T2 L2: Ascending and descending tracts of the spinal cord Flashcards
What is found at the dorsal horn of grey matter?
Neurones receiving sensory input
What is found at the lateral horn of grey matter?
Preganglionic sympathetic neurones of the thorax only
What if found at the ventral horn of grey matter?
Motor neuronal cell bodies
What type of neurone is found between/within levels of the spinal chord
Interneurons
What is meant by tracts?
Axons travelling up or down in the spinal chord
What type of sensory information do ascending tracts carry?
Afferent (sensory) impulses to the centres within the brain
What type of sensory information do descending tracts carry?
Efferent (motor) impulses from centres within the brain
What type of tracts does the dorsal column contain?
Ascending tracts
What type of tracts does the lateral column contain?
Descending and ascending tracts
What type of tracts does the ventral column contain?
Descending tracts
What is proprioceptive information?
Originating from within the body Eg, muscles, joints, tendons
What is Exteroceptive information?
Originating from outside the body Eg, pain, temperature, tough
What 2 types of information do ascending tracts carry?
Proprioceptive and exteroceptive sensory
Which neuron of an ascending circuit enters the spinal cord via the dorsal root?
The first order (primary sensory) neuron
Which neuron out of an ascending circuit ascends the spinal cord or brainstem?
The second order neuron
Which neuron out of an ascending circuit projects into the cortex?
The third order neuron
What do cutaneous mechanoreceptors detect?
Fine tough/ vibration
What do muscle spindles detect?
Stretch. They tell the brain how much and how fast a muscle is lengthened or shortened. Proprioception
What do Golgi tendon organs detect?
Tension on the muscle. Proprioception
Where is the Fasciculus gracilis?
It’s medial
What is the DCML pathway?
The Dorsal column-medial lemniscus pathway. It’s a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.
Where is the Fasciculus cuneatus?
It’s lateral
What do first-order neurones do when they reach the spinal cord in the DCML pathway?
They ascend the dorsal column
What is the difference between fasciculus Gracilis and Cuneatus?
Cuneatus is associated with higher extremities and Gracilis is to do with the lower. There is no Fasciculus below the mid-thoracic spinal cord
Where do first-order neurones synapse in the DCML pathway?
On second-order neurones in the medulla
Where does Fasciculus Gracilis terminate?
In the nucleus Gracilis (Gracile) found on the Gracile tubercle in the medulla
Where does Fasciculus Cuneatus terminate?
In the nucleus Cunteatus (Cuneate) found on the Cuneate tubercle in the medulla
Where do second-order neurones cross in the DCML pathway?
In the thalamus and then ascend to the thalamus
What is the medial lemniscus?
The area where the second-order neurones cross before they reach the cortex
Where do third-order neurones project?
From the thalamus to the somatosensory cortex
What is multiple sclerosis?
An autoimmune disease that causes destruction of the brain and nerves
What is sensory ataxia?
Loss of coordination and balance due to lack of proprioceptive input
What is Romberg’s sign?
Severe swaying on standing with eyes closed and feet together
What does a lesion on one side of the dorsal column of the DCML pathway of the spinal cord cause?
Loss of tactile discrimination and proprioception on the same side
What is the Spinothalamic tract for?
Pain from nociceptors, temperature, and course non-discriminative touch
What happens to first-order neurones when they reach the spinal cord in the Spinothalamic tract?
They enter the dorsal horn and form the tract of Lissauer
Where do first-order neurones in the Spinothalamic tract synapse?
In the dorsal horn with second-order neurones
Where do second-order neurones of the Spinothalamic tract cross?
In the dorsal horn at each level
Where do second-order neurones ascend in the Spinothalamic tract?
In the anterolateral column towards the thalamus
Information from which limbs is carried in the lateral anterolateral column in the Spinothalamic tract?
Fibres from the lower limbs
Information from which limbs is carried in the medial anterolateral column in the Spinothalamic tract?
