BASAL GANGLIALecturer: Dr. Eufemio Sobrevega

What are the Basal Ganglia?Deep Gray Matter of the Cerebrum

• Consists of:– Basal forebrain nuclei – associated with

memory– Basal ganglia – involved in motor control– Claustrum – a nucleus of unknown function

• Amygdala – located in cerebrum but is considered part of the of the limbic system

• A group of nuclei deep within the cerebral white matter

– Caudate nucleus – arches over the thalamus

– Lentiform nucleus – “lens shaped”• Together, these nuclei are called the CORPUS

STRATUM.• Lentiform nucleus

– Divided into two parts• Globus pallidus • Putamen

• Cooperate with the cerebral cortex in controlling movements

• Receive input from many cortical areas• Evidence shows that they:

– Start, stop, and regulate intensity of voluntary movements

– In some way estimate the passage of timeThe basal ganglia include…

• Neostriatum – Caudate nucleus– Putamen – Nucleus Accumbens

• Globus Pallidus – Internal segment– External segment– Ventral pallidum

• Subthalamic nucleus• Substantia nigra

– Pars compacta – Pars reticulata

• Pedunculopontine nucleus**Subgroups of the basal ganglia

• Striatum– Caudate nucleus– Putamen

• Lenticular nuclei

– Globus pallidus – Putamen

• Corpus striatum– Caudate– Lenticular nuclei

How are the basal ganglia arranged in the brain?

Caudate Nucleus• C shaped structure • Lateral wall of lateral ventricle• Head, body and tail of caudate

are parallel to anterior horn, body and inferior horn of the lateral ventriclePutamen and Globus Pallidus

• Putamen + Globus Pallidus = lentiform or lenticular nuclei

• Fills in space between the inferior horn and the anterior horn and body of the lateral ventricle.

• Gap between the lentiform nuclei and the lateral ventricle filled by the caudate nucleus.

• The posterior limb of the internal capsule separates the lentiform nuclei from the thalamus.

• Subthalamic nucleus• Substantia nigra • Ventral tegmental area

Functions of the Basal Ganglia• Extrapyramidal motor system• Motor planning, sequencing and learning• Striatal neuronal activity is not sufficiently explained

by the stimuli presented or the movements performed

• Dependent on certain behavioral situations, certain conditions or particularly types of trials

• -sensory stimuli but only when they elicit movements

• -instruction cues (go-no go)• -memory related cues• -reward (especially ventral

striatum)• -self-initiated moves

• Basal ganglia distinguished from cerebellum by connections with limbic system

Architecture of the basal ganglia: cellular and neurochemistry

• Main neurotransmitter in basal ganglia is GABA• 95% of neurons in neostriatum are medium spiny

neurons

– Contain GABA– Principal neurons: project to globus

pallidus and SNpr – Subpopulations are distinguished by

peptides, neurotransmitter receptors and connections

– Receive bulk of afferent input• Several populations of interneurons

– aspiny – ACh, somatostatin, GABA/parvalbumin

Diseases associated with basal ganglia dysfunction/pathology

Huntington’s and Parkinson’s diseases• Neurodegenerative diseases• Motor dysfunction• Brainwide pathology with focus on basal ganglia

elements• Genetic and/or environmental causes

Huntington’s DiseaseClinical symptoms

• Chorea, • Dementia

Pathology hallmarks• Striopallidal degeneration• Decreased striatal volume• Decrease in 5-HT1B receptors in ventral pallidum

Parkinson’s DiseaseClinical symptoms

• Tremors• Cogwheel rigidity• Slowed Movements

(Bradykinesia) Pathology hallmarks

• Nigostriatal degeneration• DA neuronal degeneration in SN

LUBAG: X Linked Dystonia of Panay

• Manifestations: dystonia, parkinsonism, • Affects only males• Usually manifests in the 3rd – 4th decade of life.• X-linked recessive• Patients usually comes from Panay Island,

Philippines.Basal Ganglia Disease

• Extrapyramidal Manifestations• Involuntary movements • EPS (Extrapyramidal Symptoms)

TREMORS

• Rhythmic, oscillatory movements of short amplitude which results from contraction small group of muscles.

