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Some TerminologiesSome Terminologies
White matterWhite matter : myelinated fibre tracts : myelinated fibre tracts Gray matterGray matter : areas of neuronal cell bodies : areas of neuronal cell bodies TractsTracts : collections of axons subserving : collections of axons subserving
similar function or location in CNSsimilar function or location in CNS NervesNerves : peripheral axons : peripheral axons NucleusNucleus : collection of neurons subserving : collection of neurons subserving
similar function in similar function in CNSCNS – e.g., red nuclei – e.g., red nuclei GanglionGanglion : collection of neurons in CNS or : collection of neurons in CNS or
PNSPNS – e.g., basal ganglia – e.g., basal ganglia
Hypothalamus
Brain stem
Cerebral cortex
Thalamus(medial)
Basal nuclei(lateral to thalamus)
Cerebellum
Spinal cord
Midbrain(Mesencephalon)
Pons
Medullaoblongata
Brain components
Cerebral cortex
Basal nuclei
Thalamus
Hypothalamus
Cerebellum
Brain stem(midbrain, pons,and medulla)
Diencephalon
Brain StemBrain Stem Similar to spinal cord but contains embedded nucleiSimilar to spinal cord but contains embedded nuclei Controls automatic behaviors necessary for survival Controls automatic behaviors necessary for survival e.g.,e.g., Cardiovascular, respiratory, and digestive control centersCardiovascular, respiratory, and digestive control centers
Associated with 10 of the 12 pairs of cranial nerves Associated with 10 of the 12 pairs of cranial nerves (olfactory and optics)(olfactory and optics)
Does the same basic sensory and motor functions for the head Does the same basic sensory and motor functions for the head that the spinal cord does for the rest of the bodythat the spinal cord does for the rest of the body
Reception and integration of all synaptic input from spinal cordReception and integration of all synaptic input from spinal cord Relaying sensory information to cerebellum, thalamus, and to Relaying sensory information to cerebellum, thalamus, and to
different portions of the brainstem & arousal and activation of different portions of the brainstem & arousal and activation of cerebral cortexcerebral cortex
Regulation of muscle reflexes involved with equilibrium and Regulation of muscle reflexes involved with equilibrium and postureposture
Role in sleep-wake cycle (maintenance of consciousness)Role in sleep-wake cycle (maintenance of consciousness) Plays a role in modulating the sense of painPlays a role in modulating the sense of pain
Reticular formationReticular formation Core of the brainstem Core of the brainstem
Receives and integrates the information Receives and integrates the information carried by most of the sensory, motor and carried by most of the sensory, motor and visceral pathways that pass through the brainstemvisceral pathways that pass through the brainstem
Red nucleus – largest nucleus of the reticular formation; Red nucleus – largest nucleus of the reticular formation; red nuclei are relay nuclei for rubro-spinal tractred nuclei are relay nuclei for rubro-spinal tract
Information is used in various reflexes - circulatory and Information is used in various reflexes - circulatory and respiratory reflexes, coughing, swallowingrespiratory reflexes, coughing, swallowing
Plays a role in modulating sensitivity of spinal reflexes and Plays a role in modulating sensitivity of spinal reflexes and regulating transmission of sensory information (esp. pain) into regulating transmission of sensory information (esp. pain) into ascending pathwaysascending pathways
Ascending fibres carry signals to arouse and activate the Ascending fibres carry signals to arouse and activate the cerebral cortexcerebral cortex
Reticular Activation SystemReticular Activation System (RAS) - controls the overall degree (RAS) - controls the overall degree of cortical alertnessof cortical alertness
Reticular formation Reticular formation Reticular Activation System (RAS):Reticular Activation System (RAS): • Controls the overall degree of cortical alertness Controls the overall degree of cortical alertness =>=> ability to direct attention ability to direct attention• Helps the cerebellum to regulate muscle tones & generate smooth movementsHelps 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 GangliaBasal Ganglia
Masses of gray matter found deep Masses of gray matter found deep within the cortical white matterwithin the cortical white matter
Composed of three partsComposed of three parts Caudate nucleusCaudate nucleus The putamen and the globus pallidus The putamen and the globus pallidus
(The lentiform nuclei)(The lentiform nuclei) Fibers of internal capsule running between Fibers of internal capsule running between
and through caudate and lentiform nucleiand through caudate and lentiform nuclei
The basal nucleii (ganglia) have an inhibitory role in motor controlThe basal nucleii (ganglia) have an inhibitory role in motor control
Act by modifying ongoing activity in motor pathwaysAct by modifying ongoing activity in motor pathways
Inhibit muscle tone (proper tone – balance the excitatory Inhibit muscle tone (proper tone – balance the excitatory and inhibitory inputs to motor neurons that innervate and inhibitory inputs to motor neurons that innervate skeletal muscle)skeletal muscle)
Select and maintain purposeful motor activity while Select and maintain purposeful motor activity while suppressing unwanted patterns of movementsuppressing unwanted patterns of movement
Monitor and coordinate slow and sustained contractions, Monitor and coordinate slow and sustained contractions, especially those related to posture and supportespecially those related to posture and support
Regulate attention and cognitionRegulate attention and cognition
Control timing and switchingControl timing and switching
Motor planning and learningMotor planning and learning
Functions of Basal GangliaFunctions of Basal Ganglia
Two pathways
1. Direct: ♦ Inhibition of internal GP so no longer keeps thalamus from exciting cortex ♦ Facilitate the ongoing action
DIRECT
Two pathways
2. Indirect: ♦ Causes subthalamus to activate internal GP, suppressing thalamic activation ♦ Suppressing unwanted movements
INDIRECT
Huntington’s diseaseHuntington’s disease - degeneration of the- degeneration of the caudate nucleuscaudate nucleus Chorea - rapid, uncontrolled jerky movementsChorea - rapid, uncontrolled jerky movements
Parkinson’s diseaseParkinson’s disease - - damage to basal ganglia neurons and damage to basal ganglia neurons and a deficiency ina deficiency in dopaminedopamine Increased muscle tone or rigidityIncreased muscle tone or rigidity Resting tremors Resting tremors Slowness in initiating and carrying out motor behavioursSlowness in initiating and carrying out motor behaviours
Damage to Basal Ganglia
Parkinson’s Disease: A Motor Disorder
Degeneration of DA neurons within theDegeneration of DA neurons within the substantia nigra (SN) which project to the striatum. substantia nigra (SN) which project to the striatum.
Under normal circumstances these terminals convertUnder normal circumstances these terminals convert tyrosine to L-dopa which is synthesized to DA. tyrosine to L-dopa which is synthesized to DA. Loss of the pre-synaptic neurons results in Loss of the pre-synaptic neurons results in DA releaseDA release
Possible to lose ~80% of DAergic cells in the SN withoutPossible to lose ~80% of DAergic cells in the SN without manifesting symptoms manifesting symptoms
Examination of a PD brain reveals loss of SN cells andExamination of a PD brain reveals loss of SN cells and the presence of Lewy bodies in large numbers. 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
SymptomsSymptoms
Bradyphrenia: slowing of thought processesBradyphrenia: slowing of thought processes
Memory, specifically retrieving info in nonstructuredMemory, specifically retrieving info in nonstructured situations/spatial working memory situations/spatial working memory
Emotional functioning: depression is commonEmotional functioning: depression is common
Decrease in executive functioningDecrease in executive functioning