Spinal cord, motor & Sensory Pathways I Flashcards
What does ipsilateral mean?
Same side of the body
What does contralateral mean?
Opposite side of the body
What is a ramus?
A branch
What is a tract?
Tract = column = bundle = funiculus = fasciculus = lemniscus
What is a decussion?
Decussion = chiasm = raphe
What are structure names based on?
Their location
What structure of the brain does the spinal cord continue from?
The medulla
Where does the spinal cord end? What spinal level is this?
At the conus medullaris (L1/L2)
What structure arises after the terminal part of the spinal cord?
The cauda equina (horse’s tail)
What is the cauda equina made up of?
It is made up of lumbar and sacral spinal nerves
How many spinal segments are there?
31 spinal segments; 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 occygeal
How many vertebral segments are there?
33; 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal
What does the cervical segment of the spinal cord supply?
supplies upper extremities
Which spinal cord segments does the cervical enlargement consist of?
C5 - T1
What spinal cord segments does the lumbar enlargement consist of?
L2 - S3
What does the lumbar enlargement supply?
Supplies lower extremities
What is a spinal cord segment?
The portion of the spinal cord supplying a single spinal nerve
Where do white and grey matter sit in the spinal cord?
grey matter inside of the cord surounded by white matter
What happens in dorsal root ganglia?
Cell bodies are collected.
What do dorsal root ganglia collect?
Sensory input
Where do dorsal root ganglia enter the spinal cord?
Via the dorsolateral sulcus
Where do cell bodies of motor neurons sit?
In the ventral horn of the spinal cord.
Where do motor neurons exit?
Via ventrolateral sulcus
Is the ventrolateral sulcus well defined and a visible structure?
No
What happens to the dorsal and ventral roots after exiting the spinal cord?
They fuse to form a mixed sensory and motor spinal nerve which exits the intervertebral foramen
What part of the body does the dorsal ramus innervate?
Dorsal area of the body
What part of the body does the anterior ramus innervate?
Ventral and lateral areas
Where do spinal nerves exit the spinal cord?
Intervertebral foramen
Do spinal cord and vertebral column develop together?
No, the spinal cord reaches fills the entire spinal column during development and then goes to L3 at birth and then L1/L2 in adults.
This is because the vertebral column grows faster than the spinal cord.
Where do cervical nerve roots exit relative to vertebral column?
One spinous process higher than corresponding vertebrae
Where do thoracic segments exit relative to the vertebrae?
2 spinous processes higher than their corresponding vertebrae
Where do lumbar vertebrae exit relative to lumbar vertebrae?
3 - 4 spinous processes higher than corresponding vertebral spinous processes
What does the higher location of the nerve root exits relative to the vertebrae they exit from mean?
Cervical nerve roots are shortest followed by thoracic nerve roots and lumbar nerve roots.
What is the dura mater?
A protective thick collagenous membrane which gives the spinal cord mechanical strength
What are the layers of the spinal meninges?
Dura mater
Arachnoid
Pia mater
What is the spinal meninges?
A thick protective membrane for the spinal cord
What does the arachnoid layer do?
Composed of web like structure (the arachnoid trabeculae), it suspends the spinal cord within the dural sheath.
What is the pia mater?
The innermost layer of the spinal cord composed of fibrous tissue attached to spinal cord surface
What is the pia mater composed of?
Dentate ligaments (tooth like projections that pierce though arachnoid and anchor the spinal cord to the dura)
Filum teminale (Terminal thread which anchors spinal cord to dural sheath)
Where do the outer meningal layers terminate? What else happens at this level
At the level of S2 they fuse and terminate
What structure is the pia mater continuous with?
The cauda equina
What is the denticulate ligament?
Extensions of pia that anchor the spinal cord to the dura. Lateral denticulate ligaments separate posterior and anterior roots
What is the epidural space?
Space between the dura and the vertebral periosteum
Where are lumbar punctures typically performed?
At the level of L1/L2-S2.
What is the location of performing lumbar punctures called?
Lumbar cistern
Does the spine have an epidural space?
Yes
Does the brain have an epidural space?
Yes but it is a “theoretical space”
What is contained in the epidural space?
Contains spinal nerves, internal vertebral venous plexuses, fat, and connective tissue
What medical procedure commonly uses the epidural space?
The use of epidural anaesthetics
Where is the subarachnoid space? What does it contain?
Between the pia and arachnoid containing CSF
What medical procedure uses the subarachnoid space?