• E.g. Tremors in Parkinson’s Disease:– Fine “pill rolling” tremors– Cogwheel Rigidity– Bradykinesia

CHOREA• Abrupt, jerky, unsustained, purposeless, assymetric,

spasmodic irregular of short duration involving the fingers, hands, arms, face, tongue or head.

• E.g. Huntington’s ChoreaSydenham’s Chorea: (rheumatic fever, post streptococcal

infection) ATHETOSIS

• Irregular, slow, snakelike, writhing movements usually involving the hands and fingers.

• E.g. In some forms of Cerebral Palsy DYSTONIA

• Similar to the twisting, turning movements of athetosis but involves the larger portions of the body (trunk, neck).

• E.g. Dystonia of Panay“Lubag”; Hereditary; X-linked RecessiveOnly males are affectedFemales are ‘carriers’

BALLISMUS• Characterized by abrupt onset of violent

flinging movements affecting the limbs, neck, and trunk, often on one side of the body.

• E.g. Wilson’s Disease: Hepatolenticular Degeneration;Abnormal Copper Metabolism;Kayser Fleicher ring in cornea of eyes

TIC• Repetetive, spasmodic movements that occur in an

irregular fashion and resemble volitional movements.

• E.g. Tourette Syndrome• Habit Spasm – Tic of long duration.

SENSORY RECEPTORS

• Sensory receptor is a part of a sensory neuron/cell that receives information from outside(environment) and relates it to central nervous system.

• SRO are activated when they are bent, squished, or disturb in some way. Others are activated by chemicals, temperature, or light.

• This is called STIMULUS.

How does the outside stimulus get transformed into nervous system signal?

• Whatever the appropriate stimulus is, that will cause a depolarization to occur in the sensory receptor organ.

• Any depolarization that is large enough in the dendrite itself will cause an action potential to be generated at the trigger zone.

• This AP will run all the way down the axon and enter the dorsal horn of the spinal cord.

How does the sensory activation stop?• 1- when the stimulus stops being applied• 2- after a while, we stop noticing the • stimulus- (Adaptation/Habituation-

means that they stop having a receptor potential after a while.)

4 Types of Skin

1- mucocutaneous- at the junction of mucous membranes, hairy skin, lip and tongue2- mucous membrane- lining the inside of

body orifices3- glabrous- skin without hair4- hairy- skin with hair

Anatomical Types

• Nonencapsulated – Free nerve endings– Merkel’s discs– Hair follicle receptors

• Encapsulated– Meissner’s corpuscles– Pacinian corpuscles– Ruffini’s corpuscles– Neuromuscular spindles

– Neurotendinous spindles

Functional Types

• Mechanoreceptors– Mechanical forces

• Thermoreceptors – Temperature

• Nociceptors – Tissue damage

• Electromagnetic receptors– Light intensity and wavelength

• Chemoreceptors – Taste, smell, oxygen, CO2

MechanoreceptorsSkin tactile sensibilities ( epidermis and dermis )

Free nerve endings Expanded tip endings

Merkel’s discs Spray endings Ruffini’s endings

Encapsulated endingsMeissner’s corpusclesKrause’s corpuscles

Hair end organs

Mechanoreceptors:Deep tissue sensibilities

Free nerve endings Expanded tip endings Spray endings Ruffini’s endings Encapsulated endings

Pacinian corpuscles Muscle endings

Muscles spindlesGolgi tendon receptors

Mechanoreceptors

Hearing Sound receptors of cochleaEquilibrium Vestibular receptorsArterial pressure Baroreceptors of carotid sinuses & aorta

