Quiz 1: PNS, Spinal Cord Flashcards
what’s made in nucleolus?
ribosomes
what nuclear feature is prominent in neurons?
nucleolus
dendrites are largely extensions of the…
…cell body
in some unusual cells, axon comes off of…
…dendrites
cell body size range in vertebrate neurons
10-100 um
dendritic tree size scale (um, mm, m?)
mm
axon length scale (um, mm, m?)
m
how did the giraffe laryngeal nerve get so long?
evolved from fish, which have no neck. simpler to just extend the loop as the neck grew.
axon diameter range
0.5-20 um
myelin only helps for axons above a certain diameter, which is…
.5 um
which way do apical dendrites go?
to the cortical surface
why is white matter white?
myelination is fatty, and fat is reflective
why is gray matter gray?
less fat content
generic name for bundles of axons
tract
if we know a function for a tract, we call it a…
…pathway
funiculus
large bundle of fasciculi
lemniscus
means ribbon/belt. flattened bundle. many of these are sensory pathways
general term for crossing fiber
decussation (from roman numeral for deca-, X)
chiasm
large decussation (chi = X)
commissure
crosses midline to the same area on the other side (like corpus callosum)
ganglion, ganglia (pl)
locations of all neuronal cell bodies in PNS
cortex means…
bark/rind/covering.
neuropil
synaptic region with lots of little processes (axons/dendrites) (pil means hair)
avg number of connections per neuron
~1,000
approx number of neurons in human brain
100 billion
is most connectivity local or distant?
local, and yet the bulk of the brain appears to be white matter
weigert stains what?
axons, instead of cell bodies
in cortex, weigert stain reveals…
…bundles going laterally and across layers
what characterizies molecular layer?
there aren’t many cells
smallest cells
granule cells
among the largest cells are the…
…purkinje cells
orthodromic spikes
the normal way that spikes go, away from cell body
antidromic spikes
an AP going towards the cell body
how can we distinguish orthodromic and antidromic spikes, if we are stimulating area A and recording from neuron B? there are 4 ways. (answer has high detail)
- antidromic spike will have fixed latency, because no synapse is involved. orthodromic spike will have varying latency.
- because vesicles deplete, orthodromic spike won’t follow high freq stimulation. antidromic spike will follow up to about 1 kHz.
- orthodromic spike would cause EPSP. antidromic would not
- gold standard is collision failure: orthodromic and antidromic spikes cancel out. this tells you that ortho- and antidromic spikes are traveling along same axon
embryo layers, outer to inner
ectoderm, mesoderm, endoderm
which layer does nervous system develop from?
ectoderm
3 steps of the formation of the neural tube
plate->groove->tube
what does the mantle layer separate into?
alar plate (dorsal), basal plate (ventral)
what does the alar plate turn into?
sensory structures, dorsal horn
what does the basal plate turn into?
motor structures, ventral horn
sulcus limitans
structure in center of neural tube
3 swellings/vesicles emerge from the front end of the neural tube, what are they? in order from fore- to hind-
prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain), and then spinal cord
3 vesicles develop into 5, what are they? in order from fore-hind
[telencephalon, diencephalon], [mesencephalon], [metencephalon, myelencephalon]
diencephalon becomes…
…thalamus and hypothalamus
telencephalon becomes…
…cerebrum (cortex and deep nuclei)
canal in myelencephalon becomes…
…4th ventricle
canal in telencephalon becomes…
…lateral ventricles
canal in diencephalon becomes…
…3rd ventricle
canal in mesencephalon becomes…
…cerebral aqueduct
canal in spinal cord becomes…
trick question. it closes, in normal development
myelencephalon becomes…
…medulla
metencephalon becomes…
…pons and cerebellum
mesencephalon becomes…
…midbrain
unlike spinal cord, in brain stem motor functions are near…
…midline
unlike spinal cord, in brain stem sensory functions are…
…lateral
in nuclei abbreviations, 1st letter, general vs special (G vs S) means…
…function is found throughout the body (general, ie somatosense), or only in one particular organ (special, ie auditory)
in nuclei abbreviations, 2nd letter, somatic vs visceral (S vs V) means…
…function is external (somatic) or internal (visceral)
in nuclei abbreviations, 3rd letter, afferent vs efferent (A vs E) means…
…in/sensory (afferent) or out/motor (efferent)
dorsal groove in neural tube
sulcus limitans [I don’t think this is right -Sally]
3 meninges, outer to inner
dura, arachnoid, pia
tela choroidea=
pia+ependyma
ependyma
thin lining of ventricular system
tela choroidea+blood vessels=
choroid plexus
what goes through the 3rd ventricle?
