Nervous System Features Quiz

Exam # 2 - Basic Features of the Nervous System

• The class median score for Exam # 2 was 76%.
• The highest score was 100%, achieved by 3 students.
• The second highest score was 98%, achieved by 5 students.
• The third highest score was 96%, achieved by 6 students.

Acetylcholine

• Acetylcholine is terminated in the synapse by an enzyme called acetylcholinesterase.
• The choline from the breakdown of acetylcholine is actively transported back into the presynaptic terminal.

### Monoamine oxidase (MAO)

• MAO inhibitors are commonly used to treat depression.
• They block the breakdown of dopamine.
• They increase the amount of dopamine available in the synapse.

Norepinephrine & Serotonin

• MDMA, SNRIs and SSRIs increase the amount of norepinephrine and/or serotonin in the synapse.
• SSRIs, like Prozac, inhibit serotonin reuptake.
• SNRIs, like Effexor, inhibit both serotonin and norepinephrine reuptake.

Dopamine

• Dopamine mesocortical pathway: dopaminergic neurons project from the ventral tegmental area (VTA) to frontal cortex and limbic system.

Nicotinic Receptors

• nicotine is an agonist at nicotinic receptors.
• Nicotinic receptors are ionotropic receptors.
• Nicotinic receptors cause rapid neuronal depolarization.

Lateralization

• Sensory information originating on one side of the body is sent to the contralateral primary sensory cortex, except for olfactory and gustatory systems.
• The primary motor cortex controls the contralateral side of the body.
• The left hemisphere is specialized more for language production and comprehension.
• The right hemisphere is specialized for non-verbal and spatial abilities.

Corpus Callosum

• The two hemispheres of the brain are connected by the corpus callosum.

Split-Brain Patients

• Split-brain patients allow researchers to study lateralization.
• The corpus callosum has been surgically severed in split-brain patients.
• Communication between the two hemispheres is disrupted.

Basal Ganglia

• The basal ganglia control movement.
• Lesions in the basal ganglia result in uncontrolled movements.
• The basal ganglia includes the caudate nucleus, putamen, globus pallidus.

Limbic System

• The limbic system plays a role in emotions and memory formation.
• The limbic system includes the cingulate cortex, amygdala, septum, and hippocampus.

Hypothalamus and Pituitary

• The hypothalamus controls the endocrine and autonomic nervous systems.
• The pituitary gland is connected to the hypothalamus, and controls the endocrine system of the body.

Experimental Ablation

• Researchers remove or destroy brain tissue in laboratory animals to observe the consequences on behavior.
• Oldest method used in neuroscience.
• Also known as lesion studies.

Methods For Producing Brain Lesions

• Radio frequency lesion:
  • Involves passing alternating current through a wire electrode.
  • Heat kills cell bodies and axons.
• Excitotoxic lesions:
  • Inject a chemical (e.g., kainic acid) through a cannula.
  • Stimulates neurons to death.
  • Kills cell bodies, not axons.
• Reversible lesion:
  • Temporary disruption of brain activity.
  • Inject a muscimol through a cannula.
  • Blocks action potentials by stimulating GABA receptors.
• Sham group:
  • Animals undergo surgery with electrode or cannula inserted but receive no current or chemical injection.
  • Control for incidental damage.

Stereotaxic Surgery

• Bregma:
  • Junction of the sagittal and coronal bones of the skull, serving as a reference point for brain targeting.
  • Used with a brain atlas to obtain coordinates for targeting specific brain regions.

Histological Methods

• Goal is to visualize brain tissue as it was during the organism's life.
• Brain tissue is placed in a fixative (e.g., formalin) to prevent decay and preserve it.
• Tissue is cut into thin sections (10-80 micrometers thick).
• Sections are stained and mounted for microscopic examination.

Immunohistochemistry

• Antibodies bind specifically to antigens in biological tissues.
• Antibodies are produced by injecting animals with the protein of interest and isolating antibodies from their serum.
• Tissue is incubated with antibodies, which bind to their specific targets, allowing visualization of these targets.

