Transcript Reminding some Terminologies

Some Terminologies
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White matter : myelinated fibre tracts
Gray matter : areas of neuronal cell bodies
Tracts : collections of axons subserving
similar function or location in CNS
Nerves : peripheral axons
Nucleus : collection of neurons subserving
similar function in CNS – e.g., red nuclei
Ganglion : collection of neurons in CNS or
PNS – e.g., basal ganglia
Brain components
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Diencephalon
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
(Mesencephalon)
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
oblongata
Spinal cord
Brain Stem – ventral and lateral view
Midbrain, Pons, Medulla – dorsal
view
Brain Stem
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Similar to spinal cord but contains embedded nuclei
Controls automatic behaviors necessary for survival
e.g., Cardiovascular, respiratory, and digestive control centers
Associated with 10 of the 12 pairs of cranial nerves (olfactory and optics)
Does the same basic sensory and motor functions for the head
that the spinal cord does for the rest of the body
Reception and integration of all synaptic input from spinal cord
Relaying sensory information to cerebellum, thalamus, and to
different portions of the brainstem & arousal and activation of
cerebral cortex
Regulation of muscle reflexes involved with equilibrium and
posture
Role in sleep-wake cycle (maintenance of consciousness)
Plays a role in modulating the sense of pain
Reticular formation
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Core of the brainstem
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Receives and integrates the information
carried by most of the sensory, motor and
visceral pathways that pass through the brainstem
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Red nucleus – largest nucleus of the reticular formation;
red nuclei are relay nuclei for rubro-spinal tract
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Information is used in various reflexes - circulatory and
respiratory reflexes, coughing, swallowing
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Plays a role in modulating sensitivity of spinal reflexes and
regulating transmission of sensory information (esp. pain) into
ascending pathways
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Ascending fibres carry signals to arouse and activate the
cerebral cortex
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Reticular Activation System (RAS) - controls the overall degree
of cortical alertness
Reticular formation
Reticular Activation System (RAS):
• Controls the overall degree of cortical alertness => ability to direct attention
• Helps the cerebellum to regulate muscle tones & generate smooth movements
Three broad columns extending through the core of the brain stem
Has axon connections with hypothalamus, thalamus, cerebellum, and spinal cord
Basal Ganglia
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Masses of gray matter found deep within the
cortical white matter
Composed of three parts
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Caudate nucleus
The putamen and the globus pallidus
(The lentiform nuclei)
Fibers of internal capsule running between and
through caudate and lentiform nuclei
Basal Ganglia
Putamen
Globus Pallidus
The basal nucleii (ganglia) have an inhibitory role in motor control
Functions of Basal Ganglia
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Act by modifying ongoing activity in motor pathways
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Inhibit muscle tone (proper tone – balance the excitatory
and inhibitory inputs to motor neurons that innervate
skeletal muscle)
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Select and maintain purposeful motor activity while
suppressing unwanted patterns of movement
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Monitor and coordinate slow and sustained contractions,
especially those related to posture and support
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Regulate attention and cognition
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Control timing and switching
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Motor planning and learning
Connectivity
between
different sections
of the basal
ganglia
Two pathways
DIRECT
1. Direct:
♦ Inhibition of internal GP
so no longer keeps
thalamus from exciting
cortex
♦ Facilitate the ongoing action
Two pathways
2. Indirect:
♦ Causes subthalamus to
activate internal GP,
suppressing thalamic
activation
♦ Suppressing unwanted
movements
INDIRECT
Damage to Basal Ganglia
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Huntington’s disease - degeneration of the caudate nucleus
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Chorea - rapid, uncontrolled jerky movements
Parkinson’s disease - damage to basal ganglia neurons and
a deficiency in dopamine
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Increased muscle tone or rigidity
Resting tremors
Slowness in initiating and carrying out motor behaviours
Parkinson’s Disease: A Motor Disorder
 Degeneration of DA neurons within the
substantia nigra (SN) which project to the striatum.
 Under normal circumstances these terminals convert
tyrosine to L-dopa which is synthesized to DA.
Loss of the pre-synaptic neurons results in DA release
 Possible to lose ~80% of DAergic cells in the SN without
manifesting symptoms
 Examination of a PD brain reveals loss of SN cells and
the presence of Lewy bodies in large numbers.
Parkinson’s Disease
• Loss of excitation from
substantia nigra to caudate &
putamen
• Results in increased activity in
indirect pathway
• Causes overactivity in the
internal GP
• Inhibits the thalamus resulting
in decreased cortical motor
activity
INDIRECT
Parkinsons’ Disease: symptoms
1.
Akinesia/Bradykinesia: poverty or slowness of
automatic and voluntary movements, incl. speech
2.
Rigidity: abnormal muscle tone consisting of stiffness
(poor range or motion), cogwheeling, spontaneous facial
movement
3.
Resting tremor: (4-7/sec freq.), referred to as “pill
rolling”; may lessen with intentional movement
4.
Postural instability: patients often unsteady, may carry
centre of gravity out front (falls); difficulty righting
5.
Gait disturbance: fixed, stooped posture and shuffling
gait
6.
Non-motor features may also occur
Disruption in writing as a result of
Parkinson's disease
Not only speed, but size of movement decreases
over time  micrographia
Parkinson’s Disease: Cognition
Symptoms
 Bradyphrenia: slowing of thought processes
 Memory, specifically retrieving info in nonstructured
situations/spatial working memory
 Emotional functioning: depression is common
 Decrease in executive functioning