Sensory and Motor spinal tracts Flashcards
State the 4 spinal curvature sections from top to bottom.
Cervical, thoracic, lumbar, sacrum
Describe the pyramidal and extrapyramidal descending motor tracts.
Pyramidal motor pathways are direct, conscious, efferent from CNS, and project axons through the pyramids of the medulla. Extrapyramidal motor pathways are indirect, unconscious/subconscious, efferent from CNS and project axons to the brain stem nuclei.
Outline the three peripheral nerve cell types.
Sensory nerves - sends messages from muscles to the CNS through the spinal cord. They detect things like temperature and texture of external stimuli and if body parts are in motion.
Motor nerves - Send impulses from the brain/CNS through the spinal cord, to skeletal muscles. It controls/determines movements of the limbs.
Autonomic nerves - controls involuntary or semi-voluntary functions, such as heart rate, blood pressure, digestion and sweating.
Describe a typical sensory pathway in normal functional activity.
There are 3 main steps to a sensory pathway - where conscious pathways reach the cerebral cortex and unconscious do not.
- The 1st order neuron is where the cell body is in the dorsal root ganglion. Sensory information comes in along an axon, passes through the grey matter and creates a chemical synapse with the 2nd neuron in the dorsal horn.
- The second order neuron will have the cell body in either the dorsal horn or the brain stem. Within the spinal cord, the axons will flow through the spinal cord and ascend up to the thalamus .
- The 3rd order neuron has the cell body in the thalamus. The thalamus will project an axon upwards into the somatosensory cortex in the post-central gyrus in the parietal lobe. This is where the sensory homunculus lies and provides an understanding of where on the body the initial sensory nerve ending signals came from.
Summarise the spinothalamic tract.
Information carried = pain, temperature, touch, pressure
2nd order neuron decussation = spinal cord (over midline of body)
3rd order neuron = Thalamus
Projection to somatosensory cortex = yes
Effect of injury = loss of function on opposite side of the body
Summarise the dorsal column pathway.
Information carried = fine touch, vibration, conscious proprioception
2nd order neuron decussation = medulla (not over midline of body)
(passes through dorsal white column)
3rd order neuron = Thalamus
Projection to somatosensory cortex = yes
Effect of injury = loss of function to same side of body
Summarise the spinocerebellar pathway.
Information carried = unconscious proprioception
2nd order neuron decussation = N/A
2nd order neuron is at the medulla and goes straight to the cerebellum
3rd order neuron = N/A
Projection to somatosensory cortex = no
Effect of injury = loss of overall function e.g., ataxia (disruption to movement)
Describe the role of the spinothalamic pathway in the transduction of pain signals to the brain.
It enables one to move away from noxious stimuli by carrying pain and temperature information from the skin, through the dorsal root ganglion and the dorsal horn in the spinal cord, to the thalamus where it is processed and transmitted to the somatosensory cortex, where the sensory homunculus determines where the pain is coming from on the body.
Describe the concept of decussation.
The action of intersecting or crossing (as of nerve fibres) especially in the form of an X, the crossing over of neurons.
Name the two motor neurons involved in each motor pathway; and describe their general location, paths and the site of synapse.
It is composed of two neurons, the upper motor neuron and the lower motor neuron. The upper motor neuron has its cell body in the primary motor cortex of the frontal lobe and synapses at the spinal cord on the lower motor neuron, which is in the ventral horn of the spinal cord and projects to the skeletal muscle where the axon exists through the ventral nerve root.
Describe the corticospinal and the corticobulbar spinal tracts.
The corticospinal tract starts at the upper motor neuron which is at the cortical cell body in the primary motor cortex (motor homunculus. Information is passed through interneurons down through the spinal cord and to the lower motor neuron which is at the ventral horn/root. 90% of fibres decussate after the medulla pyramids and control the limbs, and 10% decussate at the spinal cord and control the trunk (back, chest, stomach).
The corticobulbar tract starts at the upper motor neuron in the facial aspects of the motor homunculus at the primary motor cortex. It then passes signals down through the pons to the lower motor neuron at the cranial nerve in the brain stem, projecting and controlling facial nerves.
Which division of the corticospinal tract controls muscle of the upper and lower limbs.
The lateral tract is responsible for controlling upper and lower limbs.
Briefly describe the rubrospinal tract.
It descends efferent motor neurons from the red nucleus in the midbrain (decussates) through to the cervical spine. It mainly controls the upper limbs by facilitating flexor muscles and inhibiting extensor muscles, and this helps with fine motor coordination.
Briefly describe the tectospinal tract.
It descends efferent motor neurons from the midbrain (decussates) down to the cervical spine. It controls neck and eye muscles, helping with head-eye coordination and interacting with both visual and auditory feedback.
Briefly describe the vestibulospinal tract.
It descends efferent motor neurons from the pons in the brain (vestibular nuclei), through the cervical spine down to the lumbar spine. It controls balance within movements by focussing on extensor muscles in lower limbs (does contribute to upper limbs too).