a connection between both diencephalons
why are lateral ventricles C-shaped?
evolutionary history, stretching and formation of human brain. deep nuclei follow this contortion. not really like this in rodents
in human, which 2 descriptive axes hold steady?
the “eriors”: superior/inferior (up/down) and anterior/posterior (front/back)
in human, which 2 descriptive axes rotate 90°?
dorsal/ventral, and rostral/caudal
what barrier demarcates peripheral and central nervous systems?
the meninges (dura/arachnoid/pia)
describe nervous system branching above parasympathetic/sympathetic nervous systems
PNS>motor>autonomic>PS/S
plexus
complex network, comprising nerves and/or ganglia
receptors
transduce energy into electrical signals
effectors
act in response to a nerve impulse
PNS equivalent of CNS’s tract
nerve
PNS equivalent of CNS’s nucleus
ganglion
typical cell type in dorsal root ganglion
pseudo-unipolar
swelling on dorsal root
dorsal root ganglion
dorsal root and ventral root fuse to form…
…spinal nerve
where is the transition from CNS to PNS?
around the dorsal/ventral root
simple spinal nerves are found at what level?
near abdomen, etc
describe a complex plexus such as those in the arm
multiple spinal cord levels criss-crossing, converging and diverging, like highway on- and off-ramps
fibroblasts
build up extracellular matrix in nerves, like collagen
roles of connective tissue
mechanical stability
epineurium
surrounds entire nerve, and also exists between fascicles
perineurium
surrounds each fascicle
endoneurium
surrounds each axons (only in PNS, outside myelin sheath)
-neuriums are only in…
…PNS. there are NO “naked” axons in PNS as there are in CNS
optic nerve isn’t really a nerve because…
…it’s not in PNS
fascicle
small nerve bundle of axons, within a nerve
mallory trichome stain stains for…
…connective tissue
leading edge of paired plasma membranes in schwann cell
mesaxon
how long is a schwann cell?
~100 um
dense line is inner or outer face of mesaxon?
inner edge
compact myelin
the mature state of myelination, when all cytoplasm has been pressed out
unmyelinated axons are still protected by….
…Schwann cells, which can ensheath many cells. this is not the same as myelination.
when a Schwann cell wants to myelinate a single axon…
…it withdraws itself from all other axons
nerve fiber names in descending order of speed/diameter (two nomenclatures)
I, II, III, IV
Aα, Aβ, Aδ, C
which muscle fibers are most excitable, following EXTRACELLULAR stimulation? largest or smallest?
largest
which muscle fibers are most excitable, following INTRACELLULAR stimulation? largest or smallest?
smallest
how could you measure size of motor axons in a muscle nerve, which has motor and sensory axons?
cut dorsal (sensory) root, wait a week, then examine cross-section, which will only contain motor axons
3 ways to classify receptors
sensory modality (visual, auditory, etc) area of functional interest (exteroceptors, proprioceptors, etc) free nerve ending vs specialized receptor cells
exteroceptors
transduce external world contact, teloceptors
interoceptors
respond to internal state
labeled line concept
each set of afferents carries information that’s interpreted in a particular way. ie, extreme touch never turns into pain
receptive field
area where the receptor responds to touch (ie a touch receptor will respond to a patch of skin)
pacinian corpuscle
onion-like cutaneous exteroceptor. large receptive fields, rapidly adapting (you don’t feel your socks)
alar/basal, sensory/motor, sulcus limitans rule only holds for…
…gray matter. bundles aren’t necessarily organized the same way
effectors of motor neurons
striated muscle, glands, smooth and cardiac muscle
efferent pathway consists of…
…somatic motor neurons, pre/post ganglionics
each muscle connects to something that spans a length of spinal cord, called…
…spinal motor neuron pools, a nucleus of distributed motor neurons
what’s the advantage to low divergence in motor units?
high specificity. this varies when you need more specificity, like in fingers vs. quads
adult spinal cord length
~18 in
adult vertebral column length
~ 28 in
why is vertebral column longer than spinal cord?
in development, the vertebral column lengthens, while the spinal cord doesn’t
cauda equina
collection of nerve roots that innervate lower body. take up space in vertebral column after spinal cord tapers out. looks like a “horse’s tail”
name the 4 spinal cord regions, rostral-caudal
cervical, thoracic, lumbar, sacral
2 ways to characterize spinal gray matter
nuclei (marginal zone, etc)
rexed’s laminae (I-X)
cytoarchitectonic divisions of gray matter take into account…
…cell architecture. density, shapes of gray matter
what are the two increased densities of gray matter in spinal cord called?
cervical and lumbo-sacral enlargements
why are there gray matter spinal cord enlargements?
