Cerebrum
Major gyri of a human cerebral hemisphere. O, Or, T, opercular, orbital, and triangular parts of the inferior frontal gyrus; SPL, superior parietal lobule.
White Matter Tracts
GYRUS
SULCUS
CORTEX
MEDULLA
SHORT ASSOCIATION FIBERS
LONG ASSOCIATION FIBERS
COMMISSURAL FIBERS (Corpus callosum)
Projection Fibers
Efferent [motor] Afferent [sensory]
Thalamus
Corticospinal and Corticobulbar tracts travel through the Internal Capsule
Anterior
HORIZONTAL SECTION – RIGHT INTERNAL CAPSULE F = Face + Head A = Arm (upper limb) T = Thorax
Cau date
A = Abdomen L = Lower limb
Anterior limb
Ge nu Genu Corticobulbar tract
Lentif orm nucle us
F A T ThalaA mus
Corticospinal tract L Posterior limb
Next slide
Layer I- few nerve cell bodies, many dendritic and axonal processes in synaptic interaction. Layer II -small neurons, which establish intracortical connections.
Layer III -medium-sized neurons giving rise to association & commissural fibres. Layer IV -termination of afferent fibres from the thalamus
Layer V is the origin of projection fibres to extracortical targets, such as BG, thalamus, brain stem and spinal cord. In the primary motor cortex of the frontal lobe, this layer contains CST cell bodies Layer VI -contains association and projection neurons.
FUNCTIONAL LOCALIZATION
Somatic sensation, body image, 3D localization of self & targets in space, language
OCCIPITAL LOBE
FRONTAL LOBE
Higher cognitive function, motor (planning/exec.) language
PARIETAL LOBE
Vision
TEMPORAL LOBE
LIMBIC – Emotional, social & sexual behaviour
Memory (short term) & learning, auditory
FUNCTIONAL LOCALIZATION Information on functional localization mostly from: -Stimulation and ablation studies -Electrophysiological recordings -Observations of regional blood flow -Post mortem studies of patients with known lesions
FUNCTIONAL LOCALIZATION Wilder Penfield --McGill (Canadian Neurosurgeon) The Montreal Surgery 1950: Before operating, he stimulated the brain with electrical probes while the patients were conscious on the operating table and observed their responses. In this way he could more accurately target the areas of the brain responsible, reducing the side-effects of the surgery. - Led to the Cortical Homunculus
FUNCTIONAL LOCALIZATION Pierre Broca -1861 –“We speak in the left hemisphere!” -(Post-mortem studies of ‘Tan’ and other patients)
Karl Wernicke- 1870’s –discovered part of the brain involved in understanding language, in the posterior portion of the left temporal lobe. People who had a lesion here could speak, but their speech was often incoherent and made no sense.
FUNCTIONAL LOCALIZATION
1. 2. 3.
From these studies, we know the brain is organized into 3 operational systems: Sensory systems: internal representation of the outside world Association systems (Integration of diverse sensory information for planning purposeful action) Motor systems
Primary Sensory Cortex Topography is essential for conscious recognition and localization of sensory stimuli
Each primary sensory area is surrounded by a larger zone of association cortex
Association Cortex Interprets the incoming signals and is appropriately connected to other parts of the cerebral cortex (association fibers) Lesions to sensory association cortices leads to: Agnosias—inability to recognize common objects Aphasias—inability to understand/vocalize speech Apraxias– inability to execute purposeful movements (motor planning disorder)
Primary Sensory Ctx (tingling, numbness)
Posterior Parietal Cortex (agnosia, neglect)
Primary Visual Cortex (visual field defects)
Visual Association Cortex (visual agnosia)
Primary Auditory Cortex
Wernicke’s Sensory Speech Area
(sound localization)
(comprehension)
(sensory, receptive aphasia)
Primary Gustatory Region (Taste Area)
Parietal, Temporal, Occipital Association Cx (Higher order, multimodal sensory analysis, memory, learning Lesions leads to different ďƒ agnosias)
Limbic Association Cx (schizophrenia, depressive illness) Prefrontal Association Cortex (personality, behavior)
Primary Olfactory Area is the uncus, parts of insula, & frontal gyri
Parietal Association Cortex= somesthetic association cortex Primary Sensory Cortex Posterior Parietal Cortex
