W6 Reflexes 2

Question 1

What is the central integrator of oral reflexes?

Answer 1

Brainstem nuclei

Cranial nerves carry sensory and motor, afferent and efferent neuronal types to and from the brainstem.

Question 2

Where are interneurones found in the brainstem and what do they do?

Answer 2

In specific nuclei of the brainstem
They integrate information from sensory neurones to determine whether there is a change in motor activity to bring about the consequence of the reflex arc.

Question 3

What kind of reflex is the jaw jerk reflex?

Answer 3

Simple reflex - monosynaptic

Question 4

What is the receptor and stimulus in the jaw jerk reflex?

Answer 4

Muscle spindles

If a muscle in the head is stretched the sensory neurone is activated.

Question 5

Describe the sensory component of the jaw jerk reflex

Answer 5

Sensory neurones have cell bodies that live outside the CNS. Information from the trigeminal nerve comes together in the trigeminal ganglion. Sensory information detects activity about the muscles. These neurones synapse with synapses within brainstem nuclei.

Question 6

Where is the location of the monosynaptic connection for the jaw jerk reflex?

Answer 6

In the pons

Question 7

What happens when the motor efferent is activated in the jaw jerk reflex?

Answer 7

The efferents travel primarily via CNV again to exit out towards the muscles, where the spindles are living, causing contraction of the jaw muscles.

Question 8

The jaw muscles involved in the jaw jerk reflex can be stretched by tapping on the chin. Why can you not test this on yourself?

Answer 8

Because you are constantly aware of what you are about to do, with the descending modulators influence overriding the reflex.

Question 9

What is the purpose of the jaw jerk reflex?

Answer 9

To determine the level of contraction in the jaw muscles which is important in adjusting the force of bite.

Question 10

Summarise the jaw jerk reflex

Answer 10

The increase in length of the jaw-closing muscles will increase muscle spindle activation, increasing force of contraction of the muscles, leading to jaw closure. The more force needed to generate, the more force of contraction of these muscles is produced.

Question 11

What can happen if the descending influence of the brain is disrupted?

Answer 11

This is an UMN lesion (e,g,m due to trauma or stroke)

The response will become exaggerated and cause hyperreflexia

Question 12

What happens to the jaw jerk reflex in patients with hyperreflexia?

Answer 12

When touching a patients chin, they may activate their jaw jerk reflex and clamp their mouth shut.

Question 13

What is the function of the gag / pharyngeal reflex?

Answer 13

Protective - prevents inappropriate swallowing

Question 14

Where are the receptors of the gag reflex?

Answer 14

Back of the oral cavity (makes dentistry hard)

Potentially mechanoreceptors

Question 15

What sensory neurones are involved in the gag reflex?

Answer 15

Once the gag reflex is activated, the sensory neurones travelling in CNIX synapse within the medulla of the brainstem. Nucleus of CNIX is involved as well as CNX through interconnections through interneurons.

Question 16

What are the efferent neurones and effectors of the gag reflex?

Answer 16

Neurones from predominantly CNX which innervates part of the upper oesophagus. Outputs part of CNIX go back to the parts of the pharynx. Contraction of these muscles results in the gag response.

Question 17

How is the vomiting response linked to the gag reflex?

Answer 17

Information from motor nuclei within the medulla also passes down (via the spinal cord and exiting into the ganglia that live within the upper part of the thorax) to be able to innervate the stomach. So if the gag reflex is activated very strongly, we might void some stomach contents.

Question 18

The gag reflex protects us but how do we stop it from protecting us from swallowing food?

Answer 18

Brain knows we are eating food from the smell and site. So it’s descending modulating influence can (to some extent) override the gag reflex and enable us to swallow.

Question 19

What are the receptors of the swallowing reflex?

Answer 19

Mechanoreceptors present on the palate, tongue and pharynx

Chemoreceptors detecting the chemistry of the food

Question 20

What neurones does the sensory information travel via for the swallowing reflex?

Answer 20

CNV and CNIX

Question 21

What is the central integrator of the swallowing reflex?

Answer 21

Within the brainstem are a collection of nuclei called the ‘swallowing centre’ which integrates taste from VII, IX and X.

Question 22

What are the motor efferents and effectors of the swallowing reflex?

Answer 22

Motor output is the CNIX, CNX, CNXII.
Multiple effectors help us move food backwards in the oral cavity.
Contractions of skeletal muscle in and around the back of the oral cavity and the pharynx enable swallowing.

Question 23

What has to happen to swallow a substance?

Answer 23

Complex series of effectors, primarily skeletal muscle. Followed by smooth muscle activity within the GIT.
Output: close larynx, open oesophageal sphincter, close glottis, prevent respiration.
Food is then propelled by peristalsis through the GIT enteric reflexes.

Question 24

Does the swallowing reflex involve somatic or autonomic reflexes?

Answer 24

Integration of somatic and autonomic information occurs, all from the activation of one set of sensory receptors.