week 9 - neuro (spinal cord and embryology) Flashcards
What are the main physical features of the spinal cord?
Dorsal median sulcus, ventral median sulcus, dorsal, ventral and lateral horns, white matter, grey matter, central canal
Where are the two enlargements of the spinal cord?
Cervical (C3-T1) to upper limb and Lumbar (L1-S3) to lower limb
What is the end point of the spinal cord called?
The conus medullaris
What is the terminal strand of connective tissue at the end of the spinal cord called?
The filum terminale
Where does the spinal cord end in babies?
L3
Where does the spinal cord end in adults?
L1/2
What are the features of the dorsal roots?
Primary afferents, cell bodes in dorsal ganglia
What are the features of the ventral roots?
Efferents, cell bodies in spinal root grey matter
What happens to the two roots when they leave the spinal cord?
They fuse near the intervertebral foramen and form a mixed spinal nerve, this divides into a small dorsal and a larger ventral ramus
Where do the cell bodies of lower motor neurons usually lie?
In the ventral horn of the spinal cord, brainstem motor nuclei of the cranial nerves with motor modalities
What is the grey matter of the spinal cord made up of?
nerve cell bodies, dendrites and synapses
Where do the nerves of muscles with the same function arise from?
The same groups of motorneuron pools - grouped together (motorneurons supplying a particular muscle are in the same location)
Where do the nerves of antagonistic muscles arise from?
The same horizonal plane as their agonist
What are rexed lamina?
ten layers of grey matter to label portions of the grey columns of the spinal cord
What is contained within the white matter of the spinal cord?
The ascending and descending tracts
What are the most dorsal tracts of the spinal cord?
Faciculus gracilis, facilulus cuneatus
What are the most ventral tracts of the spinal cord?
Tectospinal, ventral corticospinal, lateral vestibulospinal and pontine reticulospinal
What are the six main descending tracts?
Corticospinal, corticobulbar, tectospinal, rubrospinal, vestibulospinal, reticulospinal
What does the corticospinal tract do?
control of voluntary muscles of the body
What does the tectospinal tract do?
head-turning in response to visual stimuli and blinking reflex
What does the rubrospinal tract do?
assists in motor functions - regulates flexor and extensor tone
What does the vestibulospinal tract do?
muscle tone and posture - body balance
What does the reticulospinal tract do?
spinal reflexes and maintains muscle tone when standing and walking
What are pyramidal and extra-pyramidal tracts?
pyramidal - originate in motor cortex, voluntary control of striated muscle
extrapyramidal - originate in brain stem, involuntary and automatic control of muscle tone, balance, posture and modulation of motor plans
What are first order/upper motor neurons?
from the cerebral cortex or brainstem to spinal cord - synapsing in the anterior gray horn
What are second order/lower motor neurons?
From spinal cord to skeletal muscles innervating them
What are the two pyramidal tracts?
corticospinal and corticobulbar
What are the four extrapyramidal tracts?
rubrospinal, vestibulospinal, reticulospinal and tectospinal
What do the corticobulbar tracts do?
From UMN in primary motor cortex terminating in the brainstem in the motor nuclei of the cranial nerves. LMN carry on as the cranial nerves and innervate the muscles of the head and neck
What is the pathway of the corticospinal and corticobulbar tracts?
primary motor cortex - corona radiata - internal capsule - brainstem - cranial nerves/spinal cord
Where do the corticospinal tracts decussate?
In the medulla
When does the corticospinal tract divide and what are the divisions?
At the lower medulla
Into anterior and lateral corticospinal tracts
Which corticospinal fibres do and do not decussate?
Lateral corticospinal decussate in the medulla
Anterior corticospinal do not decussate
What do the lateral and anterior corticospinal tracts do?
Anterior - skeletal muscle of trunk
Lateral - skeletal muscle of limbs
Where does the rubrospinal tract originate?
In the red nuclei in the midbrain tegmentum at the level of the superior colliculi
What are the two divisions of the vestibulospinal tracts?
Lateral and medial vestibulospinal tracts
How do the medial and lateral vestibulospinal tracts differ?
medial - from medial vestibular nucleus and stops mid-thorax (neck tone and posture)
lateral - from lateral vestibular nucleus continues the full length of the spinal cord (body posture stabilisation)
Do the vestibulospinal tracts decussate?
No
Where do the reticulospinal tracts originate?
In the reticular formation of pons and medulla
What is the reticular formation?
A set of interconnected nuclei that perform CV and resp control, consciousness, circadian rhythm and coordination of voluntary movement
Do the reticulospinal tracts decussate?
No
Where does the tectospinal tract originate?
The superior colliculus
Do the tectospinal tracts decussate?
Yes, in the medulla
What are corticofugal fibres?
Fibres that originate in the cortex
Neurons in which cortical layer give off the most corticofugal projections?
layer V
What do the spinothalamic tracts do?
Lateral: pain and temperature
Medial: crude touch
What do the spinocerebellar tracts do?
Dorsal: proprioception from lower limb and trunk
Ventral: proprioception from lower limb
What does the spinoreticular tract do?
Influences levels of consciousness, transmits deep/chronic pain
What are the ascending spinal tracts?
DCML (Gracile and cuneate tracts)
Anterior spinothalamic tract
Lateral spinothalamic tract
Anterior spinocerebellar tract
Posterior spinocerebellar tract
Spinotectal tract
Spino-olivary tract
Spinoreticular tract
What does the DCML do?
Fine touch, discrimination and proprioception
How many orders of neurons are in the DCML and where are they?
- skin to spinal cord - ascend ipsilaterally for 1/2
- spinal cord - decussate immediately - travel to thalamus
- thalamus - to primary somatosensory cortex
what are the gracile and cuneate fasciculus?
Gracile = lower limb = medial
cuneate = upper limb = lateral **
What are the three germ layers of the embryo?
Ectoderm, mesoderm and endoderm
Which germ layer does neural tissue arise from?
Ectoderm - neuroectoderm
What is neurulation?
The formation of a neural tube in vertebrates
How is the neural tube formed?
Neural folds form in parallel along the embryo. The two neural folds come together from the middle of the embryo - moving caudally and cranially, they meet to form the neural tube and the neural crest cells separate from the neural folds
What are the two divisions of the prosencephalon?
Telencephalon and diencephalon
What are the two divisions of the rhombencephalon?
The metencephalon and the myelencephalon
What does the telencephalon become?
Cerebrum
What does the metencephalon become?
Cerebellum and pons
What does the mesencephalon become?
The midbrain
What does the myelencephalon become?
The medulla
What does the diencephalon become?
internal brain structures (thalamus, subthalamus, epithalamus, hypothalamus)
What does the neural tube become?
The brain and spinal cord
What does the neural crest become?
Ganglia and meninges
What are the main conditions caused by failure of the neural tube to close?
Anterior deficit - anencephaly
Posterior deficit - spina bifida
What is the most common reason for failure of the neural tube to close?
Folate deficiency
What is the cauda equina?
The bundle of nerves that carry on in the vertebral foramen after the end of the spinal cord
What is the pathway of a stretch reflex?
Muscle/tendon - posterior roots - alpha motor neurons - anterior roots - muscle contraction
What does the DCML do?
Fine touch, vibration, two-point discrimination and proprioception
What does the spinothalamic tract do?
Pain, temperature and general touch
What are the three main nuclei of the cerebellum?
dentate nuclei, interposed, fastigial
What does the notochord become in humans?
Vertebral column - nucleus pulposus
What is a slipped disc?
Where the nucleus pulposus comes out of the annulus fibrosus