Visualizing The Human Brain

• CT Scan:
  • Oldest method, involves passing X-ray beams through the head.
  • Blood absorbs a lot of radiation, making it appear brighter in scans.
• MRI Scan:
  • Offers higher resolution than CT scans.
  • Does not use X-rays.
  • Uses strong magnetic fields and radio waves to produce images.
• Diffusion Tensor Imaging:
  • Modification of MRI scanner.
  • Based on the movement of water molecules.
  • Visualizes bundles of axons by tracing water movement along them.

Electrophysiological Recordings

• Allows for recording neural activity while an animal is performing a task.

Finding Neuroscience Research Opportunities

• Search for faculty interests online at Hunter College using the provided links.
• Look for faculty at nearby institutions like Mount Sinai School of Medicine, NYU, Cornell Medical Center, Albert Einstein Medical Center, The Rockefeller University, and other CUNY schools.
• Email faculty and express interest in their research, attaching your transcript and providing your GPA, Hunter year, and volunteer availability.

Measuring Neural Activity: Electrophysiological Recordings

• Single Unit Recordings: Utilize microelectrodes to record activity of individual neurons, allowing for electrode movement.
• Multi-Unit Recordings: Use macroelectrodes to record postsynaptic potentials of thousands of cells in a single location.
• Electroencephalogram (EEG) Recordings: These recordings are used in humans and offer a non-invasive method similar to multi-unit recordings, collecting neural activity from the scalp.

Measuring Neural Activity: Ex Vivo Brain Tissue

• Immediate Early Genes (IEGs): IEGs like Fos and Arc are activated when neurons become active.
• Fos Protein Expression: The expression of Fos can be induced behaviorally or by applying current.

Measuring Neural Activity: In Humans

• Positron Emission Tomography (PET): The first functional imaging method, PET involves administering a radioactive tracer (2-deoxyglucose) that is taken up by active cells and emits a signal.
• PET Imaging: Increased uptake of 2-deoxyglucose in brain regions indicates higher metabolic rates.
• Functional Magnetic Resonance Imaging (fMRI): This method provides the best spatial and temporal resolution and involves detecting oxygen levels in brain blood vessels using the BOLD signal.

Manipulating Specific Circuits: Targeted Mutations in Mice

• Mutated Genes: Genes can be mutated in the lab and inserted into mouse chromosomes.
• Constitutive Knockout Mice: These mice have a target mutation that prevents the production of a certain protein.
• Conditional Knockout Mice: These mice allow for temporal control over gene expression, enabling normal development before the specific gene is targeted.

Targeted Mutations in Mice

• Mutated genes can be produced in a laboratory setting and inserted into mouse chromosomes.
• Constitutive Knockout Mice: The mutation prevents the production of a specific protein.
  • Limitation: Compensatory mechanisms can occur.
• Conditional Knockout Mice: Temporal control over the gene expression allows for normal development.
  • Advantage: Mice can develop normally.

Manipulating Circuits Using Optogenetics

• Channelrhodopsin-2 (ChR2): A photosensitive protein found in green algae.
  • Function: Controls ion channels.
  • Activation: Responds to blue light by opening sodium and calcium channels.
• Halorhodopsin (NpHR): A photosensitive protein found in bacterium.
  • Function: Controls transporter.
  • Activation: Responds to yellow light by moving chloride into the cell.

The Visual System

• Sensory Receptors: Specialized neurons that detect physical stimuli in the external world.
• Sensory Transduction: The process of converting external stimuli into electrical changes.
  • Outcome: Changes in membrane potential.
  • Example: Light is transformed into electrical signals in the eye by photoreceptors.

The Eye

• The eye is part of the central nervous system (CNS).
  • The retina is a part of the brain.
• Location: Suspended in the orbits of the skull.
• Movement: Six extraocular muscles attach the eye to the skull, allowing for eye movements.

Eye Structure:

• Outer White Covering: Sclera (no entry of light).
• Hole where Light Enters: Pupil.
• Muscular Ring Controlling Light Entry: Iris.
• Lens-like structure that focuses light on the retina: Lens.
• Location of Sensory Receptors & Transduction: Retina.
• Part of the Retina that Produces Output to the Brain: Optic Nerve.

