Terminology: 28-31 Flashcards
Stimulus
Detected change in the environment
Sensory Receptor
Specialized dendrites of sensory neurons that receive specific types of stimulus.
Sensory Pathway
Consists of the chain of neurons from a receptor organ to the cerebral cortex responsible for the perception of sensations.
CNS
Brain and spinal cord in which sensory information is received, processed, and motor signals are outputted.
Motor Pathway
A neural pathway that originates in the brain and descends down the spinal cord to control motor neurons.
Effector
Cell or a group of cells that performs a specific function in response to motor signals.
Response
An action triggered by stimulus.
Bats & Moths
- Bats track prey through sonar.
- Some moths have evolved to detect bat sonar and take evasive action.
Action Potential
The electrical mechanism through which nerve cells conduct information. When a neuron is depolarized, it triggers a wave of depolarization across adjacent cells.
- Resting potential is -70mV, stimulus disturbs the resting voltage and increases the voltage (depolarization)
- Sufficient stimulus to depolarize past the trigger threshold (-55mV) will trigger an action potential event.
- When triggered, rapid depolarization causes the membrane potential to increase and peak at +40mV. This causes other neurons to also depolarize, rippling across all adjacent neurons.
- The membrane potential then rapidly repolarizes after the peak, dipping down to -75mV. It will steadily return to its resting potential of -70mV during which it is hyperpolarized.
Nerve Impulse
Action Potential
Stimulus is converted into electrical impulses.
A cascading wave of electrical depolarization across a nerve fiber terminating at the CNS.
Sensory Transduction
The conversion of sensory stimulus into electrical impulses.
Resting Membrane Potential
When the inside of the neuron is more negative than the outside.
-70mV
Depolarization
The positive change of a cell’s membrane potential. As voltage-gated Na+ channels open:
Na+ ions flow OUT of the cell.
K+ ions flow INTO the cell.
When an action potential is triggered past the -55mV threshold, it peaks at +40mV.
The level of depolarization is proportional to the intensity of the stimulus
Repolarization
The negative change of a cell’s membrane potential. Voltage-gated Na+ channels close, voltage-gated K+ channels open:
Na⁺ ions flow back INTO the cell.
K+ ions flow OUT of the cell.
After an Action Potential’s peak of +40mV, the membrane potential drops back to a negative charge.
Hyperpolarization
Negatively charging a cell’s membrane potential below the resting potential of -70mV to -75mV. This induces a refractory period in which Na+ ions are filtered back out the cell until membrane potential is reset to resting potential. A neuron cannot be triggered again until it resets to resting potential.
-75mV
The level of hyperpolarization is proportional to the intensity of the stimulus
7 Types of Sensory Receptors
- Nociceptors
- Thermoreceptors
- Mechanoreceptors
- Chemoreceptors
- Photoreceptors
- Electroreceptors
- Magnetoreceptors
Nociceptors
Detects pain stimulus
Thermoreceptor
Detects temperature stimulus
Mechanoreceptor
Detects pressure changes
(e.g. hair cells of ear)
Chemoreceptor
Detects changes in molecular concentrations
(e.g. CO₂, O₂, pH)
Photoreceptor
Detects particular wavelengths of light
Electroreceptor
Detects electrical fields
Magnetoreceptor
Detects magnetic fields
Hearing Process
- Sound waves are collected by the Pinna (outer ear).
- Those waves travel through the ear canal to the tympanic membrane (eardrum).
- The sound is amplified and by the ear ossicles (tiny bones).
- Air based sound is converted to liquid based sound in the cochlea, which vibrates the basilar membrane.
- Hair cells of the basilar membrane perform sensory transduction to translate the vibrations to electrical signals.
Pinna
The outer ear.
Made of cartilage and skin.
Tympanic Membrane
- Also known as the eardrum.
- A thin membrane that separates the outer ear from the middle ear.
- Transmits sound from the air to the ossicles in the middle ear.
- Also protects the middle and inner ear from pathogens and debris.
Cochlea
Hollow spiral bone shaped like a snail shell. It is fluid filled.
Contains the Basilar Membrane and the Organ of Corti.
Ear Ossicles
Tiny bones of the middle ear involved in the translation of air based sound of the outer ear to liquid based sound of the cochlea.
- Malleus
- Incus
- Stapes
Basilar Membrane
A membrane that separates the scala media and the scala tympani fluids within the cochlea.
The basilar membrane moves up and down in response to sound waves, which are converted to electrical signals by hair cells.
Oval Window
The membrane between the middle ear and the inner ear, facilitating the translation of air based sound to liquid based sound of the cochlea.
Hair Cells
Sensory receptors of the auditory and vestibular (balance) system.
Hair cells are afferent sensory neurons that function as mechanoreceptors.
Sound deflects the stereocilia of the cell, which triggers the release of neurotransmitters at the basal end of the cell. This neurotransmitter then induces action potentials to be generated at a nerve terminal.
How is Loudness & Pitch Coded?
Loudness: Louder sounds cause more hair cells to be stimulated, which is interpreted by the brain to be loud.
Frequency: The basilar membrane vibrates at different frequencies across the cochlea. The position of the stimulated hair cells within the basilar membrane determines the interpreted frequency.
Eyeball structure
General Layers:
1. Sclera
2. Choroid
3. Retina
Forward Structures:
1. Cornea
2. Iris & Pupil
3. Lens
Eyeball layers
- Sclera
- Choroid
- Retina
Cornea
- The outermost forward structure of the eye. Transparent.
- The cornea refracts light, contributing most of the eye’s focusing power (along with fluid and the lens).
- The focus of the cornea is fixed.
Lens
- A forward structure underneath the iris and pupil of the eye. Transparent.
- Refracts light, focusing it onto the retina.
- Can adjust the focal length of the eye, enabling it to focus on objects at varying distances.
Sclera
- The white outer layer of the eye.
*Protective function
Choroid
- The middle layer of the eye.
- Provides oxygen and nourishment to the retina.
Retina
- The innermost layer of the eye.
- The retina contains the photoreceptor cells that detects light and converts it into electrical signals.
Layers of Retina
1. Ganglion Cells
2. Bipolar Cells
3. Photoreceptor Cells (Rods & Cones)
4. Pigmented Epithelium
Rod Photoreceptors
Photoreceptors of the retina that functions in dim light and provide monochromatic vision.
Cone Photoreceptors
Photoreceptors of the retina that functions in well-lit conditions and provides color perception.
Iris
A thin structure under the cornea that contains a sphincter muscle that contracts the iris to control the amount of light received by the retina.