T2L3 structure and function of the spinal chord Flashcards
at L1
- spinal chord narrows to form conus medullaris
- terminal filum attaches to coccyx
the spinal chord
- sits within the vertebral column for protection (in vertebral canal)
- surrounded by meninges (dura, arachnoid, pia)
divisions of the spinal chord
c1-c8 cervical
t1-t12 thoracic
L1-L5 lumbar
s1-s5 sacral
lumbar cistern:
s4
cervical enlargement- innervation to upper limb
lumbosacral enlargement- innervation to lower limb
spinal nerves
- connect periphery to spinal chord
- 31 pairs, each formed by a ventral and a dorsal root
ventral roots
efferent fibres
dorsal roots
afferent fibres
internal anatomy of sc
inner core = grey matter
- h shaped
- formed of neuronal cell bodies
- the grey area has a ventral, dorsal and lateral horn
outer = white matter
- myelinated axons
- white tracts
has dorsal, lateral, ventral HORNS
also dorsal, lateral, ventral TRACTS
s9,s7
INCREASE GREY MATTER AT LEVELS THAT SUPPLY LIMBS (the cervical and lumbosacral enlargements)
generally:
dorsal horn = neurons receiving sensory input
lateral horn = preganglionic sympathetic neurons
ventral horn = motor neurons
dorsal horn
dorsal horn = neurons receiving sensory input
ventral horn
lateral horn = preganglionic sympathetic neurons
lateral horn
ventral horn = motor neurons
white matter organisation within sc
- contains tracts
- long ascending tracts carry afferent (Sensory) impulses to centres within the brain
- long descending tracts carry efferent (motor) impulses from centres within the brain
the tracts cross ie left cerebral hemisphere controls right side of body
dorsal column = ascending tracts
lateral column = descending and ascending tracts
ventral column = mainly descending tracts
dorsal column
dorsal column = ascending tracts
lateral column
lateral column = descending and ascending tracts
ventral column
ventral column = mainly descending tracts
2 types of info carried by sensory (ascending) tracts
proprioceptive- info originating from inside the body eg from muscles, joints, tendons
exteroceptive- info originating from outside the body (pain, temperature, touch)
ascending tract anatomy
3 neurons in circuit:
- first order neuron (primary sensory)
- enters spinal chord via dorsal root - second order neuron
- ascends spinal chord or brainstem - third order neurons
- projects to cerebral cortex
s11
medial lemniscus pathway
s16
in DORSAL COLUMN
- fine touch (from cutaneous mechanoreceptors), tactile discrimination and vibration
- proprioception (from muscle spindles, joints, Golgi tendons), provides brain with positional information
first order neurons:
enter sc and ascend dorsal column on same side within the fasciculus gracilis (medial) and fasciculus cuneatus (lateral)
fibres ascend dorsal column uncrossed (longest neurons in body)
first order neurons synapse on second order neurons in MEDULLA
fasciculus gracilis terminates at nucelus gracilis
- info from lower limb
fasciculus cuneatus terminates in nucleus cuneatus
- info from upper limb
second order neurons:
- cross in medulla and ascend to thalamus
- form medial lemniscus s15
third order neurons:
- project from thalamus to somatosensory cortex
damage to dorsal column
lesion on one side of sc:
- eg multiple sclerosis
- loss of tactile discrimination and proprioception on the same side
- sensory ataxia (loss of coordination and balance) due to no proprioception
- tested using rombergs test (standing with eyes closed>severe swaying)
spinothalamic tract
s20
- pain, temperature and crude touch (from nociceptors)
first order neurons:
- enter dorsal horn and form tract of Lissauer
synapse in dorsal horn to 2nd order neurons
second order neurons:
- cross in dorsal horn at each level
- ascend in anterolateral column to thalamus
third order neurons:
- project from thalamus to somatosensory cortex
damage to anterolateral column
lesion on one side of sc:
- loss of pain, temp and crude touch on opposite side
outside compression of chord:
- loss of lower limb pain
inside grey matter tumour
- loss of upper limb first
spinocerebellar tracts
unconscious muscle proprioception (eg from muscle spindles)
for smooth motor coordination
two uncrossed neurons only. four tracts
eg anterior and posterior spinocerebellar tracts
- carries proprioceptive info from trunk to lower limb
posterior spinocerebellar tract
first order neurons:
- synapse in dorsal horn
second order neurons
- ascend lateral column to cerebellum
- very fast axons
- cross over and then cross back (lol why tho)
lesion on one side of sc
- uncoordinated lower limb muscular activity on same side
corticospinal tract
VOLUNTARY MOTOR PATHWAY
2 neurons in circuit:
- upper motor (premotor) neuron
- cerebral cortex > ventral horn - lower motor neuron
- ventral horn > skeletal muscle
pyramidal tract (within corticospinal tract) primary motor cortex>pyramids of medulla>lateral/anterior corticospinal tract
80% tracts cross (lateral corticospinal tract)
20% on same side (anterior corticospinal tract)
see s28 in sc: medial = trunk anterolateral = proximal limb segments posterolateral = distal limb segments
upper motor neuron disease
degeneration of upper motor neurons
- spastic paralysis (increase muscle tone)
- overactive tendon reflexes
- no muscle atrophy
if above pyramids - opposite side
if below pyramids - same side
eg after stroke
lower motor neuron disease
degeneration of lmn in ventral horn
- flaccid paralysis (no muscle tone)
- no tendon reflexes
- muscle atrophy
eg spinal muscular atrophy
- caused by defects in SMN1 gene
amyotrophic lateral sclerosis
selectively affects upper and lower motor neurons
- progressive muscle weakness and atrophy but intact mind
- life span 5 years due to respiratory failure
extrapyramidal tracts
- don’t pass through pyramids
- descending tracts form basal ganglia, cerebellum and pons
eg reticulospinal chord
- From reticular formation (pons) to spinal cord
Regulates ventral horn motor activity/reflexes
Facilitates and inhibits lower motor neurons
Important for posture and locomotion
