Neurotransmitter Review Quiz

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Questions and Answers

In the mesocortical pathway, where is dopamine released?

Ventral tegmental area (VTA) (correct)

Substantia nigra

Frontal cortex

Limbic system

What natural ligand binds to nicotinic receptors?

Acetylcholine (correct)

Norepinephrine

Dopamine

Nicotine

Which feature is characteristic of muscarinic ACh receptors?

They are metabotropic and slow in response. (correct)

They are ionotropic and fast-acting.

They are stimulated by dopamine.

They primarily function at the neuromuscular junction.

What is the exception to the contralateral sensory information processing in the nervous system?

Olfactory system Signup and view all the answers

What is the primary role of the primary motor cortex?

Controlling the contralateral side of the body Signup and view all the answers

Which hemisphere of the brain is primarily responsible for language production?

Left hemisphere Signup and view all the answers

What does the corpus callosum connect?

The two hemispheres of the brain Signup and view all the answers

What happens to lateralization effects when the corpus callosum is cut?

They can be more readily observed Signup and view all the answers

What role does the amygdala play in brain function?

Emotion and emotional memory formation Signup and view all the answers

What are the basal ganglia primarily involved in?

Control of movement Signup and view all the answers

Which structure acts as the 'master gland' of the endocrine system?

Pituitary gland Signup and view all the answers

Which function is NOT associated with the hypothalamus?

Regulating sensory information Signup and view all the answers

What effect does a drug that blocks acetylcholinesterase have on acetylcholine levels?

It prevents acetylcholine breakdown. Signup and view all the answers

Which mechanism does monoamine oxidase (MAO) inhibit to treat depression?

Inhibition of dopamine breakdown. Signup and view all the answers

What is the primary function of monoamine oxidase inhibitors in synaptic transmission?

They allow dopamine to accumulate in the synapse. Signup and view all the answers

Which of the following correctly describes how selective serotonin reuptake inhibitors (SSRIs) function?

They inhibit the reuptake of serotonin. Signup and view all the answers

Which drug would lead to a decrease in norepinephrine levels in the synapse?

SNRIs Signup and view all the answers

What role does acetylcholinesterase play in synaptic transmission?

It breaks down acetylcholine after transmission. Signup and view all the answers

What effect do drugs that are agonists for a neurotransmitter typically have?

They mimic the neurotransmitter's effects on receptors. Signup and view all the answers

Which of the following describes a common function of reuptake inhibitors?

Increase the availability of neurotransmitters in the synapse. Signup and view all the answers

What is the primary purpose of the Nissl Stain in mouse brain studies?

To visualize cell bodies only Signup and view all the answers

Which imaging technique provides a higher resolution than CT scans?

MRI Scan Signup and view all the answers

What does Diffusion Tensor Imaging specifically visualize?

Bundles of axons Signup and view all the answers

What is the primary function of antibodies in immunohistochemistry?

To bind to specific antigens in tissues Signup and view all the answers

What is a limitation of using CT scans for visualizing the brain?

They do not provide detailed images of soft tissues. Signup and view all the answers

What is the main method used in experimental ablation in neuroscience?

Removing or destroying tissue to study behavior effects Signup and view all the answers

What is the purpose of a sham group in lesion studies?

To control for incidental damage during surgery Signup and view all the answers

How are excitotoxic lesions produced in the brain?

By injecting a chemical that stimulates cell death Signup and view all the answers

What does a reversible lesion achieve in neuroscience research?

Temporary disruption of brain activity without permanent damage Signup and view all the answers

What is the significance of the bregma in stereotaxic surgery?

It acts as a reference point for targeting brain regions. Signup and view all the answers

What is the main purpose of histological methods in neuroscience?

To visualize brain tissue as it was in the living organism Signup and view all the answers

What technique is commonly used to cut brain tissue into thin sections for histological study?

Microtome Signup and view all the answers

What is the primary function of placing brain tissue in formalin during histological preparation?

To prevent postmortem decay and preserve natural state Signup and view all the answers

What is the primary purpose of single unit recordings in electrophysiological research?

To implant microelectrodes for measuring individual neuron activity Signup and view all the answers

Which statement accurately describes multi-unit recordings?

