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Organization of Nervous System (Imaging the Brain (why MRI > CT (more…
Organization of Nervous System
Nervous System Divisions
CNS
central division – consisting of brain & spinal cord
cerebrum
cerebellum
brainstem
cranial nerves (12)
mostly innervate head
composition = axons from CNS, somatic PNS, visceral PNS
spinal cord
conduit of information (brain <–> body)
dorsal root – somatic & visceral sensory (afferents)
Dorsal root ganglia – contains somas of sensory afferents
Ventral root – somatic & visceral motor (efferents)
Meninges – surround brain & spinal cord
dura mater
periosteal layer
covers inner surface of skull
meningeal layer
covers outer surface of brain & goes in sulci too
arachnoid
subarachnoid space contains cerebrospinal fluid (CSF) & blood vessels
pia mater
PNS
peripheral division – consisting of network of nerves throughout body
Imaging the Brain
why MRI > CT
more detail
does not require x-rays
uses info on how hydrogen atoms respond in brain to perturbations of strong magnetic field
Diffusion Tensor Imaging
application of MRI
measures diffusion of water in brain
enables visualization of large axon bundles
Functional Brain Imaging
functional MRI (fMRI)
principles
active neurons have increase O2 demands & require more blood
detect changes in regional blood O2 w/in brain
Development of CNS
CNS forms from walls of fluid-filled neural tube
inside of tube = ventricular system
Forebrain
Telencephalon
cerebral cortex
analyze sensory input & command motor output
Neocortex
4 brain lobes
only in mammals
6 layers
areas of neocortex (52) = brodmann's areas
6 gray matter layers in all neocortex
primary receiving areas
vision – LGN –> V1 (area 17)
hearing – MGN –> A1 (areas 41,42)
somatosensory – VPL/VPM –> S1 (areas 1,2,3)
motor – VL/VA –> M1 (area 4)
Archicortex
hippocampus
paleocortex
olfactory cortex/piriform lobe
separated from neocortex by rhinal fissure
olfactory bulbs
basal telencephalon
hippocampus
basal ganglia
amygdala
ventricle = lateral ventricles
Diencephalon
thalamus
gateway to cortex
axons from thalamus –> cortex pass through inter capsule
carry info from contralateral side of body
hypothalamus
controls
autonomic nervous system (ANS)
endocrine system (hormones)
homeostatic behaviors (i.e. drinking/feeding)
ventricle = 3rd ventricle
Midbrain
descending axons
axons descending from cortex –> brain stem & spinal cord, motor systems
i.e. corticospinal tract = motor cortex –> spinal motor neurons
ascending axons
info conduit from spinal cord & brainstem, –> forebrain, sensory systems
tectum
sensory orientation
superior colliculus – sensory info from eye
inferior colliculus – sensory info from ear
tegmentum
ventricle = cerebral aqueduct
Hindbrain
Pons
pontine nuclei receive input from corticospinal tract axons
relays info to contralateral cerebellum
Cerebellum
coordination of movements
Corticospinal fibers
continue toward spinal cord in medullary pyramids
ventricle = 4th ventricle
Ventricular System
ventricles = cerebrospinal fluid-filled caverns & canals inside brain
CSF
produced by choroid plexus in ventricles
choroid plexus: specialized ependymal cells surrounding capillaries in ventricles
protects brain – cushions it
conduit for hypothalamic peptide hormones
path
1) produced in choroid plexus
2) circulates through ventricles into subarachnoid space
3) reabsorbed in arachnoid villi & arachnoid granulations into venous sinuses (i.e. superior sagittal sinus = venous blood)
