Lectures 4-6 - Locomotion Flashcards
why study locomotion?
- spinal cord injury is relatively common and results in a complete loss of sensorimotor control below the site of injury
- if we understand how locomotion is generated by the CNS we have a much better chance of restoring function after spinal cord injury
- provides insight into anatomy and physiology of neural circuitry within the CNS
how many animal species locomote?
all
what are the two phases of locomotion?
- swing/flexion
- stance/extension
specific pattern of motorneuron/muscle activation is more complex with:
the activation of different pools of motor neurons varying throughout the step cycle
not all flexor muscles are activated at the same time and not all extensor muscles are activated at the same time, the activation is much more:
nuanced (some muscles are active during both swing and stance)
activation of flexors will:
supress activity of extensors (and vice versa)
a neural network can generate:
locomotor activity
through spinalizing cats, ______ discovered that you don’t need a brain or sensory information to walk and that there is an innate neural circuit in the spinal cord responsible for locomotion
Thomas Graham Brown
the locomotor central pattern generator (CPG) can generate:
complex locomotor patterns
Meyer and Akay electrically stimulated cutaneous nerves in the legs of infants and got a walking response. this indicates that:
neural circuitry is capable of making complex motor decisions
supraspinal structures/sensory are not necessary for ______; however, they are resonsible for ______
the production of the basic locomotor rhythm; initiating activity within the locomotor CPG and modulating its output to suit the terrain
what does the stumbling corrective response do?
fixes actions when tripping
the locomotor CPG in the spinal cord independently generates:
stepping
the mammalian spinal cord has a _____ distribution
laminar
how many lamina are in the spinal cord?
ten
neurons in different lamina have:
related functions
distinct cellular layers in the grey matter of the spinal cord
lamina
which lamina are found in the dorsal horn?
lamina I-V
what lamina are found in the intermediate nucleus?
lamina VI-VIII, X
which lamina are found in the ventral horn?
lamina IX
lamina I-V of the spinal cord contains:
sensory related interneurons (where sensory afferents terminate)
lamina VI-VIII, X of the spinal cord contains:
sensory and motor related interneurons
lamina IX of the spinal cord contains:
motor neurons
intreneurons with variable functions are:
intermingled in the intermediate and ventral spinal cord
what types of glia can be found in the spinal cord?
astrocytes and oligodendrocytes
what types of neurons are found in the spinal cord?
motor neurons and interneurons
true or false: interneurons can be both excitatory and inhibitory
true
what types of inhibitory neurotransmitters are found in the spinal cord?
GABA and glycine
neurons have an endless number of:
axonal projection patterns
the spinalized cat preparation was first used in the:
1960s
in a spinalized cat preparation, stimulation of flexor reflex afferents (FRA) results in:
the crossed extension reflex (aka withdrawal reflex)
a contralateral reflex that allows the body to compensate on one side for a stimulus on the other (ex: stepping on a nail with your left foot and reflexively put weight on your right foot)
crossed extension reflex
in a spinalized cat preparation, stimulation of flexor reflex afferents (FRA) after application of L-DOPA results in:
ongoing left-right alternation of the hindlimbs similar to stepping
the first studies attempting to identify the spinal neurons that comprised the locomotor CPG involved:
recording from spinal interneurons and identifying those that received input from FRA afferents
the majority of the neurons involved in locomotion were found in the _____ of the spinal cord
intermediate nucleus
the electrical brainstem stimulation technique was utilized in the:
1960s
during electrical brainstem stimulation, a site of the midbrain of cats was identified that could evoke locomotion (activity in the hindlimbs) when stimulated, this site was refered to as:
the mesencephalic locomotor region (MLR)
in how many species does the mesencephalic locomotor region (MLR) exist?
all species studied
the site of the brainstem thought to be responsible for initiation of stepping in intact mammals
mesencephalic locomotor region (MLR)
what are the two main parts of the mesencephalic locomotor region (MLR)?
the pendunculopontine nucleus (PPN) and the cuneiform nucleus (CN)
electrical brainstem stimulation provided a ______ method to evoke locomotor activity in experimental animals as opposed to ______
more “physiological”, spinalization and drug application
true or false: in electrical brainstem stimulation, the strength of the stimulation is proportional to the size of the response
true
the MLR projects to the _____ which descends to the neurons of the _____ via the _____
reticular formation, locomotor CPG, reticulospinal tract
indentification of the MLR led to a preparation in which the experimental animal was:
decerebrated, paralyzed, deafferented, and electrophysiological recordings were made from cut muscle nerves
experimental technique were the experimental animal is decerebrated, paralyzed, deafferented, and the electrophysiological recordings are taken from cut muscle nerves
in vivo fictive locomotor preparation
electrical stimulation of of the MLR resuts in rhythmic alternation of flexor and extensor related muscle nerves on either side of the animal, this pattern of activity is known as:
fictive locomotion
the in vivo fictive locomotor preparation provided an immobilized experimental subject where it was straightforward to:
record from neurons and stimulate afferents to look at the effect of sensory input on locomotory activity
in vivo fictive locomotion experiments found that the majority of locomotor related neurons were located in the:
intermediate nucleus of the spinal cord
this preparation enabled sensory afferents to be stimulated to investigate how sensory input modulates the step cycle
in vivo fictive locomotion
the in vivo fictive locomotor preparation led to the invention of the:
in vitro locomotor preparation
what is the in vitro locomotor preparation?
rodent spinal cord is isolated and can be tested for activation of motor neurons given certain stimuli
what is the benefit to in vitro fictive locomotion over in vivo locomotion?
have more control than in vivo (can test whatever drugs without having to worry about systemic effects on the body)
the L2 spinal nerves innervate the:
flexor muscles
the L5 spinal nerves innervate the:
extensor muscles
over the past century, two general techniques have been used to study the locomotor CPG:
1) electrophysiological studies
2) anatomical tracing studies
what do electrophysiological studies do?
measure intracellular recording from single neurons, or extracellular recordings of groups of neurons during locomotion
what do anatomical tracing studies do?
use anterograde/retrograde tracers to visualize axonal projection of neurons
what are the two main problems with using electrophysiological studies and anatomical tracing studies to investigate the locomotor CPG?