They can record postsynaptic potentials from thousands of cells. Signup and view all the answers

What key information should be included when emailing faculty to inquire about undergraduate opportunities?

Availability to volunteer including hours and semesters Signup and view all the answers

Which of the following is an advantage of using electrophysiological recordings?

They allow for real-time recording of neural activity during tasks. Signup and view all the answers

What is a common approach when searching for neuroscience research opportunities?

Searching for faculty interests online and at nearby institutions Signup and view all the answers

What defines Immediate Early Genes (IEGs)?

They turn on when neurons become active. Signup and view all the answers

What is a significant limitation of Positron Emission Tomography (PET)?

It requires the use of radioactive tracers. Signup and view all the answers

Which imaging technique provides the best spatial and temporal resolution?

Functional MRI (fMRI) Signup and view all the answers

What is a characteristic feature of Conditional Knockout mice?

They allow temporal control over gene expression. Signup and view all the answers

How does Functional MRI (fMRI) detect brain activity?

By tracking changes in blood flow and oxygen levels. Signup and view all the answers

What does the BOLD signal represent in the context of fMRI?

Blood oxygen level-dependent changes in brain activity. Signup and view all the answers

What could be a behavioral cause for the expression of Immediate Early Genes?

Engaging in learning or memory tasks. Signup and view all the answers

What is a primary limitation associated with Constitutive Knockout mice?

They may trigger unwanted compensatory mechanisms. Signup and view all the answers

What structure controls how much light enters the eye?

Pupil Signup and view all the answers

Which type of photoreceptor is primarily responsible for color vision?

Cones Signup and view all the answers

What part of the retina contains no visual receptors and creates a blind spot?

Optic disk Signup and view all the answers

Which photoreceptor type is more sensitive to low light levels?

Rods Signup and view all the answers

Where in the retina are most of the cones concentrated?

Fovea Signup and view all the answers

What is the primary role of photoreceptors in the eye?

Convert light into electrical signals Signup and view all the answers

How does light travel through the eye before reaching the retina?

Through the vitreous humor Signup and view all the answers

What is the main function of the sclera?

Provide structural support Signup and view all the answers

What does optogenetics primarily manipulate in neuroscience research?

Light-sensitive proteins to control neuronal activity Signup and view all the answers

What is a limitation of constitutive knockout mice?

Compensatory mechanisms can mask the effects of the mutation. Signup and view all the answers

How does channelrhodopsin-2 (ChR2) respond when activated?

It opens sodium and calcium channels in response to blue light. Signup and view all the answers

What is the main advantage of conditional knockout mice compared to constitutive knockout mice?

They allow for targeted gene deletion at specific developmental stages. Signup and view all the answers

What process converts external physical stimuli into electrical changes in sensory receptors?

Sensory transduction Signup and view all the answers

Which protein is involved in controlling ion channels and is found in green algae?

Channelrhodopsin-2 Signup and view all the answers

What does sensory adaptation refer to?

The reduced sensitivity to a constant stimulus over time. Signup and view all the answers

What occurs when halorhodopsin (NpHR) is activated?

Chloride ions are transported into the cell. Signup and view all the answers

What occurs during posterior vitreous detachment (PVD)?

The vitreous gel separates from the retina Signup and view all the answers

What is the role of ganglion cells in the retina?

They synapse with bipolar cells to transmit visual information Signup and view all the answers

What happens to photoreceptors in darkness?

They become depolarized and continuously release neurotransmitters Signup and view all the answers

What forms the optic nerve?

Axons of ganglion cells Signup and view all the answers

What happens at the optic chiasm?

Axons from the inner halves of each retina cross to the opposite side of the brain Signup and view all the answers

Which component of photopigments is derived from vitamin A?

Retinal Signup and view all the answers

What physiological change occurs when photopigments are exposed to light?

Photopigments split into opsin and retinal Signup and view all the answers

The outer segment of photoreceptors is primarily composed of what structure?

Lamellae Signup and view all the answers

What happens to the information from the visual fields after it reaches the optic chiasm?

It is processed contralaterally. Signup and view all the answers

What is the primary role of the lateral geniculate nucleus (LGN)?

To serve as the first synapse in the visual pathway. Signup and view all the answers

Why is visual acuity lower in the periphery of the retina compared to the fovea?

