Quiz 4 + Midterm 2 (Lectures 8-11) - 231 Lecture

Make sure to study Lecture 7 Slides

Reticular Formation (L7)

• Sensory neurons carry information up the spinal cord to the brain stem

• Retricular Activating System (RAS) neurons in the brain stem are stimulated by the incoming sensory information

• RAS neurons projects these signals to the thalamus

• Thalamus selectively sorts and filters the information, passing vital sensory messages to specific areas of the cerebral cortex for conscious perception

• Continuous strea, of sensory information keeps the cerebrum aroused and alert

Caffeine (L7)

• Caffiene is an antagonist

• Similar structure to Adenosine

• Caffiene can fit into the same receptors as Adenosine, essentially blocking Adenosine from binding

• Adenosine is prevented from inducing drowsiness

Learning and Memory (L7)

Outside Stimuli

→ General and special sensory receptors

• → Temporary storage

  • → (Data Permanently Lost)

  • → Short-Term Memory (STM)

    • → Excitement, Rehearsal, Association of old and new data

      • → Long-Term Memory (LTM)

Consolidation = process of stabilizing and transforming short-term memories into long-term memories

• Done through:

  • Excitement

  • Rehearsal

  • Association of old and new data

Declarative and Procedural Memory (L7)

Declarative Memory = the conscious recall of facts and events (“knowing what”)

• Loop:

  1. Sensory Input →

     • raw input processed in primary sensory cortices then passed on to high-level processing in association cortex

  2. Association cortex →

     • brain gives meaning to the raw input - ex: recognizing a song or face

  3. Medial temporal lobe →

     • receives processed information from association cortex and associated sights, sounds, etc. into a single memory

  4. Thalamus →

     • routes information from the medial temporal lobe to other regions

  5. Prefrontal cortex

     • during encoding, PFC helps select, organize, and evaluate incoming information based on relevance to the individual’s goals

     • can send signals back to the thalamus or MTL to reconstruct memory

Procedural (Skills) Memory = unconscious execution of motor and cognitive skills (“knowing how”)

• Loop:

  1. Sensory and motor inputs

     • raw input → primary sensory cortex → association cortex

  2. Association cortex

     • integrate sensory data with context, spatial awareness, and memory

  3. Basal nuclei

     • project information to specific nuclei in the motor thalamus

  4. Thalamus

     • send excitatory signals to excite the cortical motor areas

  5. Premotor cortex

     • receives information from thalamus

     • map out muscle sequences and prepare the body to execute

  6. Cerebellus acts in the background to refine motor sequences

     • balance and coordination

     • motor memory

How to improve formation of long-term memories (L7)

Re-study and re-test mastered terms

Why are there enlargements? Where does the spinal cord end?

Cervial and Lumbar Enlargements =

• More gray matter due to higher amount of innervation to these regions

Spinal cord ends near L1 vertebrae

PNS

Peripheral Nervous System =

• cranial nerves and spinal nerves

• Communication between the CNS and the rest of the body

Lumbar Puncture

Retracts CSF from subarachnoid space

• In the lumbar area, past the spinal cord

• For example, to identify infenction of menigies/meningitis

Spinal Cord

• Dorsal root = sensory neurons

• Dorsal root ganglion = holds sensory unipolared neurons

• Ventral root = motor neurons

• Spinal nerve = where sensory and motor neurons meet

Gray Matter vs White Matter

Gray Matter =

• Horns

• Nuclei

White Matter =

• Columns (tracts)

  • Ascending tracts = carry sensory information to the brain

  • Descending tracts = carry commands to motor neurons

Sensory (Ascending) Pathways

• DECUSSATION occurs in the BRAINSTEM or SPINAL CORD

• 3 neuron circuits from receptor to Primary Somatosensory Cortex

Motor (Descending) Pathways

• DECUSSATION occurs in the BRAINSTEM or SPINAL CORD

• Two or Three neuron circuits from Primary Motor Cortex to the muscle

Spinal Cord Injuries

Deficits = any loss or impairment of sensory, motor, cognitive, or bodily function caused by damage to the nerve pathways within the spinal cord

• Deficits inferior to the site of damage:

  • loss of sensation

  • loss of motor function

Paralysis due to spinal cord injury

• How far down the spinal injury is in the spine is relevant to the extent of the paralysis

• You don’t kill the neurons, unless you crush the cell bodies, you just tear the axons

• After effects of the spinal cord injury can cause cell bodies to die

• You are able to regrow axons, but it is hard to due to scar tissue

Regeneration of axons in spinal cord in fish is better than in mammals

• Mammals = axons get stuck in scar tissue

• Fish = able to regenerate spinal columns

Treatments for spinal cord injury

• Stem cell therapy

  • Optimal time is before the scar formation, and after the inflammatory reaction

• Electrical Stimulators

  • Can recover some function by stimulating neurons

Peripheral Nervous System: Visceral vs Somatic

Visceral = internal organs

• organ stretch, nausea, hunger, changes in chemical composition

• largely unconscious

Somatic = external, body-wall structures

• touch, pain, temperature, etc

• highly conscious

Gray Matter vs White Matter (spinal cord)

