Lecture 3 Organisation of the central nervous system: Spinal cord to the diencephalon Flashcards
What is the CNS formed from
ectoderm
What is the CNS formed from
ectoderm
how is the CNS formed
neuroectoderm cells recieve inductive signals from notochord (mesoderm)
cells thicken to form neural plate
lateral neural margin folds inwards to form neural tube
what are the cells at the edge of the neural plate called
neural crest cells
when does the CNS form from the ectoderm
embryonic day 20
aka neurulation
what happens to neural crest cells on embryonic day 24
migrate into periphery and differentiate into autonomic sonf sensory neurons and glia cells of adrenal gland melanocytes skeletal/connective tissue of head neural tube thickens
what is the structure of the neural tube like at day 20
neural plate with neuroectoderm in middle
notochord beneath
folds, creates neural groove
what is the structure of the neural tube like at day 24
ectoderm over top
neural crest cells
tube with mantle layer on outside
ependymal layer inner layer with lumen
what does the mantle layer become
brain parenchyma
what does the ependymal layer become
lines ventricles
what does the lumen become
ventricles and central canal
how often do neural tube defects occur
about 1/1000 established pregnancies
what happens if the anterior neuropore fails to close
leads to degeneration of forebrain and skull
what happens if the posterior neural tube fails to close
spina bifida (divided by a cleft)
what are the types of spina bifida
occulta (hidden, vertebral arch defect only)
cystica (eg meningocele so meninges projects out in a cyst)
how do the primary brain vesicles form
expansion of cranial end of neural tube to form main brain regions known as primary vesicles
what are the main brain regions
prosencephalon - forebrain
mesencephalon - midbrain
rhombencephalon - hindbrain
spinal cord
how do the main brain regions begin to develop flexures
folds
cephalic flexure between fore and mid brain
cervical flexure between hind brain and spinal cord
how do the secondary brain vesicles form
day 36
cranial end continues to expand into secondary vesicles
what does the prosencephalon form
telencephalon (cerebral hemispheres)
optic vesicles (eyes)
diencephalon (thalamus/hypothalamus)
what does the mesencephalon form
midbrain still
what does the rhombencephalon form
mesencephalon (pons/cerebellum)
mylencephalon (medulla)
how do the flexures develop as the secondary vesicles develop
pontine flexure between mesencephalon (pons/cerebellum) and mylencephalon (medulla)
what does rostral, ventral, dorsal and caudal mean
Dorsal at back and continues superiorly, ventral continues inferiorly
Rostral – front
Caudal – back of brain and bottom of spinal cord
what makes up the CNS
grey and white matter
what is grey matter
mainly neuronal cell bodies (eg cerebral cortex, brain nuclei)
what is white matter
mainly myelinated axons
what does the spinal cord do
reflexes and basic processing
what is the function of the spinal cord
receives primary afferent fibres from somatic and visceral structures
sends motor axons to skeletal muscles
autonomic function
regulation of bodily functions at unconscious level
conveys ascending and descending tracts
where does the spinal cord extend
atlas (C1) to L1
what is found at the end of the spinal cord
cauda equina (lumbar and sacral dorsal and ventral roots) in lumbar cistern terminal hilum (pia extension) attaches to coccyx
what happens to the spinal cord at L1
narrows to form conus medullaris
where is the spinal cord found
in vertebral canal
surrounding by dura and epidural fat
where does the spinal cord receive its blood supply from
anterior (1) and posterior (2) spinal arteries (from vertebral arteries)
segmental spinal arteries (at each level)
what is the spinal cord divided into
cervical region (1-8) thoracic region (1-12) lumbar region (1-5) Sacral region (1-5) lumbar cistern (contains cauda equina)
what happens to the spinal cord in the cervical spine
enlarges to innervate the upper limbs
what happens to the spinal cord in the lumbar region
lumbosacral enlargement to innervate lower limb
followed by conus medullaris
terminal hilum (int pia, ext dura)
what happens to the spinal cord in the lumbar region
lumbosacral enlargement to innervate lower limb
followed by conus medullaris
terminal hilum (int pia, ext dura)
what do spinal nerves do
connect periphery to spinal cord
form peripheral nervous system
31 pairs
what makes up spinal nerves
each formed by a dorsal (afferent) and ventral (efferent) roots
what is the structure of spinal nerves
inner core - grey matter
