Brain and Behavior Flashcards - Day 2
Anterograde transport: motor protein
Kinesin
Anterograde transport: direction
toward synapse
Retrograde transport: motor protein
Dynein
Retrograde transport: direction
toward cell body
Anterograde transport: materials
organelles, vesicles, membranes, cytoskeletal and other proteins
Retrograde transport: materials
trophic factors, signaling molecules, endosomes & lysosomes
Charcot-Marie-Tooth
demyelination disorder caused by dominant mutations in PMP22 (peripheral myelin protein 22)
Differences between PNS and CNS synaptic transmission
CNS: postsynaptic ion channels can open or close, produce excitatory or inhibitory stimulus (depending on the NT)
PNS: one end plate potential always generates muscle contraction
Botulinum, tetanus toxin: site of action
affect proteins involved in vesicle fusion at synaptic cleft
presynaptic inhibition: mechanism
Opening of voltage-gated K+ channels (decreasing Ca++ influx by decreasing duration of AP)
Inducing increased conductance to Cl-, decreasing amplitude of AP in presynaptic terminal & opening of fewer Ca++ channels
Direct inhibition of NT release independent of Ca++ influx
presynaptic facilitation: mechanism
Enhanced influx of Ca++ (sometimes by closing of K+ channels); broadens the AP and allows Ca++ influx to persist for longer period of time
Factors inhibiting regeneration of CNS neurons
glial scar inhibits regenerative growth, molecules (Nogo, MAG, Slit) inhibit growth, and adult neurons have low intrinsic growth potential
Spinal cord ends at what level?
L2
How are the 31 cord segments divided?
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
At what level(s) is a lumbar puncture performed?
L2 - S2
Where are cell bodies of axons in dorsal root?
Dorsal root ganglion
Dorsal root, median division fibers are…
large-diameter, heavily-myelinated axons (Ia, Ib, II, A-beta fibers); send fibers somewhere other than dorsal root (ventral horn) → proprioceptive fibers that provide the mechanism to generate reflex action
Class Ia fibers
arise from muscle spindles in skeletal muscle
Class Ib fibers
arise from Golgi tendon organ in muscle tendon
Class II fibers
innervate muscle spindles
A-beta fibers
innervate mechanoreceptors in skin (touch, vibration, pressure)
A-delta fibers
lateral division, thinly-myelinated, sense sharp pain and cold
C fibers
lateral division, unmyelinated, sense dull pain and warmth
Neuron types in ventral horn
alpha, gamma motor neurons
Alpha motor neurons
make muscle contract, cell bodies in VH, leave & innervate skeletal muscle
Gamma motor neurons
innervate muscle spindle, respond to increased stretching (increase sensitivity of the spindle)
Enlargements / large VH occur in what spinal cord segments?
C5 - T1, L2 - S2
Topographic organization of ventral horn
proximal muscles → distal muscles (medial → lateral); flexors → extensors (dorsal → ventral)
How many neurons are required for voluntary skeletal muscle contraction?
2 (upper and lower motor neuron)
Cell bodies of lower motor neurons are where?
Spinal cord gray matter (ventral horn)
Location of cell bodies and axons of upper motor neurons?
Cell bodies: primary motor cortex (precentral gyrus); axons: cross midline @ pyramidal decussation, travel down spinal cord in lateral corticospinal tract
Location of cell bodies and axons of lower motor neurons?
Cell bodies: ventral horn of spinal cord gray matter; axons: leave spinal cord via ventral root, join dorsal root in spinal nerve
Lower motor neurons are _____ to the innervated muscle
ipsilateral
Upper motor neurons are _____ to the innervated muscle
contralateral
Path of lateral corticospinal tract axons
Internal capsule → leave cerebral cortex → ventral midbrain → ventral pons → ventral medulla
Reticulospinal, vestibulospinal tracts
Extensor-biased UMNs; bilateral innervation from brainstem UMNs
Fasciculus cuneatus
Lateral dorsal column; carries upper limb first-order neurons ipsilateral to innervated muscle; T5+
Fasciculus gracilis
Medial dorsal column; carries lower limb first-order neurons ipsilateral to innervated muscle; T6-
Medial lemniscal system: functions
conscious proprioception, fine touch, vibration, two-point discrimination, pressure
Medial lemniscal system: 1st and 2nd order neurons synapse where?
Nucleus cuneatus, nucleus gracilis; ipsilateral to innervated muscle
Dorsal column - medial lemniscal system: cell bodies
First-order neuron: dorsal root ganglion, enter cord via large-diameter, myelinated, Ia, Ib, II, A-beta dorsal root fibers; Second-order neuron: medulla, ipsilateral to first order neuron; Third-order neuron: thalamus (ventropostero-lateral nucleus, VPL), contralateral to first and second order neurons
Dorsal column - medial lemniscal system: axons
First-order neuron: enter in medial dorsal root, ascend in the dorsal columns (Fasciculus cuneatus: upper limb, T5+ (lateral column), Fasciculus gracilis: lower limb, T6- (medial column)); Second-order neuron: crossed axons in medial lemniscus ascend through brainstem and project to VPL; Third-order neuron: project to primary somatosensory cortex (parietal lobe)
Anterolateral system - functions
pain and temperature
second order neurons of dorsal column - medial lemniscal system cross where
second order neurons cross only in the medulla
anterolateral system - cell bodies
First-order neuron: dorsal root ganglion, enter cord via thinly-myelinated (A-delta) or unmyelinated (C) fibers; Second-order neuron: dorsal horn of spinal cord segment 1-2 segments above first order neuron, ipsilateral; Third-order neuron: thalamus (ventropostero-lateral nucleus, VPL), contralateral to first and second order neurons
anterolateral system - axons
First-order neuron: enter in lateral dorsal root, ascend 1-2 spinal cord segments in Lissauer’s tract and enter dorsal horn; Second-order neuron: ascend in spinothalamic tract; Third-order neuron: project to primary somatosensory cortex (parietal lobe)
spinocerebellar system - function
convey unconscious proprioception from muscle spindles and Golgi tendon organs to the cerebellum [smoothly execute muscle contractions]
spinocerebellar system - cell bodies
First-order neuron: dorsal root ganglion; Second-order neuron: Clarke nucleus (lower limb) in spinal cord; or external cuneate nucleus in caudal medulla (upper limb)
spinocerebellar system - axons
First-order neuron: enter spinal cord by by of Ia, Ib dorsal root fibers; Second-order neuron: lower limb/trunk fibers travel ipsilaterally via dorsal spinocerebellar tract; upper limb/trunk fibers travel ipsilaterally via cuneocerebellar tract
Micturition: lesions in sacral cord, conus medullaris
flaccid / atonic bladder
Micturition: lesions between micturition center (pons) and sacral cord
spastic bladder
Micturition: lesions above pons
infantile bladder
