muscles what about muscles for the the Torso or the trunk uh you have um several group muscle groups the first group is erector spiny um it forms by the three different muscles uh or three divisions so when it close to spine or connects spine to spine that's um spinalis and then if it um connect uh um transverse process to transverse process it's uh longissimus if it's um connect rib to reib it's ilio um costalis so these three um different muscle form the erector spin uh if you look at this um you know when contract bilaterally uh it going to function to extend the neck and the trunk right if it uh function unilaterally it'll ler bend the trunk and the neck to the same side and you can see that it's so close to the Bone so the the moment arm for this muscle to activate is really really short so that means um you would need to have large uh muscle Force to to function function this way and that's why um it's primary it's the primary factor for uh back injury especially for those um more mobile um spine like C spine and L spine these are uh quite easy to hurt because you need to generate a lot of muscle Force for trunk to to exent you may um well I have um a way to memorize this because I'm you know I'm from Asia Asia Asia um so I like uh to make things uh with food because I'm foodie so here you see um I is ilio cost costalis l lisus s uh for the spine spinalis excuse me I typically call it I love Susy um so that that that that helped me remember and you don't have to follow this that's just me um if you go deeper um you will see uh another group of muscle um it's it's going to group um and call um transversal spinalis um the transversal spinalis uh it's many function to rotate um the spine okay um so if you if you look at the insertion um um it's it's at the U uh spinal U spinus process and origin is uh at the transverse process you can kind of see that they're really really short and Tiny and you know really down to U the spine okay and then when when they uh come when these group of muscle contract it kind of turn the trunk so when the trunk turns right which facing to the right it really is the you know if you look at the the spinus uh process it's the spinal process moving to the left so that's a bit confusion or confusing to people but if you look at the muscle Direction you it's it's not too hard to understand because kind of the muscle fiber going to go from the spinus uh spinus process to transp process and when it's kind of pull it kind of turn the body to uh to the right when it kind of uh when the left side kind of contract so these is another group of muscle um and I'm not I'm not asking you to to memorize the origin of these muscle because there too many um but you need to know there are um few different muscle group and U the erector Spate well you have to know the origin insertion and stuff so those are the back muscle okay so let's talk about the muscles at the uh ventral um area or anterior um area so uh the first um part is is uh rectus um abdominus right here you know by if you look at the muscle fiber you see kind of you know rectus is kind of straight line and you know it's at the at the center so it's not hard to to toine and its function is to uh bend the trunk or do trunk flexion uh if it's over stretched like you know you uh gain weight or um you have um um uh if you're pregnant that would overstretch the muscle and what would what will be the result or or consequence after that is uh you um that this muscle lose um it gets loose so it would get more uh it would lead to more anterior pelvic til which would lead to more lumbar I'm sorry this is a typle right here onar um [Music] lordosis okay another layer if you go um to different layers so another layer is uh external oblix if you look at the muscle fiber it's similar to to uh put your hand into the pocket that kind of Direction so uh if it it's action is when it when it act bilaterally again it help to uh to uh Flex the trunk if it's uh if it work unilaterally it'll do a lateral band or rotation to uh the the opposite side of the body and if you go to a different layer a deeper layer you see the internal Ox you see here the muscle fiber kind of go to the opposite direction as external oix so external oix is kind of put your hand in in the pocket that kind of Direction and the internal um object is kind of cross your forearm um to your chest that kind of um Direction kind of kind of opposite to external object and but um when the two sides of um the internal o contract it bend the trunk if it working unilaterally again it kind of going to bend um um the trunk laterally and it rotate to the same side of the body so when this contract going to go this way the same side if it's let's go back if it's external rotation uh I'm sorry external obl um can of go this way right going of Turn Down The the body to the opposite side okay okay and then the deeper layer of of this uh abdominal muscle is transverse if you look at the muscle fiber it's going to horizontally so that's why it's called transversus um abdominus okay and its function um is to support the internal organs um and in terms of movement if you U contract bilaterally it help help uh to flex the trunk and unilaterally uh again it help to for trunk Lal flection and rotation the trunk to the same side if we look from the back and you know very close to the Bone we see here another muscle called quadratus larum uh we've learned that for uh the pelvic section or lower extremity section ction uh but this uh quadrus muscle functioned to protect the abdominal content when it um Flex bilaterally it'll raise up the pelvis if it's functioning uh unilaterally or one side it will raise one side of the pelvic okay and it kind of help to do the trunk lateral fraction so you see um um there are three different group of muscle erector spiny transversal spinalis and abdominal muscles so muscle in the back they do trunk U um extension and uh uh and then some of them do a little flection some of them do rotation and then again same thing here in the abdominal muscle it's in the front so it's in charge of trunk flexion and but it also function to uh to uh for rotation so you can kind of imagine that the rotation force can be canceled out when uh one individual wants to do flexion or extension by can engage um um muscle bilaterally right so the rotation force can be canceled out so that this person have can have more p your um flexion or extension if this person want to do rotation then all muscle will kind of work together to to make that happen so for example here if uh one person wanted to turn their trunk to the left the acist is uh the right external obl and the left internal obl so the anus is is the totally opposite which is the left external and right internal okay and again uh my tip to uh identify the muscle is for the external obli is you know put your hand in the pocket the internal o is the opposite is a form crossing over the upper um um chest okay so um so what's the function of the trunk well um depending on it's it's really related to uh the spine's relationship with the uh scapula and the hip okay and mostly the trunk kind of provide um stabilization for the lower extremity and upper ex the function so it's more like a a stable base for example um if um this person wants to do hip flexion okay um the hip flexor will kind of pull U the pelvis doing so but to allow this person to do the hip flexion the rectus abdominus will will guar will generate a stabilizing Force by pulling the pelvis up so that the hip flexor can contract smoothly okay and if uh if one person wants to do uh the appr proximity so um um the trunk can provide a stable base for the upper extremity to function if one person has weak uh or unstable scapula so need this person needs to uh compensate so often times um the a um so so um she has let's say she has a unstable right scab so the left external obl will will uh compensate to help this person uh for reaching by you know turning the trunk um in in a direction that can help um her to do the reach so um that's the structure of the neck and the structure of um the Torso