Exam 4 Flashcards
What are reflexes
rapid, stereotyped, involuntary
what are rhythmic motor patterns
voluntarily initiated and terminated
maintained through reflexes and central pattern generators
Ex. breathing, walking, running
what are voluntary movements
purposeful
learned
ex. Typing, piano
How do muscles work
muscles pull on bones to move them at joints; muscles CANNOT push on bones
what are flexors
decrease joint angle
what are extensors
increase joint angle
what are agonist muscles
main muscles that move bones
what are antagonist muscles
muscles that decelerate movement by agonist muscles and move limbs in opposing directions
what are axial muscles
move the trunk and maintain posture
what are proximal muscles
close to the trunk
control the shoulder, elbow, pelvis, and knee joint
critical for posture and locomotion
what are distal muscles
further from the trunk
control hands, feet, fingers, toes, eyes, face
used for fine manipulation of objects, binocular vision, and facial expression
what is the medial part of the ventral horn
motor neurons that control proximal and axial/trunk muscles
involved in maintaining posture
what is the lateral part of the ventral horn
motor neurons that control distal muscles
involved in fine manipulation
what is the dorsal part of the ventral horn
flexor muscles
what is the ventral part of the ventral horn
extensor muscles
what is a motor unit
one motor neuron and all the muscle fibers it innervates
what is paresis
partial paralysis
what is the relationship between motor unit size and precision
inversely correlated
less precision –> Large motor units
more precision –> small motor units
what are upper motor neurons
cells bodies in the neocortex or brainstem nuclei
affect muscles indirectly
what are lower motor neurons
cell bodies in spinal cord or cranial nerve nuclei
directly contract muscles
what is the corticospinal tract
mainly involved in conscious control of movement
what are 40% of the corticospinal tract fibers
originate largely in the somatosensory cortex
terminate in the dorsal horn
modulate proprioception and nociception
what are 60% of the corticospinal tract fibers
originate in motor and premotor cortical areas
terminate in the ventral horn of the spinal cord
control voluntary movements
what is the pathway of the corticospinal tract
neocortex –> corona radiata –> internal capsule –> cerebral peduncle –> pons –> pyramids –> spinal cord
what is the corona radiata
descending axons from cortical neurons
what is the internal capsule
descending UMN axons in the corona radiata come together and mostly travel in the posterior limb of the i.c
where do axons of the corticospinal tract decussate
lower medulla (pyramidal decussation)
what is the lateral corticospinal tract
axons decussate in lower medulla
innvervates neurons that control distal muscles
synapse in ventral horn
what is the anterior corticospinal tract
axons decussate in the spinal cord near the level where they terminate
innervates neurons that control axial and proximal muscles
what is the corticobulbar tract
upper motor axons from the primary motor cortex projecting to cranial nerve nuclei in the brainstem
controls movements of the face, tongue, pharynx, and larynx
what is lower motor syndrome
caused by damage to lower motor neurons
characterized by:
weakness, paralysis
hypotonia
muscle atrophy
hyporeflexia
what is upper motor neuron syndrome
characterized by:
muscle weakness
hypertonia
no muscle atrophy
hyperreflexia
what are renshaw cells
spinal interneurons found in the ventral horn
activated by collaterals of motor neurons
prevent ongoing muscle contraction
inhibition of these cells increases the duration of muscle contractions
what is tetanus
painful muscle spasms and rigidity
blocks release of glycine from renshaw cells
what is the medial pathway
tracts travel primarily in the ventromedial column
controls proximal extensor motor neurons and trunk motor neurons
plays a large role in the descending control of posture
what are the main tracts of the medial pathway
tectospinal, vestibulospinal, reticulospinal
what is the tectospinal pathway
originates in the tectum which orients reflexes
tectum receives visual, auditory, somatosensory input
innervates interneurons that control neck motor neurons and coarse eye movements
what is the vestibulospinal tract
originates in the medial and lateral vestibular nuclei
relays info from vest. system
contributes to:
postural control, sensitivity of stretch reflexes, head and neck movements that compensates for changes in body position
what is the reticulospinal tract
originates in the reticular formation
receives vestibular, visual, auditory, somatosensory, cerebellar, and cortical inputs
controls functions such as:
posture, orienting movements, crude voluntary movements (e.g. reaching)
what are the types of proprioceptors
muscles spindles
golgi tendon organs
