Some TerminologiesSome Terminologies

• 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., caudate nucleus, red nuclei• Brainstem: Midbrain (Mesencephalon) + Pons +

Medulla Oblongata

• Folia : LeavesFolia : Leaves• Vermis: WormVermis: Worm

Table 5.3 (1)Page 144

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain(Mesencephalon)

Pons

Medullaoblongata

Brain componentsBrain components

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

Diencephalon

The CerebellumThe Cerebellum

• Located dorsal to the pons and medulla

• Makes up 11% of the brain’s mass

• Cerebellar activity occurs subconsciously

• Provides precise timing and appropriate patterns of skeletal muscle contraction Programming ballistic movements

• Acts as comparator for movementsComparing intended and actual movement

• Correction of ongoing movements Internal & external feedback

Deviations from intended movement • Motor learning

Shift from conscious ---> unconscious

Anatomy of the CerebellumAnatomy of the Cerebellum

2 symmetrical hemispheres connected medially by the Vermis

Folia: Transversely oriented gyri

3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN)

Neural arrangement: Gray matter (Cortex), White matter (Internal), Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial

Arbor vitae (tree of life): distinctive treelike pattern of the white matter

FoliumFolium

CerebellumCerebellum

Regulation of muscle tone,coordination of skilled voluntary movement

Planning and initiation of voluntary activity

Maintenance of balance, control of eye movements

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Anterior Lobe

Posterior Lobe

Flocculo-Nodular Lobe (FN lobe)

Folia

Primary fissure

CerebellumCerebellum

Lateral part

Intermediate part

Cerebellum:Cerebellum: the Structure the StructureInputs to the cerebellar cortex:Inputs to the cerebellar cortex: Climbing fibers Climbing fibers && Mossy fibers Mossy fibersClimbing fibers:Climbing fibers: originate in the inferior olive of the medulla originate in the inferior olive of the medullaMossy fibers:Mossy fibers: originate in all the cerebellar afferent tracts apart from inferior olive originate in all the cerebellar afferent tracts apart from inferior olivePurkinje cells:Purkinje cells: The The finalfinal output of the cerebellar cortex output of the cerebellar cortex

3 Layered 3 Layered CerebellarCerebellarCortexCortex

Climbing fibers:Climbing fibers: excite the Purkinje cells excite the Purkinje cells Mossy fibers:Mossy fibers: excite the granule cells excite the granule cells Granule cells:Granule cells: make excitatory contact with the Purkinje cells make excitatory contact with the Purkinje cellsPurkinje cells:Purkinje cells: Tonic Tonic inhibitioninhibition on the activity of the neurons of the cerebellar nuclei on the activity of the neurons of the cerebellar nuclei =>=> All excitatory inputs will be converted to the inhibition All excitatory inputs will be converted to the inhibition =>=> Removing the excitatory influence of the cerebellar inputs ( Removing the excitatory influence of the cerebellar inputs (erasingerasing))

Cerebellum:Cerebellum: 3 layered cortex 3 layered cortex

Cerebellar PedunclesCerebellar PedunclesThree paired fiber tracts connect the cerebellum to the brainstem:

♦ Superior peduncles connect the cerebellum to the midbrain;

♦ Middle peduncles connect the cerebellum to the pons and to the axis of the brainstem;

♦ Inferior peduncles connect the cerebellum to the medulla.

CerebellarPeduncles

Cerebellar PedunclesCerebellar Peduncles

Superior peduncles (to the midbrain):

Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus)

Middle peduncles (to the pons):

Cerebellum receives information advising it of voluntary motor activities initiated by motor cortex

Inferior peduncles (to the medulla):

Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord)

Cerebellar InputCerebellar Input

Inputs to cerebellum from spinocerebellar tracts have a somatotopic organization.

2 maps of body Primary fissure

Signals from the motor cortex, which is also arranged somatotopically,project to corresponding points in the sensory maps of the cerebellum.