Photoreceptors converge on single ganglion cells. Signup and view all the answers

What best describes the function of 'ON' cells in the retina?

They show an excitatory response when the retina is illuminated. Signup and view all the answers

How do receptive fields in ganglion cells typically respond to light?

They exhibit center-surround organization responding oppositely. Signup and view all the answers

What is the effect of having multiple photoreceptors converge on a single ganglion cell in the periphery?

Reduced visual clarity and acuity. Signup and view all the answers

What determines the location of a neuron's receptive field in the visual system?

The location of photoreceptors providing visual information. Signup and view all the answers

What mechanism enables ganglion cells to encode changes in illumination?

The center-surround organization of their receptive fields. Signup and view all the answers

What is the primary function of the ventral stream in visual processing?

To process what an object is Signup and view all the answers

Which structure in the ear acts as a border between the outer and middle ear?

The tympanic membrane Signup and view all the answers

How do vibrations from the tympanic membrane reach the inner ear?

Via the ossicles Signup and view all the answers

Which part of the ear is primarily responsible for amplifying sound?

The ossicles Signup and view all the answers

What two pathways does visual information take from V2?

Ventral stream and dorsal stream Signup and view all the answers

What is the primary function of the retinal ganglion cells in the visual system?

To encode light intensity and wavelength Signup and view all the answers

Why is the primary visual cortex also referred to as the 'striate cortex'?

Due to the presence of a dark staining layer Signup and view all the answers

Approximately what percentage of V1 is dedicated to processing information from the fovea?

25% Signup and view all the answers

What characteristic feature do most neurons in V1 exhibit sensitivity to?

Orientation of stimuli Signup and view all the answers

How do cells in V1 obtain information about visual stimuli?

By collecting from multiple retinal ganglion cells Signup and view all the answers

What is the primary role of the Organ of Corti in the inner ear?

To convert sound pressure into neural signals. Signup and view all the answers

Which structure is primarily responsible for anchoring the hair cells in the Organ of Corti?

Basilar membrane. Signup and view all the answers

How do inner hair cells differ from outer hair cells in the Organ of Corti?

Inner hair cells do not connect to the tectorial membrane. Signup and view all the answers

What initiates the release of neurotransmitters from the hair cells in the Organ of Corti?

Bending of cilia due to fluid movement. Signup and view all the answers

What aspect of sound affects the bending of the basilar membrane in the cochlea?

The frequency of the sound. Signup and view all the answers

What role do the ossicles play in the process of hearing?

They amplify and transfer vibrations to the oval window. Signup and view all the answers

What are the three canals of the cochlea filled with?

Fluid. Signup and view all the answers

Which membrane lies directly over the hair cells in the Organ of Corti?

Tectorial membrane. Signup and view all the answers

What is the primary auditory cortex adjacent to in the brain?

Upper bank of the lateral fissure in the temporal lobe Signup and view all the answers

Which part of the auditory system is involved in sound localization?

Dorsal stream Signup and view all the answers

How does information primarily reach the cortex from the auditory nerve?

Via the medial geniculate nucleus Signup and view all the answers

What type of sounds does the ventral stream in the auditory system primarily process?

Complex sounds Signup and view all the answers

In the auditory system, where do most cochlear axons synapse?

Cochlear nucleus Signup and view all the answers

What percentage of recovery for stage 1 and 2 sleep occurs after sleep deprivation?

7% Signup and view all the answers

What function of slow-wave sleep (SWS) is hypothesized in the context of brain activity?

Restoration process Signup and view all the answers

In adults, which type of memory is predominantly consolidated during slow-wave sleep?

Declarative memory Signup and view all the answers

How much REM sleep do newborns typically spend during their total sleep time?

70% Signup and view all the answers

After sleep deprivation, what percentage of recovery for REM sleep is typically observed?

53% Signup and view all the answers

Which neurotransmitter is primarily involved in activating the cortex and facilitating learning?

Acetylcholine Signup and view all the answers

What effect does stimulation of norepinephrine neurons in the locus coeruleus have?

Increases vigilance and anxiety Signup and view all the answers

Which brain region is primarily associated with REM sleep and cholinergic neurons?