Photoreceptors

• Function: Convert light into electrical signals.
• Types:
  • Cones (6 million): Provide most of the visual information about our environment.
    • Function: Responsible for daytime vision; high visual acuity; process color.
  • Rods (120 million): More sensitive to light.
    • Function: Better for nighttime vision; provide vision of poor acuity.

The Fovea

• Location: Central region of the retina.
• Significance: Contains almost all of the cones in the retina, mediating our most acute vision.
• Function: When we look at something, our ocular muscles work to position the light emitted from the object directly on our fovea.

Optic Disk

• Location: Part of the retina where axons carrying visual information leave the eye to form the optic nerve.
• Characteristics: Contains NO receptors, producing a blind spot.

Optogenetics

• Optogenetics uses light to control the activity of neurons
• Channelrhodopsin-2 (ChR2) is a photosensitive protein that opens sodium and calcium channels in response to blue light
• Natronomonas pharaonis halorhodopsin (NpHR) is a photosensitive protein that moves chloride into the cell in response to yellow light

Targeted Mutations In Mice

• Mutated genes can be produced in the laboratory and inserted into the chromosomes of mice
• Constitutive knockout mice have a mutated gene that prevents the production of a certain protein
• Conditional knockout mice allow for temporal control of gene expression

The Visual System

• The eye is part of the central nervous system (CNS)
• The retina is part of the brain
• Six extraocular muscles attach the eye to the skull
• The lens focuses light on the retina
• The retina contains photoreceptors that convert light into electrical signals
• There are 2 types of photoreceptors: cones and rods
• Cones are responsible for daytime vision and color perception
• Rods are more sensitive to light and provide vision in low light conditions
• The fovea is the central region of the retina and contains a high concentration of cones
• The optic disk is the part of the retina where axons carrying visual information leave the eye to form the optic nerve
• The optic disk contains no receptors and creates a blind spot.

Retina Anatomy

• The retina has three main layers: photoreceptors, bipolar cells, and ganglion cells.
• Photoreceptors are responsible for detecting light and include cones and rods.
• Bipolar cells receive input from photoreceptors and synapse with ganglion cells.
• Ganglion cells receive input from bipolar cells and are responsible for sending visual information to the brain via the optic nerve.
• Posterior vitreous detachment (PVD) is a common condition where the vitreous humor detaches from the retina, causing symptoms such as floaters, flashes of light, and reduced vision.

Photoreceptors

• Photoreceptors are composed of an outer segment containing lamellae and an inner segment.
• Lamellae contain photopigments which are responsible for detecting light.
• Photopigments consist of opsin (a protein) and retinal (a lipid synthesized from vitamin A).
• When light strikes the photopigment, it splits into its two components and causes hyperpolarization of the photoreceptor.
• Light exposure decreases neuronal activity, causing a release of neurotransmitter.

Neural Circuitry in the Retina

• Photoreceptors and bipolar cells do not generate action potentials, but instead signal information through changes in neurotransmitter release.
• Photoreceptors are depolarized in the dark and continuously release neurotransmitter.
• When photoreceptor neurotransmitter binds to bipolar cells, it leads to a change in their activity.
• Ganglion cells, however, do generate action potentials to transmit visual information to the brain.

Beyond the Retina

• Ganglion cell axons form the optic nerve, which leaves the retina and travels towards the brain.
• The optic nerve crosses at the optic chiasm, at the base of the brain.
• Axons from the inner halves of each retina (nasal side) cross to the opposite (contralateral) side of the brain.
• Axons from the outer halves of each retina (temporal side) do not cross and stay on the ipsilateral side.
• Information from the right visual field ends up on the left side of the brain and vice versa.

Lateral Geniculate Nucleus

• After the optic chiasm, ganglion cells travel to the lateral geniculate nucleus (LGN) of the thalamus, where the first synapse occurs.
• LGN neurons send their axons via the optic radiations to the primary visual cortex.