A lesion to the parietal association cortex is often incomplete. The ability to feel an object may be present, but there may be a defect in the ability to interpret this sensation= TACTILE AGNOSIA ex) shut eyes and hold an object= cannot identify it
Astereognosia is the loss of awareness of the spatial relations of parts of the contralateral side of the body Cortical Neglect: an extreme form of astereognosia in which the patient ignores/denies one side of the body and the corresponding visual field (usually right parietal lesion)
Primary Sensory Cortex Posterior Parietal Cortex
Drawings from people with Cortical Neglect
Cortical neglect
Do not recognize or ‘own’ one side of their body -make up on one half of face -dress one half of themselves -try to rid themselves of their limbs
normal
Do not see from one side of visual Field -eat half of their plate -make above drawings Cortical neglect
Vision
Primary Visual Cortex (visual field defects) Visual Association Cortex (visual agnosia)
Visual Association Cortex Lesions Have association fibers to thalamus and many cortical regions -therefore many types of agnosias can occur depending on the location of lesion
where
what
Ventral Stream colour -letters -faces -visual memories
Dorsal Stream 3D visual understanding of object Motion of object
Auditory Association Lesions lead to various auditory agnosia Primary Auditory Cortex (sound localization)
Bilateral destruction of auditory association cortex -fail to identify and respond to sounds (patient hears it, just doesn’t respond appropriately -ex) can’t understand the difference b/w someone’s voice and other sounds -amusia right-side lesion leading to inability to recognize previously ‘familiar’ voices and music
Primary Olfactory Area is the uncus, parts of insula, & frontal gyri Primary Gustatory Region (Taste Area)
Olfactory and gustatory association cortices intermix -both send association fibers to gain emotional response to smell/taste -evolutionary -anosmia (loss of smell) leads to lack of taste sensation
Olfactory association fibers sent to limbic system -to acquire and recall memories associated with smell -emotional response to smell
To be discussed with limbic system and behaviour lectures
Parietal, Temporal, Occipital Association Cx (Higher order, multimodal sensory analysis) (# ďƒ agnosia)
Limbic Association Cx (schizophrenia, depressive illness) Prefrontal Association Cortex
Aphasias
Primary Auditory Cortex (sound localization) Wernicke’s Sensory Speech Area (comprehension) (sensory, receptive aphasia) Broca’s Motor Speech Area (formulation) (motor, expressive aphasia) Arcuate Fasiculus (white matter tract) (conduction aphasia, but good spontaneous speech)
Right Hemisphere Left Hemisphere Awareness of body Awareness of body position Appreciation of 3D shapes Musical ability
(Bilateral) lesions lead to various agnosias
Language Broca’s motor speech area (frontal lobe) Wernicke’s sensory speech area
Lesions lead to various aphasias Dominant hemisphere 75% of people are right-handed (which Is controlled by left hemisphere)
Commissurotomy studies -left hand better at building with blocks etc
Lesion or stroke more detrimental 90% of right-handed people and 70% of lefties have language in left hemisphere
FUNCTIONAL LOCALIZATION
1. 2. 3.
From these studies, we know the brain is organized into 3 operational systems: Sensory systems Association systems (Integration of diverse sensory information for planning purposeful action) Motor systems
Motor Cortex and Motor Association Cortices
Primary Motor Cortex (Cx) Premotor Cortex Supplementary Motor Cx/Area [SMA] Broca’s Motor Speech Area (formulation) (motor, expressive aphasia)
To vocally respond to a verbal question:
5
2 4
1. Listen (primary auditory cortex) 2. Comprehend (Wernickes area) 3. send association fibers through Arcuate fasiculus to 4.Broca’s motor speech area to formulate speech 5. Activate UMN for speech muscles (larynx, lips etc)
1
Primary Motor Cortex (Cx) Primary Auditory Cortex (sound localization) Wernicke’s Sensory Speech Area (comprehension) (sensory, receptive aphasia) Broca’s Motor Speech Area (formulation) (motor, expressive aphasia)
MOTOR SYSTEMS • CNS extracts information necessary to plan and guide voluntary movements • movements are generated and controlled by a set of MOTOR SYSTEMS
• This is done by converting Neural information Physical energy HOW? 1.