Dorsolateral pons Signup and view all the answers

What happens to norepinephrine neuron activity during REM sleep?

It falls to zero Signup and view all the answers

Which of the following neurotransmitters is primarily secreted by the motor axons of the peripheral nervous system?

Acetylcholine Signup and view all the answers

How long is each cycle of sleep?

90 minutes Signup and view all the answers

What usually characterizes narcolepsy?

Sleep attacks lasting 2-5 minutes Signup and view all the answers

What is a primary symptom of REM Sleep Behavior Disorder?

Acting out dreams while asleep Signup and view all the answers

What physical effects were observed in rats subjected to sleep deprivation?

Loss of body temperature regulation Signup and view all the answers

What distinguishes cataplexy from other forms of sleep disorders?

It is characterized by sudden muscle weakness. Signup and view all the answers

Which of the following best describes a sleep attack?

A sudden intense urge to sleep lasting 2-5 minutes Signup and view all the answers

What is a common misconception about sleep deprivation in humans?

It leads to significant health deterioration. Signup and view all the answers

What is the role of REM sleep in the sleep cycle?

It is primarily associated with memory consolidation. Signup and view all the answers

What type of activity is signified by alpha activity in the EEG?

State of relaxation Signup and view all the answers

Which formula best represents the frequency of delta activity in sleep stages?

< 3.5 Hz Signup and view all the answers

What occurs during REM sleep?

Rapid eye movements and vivid dreams Signup and view all the answers

In which stages of sleep is the subject typically unaware that they are asleep?

Stage 1 and 2 Signup and view all the answers

What is the primary characteristic of slow-wave sleep?

Presence of low-frequency delta activity Signup and view all the answers

How often do REM sleep periods occur throughout the night?

Every 90 minutes Signup and view all the answers

What is the effect of muscle tone during slow-wave sleep?

Slight presence of muscle tone Signup and view all the answers

What brain activity pattern is commonly observed during REM sleep?

Desynchronized and resembling awake state Signup and view all the answers

What is the primary tool used to monitor muscle activity during sleep studies?

Electromyogram (EMG) Signup and view all the answers

What percentage of sleep is typically characterized by REM sleep?

20-25% Signup and view all the answers

Study Notes

Exam 2 Review

The class median was 76%
3 students achieved the highest score of 100%

Acetylcholinesterase

Acetylcholine (ACh) is broken down in the synapse by the enzyme acetylcholinesterase (AChE)
After breakdown, the choline is actively taken back up into the presynaptic terminal and recycled

Monoamine oxidase

Monoamine oxidase (MAO) is an enzyme that breaks down dopamine, norepinephrine, and serotonin
MAO inhibitors are used to treat depression by blocking MAO and preventing the breakdown of these neurotransmitters, increasing their levels in the synapse.

Drugs That Affect Norepinephrine and Serotonin

Selective Serotonin Reuptake Inhibitors (SSRIs) increase the amount of serotonin in the brain by inhibiting its uptake
Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs) inhibit the reuptake of both serotonin and norepinephrine
MDMA (Ecstasy) reverses the direction of the norepinephrine and serotonin transporters, causing them to release these neurotransmitters instead of taking them back up.

Dopamine Pathways

The mesocortical pathway releases dopamine in the frontal cortex, amygdala, and limbic system
The mesolimbic pathway releases dopamine in the striatum (caudate nucleus, putamen, nucleus accumbens)
The nigrostriatal pathway releases dopamine in the substantia nigra

Nicotinic Receptors

Nicotinic receptors are ionotropic and very fast-acting
Nicotinic receptors are found at the neuromuscular junction and in the CNS
Acetylcholine is the natural ligand that binds to nicotinic receptors

Sensory and Motor Cortex

Sensory information originating on one side of the body is sent to the contralateral primary sensory cortex (except for the olfactory and gustatory systems)
The primary motor cortex controls the contralateral side of the body

Hemispheres of the Brain

The left hemisphere is specialized for language production and comprehension
The right hemisphere is specialized for non-verbal and spatial abilities
The two hemispheres are connected by the corpus callosum

Split-Brain Patients

The corpus callosum is severed, preventing communication between the left and right hemispheres
This allows researchers to observe lateralization effects

