Tracts Pathways PHYSIOLOGY

7/17/2019 Tracts Pathways PHYSIOLOGY

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Tracts-Pathways



Tracts of the Nervous System

•CNS communicates with body structures via pat

• sensory or motor information

• processing and integration occur continuously

• Pathways travel through the white matter of the

cord.

• Connect various CNS regions with peripheral ner



Sensory and Motor Tracts

•Communication to and from the brain involves tr

• Ascending tracts are sensory

• eliver information to the brain

• escending tracts are motor• eliver information to the periphery



!ross anatomy of the Spinal Co



Sensory and Motor Tracts

•

Naming the tracts

• "f the tract name begins with #spino$ %as inspinocerebellar&' the tract is a sensory tractdelivering information from the spinal cord to

cerebellum %in this case&

• "f the tract name ends with #spinal$ %as incorticospinal&' the tract is a motor tract that d

information from the motor corte( %in this casthe s inal cord







•

Pathway crosses over from one side of the body to the oat some point in its travels.

• The left side of the brain processes information from theside of the body' and vice versa.

• All pathways are composed of paired tracts.

• A pathway on the left side of the CNS has a matching tra

right side of the CNS.

• )oth left and right tracts are needed to innervate both tand right sides of the body.

• Pathways are composed of a series of two or three neurowor* together.



Sensory Tracts

• There are three ma+or sensotracts• The posterior column tract

• The spinothalamic tract• The spinocerebellar tract





Sensory Tracts

•

The three ma+or sensory tracts involve chains ofneurons

• ,irst-order neuron• elivers sensations to the CNS

• The cell body is in the dorsal or cranial root ganglion

• Second-order neuron• An interneuron with the cell body in the spinal cord o

• Third-order neuron• Transmits information from the thalamus to the cereb

corte(



Sensory Tracts

•Neurons in the sensory tracts aarranged according to threeanatomical principles•

Sensory modality•Somatotropic

•Medial-lateral rule



Sensory Tracts

•

Sensory modality• ,ine touch sensations are carried in one sensory tract

• Somatotopic• Ascending tracts are arranged according to the site o

• Medial-lateral rule• Sensory neurons that enter a low level of the spinal c

more medial within the spinal cord

• Sensory neurons that enter at a higher level of the spare more lateral within the spinal cord

















Spinocerebellar tract

• Transmits proprioceptionsensations to the cerebellum







Motor tracts

•

These are descending tracts• There are two ma+or descending tract

•CorticospinalCorticobulbar tractConscious control of s*eletal muscle

•Subconscious tract Subconsciousregulation of balance' muscle tone' hand' and upper limb position

The Corticospinal /pyramidal Pathway



The Corticospinal /pyramidal Pathway

Upper motor neurons begin at the primary motor cortex

Synapses with lower motor neurons occur in two tracts

Corticobulbar (bulbar, brain stem) tracts

move the eye, aw, !ace, and some muscles o! nec" and

pharynx

Synapses in motor nuclei o! cranial nerves

Corticospinal tracts

Provide conscious control over s"eletal muscles that mov

various body areas

Synapse in the anterior gray horn in the spinal cord

#ibers o! lateral corticospinal tracts ($% &) cross over at

level o! the medulla (pyramids)









The Subconscious Motor Tracts

•

Consists of four tracts involved in monitoring thsubconscious motor control

•/estibulospinal tracts-muscle activity associatwith balance %inner ear' cerebellum&

• Tectospinal tracts0 re1e( posturalmovements

response to visual stimuli•2eticulospinal tracts-in1uence involuntarymovements and re1e( activity

•2ubrospinal tracts-"nhibitory in1uence in mus





Stretch 2e1e(

•

"t is re1e( contraction of muscle resulfrom stimulation of the muscle spindle% which is the receptor that is located muscle 3 detects changes in muscle &by stretch





Stretch re1e( -Components

•

2eceptor%muscle spindle&•A4erent %annulospiral51ower spray&

•Centre%A6C&

•74erent % motor nerve%alpha 8bers9:

e(trafusal muscle 8bers 5gamma e4<:; to muscle spindle intrafusal 8be

•74ector%muscle&





Muscle Spindles

•

Are composed of a few intrafusal muscle 8that lac* actin and myosin in their centralregions' are noncontractile' and serve asreceptive surfaces.

• Muscle spindles are wrapped with two type

a4erent endings primary sensory endingstype "a 8bers and secondary sensory enditype "" 8bers.

• These regions are innervated by gamma e8bers.





Th ! l i t d 1 %i



The !olgi tendon re1e( %inversestretch re1e(&





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Tracts Pathways PHYSIOLOGY