outer core - white matter
what happens to grey matter at levels that supply limbs
expanded
what is contained in the grey matter of spinal nerves
neuronal cell bodies
H shaped
ventral, lateral and dorsal horns
what is contained in the white matter of spinal nerves
myelinated axons
white columns (dorsal, ventral, lateral)/tracts/funiculi
division at top - posterior median sulcus
division at bottom - anterior median fissure
what is the brainstem
most primitive part of the brain
continuous with spinal cord
what is the function of the brainstem
contains cranial nerve nuclei
autonomic role
vital respiratory and cardiovascular centres
vomiting centre
nuclei involved with motor control, sleep
white matter tracts
what happens if the brainstem is damaged
often devastating and life threatening
what are the components of the brainstem
midbrain (mesencephalon)
pons and medulla (rhombencephalon)
(pineal gland at top)
what is the role of the medulla oblongata
contains nuclei important in controlling respiration and cardiovascular system
what is seen on the ventral side of the medulla oblongata
pyramid (corticospinal tract - main voluntary motor pathway)
olive (formed by olivary nuclei, motor relay to cerebellum)
what is seen on the dorsal side of the medulla oblongata
cuneate and gracile tubercle - nuclei form part of ascending tract
gracile to middle and cuneate lateral
what is the. function of the pons
relays info to cerebellum
above medulla oblongata but below midbrain
what is seen on the ventral side of the pons
transverse fibres forming cerebellar peduncles (like parted hair)
what is seen on the dorsal side of the pons
middle cerebellar peduncle (white matter tracts linking BS with cerebellum)
contains reticular info (nuclei concerned with sleep and motor control)
what is the mid brain
continuous with forebrain
what is seen on the ventral side of the midbrain
cerebellar peduncles (crus cerebri)
corticospinal tract
just above pons, mirrored
what is seen on the dorsal side of the midbrain
superior colliculus - vision (eye movement)
inferior colliculus - auditory (relay nuclei)
blobs either side and below pineal gland
what is within the midbrain
substantia nigra lies within
what is the structure of the midbrain
cerebral peduncles over substantia nigra red nuclei (2) dorsal side - superior colliculus
what does the substantia nigra do
dopaminergic neurons
part of basal ganglia
what do the red nuclei do
motor coordination - relay between cortex and cerebellum
what does the cerebellum do
unconscious motor function
where is the cerebellum
posterior to brainstem
what is the function of the cerebellum
Primarily involved with motor control:
- Control of posture
- Coordinating and planning limb movements
- Control of eye movements
what do cerebellar lesions cause
gait disturbances, upper limb ataxia and eye movement disorders
what is the structure of the cerebellum
outer grey matter underlying white matter 2 hemispheres 3 lobes (divided) contains nuclei similar to cerebral hemispheres
how is the cerebellum connected to the brainstem
by cerebellar peduncles
what are the lobes of the cerebellum
anterior
flocculonodular
posterior
divided into 2 hemispheres by vermis
what is the internal structure of the cerebellum like
highly folded
lobules with cerebellar cortex - arbor vitae
what are the cerebellar inputs
from periphery, spinal cord and BS, and cerebellar cortex via 2 afferent systems
what are the 2 afferent systems that send inputs to cerebellum
mossy fibres (from pons and spinal cord) climbing fibres (from medulla)
what are the outputs from the cerebellum
motor outputs to thalamus (cortex) and brainstem
what does the diencephalon do
relay and coordination centres
where is the diencephalon found
continuous with midbrain
comprises the thalamus and hypothalamus
main functions of diencephalon
relays sensory info to cortex
involved in consciousness, sleep, memory and motor functions
how is the diencephalon clinically relevant
Targeting nuclei may be effective treatment for epilepsy, Parkinson’s disease, pain, psychiatric disorders
what is the structure of the diencephalon
paired structure
divided into nuclear groups
thalamus and hypothalamus
inter thalamic adhesion between 2 sides of thalamus
where is the hypothalamus found
inferior to thalamus
superior to pituitary gland
sits between the optic chiasm and mammillary bodies
main function of hypothalamus
coordinates autonomic NS and NE system
thermoregulation, feeding, drinking, circadian rhythms
inputs from limbic system
how is the hypothalamus clinically relevant
Hypothalamic lesions linked to endocrine syndromes
