Exam 3: Cerebellum and Locomotion Flashcards
movement synergy
coordinating multiple muscles ⇒ adaption to feedback to adjust muscle control autonomically
movement synergy includes (3)
- Muscle tension and movement speed/fluidity
- Balance and posture
- Motor learning
→ also involved in cognitive processes ⇒ attention, reward learning
Tentorium cerebelli
dura sheet (meninges) sitting between the cerebellum and the underside of the occipital lobe in the cerebrum
3 lobes of the cerebellum
- anterior => front and top
- posterior => largest part and rest of area
- flocculondular => small chunk between anterior and posterior on the middle inside
vermis
this is in the midline area defining parts of the cortex and surface of cerebellum
hemispheres of the cerebellum
on the lateral sides of the cerebellum
cerebellar cortex
the external surface
- the cerebellum has its own cortex organized very specifically ⇒ cerebellar cortex (stripe appearance from a medial to lateral position)
folia
run medial lateral ⇒ like gyri in cerebral cortex
arbor vitae
Internal white matter tracts
3 peduncles of the cerebellum
- Superior ⇒ connects to midbrain
- Middle ⇒ connects to pons
- Inferior ⇒ connects to medulla
→ all axons into and out of the cerebellum go through these peduncles
cerebellar peduncles definition
connect the brain to the cerebellum via hanging off the back of the brainstem
Superior peduncle is on the top and comes and goes from cerebellum connected to the midbrain
The inferior peduncle is below that connected to the medulla of the brainstem
how are cerebellar neurons arranges? (2)
2 main location
1. Cerebellar cortex ⇒ surface layers
2. Deep cerebellar nuclei
3 components of the deep cerebellar nuclei
- Fastigial nuclei (medial)
- Interposed nuclei
- Dentate nuclei (lateral)
where do axons of cerebellar cortex neurons connect?
to deep nuclei
what is the main anatomical output of the cerebellum?
deep cerebellar nuclei
3 layers of cerebellar cortex
- molecular
- purkinje
- granular
molecular cerebellar layer
made up of axons, dendrites, and smaller neurons
purkinje cerebellar layer
houses purkinje cell bodies (band layer)
granular cerebellar layer
houses granular cell bodies
most numerous neuron type in the brain?
granular cells
granule cells
send axons up into the molecular layer (dense) where they split (2) and run both directions parallel to the cerebellar folia (communicate locally)
which cerebellar cortex layer is the most diffuse?
molecular layer
purkinje cells
Extend dendrites up into the molecular layer where they fan out in a single plane, perpendicular to the direction of the cerebellar folia
- allows for purkinje cells to get a lot of information
what cell axons are the only ones to leave the cerebellum?
purkinje cells
difference between granule and pukinje cells
granule cells send their axons while purkinje cells send their dendrites into the molecular layer
2 inputs into the cerebellar cortex
- mossy fibers
- climbing fibers
mossy fibers
contact granule cells and come from many places
where do mossy fibers come from? (3)
Cerebral cortex, vestibular nucleus, spinal cord
climbing fibers
contact purkinje cells and wind up around their cell body and dendrites
- important for regulating cortical function
where do climbing fibers come from?
from the medulla
- Cell bodies send axons from the inferior olivary nucleus (upper lateral) of the medulla and extensively wrap around purkinje dendrites
how many climbing fibers does a purkinje cell receive?
only 1
- feedback loop from the medulla is very important
where do purkinje cells send their axons?
to deep cerebellar nuclei which send axons out of the cerebellum
red nucleus
sends its commands via the cerebrospinal tract and coordinates movements for posture control/movement corrections
- gets info from deep cerebellar nuclei
- sends a signal to inferior olivary nucleus and rubrospinal tract
spinocerebellum
the body that has information processed into the middle vermis portion
- Information in the cerebellar cortex relating to information from the body
cerebrocerebellum
information originating in the cerebral cortex of the cerebrum relating to complicated things like movement, motor planning, adjustments, cognitive domains, motor functions (brown)
vestibulocerebellum
critical for movement synergy and gravity adaptation to appropriately respond to movement and muscle tension
- Integrates the vestibular system with cerebellum in flocculonodular lobe
spinocerebellar input?
main input is spinocerebellar tracts and cranial nerves carrying proprioceptive information
what kind of information does the spinocerebellum get?
position, tension on muscles in the body
- Input is somatotopically organized in the cerebellum
where is spinocerebellum information processed?
in vermis and intermediate hemispheres of cerebellar cortex
what is the output of the spinocerebellum?
output is to interposed nuclei which outputs to red nucleus
- red nucleus projects to spinal cord and cranial nerve nuclei (rubrospinal tract)
cerebrocerebellar input?
from cerebral cortex, via pontine nuclei
- pontine nuclei send axons to the contralateral side of the cerebellum via the middle cerebellar peduncle
where is cerebrocerebellar output?
to dentate nucleus, then ventrolateral nucleus of the thalamus, which projects to cerebral cortex (loop)
- Involved in coordinating movement planning, learned movements, cognition
vestibulocerebellar input? Where is it processed?
vestibular nuclei and vestibular nerve
- processed in flocculonodular lobe of the cerebellum
vestibulocerebellar output?
to the vestibular nucleus which project to spinal cord and cranial nerves to maintain balance, coordinate head/eye movements
ataxia (cerebellar pathology)
inaccuracy in speed and force movements, inaccurate estimate of distances
tremor (cerebellar pathology)
involuntary movements, shakes/jiggles
nystagmus (cerebellar pathology)
involuntary movement of the eyes
how are rhythmic motor patterns of locomotion generated?
