of the stimulus.
Dilator pupillae muscle contraction increases pupil size
type of response reflex for ciliospinal reflex
The reflex is not consensual because the contralateral pupil does not dilate.