Part 1 Learning Objectives Flashcards
Bone, blood, brain, CSF on CT scan
Bone is white, blood is white, brain is grey, CSF is black
Gray matter, white matter, CSF on T1 MRI
T1 is “fairthful to neuroanatomy”: white matter is white, gray matter is gray, CSF is black
Gray matter, white matter, CSF on T2 MRI
White matter is black, gray matter is gray, fluid/CSF/edema is white (good for seeing problems)
Axial, coronal, sagittal cuts on imaging
Axial = horizontal, coronal = parallel to face, sagittal = vertical
Right/Left on neuroimages
reversed. “through the feet”
Epidural hematoma
On top of dura; tends to be arterial; limited by sutures; fills up faster; appears as bulge on imaging.
Subdural hematoma
Below dura; tends to be venous; not limited by sutures; fills up more slowly; appears as crescent on imaging
Anterior-posterior patterning of neural tube
Early, wnt = posterior; later, combinatorial code of hox genes specifies segments (rombomeres)
Dorsal-ventral patterning of neural tube
Notochord secretes Shh, inducing more Shh from ventral portion. Ectoderm secretes BMPs, patterning dorsal portion
How do neurons assume specific identities?
Extrinsic patterning: multipotent cells differentiate in response to extrinsic signals which induce combinatorial code of TFs
Cell migration in developing CNS
Excitator cells only: radial migration. New neurons move past older neurons to form new layers (lamination or “inside-out maturation”). Inhibitory: transverse migration. Neurons born in different regions of telencephalon and migrate (requires MTs)
How do axons find their targets?
Growth cone guided by long range (chemoattractive and chemorepulsive) and short-range (contact repulsion or adhesion) cues. Navigation of cue gradients depends on axon receptor profile
How does neuron survival depend on target finding?
Neurons that find targets get neurotrophins: factors secreted by post-synaptic cells (different neurons need different trophins). Local (growth cone/synapse) and nuclear (anti-apoptotic) action.
Resting membrane potential
-65mV (usually)
Types/locations of synaptic potentials
EPSPs: usually axo-dendritic; IPSPs usually axo-somatic
Principles of synaptic transmission
AP-> Calcium influx -> vesicle fusion -> NT release. (Amount of NT depends on amount of Ca2+)
Consequences of axon injury in PNS
Wallerian degeneration/chromatolysis-> MPhages remove debris -> Schwann cells support re-growth of axon.
consequences of axon injury in CNS
Wallerian degeneration (much slower than PNS)/chromatolysis-> microglia remove debris -> Damage spreads
Basic spinal organization (Dorsal columns, gray matter)
Dorsal columns are sensory tracts. Dorsal horns are interneurons receiving sensory input. Intermediate zone is interneurons and preganglionic ANS neurons. Ventral horns are motor neuron soma/dendrites
Muscle spindles
sense muscle stretch. innerated by single Ia, single II, two gamma neurons
Golgi tendon organs
sense tension. Innervated by single Ib neuron
Myotactic (stretch) reflex organization
Ia axon ipsilaterally excites motor neuron innervating same muscle, ipsilaterally inhibits antagonist muscle via an interneuron
Golgi tendon organ reflex
Ib axon ipsilaterally inhibits MN innervating same muscle (via interneuron) and ipsilaterally excites antagonist MN (via interneuron)
properties of spinal reflexes
unconcious, rapid, graded. SUBJECT TO DESCENDING CONTROL
withdrawal reflex
A-delta afferents –> ipsilateral flexion/contralateral extension (via interneurons). proportional to stimulus intensity
Criteria for identifying transverse spinal sections
Large ventral horn –> Limb (C5-T1 or L2-S2); Both dorsal columns present –> above T5; Lateral horn present –> T1-L2 (and Clarke’s present); thick central gray matter –> Sacral
Organization of spinal cord
31 segments: 8C, 12T, 5L, 5S, 1C. chord ends around L2.
Dorsal root organization
Sensory. Cell bodies in DRG. lateral division: pain and temp. medial division: touch, pressure, vibration
Sensory neuropathy general features
often length-dependent. Sensory response diminished on EMG
Radiculopathy general features
Often result from compression. Sensory responses look normal on EMG but nothing will be felt. Numbness/weakness
Motor neuropathy general features
collateral sprouting, atrophy/hypertrophy
Motor synapse defect general features
reduction in response to AP. presynaptic defect –> increment response. postsynaptic –> decrement response.