Basal Ganglia

The basal ganglia are involved in the control of movement and consist of the caudate nucleus, putamen, and globus pallidus
Lesions to the basal ganglia result in uncontrolled movements
Diseases of the basal ganglia include Parkinson's disease and Huntington's disease

Limbic System

The limbic system is a collection of brain structures involved in emotions and memory formation
Key structures include:
- Cingulate Cortex: emotion
- Amygdala: emotion and emotional memory formation
- Septum: "rage" is produced after lesions
- Hippocampus: memory

Thalamus and Hypothalamus

The thalamus relays sensory information from the brainstem to the forebrain and cortex.
The hypothalamus controls the endocrine and autonomic nervous systems
The hypothalamus is involved in the "4 F's" (fighting, fleeing, feeding, and mating)

Pituitary Gland

The pituitary gland is connected to the hypothalamus and is the "master gland" that controls the endocrine system of the body.
It has two regions: the anterior pituitary and the posterior pituitary.

Experimental Ablation

Oldest method used in neuroscience
Involves removing or destroying tissue in a lab animal to study the resulting behavioral consequences

Methods for Producing Brain Lesions

Radio frequency lesion:
- Involves passing alternating current through a wire electrode
- Heat generated kills cell bodies and axons
Excitotoxic lesion:
- Involves injecting a chemical through a cannula
- Chemical stimulates glutamate receptors (kainic acid)
- Kills neurons by stimulating them to death, primarily targeting cell bodies
Reversible lesion:
- Temporarily disrupts brain activity
- Involves injecting a chemical like muscimol
- Blocks action potentials by stimulating GABA receptors
Sham group:
- Animals undergo surgery with the electrode or cannula inserted, but no current or chemical is injected
- Controls for potential damage caused by the surgery itself

Stereotaxic Surgery

Bregma:
- Serves as a reference point
- Junction of the sagittal and coronal bones of the skull
- Used for precise targeting of brain regions based on coordinates from a brain atlas
- Coordinates represent anterior-posterior and medial-lateral positions

Histological Methods

Aims to visualize brain tissue as it was in the living organism
Involves multiple steps:
- Fixation: Using formalin to preserve tissue and prevent decay
- Sectioning: Cutting the tissue into thin slices (10-80 μm thick)
- Staining and mounting: Staining and placing sections on a slide for visualization

Staining

Nissl stain: Visualizes cell bodies of neurons and glial cells
Doublecortin stain: Visualizes young neurons using immunocytochemistry

Immunohistochemistry

Involves antibodies binding to specific antigens in biological tissues
Antibodies are created by injecting animals with the protein of interest and isolating the antibodies from their serum
Tissue is incubated in antibodies that bind to the target protein

Visualizing the Human Brain

CT Scan (Computerized Tomography):
- Oldest method
- Involves X-ray beams passing through the head
- Blood absorbs a lot of radiation, making it appear brighter in the image
MRI Scan (Magnetic Resonance Imaging):
- Higher resolution than CT scans
- Does not use X-rays
- Involves passing a strong magnetic field and radio waves through the head
Diffusion Tensor Imaging:
- Modification of the MRI scanner
- Visualizes bundles of axons based on water molecule movement

Electrophysiological Recordings

Allow for recording neural activity while the animal is performing a task
Provides insight into real-time brain activity during behavior.

Finding Neuroscience Research Opportunities

Identify a lab by searching faculty interests online.
Search for faculty at nearby institutions like Mount Sinai School of Medicine, NYU, and Cornell Medical Center.
Email professors expressing interest in joining their lab.
Be sure to include your transcript, GPA, year at Hunter, and availability to volunteer in your email.

Electrophysiological Recordings

There are two types of electrophysiological recordings: single-unit and multi-unit recordings.
Single-unit recordings involve the implantation of microelectrodes to record the activity of individual neurons.
Multi-unit recordings involve the implantation of macroelectrodes which record postsynaptic potentials from thousands of cells in one location.
Electroencephalogram (EEG) recordings from the scalp are similar to multi-unit recordings in humans.

IEG Expression

Immediate early genes (IEGs) are turned on when neurons become active.
Commonly used IEGs are Fos and Arc.
IEG expression can be induced by behavioral stimuli or direct current application.

