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 For example, the arm will suddenly be withdrawn if it touches a very hot object.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.

[priscillavarela]

You make such a complex chapter seem so clear and easy to understand your amazing dr campbell!!

[HeartofGold]

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!

[st.sevensins]

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

[Lolaaaz]

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

[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. 🌸

[bevans]

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.

[catarinasantos]

You are the best educator ever. Everything with you is simple

[yemaneberhane]

I really like your plausible, clear and attractive lectures lectures.

[nadiacharafi]

thank you you have made it so simple and clear to understand

[PalaceIV]

Thank you for explaining this. It was very helpful for my understanding.

[Amy_jane]

oh my. i am so glad that i found your channel just in time! doing a health science degree at uni. THANK YOUUUU

[noel]

thankyou sir your explanation really helps in my study thankyou so much

[santoshburud]

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

[cephasmwewa]

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

[nvmisnvm]

these video are so useful! thank you so much

[patsang]

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

[Abhaywr]

Bro is a life saviorfor NEET aspirants

[mohrma]

Very informative videos. Thanks a lot.

[TheBeach]

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