Dystrophy generally
Active breakdown/regeneration (stops eventually) with scarring
Myopathy generally
intrinsic weakness, microscopic changes
Nemaline myopathy
defect of thin filaments (nebulin/actin). Mutx determines severity. thready redness on trichrome stain
Duchenne MD
XLR. Proximal/progressive weakness. pseudohypertrophy. elevated CK. cardiomyopathy and respiratory insufficiency. Gower’s/Trandelenburg. Dystrophin: large protein anchors sarcolemma
AMPA-R and antagonists
Glutamate-R Channel. Mediates fast excitation. Sensitive. Antagonists are anti-epileptic
NMDA-R and antagonists
Glutamate-R Channel. Slower kinetics than AMPAR. Normally Mg2+ clogs pore, depolarization removes. Ca2+ permeable –> second messengers. Antagonists cause halucinations
Safety Factor
EPP - (minimum change to cause contraction). When present, ensures that every AP triggers muscle
AChE
Degrades ACh in NMJ, terminating transmission
Basic functions of thalamus
Relay: sensory, motor, associative, limbic; under heavy cortical control. Gate: transitions between waking and sleeping states (mediated by neuromodulation).
Basic functions of cortext
Generate sensory and motor representations of the external/internal world. Generate conciousness (depends on thalamocortical loops)
Role of thalamus in sleep
Switches from single spike/tonic mode to bursting mode. Mediated by T-type Ca2+ channels which are active at hyper-polarized RMP (-80mV). Makes the whole brain rhythmic. Bursting incompatible with coding.
Role of neuromodulators in sleep
hyperpolarized RMP acheived by K+ leakage into cell, because neuromodulators (NE, 5HT, DA) are less active while entering sleep
rhythmic movements
generated by CPGs in spinal cord and brain stem. chewing, swallowing, walking, etc
Voluntary movements
goal-directed, generated internally, improve with practice
Feedback (voluntary movements)
“error signal” produces compensatory changes
Feedforward (voluntary movements)
Anticipatory contraction. Essential for rapid movements. Depends on ability to predict (experience). Cortical commands project to reticular formation (pontine/medullary) which modifies medial motor pathway in anticipation of lateral action.
Population encoding
Non-1-to-1 encoding (applies to motor cortex). “Each cell votes” (although there are “sweet spots” for certain muscles, e.g.)
Supplementary motor area (SMA)
Important for memorized sequential movements (instructed delay or internally initiated complex tasks). Planning
Lateral premotor areas
Movement triggered by sensory stimuli (integration). Anticipatory firing. Mental rehearsal or watching others (“mirror”) recapitulates firing.
Lateral motor system (cord)
controls distal limbs. dorso-lateral MNs (within ventral horn) lateral propriospinal/local interneurons (within intermediate zone)
Medial motor system (cord)
Controls posutral muscles. MNs located in antero-medial spinal gray. local propriospinal interneurons located medially in the intermediate spinal grey
Locomotor movement circuit
Cortex –> Mesencephalic Locomotor Region (MLR) –> reticular formation –> RST –> CPG. Excitatory output of MLR determines speed. Lots of feedback/adjustment. Isolated CPG capable of generating movement
Anatomical organization of cerebellum
primary fissure divides ant/post lobes. posterolateral fissure separate floculonodular lobe
functional organization of cerebellum
unrolled, central vermis, intermediate and lateral zones (each hemisphere). deep nuclei are output
cell types/circuit of cerebellum
climbing fibers (input 1) from olive wrap around Purkinge cells (1 fiber/PC, 5-10 PCs/fiber) high safety factor. Mossy fibers (input 2: cortical and sensory) terminate on GCs. GCs extend axons through molecular layer (highly convergent and divergent). Single output (except vestibulocerebellum): PCs –> DCNs –> descending motor systems
somatotopic organization and function of spinocerebellum
spinocerebellum = vermis + IZs. Makes corrections during movement. discontinuous maps (fractured somatotopy) with head/axial muscles in vermis and limbs in IZs.
inputs to spinocerebellum
Proprioceptive via spinocerebellar tracts, ICP. Motor via corticopontine fibers, MCP.
outputs from spinocerebellum
limbs: interposed N –> SCP–> VL –> M1 (contralateral). Axial: fastigial N –> medial motor systems
function and ouput of cerebrocerebellum
active before movement, during planning. Dentate N –> SCP –> VL –> association, premotor, M1 (contralateral). Also has cognitive functions (judging time, tactile identification)
Function, input, and output of vestibulocerebellum (floculonodular lobe)
coordinates eye movements during head movements, maintains balance. Input from vestibular system. Output to MLF, vestibulospinal
General basal ganglia function
movement (posture, speed, tone), cognition, behavior. Feedback/Modulatory loop with thalamus/cortex
Input to basal ganglia
Cortext –> striatum
output from basal ganglia
GP + SN –> VA/VL –> frontal cortex
pharmacology of SNc
dopaminergic input from SNc facilitates direct/inhibits indirect –> enhanced motor output
Hallmarks of basal ganglia disease
Bradykinesia, Rigidity, postural instability, hyperkinetic abnormal movements (chorea, tremor)