Exam 5 Neurobiology Objectives

How are receptors in somatosensation different from other senses (such as vision, olfaction, etc.)?

they are not confined to compact sense organs and have receptors located throughout the body

What is the morphology of a Pseudounipolar neuron? Name 2 examples of Pseudounipolar neurons.

A pseudounipolar neuron has a single process that splits into a peripheral and central branch (ex. dorsal root ganglion neurons)

Depolarizing receptor potential in mechanoreceptors is proportional to what?

the strength of the mechanical stimulus applied

Describe how Piezo channels function

piezo channels open in response to mechanical deformation of the cell membrane, allowing cations to enter and depolarize the receptor

What are the 4 types of mechanoreceptors?

merkel cells, meissners corpuscles, ruffini corpuscles, and pacinian corpuscles

What is the difference between slowly adapting cells and rapidly adapting cells?

Slowly adapting receptors continue firing during a sustained stimulus while rapidly adapting receptors show changes like when a stimulus starts or stops

Describe the characteristics of Merkel Cells

slowly adapting receptors that detect fine touch and pressure providing high spatial resolution like that used for reading braille

Describe the characteristics of Meissner’s corpuscle

rapidly adapting receptors that detect light touch and texture

Describe the characteristics of Ruffini corpuscle

slowly adapting receptors located deeper in the skin that respond to stretch and sustained pressure

Describe the characteristics of Pacinian corpuscle

rapidly adapting receptors that detect vibration and deep pressure through their lamellar structure

What are hair follicle receptors?

rapidly adapting mechanoreceptors that detect movement of individual hairs

What is the dermatome and what part of the body enters the spinal cord at each section?

an area of skin innervated by a single spinal nerve with combining sensory information from parts of the body into one UMN pathway

After primary afferents enter the spinal cord, what is the GENERAL pathway to the primary somatosensory cortex?

primary afferents ascend via the dorsal column-medial lemniscus pathway to the thalamus, then project to the primary somatosensory cortex

How is the pathway of somatosensation different in the face?

facial sensation travels through the trigeminal nerve to the trigeminal nuclei in the brainstem before projecting to the thalamus and somatosensory cortex

Understand what the homunculus is for the somatosensory cortex is. What does it mean for the homunculus to have larger cortical representation?

the homunculus maps body parts onto the cortex with larger cortical representation for areas with finer sensory discrimination like the hands and lips

Explain the difference between pain and nociception. Provide an example of each.

Nociception is the neural process of detecting tissue damage while pain is the conscious perception of damage and is typically related to an emotional response

Understand how neurons with nociceptors transduce stimuli different from other sensory neurons (such as thermoreceptors)

Nociceptors respond to potentially harmful mechanical, thermal, and chemical stimuli that reach a damaging threshold unlike mechanoreceptors that respond to nondamaging touch and pressure

Compare the 2 types of fibers that are involved in the processing of pain.

A-delta fibers are myelinated and transmit sharp, fast pain while C fibers are unmyelinated and carry slower secondary pain

What type of channel are TRP channels? How are they involved in pain?

TRP channels are nonselective cation channels that open in response to heat, cold, or chemicals and initiate depolarization in nociceptors

How is pain sensitized in the PNS?

pain is sensitized when inflammatory mediators lower the activation threshold of nociceptors, making them more responsive to stimuli.

Nociception/pain is carried in which pathway from the spinal cord to CNS for the body? And which pathway for the face? What type of pain is carried in these pathways?

The pain signals travel through the spinothalamic tract of the anterolateral system in the body but in the face they travel through the trigeminothalamic pathway. They both carry conscious localized pain and temperature sensations from a-delta fibers

C fibers also feed into the Anterolateral System, but they don’t terminate in the somatosensory cortex (like A-delta fibers do). Instead, they terminate where?

C fibers terminate in the brainstem and limbic regions which process emotional and autonomic aspects of pain

What is referred pain? Why does this occur?

referred pain happens when visceral and skin afferents synapse on the same second-order neuron, causing the brain to misinterpret internal pain as coming from the skin, like shoulder pain during a heart attack

Auditory stimuli are characterized as what type of molecules?

vibrating air molecules

The amplitude of auditory stimuli refers to what?

sound intensity

The wavelength of auditory stimuli refers to what?

frequency/pitch

Explain the general role of the following structures of the ear:

○ Tympanic membrane

○ Malleus, Incus and Stapes

○ Oval window

The tympanic membrane vibrates in response to sound waves and transfers energy to the ossicles. The ossicles amplify vibrations and transmit them from the tympanic membrane to the oval window. The oval window receives vibrations from the stapes and transmits them into cochlear fluid as pressure waves.  

The fluid wave within the cochlea leads to the movement of the organ of corti via displacement of what part?

the basilar membrane

What are inner hair cells are responsible for?

the inner hair cells are primary sensory receptors that encode sound and send information to the brain

Outer hair cells are responsible for what?

amplifying and tuning basilar membrane motion

What is the function of efferent inputs to the OHCs?