Information Coding in the Visual System: The Retina

• Foveal vision has greater visual acuity than peripheral vision due to less convergence of photoreceptors onto a single ganglion cell.
• The retina contains three types of ganglion cells, but we are concerned with two: ON cells and OFF cells.
• ON cells respond with an excitatory burst when the retina is illuminated.
• OFF cells respond with an excitatory burst when the light is turned off.
• These cells are responsible for encoding changes in illumination as you move and look at things.

Receptive Fields

• The receptive field of a neuron in the visual system is the part of the visual field that affects the neuron's firing rate.
• The location of a receptive field depends on the location of photoreceptors that provide visual information.
• The receptive fields of ganglion cells have center-surround organization, meaning that the center and surround regions respond to light in opposite ways.

Light

• Retinal ganglion cells encode the amount of light falling on the center and surround of their receptive fields
• They carry information about the wavelength of light, which is color

Primary Visual Cortex

• The primary visual cortex, also known as the striate cortex, is found in the occipital lobe
• The primary visual cortex is characterized by its dark staining layer
• Approximately 25% of V1 processes info from the fovea, which represents a small part of the visual field
• Cells in V1 respond to specific features of the visual world
• Each V1 cell receives information from several retinal ganglion cells

Orientation & Movement

• Most neurons in V1 are sensitive to orientation
• A cell is maximally responsive to a particular orientation, for example a vertical line

Visual Association Cortex

• V1 cannot “see” a whole object, only features
• The output of V1 is sent to the adjacent extrastriate cortex (V2)
• V2 cells receive input from several V1 cells, and information from V1 begins to be reassembled to “rebuild” the visual scene
• Two pathways emerge from V2:
  • The Ventral Stream, projecting to the inferior temporal lobe, processes "what" an object is
  • The Dorsal Stream, projecting to the posterior parietal lobe, processes "where" an object is

Sound as a Stimulus

• Sounds are produced by objects that vibrate
• Vibrating objects cause air molecules to condense together and pull apart, creating a sound wave

Structure of the Human Ear

• The outer ear collects sound from the environment
• The pinnae funnel sound waves into the ear canal
• The length and shape of the ear canal enhances certain sound frequencies
• The tympanic membrane (ear drum) is a thin membrane at the end of the outer ear canal
• It vibrates in response to sound, defining the border between the outer and middle ear

Middle Ear

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

Inner Ear

• The inner ear converts fine changes in sound pressure into neural signals
• The inner ear is analogous to the retina
• It contains the cochlea, which is a spiral structure that contains the organ of Corti
• The cochlea is filled with fluid in three parallel canals: the vestibular, tympanic, and middle canals
• The three canals are separated by two membranes: Reissner's membrane and the basilar membrane.

The Organ of Corti

• The Organ of Corti has 3 major parts:
  • Hair cells, which are the receptive cells of the auditory system
  • Basilar membrane which anchors the hair cells
  • Tectorial membrane that lies over the hair cells

Hair Cells

• Hair cells are embedded in the basilar membrane
• Each hair cell contains a soma and cilia that protrude from the top
• There are two major types of hair cells:
  • Inner hair cells are less numerous and do not touch the tectorial membrane but move when fluid moves.
  • Outer hair cells are more numerous and attached directly to the tectorial membrane.
• Hair cells synapse with bipolar cells whose axons bring the information from the inner ear to the brain.

Transduction of Sound

• Sound waves entering the ear cause the tympanic membrane to vibrate at the same frequency.
• Vibrations are transmitted to the ossicles, which transfer them to the oval window of the cochlea.
• Vibrations at the oval window cause the basilar membrane and tectorial membrane to flex up and down
• Bending cilia of the hair cells initiates 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 auditory system processes sound waves
• The ear is composed of three parts: the outer ear, the middle ear, and the inner ear
• Sound waves enter the ear through the outer ear
• The outer ear consists of the pinna (the flap of cartilage that captures sounds) and the auditory canal (the tunnel that leads to the middle ear)
• The sound waves hit the tympanic membrane (eardrum) at the end of the auditory canal
• This causes the ossicles, the three smallest bones in the body (malleus, incus, and stapes) to vibrate
• The stapes pushes against the oval window, a membrane that separates the middle ear from the inner ear
• This causes the fluid inside the cochlea to move which stimulates the hair cells of the organ of Corti
• The organ of Corti is the structure inside the cochlea that contains the hair cells
• The hair cells transform the mechanical energy of the vibrations into electrical signals
• These electrical signals travel to the brain through the auditory nerve.

