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 Stem – ventral and lateral viewBrain Stem – ventral and lateral view

Midbrain, Pons, Medulla – Midbrain, Pons, Medulla – dorsal viewdorsal view

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

Basal GangliaBasal Ganglia

PutamenGlobus Pallidus

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

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 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