PSL 431 Exam 3

function of RAS in sensation

responsible for interpretation of pain (awareness, alertness and arousal)

Compare and contrast Conductive Deafness and Sensorineural Deafness in terms of which anatomical structures are affected and which type of deafness is reversible.

1) Anything that Blocks Sounds Waves from Getting in Causes Conductive Deafness . Sound waves not adequately conducted through the external and middle parts of ear This means the internal fluids are not set in motion so less movement of Hair Cells 2)Sensorineural Deafness Occurs if Sound Waves Can't be Detected due to DAMAGE: •Damage (lesion) to any portion of auditory pathway IN the brain (including auditory cortex) •Damage to Auditory Nerve conveying info from Inner Ear TO the brain •Damage to Inner Ear Organ of Corti that results in LOSS OF HAIR CELLS!

Major function of the discrete brain regions

1. Forebrain = Cerebrum + Diencephalon Cerebrum = Cerebral cortex + Corpus callosum + Sub-cortical nuclei. Cerebral cortex: Outer gray matter and inner white matter - deeply folded and lobed. Essential for sensation, perception, reasoning, learning, memory, and generation of skilled movements. Corpus callosum: Massive bundle of neuron fibers interconnecting left and right cerebral cortical hemispheres. Sub-cortical nuclei (basal nuclei, basal ganglia). Diencephalon = Thalamus + Hypothalamus Thalamus: Synaptic relay station in sensory pathways. Hypothalamus: Control center for bodily homeostasis. Hypothalamus connected to pituitary gland (hypophysis). 2. Cerebellum 3. Brainstem = Midbrain + Pons + Medulla

What are the 5 functional components involved in reflex? Do they belong to CNS or PNS?

1. Sensory Receptor Endings 2. Sensory Neurons 3. Central synapses 4. Motor Neuron 5. Effector Organ CNS

Dorsal column system and somatotopic organization

AP>> Dorsal ganglion>> Anterolateral column of spinal cord>> acending fibers (not afferent or efferent)>> Thalamus>> Somatosensory cortex = Sensation

Describe the general arrangement of Cortex and why this arrangement is important for sensory perception.

All cortex is organized into columns of cells, which allows for processing of multiple features of the stimulus. This enhances sensory perception

Discriminate presynaptic and postsynaptic neurons

At the synapse, the firing of an action potential in one neuron, the presynaptic, or sending, neuron—causes the transmission of a signal to another neuron—the postsynaptic, or receiving, neuron—making the postsynaptic neuron either more or less likely to fire its own action potential.

Discriminate CNS and PNS (what is the key difference)

CNS: Spinal cord and brain PNS: Nerves and ganglia outside of brain and spinal cord Structure Cluster of neuron cell bodies Bundle of neuron axons In CNS Nucleus(nuclei) Pathway, tract In PNS (peripheral nervous system) Gaglion (ganglia) Nerve

Identify the photoreceptors that mediate color vision, how they detect different colors, and how they are disrupted to cause color blindness.

Cones mediate the visual perception of color. S cones>>>short wavelength>>>>BLUE M cones>>> medium wavelength>>>> GREEN L cones>>> long wavelength>>>> RED Mutation or loss of cone opsins causes color blindness

Define the concept of Dark Adaptation. Give an example of when it might occur in your life, and explain why it can occur, being sure to reference the phototransduction process.

Dark adaptation is a lag in cGMP Regeneration. Can occur wen going from a brightly lit room to a dark one. This occurs because the light activates the G protein, the alpha subunit then binds to the effector enzyme PDE which breakdown the second messenger cGMP (which is normally in a dark cell) which means the cGMP gated Na+ channel will close causing hyperpolarization. When you travel to a dark room there is a lag in cGMP regeneration, but once there is a sufficient amount of cGMP it will open the cGMP gated Na+ channel.

Diagram how visual info from each eye crosses (or not) in the brain and which side of the primary visual cortex will receive visual info from each eye. Explain how this arrangement allows for visual processing from each eye to be processed in the same area of cortex.

Fibers from Temporal Retina DO NOT cross. Fibers from Nasal Retina cross to opposite side of brain at optic chiasm. If brain receievs input from BOTH eyes it enables BINOCULAR VISION Right Cortex: Left Nasal Right Temporal Left Cortex: Right Nasal Left Temporal

Compare and contrast the structure and function of the two types of retinal photoreceptor cells. You should be able to comment on their photopigments, type of vision they mediate, abundance throughout the retina and their acuity.

General Structure of Photoreceptors: Outer Segment (specialized for phototransduction, contains photopigments) >> Inner Segment (acts as cell body, w/ nucleus)>>> Axon Terminal ( Releases Glutamate to bipolar cells to convey visual info) Rods: Night Vision, High light sensitivity, Lots of photopigment (RHODOPSIN), High amplification ( single photon detection), Slow response, Not in Fovea, Low acuity. Cones: Day vision, Lower light sensitivity, less photopigment (3 types), Lower amplification, fast response, In Fovea, High acuity.

Discriminate white matter and grey matter

Gray matter: General term for area that is mostly neuron cell bodies and dendrites (so lots of _synapses_). White matter: General term for area that is mostly axons (white because many of the axons are covered with _myelin___.

Discuss how Photopigments are similar to GPCRs, and identify the intracellular proteins and second messengers of this GPCR-type pathway.

Have 7- transmembranes G Proteins: Transducin Effector Enzyme: PDE (Phosphodiesterase) Second Messenger: cGMP

Explain why light reception is imperfect via most parts of retina, but is clearest in the Fovea.