Central Auditory Pathways

• Auditory information travels from the cochlear nucleus to the inferior colliculus, then the medial geniculate nucleus, and finally to the auditory cortex
• The auditory cortex is the final destination of auditory information in the brain
• Most cochlear axons cross over to the other side of the brain and synapse in the cochlear nucleus.

Auditory Cortical Areas

• The primary auditory cortex is responsible for processing basic auditory information
• The auditory association cortex surrounds the primary auditory cortex and processes more complex auditory information, such as language
• There are two streams of auditory information flow: the dorsal stream and the ventral stream
• The dorsal stream is involved in sound localization ("where" the sound is coming from)
• The ventral stream is involved in processing the characteristics of sounds ("what" the sound is)

What is Sleep?

• Sleep is a state of altered consciousness characterized by reduced sensory awareness and a decrease in muscle activity
• Sleep is studied in a lab by measuring brain activity and muscle activity using the following instruments:
  • Electroencephalogram (EEG)
  • Electromyogram (EMG)
  • Electrooculogram (EOG)

The Study of Sleep

• Brain activity during sleep can be categorized into two patterns:
  • Alpha Activity (state of relaxation)
  • Beta Activity (state of arousal)
• The EEG becomes more synchronized as sleep progresses through stages 1-4, and the brain waves become slower
• REM sleep looks like the awake state.

Non-REM Sleep

• Stages 1-4 of sleep are called "non-REM sleep"
• Stages 1-2 are transitional, and the person is usually not aware that they are asleep
• Stages 3-4, or slow-wave sleep, are characterized by the presence of low-frequency delta activity
• Slow-wave sleep is characterized by:
  • Light, even respiration
  • Presence of muscle tone
  • Difficulty in arousing the subject

REM Sleep

• REM Sleep occurs every 90 minutes throughout the night
• It is characterized by:
  • Enhanced respiration and blood pressure
  • Rapid eye movements (REMs)
  • Complete loss of muscle tone (paralysis)
  • Vivid, emotional dreams

Cycles of Sleep

• We alternate between REM and non-REM sleep cycles.
• Each cycle is approximately 90 minutes long and contains about 20-30 minutes of REM sleep.
• There are 4 to 5 periods of REM sleep in a night (8 hours).

Disorders of Sleep

• Sleep disorders can significantly impact a person's well-being and daily functioning.

Insomnia

• Difficulty falling asleep after going to bed or waking up during the night.
• Sleep Apnea is a form of insomnia where the individual falls asleep and stops breathing. This is usually caused by an obstruction in the airway
• Narcolepsy is characterized by uncontrollable sleepiness and an inability to regulate sleep-wake cycles.
• Cataplexy is a symptom of narcolepsy involving sudden muscle weakness or paralysis, often triggered by emotions.
• Sleep Paralysis is a symptom of narcolepsy where a person feels unable to move or speak while falling asleep or waking up.
• Hypnagogic Hallucinations are vivid dreams that occur just before falling asleep and may be accompanied by sleep paralysis.

REM Sleep Behavior Disorder

• The sleeper acts out their dreams.
• This occurs because the brain is unable to produce paralysis during REM sleep.
• This may be caused by a neurological disease that damages the brain mechanisms responsible for producing REM sleep paralysis.

Why Do We Sleep?

• Sleep appears to serve essential functions for both physical and cognitive health.

Sleep Deprivation Studies

• Studies on animal sleep deprivation demonstrate harmful consequences, including physical weakness, impaired coordination, and death.
• In humans, sleep deprivation doesn't have obvious physical effects, but it significantly impairs cognitive functioning, leading to hallucinations, difficulty concentrating, and memory problems.
• When sleep-deprived people are allowed to sleep again, they never recover all the sleep they lost.
• REM sleep is not associated with the recovery or restoration of muscles, but is more important than other stages for cognitive function.

