Nervous system 3, Reflex arc.

Reflexes occur to protect the body from tissue damage; they are rapid involuntary actions. For example, the arm will suddenly be withdrawn if it touches a very hot object. A reflex arc describes an arrangement of three neurones which detect the stimulus and relay the information across the spinal cord to a motor neurone which will move an appropriate muscle.
The initial sensation is detected by peripheral sensory receptors and transmitted along the dendrite of a sensory neurone to the cell body. From the cell body it is then transmitted along the axon of the sensory neurone. This fibre then goes into the spinal cord where it synapses with a relay neurone. The relay neurone will carry the impulse across the spinal cord from the back, where the sensory neurones enter, to the front where the motor neurones leave. This relay neurone then synapses with the cell body of a motor neurone which carries the impulse away from the spinal cord to the appropriate muscle which is innervated to contract, withdrawing the hand away from the hot object.
In addition an ascending neurone carries the information up the spinal cord to inform the brain of what has happened. This means that the reflex can occurbefore the brain becomes aware that there is a problem. This saves a lot of time; if the message had to go up to the brain and a further message sent down to the muscle there would be a time delay during which injury could occur. There are many other examples of reflexes including the eyelash and gag reflexes.
Sensory neurones always approach the spinal cord from the back and the motor neurones always leave the spinal cord from the front. The nerve containing the sensory neurones which pass into the spinal cord is termed the posterior root and the one containing motor neurones the anterior root. Posterior always means towards the back and anterior towards the front.

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[@HeartofGold16]

Holy moly. I have a physiology test tomorrow and was looking for a video to explain this to me and every one I found, either the sound was WAY too low so I could barely hear it, or the explanation was stuffed into a video about just the nervous system and the topic was glossed over. Great explanation. I'm going to be drawing this diagram myself to help me learn this! Thank you, Dr. Campbell!

[@Lolaaaz1341]

Thank you, Dr. John:-) Your helping me understand these overwhelming concepts in the most simplified way. #FutureRN

[@st.sevensins]

Am taking a physiology test tomorrow and this was extremely helpful! New sub :)

[@strawberryrhubarbpie]

Brilliant. My teacher went over this quickly and not in this much detail. This helped me a lot!

[@kittycatobsession]

Thank you! Fantastic explanations. I like your relaxed demeanor, you don't rush through and the repetition makes the information stick. 🌸

[@santoshburud]

Dr . John , your explanations simply amazing! thank you sir

[@cephasmwewa1207]

Thank you Mr John, I have really understood your explanation over the reflex arc...

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You truly have a gift and inspire me to be detailed oriented whiles on this journey of becoming a doctor. Thank you for your simplicity.

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Excellent explanation, thanks!!

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Thank you very much Dr Campbell ,this was very helpful

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[@user-hc7cp8zu3m]

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Wonderful, lucid

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[@GiftyMadobe]

Thank you Doc

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Thanx it so clear

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Hats off 🎉

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thank you sir...

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Thank you so much Sir🙏

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Thanks it was very helpful

[@muhammadyaseenmahtaab7820]

Thank you...

[@patsang4507]

Very good, introducing terminology in an easy way abd explaining too. Excellent for teaching online and tutoring.

[@onehundredyears]

Thanks indeed.

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Great video and well explained and by the way every moment he takes a breath that made me uneasy 😂😂😂

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This guy is experienced.... I have seen his vidio that he made years ago

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Thank you so much sir... Extremely helpful

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Thanks

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Amazing lecture...so crystal clear.understanding very scary chapter.

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god bless u

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Dr john Campbell sir great you are importing such a valuable knowledge to millions of knowledge seekers including myself god bless you with sound health and prosperity thanks 15/07/2022

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Brilliant, world class🌍🤓

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beautifully explaimed🎉

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[@TheBeach604]

good explanation. Have anatomy exam tomorrow. thank you :)

[@Campbellteaching]

Hope the exam goes well

[@clairenixon2965]

Brilliant explanation! helps with my exam tomorrow :)

[@Campbellteaching]

Hope they go well

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Super

[@whiteroserebelap]

Thank you! Your delivery makes it easier to understand. Could you answer a question for me? We are learning about nerves in class, and they mentioned epidurals are injected into the epidural layer within the spinal cord. I asked what theoretically would happen if the injection put the anesthetic into the spinal meninges or areas deeper within the spinal cord. My teacher wasn't sure what results would be. Do you know please? Just out of curiosity. Thanks again for helping to solidify my knowledge...it all goes towards helping in my assignment.

[@shehnazsoomro9046]

sir i need to understabd blood composition with their function and enzymes

[@mohamadtaleb9565]

please can you explain autonomic reflex arc ?

[@sahana9114]

How will the nerve impulse from sensory neuron reach the brain after entering the spinal cord?

[@mmercier0921]

The complexity and beauty of the structure is only matched by those of the structure trying to consciously understand the physical mechanisms.

[@rameshkandagatla738]

How would information flow from nerve endings towards cell body sir.

[@dr.hasnainramzan9754]

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[@Pompeybell]

Another excellent video, I’m currently studying pain and have watched your videos on this subject too. I do understand the reflex arc but find myself wondering the relationship with people who ‘self harm’ ? How does the body not automatically pull away from the stimulus. Is the brain able to override this?

[@rachaelrodgers1636]

Interesting question 🤔

[@TheAnnaMarie]

My father is paralyzed, has been for 42 years. As he ages he gets worse and worse spasms in his body. They call them autonomic reflexes. They are dangerous for him and difficult to treat.

[@rameshkandagatla738]

As from the posterior root that you shown Dr.

[@rameshkandagatla738]

Is it possible, that the information flow from Axon towards cell body.

[@dr.yuvarajanpalanisamy9805]

Super explaination .Does this arch has memory or just act as just swift reflex sir.

[@Campbellteaching]

Good question, nerve pathways do become reinforced with use, but the traditional understanding is that it is a fixed system.

[@dr.yuvarajanpalanisamy9805]

@@Campbellteaching sir I feel very happy because of your reply each time to me .you are a great teacher I am an average at college want to understand better and I am unable to do my post graduation .Your videos are giving me a great inspiration and understanding ... Thank you very much sir ....

[@jaxcoxon3019]

Why is the endocrine system ill-suited to the co-ordination of a reflex such as the withdrawal response?
Thanks.

[@Campbellteaching]

it takes too long for the hormones to be released and then circulate in the blood

[@jaxcoxon3019]

@@Campbellteaching thank you

[@ME-xh5zq]

Sorry, do neurones in the periphery not exist in end-to-end chains or are they long enough to go to and from the spinal cord? I’ve always imagined nerves to be linked in long repeating chains.

[@Campbellteaching]

They are long enough
, so the neurones from the toes to the spinal cord may be over a metre long

[@ME-xh5zq]

@@Campbellteaching thank you.

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Could you maybe organize your playlists a little better? They aren't in order and I'm not sure if I re-organized this one right😅.

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9:06

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