Central pattern generators ⇒ neural circuits in the spinal cord (CNS)
How are rhythmic motor patterns modulated for complex locomotion?
Ascending and descending input (both) onto central pattern generator (CPG) circuits
central pattern generators (CPGs)
a network of neurons (typically in spinal cord) that are capable of generating rhythmic pattern of activity without requiring sensory feedback
fictive locomotor activity
the spinal cord is not directly attached to muscles but you can add drugs like NMDA or 5HT or dopamine/serotonin and you can monitor locomotive activity
what produces a gate?
alternation of activity
flexor vs extensor
flexor bends the limb while extensor straightens it
- alternation between these two within the same limb aside from just left and right alternation
how does coordination happen?
mutually inhibiting spinal networks utilizing excitatory and inhibitory interneurons
- These are coordinated between the inhibitory neurons so the flexor and extensor can communicate
when one extensor or flexor neuron is excited what does it do to the other neuron?
inhibits the opposite neuron
what do motor neurons do? What are they controlled by?
control muscle groups and they are controlled by flexor and extensor interneurons
- mutual inhibition coordinates ipsilateral flexor/extensor opposition as well as contralateral opposition
what is crossed inhibition?
There are inhibitory interneurons crossing the midline of the spinal cord inhibiting the motor neuron on the other side
EphA4
a gene that encodes a receptor for the protein family ephrin
Ephrin
found in the middle of the spinal cord during development and activation of the EphA4 receptor repels axon growth, preventing excitatory interneurons from crossing
what happens when you have contralateral excitation instead of inhibition?
there is a hopping movement instead of a walking movement
what happens if you have no EphA4 gene?
growth of excitatory interneuron across spinal cord and contralateral excitation
Modulation
recognizing there is an object in your way and how you are circumventing it
how does a deceberate cat still walk on the treadmill when harnessed?
Ascending proprioceptive sensory information without cortical involvement is sufficient to control step speed
proprioceptive information (2)
- muscle stretch reflex
- muscle contraction
muscle stretch reflex
1a afferents from muscle spindles
muscle contraction
1b afferents from golgi tendon organs ⇒ how much the muscle is flexed based on weight bearing
walking pattern
stretching the hip flexor muscle (too much) → activates muscle spindle in flexor muscle (reaction against stretch) → inhibits MN to relax extensor muscle ⇒ as you flex you don’t want to extend simultaneously
how do Golgi tendon organs influence walking?
golgi tendon organ (GTO) sends signals to the spinal cord when it is squeezed during muscle contraction ⇒ about state of flexion
- This transmits information on muscle load and weight bearing (1b)
what are the pathways for the central bipedal locomotion circuit?
- Directly by monosynaptic connection
- Bisynaptic where it activates an interneuron to activate extensor
- Polysynaptic pathway where it hits the interneuron which activates extensor interneuron and then activates the interneuron at 2
→ there are multiple ways that 1a and 1b interact with the circuit so that it works correctly
1a vs 1b muscle fibers?
1a = muscle spindles and 1b = Golgi tendon organs
mesencephalic locomotor region (MLR)
can initiate walking, even in decerebrated prep (in the pons) ⇒ send signals to CPG in spinal cord to initiate locomotion
mesencephalic locomotor region (MLR) pathway
MLR → reticular formation (medulla) → axons in ventrolateral funiculus spinal cord → CPG → initiates locomotion
- can be done with electrode stimulation
sub thalamic locomotor region
includes subthalamic nucleus
pontine peduncular nucleus
in the pons involved in gait modulation but not critical for initiation
what 2 things are stimulates by electrodes in the MLR?
- sub thalamic locomotor region
- pontine peduncular nucleus
what do descending locomotor pathways require?
glutamatergic activation to initiate walking
what is sufficient to initiate stepping but not necessary?
norepinephrine (NE aka norepinephrine from the locus coeruleus) and serotonin (5-HT from raphe nucleus)
- glutamate is what is necessary for locomotion ⇒ serotonin, dopamine, NE will modulate how fast the activity is
dorsal spinocerebellar tract
receives proprioceptive information and where the limbs are in space
ventral spinocerebellar tract
afferent from CPGs and tells what the pattern of limb movement is
the cerebellum combines information on what 4 things?
- Current limb position
- Current motor pattern
- Intended motor commands
- Upcoming motor commands
what is the cerebellums role in locomotion?
the cerebellum fine tunes locomotion patterns and corrects errors
- Critical to adjust movements depending on the environmental situation/context you are in
how does Visuomotor coordination require the motor cortex?
subjects with motor cortex lesions can walk on simple surfaces just fine but deficits exist with complex, visuomotor tasks
- When stepping over an object (out of sight) its position relative to the limbs is kept in working memory
- The posterior parietal cortex is critical for this function