Cerebellar InputsCerebellar InputsVermis Receives input from spinal cord regarding somatosensory and kinesthetic information (intrinsic knowledge of the position of the limbs) Damage leads to difficulty with postural adjustments (cerebellar ataxia)

Intermediate Zone Receives input from the red nucleus and somatosensory information from the spinal cord Damage results in rigidity & difficulty in moving limbs

Lateral Zone Receives input from the motor and association cortices through the pons Projects to the dentate nucleus, which projects back to primary and premotor cortex Damage leads to 4 types of deficits:

- Ballistic movements (cerebellar ataxia) - Coordination of multi-joint movement (lack of coordination: asynergia) - Muscle learning (loss of muscle tone: hypotonia) - Movement timing

Outputs of the CerebellumOutputs of the Cerebellum

Dentate nuclei: project contralaterally through the superior cerebellar peduncle to neurons in the contralateral thalamus & from thalamus to motor cortexFunc.: influence planning and initiation of voluntary movement

Emboliform & Globose nuclei: project mainly to the contralateral red nuclei & a small group is projected to the motor cortex Red Nuclei Rubrospinal Tract control of proximal limb muscles

Fastigial nuclei: project to the vestibular nuclei & to the pontine and medullary reticular formation Vestibulospinal & Reticulospinal tracts

Cerebellar nuclei: dentate, globose, emboliform, fastigial

Inputs and outputs of the CerebellumInputs and outputs of the Cerebellum

Clinical Findings and Localization of Cerebellar LesionsClinical Findings and Localization of Cerebellar Lesions

AtaxiaAtaxia refers to disordered contractions of agonist and antagonist refers to disordered contractions of agonist and antagonistmuscles and lack of coordination between movements at muscles and lack of coordination between movements at different joints typically seen in patients with cerebellar lesions.different joints typically seen in patients with cerebellar lesions.

Normal movements require coordination of agonist and antagonistNormal movements require coordination of agonist and antagonistmuscles at different joints in order for movement to have muscles at different joints in order for movement to have

smoothsmoothtrajectory.trajectory.

In ataxia movements have irregular, wavering In ataxia movements have irregular, wavering course consisting of continuous course consisting of continuous overshooting, overcorrecting and overshooting, overcorrecting and then overshooting then overshooting

again around the intended trajectory.again around the intended trajectory.

Dysmetria =Dysmetria = abnormal undershoot or overshoot abnormal undershoot or overshoot during movements toward a target during movements toward a target (finger-nose-finger test).(finger-nose-finger test).

Cerebellum and Motor LearningCerebellum and Motor Learning

• Deficits in learning complex motor tasks after cerebellar lesions

• fMRI studies : cerebellum active during learning of novel movements

• Postulated that cerebellar nuclei store certain motor memories

• May be involved in cognitive functions

Cerebellum: Control of Voluntary MovementCerebellum: Control of Voluntary Movement

Information sources: lesions & damages & experimental stimulation of cerebellar nuclei

Primary function: 1. To supplement & correlate the activities of other motor areas2. Control of posture 3. Correction of rapid movements initiated by cerebral cortex4. Motor learning

Frequency of nerve impulses in the climbing fibers almost doubles when a monkey learns a new task

Movement Control:a. Inputs from motor cortex inform the cerebellum of an intended

movement before it is initiatedb. Sensory information is then received via the

spinocerebellar tractc. An error signal is generated and is fed back to the cortex

Cerebellum has no direct connection to the spinal motoneurons (indirect effect).

Cerebellar ProcessingCerebellar Processing• Cerebellum receives impulses of the intent Cerebellum receives impulses of the intent

to initiate voluntary muscle contractionto initiate voluntary muscle contraction• Proprioceptors and visual signals “inform” Proprioceptors and visual signals “inform”

the cerebellum of the body’s conditionthe cerebellum of the body’s condition• Cerebellar cortex calculates the best way Cerebellar cortex calculates the best way

to perform a movementto perform a movement• A “blueprint” of coordinated movement is A “blueprint” of coordinated movement is

sent to the cerebral motor cortexsent to the cerebral motor cortex

Cerebellar Cognitive FunctionCerebellar Cognitive Function• Plays a role in language and problem solvingPlays a role in language and problem solving• Recognizes and predicts sequences of eventsRecognizes and predicts sequences of events

DiencephalonDiencephalon

• Central core of the forebrainCentral core of the forebrain

• Consists of three paired structures – Consists of three paired structures – thalamus, hypothalamus, and epithalamusthalamus, hypothalamus, and epithalamus

• Encloses the third ventricleEncloses the third ventricle

Table 5.3 (1)Page 144

Hypothalamus

Thalamus(medial)

DiencephalonDiencephalon

ThalamusThalamus

Paired, egg-shaped masses that form the Paired, egg-shaped masses that form the superolateral walls of the third ventriclesuperolateral walls of the third ventricle

Contains four groups of nuclei : Contains four groups of nuclei : anterior, ventral, dorsal, and posterioranterior, ventral, dorsal, and posterior

