Sensory and Motor Systems 2 Flashcards
Where does the gracile fasiculus receive axons from?
The lumbar and saccral vertebrae- lower body and it is more medial in the dorsal column of the spinal cord
Where does the cuneate fasiculus receive axons from?
More lateral in the dorsal horn-Cervical and thoracic axons for upper body
Which pathways follow conscious sensation?
Dorsal column pathway and the spinothalamic pathway
Which pathways follow unconscious sensation?
Spinocerebellar, spinotectal, spinoreticular and spino-olivary tract
How does sensation travel from the peripheries to the somatosensory cortex?
What is the signficance of level T6?
Above T6, cunneate fasiculus in the dorsal column transmits the first order neurons. Below T6, gracile fasiculus in the dorsal column transmits the first order neurons.
What is the dorsal column pathway?
Sensation of fine touch, vibration, pressure and propioception
What is the dorsal column pathway?
Sensation of fine touch, vibration, pressure and propioception
What is an overview of the dorsal column pathway?
Sensory receptors -> cunneate/gracile fasiculus of spinal cord and ascends ipsilaterally-> cunneate/gracile nucleus of the medulla -> decussates and ascends the medial leminsicus of the medulla as second order neuron and ascends contralaterally -> synapses at the thalamus -> somatosensory cortex
What is the first oder neuron of the dorsal column pathway?
In the gracile/cunneate fasiculus of spinal cord
What is the 2nd order neuron of the dorsal column pathway?
Gracile/cunneate nucleus of the medulla and ascends the medial leminiscus after decussation contralaterally
What is the 3rd oder neuron of the dorsal column pathway?
Thalamus
What is the spinothalamic tract?
Sensation of crude touch, pain and temperature
What is the role of the anterior spinothalamic tract?
Crude touch
What is the role of the lateral spinothalamic tract?
Pain and temperature
What is Lissauer’s tract?
Bundle of fibres which transmit first order neuron impulses of the spinothalamic tract to ascend 1-2 segments before decussating at the ventral white commisure contralaterally
Where does decussation occur in the dorsal column?
In the medial leminiscus of the medulla
What is the internal arcuate fibres?
The crossing of the axons from the cuneate and gracile nucleus of the medulla which make up the medial leminiscus
Where does decussation occur in the spinothalamic tract?
In the ventral medial commisure of the spinal cord contralaterally to the ventral horn
What are the consequences of brainstem lesions?
Loss of sensation in both pathways on the contralateral side below the lesion
What are the consequences of spinal cord lesions?
Loss of sensation in the dorsal column pathway ipsilaterally below the lesion
Loss of sensation in the spinothalamic pathway contralaterally
How does motor information pass from the CNS to the rest of the body?
Via the upper motor neurons and lower motor neurons which synapse in the ventral horn of the spinal cord
What are the upper motor neurons?
Originate in the cerebrum/ cerebellum/midbrain and create descending tracts to project to the lower motor neurons
What are the lower motor neurons?
Exit the CNS at either the brainstem or the spinal cord and project onto the muscles of the body
What are cranial nerves?
Lower motor neurons which exit at the nuclei of the brainstem
What are spinal nerves?
Lower motor neurons which exit at the CNS at the ventral horn of the spinal cord
What is the function of the dorsal lateral corticospinal tract?
Supplies the distal muscles for fine movement
What is the function of the ventromedial corticospinal tract tract?
Supplies the trunk and proximal muscles for posture correction and gait
How are the dorsolateral and ventromedial tracts divided?
Dorsolateral decussates at the pyramids of the medulla oblaganta. Ventromedial continues ipsilaterally
What are the upper motor neurons of the dorsolateral pathway?
Lateral corticospinal tract and rubrospinal tract
What are the upper motor neurons of the ventromedial pathway?
Reticulospinal tract, tectospinal tract, anterior corticospinal tract and vestibulospinal tract
What is the lateral corticospinal pathway?
Skeletal muscle control
What is the role of the reticulospinal tract?
For posture correction and gait
What is the pathway of the reticulospnal tract?
First order neurons arise from the reticular formation of the pons and medulla and does not deucssate and moves ipsilaterally polysegmental (across the legnth of the spinal cord) to the ventral medial horn where it synapses to supply the proximal muscles and the trunk
What is the role of the tectospinal tract?
To turn our head towards the stimulus and coordinate head and neck movement
What is the pathway of the tectospnal tract?
First order neurons in the colliculi of the posterior midbrain and decussate to move contralaterally in the midbrain and syanpses with the cervical spinal cord nuclei to supply the shoulder girdle and neck muscles
What is the role of the vestibulospinal tract?
For balance and control of the shoulder girdle and neck muscles
What is the pathway of the vestibulospinal tract?
First order neurons in the vestibular nuclei of the pons or medulla. They descend ipsilaterally. The medial vestibulospinal tract ends at the cervical spinal cord to supply the shoulder girdle and neck. The lateral vestibulospinal tract is polysegmental and supplies the whole trunk and proximal muscles
What are the consequences of a unilateral lesion?
No obvious defect
What are the consequences of a bilateral lesion?
Loss of trunk mobility, navigational control and balance
What is the role of the rubrospinal tract?
For muscle tone and control of movement by modulating the cerebellum
What is the pathway of the rubrospinal tract?
First order neuron in the red nuclei of the midbrain which decussate and continue contralaterally to the ventral horn of the spinal cord to supply the skeletal muscle of the upper limbs and the trunk
What is the consequeneces of a lesion in the rubrospinal tract?
Intention tremors due to issue with modulating cerebellum and impaired distal arm and hand movements
What is the internal capsule?
Allows communication between the cortex and the rest of the body and has a somatotropic map
What is the corona radiata?
White matter extensiosn from the motor cortex which continues as the internal capsule
What is the pathway of the corticospinal tract?
First order neuron from the premotor cortex or the motor cortex or the sensorty cortex travels down the cerebral peduncles to the pyramids where majority decussate as the lateral corticospinal tract to continue contralaterally and leave the spinal cord in the dorsal horn to synpase with the lower motor neurons. Those that don’t decussate in the pyramids continue ipsilaterally as the anterior corticospinal tract to synapse with the lower motor neurons in the ventral horns
What is the function of the corticospinal tract?
To supply the skeletal muscle of the limbs and the trunk, fine movement and sensory modulation
What is the function of the lateral corticospinal tract?
Skeletal muscle control of the limbs
What is the function of the anterior corticospinal tract?
Skeletal muscle control of the axial trunk
What is the +Ve Babinski sign?
Testing for myelination of the axons in the corticospinal tract where you run a pen along the side of the foot. +ve means there is no dorsiflexion so issue with corticospinal tract. This is abnormal but normal in infants under 2 years old
What is spastic paresis?
High muscle tone where there is stiffness in the limbs
What is the consequences of a lesion in the corticospinal tract?
Above the decassation in the pyramids: contralateral spastic paresis and + ve babinski
Below the decassation in the pyramids: ipsilateral spastic paresis and + ve babinski
