6.4 Spinal chord Flashcards
Describe spinal chord - where does it end? what are its functions?
- Location
- in vertebral column
- begins at foramen megnum (continuous with medulla)
- adult ~42 cm long
- ends at Conus medullaris at L1
- Functions
- provides two way communication to and from brain
- contains spinal reflex centres
Ho many spinal nerves do we have?
where do they exist?
- 31 pairs
- c1-c7 exit above vertebrae of same #
*have 7 cervical vertebrae but 8 nerves
- all other exit below vertebrae
- has cervicla and lumbar enlargements (info for upper and lower limbs comes in and out)
How many nerves are in cervial, thoracic, lumbar, sacral and coccygeal areas?
Cervial: 8
Thoracic: 12
Lumbar: 5
Sacral: 5
Coccygeal: 1
How is the spinal chord protected?
- Bone, meninges, and CSF (in subarachnoid space)
- cushion of fat and network of viens in epidural space between vertebrae and spinal dura mater
- Denticulate ligaments: lateral extensions of pia pater that secure cord to dura mater
spinal chord proteciton at lower level
- dural & arachnoid mater extend to S2
- cauda equina: collection of nerve roots inferior to conus medullaris in subarachnoid space
*ext from end of spinal chord to subsrachnoid space
Filum terminale: extension of pia mater from conus medularis -> coccyx
What do you see if you take a cross section of the spinal chord?
- divded by 2 lengthwise grooves: sep left and right halves
- Ventral (anterior) meidal fissue
- Doral (posterior) median fissue
- gray commissure: connects masses of gray matter; encloses central canal
*basiaclly ther is a groove in the fron and back that divides left and right
What anchors the spinal chord superiorly? Posteriorly?
Superiorly: brain stem
Inferiorly: filium terminale
Describe Gray Matter
Ventral Horns: somatic motor neurons whose axons exit via ventral roots (motor)
lateral horns: only in thoracic & lumbar regions (motor)
dorsal horns: interneurons receiving somatic an dvisceral sensory input
-> dorsal root anglia: cell bodies of sensory neurons (on dorsal)
* looks like butterfly in middle of spinal chord, note in cerebral hemiphsere gray was on the outside
Describe the nerve innervation of spinal chord gray mater
Somatic sensory neuron: interneurons receiving input from somatic sensory neuron
Visceral sensory neuron: interneurons receive input from visceral sensory neurons
Visceral Motor neuron:
Somatic motor neurons:
what pathway generalizations are made in spinal chord
- Either ascending (sensory, coming up to brain)) or descending (motor, brain tells body how to move)
- Most pathways decussate (cross over)
*allows left brain to comm ith right body
- Most exhibit somatotopy (precise spatial relationships)
- Pathways are paired symmetrically (one on each side of spinal cord or brain)
- Name of pathway often gives information on start & end
Describe White matter in the spinal chord
- in spinal tract: collections of axons with similar functions
- consists of bilateral tracks in 3 white columns (funiculi)
- > Ascending/Sensory tracts (Dorsal, Lateral + Ventral columns)
- > Descending/Motor tracts (Lateral + Ventral columns)
- >Transverse tracts (commissural fibers) cross from one side to other
Describe the big picture of the ascenting pathway
- First orer neuron
- conducts impulses from cutaneous receptors (skin) and proprioceptors (awareness of body in space)
- Branches diffusely as it enters spinal cord or medulla
- Synapses with second-order neuron
- Second - order neuron
- in CNS
- interneuron
- cell body in dorsal horn of spinal chord (grey matter) or medullary nuclei
- axons extend to thalamus or cerebellum
- Third order neuron
- interneuron in CNS
cell body in thalamus - axons exten to somatosensory ortex
- interneuron in CNS
What 2 pathways transmit somatosensory info to sensory cortex
does this via thalamus
- Dorsal column-medial lemiscal pathway (DCML)
- Spinothalamic pathway (anterolateral pathway) (pain and temp path
- spinocerebellar tracts terminate in Cerebellum (unconscious processing)
what information does Dorsal Column- Medial Lemniscal (DCML) Pathway transmit
discriminative touch & vibrations
decribe pathway of Dorsal Column- Medial Lemniscal (DCML) Pathway
1a. information comes in dorsaly from touch receptor -> dorsal column white matter highway (lower limbs)
1b. info comes in from proprioceptor, through spinal nerves -> doral root ganglion
2. info crosses (decussation) at medulla oblongata -> first order nueron synpase on 2nd order neuron
3. 2nd roder nueron ends in thalamus (exact location depends on where in body sensation was)
What information does the lateral spinothalamic tract transmit
pain and temperature impulses
what info does ventral spinothalamic tract transmit
crude touch and pressure impulses
pathway of lateral spinothalamic tract
- info from temperature and pain receptors -> can come from doral root
- first neuron synpases on dorsal horn, get decussion at level of entry
*synases as level where it enters and crosses over
- 2nd neuron synapses in thalamus then sends 3rd neuron to primary somatosensory cortex
What information does the spinocerebellar tract convey?