what are muscle spindles
maintain muscle length
what are golgi tendon organs
maintain muscle tension
what are the sensory neuron fibers
Ia sensory afferents (MS)
II sensory afferents (MS)
Ib sensory afferents (GTO)
what are the motor neuron fibers
alpha (to skeletal muscle)
gamma (to muscle spindles)
where are muscle spindles located
embedded in skeletal muscles
run parallel with extrafusal fibers
what are the phases of muscle stretch
static (constant length)
dynamic (muscle length is changing)
describe Ia afferents
rapidly firing
firing rate changes during dynamic
firing during static is proportional to amount of stretch
senses both velocity of stretch and amount of muscle stretch
describe II afferents
slowly adapting
firing rate during static phases is proportional to amount of stretch
senses amount of muscle stretch during static phases
where is the golgi tendon organ located
capsule containing collagen fibers
attached to muscle on one end and to a tendon on the other
in series with extrafusal muscle fibers
Describe how golgi tendon organs sense muscle tension
Tension on the GTO compresses the branches of the Ib afferents causing them to depolarize
what is a difference between muscle spindles and GTO
with isometric contraction, GTO is activated because muscle tension has increased (despite no change in muscle length)
what is the neuronal circuit for the stretch reflex
1) monosynaptic activation of agonist muscle
2) Disynaptic inhibition of the antagonist muscle
what is the feedback correction circuit for an increased load
add weight –> Ia afferent from muscle spindle activated by stretch –> alpha motor neuron for agonist muscle act.–> Agonist muscle contracts
what is the feedback correction circuit for a decreased load
reduce weight –> Ia afferent less active –> alpha motor neuron for agonist is less active –> agonist muscle relaxed
what is alpha gamma coactivation
gamma neurons contract intrafusal fibers in muscle spindles
what is the golgi tendon reflex
activation of Ib fibers excites Ib inhibitory interneuron in spinal cord which inhibit the alpha neurons to same muscle causing it to relax
what is the withdrawal reflex
Adelta nociceptive afferents:
excite ipsilateral flexor muscle
inhibit ipsilateral extensor muscle
what is the crossed extensor reflex
Side with painful stimulus:
extensors inhibited
flexors contract
Other side:
extensors contract
flexors inhibited
what are the three parallel striatal cortical loops
motor circuit (motor control)
associative circuit (cognitive function)
limbic circuit (motivated behavior)
what are the components of the basal ganglia
striatum (caudate + putamen)
globus pallidus (interna +externa)
subthalamic nucleus
substantia nigra (pars reticulata + pars compacta)
what is the function of the striatum
receives excitatory input from cortical regions
sends inhibitory output to globus pallidus
what is the function of the caudate
eye and head movments
what is the function of the putamen
body movements
what is the function of the globus pallidus
receives inhibitory input from the caudate and putamen
sends inhibitory output to the thalamus and subthalamic nucleus
what is the function of the substantia nigra
receives inhibitory input from striatum and excitatory input from subthalamic nucleus
located in midbrain
GABAergic output to the thalamus and dopaminergic output to the striatum
what is the function of the pars compacta
dopaminergic
what is the function of the pars reticulata
GABAergic
what is the function of the subthalamic nucleus
receives inhibitory input from GPe
sends excitatory input to GPi
what is the function of the thalamus
receives inhibitory input from the GPi
When it is disinhibited, it excites MI for movement
what are the regions that send excitatory (glutamatergic) input
cerebral cortex
thalamus
subthalamic nucleus
what are the regions that send inhibitory (GABAergic) input
striatum
GPe
GPi
SNr
what is the region that sends dopaminergic input to the striatum
SNc
Describe Medium spiny neurons in the caudate and putamen
get input from cortical, thalamic, and brainstem structures
inhibit GPi, GPe, or SNr
when are medium spiny neurons active
just before a movement starts and just before a movement ends
describe striatal neurons
do not fire unless they receive excitatory drive from the cortex
describe globus pallidus neurons
- fire at high rates without requiring external drive
- Inhibit thalamus under baseline conditions
- have to be inhibited
what are the two types of dopamine receptors in the striatum
D1: excitatory (depolarizing)
D2: inhibitory (hyperpolarizing)
what is the effect of dopamine on the direct pathway in healthy individuals
increases disinhibition of the thalamus, which is permissive for movement
what is the effect of dopamine in the indirect pathway in healthy individuals
prevents inhibition of the thalamus which is permissive for movement
