hello in this video we're going to talk about somatosensory pathways focusing on the dorsal column also known as the medial meniscal pathway the pathways from sensory receptors to the cortex are different for the various sensations we will mainly be focusing on the pathways which carries touch vibratory sense and proprioception sensations to the cerebral cortex this pathway is the dorsal column also known as a medial meniscal pathway let's revise the spinal cord anatomy and some tracks here is a section of the spinal cord the dorsal root here will carry sensory neurons from the periphery to the central nervous system so a spinal cord the ventral roots carry motor neurons from the central nervous system to the peripheral nervous system the dorsal column tract is here at the back of the spinal cord it can be divided into two parts laterally is a fasciculus cuny Attis and medially is a fasciculus gracilis the dorsal column tracts are responsible for carrying sensory information on touch pressure vibration and proprioception to the somatosensory cortex in the brain let's take a cross-section of the brain and at the somatosensory cortex here the somatosensory cortex is where the somatic sensory information is perceived the thalamus here is an important relay station in the ascending pathway the cerebrum continues to the brainstem which is made up of three parts the midbrain pons and the medulla the spinal cord is here and we're focusing on the cervical spinal cord as well as the lumbar spinal cord cross sections dorsal aspect of the spinal cord is the dorsal column tract part of the white matter which again carries sensory information on touch pressure vibration and proprioception the cutaneous receptors so the skin receptors for touch and pressure including vibration are the mechanoreceptors now mechanoreceptors are found in a number of cells mechanoreceptors include Merkel cells which carry touch and pressure information from the superficial skin this cell will carry this sensory information to the dorsal column of the spinal cord in this case the cervical spinal cord Ruffini endings are stimulated by sustained pressure Meissner corpuscles are stimulated by sensory input of tap and flutters 'singing corpuscles pickup sensation including deep pressure as well as vibration so when you use a tuning fork on the skin the pacinian corpuscles can detect these change and send sensory information to the central nervous system each of these cells which are stimulated by touch pressure or vibration will carry this sensory information to the dorsal column tract this cell is called the first order neuron now again the dorsal column if you remember is divided into two sections the fasciculus q8s and the fasciculus gracilis the fasciculus Kuni Attis is responsible for carrying sensory information from the upper body and so because this is the cervical spinal cord this would constitute the upper body so this first neuron will travel up the fasciculus Kuni a two section of the dorsal column towards the medulla where it will synapse with the second order neuron at the nucleus cuny ATIS the second order neuron will cross over at the midline of the medulla and travel up the medial meniscal tract of the brainstem towards the contralateral ventral posterior lateral nucleus the thalamus here the second order neuron will synapse with a third order neuron which will then carry the sensory information in a highly specific way to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe the somatosensory cortex is divided into regions that correlate with specific areas in the body such as the face hands legs specific areas of the somatosensory cortex in this case the hand because this is where the sensory receptors detected something this ascending system is called the dorsal column or the medial meniscal system it involves first-order neuron second-order neuron and third or neurons the other thing I wanted to highlight is that sensation that is felt on the left side of the body is perceived by the right side side of the brain as shown similarly sensation that is perceived by the right side of the body is pursued on the left side of the brain remember there are two sections of the dorsal column the fasciculus cuny ATIS and the fasciculus gracilis fasciculus gracilis is a part involved in carrying sensory information from the lower limbs in the lumbar spinal cord depicted here only the fasciculus crystallis exists whereas in the cervical spinal cord the fasciculus cuny Attis and the fasciculus gracilis both exist so imagine if this first-order neuron is carrying sensory information from the foot and the lower leg it will come to the dorsal column from the dorsal root of the spinal cord it will travel up the fasciculus gracilis towards the medulla where it will synapse with the second-order neuron at the nucleus gracilis the second-order neuron will cross over at the midline of the medulla and travel up the medial meniscal tract to the end at the contralateral ventral posterior lateral nucleus of the thalamus here the second-order neuron will sign up to the third-order neuron which will carry then the sensory information in a highly specific way to the primary somatosensory cortex and specifically to the region of the somatosensory cortex which represents the foot to the leg so those are examples of the somatosensory pathways of touch pressure and vibration let's not talk about proprioception proprioception is defined as the sense through which we perceive the position and movement of our body including sense of equilibrium and balance it basically is a sensation that allows us to keep our body balanced in space when you think about proprioception you think about proprioceptors which are the receptors and these proprioceptors are located in our muscles tendons and joints and relay information about muscle length and tension so let's recap the anatomy again quickly first here again is a somatosensory cortex the midbrain pons and the medial meniscal tracts the medulla which have the nucleus gracilis and the nucleus CUNY Attis the spinal cord is here let's just say it's the cross of the cervical spinal cord okay let's talk about proprioception and appropriate receptors let's look at the right elbow joint as an example of changes in muscle tension and stretch our muscles contain muscle spindles the muscle spindles is a type of proprioceptive that provides information about changes in muscle length the Golgi tendon is another sensory receptor a type of proprioceptive which basically lies on the tendons the propria receptors will detect changes in muscle tension and length and then will relay this information through the dorsal column up to the brain in this case because it is the upper body the first order neuron will travel up the fasciculus to knee Attis and will go up towards the medulla where it will synapse at the nucleus sakuni ATIS with a second order neuron the second order neuron will cross over at the midline of the medulla and travel up the medial meniscal tract to the end at the contralateral side to the central posterior lateral nucleus here the second order neuron will sign up to the third order neuron which will carry sensory information in a highly specific way to the primary somatosensory cortex to the region of the elbow joint for example you