Physiology - Midterm 1

How do most sensory signals reach the brain?

They pass through the thalamus first.

How is the olfactory pathway different from other sensory pathways?

Olfactory signals go directly to the olfactory cortex and limbic system, bypassing the thalamus.

What is the relationship between basilar membrane displacement and neurotransmitter release?

Greater displacement of the basilar membrane causes greater neurotransmitter release from hair cells.

What structure’s movement is central to pitch discrimination?

Movement of the basilar membrane.

What type of receptors are involved in taste and smell?

Chemoreceptors.

From an evolutionary perspective, chemoreception is what?

One of the oldest senses.

What is smell?

Detection of gaseous molecules in air.

What is taste?

Detection of chemicals dissolved in food and drink.

What must both smell and taste stimuli be dissolved in?

Water.

Where are taste receptors located?

Taste buds, primarily on the tongue.

What structures extend from taste cells?

Microvilli.

What surrounds taste cells?

Saliva.

What type of cells are taste cells?

Non-neural epithelial cells.

How are taste cells activated?

Chemicals bind to G-protein-coupled receptors → depolarization.

What happens after depolarization?

Neurotransmitter release stimulates sensory neurons.

Which cranial nerves carry taste information?

Facial, glossopharyngeal, and vagus.

What additional input is required for full taste perception?

Olfactory (smell) input.

Sweet is stimulated by?

Sugars (glucose, fructose, sucrose).

Salty is stimulated by?

Sodium ions.

Sour is stimulated by?

Hydrogen ions (acids).

Umami is stimulated by?

Glutamate.

Bitter is stimulated by?

Alkaloids.

What type of neurons are olfactory receptors?

Bipolar sensory neurons.

Which cranial nerve carries smell?

Olfactory nerve (CN I).

What is the smell pathway?

Olfactory nerve → olfactory bulb → olfactory tract → cortex.

What structures are on olfactory neurons?

Multiple cilia.

How many receptor types exist?

About 400.

How many smells can humans detect?

About 10,000.

Which brain structure links smell to emotion?

Amygdala.

Which structure stores smell-related memories?

Hippocampus.

The olfactory bulb is part of which system?

Limbic system.

What provides the sense of equilibrium?

Vestibular apparatus of the inner ear.

Main structures involved in equilibrium?

Utricle, saccule, semicircular canals.

Where are sensory cells located in the vestibular system?

In otolith organs and ampullae.

What are hair cells?

Modified epithelial cells.

How many projections do hair cells have?

~50 hair-like extensions.

What types of projections do hair cells have?

Stereocilia and one kinocilium.

Bending toward kinocilium causes what?

Depolarization and neurotransmitter release.

Bending away from kinocilium causes what?

Hyperpolarization and reduced neurotransmitter.

What is the specialized epithelium in utricle and saccule?

Macula.

What surrounds hair cells in the otolith organs?

Otolithic membrane with crystals (otoliths).

Utricle detects what type of movement?

Horizontal movement.

Saccule detects what type of movement?

Vertical movement.

How many semicircular canals are there?

Three at different angles.

Where are sensory hairs located in the semicircular canals?

Ampulla.

What structure embeds the hairs in the semicircular canals?

Cupula.

What movement do semicircular canals detect?

Rotational movement.

What initiates hearing?

Sound vibrating the tympanic membrane.

What transmits vibrations to the inner ear?

Ossicles.

What structure is pushed by ossicles?

Oval window.

What does this create in the cochlea?

Pressure waves that move the basilar membrane.

What is the path of fluid movement in the cochlea?

Scala vestibuli → end → back through scala tympani.

What is the functional unit of hearing?

Organ of Corti.

Where are stereocilia located in the cochlea?

On basilar membrane.

What membrane covers stereocilia?

Tectorial membrane.

Bending toward tallest cilia does what?

Opens Na⁺ channels → depolarization.

Bending toward shortest cilia does what?

Closes channels.

How is pitch determined?

Location of basilar membrane movement.

What happens with low-frequency sounds?

They travel farther in cochlea.

What happens with high-frequency sounds?

They affect regions near the base.

Where is light focused in the eye?

Retina.

What do retinal sensory cells do?

Convert electromagnetic energy into nerve impulses.

Why don't we see infrared light?

Energy too low to stimulate receptors.

Why don't we see ultraviolet light?

Filtered by the lens.

What does the lens do?

Refracts light to focus on retina.

What is accommodation?

Adjusting focus for different distances.

What causes accommodation?

Contraction of ciliary muscle.

What are the two types of photoreceptors?

Rods and cones.

What is the function of rods?

Low-light, black-and-white (scotopic vision).

What is the function of cones?

Color and high acuity (photopic vision).

What pigment do rods contain?

Rhodopsin.

What happens when light hits rhodopsin?

It dissociates into components.

How many cone types are there?

Three.

What proteins do cones contain?

Opsins.

What are the cone color sensitivities?

Red, green, blue.

What is phototransduction?

Light energy triggers a G-protein cascade producing an electrical signal.

Approximate photoreceptor numbers per retina?

~120 million rods, 6 million cones.

How many optic nerve fibers are there?

~1.2 million.

What is the special region for highest acuity?

Fovea.

What is the cone-to-neuron ratio in the fovea?

1:1.

What is the signal pathway in the retina?

Rods/cones → bipolar cells → ganglion cells.

What forms the optic nerve?

Axons of ganglion cells.

Where does the right visual field project?

Left side of both retinas.

Where does this information go?

Left thalamus (lateral geniculate nucleus).

What does each thalamus receive?

Input from both eyes for the opposite visual field.

What happens when a sensory receptor detects a stimulus?

It generates an action potential in a sensory neuron.

What do sensory receptors convert?

Environmental energy into neural signals interpretable by the brain.

What are interoceptors?

Receptors that monitor the internal environment.

What are exteroceptors?

Receptors that monitor the external environment.

How are sensory receptors classified?

By the type of energy they convert.

What do chemoreceptors respond to?

Chemicals.

External chemoreceptor examples?

Taste and smell.

Internal chemoreceptor examples?

O₂, CO₂, pH, glucose.

What do mechanoreceptors respond to?

Membrane deformation (pressure, vibration, acceleration, sound).

Approximate number of mechanoreceptors in the cochlea?

~16,000.

What do photoreceptors respond to?

Light photons.

Types of photoreceptors?

Rods and cones.

Approximate number of photoreceptors in the eye?

~126 million.

What do thermoreceptors detect?

Temperature changes.

Where are most thermoreceptors located?

Skin (some internal for temperature regulation).