- impulses from trunk and lower limb proprioceptors -> same side of cerebellum for subconscious porprioception
*same side of brain controls same side of body affected
pathway of spinocerebellar tract
- only 2 neurons
- has lateral dorsal and lateral ventral part
*does not go to thalamus
- info from muscle spindle (proprioceptor) togoes to interneurons of dorsal horn
- ipsilateral: dorsal never crosses, ventral crosses then crosses back
*same side of body communicated with same side of the brain
- synases at level it enders, terminates by synapse in cerebellum
* NOT IN UPPER LIMBS, transmits impulses from trunk & lower limbs
(blue pathway in image)
Describe the big picture of descending pathways: what are the two types of pathways and what neurons do they involve?
- deliver efferent impulses from brain to spinal cord
- > Direct pathways: Corticospinal/pyramidal tract
- > Indirect pathways: all the others one
Involves:
- > Upper motor neurons: cortex to spinal cord
- > lower motor neurons: spinal chord ot skeletal muslce (ventral horn motor neurons
describe the direct pathway
aka Pyramidal Tract or Corticospinal Tract
- impulses from pyramidal enurons in precentral gyri pass through pyramidal tracts (upper motor neurons)
^ first neuron in pathway
- axons synpase with interneurons or ventral horn mototr neurons (lower motor neurons)
*regulares fast and fine (skilled) movements
describe pathway of direct pathway
- starts in cell body of Pyramidal cells (upper motor neurons) of cerebrum
^in primary cortex, sends info around thalamus
- Lateral: decussate in pyramids of medualla (85%). Ventral cross over at spinal chord level (15%)
- termination with ventral horn interneurons
describe the indirect (extrapyramidal) system pathway
*Pathways are complex & multisynaptic
- Tectospinal tract: mediate head movements in responds to visual stimuli (contralateral)
- Vestibulospinal tract: maintain balance duringstanding & moving (Ipsilateral)
- Corticobulbar tract: motor to skeletal muscle of cranial nerves (both contralateral & ipsilateral)
if you sever left side of spinal chord in thoracic region what would happen
* T3 only impacts lower limbs, everything that happens above could get thouse
*loss of ability would be confined to one side
- DCLM: General touch
- crosses in medualla
- information on left could not get thorugh -> lostt general touch on left
- Latspinothalamic
- crosses @ level it enters
- loss pain and temp on right (below lesion)
- Lateral corticospinal
- crosses at medulla
- loss movement on left below lesion
what are teh 3 levels of motor control
precommand level (higihest)
projection level (middle)
segmental level (lowest)
describe the precommand level of motor control
- highest
- cerebellum (makes music sound good) and basal nuceli (when to start/end music)
- rpograms and instructions (modified by feedback) -> doesnt make the movement itself
Describe the projection level of motor control
(middle level)
- motor cortex (pyramidal pathways) and brain stem nuclei (vesticular, red, reticular formation etc)
- converys instructions to spinal chord motor neurons and sends a copy of that info to higher levels
*communicated with precommand and segmental levels
describe the segmental level of motor control
- spinal chord
- contains central pattern generators