Functions of Slow-Wave Sleep

• One theory suggests that slow-wave sleep (SWS) is a restorative process.
• Areas of the brain that are stimulated during the day show more delta activity and lower metabolic activity during SWS.
• SWS may indicate that a brain region is resting.

Functions of REM Sleep

• REM sleep may promote brain development, especially in infants and children who spend a high percentage of their sleep in REM.
• In adults, REM and slow-wave sleep may be involved in memory consolidation.
• Nondeclarative memory (learning skills, procedures, and habits - like how to drive a car or recognize a face) may be strengthened during REM sleep.
• Declarative memory (memories of past experiences) may be strengthened during SWS.

Neural Regulation of Arousal

• To understand what produces sleep, we must understand what causes us to stay awake.
• Electrical stimulation of the brainstem induces arousal and vigilance.
• Several neurotransmitters play crucial roles in arousal, including:
  • Acetylcholine (ACh)
  • Norepinephrine (NE)
  • Serotonin (5-HT)
  • Histamine (HA)

Acetylcholine (ACh)

• Acetylcholine is the primary neurotransmitter secreted by the motor axons of the peripheral nervous system.
• It controls muscle movements.
• Acetylcholine is also widely distributed in the brain, with significant concentrations in three regions:
  • Dorsolateral pons: Involved in REM sleep and dreaming.
  • Medial Septum: Involved in hippocampal function and certain types of memory.
  • Basal Forebrain: Plays a key role in activating the cortex, facilitating learning, and is important for arousal.

The Nucleus Basalis

• The ACh neurons in the nucleus basalis (in the basal forebrain) appear to be crucial for cortical arousal.
• Stimulation of ACh neurons produces cortical activation and desynchrony of the EEG.
• Levels of ACh in various brain regions are elevated during wakefulness and alertness.

Norepinephrine (NE)

• Most NE effects are excitatory.
• Release of NE by the sympathetic nervous system prepares the body for “fight or flight" responses.
• Most NE neurons in the brain are clustered in the locus coeruleus (LC) in the brainstem.
• Activation of the LC produces alertness, vigilance, and anxiety.

Norepinephrine and the Sleep-Wake Cycle

• Catecholamine agonists, such as amphetamine, cocaine, and MDMA, induce arousal and wakefulness by stimulating the noradrenergic cells in the LC.
• The activity of LC neurons closely corresponds with arousal and wakefulness.
• Activity of LC neurons decreases during sleep and becomes zero during REM sleep.

Anatomy of the Ear

• The Organ of Corti is located in the inner ear and is responsible for converting sound waves into neural signals.

Central Auditory Pathways

• The auditory nerve synapses in the cochlear nucleus.
• Most cochlear axons cross over and synapse in the inferior colliculus.
• The next synapse is in the medial geniculate nucleus.
• The cortex is the last synapse in the central auditory pathway.

Auditory Cortical Areas

• The primary auditory cortex is located in the temporal lobe.
• The auditory association cortex surrounds the primary auditory area.
• There are two streams of auditory information flow:
  • The dorsal stream terminates in the posterior parietal region and is involved in sound localization.
  • The ventral stream terminates in the temporal lobe and is involved in processing of complex sounds.

What is Sleep?

• Sleep is studied by measuring the activity of the brain and two muscle groups:
  • The Electroencephalogram (EEG) measures the collective activity of thousands of brain cells, usually on the cortical surface.
  • The Electromyogram (EMG) monitors muscle activity.
  • The Electrooculogram (EOG) monitors eye movements.

The EEG

• Alpha activity is associated with relaxation and has a frequency of 8-12 Hz.
• Beta activity is associated with arousal and has a frequency of 13-30 Hz.
• Delta activity is associated with slow-wave sleep and has a frequency of <3.5 Hz.
• During sleep, the EEG becomes more synchronized as sleep progresses from stages 1-4.
• The waves become slower as sleep progresses from stages 1-4.
• During REM sleep, the EEG looks like the awake state.