more motor neurons to control limbs
why does spinal cord get larger as you go rostral?
because you collect sensory and motor fibers from the periphery as you go to the brain
how does ratio of white:gray matter change as you go caudal?
it gets much smaller as you go caudal
nucleus thoracicus or nucleus dorsalis location
at the base of the dorsal horn
where does parasympathetic nervous system emerge?
craniosacral
where does sympathetic nervous system emerge?
thoracolumbar
parasympathetic preganglionic locations
cranial nerve nuclei for III, VIII, IX, and X, and S2-4
sympathetic preganglionic locations
lateral horn of T1-L2
parasympathetic ganglia locations
on or near end organs
lateral horn
little triangle that sticks out between the dorsal and ventral horns on the same level as the central canal; only occurs in the thoracic region and thus can be used as an identifying feature
ramus
branch
ANS
homeostasis, regulation of internal environment
3 principles of pathway organization
modality laterality (symmetry) topography/somatotopy (mapping)
name for pathways that remain in the spine, don’t go to brain
propriospinal (locomotion is one example)
what information does spinothalamic tract carry, and what’s another name for it?
pain/temperature; also known as ALS anterior lateral system
5 types of somatosensory information
fine tactile-discriminatory (small two-point touch, textures, figure out what an object is)
crude touch (knowing something is there pain/temp (these two are often the same pathway?)
proprioceptive (states of muscles/joints)
autonomic (from viscera, smooth muscle, glands)
fine tactile sensation pathway
dorsal column/medial lemniscal
how are touch receptors innervated?
several or multiple axons come in and weave through the corpuscle
what’s weird about spike propagation in somatosensation?
antidromic/orthodromic spike definition breaks down, since spike can propagate towards cell body in pseudo-unipolar cell
2 slow adapting touch receptors
merkel’s disk, ruffini’s corpuscle
2 fast adapting touch receptors
meissner’s corpuscle, pacinian corpuscle
specific classes of nerve axons are paired with specific…
…receptor types
what’s on the midline in the diencephalon?
3rd ventricle
anterolateral system carries what information?
pain/temp/crude touch
what type axons carry pain/temp/crude touch?
C/IV, Aδ
which type axons carry fine touch?
Aβ
first synapse in anterolateral system?
in dorsal horn, at/near level of entry
first synapse in fine touch pathway?
all the way up the spinal cord
general topography outer to inner in SC white matter?
lower stuff is further out, because as we go up we keep adding stuff to the center
belly button spinal cord section
T10. but actually innervates T8, a little bit higher.
is cerebellum ipsilateral or contralateral?
ipsilateral
spinocerebellar pathways carry what info?
unconscious proprioception
topography throughout LCST tract?
high to low is medial to lateral
where does lateral corticospinal tract (LCST) originate?
60% frontal cortex, 40% parietal cortex. this is why it’s better to call it a descending tract than a motor tract.
where is cingulate sulcus?
curving above the cingulate gyrus, which curves above the corpus callosum
upper vs lower motor neuron
lower motor neuron refers to actual motor neurons. upper motor neurons refer to the descending spinal tract
3 results of lower motor neuron lesion
flaccid paralysis (limp)
areflexia (no reflexes)
severe muscle wasting (atrophy. look like a skeleton)
4 results of upper motor neuron (anywhere along pathway, above the actual lower motor neurons) lesion
spastic paralysis (tense, stiff)
hyper-reflexia
mild muscle wasting
babinski reflex appears (contraction of the toe. normal in infant, abnormal in adult)
level of decussation of dorsal column (aka medial lemniscal system)
in the medulla, by the 2nd order neurons that project from the nucleus gracilis or nucleus cuneatus
level of decussation of anterolateral system (pain/temp/coarse touch pathway)
in the spinal cord, a few levels up from where ever the dorsal root ganglion cell enters the spinal cord
topography of homunculi in primary somatosensory and motor cortex
from medial to lateral: legs, trunk, arms, neck, head (approximately, b/c there may be some blending between areas)
in the spinothalamic pathway/ALS, which lamina of the dorsal horn do the dorsal root ganglia project to/2nd order neurons originate in?
lamina I, IV, V
which parts of the body do axons in the fasciculus gracilis carry information about? what kind of information?
lower limbs; fine tactile discrimination (but there’s not a lot of it in the lower limbs so fasciculus gracilis is smaller)
which parts of the body do axons in the fasciculus cuneatus carry information about? what kind of information?
upper limbs; fine tactile discrimination (and there’s a lot of it in our hands so fasciculus cuneatus is bigger)
where does the lateral corticospinal tract decussate?
in the pyramidal decussation in the medulla
which is bigger, fasciculus or funiculus?
funiculus
