311 Session 4 Ascending and Descending Pathways

What is the main function of DCML

Ascending tract that provides informaiton on touch, vibtraion, pressure, proprioception, and two point discrimination

Mechanoreceptors / proprioceptiors →

dorsal root ganglion (first order neuron) →

dorsal root → spinal cord →

fasciculus gracilis / cunueates →

medulla (either nucleus gracislis / cuneatus [2nd order neuron]) →

DECCUSATE forming the Medial Lemniscus pathway →

VPL thalamus (third order neuron)

First order neuron in the DCML might be in the DRG but where does the fist synapse occure

Medulla oblangata (nucleus gracilis / cuneatus

What are the two divisions of the dorsal column

Fasciculus Gracilis (sensations from lower part of body [T7 and below])

Fasciculus Cuneatus (sensations form upper parts of the body)

What are the 1st, 2nd, and 3rd order neurons for the DCML

1st = DRG

2nd = medulla (nucleus gracilis / cuneatus)

3rd = VPL Thalamus

Where do the descending somatic pathways originate

Cerebral cortex

Brainstem

Where is the upper motor neurons vs the lower motor nueron for descending somatic pathways

Upper: motor cortex

Lower: ventral horn of spinal cord (efferent region)

What spinal tract is responsible for volunatry movements

Corticospinal tract

Trace the Corticospinal tract

Upper motor neuron: primary motor cortex →

Corona radiata →

internal capsule →

cerebral peduncle of midbrain →

medulla and decussates → forms the lateral corticospinal fibre →

• if it doesnt cross = anterior corticospinal tract

descend contralaterally →

synapse with contralateral ventral horn (lower motor neuron) →

ventral root →

distal movements

Where does axons that control motor innervation of the lower vs upper limbs terminate

Upper limbs: terminate in cervical region (more medially)

Lower limb: Lumbar region (more lateral)

Majority of the fibres deccusate in the corticospinal tract, but where do the undecussated fibers go

Travel downwards IPSILATERALLY and reach the anteriror column only decussating at the desired spinal cord level

Reticulospinal tract; origin

Reticular formation in pons and medulla

Does the pontine reticulospinal tract deccusate

No

Where does tectospinal or “colliculospinal” tract originate

Originate in superior colliculi of midbrain →

descend and enter the spinal cord →

synapse on interneurons in ventral horn of spinal cord

What is the function of the tectospinal tract

Turns / orients head and neck towards auditory stimuli

Where does the rubrospinal tract originate

Red nucleus of the midbrain → decussates → descends to spinal cords lateral white matter →

synapse w interneurons in ventral horn → terminates in cervical regions

Rubrospinal tract function

Regulates flexor and extensor muscle activity in upper limb

Vestibulospinal tract; origin and trace

Originates in vestibular nuclei → DOESNT DECCUSATE

→ synapses on interneurons in ventral horn of spinal cord

Vestibulospinal tract function

maintains balance and posture by regulating postural/extensor muscles

What are the five descending tracts

Corticospinal

Reticulospinal

Rubrospinal

Vestibulospinal

Tectospinal

How do crossed and uncrossed connections explain bilateral influence on trunk muscles

The anterior corticospinal tract can influence motor neurons on both sides of the spinal cord!!!!! So it has bilateral control over axial / trunk muscles

Compare and Contrast lateral vs anterior corticospinal tract IN TERMS of;

crossing

spinal location

main control

side

Trace the paterllar/knee-jerk stretch reflex

Quad stretches

Muscle spindle detects stretch

Sensory neuron enters spinal cord

activates lower motor neuron

Quads contract

leg extends

What is the basic somatic motor pathway

CNS → lower motor neuron → skeletal muslce

Where is the cell body of a somatic lower motor neuron?

In the CNS; its axon travels directly to skeletal muscle

Autonomic motor pathway;

trace

targets

CNS → preganglionic neuron → autonomic ganglion → postganglionic neuron → target

• Smooth muscle, cardiac, glands

Where are the cell bodies and synapse in the autonomic motor pathway

Preganglionic cell body = CNS → synapse in peripheral autonomic ganglion → postganglionic neuron → target

What is the general organization of the sympathetic nervous system

Thoracolumbar origin → ganglia generally closer to the CNS → short pre + long post

What is the general organization of parasympathetic nervous system

Cranisacral origin → ganglia near/in target organs → long post + short pre

What is the broad role of the enteric nervous system

Neural networks in the gut wall organize local GI activity and receive autonomic influence

What CNS regions broadly contorl autonomic function?

Mainy the hypothalamus and brainstem