what are the motor symptoms of parkinsons disease
hypokinesia
bradykinesia (slow movements)
Akinesia (lack of movement)
resting hand tremor
what is the cause of parkinsons
loss of dopaminergic neurons
how is dopamine effected in parkinsons in the direct pathway
loss of DA prevents disinhibition of the thalamus which is not permissive for movement
how is dopamine effected in parkinsons in the indirect pathway
increases inhibition of the thalamus, which is not permissive for movement
what are the movement symptoms of huntingtons disease
hyperkinesia
largely in limbs
chorea (dance)
what are other symptoms of huntingtons
mood changes
impaired cognition
dementia
what is the pathology of huntingtons disease
– loss of GABAergic striatal neurons in the indirect pathway
– Overactivation of the thalamus
– Late in HD, overall dopamine tone is also reduced which leads to akinesia
what are the functions of the cerebellum
motor planning
comparator
motor learning
what do cerebellar lesions cause
uncoordinated movements
impaired balance
inability to change/update motor programs
what are the lobes of the cerebellum
anterior
posterior
flocculonodular lobe
what are folia
parallel fold running along the outer surface of the cerebellar cortex
what are the deep cerebellar nuclei
groups of cell bodies (gray matter) inside the white matter of the cerebellum
– Receive input from collaterals of axons projecting to the cerebellar cortex
– output from the cerebellar cortex goes to these nuclei
What are the cerebellar peduncles
cerebellum is connected to the brainstem via three of them (superior, middle, inferior)
what are the deep cerebellar nuclei
dentate nuclei, interposed nuclei, fastigial nuclei
what are the three input/output pathways of the cerebellum
vestibulo-cerebellar
spino-cerebellar
cerebro-cerebellar
what is the vestibulo cerebellar pathway
receives input from: CN VIII and vestibular nuclei
Output to Deep nuclei:
- Oculomotor brainstem nuclei
- vestibular nuclei
what does damage to the vestibulo cerebellar pathway cause
nystagmus
disturbances of equilibrium
truncal ataxia
what is the spino cerebellar pathway (vermis division)
receives input from: proximal musculature
Output to: fastigial nuclei
what is the function of the spino cerebellar pathway
error correction during movement of proximal muscles
what does damage to the spinocerebellar pathway cause
gait ataxia
dysarthria (slowed/slurred speech)
hypotonia
what is the spinocerebellar pathway (intermediate division)
receives input from: distal musculature and motor cortex
output to: interposed nuclei
what is the function of the intermediate division of the spino cerebellar pathway
error correction during movement of distal muscles
what does damage do to the intermediate division of the spinocerebellar pathway
limb ataxia
dysmetria
intention tremor
hypotonia
what is dysmetria
errors in smoothness and direction of targeting movements
what is the cerebro-cerebellar pathway
receives input from:
- primary somatosensory cortex
- supplementary and pre motor cortices
- primary motor cortex
- primary visual cortex and parts of the parietal cortex visual areas
Output: dentate nuclei
what is the function of the cerebro cerebellar pathway
skilled movements
dexterous movements
complex movements
assists premotor cortical regions in selecting efficient motor programs
what does damage to the cerebro cerebellar pathway do
delayed initiation and termination of movement
dysmetria
dysdiadochokinesia
what is dysdiadochokinesia
the inability to perform a series of rapid alternating movements
what are purkinje cells
inhibitory projection neurons
large, flat dendritic tree
parallel to one another along folia
sole output of cerebellar cortex
what are granule cells
excitatory interneurons
innermost layer of cerebellar cortex
axons are the parallel fibers which run along folia
form weak synapses onto purkinje neurons
what are golgi cells
cell bodies in granule cell layer
excited by parallel fibers
provide feedback inhibition to granule cells
what are basket cells
cell bodies in molecular layer
excited by parallel fibers
provide feedforward inhibition to purkinje cells
what are climbing fibers
provide input to: inferior olivary nuclei
Send projection to: purkinje cells and deep cerebellar nuclei
excitatory
what are mossy fibers
provide excitatory input from: vestibular nuclei, spinal cord, trigeminal brainstem nuclei, pontine nuclei
send projections to: deep cerebellar nuclei and granule cells
what is the function of the cerebellar circuitry
Mossy fiber/parallel fiber inputs:
- weak excitatory synapses
- many together trigger simple spikes in purkinje cells
Climbing fiber inputs:
- strong excitatory synapses
- Trigger complex spikes in purkinje cells
what are the layers of the cerebellar cortex
Molecular layer (outermost layer)
Purkinje Cell Layer (middle layer)
Granule Cell Layer (innermost layer)
