Lecture 8 Flashcards
muscle contractions and relaxations that are rapid, stereotyped, involuntary, and coordinated (knee jerk, swallowing, pain withdrawal)
reflex responses
initiation and termination are
voluntary and triggered by peripheral stimuli (running, walking, chewing)
rhythmic motor patterns
initiated movements to accomplish a specific goal; largely learned movements that improve with practice (as one learns to anticipate and correct for environmental obstacles)
voluntary movements
What is the upper motor system responsible for?
planning and selecting movements
What is the lower motor system responsible for?
- executing movements
* simple sensory-motor reflexes
measures electrical activity in muscles
EMG - electromyograph
type of motor neurons that originate in ventral horn of spinal cord; form the “final common pathway”
Aα type
Each Aα type motor neuron innervates fibers within a ___. Each muscle fiber innervated by a ___.
single muscle
single motor neuron
All motor neurons innervating a single muscle are grouped in clusters called ____.
motor pools
Motor pools are located with a slight spread along the ____.
anterior-posterior axis
Describe the proximal to distal spatial map for the ventral horn.
Distal muscles are located at the outer edges, axial muscles are located toward the center
Describe the flexor to extensor spatial map for the ventral horn.
Flexors are located more dorsal (towards back), extensors are located more ventral (towards front)
What are some characteristics of lower motor neuron diseases?
decreased tone, weakness, retardation of movement, hyporeflexia, and muscle wasting
How is polio spread?
- spread by fecal-oral route
- attaches to receptors in cells of small intestine
- diarrhea and/or upset stomach
Polio that stops at the GI tract
abortive poliomyelitis
15% of polio cases result in this
aseptic meningitis
____ occurs in __% of cases. It targets motor neurons to cause muscle weakness (~__% of nerves affected. Nerve death results in ___. Progression stops only when ___ (paralysis is permanent).
paralytic poliomyelitis 1-5 50 paralysis immune system overcomes the virus
ALS (___) is the result of both genetic and spontaneous mechanisms. It can results from mutations in ___, which is __. It causes hardening of ___.
Amyotrophic lateral sclerosis
SOD1
autosomal dominant
lateral corticospinal columns
What are the symptoms of ALS?
- muscle wasting
- hyper-reflexia (combination of both upper and motor neuron signs of disease)
- increasing muscle weakness (especially in arms and legs)
- clumsiness
- muscle cramps and spasms
- difficulty speaking, swallowing, and breathing
lower motor neuron and all the muscle fibers it innervates
motor unit
____ are small fibers and with small motor units. “Red” fibers contract slowly but are relatively ____. They are rich in ___ (oxidative phosphorylation) and allow for ____ (e.g., posture).
slow (S), aka Type I
resistant to fatigue
mitochondria
sustained muscle contraction
___ are large fibers and involve larger, more powerful motor units. They are the larger pale muscle fibers. The contain sparse mitochondria (use ___ instead) and are ____.
fast fatigable (FF), aka Type IIa
mitochondria
glycolysis
easily fatigued
__ fibers are intermediate in size and ___ than FF but ___.
fast fatigue-resistant (FR), aka Type IIb
slower
less fatigable
What is Henneman’s Size Principal?
That fibers are recruited in order of size. Aka., low stimulation – only Type I fibers, then IIb, then IIa. There is a range of forces to perform different motor tasks. The largest motor units recruited only when maximum force is needed
Describe (temporal) summation in muscle fibers.
muscle fiber activated by new AP before relaxed from the previous AP –> produce more force; forces generated by temporally overlapping contractions are summed
tereotyped movements elicited by activation of skin or muscle receptors
spinal reflexes
innervate extrafusal muscle fibers; generate forces needed for movement
α motor neurons
innervate intrafusal muscle fibers; embedded within connective tissue of muscle; innervated by both sensory and motor neurons; report info about length and tension of muscle
γ motor neurons
sensory organ for determining muscle length and stretch; embedded in muscle
muscle spindle
During the stretch (___) reflex, discharge of ___ occurs related to ___ of muscle. When muscle stretched, it ___ firing rate.
When muscle is shortened (goes slack), it ____ firing rate. Ia axon synapses on ___ and is ____.
myotatic Ia sensory axons length increases decreases alpha motor neuron monosynaptic
large diameter sensory fibers coiled around muscle spindles; thickest myelinated axons in body; fastest
Ia sensory axons
Stretch imposed on a muscle stretches ___ –> activates mechanically gated ion channels in ___ and initiates an AP. These sensory neurons synapse with ___ in the same muscle and with synergistic muscles in ___.
The sensory neurons activate local ___ connections for ___ muscles.
intrafusal muscle fibers Ia axons motor neurons spinal cord ventral horn inhibitory antagonistic
a polysynatpic reflection that compensates posture during withdrawal from pain
flexor (withdrawal) reflex
During the flexor reflex, pain axon enters spinal cord
and activates ____, which eventually excite ___ that control ___ muscles of affected limb. Other ___ inhibit ___ that control ___.
interneurons alpha motor neurons flexor inhibitory interneurons alpha motor neurons extensors
A reflex that activates extensor muscles and inhibit flexor muscles on the opposite side in response to a flexor reflex
crossed extensor reflex
inhibition that compensates for the excess load imposed by limb withdrawal
reciprocal inhibition
limb is extended and in
contact with the ground (can get quicker)
stance phase
limb is flexed to leave the ground and then brought forward to bring the next stance phase (stays relatively constant)
swing phase
Where are central pattern generators (CPG) located?
spine
individual neurons whose membrane properties allow them to generate rhythmic activity
pacemaker neurons
Pacemaker neurons neuron possesses both __
channels and ___ channels. They will fire rhythmically when stimulated with ____.