PET Imaging

The first functional imaging method, involving the administration of a radioactive tracer (2-deoxyglucose).
Active cells take up the tracer and emit a positron signal.
Extremely expensive with poor spatial and temporal resolution.

fMRI

Offers the best spatial and temporal resolution.
Detects oxygen levels in brain blood vessels through the Blood Oxygen Level Dependent (BOLD) signal.

Targeted Mutations In Mice

Mutated genes can be produced and inserted into the chromosomes of mice in the lab.
Constitutive Knockout mice: The target of the mutation prevents the production of a specific protein.
Conditional Knockout mice: Temporal control over the gene using conditional knockout mice allows for normal development in the mice.

Manipulating Circuits

Optogenetics is a technique used to manipulate specific circuits in the brain.
Channelrhodopsin-2 (ChR2) is a light-sensitive protein found in green algae that controls ion channels and responds to blue light by opening sodium and calcium channels.
Halorhodopsin (NpHR) is a light-sensitive protein found in bacteria that controls a transporter and responds to yellow light by moving chloride into the cell.

Targeted Mutations In Mice

Mutated genes can be produced and inserted into the chromosomes of mice.
Constitutive Knockout Mice: The target of the mutation prevents the production of a certain protein; compensatory mechanisms are a limitation.
Conditional Knockout Mice: Allow for temporal control over the gene expression, benefiting from mice developing normally.

The Visual System

Sensory Receptors: Specialized neurons that detect physical stimuli in the external world.
Sensory Transduction: The process of transforming stimuli from the external world into electrical changes.
The Eye: Part of the CNS, the retina is an extension of the brain; suspended in the orbits of the skull; six extraocular muscles attach the eye to the skull.

The Eye components

Sclera: Outer white covering.
Hole: Where light enters.
Muscular Ring: Controls how much light gets in.
Lens-like Structure: Focuses light on the retina.
Location of Sensory Receptors & Sensory Transduction: The retina.
Part of the CNS: Output to the brain.

Photoreceptors

Photoreceptors convert light (electromagnetic radiation) into electrical signals (sensory transduction).
Cones: 6 million - responsible for daytime vision, high visual acuity, and processing color.
Rods: 120 million - better for nighttime vision, provide vision of poor acuity, and are more sensitive to light.

The Fovea

The central region of the retina.
Concentrates most of the cones in the retina.
Mediates our most acute vision.

Optic Disk

Located on the retina.
Where axons carrying visual information leave the eye to form the optic nerve.
Doesn’t contain receptors, resulting in a blind spot.

The Visual System

Posterior vitreous detachment (PVD) occurs when the vitreous humor separates from the retina, leading to floaters, flashes of light, and reduced vision.

Retina Anatomy

The retina contains three main cell types: photoreceptors (rods and cones), bipolar cells, and ganglion cells.
Photoreceptors are responsible for light detection.
Bipolar cells relay information from photoreceptors to ganglion cells.
Ganglion cells generate action potentials and form the optic nerve, transmitting visual information to the brain.

Photoreception and Light

Photoreceptors have outer and inner segments.
Outer segments contain lamellae, which hold photopigments.
Photopigments consist of opsin (a protein) and retinal (derived from vitamin A).
Light exposure splits the photopigment, leading to hyperpolarization of the photoreceptor.
Hyperpolarization decreases neurotransmitter release.

Neural Circuitry in the Retina

Photoreceptors and bipolar cells do not fire action potentials.
Depolarization increases neurotransmitter release.
Hyperpolarization decreases neurotransmitter release.
Photoreceptors are depolarized in darkness and continuously release neurotransmitter.
When neurotransmitter binds to bipolar cells, it triggers downstream signals.

Information Flow

Light triggers a cascade of events, ultimately resulting in hyperpolarization of photoreceptors.
This signal is transmitted through bipolar cells to ganglion cells.
Ganglion cells fire action potentials, relaying visual information to the brain via the optic nerve.

Beyond the Retina

Ganglion cell axons form the optic nerve.
The optic nerve fibers cross at the optic chiasm, forming the optic tracts.
Axons from the nasal (inner) half of each retina cross to the contralateral side of the brain.
Axons from the temporal (outer) half of each retina stay on the ipsilateral side.

