Neuro > Localization > Flashcards

Localization Flashcards

(49 cards)

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1
Q

General overview of somatotropic organization in the sensory and motor homonculus

A

Face is most lateral, leg/foot is most medial, arm is in the middle of the two

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2
Q

Sensory pathways

A

-Spinothalamic: pain + temperature
-Dorsal column/medial lemniscus: vibration + propioception
-Trigeminal nerve (CN V): pain, temperature, and touch in the face

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3
Q

Pathway of the spinothalamic tract

A

3 neurons involved:
1st neuron: brings sensory info to the spinal cord, synapses on 2nd neuron
2nd neuron: decussates in the spinal cord then ascends to the thalamus and synapses on the 3rd neuron
3rd neuron: goes from the thalamus to the sensory cortex

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4
Q

Lesions in the spinothalamic tract (spinal cord vs brainstem/brain)

A

-Spinal cord (before decussation): ipsilateral loss of pain + temperature sensation
-Brainstem/brain: contralateral loss of pain and temperature sensation

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5
Q

Pathway of the dorsal column/medial lemniscus

A

3 neurons involved:
1st neuron: enters the spinal cord and ascends to the medulla, synapses on the 2nd neuron in the nucleus gracilis (lower limbs/trunk, below T6) or the nucleus cuneatus (upper limbs/trunk, above T6)
2nd neuron: decussates at the synapse in the medulla, ascends to the thalamus, and synapses on the 3rd neuron
3rd neuron: goes from the thalamus to the sensory cortex
-From the legs (gracilis) goes to the medial sensory cortex
-Info from arms (cuneatus) goes to the lateral sensory cortex

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6
Q

Lesions in the dorsal column/medial lemniscus

A

-Below the medulla (dorsal column): ipsilateral loss of vibration and proprioception sensation
-Above the medulla (medial lemniscus): contralateral loss of vibration and proprioception sensation

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7
Q

Nerves of the spinothalamic tract vs DC/ML

A

Spinothalamic tract: small, unmyelinated
DC/ML: small, unmyelinated

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8
Q

Visual pathway (7)

A

Retina –> optic nerve –> optic chiasm –> optic tract –> thalamus (lateral geniculate nucleus) –> optic radiations (white matter tracts) –> primary visual cortex

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9
Q

Optic nerve lesion

A

Total loss of vision in the affected eye

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10
Q

Heteronymous hemianopsia

A

-Lesion in the optic chiasm
-Loss of vision of both lateral visual fields (input from medial retina)

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11
Q

Homonymous hemianopsia

A

-Lesion in the optic tract
-Lose vision in either the left or right visual fields in both eyes (input from one medial retina and one lateral retina)

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12
Q

Quadrantanopia

A

Loss of vision in either the upper left or right quadrants of the visual field in both eyes
Caused by temporal lobe - optic radiation tract (Meyer’s loop) lesion

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13
Q

Lesions in the other sensory systems (hearing, taste, smell)

A

These systems have bilateral representation in the brain, so unilateral cortical lesions don’t cause loss of hearing, taste, or smell

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14
Q

Two general systems of motor pathways

A

Pyramidal: direct motor pathways, control voluntary, precise movements
-Corticospinal tract
Extrapyramidal: indirect motor pathways, modulation + coordination of movement (posture, tone, balance, autonomic/habitual movements)
-Basal ganglia
-Cerebellum

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15
Q

Basal ganglia communication pathway in the brain

A

Cortico-BG-thalamo-cortico loop:
cortex –> BG –> thalamus –> cortex

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16
Q

Two examples of lesions in the basal ganglia

A

-Lesion in the substantia nigra = Parkinson’s
-Lesion in the caudate nucleus = Huntington’s

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17
Q

Function of the cerebellum

A

Precise, coordinated movement
Ex: finger to nose coordination - smooth, direct line movements

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18
Q

What are the inputs to the cerebellum? (3)

A

-Cerebral cortex (cortical input)
-Vestibular system (vestibular input)
-Spinal cord (spinal input)

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19
Q

Pathway of cerebellar output

A

Cerebellum –> contralateral thalamus –> ipsilateral motor cortex –> corticospinal tract

*The cerebellar output decussates twice (the corticospinal tract decussates in the medulla), which means that output ultimately affects the ipsilateral side of the body

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20
Q

Lesions in the cerebellum cause what?

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A

Ipsilateral ataxia - impaired coordination of voluntary muscle movement

21
Q

Corticospinal tract overview

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A

Efferent (descending) pathway - motor control of skeletal muscles (voluntary movement)

22
Q

Corticospinal tract pathway

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A

UMN: primary motor cortex –> internal capsule –> midbrain –> pons –> medulla (pyramidal decussation) –> LMN (in the spinal cord)
*The LMN is NOT part of the tract. It goes from the spinal cord –> skeletal muscle

23
Q

Lesions of the corticospinal tract (UMNs) cause what? (3?)

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A

-Weakness (of affected region)
-Hyperreflexia
-Spasticity

24
Q

Why do UMN lesions cause hyperreflexia and spasiticy?

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A

Because the UMNs normally send inhibitory signals down to spinal reflex circuits, keeping muscle tone + reflexes under control.
When there’s a lesion, inhibitory control is lost, and the LMNs and reflex arcs in the spinal cord become overactive.