1) the number of neurons in the mammalian spinal cord
2) the extent to which these cells are intermingled
(these techniques can give detailed information on a single cell, but this is little help when attempting to identify structure or mechanism of functions of the locomotor CPG)
the process by which the blastula is produced from a fertilized ovum
blastulation
the blastula consists of:
a spherical layer of cells with a large fluid filled space called the blastocoel
gastrulation is the process during which the morphology of the embryo is reorganized to form germ layers:
ectoderm, mesoderm, and endoderm
the process during which the nervous system is formed from a specialized region of the ectoderm
neurulation
how long does neurulation take in mice?
~7-8 days
how long does neurulation take in humans?
~4 weeks
layer of the blastocyst that gives rise to the gut, lungs, and liver
endoderm
layer of the blastocyst that gives rise to muscle, connective tissue, and the vascular system
mesoderm
layer of the blastocyst that gives rise to the skin, CNS, and PNS
ectoderm
the developing neural tube secretes signalling molecules in a gradient manner. these signalling molecules result in:
the specification of spinal neurons
dorsal cells respond to _____ release from the neural crest cells/roof plate
bone morphogenic protein (BMP)
what is the function of bone morphogenic proteins (BMPs)?
they phosphorylate SMAD proteins which translocate to the cell nucleus and regulate gene expression
the process by which BMP impacts gene expression of early nerve cells is:
concentration dependent
BMPs direct different cell fates at:
different concentration thresholds
in embryos, how many dorsal interneuronal cell populations are there?
6 (dl1-dl6)
ventral cells respond to _____ release from notochord/floor plate
sonic hedgehog (SHH)
what is the function of sonig hedgehog (SHH)?
binds to patched protein, activates smoothened protein which activates the Gli transcription factor which regulates gene expression
like the BMPs, SHH directs different cell fates at:
different concentration thresholds
in embryos, how many ventral cell populations are there?
5 (V0-V3, VMN)
each ventral cell population (V0-V3, VMN) udergoes a _____ and takes up its final position in the spinal cord shortly before _____
specific migration pattern, birth
interneuronal cell types can be identified by:
immunohistochemistry using antibodies raised against specific transcription factors at early time points
in developing mice, transcription factors are only expressed from:
embryonic day 10 - embryonic day 13 (E10-E13)
how can interneuronal cell populations be followed from their birth to functional maturity?
by using transgenic mice that express reporter genes (ex: GFP or LacZ)
transgenic mice that express receptor genes (like GFP or LacZ) allow:
- immunohistochemical and anatomical techniques to characterize these cell populations
- electrophysiological techniques to determine whether specific populations are part of the locomotor CPG and their role in the production of locomotor behaviour
which cell population is found at the most dorsal end of the ventral spinal cord?
V0
the transcription factor ____ is expressed in all V0 interneurons from ____
Dbx1, E10.5-E12
V0 interneurons can be visualized postnatally using:
the Dbx1LacZ mouse
V0 cells are located almost exclusively in:
lamina VIII of the spinal cord
electrophysiological and anatomical techniques can be used to target V0 cells and identify:
whether they are necessary for locomotor behaviour
V0 interneurons contact:
contralateral motorneurons
retrograde, transynaptic tracer applied to hindlimb muscles of Dbx1LacZ mice co-localizes with:
V0 cells in the contralateral spinal cord
electroneurogram recordings from lumbar ventral roots are used to:
monitor locomotor activity
what evidence do we have that suggests V0 cells play a role in coordinating left-right alternation during walking?
V0 cells are rhythmically active during locomotion, and are out of phase with contralateral motor bursting
loss of V0 interneurons results in:
left-right alternation deficits
transgenic mice that are Dbx-/- (lack V0 interneurons) display:
frequent co-bursts of left and right sides (ex: flexors on the left and right sides are firing at the same time)
recent works have incorporated a(n) ______ approach to investigate the functional relevance of the MLR
optogenic
what is optogenics?
insertion of light sensitive channels (ex: rhodopsin) into a cell population of interest, and when sufficiently activated the neuron will depolarize
optogenic channels will be inactive unless:
exposed to a certain wavelength of light
in the molecular dissection of MLR, ______ is inserted into excitatory neurons throughout the CNS
channelrhodopsin
activation of excitatory neurons in the cuniform nucleus (CnF) or pedunculopontine nucleus (PPN) via optogenics is sufficient for:
controlling slower alternating locomotor behaviour
optogenic experiments in the MLR show that GlutNs in the CnF are necessary for:
high-speed synchronus locomotion
optogenic experiments in the MLR show that the PPN plays a role in regulating:
left-right alternation
what is the point of the PPN?
exploratory locomotor activity
