Lec 4: Basal Ganglia Flashcards
Components of Basal Ganglia
- Caudate (striatum)
- Putamen (striatum & lenticular nucleus)
- Globus Pallidus (lenticular nucleus)
- Subthalamic nucleus
- Substantial Nigra
Basal Ganglia Circuitry
-BG are collection of grey matter nuclei
-caudate and putamen are separated by penetrating fibers of the internal capsule but remain joined by cellular bridges
-within BG= complex excitatory and inhibitory connections utilizing different neurotransmitters
BG involvement in motor control
-hyperkinetic
-hypokinetic
-eye movement
-associative function (Cognitive)
-limbic (emotion and memory)
Functions of BG
- Initiates and integrates behavior and movement
- Integrates executive functions, emotion, and motor activity
- Removes unwanted and inappropriate movement
- Plans motor activity
- Associations with attention, time estimation
- Regulates motor habits (functional activities)
- “Rewards and Motivation”
BG Influences & Medial Motor Systems
-Cortex influences BG directly
-BG influences the cortex via the thalamus
-Influences the motor system through the spinal cord pathway
-Medial motor systems terminate on interneurons that project to both side of the spinal cord
Overview of Motor Pathways
- Skilled movements arise from motor cortex via corticospinal tracts and brain stem
- Selection/ Initiation of motor programs from basal ganglia to thalamus and basal ganglia to brain stem, respectively
- BG circuitry to the brain stem via:
-reticulospinal tract (maintains tone, balance, & posture)
-vestibulospinal tract (position of the limbs and head; supporting posture and maintaining balance)
-rubrospinal tract: red nucleus to cerebellum - Spinal cord (central pattern generation, muscle movement, sensory receptors, reflexes)
- Cerebellum
BG Common Pathways for Motor System
Cortical input begins in striatum (putamen)
-SN provides dopamine to promote BG -function (striatum)
Direct vs Indirect Pathways:
1. Direct: Striatum —in.—GPi—in.—Thalamus—ex.—to cortex
2. Indirect: Striatum—in. & ex.—GPe—-in.—STN—ex.—GPi—in.—to cortex
Changing Viewpoint of Basal Ganglia and Motor Function
-intimately connected with cortex through parallel loops
-loops subdivided into: Motor, Associate (cognition), and Limbic
-dysfunction with BG and it’s connectivity can lead to… movement disorders (dyskinesias): Akinesia, Bradykinesia, Hyperkinesia
BG outputs, inputs, neurotransmitters, and parallel loops
Outputs: Limbic, Thalamus, Midbrain
Inputs: Cerebral cortex, Limbic
Neurotransmitters: Dopamine, Glutamate
Parallel Loops: Cognitive (associative), Voluntary, Emotional
Motor Functions of BG
involved in both preparation and execution of movements, motor control, & learning of motor sequences and habit (implicit learning)
Pathologies characterized by non-motor loops
Emotional, cognitive, and psychiatric deficits: OCD, Tourette’s, and Attention Deficit Disorders
BG & Perceptual Motor Decision Making
Interpreting sensory information from the environment and making motor decisions:
Turning= planning of cervical and trunk rotation, changing angles of hip rotation, while anticipating environmental disruptions
e.g. PD pt: slow, small and narrow steps, en bloc
Non motor loops of BG
(inputs to BG)
- Prefrontal Loop: connection from prefrontal cortex for initiation and selection of motor activities
- Limbic Loop:
connection from limbic system (hippocampus, amygdala, anterior cingulate) influences motor output
Indirect vs Direct Pathway Dysfunction
- Damage in direct pathway: more inhibition of cortex (under-stimulation) = rigidity & bradykinesia
e.g. Parkinson’s (loss of automatic movement ) - Damage in indirect pathway: less inhibition of cortex (over-stimulation) = chorea and other involuntary movements
e.g. Huntington’s
Basal Ganglia Pathology: Movement Speed
Slow —> Fast
1. Bradykinesia, hypokinesia
2. Rigidity
3. Dystonia
4. Athetosis
5. Chorea
6. Ballismus
7. Tics
8. Myoclonus
9. Tremor
Bradykinesia Definition
-Loss of function: neurotransmitter dopamine
-Loss of (-) pathways from striatum
-Loss of automatic mvmt
Dystonia Definition
-Abnormal twisted positions
- Generalized, focal, unilateral
-Focus torticollis
-No exact focal lesion found
Athetosis Definition
-Writhing
-twisting of the limbs, face, and trunk
-Seen in Huntington’s, perinatala anoxia, kernicterus (infant jaundice untreated)
Chorea Definition
-“dance” , “break dancing”
-continuous involuntary movement
-jerk, constantly varying quality
-increases with ambulation
Ballistic Definition
-flinging with large amplitude
-Hemiballismus: unilateral flinging contralateral to BG lesion
-classic cause is infarct of subthalamic nucleus
Tics Definition
-Tourette’s Syndrome
-4X more in girls than boys
-increased in ADHD
-symptoms wax and wane
Tremors Definition
-Both agonist and antagonist involved
-bidirection movement
-asymmetrical (e.g. pinrolling tremor with PD)
Resting tremor: common in PD, postural tremor vs intentional tremor
Rigidity
-Normal stretch reflexes, shoulders and cervical spine first affected, prolonged results in contracture
-Lead pipe rigidity: continuous throughout, agonist and antagonist
-Cogwheel rigidity: ratchet like interruptions as the limb is passively moved
Parkinson’s Disease
-loss of dopaminergic production in substantia nigra
-Festinating gait= shuffling and slow, difficult to initiate
-Difficulty turning corners (shortened stride length), changing directions
-Gait impediments coincide with visual, decision making and motor control deficits
-Freeze with impediments: doorways, items in their immediate path
-Tremors: resting
-Classic posture: stooped forward
Origination of Gait
-Located in brainstem and descending to SC
-Descending pathways originate in Mesencephalic Locomotor Region (MLR) and lateral hypothalamus
-areas project to neurons in pons and medulla, which project themselves t/o SC to activate CPG’s for locomotion
-Reticular formation tract in pons plays an improtant role in inducing locomotion
Current concepts of PD: Connections to midbrain and SC
-MLR region of brainstem is implicated in control of gait and balance in humans
-Dysfunction of cholinergic neurons of pedunculopontine nucleus (PPN), located in MLR: plays imp. role in appearance of axial symptoms in PD
-stimulating structures considered to be part of MLR alleviates locomotor symptoms of patients with PD
Additional BG Diseases
- Brain anoxia that causes choreoathetosis (dyskinetic CP)
-common prior to 1970 brain anoxia - Genetics (Huntington’s)
- Stroke (Hemiballismus)
Movement Problems in BG: Umbrella term of Dyskinesias
- Choreoathetosis CP (child)
- Hemiballismus (stroke)
- Huntington’s Disease
Where movement occurs
1.Preplanning= prefrontal cortex
2. Preparation of mvmt= Premotor cortex (motor units, firing, and rate)
3. Initiation, Selection, Memory, Emotion= Basal Ganglia
4. Activation= Primary Motor Cortex