Processing in the Lateral Geniculate Nucleus (LGN)

After the optic chiasm, axons reach the LGN of the thalamus.
LGN neurons receive visual input from the retina, acting as the first synapse.
LGN neurons send axons via the optic radiations to the primary visual cortex in the brain.

Information Coding in the Retina

Fovea: The central point of the retina responsible for high resolution vision.
Peripheral: Less visual acuity due to increased convergence of photoreceptor input onto ganglion cells.

Types of Ganglion Cells

"ON" cells: Fire action potentials in response to increases in light intensity.
"OFF" cells: Fire action potentials in response to decreases in light intensity.
These cells allow for the detection of changes in illumination as you move your eyes.

Receptive Fields

The receptive field of a visual neuron is the region of the visual field that affects its response.
Ganglion cells have center-surround receptive fields:
- The center and surround respond to light in opposite ways.
- This allows for contrast detection and edge enhancement.

Light

Retinal ganglion cells encode how much light falls on the center and surround of their receptive fields.
They carry information about the wavelength of light (color).

Primary Visual Cortex

Also known as the "striate cortex" because it contains dark-staining layer.
Approximately 25% of V1 is devoted to processing information from the fovea.
Cells in V1 respond to specific features of the visual world, each individual cell in V1 collects information from several different retinal ganglion cells.

Visual Association Cortex

V1 cannot “see” a whole object, only features.
Output of V1 is sent to the adjacent extrastriate cortex, or V2.
V2 cells receive input from several V1 cells.
Information begins to be reassembled to “rebuild” visual scene.
The visual information then takes one of 2 paths:
- The Ventral Stream – projects to the inferior temporal lobe, processes “what” an object is.
- The Dorsal Stream – projects to the posterior parietal lobe, processes “where” an object is.

Sound as a Stimulus

Sounds are produced by objects that vibrate.
A vibrating object causes the molecules of air to alternately condense together and pull apart, creating a sound wave.

The Outer Ear

Sound is first collected from the environment by the pinnae.
Sound waves are funneled by the pinnae into the ear canal.
The length and shape of the ear canal enhances certain sound frequencies.

The Tympanic Membrane

The tympanic membrane is the ear drum.
It is a thin membrane at the end of the outer ear canal.
It vibrates in response to sound.
It borders the outer and middle ear.

The Middle Ear

The ossicles are three tiny bones that amplify and transmit sounds to the inner ear.
They are the smallest bones in the body.
Vibrations from the tympanic membrane first reach the malleus (hammer).
The malleus connects with the incus (anvil).
The incus connects to the stapes.
The stapes is attached to the oval window of the cochlea.
The stapes is the smallest bone in the body.

The Inner Ear

The inner ear is where fine changes in sound pressure are translated into neural signals.
Its function is analogous to that of the retina.
It consists of the cochlea.
- The cochlea is a spiral structure.
- It contains the Organ of Corti.
- It is filled with fluid in three parallel canals.

Three Canals of the Cochlea

The three canals of the cochlea are:
- Vestibular canal
- Tympanic canal
- Middle canal
Three canals are separated by membranes:
- Reissner’s membrane
- Basilar membrane

The Organ of Corti

The Organ of Corti has 3 major parts:
- Hair Cells – the receptive cells of the auditory system.
- Basilar Membrane – anchors the hair cells.
- Tectorial Membrane – lies over the hair cells.

Hair Cells

Hair cells in the Organ of Corti are embedded in the basilar membrane.
Each hair cell contains a soma and a number of cilia that protrude from the top.
Two major types of hair cells:
- Inner Hair Cells – less numerous; do not touch overlying tectorial membrane but moves when fluid moves
- Outer Hair Cells – more numerous; directly attached to the tectorial membrane.
The hair cells make synapses with bipolar cells whose axons bring the information from the inner ear to the brain.