Nuclei project and receive fibers from the Nuclei project and receive fibers from the cerebral cortexcerebral cortex

Table 5.3 (1)Page 144

Hypothalamus

Thalamus(medial)

Thalamus

Thalamic FunctionThalamic Function

• Afferent impulses from Afferent impulses from all sensesall senses converge and synapse in the thalamusconverge and synapse in the thalamus

• Impulses of similar function are sorted out, Impulses of similar function are sorted out, edited, and relayed as a groupedited, and relayed as a group

• All inputs ascending to the cerebral cortex All inputs ascending to the cerebral cortex pass through the thalamuspass through the thalamus

• Plays a key role in mediating sensation, Plays a key role in mediating sensation, motor activities, cortical arousal, learning, motor activities, cortical arousal, learning, and memoryand memory

Hypothalamic NucleiTable 5.3 (1)Page 144

Hypothalamus

Thalamus(medial)

Hypothalamic FunctionHypothalamic Function• Regulates blood pressure, rate and force of Regulates blood pressure, rate and force of

heartbeat, digestive tract motility, rate and depth heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activitiesof breathing, and many other visceral activities

• Is involved with perception of pleasure, fear, and Is involved with perception of pleasure, fear, and ragerage

• Controls mechanisms needed to maintain Controls mechanisms needed to maintain normal body temperaturenormal body temperature

• Regulates feelings of hunger and satiety Regulates feelings of hunger and satiety • Regulates sleep and the sleep cycleRegulates sleep and the sleep cycle• Endocrine Functions of the HypothalamusEndocrine Functions of the Hypothalamus

Frontallobe

Central sulcus

Parietallobe

Parietooccipitalnotch

Occipitallobe

Preoccipitalnotch

Temporallobe

Lateralfissure

The Cerebral CortexThe Cerebral Cortex

The cerebral cortexThe cerebral cortex• Cerebral Cortex : outer layer of gray matter Cerebral Cortex : outer layer of gray matter • It covers an inner core of white matter It covers an inner core of white matter • The gross structure has gyri and sulci The gross structure has gyri and sulci

Different Lobes:Different Lobes: Frontal :Frontal : voluntary motor activity, speaking ability, and voluntary motor activity, speaking ability, and

elaboration of thought; stimulation of different areas of its elaboration of thought; stimulation of different areas of its primary motor cortex moves different body regions, again primary motor cortex moves different body regions, again primarily on the opposite side of the body.primarily on the opposite side of the body.

Parietal :Parietal : somatosensory processing; each region of its cortex somatosensory processing; each region of its cortex receives somaesthetic and proprioceptive input from a specific receives somaesthetic and proprioceptive input from a specific body area, primarily from the opposite body side.body area, primarily from the opposite body side.

Temporal :Temporal : receives sound sensation receives sound sensation

Occipital :Occipital : initial processing of visual input initial processing of visual input

Supplementary motor area(programming of complex movement)

Primary motor cortex(Voluntary movement)

Centralsulcus

Somatosensory cortex(Somesthetic sensation and proprioception)

Posterior parietal cortex(integration of somatosensory and visual input)

Wernicke’s area(speech understanding)

Parietal lobe

Parietal-temporal-occipitalassociation cortex(integraton of all sensory input-imp in language)

Occipital lobe

Primary visual cortex

Temporal lobeLimbic association cortex(motivation, emotion, memory)

Primary auditory cortex

Broca’s area(speech formation)

Frontal lobe

Premotor cortex(coordination of complex movements)

Prefrontal association cortex(planning for voluntary activity; decision making;personality traits)

Parietal Lobe - Somatosensory cortexParietal Lobe - Somatosensory cortex

• Somesthetic sensationSomesthetic sensation - - sensations from the surface of the body - touch, pain, sensations from the surface of the body - touch, pain, pressure, heat and coldpressure, heat and cold

• This info is projected to the somatosensory cortex - site for initial cortical This info is projected to the somatosensory cortex - site for initial cortical processing and perception of somesthetic and proprioceptive input processing and perception of somesthetic and proprioceptive input

• Body regions are topographically mapped -Body regions are topographically mapped - sensory homunculussensory homunculus

• Sensory cortex - receives information from the opposite side of the bodySensory cortex - receives information from the opposite side of the body (e.g., damage on right side results in sensory loss on left side)(e.g., damage on right side results in sensory loss on left side)

