Nervous System Part 4 Flashcards
Motor structures found deep within the cerebral cortex (subcortical structures).
-Important for inhibitory and excitatory effects
-Complement the cerebral cortex in producing motor actions/activity
Basal Ganglia
Subcortical motor nuclei that are interconnected with the cerebral cortex, thalamus, and brainstem. All must work together in a coordinated fashion to produce normal movement.
Basal Ganglia
Consists of myelinated axons/fibers that originate up in motor areas of the cerebral cortex, which are funneled down into the brainstem.
-Also have fibers running from the thalamus projecting to the cerebral cortex.
Internal Capsule
Not a Basal Ganglia structure.
-Gives rise to the Rubro-spinal Tract Pathway
-Doesn’t function for very long in life. Very primitive.
-Goes to lower thoracic segments and goes away once we build up more prominent pathways
-Valuable to newborns and that’s it
Red Nucleus
Regulate movement along with the Cerebral Cortex
Automatic Action Motor Selection and Initiation:
-Help initiate a specific motor task (Ex: reaching and grabbing something)
-Integration of motor commands to perform the task. Have to have several systems together to carry out complete motor tasks.
Can be inhibitory (-) or excitatory (+).
Basal Ganglia
Excitatory impulses are initiated from the Cerebral Cortex onto the Caudate Nucleus and Putamen. Then, the Putamen exercises an excitatory control over the Globus Pallidus, which projects it up to the Thalamus and then the Cerebral Cortex.
The Cerebral Cortex can exert excitatory or inhibitory stimuli on the Putamen. (circular diagram).
-Inhibitory signals can follow this same pathway.
Motor System of the Basal Ganglia
Projects inhibitory signals to the Caudate Nuleus and the Putamen in exchange for them sending back down an excitatory impulse.
-Issues here = Dyskinesia (Parkinson’s)
Substantia Nigra
Projects an inhibitory signal to the Globus Pallidus in exchange for it sending back down an excitatory impulse.
-Issues here = Dyskinesia (Hemiballismus)
Subthalamic Nucleus
Muscles are firing at will all the time. Subtle form of writhing movements, or can be explosive limb movements.
Hemiballismus
Unwanted muscle activity because inhibition has been taken off of the basal ganglia and Excitatory signals are unmatched. Now have excitatory signals pouring into the nervous system and delivered out to the muscles to make them contract at unwanted times.
Dyskinesias (lesions in Substantia Nigra or Subthalamic nucleus)
Motor Cortex of Cerebral Cortex projects to cerebellum (via the Pons) and basal ganglia.
-Both cerebellum and basal ganglia send feedback via the Thalamus to the Motor Cortex.
-Cerebellum = Excitatory feedback
-Basal Ganglia = Inhibitory Feedback
Final output is determined by which system is dominating.
Basal Ganglia/Cerebellum Influence on the Cerebral Cortex
Loss of the substantia nigra or subthalamic nucleus loses our inhibitory feedback, making the whole cerebral cortex be fueled by excitatory impulses, causing dyskinesias
Loss of Basal Ganglia
Balance between these two opposing systems allows for smooth, coordinated movement to carry out functional tasks.
-Structures must be connected together in a normal fashion to share information with each other for muscles to work together without excessive dyskinetic movement
Basal Ganglia and Cerebellum
Problem with Basal Ganglia. Excessive movement
Dyskinesia
Problem with Cerebellum. Extraneous movement. Have intentional tremors: occur only when you’re trying to do something
-Ex: Friedrich’s Ataxia
-Results from dysfunction or failure of pathways to form properly that carry information from the spinal cord to the Cerebellum (Anterior lobe)
-Cerebellum cannot tell the Cerebral Cortex to contract muscles synergistically.
-Alcohol related (FAS)
Dysynergia
Alcohol use during the 1st trimester (during neural tube fomration)
-Negative effects on CNS & Cerebellum = dysynergia
-Small eye openings, smooth philtrum, thin upper lip
-Effects on CN development
Fetal Alcohol Syndrome
Congenital Condition that produces serious disordered movement patterns, enough that the person is disabled.
Swaying while walking (truncal ataxia) and widespread gait (limb ataxia). Dysynergia.
Friedrich’s Ataxia
S/Sx:
-Tremor, head bobbing, stooped posture, mask-like face, muscle rigidity (lead pipe), distal extremity tremor at rest (tremor goes away when trying to accomplish a task)
-Dyskinesia
Parkinson’s Disease
Inherited disorder in which basal ganglia (and cerebral cortex) undergo severe degeneration.
-Fatal, prolonged disease
-Every muscle is trying to contract at once in different directions - get flailing extremities and unsteady gait
Huntington’s Chorea
Coverings of the Brain and Spinal Cord.
A trilaminar sac (3 layers)
-Spinal and Cranial ___ are continuous with each other
-Protect CNS from Mechanical Injury
Meninges
Layer of meninges found just deep to the inner table of the skull.
-Very durable
-Thick, fibrous layer
Dura Mater
Layer of meninges deep to the Dura Mater.
-Spiderweb appearance
Arachnoid Mater