Thermoreceptors

1. Cold Cold receptors2. Warmth Warmth receptors

Nociceptors

1. Pain Free nerve endings

Electromagnetic receptors

Vision Rods Cones

Chemoreceptors

1. TasteReceptors of taste buds

2. SmellReceptors of olfactory epithelium

3. Arterial oxygen Receptors of aortic & carotid bodies

4. Osmolality Neurons in or near supraoptic nuclei

5. Blood CO2 Receptors in or on surface of medulla & in aortic and carotid bodies

6. Blood glucose, AA, fatty acids Receptors in hypothalamus

Hair Follicle Ending• A-beta• Responds to hair displacement.• Wraps around hair follicle in,

of course, hairy skin.

Ruffini’s ending• A-beta• Responds to pressure on skin.• Dermis of both hairy and glabrous skin.

Krause Corpuscles• A-beta• Responds to pressure.• Lips, tongue, and genitals.

Pacinian Corpuscles• A-beta• Responds to vibration.• Most sensitive in 150-300 Hz range• Deep layers of dermis in both hairy and glabrous

skin.

Meissner Corpuscle• A-betaResponds to vibration. • Most sensitive in 20-40 Hz range• Dermis of glabrous skin.

Free Nerve Ending• A-delta and C• Different types of free nerve endings that respond

to mechanical, thermal or noxious stimulation. • Various types are found throughout the skin.

Merkel’s Discs• A-beta• Responds to pressure of the skin.• Epidermis of glabrous skin.

Joint Receptors Function: provide the CNS with information

regarding the position and movements of the joint.

• 1- neuromuscular spindles/muscular spindles:– found in skeletal muscles – are numerous toward the tendinous

attachment of the muscle.– concerned with muscle length & rate of

change in muscle length necessary for control of muscle activity.

• 2- neurotendinous spindles • (Golgi tendon organ): • provide the CNS w/ information regarding the

tension of muscles.• present in tendons & located near the junctions of

tendons w/ muscles.

Receptor Associated Function

Free nerve endings Pain, touch,pressure, ?cold & heat

Merkel’s disc Touch and pressure

Hair follicle receptor Touch

Meissner’s corpuscles Touch(2-pt discrimination)

Pacinian corpuscles Pressure and vibration

Ruffini’s corpuscles Stretch

Neuromuscular spindles

Elongation of muscles (stretch)

Neurotendinous spindles

Tension

Comparison of Receptor Types

Receptor Location Stimulus Sensory Modality

Free nerve endings

Epidermis, cornea, gut, dermis, ligaments, joint capsules, bone, dental pulp

Mechanoreceptor

Fast & slow pain, crude touch, pressure

Merkel’s discs Hairless skin

Mechanoreceptor

Touch

Hair follicle receptors

Hairy skin Mechanoreceptor

Touch

Meissner’s corpuscles

Dermal papilla of skin of arms & sole foot, nipples

Mechanoreceptor

Touch

Pacinian corpuscles

Dermis, ligaments, joint capsules, peritoneum, pleura,

Mechanoreceptor

Vibration

external genitalia

Ruffini’s corpuscles

Dermis of hairy skin

Mechanoreceptor

Stretch

Neuromuscular spindles

Skeletal muscle

Mechanoreceptor

Stretch-muscle length

Neurotendinous spindles

Tendons Mechanoreceptor

Compression-muscle tension

MOTOR PATHWAYSLecturer: Dr. Eufemio Sobrevega

Functional organization of the nervous system

The cerebral cortex...• controls the spinal neurons along two pathways,

the corticobulbar tract and the corticospinal tract. • The corticospinal tract control spinal motor

neurons either directly or indirectly, i.e. via brain stem pathways.

• One third of the about 1 million axons of the corticospinal tract originate from area 4, area 6, and areas 1+2+3 each.

• About ¾ of corticospinal fibres cross the midline in the pyramidal decussation at the junction of the medulla and the spinal cord.

