L6 Cerebellum and Basal Ganglia Flashcards
What is the role of the basal ganglia?
regulate the activity of the upper motor neurons DIRECTLY. This INDIRECTLY influences lower motor neurons
looks at a motor task and decides if that plan should be reinforced or inhibited
helps select the most appropriate motor action
Striatum is responsible for…
input
receives input related to movement, plays a role in coordinating motor activities
Pallidum is responsible for
output
processes movement signals and contributes to motor control
output goes through VA/VL thalamus back to cortex
Substantia Nigra Pars Compacta and Subthalamic Nucleus
provide input to striatum and pallidum, influencing their functions
Medium spiny neurons
found in the striatum
play a crucial role in processing of neural signals related to motor and cognitive functions
GABA neurons, inhibitory influence
modulated by dopamine from the substantia nigra, can also receive serotonin from raphe nuceli
Excitation of MSP
comes from the cortex (like frontal and parietal lobes)
these axons form the coticostriatal pathways and carry glutamate to the MSPs
When do medium spiny neurons become active?
- Firing is associated with occurrence of movement
- Can precede the movement, so anticipatory discharges
- May help with the decision to move, rather than direction or amplitude
- Increase firing at termination
What are the inputs to the basal ganglia?
Parietal and Frontal Cortex –> go to the striatum
Substantia nigra pars compacta –> go to striatum, using dopamine
(also intralaminar nuclei use glutamate to striatum)
Striatum is made up of
caudate
putamen
(nucelus accumbens)
Outputs of basal ganglia
- Substantia nigra pars reticulata –> superior colliculus (head and neck)
- Globus pallidus internal –> VA/VL –> frontal cortex (rest of body)
- Globus pallidus external –> subtahalmic nuclei –> GPi –> Va’VL –> frontal cortex
Example: Eyes fixating on visual target
Tonic inhibition from SnPr
Medium spiny neurons inhibit SnPr via GABA, this disinhibits UMNs of superior colliculus and allows saccades to happen
Direct pathway
Provides means for basal ganglia to facilitate the initiation of voluntary movement
Substantia nigra pars compact –> (+) caudate putamen –> (-) globus pallidus –> (-) VA/VL –> (+) frontal cortex
Indirect pathway
modulates the disinhibitory actions of the direct pathway
Substantia nigra pars compact –> (-) caudate putamen –> (-) globus pallidus external –> (-) subthalamic nucleus –> (+) Globus pallidus internal –> (-) VA/VL –> (+) frontal cortex
Indirect and direct pathways faciliatate
selection of a motor program and suppress competing motor programs that could interfere with the expression of sensory driven or goal oriented behavior
Dopamine Modulates Basal Ganglia
SnPc contains dopamine
dopamine interacts with the medium spiny neurons, the effect is dependent on what kind of receptor the dopamine goes to
D1 Receptors
enhance the excitatory input from the cortex
enhances the direct pathway
D2 Receptors
suppresses the excitation from the cortex
involved with the indirect pathway, helps to decrease the excitation that occurs on the frontal cortex
Parkinson’s disease
second most common degenerative disease of NS
causes a breakdown of the substantia nigra pars compacta
lack of dopamine inputs, making it more difficult to generate the transient inhibition from the striatum
causes the direct pathway to increase or sustain the inhibition to the globus pallidus, making thalamic exicitation of the motor cortex less likely
Huntington’s Disease
The striatum size is dramatically reduced
the projection from the striatum to the globus pallidus external is dimished
increases the tonic inhibition from the globus pallidus (indirect pathway), making the inhibitory pathway less effective, causing increased excitation of the cortex
unwanted motor activity
Prefrontal loops of BG
may regulate the initiation and termination of cognitive processes like planning, short term memory, and attention
Limbic loop of BG
may regulate emotional and motivated behavior, as well as the transitions from one state to another
Role of the cerebellum
Critical for prediction and improvement
Does not act directly on LMNs, but regulate UMNs
Copy of the motor command goes to the cerebeullum, and then it can send back the expected sensory feedback
also communicates with the inferior olives, which send back errors to the cerebellum
Cerebrocerebellum
receives input from much of the cortex
regulation of highly skilled movements
Spinocerebellum
receives input directly from the SC
concerned with movements of proximal muscles and some eye movements
Vestibulocerebellum
flocculus and nodules
receives input from the vestibular nuclei, does VOR and movements that help maintain posture/equilibrium
Cortical Projections to the Cerebellum
Most comes from the cortex –> inspilateral pontine nuclei –> contralateral cerebellum via middle cerebellar peduncle
Sensory Projections to Cerebellum
- Vestibular axons from pons and medulla, which go to the vestibulocerebellum
- Clarkes nucleus and ex. cunneate nucleus carry proprioceptive info to the spinocerebellum
- Face info comes from trigeminal nucleus, to spinocerebellum
Entire cerebellum receives…
modulatory inputs from the inferior olivary nucleus
plays an important role in learning and memory functions
Outputs from the cerebellum
- Cerebellar cortex –> DCN –> UMNs
- Dentate nucleus –> premotor and association cortex, doing planning of movements
- Red nucleus to inferior olive, helps to provide feedback on major inputs
Cerebrocerebellum nucli and peduncles
Dentate nucleus
Superior and middle peduncle
Spinocerebellum nuclei and peduncle
Interposed nuceli
Inferior peduncle
Vestibulocerebellum nuclei and peduncle
Fastigial nucleus
Inferior peduncle