Identification & localization of targets in space posterior parietal cortex
2.
Formulation of a plan of action premotor cortex & supplementary motor cortex (SMA)
3.
Execution of the movement 10 motor cortex
Premotor cortex and SMA III. Central Motor Program (black box) Fed into 10 motor cortex: Motor commands conveyed via Descending Motor Pathways
(Posterior Parietal Cortex) 5 4 6
312
7
II. Information conveyed to Sensory & Motor areas of cortex via association fibres
VISUAL AUDITORY
UPPER MOTOR NEURON
LOWER MOTOR NEURON IV. Stimulus leads to Muscle contraction = PHYSICAL ENERGY
I. Stimuli from external & Internal environment = NEURAL INFORMATION
NEURAL INFORMATION ďƒ PHYSICAL ENERGY
MOTOR SYSTEMS • Note: There is continual surge of sensory information critical for motor systems to work! • motor commands controlling skeletal muscle travel over several descending motor pathways involving the UMN Corticospinal Corticobulbar Corticoreticular Reticulospinal Vestibulospinal Rubrospinal Note: There is hierarchical organization to the musculoskeletal pathway!
UPPER AND LOWER MOTOR NEURON CONCEPTS CEREBRUM
INHIBIT
EXCITE
Activity in the UMN can excite or inhibit the LMN
UMN
BRAINSTEM or SPINAL CORD
Only the axon of the LMN extends to skeletal muscle
UMN
+ve
- ve
LMN
LMN
DIS - INHIBIT
UPPER MOTOR NEURON LESION
UMN
= Disinhibition of the LMN
LMN
SPASTIC PARALYSIS
LOWER MOTOR NEURON LESION
UMN
LMN
FLACCID PARALYSIS
HIERARCHICAL ORGANIZATION OF THE CNS
HIERARCHICAL Corticospinal Corticobulbar
PREMOTOR & SUPPLEMENTARY MOTOR CORTEX
=‘pyramidal’
PRIMARY MOTOR CORTEX
PARALLEL Corticoreticular Reticulospinal Vestibulospinal Rubrospinal =‘extrapyramidal’
BRAINSTEM
SPINAL CORD ANT. HORN CELL
LMN
MOTOR SYSTEMS • Corticospinal tract= voluntary control of LMN
• Modulated by input from the basal ganglia and the cerebellum to ensure smooth, coordinated, purposeful movement – Basal ganglia lesion (PD, Huntingtons Chorea) – Cerebellar lesion=ataxia
• Subsidiary descending pathways are known as the extrapyramidal tracts – Corticoreticulospinal tract= excitatory to leg extensors and arm flexors – Vestibulospinal tract= excitatory to arm/leg extensors and inhibitory to arm/leg flexors – Rubrospinal tract= inhibitory to arm extensors and excitatory to arm flexors. No effect on leg muscles – Tectospinal tract= influences neck muscles
Decorticate posturing: -CST lesion (paralyzed) -Extrapyramidal tracts are functional. -Rubrospinal tract = flex upper body -Corticoreticulospinal tract=flex upper body, extend lower body --Vestibulospinal tract= excitatory to arm/leg extensors (arm muscles extensors are overruled by the reticulospinal and rubrospinal tracts!) and inhibitory to arm/leg flexors
CRST=extend VST=extend
CRST=flex RST=flex VST=extend
Decerebrate posturing: Brainstem lesion/injury -CST, and Rubrospinal tract = not active -Corticoreticulospinal tract=flex upper body (overruled by VST!), extend lower body -Vestibulospinal tract= excitatory to arm/leg extensors and inhibitory to arm/leg flexors
CRST=extend VST=extend
CRST=flex VST=extend