Some Terminologies White matter : myelinated fibre tracts White matter : myelinated fibre tracts Gray matter : areas of neuronal cell bodies Gray matter : areas of neuronal cell bodies Tracts : collections of axons subserving similar function or location in CNS Tracts : collections of axons subserving similar function or location in CNS Nerves : peripheral axons Nerves : peripheral axons Nucleus : collection of neurons subserving similar function in CNS – e.g., red nuclei 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 Ganglion : collection of neurons in CNS or PNS – e.g., basal ganglia

Hypothalamus Brain stem Cerebral cortex Thalamus (medial) Basal nuclei (lateral to thalamus) Cerebellum Spinal cord Midbrain (Mesencephalon) Pons Medulla oblongata Brain components Cerebral cortex Basal nuclei Thalamus Hypothalamus Cerebellum Brain stem (midbrain, pons, and medulla) Diencephalon

Brain Stem – ventral and lateral view

Midbrain, Pons, Medulla – dorsal view

Brain Stem Similar to spinal cord but contains embedded nuclei Similar to spinal cord but contains embedded nuclei Controls automatic behaviors necessary for survival e.g., Cardiovascular, respiratory, and digestive control centers 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 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 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 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 Regulation of muscle reflexes involved with equilibrium and posture Role in sleep-wake cycle (maintenance of consciousness) Role in sleep-wake cycle (maintenance of consciousness) Plays a role in modulating the sense of pain Plays a role in modulating the sense of pain

Reticular formation Core of the brainstem Core of the brainstem Receives and integrates the information carried by most of the sensory, motor and visceral pathways that pass through the brainstem Receives and integrates the information carried by most of the sensory, motor and visceral pathways that pass through the brainstem Red nucleus – largest nucleus of the reticular formation; red nuclei are relay nuclei for rubro-spinal tract Red nucleus – largest nucleus of the reticular formation; red nuclei are relay nuclei for rubro-spinal tract Information is used in various reflexes - circulatory and respiratory reflexes, coughing, swallowing Information is used in various reflexes - circulatory and respiratory reflexes, coughing, swallowing Plays a role in modulating sensitivity of spinal reflexes and regulating transmission of sensory information (esp. pain) into ascending pathways Plays a role in modulating sensitivity of spinal reflexes and regulating transmission of sensory information (esp. pain) into ascending pathways Ascending fibres carry signals to arouse and activate the cerebral cortex Ascending fibres carry signals to arouse and activate the cerebral cortex Reticular Activation System (RAS) - controls the overall degree of cortical alertness 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 Controls the overall degree of cortical alertness => ability to direct attention Helps the cerebellum to regulate muscle tones & generate smooth movements 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 Masses of gray matter found deep within the cortical white matter Masses of gray matter found deep within the cortical white matter Composed of three parts Composed of three parts Caudate nucleus Caudate nucleus The putamen and the globus pallidus (The lentiform nuclei) The putamen and the globus pallidus (The lentiform nuclei) Fibers of internal capsule running between and through caudate and 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

Act by modifying ongoing activity in motor pathways Act by modifying ongoing activity in motor pathways Inhibit muscle tone (proper tone – balance the excitatory and inhibitory inputs to motor neurons that innervate skeletal muscle) Inhibit muscle tone (proper tone – balance the excitatory and inhibitory inputs to motor neurons that innervate skeletal muscle) Select and maintain purposeful motor activity while suppressing unwanted patterns of movement Select and maintain purposeful motor activity while suppressing unwanted patterns of movement Monitor and coordinate slow and sustained contractions, especially those related to posture and support Monitor and coordinate slow and sustained contractions, especially those related to posture and support Regulate attention and cognition Regulate attention and cognition Control timing and switching Control timing and switching Motor planning and learning Motor planning and learning Functions of Basal Ganglia

Connectivity between different sections of the 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 disease - degeneration of the caudate nucleus Huntington’s disease - degeneration of the caudate nucleus Chorea - rapid, uncontrolled jerky movements Chorea - rapid, uncontrolled jerky movements Parkinson’s disease - damage to basal ganglia neurons and a deficiency in dopamine Parkinson’s disease - damage to basal ganglia neurons and a deficiency in dopamine Increased muscle tone or rigidity Increased muscle tone or rigidity Resting tremors Resting tremors Slowness in initiating and carrying out motor behaviours Slowness in initiating and carrying out motor behaviours Damage to Basal Ganglia

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