Results:
-Even minor sensory inputs can trigger exaggerated reflexes
-Increased muscle tone (spasticity) - muscles resist being stretched because of stretch reflex being active

25
Spasticity vs Rigidity
Both mean increased muscle tone. -**Spasticity:** velocity dependent increase in muscle tone (resistance increases with faster stretch), caused by UMN lesions which hyperactivate the stretch reflex -**Rigidity:** constant increase in muscle tone (doesn't change with speed), caused by lesions in the extrapyramidal system
26
Stretch reflex
An autonomic spinal reflex that contracts a muscle when it's stretched **Goal:** to resist further stretching and maintain posture/tone
27
Lesions in the corticospinal tract (before vs after medullary pyramids)
-Before: contralateral weakness Ex: stroke, MS -After: ipsilateral weakness Ex: spinal cord injury
28
LMN pathway (5)
Spinal cord --> ventral spinal nerve root --> plexus (brachial **C5-T1** or lumbosacral **L1-S5**) --> periphearl nerves --> neuromuscular junction
29
Effects of LMN lesions (3)
-Diminished reflexes -Severe atrophy (loss of muscle innervation) -Decreased muscle tone (flaccid)
30
What type of junction is the neuromuscular junction?
Chemical (not electric)
31
What neurotransmitter do LMNs release at the NMJ?
Acetylcholine - binds to nicotinic ACh receptors and causes muscle contraction
32
Main role of the autonomic NS
Maintain homeostasis
33
The autonomic NS is regulated by what? (2)
Brainstem nuclei + hypothalamus
34
Sympathetic NS pathway (5)
1. Preganglionic neurons (short) originate in **T1-L2** regions of the spinal cord 2. Exit the spinal cord via the ventral root 3. Enter the sympathetic chain ganglia 4. Can then do one of 3 things -Synapse at that level -Ascend or descend the chain to synapse at a different level -Pass through w/o synapsing and then synapse in a prevertebral ganglion 5. The postganglionic neuron (long) then travels to the target organ
35
Parasympathetic NS pathway (3)
1. Preganglionic neurons (long) originate in **S2-S4** regions of the spinal cord and **CN III, VII, IX, X** 2. Travel to a ganglion near or within the target organ and synapse on the postganglionic neuron 4. Postganglionic neuron (short) innervates the effector tissue
36
Organization of the thalamus - sensory nuclei
-**VPL + VPM:** somatosensory (body + face) --> parietal cortex -**Lateral geniculate (LGN)**: visual info from optic tracts --> occipital cortex -**Medial geniculate nucleus (MGN):** auditory info from brainstem --> temporal cortex
37
Organization of the thalamus - motor nuclei
**Ventral anterior + lateral:** info from the cerebellum and basal ganglia --> motor cortex
38
Organization of the thalamus - limbic nuclei
Thalamus involvement in: -**Memory:** part of the circuit of Papez - mamillary bodies (hypothalamus) --> cingulate cortex -**Emotions**: connections to the oflactory cortex, amyglada, and prefrontal cortex
39
Pathways that pass through the brainstem (5)
-Corticospinal tract -Medial lemniscus -Spinothalamic tract -Reticular activating system (consciousness) -Cerebellar pathways
40
Extraocular movement muscles (6)
-Superior rectus: up (CN III) -Inferior rectus: down (CN III) -Medial rectus: adduction (CN III) -Lateral rectus: abduction (**CN VI**) -Superior oblique: down + out (intorsion - **CN IV**) -Inferior oblique: up + out (extorsion - CN III)
41
What happens with extraocular muscle palsy? (2)
-Ocular misalignment -Diplopia
42
Blood supply to the brain (2 pathways)
**Internal carotid arteries:** supply the anterior and middle parts of the brain -Common carotid --> internal carotid --> anterior cerebral artery, middle cerebral artery, posterior communicating artery **Vertebral arteries:** supply the posterior parts of the brain -Subclavian artery --> vertebral artery --> basilar artery --> posterior cerebral artery
43
Circle of Willis
Arterial network that connects the anterior and posterior circulations
44
Use of infused CT of the brain
Allows for identification of areas where the BBB has broken down (inflammation, infection, ischemia) *Uses IV contrast
45
Use of CTA of the brain
Allows for evaluation of the anatomy and pathology of blood vessels *Uses IV contrast
46
Pros + cons of MRI of the brain
-**Pros:** higher detail than CT, no radiation, better for smaller and/or acute lesions -**Cons:** slower + more expensive
47
SPECT scan
Measures perfusion of brain tissues (functional MRI can do this too)
48
**EEG** vs **nerve conduction studies** vs **EMG** - what does each measure?
**EEG:** brain rhythms + waves **Nerve conduction studies:** conduction of electricity along peripheral nerves **EMG:** activity of muscle fibers
49
Crossed sign
Means that CN findings are on one side of the face, while motor or sensory deficits are on the opposite side of the body. **Why?** -CNs emerge from nuclei in the brainstem, and supply the ipsilateral face -Motor + sensory tracts decussate below or within the brainstem before descending to the contralateral body So a lesion in the brainstem can damage CNs on the same side and sensory/motor tracts on the opposite side
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