• CORTICOSPINAL TRACT• PYRAMIDAL TRACT• EFFERENT PATHWAYS

Motor Neurons 2 motor neurons:

Upper motor neuron cell body is in the CNS may facilitate or inhibit LMN

Lower motor neuron cell body is in brainstem or spinal

cord activation triggers muscle

contraction UPPER MOTOR NEURON:

FROM THE PRECENTRAL GYRUS OF THE FRONTAL LOBE

LOWER MOTOR NEURON: FROM THE ANTERIOR HORN CELL

OF THE SPINAL CORD FROM THE PRECENTRAL GYRUS GIVES OFF AXON THAT WILL PASS THRU: CORONA RADIATA INTERNAL CAPSULE CEREBRAL PEDUNCLE (MIDBRAIN) CORTICOSPINAL TRACT (PONS,

MEDULLA) PYRAMIDAL DECUSSATION (LOWERMOST

MEDULLA) PYRAMIDAL TRACT, CORTICOSPINAL TRACT

(SPINAL CORD)

Corticospinal Tract: Upper Motor Neuron Origin: Cerebral Cortex

Brodmann Area 4 (Primary Motor Area, M I) Brodmann Area 6 (Premotor Area, PM ) Brodmann Area 3,1,2 (Primary Somesthetic

Area, S I) Brodmann Area 5 (Anterior Portion of Sup.

Parietal Lobule) Corona Radiata lnternal Capsule, Posterior Limb Crus Cerebri, Middle Portion Longitudinal Pontine Fiber Pyramid - pyramidal decussation Corticospinal Tracts: - Lateral (crossed) - 85% - Anterior (Not crossed) - 15% Termination: Spinal Gray (Rexed IV-IX)

Corticospinal Pathway Sometimes called the pyramidal system Provides voluntary control over skeletal muscles:

system begins at pyramidal cells of primary motor cortex

axons of these upper motor neurons descend into brain stem and spinal cord

synapse on lower motor neurons that control skeletal muscles

Primary Motor Cortex The primary motor area is located in the precentral

gyrus of the frontal lobe (Figure 16.6b) upper motor neurons initiate voluntary

movement The adjacent premotor area and somatosensory

area of the postcentral gyrus also contribute axons to descending motor pathways.

The cortical area devoted to a muscle is proportional to the number of motor units.

More cortical area is needed if number of motor units in a muscle is high

vocal cords, tongue, lips, fingers & thumb

The primary motor area is located in the precentral gyrus of the frontal lobe (Figure 16.6b)

upper motor neurons initiate voluntary movement

The adjacent premotor area and somatosensory area of the postcentral gyrus also contribute axons to descending motor pathways.

The cortical area devoted to a muscle is proportional to the number of motor units.

More cortical area is needed if number of motor units in a muscle is high

vocal cords, tongue, lips, fingers & thumb

The cerebral cortex...• ....The corticobulbar tract controls the motor nuclei

in the brain stem that innervate facial muscels. • Motor nuclei innervating muscles in the

upper part of the face receive an equal number of axons from both hemispheres, whereas those innervating the lower face receive mainly contralateral fibers*.

Corticobulbar Tracts Originate from the facial region of the motor

homunculus within the primary motor cortex. Axons extend to the brainstem, where they synapse

with lower motor neuron cell bodies that are housed within brainstem cranial nerve nuclei.

Axons of these lower motor neurons help form the cranial nerves.