Fibres from the medial tract (lower limbs)
What are the side effects of damage to the anterolateral column by a lesion on one side of the spinal cord?
Loss of pain, temperature sensation and crude touch on the opposite side
What would the symptoms of outer tract injury in the anterolateral column cause?
Loss of lower limb pain first because the fibres sit laterally
Which part of the anterolateral column would a herniated disk affect?
The outer tract
What would the symptoms of inner tract injury in the anterolateral column cause?
Loss of upper limb pain because the fibres sit medially
Which part of the anterolateral column would be injured with a grey matter tumour?
The medial part
What are the spinocerebellar tracts for?
Unconscious muscle proprioception from muscle spindles and golgi tendon organs. Its all for smooth motor coordination
Describe the structure of spinocerebellar tracts
Has 2 neurones in the pathway. Comprises of 4 tracts that don’t cross at any point
In which spinocerebellar tracts is information from the trunk and lower limbs carried?
In the ventral and dorsal spinocerebellar tracts
In which spinocerebellar tracts is information from the upper limbs carried?
Rostral spinocerebellar and cuneocerebellar tracts
Where do first-order neurones from the dorsal spinocerebellar tracts synapse?
In the dorsal horn
Which column do second-order spinocerebellar neurones ascend on?
The lateral column to the cerebellum
Where is the lesion when someone has uncoordinated lower limb muscular activity on the same side?
A lesion on the same side found in the dorsal spinocerebellar tracts
What is the corticospinal tract for?
For voluntary motor movement
Describe the structure of a corticospinal tract pathway
A pyramidal tract formed of 2 neurones
Where do the upper motor neurones in the corticospinal tract synapse?
In the ventral horn
Where do the lower motor neurones from the corticospinal tracts synapse?
In the skeletal muscle
Why are pyramidal tracts called that?
Because they pass through the pyramids of the medulla
What is the pathway of pyramidal tracts from the primary motor cortex to the pyramids of the medull?
Primary motor cortex - internal capsule - cerebral peduncle - pons - pyramids of medulla
What is a motor homunculus?
A topographic representation of the body parts and its correspondents along the precentral gyrus of the frontal lobe
Describe what happens at the pyramids of decussation
Within the pyramids of the medulla, the nerve fibres decussate (cross). 80% cross the midline and become the lateral corticospinal tract. 20% remain on the same side and become the anterior corticospinal tract
What is upper motor neurone disease?
The degradation of upper motor neurones that causes spastic paralysis (increased muscle tone), overactive tendon reflexes but significant muscle atrophy
Why does upper motor neurone disease not cause muscle atrophy?
Because there are still lower motor neurones that provide what is needed for the muscles to survive
What is lower motor neurone disease?
The degradation of lower motor neurones that causes flaccid paralysis (no muscle tone), no tendon reflexes and muscle atrophy
What is spinal muscular atrophy?
A genetic condition that makes the muscles weaker and causes problems with movement.
What is Guillain-Barre syndomre?
An autoimmune disorder that causes damage to the nerves, causing muscle weakness and sometimes paralysis. It involves degradation of myelin
What is Amyotrophic lateral sclerosis?
A genetic disease that selectively affects lower and upper motor neurones and destroys them but keeps the mind intact. Causes a short life-span due to respiratory failure
What are Bulbar signs?
Speech and swallowing difficulties associated with cranial nerves
Where do Rubrospinal extrapyramidal tracts originate from?
From the red nucleus in the midbrain
Where do Reticulospinal extrapyramidal tracts originate from?
From the reticular formation in the pons
Where do Vestibulospinal extrapyramidal tracts originate from?
From the vestibular nuclei in the medulla
What are extrapyramidal tracts important for?
For maintaining posture and regulating involuntary movements
What are the symptoms of extrapyramidal tract lesions?
Movement disorders
What is Dyskinesia?
Involuntary muscle movements
What is Dystonia?
Involuntary muscle contractions