They modulate ohc motility to control amplification and protect from loud sounds

Understand the tonotopic map of the basilar membrane

the map shows that high frequencies peak at the base and low frequencies peak at the apex

What are stereocilia? How is the kinocilium different?

graded actin filled projections on hair cells while the kinocilium is the single tallest cilium that sets polarity

Stereocilia are connected to each other via what structure? This structure is connected to what type of channel on the stereocilia?

tip links connect stereocilia via mechanically gated potassium (K+) channels

Explain the steps of auditory transduction in the hair cell? Explain the mechanism if stereocilia move towards or away from the kinocilium

Sound induces motion of the basilar membrane, deflecting the stereocilia. Deflection toward the kinocilium increases tip-link tension allowing k+ influx from endolymph to flow, depolarizing the cell. Deflection away from kinocilium relaxes tip links closing k+ channels leading to hyperpolarization and reduced transmitter release. This is a graded receptor potential encoding both magnitude and direction of mechanical displacement

What is the difference between the endolymph and perilymph? How do they contribute to the transduction of auditory stimuli?

Endolymph bathes stereocilia containing very high k+. Perilymph surrounds the basolateral membrane and contains low k+ which allows K+ to exit the cell after depolarization, restoring it to its resting state. This arrangement enables hair cells to use potassium entry as the depolarizing current which is metabolically efficient. 

Describe the central transmission of auditory information

Hair cells to the cochlear nerve to cochlear nuclei to inferior colliculus to medial nucleus to primary auditory cortex

What is the vestibular labyrinth composed of and what are their functions?

composed of semicircular canals detecting angular acceleration and the utricle and saccule which detect linear acceleration and head tilt

What is the Cupula? What type of fluid is the cupula housed in?

a gelatinous structure in the ampulla that bends with endolymph movement because it is immersed in endolymph

What is the otoconia?

calcium carbonate crystals that add mass and allow detection of acceleration and gravity (ear rocks)

The intensity and the energy of light refers to what?

The intensity is the number of photons and the energy refers to the wavelength

Cornea

the highly refractive outer surface of the eye which focuses light

Iris

pigmented, adjusts pupil size

Pupil

Opening controlled by the iris determining how much light enters the eye

Lens

changes shape to focus images on the retina

Retina

neural tissue containing photoreceptors, transduces light

Vitreous humor

gel maintaining eye shape

Fovea

region of highest cone density and visual acuity

Optic disk

blind spot where cranial nerves exit the eye

What is the role/function of the retina?

Transduces light into electrical signals to send action potentials

What does the pigment epithelium do?

supports photoreceptors by recycling, absorbing stray light and maintaining health

What do photoreceptors do? What are the two types of photoreceptors?

photoreceptors convert light into graded electrical signals, rods and cones 

Horizontal cells

lateral inhibition, enhance contrast

Bipolar cells

relay photoreceptor signals to ganglion cells

amacrine cells

interneurons that modulate bipolar ganglion signaling

ganglion cells

output neurons of the retina that generate action potentials

What are the 3 segments of photoreceptors and what are their functions?

the outer segment contains the optic disc and opsins, the inner segment contains metabolic machinery, and the synaptic terminal releases glutamate

Compare and contrast Rods and Cones

rods detect light and dark are highly sensitive and function better than cones in low light. cones are concentrated in the fovea and provide color vision

During phototransduction, does light hyperpolarize or depolarize photoreceptors? How does this happen?

Light hyperpolarizes photoreceptors by activating opsins which activate transducin triggering PDE to lower cGMP which closes cation channels

Describe the effect that dark and light environments have on the transduction of rods.

In dark environments there is a lot of cGMP keeping cation channels open leading to high glutamate release while in light the cells hyperpolarize and glutamate release decreases.

Explain how transduction is initiated in the retina.

photon absorption by opsin converts 11-cis retinal which ultimately activates transducin

Describe how the activation of Transducin leads to hyperpolarization?

Transducin activates PDE → PDE lowers cGMP → cation channels close → membrane hyperpolarizes.

Why are we able to differentiate between visual inputs in the fovea better than peripheral regions of the retina?

High cone density, small receptive fields, and minimal convergence onto ganglion cells

What are the three types of opsins found in cones?

short (blue), medium (green), long (red)

All 4 opsins activate transducin, so how are we able to see different colors?

Each opsin absorbs different wavelengths, and compares activity across cone types

What are the two types of ganglion cells?

the on center and off center

What NT does horizontal cells release? What effect do horizontal cells have on vision?

GABA, it mediates lateral inhibition to enhance contrast

Explain how disinhibition is involved in the ganglion cell depolarization and hyperpolarization?

Photoreceptor hyperpolarization reduces glutamate release which can relieve inhibition on bipolar cells, allowing them to depolarize depending on receptor type (on vs off pathway)

Explain the Off-center pathway in the light and dark:

In the dark the photoreceptor is depolarized releasing lots of glutamate causing ionic receptor depolarization off bipolar and depolarize the off ganglion. In the light the photoreceptor is hyperpolarized causing less glutamate release so the off bipolar hyperpolarized and the off ganglion decreases firing.

Explain the On-Center pathway in the light and dark:

In the dark the photoreceptor depolarizes then glutamate activated mGluR6 causing the on bipolar to hyperpolarizes and the ON ganglion decreases firing. In the light the photoreceptor hyperpolarizes causing less glutamate release and mGluR6 inhibition is removed so the on bipolar depolarizes and the ON ganglion increases firing 

Describe the central visual pathway from optic nerve to primary visual cortex

optic nerve to the optic chiasm to optic tract to the lateral geniculate nucleus to the optic radiations to the primary visual cortex

How much information crosses over at the chiasm?

only nasal retinal fibers cross while temporal fibers stay ipsilateral

Describe the orientation of retinal maps in the brain.

maps are reversed and inverted