Nervous System: Tracts

posterior columns

aka dorsal columns or medial lemniscal columns; tract that carries highly localized information from skin and musculoskeletal system about proprioceptive (limb position), fine-touch, pressure, and vibration sensations to primary sensory cortex on opposite side of body (crosses at medulla); also, the type of stimulus, exact site of stimulation, and when stimulus starts/stops -- aka "what" "where" "when" CN V, VII, IX, X

fasciculus cuneatus

aka tract of Burdarch; ascending tract of posterior column that carries information from above or at T6 (upper limbs) to spinal cord nucleus is in medulla oblongata

fasciculus gracilis

aka tract of Goll; ascending tract of posterior column that carries information from below T6 (middle thoracic, lower limbs) to spinal cord nucleus is in medulla oblongata

ALS

amyotrophic lateral sclerosis; progressive disease that that affects motor neurons that innervate skeletal muscle (sensory neurons left intact) --> loss of motor control

posterior spinocerebellar tract

carries axons that do not cross over to opposite side of spinal cord which ascend to cerebellar cortex through inferior cerebellar penducle to transfer proprioceptive info

anterior spinocerebellar tract

carries axons that have crossed over to other side of spinal cord to ascend to cerebellar cortex through superior cerebellar penducle axon fibers then decussate again within cerebellum to end in ipsilateral cerebellum to transfer proprioceptive info

anterior corticospinal tract

conscious motor tract that contains axons that do not cross over in brain stem but at spinal segment it (upper motor neuron) targets in anterior white commissure on lower motor neuron in anterior gray horns for cervical and upper thoracic regions

lateral corticospinal tract

conscious motor tract that contains most of motor fibers that crossover within brain stem to synapse on lower motor neurons in anterior gray horns of all levels of spinal cord maintain motor control and muscle tone (if impaired, rubrospinal tract takes over)

pons (and medulla oblongata)

controls balance reflexes and complex respiratory reflexes

inferior medulla oblongata

controls basic respiratory reflexes

hypothalamus

controls motor patterns related to eating, drinking, and sexual activity; modifies respiratory reflexes

thalamus (and mesencephalon)

controls reflexes to visual and auditory stimuli

brain stem (spinal cord)

controls simple cranial and spinal reflexes

cerebellum

coordinates complex motor patterns

decussation

crossover of first-order or second-order neurons to opposite side of spinal cord or brain ex: sensory info from left side of body is delivered to right side of brain

upper motor neuron

delivers motor commands to motor nuclei in brain stem or spinal cord cell body lies in CNS processing center

corticobulbar tract

descending tract that has motor fibers that distribute to lower motor nuclei in brain of cranial nerves III, IV, V, VI, VII, IX, XI, XII to provide conscious control over facial muscles and neck and pharynx

motor homunculus

map of primary motor cortex and areas are proportional to number of motor units involved rather than size (provides degree of fine motor control available)

basal nuclei

modify voluntary and reflexive motor patterns at subconscious level

reticular formation

network of neurons that extends throughout brain stem with interconnections with cerebrum, cerebellum, and brain stem nuclei; and receives input from almost every ascending and descending tract

cerebral cortex

plans and initiates motor activity

vestibular nuclei

receives information through vestibulocochlear nerve (CN VIII) from receptors in inner ear that monitor position and movement of head and sends motor commands to alter muscle tone, extension, position of neck, eyes, head, limbs maintain posture and balance

colliculi

receives visual (superior) and auditory (inferior) sensations and coordinates/directs reflexive responses to the stimuli superior also receives auditory info from inferior and collateral somatosensory info

lower motor neuron

relays motor commands from CNS motor nuclei to skeletal muscle fibers; only capable of exciting skeletal muscle fibers located in motor nucleus of brain stem or spinal cord

sensation

sensory information that is passed from receptor to CNS through action potentials in an afferent fiber

third order neuron

sensory neuron in thalamus that second order neuron synapses on axon carries sensory info from thalamus to appropriate sensory area of cerebral cortex

first order neuron

sensory neuron that delivers sensations to CNS cell body in dorsal root ganglion or cranial nerve ganglion

second order neuron

sensory neuron that first order neuron synapses on cell body in spinal cord or brain stem

tectospinal tract

subconscious motor tract from superior colliculi that controls reflexive changes in position in response to auditory or visual stimuli; gross movement of trunk and proximal limb muscles through superior and inferior colliculi in tectum (roof) of mesencephalon

vestibulospinal tract

subconscious motor tract that carries motor commands that reflexively control posture and balance FROM vestibular nuclei gross movement of trunk and proximal limb muscles through upper motor neurons in vestibular nuclei in brain

rubrospinal tract

subconscious motor tract that extends only to cervical spinal cord to adjust upper limb position and muscle tone during voluntary movements, typically facilitating flexor muscles and inhibiting extensor muscles helps control distal limb muscles for precise movement

reticulospinal tract

subconscious motor tract that originates in reticular formation (diffuse network of neurons in brain stem) and functions vary depending on area of reticular formation that is stimulated; gross movement of trunk and proximal limb muscles through reticular formation in brain

pyramids

thick bands made up of corticospinal tracts along ventral surface of medulla oblongata

medial lemniscus

tract for second-order neurons to cross over from medulla oblongata to contralateral side to thalamus

anterior spinothalamic tract

tract that carries crude touch and pressure sensations to primary sensory cortex on opposite side of body (crosses in spinal cord at level of entry)

spinocerebellar tract

tract that carries proprioceptive information (position of muscles, tendons, joints) to cerebellum (responsible for fine coordination of body movements) to be processed subconsciously as it did not enter thalamus

lateral spinothalamic tract

tract that carries sensations of pain and temperature to primary sensory cortex on opposite side of body (crosses in spinal cord at level of entry)

sensory homunculus

"little human" sensory map of primary sensory cortex with areas proportional to number of sensory receptors it contains, not proportional to individual

corticospinal tract

"pyramidal tract" direct motor tract that provides conscious, voluntary control over skeletal muscles, beginning at pyramidal cells of primary motor cortex and descending to synapse on lower motor neurons may also be indirect (innervates other motor centers of subconscious motor pathway)