Lecture 21 Flashcards
The nuceli form two distinct pathways
-direct
-indirect
Differentiate the direct and indirect pathways
Role of basal ganglia
-activated when motivated to do a movement and helps reinforce it
-through balance of direct and indirect pathways
Goal of describe the direct pathway
-acts to increase thalamus output to cerebral cortex
-“the accelerator”
Describe pathway of direct pathway
-cerberal cortex has excitatory inputs on the striatum
-striatum has inhibitory inputs on globus pallidus internus
-more inhibition from striatum to internus, reduces the inhibition of internus on the thalamus - two negatives make a positive (disinhibition- two inhibitions in a row)
-thalamus has more excitatory output on the cortex and net effect of increasing excitatory outputs from cortex
Describe different thalamus outputs with rest vs movement (direct pathway)
-at rest globus palidus internus and substantia nigra pars reticulata have high resting firing rates-> leads to inhibition and decreased thalamus outputs
-during movement -decreased outputs from internus and SNr-> greater outputs from thalamus
Goal of indirect pathway
-act to decrease thalamus output to cerebral cortex
-“the brake” reducing excitation on the cortex
Describe indirect pathway
-cortex has excitatory inputs on the striatum
-striarum has inhibitory inputs on globus pallidus externus which reduces the inhibition onto subthalamic nuceli leading to more excitation back onto globus palidus internus
-more inhibition from internus onto the thalamus reduces the excitatory inputs back to the cortex (net effect of decraesing outputs from cortex)
Describe the effect of dopamine
-direct and indirect pathways modulated buy dopamine
-striatal neurons for direct pathway are excited by dopamine
-straital cells for indirect pathway are inhibited by dopamine
-therfore dopamine= more accelerator, less brake
Possible functions of basal ganglia
-affect contra-lateral movements: receives ipsi input from thalamus and ipsi cortex- cortex controlling contra side
-“go” signal for internally-triggered movement: facilitates activity
-predictive control over movements:
1. adjusts correct tone of muscles/amplitude of movement
2.coordinates trunk movements with limb movements
Describe parkinsons disorder
-caused by degeneration of dopaminergic neurons in substantia nigra pars compacta (>85%): need to lose 85% to see physical symptoms, significant neuronal loss before symptoms emerge
-idiopathic presentation, unknown cause: genetic? envirnmental toxins? virus?
-affects adults 40-70years
-Progressive disorder
-iniatially unilateral, may progress bilateral
-affects contralateral side
Describe known causes for other non-ideopathic conditions with parkinsonisms
-trauma (e.g. boxers dementia)
-disease
-medication
-vascular damage from stroke
Explanation for parkinsons symptoms
-no domapine to striatum, get brake and gas at the same time, not having a faciliatory effect
-not enough gas, too much brake
Hallmark symptoms of PD
-bradykinesia- movements are slow in speed and small in amplitude e.g. even with blinking, speaking
-resting tremor- involuntary shaking at rest, disappears with iniation of movement e.g. with hand, fingers, jaw, feet/legs
-rigidity- stiffness caused by increase in muscle tone, rate and force indepedent- “lead pipe” or “cog-wheel” rigidity, feels like clicking through cog, jerking
-postural instability- sense of imbalance resulting in unsteady gait/balance (usually seen in later stages)
Describe other symptoms of PD
-stooped posture
-shuffling gait
-diminished arm swing while walking- loss of associated movements
-difficulty turning- with coordination of trunk and limb- loss of axial control
-freezing- often happens during teransitions e.g. iniation of gait or going through doorway (level of floor), sometimes can be overcome by external cues and sensory inputs e.g. lines on floor, auditory cues
-expressionless face- masked face
-micrographia- hand writting very small in amplitude and condensed, symptom of bradykinesia
Describe Hoehn and Yahn scale for assessing severity of PD symptoms
I- unilateral symptoms; no postural instability
II- bilateral symptoms; no postural instability
III- bilateral symptoms with postural instability
IV- considerably impaired walking or balance
V- wheelchair bound or walking only with assistance
