SAP notes
Physiological Basis of Sensory-Perceptual Systems
Functional Organization
Brodmann areas defined and numbered from 1 to 47 by Korbinian Brodmann in 1909.
Nissi staining method used for identification.
Brodmann area: region of cerebral cortex defined by cytoarchitecture (neuron arrangement).
Macroscopic Anatomy
Functional Organization of Brodmann’s Areas
Visual System
Primary: Area 17
Secondary: Areas 18, 19, 20, 21, 37
Auditory System
Primary: Area 41
Secondary: Areas 22, 42
Somesthesis
Primary: Areas 1, 2, 3
Secondary: Areas 5, 7
Tertiary Sensory
Areas 7, 22, 37, 39, 40
Motor System
Primary: Area 4
Secondary: Area 6
Eye movement: Area 8
Speech: Area 44
Tertiary Motor: Areas 9, 10, 11, 45, 46, 47
Sensory-Perceptual Systems
Comprised of structures that collect and transmit information from sense organs to the cerebral cortex:
Somatesthesia
Auditory
Visual
Vestibular
Gustative
Olfactory
Each system provides "elementary or unitary cognition" for higher mental functions.
General Principles
Each sensory-perceptual system consists of three structures:
Receptors: Detect and transform sensory stimuli.
Information Pathways: Transmit signals to the brain
Cortical Receptive Areas: Process visual, auditory, and somatic information.
Receptors
Capable of detecting sensory stimuli, leading to bioelectrical impulses through transduction.
Classification:
By Morphology:
Free nerve endings: Non-encapsulated neurons.
Encapsulated: Specialized structures.
Specialized cells: Uniquely adapted receptor cells.
By Energy Type Response:
Mechanoreceptors: Touch, pressure, vibration, sound.
Chemoreceptors: Chemical composition changes.
Photoreceptors: Light detection.
By Stimuli Source:
Exteroceptors: External stimuli.
Proprioceptors: Muscle and joint tension.
Interoceptors: Internal organ information.
Somatoperceptual Pathways
Except olfactory, consist of three neuronal links synapsing at relay nuclei:
First neurons: Located in sensory ganglia.
Second-order neurons: Located in sensory nuclei, cross before reaching the thalamus.
Third neurons: Project to cortical areas via the internal capsule.
Cortical Areas
Primary Areas: Direct thalamic axon receptors, responsible for sensation.
Secondary Areas: Higher processing areas for complex information integration.
Associative Areas: Integrate multiple modalities, supporting complex cognitive functions.
Pathways of Somatosensory Sensitivity
Two main systems:
General Sensitivity: Exteroceptive and proprioceptive feedback.
Visceral Sensitivity: Information from internal organs.
General Sensitivity Pathways
Posterior Column-Medial Lemniscus System: For fine touch, vibration, and proprioception.
Anterolateral Spinothalamic System: For temperature and gross pressure detection.
Neural Pathways for Sensitivity
First Neurons: In spinal ganglia, travel through posterior roots.
Second Neurons: Located in the medulla, axons cross to form the medial lemniscus.
Third Neurons: In the thalamus, project to the somatosensory cortex.
Sensitivity of the Head
Handled by the trigeminal thalamic system:
First Neurons: Located in cranial nerve ganglia.
Second Neurons: In trigeminal sensory nucleus, cross and form trigeminal thalamic tract.
Third Neurons: Carry info to the cortex.
Solitary Nucleus System
Carries visceral information from internal organs:
First Neurons: From glossopharyngeal and vagus ganglia.
Second Neurons: Direct info to the thalamus and other brain regions.
Third Neurons: Project from thalamus to cortex.
The Somatosensory Cortex
Comprised of primary (Brodmann areas 3-1-2) and secondary areas (Brodmann areas 5-7).
Each area has a sensory map representing different body parts.
Auditory Information System
Sound: Variations in pressure waves from vibrating air molecules.
Hearing device captures sound, transmits to cochlea for transformation into nerve impulses:
Comprises the hearing apparatus, acoustic pathway, and auditory cortex.
Acoustic Pathway
Set of neurons carrying impulses from cochlea to auditory cortex:
First Neuron: Cochlear nucleus ganglia.
Second Neuron: Cochlear nucleus.
Third Neuron: Inferior colliculus and medial geniculate nucleus (thalamus).
Auditory Cortex
Located in the temporal lobe, includes:
Primary Auditory Area (Brodmann's areas 41/42): Tonotopic representation.
Secondary Auditory Area (Brodmann's area 22): Involved in auditory perception.
Vestibular Information System
Maintains balance, integrates signals from:
Visual system
Proprioceptive sensitivity system
Vestibular system
Registers linear and angular accelerations from inner ear receptors.
Equilibrium Receptors
Membranous labyrinth contains five receptors:
Two maculae for linear accelerations.
Three ampullary crests for angular accelerations.
Maculae and Sensory Epithelium
Maculae consist of hair and supporting cells in a gelatinous mass, with orientation determining function.
Reflex Derivations
Integration centers for balance involve connections with vestibular nuclei, cerebellum, spinal cord, and brainstem.
Visual Information System
Electromagnetic radiation from light stimulates photoreceptors in retina, leading to image processing in cerebral cortex.
Integrates information for image identification and recognition.
Retina Structure
Layers include:
Pigment layer: Reduces reflections.
Photoreceptor layer: Contains rods and cones.
Neuronal layers: Include bipolar, ganglion, and sync fibers layers.
Optical Pathway
Optical nerves converge and cross at the optic chiasm, transmitting visual information to the visual cortex:
First neurons: Bipolar cells in retina.
Second neurons: Ganglion cells, forming optic nerves.
Third neurons: Located in lateral geniculate body, project to visual cortex.
Visual Cortex
Primary Visual Cortex (Brodmann’s Area 17): Area of visual sensation.
Secondary Visual Cortex (Areas 18, 19, etc.): Processing of visual images.