moving on from our sensory Pathways and our second learning objective focuses on the motor pathways or the pathways that nerve impulses take from our brain out to our effectors so our motor pathways which are also called descending Pathways because they transmit motor information down from the central nervous system to the effectors in the peripheral nervous system once that information reaches the effector an output occurs which may be the contraction of a muscle or the secretion of a substance from a particular gland so here we have a motor nerve impulse originating from the motor cortex it travels down or descends through the brain stem it decussates or crosses over to the other side it runs down the spinal cord to where it exits via a spinal nerve and innovates a scal muscle so where our sensory neural pathways are typically broken up into first second and third order neurons our motor pathways are organized into upper and lower motor neurons so an upper motor neuron is the motor neuron that originates from the cerebral cortex or the brain stem upper motor neurons from the cerebral cortex allow for the execution of voluntary movements of the body upper motor neurons originating from the brain stem regulate things like muscle tone and the muscles that control posture balance and the orientation of the head and the body upper motor neurons then sinapse with lower motor neurons which have their cell bodies in the brain stem or the spinal cord from the cell bodies in the brain stem these lower motor neurons extend through cranial nerves to innovate sceletal muscles of the face and the head and from the cell bodies in the spinal cord they exit through our spinal nerves to innovate sceletal muscles of the limbs and the trunk now next week we begin to look at muscles in the lectures in the labs however very briefly sceletal muscle is that muscle that's connect to Bone and produces movement these are all also the muscles that we can voluntarily control now the axons of the upper motor neurons extend down from the brain and the brain stem via two types of Pathways either direct or indirect a direct motor pathway provides input to lower motor neurons by axons that's extend directly from the primary motor cortex indirect motor Pathways provide input to lower motor neurons from other regions of the brain so motor sensors in the basil nuclei or ganglia the cerebellum and other areas of the cerebral cortex once this input reaches the lower moded neurons however the output generated or the nerve impulses received by those lower moded neurons which go on to innovate sceletal muscles is still exactly the same so nerve impulses for voluntary movements propagate from the primary motor cortex to lower motor neurons via direct motor pathways the direct motor pathways are also known as the pyramidal pathways due to the shape of the cell bodies of these neurons which look like a pyramid now we have two direct motor pathways or pyramidal Pathways these are known as the corticospinal pathways and the cortico bulber pathway now indirect Pathways which are also called the extra pyramidal Pathways because they are outside those pyramidal cells include all of the other sematic motor tracts outside of the cortico spinal and the cortico Bulba tracts so these descend from various nuclei in the brain stem and they influence activities such as the voluntary movement of our distal limbs reflexive movements of the head and the eyes and posture and balance so our indirect Pathways include the rubos spinal the tectospinal the vestibulospinal and the reticul spinal Pathways so the first of our direct motor pathways so coming directly from that motor cortex are the corticospinal pathways and these Pathways conduct impulses for the control of sceletal muscle of the limbs and the trunk ax of upper M neurons form the corticos spinal tracts which we can see here are our lateral corticos spinal tract and our anterior corticospinal tract which descend through the cerebral cortex and the midbrain to the Medela where those bundles of axons form the bulges on the front side of the medala that we know as the medall pyramids about 90% of the axons in the cortico spinal tract will decussate or they cross over in the Medela and then descend into the spinal cord where they then syapse with the lower motor neuron the 10% that don't decussate in the Medela will descend through the Medela and then cross over lower down in the spinal cord now as we pointed out in this image within the corticos spinal pathway there are two corticos spinal tracts the lateral corticos spinal tract and the end interior corticospinal tract the corticospinal axons that decussate or cross over in the Medela form our lateral corticospinal tract so they run up or run down sorry the lateral column of the spinal cord which remember is these parts here and here these axon sign ups with lower motion neurons in the spinal cord and then exit the spinal cord via a spinal nerve innovates the sceletal muscle that controls movements of the distal parts of the limbs so the distal parts of the limbs like our hands and our feet are responsible for quite precise agile and highly skilled movements so think about things like playing the piano or even buttoning up your shirt it's quite a skilled precise movement the corticospinal axons so about the 10% of those corticospinal axons that do not cross over in the Medela form our anterior corticos spinal tract it runs down the anterior white column of the spinal cord and at each spinal cord level these axons will decussate or cross over and that's where they will then syapse with the lower motor neurons and exit via spinal nerves to innovate sceletal muscle that controls movements of the trunk and the proximal parts of Limbs so our trunk or our midsection kind of our shoulders and and our hip regions now these movements will be larger and stronger but less precise than those achieved by the hands and the feet so this image is just for showing that full neural pathway so we have the lateral cortico spinal pathway on this side here where these is uh this pathway forms the axons that cross over or decussate in the Medela and then run down and exit the spinal nerve our anterior corco spinal tract is the tract that runs down it doesn't cross over in the Medela it crosses over at the region or the level of the spinal cord where that lower motor neuron will actually exit the cortico Bulba pathway is our other type of direct pathway that conducts nerve impulses for the control of sceletal muscles in the head axons of upper motor neurons from the motor cortex form the cortico bulber tract which descend through the cortex in the mid brain kind of alongside those cortico spinal tracts now some of the axons of the cortico bul trct decussate and others do not so not even lower down they just don't cross over at all the axons of the upper motor neurons of this pathway will terminate in the motor nuclei of nine pairs of our cranial nerves in the brain stem the lower motor neurons of these cranial nerves will then carry these nerve impulses that control precise voluntary movements of the eyes the tongue and the neck to allow things like chewing facial expression speech and swallowing so the cortico spinal tracks control the movement of our trunk and our limbs the cortico bulber tract or pathway controls movement of our head and our neck so once more just giving you that visual here so we've got these neurons extending from the primary mode to Cortex some will decussate and exit via our Cranium nerve some will stay on that same side of the body and exit on a cranial nerve on that same side now lastly the indirect motor pathways are those outside of the CTIC spinal and the cortico bulber tracks and these ones have upper motor neurons which descend from areas of the cortex that sit outside of the primary motor cortex so similar to the sensory spinos Cabell trct I don't need you to know about these Pathways in detail but you do need to be aware that they exist and I guess have some idea of their presence and their General function So within the indirect Pathways we have the rubos spinal pathway so so this innovates contralateral muscles so muscles on the opposite side of the body which govern precise movements of the distal parts of the upper limbs so essentially your hands the tecto spinal pathway also innovates Contra lateral muscle so muscles on the opposite side of the body but in this pathway they innovate muscles which are reflexively moved in the head the eyes and the trunk in response to visual or auditory stimuli so for example when you hear a really light loud bang or some something makes a really loud noise and you kind of pull your head away reflexively the tecto spinal pathway will be involved with that Movement we then have the vestibular ccka pathway so this innovates Ipsy lateral movement so these are muscles on the same side it's in the trunk and the proximal part of the limbs these muscles help maintain posture and balance in response to head movements and then lastly we have the medial and the lateral reticular spinal pathway which also innovates Ipsy lateral muscles of the trunk and the proximal Limbs and this helps maintain posture and muscle tone in response to body movements so vestibular ccka pathway is maintaining posture in response to head movements our medial and lateral reticular spinal pathway uh maintains posture and muscle tone in response to body movements