Ascending Tracts

Internal Structure of the Spinal Cord Grey matter –cervical and lumbar enlargements White matter –most abundant superiorly

Cell Types alpha gamma propriospinal medium sized relay neurons Lamina of Rexed

Alpha motor neuron Motor neuron to main bulk of voluntary muscle. Group - medial group  innervates axial musculature dorsal medial group  innervates anterior trunk ex) rectus abdominis, intercostals ventral medial group  innervates back muscles ex) erector spinae - lateral group  innervates appendicular musculature (limbs) upper limb proximal to distal  arm, forearm, hand lower limb proximal to distal  thigh, lower, foot - flexor group  dorsal - extensor group  ventral - intemediolateral group  parasympathetic system sacral region of spinal cord - central group  innervates diaphragm C3 to C5

Gamma motor neuron - Motor neuron to intrafusal fibers  stretch receptor intrafusal fiber  muscle fiber of muscle spindle Renshaw cell - interneuron

Pathways Ascending  somewhat sensory for most part Main sensory neuron  dorsal root ganglion (spinal ganglion) Spinal Ganglia (Dorsal Root Ganglion) Thoracic : smaller than lumbar, cervical, 50,000 Neuron  pseuounipolar Has cell body, process somes out of cell body splits into two processes  centripetal and centrifugal centripetal  goes into CNS (spinal cord, brainstem) centrifugal  goes toward receptor Cervical and lumbar- more neurons due to plexus, 100,000 Enter both dorsal (sensory) and ventral (motor) roots

Conscious Sensation Perceived by cerebral cortex Aware of it  goes to cerebral cortex Type - Exteroceptive (outside) -vision, hearing, touch, pressure, heat, cold, pain - Proprioceptive - position sense, kinesthetic sense

Unconscious Sensation Perceived in the cerebellum Enteroception (inside of body) - visceral reflexes - causing various changes to occur ex) blood pressure Proprioception - motor coordination - minute changes in muscle tone - fine motor tuning to maintain position in space

Somatic Sensory Pathways Sensations happening to body Distinguish touch, temperature, pain … First order neuron is in DRG - centrifugal goes to receptor Second order neuron’s => in CNS - cell body is ipsilateral second order neuron axon - terminates in the contralateral side of thalamus Third order neurons in thalamus - project to postcentral gyrus  somatosensory cortex

Somatic Sensory Pathways II Somatotopic  map body through entire pathway - cuneate and gracile fascilcles - medial  lower body - lateral  upper body Modulated by interneurons

Dorsal Column-Medial Lemniscus Ascending pathway Dorsal column  pertains to 2 columns on dorsal side of spinal cord - gracile, cuneate fasciculus Medial lemniscus  pertains to fibers running through brain stem Function –proprioception –discriminative touch AKA epicratic touch know difference btw two points adjust pressure  how much pressure to apply light touch Neurons and tracts - First Order – DRG fibers enter spinal cord and travels up cuneate or gracile fasciculus information about LOWER body  gracile fasciculus through spinal cord information about UPPER body  cuneate fasciculus through ONLY ½ of upper spinal cord Second Order – synapses at Nucleus of. Cuneatus and Gracilis in medulla nucleus => where actual cell bodies are, and fibers exit nucleus cross over other side of medulla internal arcuate fibers  sweeping corss over of fibers go upward through brainstem, goes to medial lemiscus Third Order - VPL

Dorsal Column-Medial Lemniscus Tracts –Fasciculus Gracilus, F. Cuneatus –Medial Lemniscus –Corona Radiata Fibers cross in the medulla

Anterolateral System (ALS) Consist of - spinothalamic tract ( direct pathway) - spinotectal tract - spinoolivar tract - spinoreticular tract ( indirect pathway) Function Pain Temperature Crude Touch

Spinothalamic Lateral –Noxious (pain), Thermal Anterior –Light touch Neuron - 1 st order  DRG (pseudounipolar: goes into gray matter and synapses - 2 nd Order - I, IV, V, (III) - 3 rd Order – VPL (ventral posterior lateral neucleus)

Spinothalamic Tracts - cross over diagonally  at anterior white commissure - Anterolateral system (ALS)  to spinal lemniscus - Goes to thalamus  end at VPL - fibers run through internal capsule and corona radiata - makes way to postcentral gyrus - can map body on pathway - Lateral  cross over 1 segment - Anterior  cross over several segments

Spinoreticular (Paleospinothalamic) Functions –awareness –emotion of sensation  pain Neuron - 1 st order  DRG (fibers enter spinal cord and synapses ) - 2 nd order  dorsal horn V, VI, VII Tract - Ascends anterior lateral system (ALS) - Goes to thalamus - fibers run bilaterally and close to midline  no cross over - Ends in the reticular formation - No somatotopography  cnnot map body on it

Cerebellar Tracts Posterior spinocerebellar - Function –unconscious proprioception : LOWER body(leg) –Conscious proprioception  Homologous to gracile portion of dorsal column medial lemniscus pathway 2 nd order - Dorsal N. Clarke (VII) - Dorsal thoracic nucleus - Found from T1-L2 Tract - fibers come from lower body - ascend through gracile fasciculus - make way to dorsal nucleus of Clarke - Fiber cross - Enter cerebellum through inferior cerebellar peduncle

Cerebellar Tracts Cuneocerebellar tract Function –unconscious proprioception  UPPER body (arm) –Conscious proprioception  Homologus to cuneate fasciculus of dorsal column medial lemniscus pathway –second order - accessory cuneate nucleus Tract - Fibers enter spinal cord - Ascend up cuneate fasciculus - Ends at medulla in accessory cuneate nucleus : leateral to cuneate nucleus - Enter cerebellum thinferior cerebellar peduncle

Cerebellar Tracts Anterior spinocerebellar - Function Monitors reflex arc Maintains reflexes run smoothly Responsible for LOWER body Tract - cross at anterior white commissure (rebel tract) - crosses again in cerebellum ( end up ipsilateral ) Rostral Spinocerebellar - Monitor reflex arc - Responsible for UPPER body - fibers enter superior and inferior cerebellar peduncle - uncrossed

Others Spinotectal - refer to colliculi of midbrain –turns head toward stimulus Spinoolivary - fibers end up going to cerebellum - through middle cerebellar peduncle –cutaneous and proprioceptive