Sensory – Somatosensory Physiology

Sensory – Somatosensory Physiology

Taste Sensation:

• Receptor: Taste buds located on taste papillae of the tongue.

• 4 Basic Tastes: Sweet, salty, sour, bitter.

• Nerve Pathways:

• First neuron: Solitary nucleus.

• Second neuron: Ventral posterior medial nucleus of thalamus.

• Third neuron: Area 43 of the cerebral cortex.

• Characteristics:

• Adaptation: Taste sensation diminishes with continuous exposure to a substance.

• Subjective influence: Preferences depend on needs, memory, experience, and other senses.

Smell Sensation:

• Receptor: Olfactory cells in the nasal mucosa.

• Nerve Pathways:

• First neuron: Axons of olfactory cells pass through the cribriform plate to the olfactory bulb, synapsing with mitral cells.

• Second neuron: Axons of mitral cells form the olfactory tract, leading to the olfactory area (28) of the cerebral cortex.

• Characteristics:

• Low threshold of stimulation: Can detect very faint odors.

• High adaptation: Smell sensation decreases rapidly with continuous exposure.

• Subjectivity: Odor can elicit different sensations in different individuals.

Vision Sensation:

• Mechanism of distance/near vision:

• Distance vision: Ciliary muscle relaxes.

• Near vision: Ciliary muscle contracts.

• Presbyopia: Decreased elasticity of the lens.

• Hyperopia: Due to short eyeball or weak convergence, the image falls behind the retina.

• Myopia: Due to long eyeball or increased convergence, the image falls in front of the retina.

• Astigmatism: Irregular curvature of the cornea/lens system, leading to uneven convergence, resulting in rays not converging at the same point.

• Cataract: Protein fibers degenerate and become solid, obstructing light transmission.

• Aqueous humor: Secreted by ciliary body.

• Tears: Secreted by lacrimal gland.

• Macula: Site of high concentration of cone cells located on the optical axis of the eye.

• Fundus: Image of the retina observed with an ophthalmoscope.

• Blind spot: Site where axons of ganglion cells converge.

• Papilledema, optic disc edema, retinal hemorrhage: Occur in cases of increased intraocular pressure.

• Receptor:

• Cone cells: Detect colored light with high intensity.

• Rod cells: Detect black and white light from strong to faint.

• Nerve Pathways:

• First neuron: From cone and rod cells to other cell types in the retinal layers.

• Second neuron: Other cells leading to the visual cortex (17, 18, 19).

• Cortical areas:

• Area 17: Detects contrast, color, and depth.

• Area 18: Analyzes the meaning of visual sensation (related to writing and reading).

• Color vision mechanism: Through the retinal and photopsin complex in cone cells.

• Photochemical mechanism: Through the breakdown of rhodopsin, scotopsin, retinal in rod cells.

Hearing Sensation:

• Receptor: Hair cells.

• Auditory cortex: Areas 41, 42 in the temporal lobe, 22.

• Damage to primary auditory area: Inability to perceive sound, deafness.

• Damage to associative auditory area: Can hear but not understand.

Touch Sensation:

• Areas without touch receptors: Cornea, auricle (epidermal cells act as receptors).

• Touch sensation center in the cerebral cortex: S-I, S-II of the parietal lobe (Brodmann areas 1, 2, 3, 5, 7 and 40).