Connection with motor cranial nerves Transmit motor information to control:

eye movements (via CN III, IV, and VI) cranial, facial, pharyngeal, and laryngeal

muscles (via CN V, VII, IX, and X) some superficial muscles of the back and

neck (via CN XI) intrinsic and extrinsic tongue muscles (via

CN XII)

Details of Pyramidal Pathways Lateral corticospinal tracts

cortex, cerebral peduncles, 90% decussation of axons in medulla, tract formed in lateral column.

skilled movements (hands & feet) Anterior corticospinal tracts

the 10% of axons that do not cross controls neck & trunk muscles

Corticobulbar tracts cortex to nuclei of CNs

III, IV, V, VI, VII, IX, X, XI & XII movements of eyes, tongue, chewing,

expressions & speech

Motor Areas – Primary Motor Cortex• Controls motor functions

• Primary motor cortex (somatic motor area)• Located in precentral gyrus

• Pyramidal cells – large neurons of primary motor cortex

Primary Motor Cortex Organization• Specific pyramidal cells control specific areas of the

body• Face and hand muscles – controlled by many

pyramidal cells for fine control• Motor homunculus – body map of the motor cortex• Somatotopy – body is represented spatially in many

parts of the CNS

Motor Areas – Corticospinal Tract (Pyramidal Tract)• Corticospinal tracts descend through brainstem and

spinal cord• Axons signal motor neurons to control fine

skilled movements • Contralateral – pyramidal axons cross over

to opposite side of the brain

Motor Areas – Premotor Cortex• Located anterior to the precentral gyrus • Controls more complex movements • Involved in the planning of movements

Motor areas Anterior to central sulcus of Rolando

• Primary motor area• Precentral gyrus of frontal lobe (4)• Conscious or voluntary movement of

skeletal muscles

• Primary motor area continued• Precentral gyrus of frontal lobe• Precise, conscious or voluntary movement

of skeletal muscles• Large neurons called pyramidal cells• Their axons: form massive pyramidal or

corticospinal tracts • Decend through brain stem and

spinal cord• Cross to contralateral (the other)

side in brainstem• Therefore: right side of the brain

controls the left side of the body,

and the left side of the brain controls the right side of the body

Homunculus – “little man”• Body map: human body spatially represented

• Where on cortex; upside down

LOWER MOTOR NEURON FINAL COMMON PATHWAY ANTERIOR HORN CELL PERIPHERAL NERVE NEUROMUSCULAR JUNCTION

Feed-forward control of feedback loops – the modulated stretch reflexInhibitory interneurons playspecial roles in coordinatedreflex actions.Ia inhibitory neurons allowhigher centers to coordinate(i.e. relaxation of the antagonist)opposing muscles at a joint through asingle command. Inhibiting inputfrom higher centers allows aco-contraction of opposing muscles.Renshaw cells inhibit the very samemotor neurons they receive inputfrom, synergist motor neurons,and the Ia neurons. Descendinginputs thus can modulate theexcitability of all motor neuronsaround a joint.

• Inhibitory interneurons playspecial roles in coordinatedreflex actions.

• Ia inhibitory neurons allowhigher centers to coordinate(i.e. relaxation of the antagonist)opposing muscles at a joint through a single command.

• Inhibiting inputfrom higher centers allows aco-contraction of opposing muscles.

• Inhibitory interneurons playspecial roles in coordinatedreflex actions.

• Renshaw cells inhibit the very samemotor neurons they receive input

from, synergist motor neurons,and the Ia neurons.

• Descendinginputs thus can modulate theexcitability of all motor neuronsaround a joint.

UPPER MOTOR NEURON LESION

LOWER MOTOR NEURON LESION

1. WEAKNESS YES YES

2. TONE SPASTIC FLACCID

3. DEEP TENDON REFLEXES

INCREASED

ABSENT/

DECREASED

4. ATROPHY NONE OR LATE

EARLY

5. FASCICULATION/

FIBRILLATION

NONE YES

6. BABINSKI YES NO

SENSORY SYSTEMLecturer: Dr. Eufemio Sobrevega

.Organization of Sensory Pathways

• First-order neurons – cell bodies in DRG or cranial nuclei– Conduct impulses from sensory receptors

to the spinal cord or brain stem to synapse w/ 2nd order neurons

• Second-order neurons – cell bodies in dorsal horn of spinal cord or

medullary nuclei– Transmit impulses to the thalamus or

cerebellum where they synapse (cross over)• Third-order neurons (only from thalamic synapses)

