Spinal Tract Anatomy and Functions Flashcards
Describe the Lateral Corticospinal tract. Is it fully myelinated?
It is the descending motor pathway controlling the voluntary movements of the extremeties, and this pathway is not completely myelinated until the second year of life, and thus babies will have a positive babinski sign.
Why do babies have a positive Babinsky sign?
Their Lateral CST is not fully myelinated until the second year of life.
What are first order neurons in the somatosensory pathway?
They are primary afferent neurons, thus they have their cell bodies in the dorsal root ganglia (or cranial ganglia) while their axons synapse on a somatosensory receptor. Once a signal is triggered it travels up the primary afferant neuron up to the CNS.
Where are second order neurons of the somatosensory pathway located?
In spinal cord in the anteriolateral system, or the bran stem in the dorsal column system.
Once the first order neurons pass their signals up to the second order neurons, what does it do and where does it go?
It crosses over at the midline whether it be in the spine or brainstem and then travel up to the thalamus. Thus each fiber is sending signals from the contralateral side.
What is the “somatosensory homunculus?”
This is found in the S1 somatosensory cortex, and it contains the “map” of the human body.
Which parts of the body have the largest representation by the somatosensory homunculus?
Face, hands and fingers.
Describe the general function of the Lateral Corticospinal tract?
Descending voluntary movement of contralateral limbs.
Describe the first order neurons of the LCST?
They are upper motor neurons, their cell bodies are in the primary motor cortex and they descend ipsilaterally through the internal capsule until the decussating (crossing over) at the caudal medulla (pyrimidal decusation) and then descend contralaterally.
Where is the decusation of the upper motor neurons? (LCST)
At the caudal medulla (pyrimidal decussation).
Where do the upper motor neurons of LCST synapse first?
Cell bodies of the anterior horn of the spinal cord.
Where are the second order neurons of the LCST originating from? Where do they synapse?
They are lower motor neurons and thus they leave from the spinal cord. Synapses at the neuromuscular junction.
What is the function of the dorsal column (medial lemniscal pathway)?
To sense ascending pressure, vibration, touch and proprioceptive sensation.
What are the first order neurons of the DC-MLP doing? Where does it synapse?
They are sensory nerve endings where the axons are in the mechanoreceptors and the cell bodies are in the dorsal root ganglion. Impulse then enters spinal cord, ascends ipsilaterally in the dorsal column. Ipsilateral nucleus cuneatus or gracilis (in the medulla).
What do second order neurons do of the DC-MLP do? Where does it synapse?
They have a decussation in the medulla and ascends contralaterally in the medial lemniscus. It synapses in the Ventral Posterior Nucleus, lateral, of the thalamus.