Spinal anaesthesia/spinal block
What is the difference between epidural and subarachnoid anaesthesia?
Epidural anaesthesia is done by keeping a catheter in the space with constant topping up of anaesthetic.
Spinal anaesthesia is done by needle.
Why aren’t spinal taps performed in other locations?
No spinal cord at that location making them relatively safe locations.
What arteries supply the spinal cord?
3 spinal arteries:
1 Anterior spinal artery
2 Posterior spinal arteries
Where does the anterior spinal artery arise from?
Vertebral arteries
Where is the anterior spinal artery located?
In the anterior median fissure
What arteries does the anterior spinal artery give rise to?
The sulcal arteries that supply anterior 2/3rds of the spinal cord (ventral column, ventral horn, lateral column)
What structures of the spinal cord do the sulcal arteries provide?
Ventral column
Ventral horn
Lateral column
Where do posterior spinal arteries arise from?
Posterior inferior cerebellar arteries (75% of people)
Vertebral arteries (25% of people)
Where do posterior spinal arteries sit?
In the posterolateral sulci
What structures do posterior spinal arteries provide?
Posterior 1/3rd of spinal cord including the dorsal column dorsal horn and central canal
What arteries reinforce the posterior and anterior spinal arteries?
Segmental medullary arteries (~C3), posterior intercostal arteries (~T7), and artery of Adamkiewicz (T9 - T12)
What veins drain the spinal cord?
Anterior and posterior spinal veins
Where do anterior and posterior spinal veins drain?
Into the anterior and posterior medullary and radicular veins
What changes in spinal cord content as we go down the spinal cord?
The grey and white matter
What is the anterior median fissure?
A rift in the middle of the spinal cord that divides the anterior surface of spinal cord into 2 lateral halves. The anterior spinal artery enters here
What is the posterior median sulcus?
Rift that divides the posterior surface of the spinal cord into 2 halves.
What is the posterolateral sulcus?
The point of entry of the posterior sensory rootlets and it is slightly lateral to the median sulcus.
This is the point of entry for the posterior vertebral arteries
What sulcus lies between the posterolateral sulcus and the posterior median sulcus?
The posterior intermediate sulcus
What is the anterolateral sulcus?
The point of exit for anterior motor rootlets
What is contained in the dorsal horns?
Interneurons receiving/transmitting somatic and visceral sensory information
What is contained in the substantia gelatinosa?
Unmyelinated sensory fibers carrying pain and temperature information.
Where is lissauer’s tract?
a tract that sits between the substantia gelatinosa and the surface of the spinal cord
What does the lissauer’s tract do?
Carries the same information as the substantia gelatinosa (sensory signals of pain and temperature)
What does the intermediate grey horn do?
Carries a little bit of sensory information and a little bit of motor functioning
What does the ventral horn do?
Contains lower (alpha) motor neurons that innervate skeletal muscle
Where is the lateral horn located?
In the lateral grey horn of the T1 - L3 neurons
Remember:
DS = Dorsal is Sensory (nintendo DS) VM = Ventral is Motor
What does frontal lobe control?
Personality, emotions and complex thinking
What does the parietal lobe?
In emotional and sensory processing
What does the occipital lobe control?
Visual information
What does the temporal lobe control?
Auditory information
Where is the central sulcus of the brain located?
Arises from the top of the brain and moves laterally separating the frontal lobe and everything else
What is located directly anterior to the central sulcus?
The precentral gyrus
What does the precentral gyrus control?
Motor function
What does the postcentral gyrus control?
Somatosensory signals
Where is the postcentral gyrus located?
Directly posterior to the central sulcus
How is the brain’s sensory and motor control mapped?
Topographically. The size of the brain section involved is directly correlated to the different inputs and outputs of that location.
What does the thalamus do?
It is the control center of the brain.
Relays all sensory information to the cortex
What does the ventral lateral segment of the thalamus regulate and relay?
Information from cerebellum
What does the ventral posterior segment of the thalamus control?
Somatosensory functions that are relayed to somatosensory cortex
Where does posterior segment of the thalamus receive input from?
Medial, spinal leminisci
Where does thalamus relay information?
To motor cortex
What are the conscious ascending sensory pathways?
Dorsal column-medial lemiscus (DCML)
Spinothalamic tracts
What ascending sensory pathway is unconscious?
Spinocerebellar tract
What kind of perception is derived from the Dorsal Column-Medial Leminiscus?