Ultimate destination of inputs (afferent pathways)
Purkinje cell
The largest of the afferent pathways
arises in cerebral cortex and terminates in the pontine nuclei of basal pons. Then, the pons will project to the cerebellum
Mossy fibers
axons that are coming from the pontine nuclei to provide input to the cerebellum
they will send fibers that synapse in the deep cerebellar nuclei and granule cells
Parallel Fibers
come from granule cells
ascend the cerebellar cortex, will bifurcate to form T shaped branches
they will then form excitatory synapses with purkinje cells
Purkinje Cell
their orientation allows for them to receive input from lots of parallel fiber
also receives input from climbing fibers, which modulate their connection to parallel fibers
Purkinje Cells and output
project to deep cerebellar nuclei
they use GABA, so the output is inhibitory, manage the climbing and mossy fiber’s outputs onto the DCN
Purkinje Cells and DCN
recognize potential errors by comparing patterns of activity
DCN will send the corrective signal to the UMNs
Hallmark of individuals with cerebellar damage
difficulty producing smooth, well-coordinated, multi-jointed movements
Movement disorders associated with the cerebellum
Cerebellar ataxia
Nystagmus
Dysdiadochokinesia
Dysmetria
Intention tremors
Dysdiadochokinesia
difficulty with rapid alternating movements
Dysmetria
over or underreaching
Attention
allocation of neural resources to the analysis of particular information at the expense of resources that might have been allocated to other concurrent info
Cocktail party effect–listener can attend to one voice in a noisy conversation and tune out other signals
Endogenous attention
consciously direct attention to a particular aspect of the environment
Exogenous attention
involuntary refers to the situation in which an unexpected noise, flash of light, movement, and or other salient stimulus causes a shift in focus
Hemispatial neglect
right parietal, superior temporal, right frontal brain damage
leads to difficulty attending to the left side of visual space or left side of objects
R impact –> influences both hemispheres
L impact –> impacts the right
Declarative memory
storage and retrieval of material that is available to consciousness and can be expressed by language
daily episodes, words/meanings, history
EX: ability to remember a phone number, words to a song, or past event
Nondeclarative memory
referred to as procedural memory
Motor skills, associations, priming cues, puzzle solving skills
not available to consciousness, involve skills and associations that are acquired and retrieved at an unconscious level
EX: playing a piano, how to shoot a basketball
Immediate memory
ability of the brain to hold onto ongoing experience for a second or so
Short term memory
ability to hold and manipulate info in the mind for seconds to minutes while it is being used to achieve a particular goal (working memory)
searching for an object
Long-term memory
retaining information in a more permanent form of storage for days, weeks, lifetime.
immediate and short term can enter into long term by conscious or unconcious practice
Consolidation
the progressive stabilization of memories that follows the initial encoding of memory traces
Involves changes in gene expression, protein synthesis, and other mechanisms of synaptic plasticity that allow the persistence of memories at the cellular level
Priming
the change in the processing of a stimulus due to a previous encounter with the same or a related stimulus with or without conscious awareness of the original encounter
not very reliable because it can be influenced by associations and biases
importance = shows info previously presented will always be influential, even without awareness
Capacity of memory…
depends on what the info in question means to the individual and how readily it can be associated with info that is already stored
motivation also helps
Conditioned learning
novel response that is gradually elicited by repeatedly pairing a novel stimulus with the stimulus that usually produces the response
classical and operant
Classical conditioning
Pavlovs dog
innate reflex is modified by associating its normal trigger with an unrealted stimulus, the unrelated stimulus eventually triggers the original response
Operant conditioning
learning a behavior is strengthened or weakened by the consequences that follow it
learned behaviors can also disapper if the reward is not given
Forgetting
we forget information to help us to be not overburdened by information
Anterograde amnesia
inability to establish new memories following neurologic injury
Retrograde amnesia
difficulty retrieving memories established prior to the neurologic injury
Declarative Memories and Hippocampus
we use the hippocampus to encode and initiate the consolidation of memories of events, creating long term memories
rats swimming–> they were able to find the submerged platform after learning the visual stimuli
Long Term Storage of Declarative
transferring information from short-term memory to long-term memory, known as memory consolidation, involves the hippocampus
as memories become more stable and well-established, they are gradually distributed to other parts of the neocortex for long-term storage. This process is often referred to as system-level consolidation.
Acquisition and storage of declarative information
Short term memory –> hippocampus
Long Term –> cortical sites including Wernickes, temporal cortex
Acquisition and storage of non-declarative information
Short-term memory: sites unknown
Long Term: cerebellum, basal ganglia, premotor cortex, motor behavior sites
Memory and Aging
Average weight of normal human brain decreases from early adulthood onward
synapse # decreases in cerebral cortex
networks of connection representing memories gradually deteriorate