Ca2+-activated K+
NMDA
glutamate
Pacemaker neurons have regular __ channels to generate APs. NMDA channel blocked by ___ at hyperpolarizing membrane potential. Internal __ dissipates and __ channel shuts off. ___ block is removed upon depolarization.
voltage-gated Na+ and K+ Mg2+ Ca2+ Ca2+ -activated K+ Mg+2
axons from ___ descend to influence local circuits in brainstem and spinal cord
upper motor neurons
What areas do upper motor pathways include?
-brainstem centers
-cortical areas in frontal
lobe
The brainstem is especially important for ___.
postural control
The motor and premotor cortex are responsible for ___.
planning and precise control of voluntary movement
The ___ is responsible for balance and posture; receives input from brainstem ___.
medial ventral horn
bilaterally
The ____ is responsible for voluntary movement of distal extremities; its controlled by ___ motor cortex (distal muscles operate
independently).
lateral ventral horn
contralateral
The primary motor cortex is located in the ___. It receives input from __, ___ (incorporates multiple sensory modalities, used for planning). It controls the ___ side of the body and uses ____.
precentral gyrus S1 posterior parietal contralateral topographic organization
over-representation of brain regions that are required for most complicated motor behaviors (i.e., more space given to fine motor control)
homunculus
The primary motor cortex has _ layers; layer V is the ___. It is mapped the same way that sensory cortex is mapped. The ___ is essential in planning movements but does not provide direct input to __; coordinates movements in space.
6
output layer (pyramidal cells)
posterior parietal
spinal cord
The direct pathway from the cortex to the spinal cord is the ___. Axons cross in the __ and innervate the ___ ventral horn.
corticospinal tract
medulla
opposite
The indirect pathway from the cortex to the spinal cord is the ___. It allows for ___, especially for axial and proximal muscles.
corticoreticulospinal tract
postural adjustments
adjacent to primary motor cortex, extensive reciprocal connections; projects directly to spinal cord
premotor cortex
In the premotor cortex, neurons fire ___; responsible for conditional motor tasks that pair movement with a ____.
earlier
visual cue
neurons fire before initiation of task; cells fire when just thinking about an event
intention
What are the symptoms of upper motor neuron lesions?
weakness spasticity increased tone hyperactive deep reflexes clonus Babinski's sign loss of fine voluntary movements
What are the symptoms of lower motor neuron lesions?
weakness paralysis decreased superficial reflexes hypoactive deep reflexes decreased tone fasciculations and fibrillations severe muscle atrophy
influence movements through upper motor neurons
basal ganglia
What are the 3 main nuclei of the basal ganglia?
caudate, putamen, globus pallidus
The basal ganglia form a loop with the ___ and the ___ to link the cortex with ___. They are required for ___.
substantia nigra
subthalamic nucleus
upper motor neurons
voluntary movements
Inputs to caudate and putamen from the cortex are ____. They also receive ___ inputs from substantia nigra. Interneurons and thalamic neurons form ___.
excitatory (glutamatergic)
dopaminergic
inhibitory synapses
Neurons in the basal ganglia fire in anticipation of a ___ (putamen = ___, caudate = ___).
movement
body movements
eye movements
Caudate and putamen send inbihitory GABAergic projections to…?
– globus pallidus (internal and external segments)
– substantia nigra (pars reticulata)
GPi (globes pallidus) neurons project back to cortex via ____.
thalamus
When striatal neurons fire (in anticipation of movement), they ____.
This allows upper motor neurons to send commands to lower motor neurons to ___.
inhibit the inhibition (i.e., disinhibition)
initiate movement
Spontaneous activity of the GABAergic GPi and pars reticulata neurons prevents ____.
unwanted movements
In the indirect pathway, the striatum projects to ___, then to ____. STN projects to ___, then to ____. STN projections are ____, which increases inhibition of GPi. (does the OPPOSITE of direct pathway!)
globus pallidus external nuclei subthalamic nuclei of central thalamus Gpi thalamus excitatory
Striatal neurons from the substantial nigra that project to GPi have __ receptors (___). Striatal neurons that project to GPe have __ receptors (____)
D1
excitatory
D2
inhibitory
Dopamine ___ the direct pathway and ___ the indirect pathway.
excites
inhibits
Huntington’s Diseases is entirely ____ and ____.
genetic
autosomal dominant
In Huntington’s disease, the coding region has an abnormal amount of ____. This gets larger with each ___. This leads to the selective loss of ___, and in turn, the loss of inhibition of ___. This results in increased stimulation of ____ by basal ganglia.
CAG repeats generation stratal GABAergric neurons GPe motor cortex
What are the symptoms of Huntington’s?
rapid, jerky movements with no clear purpose (chorea)
psychiatric symptoms as well
A neurodegenerative movement disorder that usually develops after age 50
Parkinson’s Disease
What are the symptoms of Parkinson’s?
difficulty walking, movement and coordination tremor rigidity akinesia postural instability
In Parkinson’s, ____ are destroyed over time. ___ accumulates in deposits called ___ within dopamine neurons.
dopaminergic neurons
alpha-synuclein
Lewy bodies
Parkinson’s is usually ___ but it has once been tied to ____ due to influenza. In 1976, contaminated batches of synthetic heroin (MPTP instead of MPPP) led to ____.
genetic
molecular mimicry
drug-induced Parkinson’s
In Parkinson’s, you lose dopaminergic neurons in ____, which decreases the ___ pathway and increases the ___ pathway. This leads to decreased stimulation of motor cortex by ____.
SN pars compacta
direct
indirect
basal ganglia
What are the most popular treatments for Parkinson’s?
L-dopa (can cross BBB)
sub thalamic deep brain stimulation