• Simple awareness of touch, pressure, temp or pain is first detected by the Simple awareness of touch, pressure, temp or pain is first detected by the thalamus, but cortex is required for perception - intensity and spatial thalamus, but cortex is required for perception - intensity and spatial discriminationdiscrimination

• This info is then projected (via fibre tracts) to association cortices for analysis This info is then projected (via fibre tracts) to association cortices for analysis and integration of sensory information - eg., perception of texture, firmness, and integration of sensory information - eg., perception of texture, firmness, temp, shape, position, location of an object you are holding)temp, shape, position, location of an object you are holding)

Regions of the Regions of the cortex involved cortex involved in motor controlin motor control

Frontal lobe - Motor cortexFrontal lobe - Motor cortex

• Primary motor cortexPrimary motor cortex - voluntary control for muscle movement - voluntary control for muscle movement

• Motor cortex on each side controls muscles on the opposite side of Motor cortex on each side controls muscles on the opposite side of the bodythe body

• Tracts originating in the cortex cross (at level of pyramids) before Tracts originating in the cortex cross (at level of pyramids) before continuing down spinal cord to terminate on continuing down spinal cord to terminate on -motor neurons that -motor neurons that directly innervate skeletal muscledirectly innervate skeletal muscle

• Body regions are represented topographically - motor homunculusBody regions are represented topographically - motor homunculus

• Extent of representation in the motor cortex is proportional to the Extent of representation in the motor cortex is proportional to the precision and complexity of motor skills required precision and complexity of motor skills required

Other cerebral brain regions Other cerebral brain regions important for motor control important for motor control

Primary motor cortex does not initiate voluntary movement

Premotor cortex (M1)Premotor cortex (M1) anterior to the primary motor cortex acts in response to external cues must be informed of body’s position in relation to target

Supplementary motor area (SMA)Supplementary motor area (SMA) responds to internal cues plays a preparatory role in programming complex sequences of movement

Posterior parietal cortexPosterior parietal cortex It is posterior to the primary somatosensory cortexinforms premotor cortex of position

Temporal lobeTemporal lobe

• Contains auditory centres that receive sensory fibres from the cochlea of each ear

• Also involved in the interpretation and association of auditory and visual information

• Temporal lobe contains the hippocampus and the amygdala

• Involves in memory

Cortical Association areasCortical Association areas

• Prefrontal association cortexPrefrontal association cortexFunctions: planning for voluntary activity, decision-making, creativity, Functions: planning for voluntary activity, decision-making, creativity, and developing personality traits. and developing personality traits. – Site of operation of working memory - temporary storage and actively Site of operation of working memory - temporary storage and actively

manipulation of information used in reasoning and planningmanipulation of information used in reasoning and planning

• parietal-temporal-occipital association cortexparietal-temporal-occipital association cortex Integrates somatic, auditory, and visual sensations from three lobesIntegrates somatic, auditory, and visual sensations from three lobes

• limbic association cortexlimbic association cortex Being involved with motivation, emotion, and memory Being involved with motivation, emotion, and memory

The cerebral hemispheres The cerebral hemispheres lateralization/dominancelateralization/dominance

• Each cerebral hemisphere receives information from both sides of the body

• The left cerebral hemisphere excels in performing logical, analytical, sequential, and verbal tasks

Better at describing facial appearances

• The right cerebral hemisphere excels in spatial perception and artistic and musical talents

Better at recognizing faces

The limbic system The limbic system

• Refers to several forebrain structures that function together – Cingulate gyrus– Hippocampus– Amygdala– Septal nuclei

• Closed circuit of information flow between the limbic system and the thalamus and hypothalamus

• Limbic system and hypothalamus - cooperate in the neural basis of emotional states

Limbic System

Figure 12.18

Limbic systemLimbic system

Plays a key role in emotion and works with the higher Plays a key role in emotion and works with the higher cerebral cortex to control behavioral patterns.cerebral cortex to control behavioral patterns.

Aggression Aggression --> lesions of amygdala produce docility, while --> lesions of amygdala produce docility, while stimulation results in rage and aggression stimulation results in rage and aggression

FearFear --> stimulation of amygdala and hypothalamus can --> stimulation of amygdala and hypothalamus can produce fear, while ablation results in an absence of fearproduce fear, while ablation results in an absence of fear

Goal-directed behaviourGoal-directed behaviour - reward and punishment - reward and punishment system- stimulation of certain areas function as a reward, system- stimulation of certain areas function as a reward, while stimulation of other areas results in a punishment while stimulation of other areas results in a punishment shockshock