– cell bodies in thalamus – conduct impulses to the somatosensory

cortex

Sensory pathways: 3 neurons• 1st: enters spinal cord from periphery• 2nd: crosses over (decussates), ascends in spinal

cord to thalamus• 3rd: projects to somatosensory cortex

Somatic Sensory Pathways• carry sensory information from the skin and

musculature of the body wall, head, neck, and limbs1. posterior column pathway2. anterolateral pathway3. spinocerebellar pathway

The Posterior Column Pathway• Carries highly localizes fine touch, pressure,

vibration, and proprioception • also called dorsal

column/medial lemniscus First-Order Neuron (DRG, CN)2 spinal tracts:

• fasciculus gracilis – lower half of body– synapse in nucleus gracilis in medulla

• fasciculus cuneatus – upper half of body– synapse in nucleus cuneatus in medulla

Second-Order Neuron• soma in nucleus gracilis in medulla• soma in nucleus cuneatus in medulla• both ascend and cross over to the opposite side of

the brain (decussation) and enter the medial lemniscus tract.

• both synapse in the ventral nuclei of the thalamus

Third-order Neuron • soma in ventral nuclei of the thalamus• arriving information is sorted

– nature of stimulus– region of body involved– the axon travels to a specific region of the

primary sensory cortex

Sensory Ascending Tracts Posterior White Column-Medial Lemniscal Pathway Modality: Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation, Kinesthesia) Receptor: Most receptors except free nerve endings Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion) Posterior Root - Posterior White Column 2nd Neuron: Dorsal Column Nuclei (Nucleus Gracilis et Cuneatus)

Internal Arcuate Fiber - Lemniscal Decussation - Medial Lemniscus 3rd Neuron: Thalamus (VPLc) Internal Capsule ----- Corona Radiata Termination: Primary Somesthetic Area (S I)

Spinothalamic pathway• Carries pain, temperature, touch and pressure

signals• 1st neuron enters spinal cord through dorsal root• 2nd neuron crosses over in spinal cord; ascends to

thalamus• 3rd neuron projects from thalamus to

somatosensory cortex

The Anterolateral Pathway• conscious, poorly localized sensations of touch,

pressure, pain and temperature• first-order neurons

– synapse on second-order neurons in the posterior gray horn of the spinal cord

• second-order neurons (soma in spinal cord)– decussate– fibers ascend in

• anterior spinothalamic tract• touch and pressure

• lateral spinothalamic tract• pain and temperature

– synapse on third-order neurons of thalamus

• third-order neurons– soma in ventral nuclei of the thalamus– arriving information is sorted

• nature of stimulus• region of body involved

– the axon travels to a specific region of the primary sensory cortex

•

Sensory Homunculus• electrical stimulation of human brains was used to

create a functional map of the primary sensory cortex

• the homunculus has a huge face because the face has the most sensory receptors and thus give the most sensory input

Unconscious proprioception: Spinocerebellar Pathway• unconscious proprioception • proprioceptive input from muscles, tendons and

joints• first-order neurons

– synapse on second-order neurons in dorsal gray horn

• second-order neurons– soma in spinal cord– axons ascend in:

• posterior spinocerebellar tract• don’t decussate

• anterior spinocerebellar tract• usually decussate

Brown-Sequard syndrome (spinal cord hemisection) Major Symptoms

1. ipsilateral UMN syndrome below the level of lesion2. ipsilateral LMN syndrome at the level of lesion3. ipsilateral loss of discriminative touch sensation and conscious proprioception below the level of lesion (posterior white column lesion) 4. contralateral loss of pain and temperature sensationbelow the level of lesion (spinothalamic tract lesion)