Transduction of Sound

Sound waves that enter the ear cause the tympanic membrane to vibrate at the same frequency.
The tympanic membrane translates the vibrations to the ossicles, which transfer them to the oval window of the cochlea.
Vibrations at the oval window cause the basilar membrane and the tectorial membrane to flex up and down.
These movements bend the cilia of the hair cells in one direction or another, which initiates the release of neurotransmitters.
The portion of the basilar membrane that bends the most is determined by the frequency of the sound.*

Anatomy of the Ear

The ear is divided into the outer, middle, and inner ear.
The outer ear captures sound waves and channels them through the ear canal to the eardrum.
The middle ear amplifies sound vibrations by the movement of three small bones (malleus, incus, and stapes) through a fluid-filled chamber.
The inner ear houses the cochlea, a snail-shaped structure containing the organ of Corti, which is responsible for converting sound vibrations into electrical signals that the brain can interpret.

Central Auditory Pathways

Auditory information travels from the cochlea to the brain via the auditory nerve, which synapses in the cochlear nucleus.
Most cochlear axons cross over to the opposite side of the brain and synapse in the superior olive, then the inferior colliculus, and finally the medial geniculate nucleus.
The auditory cortex is the last stop in the auditory pathway, where sound information is processed and interpreted.

Auditory Cortical Areas

The primary auditory cortex is located in the temporal lobe and receives information from both ears, primarily from the contralateral ear.
The auditory association cortex surrounds the primary auditory area and further processes auditory information.
There are two streams of auditory information flow: the dorsal stream, which is involved in sound localization ("where"), and the ventral stream, which is involved in processing complex sounds ("what").

What is Sleep?

Sleep is a state of altered consciousness characterized by decreased awareness and responsiveness to the environment.
Brain activity during sleep can be measured using an electroencephalogram (EEG), which records the electrical activity of the brain.
Muscle activity during sleep can be measured using an electromyogram (EMG) and eye movements using an electrooculogram (EOG).

Stages of Sleep

Sleep is divided into stages based on brain wave patterns and other physiological measures.
There are two main types of sleep: non-REM sleep (stages 1-4) and REM sleep.
Non-REM sleep is characterized by progressively slower and more synchronized brain waves, whereas REM sleep is characterized by brain waves that resemble wakefulness, rapid eye movements, and muscle paralysis.

Non-REM Sleep

Stages 1 and 2 of sleep are transitional and the individual may not be aware they are asleep.
Stages 3 and 4 are known as slow-wave sleep, characterized by low-frequency delta activity, light breathing, muscle tone, and difficulty waking up.

REM Sleep

REM sleep typically occurs every 90 minutes throughout the night.
It is characterized by rapid eye movements, complete loss of muscle tone, vivid dreams, increased respiration, and increased blood pressure.

Cycles of Sleep

We cycle through periods of REM and non-REM sleep throughout the night.
Each sleep cycle is approximately 90 minutes long and contains around 20-30 minutes of REM sleep.

Disorders of Sleep

Insomnia is the inability to fall asleep or stay asleep.
Sleep apnea is a disorder where breathing repeatedly stops and starts during sleep, often caused by airway obstruction.
Narcolepsy is characterized by excessive daytime sleepiness, sleep attacks, and cataplexy (sudden loss of muscle tone).
REM sleep behavior disorder involves acting out dreams during sleep due to a lack of muscle paralysis during REM sleep.

Why Do We Sleep?

Sleep is essential for survival and proper functioning.
Sleep deprivation can lead to impaired cognitive function, reduced performance, and even death in animals.
The functions of sleep are still being researched, but they are thought to include restoration, memory consolidation, and brain development.

Functions of Slow-wave Sleep

Slow-wave sleep (SWS) may be involved in restoration, allowing brain regions that are more active during the day to rest.
SWS is characterized by low levels of metabolic activity and is thought to allow brain regions to recover and repair.

Functions of REM Sleep

REM sleep in children may promote brain development.
In adults, REM sleep and SWS may be involved in memory consolidation processes.
REM sleep is thought to be important for nondeclarative memory, while SWS is thought to be important for declarative memory.

Mechanisms: The Neural Basis of Arousal

Many neurotransmitters are involved in regulating arousal and wakefulness.
The brainstem plays a crucial role in regulating sleep-wake cycles.

Acetylcholine

Acetylcholine (ACh) is a neurotransmitter involved in muscle movement and is also widely distributed in the brain.
ACh neurons in the basal forebrain play a key role in cortical arousal.
Stimulation of ACh neurons increases cortical activation and desynchrony of the EEG.
ACh levels are higher in multiple brain regions during wakefulness and alertness.