Fine/discriminative touch, vibration, proprioception
What are the 2 divisions of the DCML and what is the basis of this division?
Gracile fasciculus - lower limbs (T6 - S5, present at all levels)
Cuneate fasciculus (C1 -T6) Upper limbs
What are the 2 sections of the spinothalamic tract and what do they do?
Anterior spinothalamic tract (crude touch and pressure)
Lateral spinothalamic tract (itch, pain and temperature)
What is another name/description of the spinothalamic tract?
Anterolateral system (based on location)
What kind of information is derived from the spinocerebellar tracts?
Unconscious proprioceptive information
What are the segments of the spinocerebellar tracts?
Posterior spinocerebellar tract
Cuneocerebellar tract
Anterior spinocerebellar tract
Rostral spinocerebellar tract
What type of sensory pathways are there?
Conscious pathway
Unconscious pathway
What does the conscious pathway consist of?
1st order neuron: Cell body in the dorsal root ganglia, sensory receptor in the periphery, projects to the spinal cord/brainstem
2nd order neuron (Cell body in the spinal cord/brainstem, decussates in the spinal cord/brainstem, projects to the thalamus)
3rd order neuron (Cell body in the thalamus and projects to the cortex)
What does the subconscious pathway consist of?
1st order neuron (Cell body in the dorsal root ganglia, sensory receptor in the periphery, projects to the spinal cord)
2nd order neuron (cell body in the spinal cord, no decussation or decussates twice in the spinal cord and cerebellum, projects to the cerebellum)
Where do the gracile and cuneate fasciculi of the DCML cross each other (decussate)?
In the medulla on the medial lemniscus.
What happens to signals moving ipsilaterally through the spinal cord at the brain?
They swap sides
How fast do axons of the dorsal column-medial lemniscus move?
30 - 120 m/s which is very fast
What happens to signals coming from the periphery in AL spinothalamic tract?
It meets spinal cord at dorsal horn and ascend via lissauer’s tract synapsing with interneuron which decussates within spinal cord and this information then carries information up to the brain and synapses with third order neurons in the thalamus.
Fibres from 1o enter spinal cord ascent 1 - 2 segments via lissauer’s tract synapsing in the substantia gelatinosa and dorsal horn
Fibres from 2o neurons decussate within spinal cord via ventral white commissure and ascent in spinothalamic tracts (lateral and anterior columns) to the VPN of the thalamus.
3o neurons in thalamus project to somatosensory cortex in postcentral gyrus
How are anterolateral spinothalamic tract neurons different from DCML neurons?
They are much slower (<30m/s)
What is the decussation point within the spinal cord for AL spinothalamic tracts?
Ventral white commissure
Do spinocerebellar tracts contain any neurons that enter the cortex?
No
Which spinocerebellar tracts relate to lower limbs?
Ventral and dorsal spinocerebellar tracts
Which spinocerebellar tracts relate to upper limbs?
Rostral and cenuocerebellar tract
Why is the spinocerebellar tract considered ipsilateral?
Because there are 2 decussation points; 1 at the spinal cord, and the other at the cerebellum.
What happens to 1o fibers entering the dorsal root ganglia of the ventral spinocerebellar tract?
They enter the spinal cord and synapse in the intermediate grey matter.
2o neurons decussate within spinal cord via ventral white commissure and ascend ventral spinocerebellar tract to the brainstem.
Fibers pass through the superior cerebellur peduncle of the brainstem and enter the cerebellum and recross the midline (No synapses involved)
What happens to 1o fibers entering the dorsal root ganglia of the dorsal spinocerebellar tract?
Information is received via sensory receptor which synapses with intermediate grey area 2o neuron (Clarke’s nucleus).
Fibers from 2o nucleus ascends in dorsal spinocerebellar tract (lateral column) to teh brainstem
Fibers pass through inferior cerebellar peduncle of brainstem and enter cerebellum.
What is the rostral spinocerebellar tract identical to?
The Ventral spinocerebellar tract
What is the caudal spinocerebellar tract equivalent to?
The dorsal spinocerebellar tract
Where does Clarke’s nucleus sit?
Just below the posterior horn in intermediate grey matter
How is the dorsal spinocerebellar tract different from the ventral spinocerebellar tract?
The dorsal spinocerebellar tract is ipsilateral the entire way through the spinal cord.
The ventral spinocerebellar tract decussates twice and is thus contralateral most of the way through the spinal cord