Non-REM Sleep

• Stages 1-4 of sleep are called non-REM sleep.
• Stages 1-2 are transitional and the subject is typically not aware they are asleep.
• Stages 3-4 are known as slow wave sleep and are characterized by the presence of low-frequency delta activity.
• Slow-wave sleep is characterized by:
  • Light, even respiration.
  • Presence of muscle tone.
  • Difficulty in arousing the subject.

REM Sleep

• REM sleep occurs approximately every 90 minutes throughout the night.
• It is characterized by:
  • Enhanced respiration and blood pressure.
  • Rapid eye movements (REMs).
  • Complete loss of muscle tone (paralysis).
  • Vivid, emotional dreams.

Cycles of Sleep

• We alternate between periods of REM and non-REM sleep.
• Each cycle of sleep is approximately 90 minutes long.
• Each cycle of sleep contains 20-30 minutes of REM sleep.
• In an 8-hour night, there will be 4-5 periods of REM sleep.

Sleep Deprivation Studies

• In animals, sleep deprivation appears to be harmful.
  • Rats forced to lose sleep became weak, uncoordinated, lost the ability to regulate their body temperature, and eventually died.
• In humans, sleep deprivation appears to have no outward physical effects.
  • Motor skills remain intact.
  • Stress hormones are at normal levels.
  • The primary function of sleep is not the recuperation of muscles.
  • Cognitive function is impaired (hallucinations, trouble concentrating, memory, etc).
• When sleep-deprived people are allowed to sleep again, they never regain all the lost sleep.
  • The percentage of recovery is not equal for all stages of sleep.
    • 7% of stages 1 and 2 are made up.
    • 68% of stage 4 sleep is made up.
    • 53% of REM sleep is made up.

Functions of Slow-Wave Sleep

• Slow-wave and REM sleep may serve different functions.
• One hypothesis is that SWS may reflect a restoration process.
  • Areas of the brain that are more stimulated during the day show more delta activity and the lowest levels of metabolic activity during slow-wave sleep.
  • The presence of SWS in a brain region indicates that region is resting.

Functions of REM Sleep

• REM sleep in children may reflect promotion of brain development.
  • Infants and children show the highest amounts of REM sleep.
  • Newborns spend about 70% of their sleep in REM.
• In adults, REM and slow-wave sleep may reflect a memory consolidation process.
  • Nondeclarative memory (learning to drive a car or recognize a person’s face) may be consolidated during REM sleep.
  • Declarative memory (memories of past episodes) may be consolidated during SWS..

Mechanisms: The Neural Basis of Arousal

Neural Regulation of Arousal

• Electrical stimulation of the brainstem induces arousal and vigilance.
• Several common neurotransmitters are involved in arousal:
  • Acetylcholine
  • Norepinephrine
  • Serotonin
  • Histamine

Acetylcholine (ACh)

• ACh is the primary neurotransmitter secreted by the motor axons of the PNS.
  • All muscle movements are controlled by ACh.
• ACh is also widely distributed in the brain.
• There are three brain regions that contain cholinergic neurons:
  • Dorsolateral Pons: involved in REM sleep (dreaming).
  • Medial Septum: involved in hippocampal function and certain types of memory.
  • Basal Forebrain: involved in activating the cortex and facilitating learning.

Norepinephrine

• Almost all NE effects are excitatory.
• The release of NE by the sympathetic nervous system prepares you for “fight or flight.”
• In the brain, most NE neurons are clustered in the brainstem in a region called the locus coeruleus (LC).
  • Activation of the LC produces vigilance and anxiety.

Norepinephrine and the Sleep-Wake Cycle

• Many catecholamine agonists, including amphetamine, cocaine, and MDMA, produce arousal and wakefulness.
• These effects are mimicked by stimulation of the noradrenergic cells in the locus coeruleus (LC) (dorsal pons).
• Activity of LC neurons shows a close correspondence with arousal and wakefulness.
• Activity of LC neurons falls during sleep until it reaches zero during REM sleep.

Test your knowledge on the basic features of the nervous system, including neurotransmitters like acetylcholine, norepinephrine, and serotonin. Understand their functions and importance in treating conditions like depression. This quiz will help reinforce key concepts discussed in class.