Lack of cell bodies at fovea allows light to pass through undistorted to the photoreceptors. So, fovea provides the clearest image of any part of the retina.

Describe why lesions to parts of the visual system (retina, optic nerve, optic chiasm, optic tract, LGN or visual cortex) would produce different extents of blindness.

Lesions of Retina/Optic Nerve: total blindness in the eye Lesion of the Optic Chiasm lose info from crossing axons Lesion at Optic Tract or LGN: partial blindness Visual Cortex Lesion: partial blindness due to loss of processing area

Major components involved in the sensation of pain

Nociceptors are bare endings of SANs. In response to noxious stimuli, nociceptors initiate afferent action potentials in SAN. Processing by central synapses. Motor response: Activation (contraction) of flexor muscles to hurt limb. Deactivation (relaxation) of the extensor muscles to the limb.

Contrast the ion composition of the Perilymph and Endolymph within the inner ear. Explain where each fluid is found, and describe how the composition of Endolymph contributes to activating the auditory receptor cells.

Perilymph (Regular ECF) is located in the scala vestibuli/ scala tympani and it has a higher concentration of Na+ Endolymph (ECF of stereocilia) is located betwee the vestibuar membrane and the Basilar Membrane and it has a very high concentration of K+ which means it WANTS to ENTER the cell.

Describe the arrangement of the cells in the retina, and how their arrangement dictates the direction of light reception and retinal visual processing.

Photoreceptor Cells (PR cells) are located in the back of the retina and detects light, Bipolar Cells come before the PR cells and receive messages from the PR cell, Ganglion Cells are in the very from of the retina and it receives messages from the Bipolar cells and their axons send messages via optic nerve to brain.

Diagram the general arrangement of all sensory systems. Next to it, diagram the arrangement of the visual system, being sure to identify the specific structures required for vision. Indicate where any "crosses" of sensory processing occur and when the visual input is being sensed outside or inside the brain.

Receptor Cells (Detect sensory stimulus)>>>>>>>Second Order Neurons(Neurons that Receive and/or process the chemical message)>>>>>>Neurons that SEND MESSAGE into the BRAIN>>>>Message is received and processed in the THALAMUS>>>> Thalamus conveys message to PRIMARY CORTEX

Explain how the tympanic membrane and the ossicles convert a sound wave to a mechanical vibration in the inner ear. Explain how the mechanical vibration gets converted into fluid movement.

Sound waves move the air in the ear canal, which moves the TM and the connected ossicles converting sound wave into mechanical movement. The stapes then rhythmically taps on the oval window of the scala vestibuli which is fluid filled therefore converting mechanical movement to fluid movement.

Identify which retinal cells can fire action potentials and which are regulated only by graded depolarization.

Rods and cones DO NOT fire action potentials, they respond to light with graded changes in Vm. Dark: depolarizes photoreceptor cell Light: hyperpolarizes photoreceptor cell Ganglion Cells fire Action Potential

Discriminate SAN, SEN, VAN, VEN, sensory neuron, and motor neuron

Somatic afferent neurons = SAN = Afferent (sensory) neurons innervating body's framework and outer wall, including -- skin, skeletal muscles, tendons, bones, and joints. Visceral afferent neurons = VAN = Afferent (sensory) neurons innervating the internal organs Somatic efferent neurons = SEN = Efferent (motor) neurons innervating skeletal muscle fibers. AP's in SEN always cause excitation-----contraction of the skeletal muscles . Autonomic (visceral) efferent neurons = VEN = Efferent (motor) neurons innervating cardiac muscle, smooth muscle and glands__. AP's in VEN cause either _excitation or inhibition on the target tissues_.

Draw a sound wave for a loud sound vs. a soft sound. Draw a sound wave for a low pitch sound vs. a high pitch sound. Using your drawings, explain how the appearance of the waves convey differences in pitch and volume.

The amplitude of the wave (height of peak) determines loudness The frequency of waves (distance between peaks) determines pitch

Describe how the location of an auditory receptor cell within the inner ear determines the pitch and volume of sound that is detected. It may be helpful to draw the portion of the inner ear on which the auditory receptor cells are found, to describe how they respond to sound waves.

The location of the Basilar Membrane deflection and the moved hair cells convey the frequency/pitch HIGH Frequency waves detected near Oval Window LOW frequency waves detected near Helicotrema •Specific Inner Hair cells convey info about the PITCH (Frequency) of sound depending on where they lay on BM Every Inner Hair Cell can convey LOUDNESS (Amplitude) via how much stereocilia bend against Tectorial membrane

Contrast how sound dissipation vs. sound reception occurs via the inner ear. It might be helpful to diagram the pathway.

The long way of fluid movement, which causes the round window to vibrate leads to the dissipation of sound energy. The short cut moves fluid from the scala vestibuli against the vestibular membrane, which causes displacement of the Basilar Membrane. This leads to sound reception.

Explain why the arrangement of retinal cells causes us to have a Blind Spot in our vision.

The portion of retina in front of the optic nerve lacks photoreceptors so it can't transmit visual info

Explain why ear pain may occur when you are in an airplane and be sure to identify the structure(s) of the ear causing the pain . Explain what "popping" your ears means, and why this helps to relieve the pain.

The tympanic membrane is bordered by air, which means it is subject to atmospheric pressure. Rapid pressure decrease cause more pressure outside the TM than inside so the eardrum bulges Opening the Eustachian Tubes equalizes pressure on each side and the eardrum pops back into normal orientation.