Gray Matter:

• Ganglia

White Matter:

• Nerves/Roots/Rami

Sympathetic trunk ganglion:

• along sides of the vertebral column in two vertical chains

• efferent pathway

• have a synapse

Nerve Structure

• Nerve →

  • Epineuirm surrounds bundles of perineurium

    • Perineurium surround buncles of endoneurium

      • Endoneurium surrounds myelin sheath

        • Myelin shealth surround axons

• Nerve = bundles of axons

Cranial Nerves

• Can be sensory, motor, or both

• Most connect to the brainstem

• Most are involved with structures in the head and neck

Spinal Nerves

All spinal nerves are mixed nerves

• Contain both sensory and motor fibers

Cranial Nerves = nerves connected to the brain

Nerve Plexuses

A complex, web-like network of intersecting nerves in the peripheral nervous system. Functioning like an electrical junction box, it sorts, combines, and redistributes nerve fibers from multiple spinal segments so that fibers traveling to a specific body part are grouped together

Innervation of Specific body regions

Dermatome = The regions of the body that are associated with a specific type of spinal nerve

• Innervation of specific body region

• Ex: Sciatica = radiating sciatic pain and sensory symptoms will follow distinct dermatomal patterns on the leg, depending on exactly which nerve root is affected

Shingles

• After an infection, the virus can retreat to the nervous system and remain dormant in the dorsal-root ganglion

• When reactivated, the virus travels down the specific sensory nerve fibers to the skin, causing a painful, blistering rash that is typically restricted to a single dermatome

Sensory System Signaling Summary

Perception =

• The interpretation of the signals from those receptors

Circuits =

• Connect sensory receptors to the CNS for perception

Receptors =

• Detect sensory input and send signals to the CNS

Sensory Systems - levels of perception

• Perceptual detection (something happened)

• Magnitude estimation (how intense was it?)

• Stimulus discrimination (where was it located?)

• Quality discrimination (what color is it)

• Feature abstraction (identify complexity)

• Pattern recognition (do I know what this is?)

Sensory Systems - classification based on the location of the receptors

General senses = found all over the entire body, including the skin, muscles, internal organs, joints, etc

• AKA Somatosensory System, monitor touch, pressure, temperature, pain, body position, etc

Special Senses = concentrated exclusively in specialized organs within the head

• eyes, ears, nose, mouth

• dedicated to procesing specific, complex, environmental stimuli (vision, hearing, balance, taste, small)

• require localized structures before sending this refined data directly to the brain

Sensory Systems - classification based on where the stimulus is coming from

Exteroceptors = external stimuli

• sight, taste, hearing

Interoceptors = internal environment

• inside (heart, lungs, stomach)

Proprioceptos = body position and movement

• at joints, muscles, tendons

Primary Sensory Coding - what do receptors tell the brain and how does it interpret that information?

Receptors tell the brain:

• Stimulus type

• Stimulus location

• Stimulus intensity

• Stimulus duration

Primary Sensory Coding - Stimulus Type (MODALITY)

Receptors have graded potentials (receptor potentials) in response to a particular type of stimulus

• Mechanoreceptors - TOUCH

  • Convert physical forces (touch, pressure, stretching, and sound waves) into electrical signals

  • Examples: Pacinian corpuscles, Merkel Cells, and hair cells in the ear

  • Mechanical force distorts the mechanoreceptor’s membrane, pulling open the mechanically-gated ion channels and causing a local change/receptor potential

  • GRADED POTENTIAL = light touch opens fewer ion channels, resulting in a weak potential; a heavy press opens up more channels, leading to a larger potential

• Chemoreceptors - TASTE and SMELL

  • Specialized sensory cells that detect chemicals in the environment and convert them into electrical signals that the brain interprets as taste and smell

• Thermoreceptors - TEMPERATURE

  • Detect temperature and changes in temperature and translate it to electrical signals

  • Free nerve endings

• Nocioceptors - PAIN

  • specialized sensory nerve endings that detect extreme stimuli and convert them into electrical signals

• Photoreceptora - VISION

  • When light hits the rods or cones in retina, they convert the light waves into electrical signals

Primary Sensory Coding: Location

Size of Receptive Fields

• Smaller receptive fields = better determination

• Receptive fields that overlap can help determine which part of the skin is stimulated

Primary Sensory Coding: Modality and Location

Specific Ascending Pathways

• Modality = specific type of stimulus being detected (ex: light, sound, temp, smell)

• Each modality has a pathway that goes through the thalamus to a specific primary sensory cortex (in a specifc lobe) then to a specific association cortex for higher level understanding and integration of that sensation

• Within the cortex, there are maps that correspond to specific parts of the body or receptive fields

Primary Sensory Coding: Stimulus Intensity

• Stronger sitmuli cause MORE action potentials in receptor

• More APs, cause release of more neurotransmitter in the synapse to cause a stronger post-synaptic potential

• Intensity coded by number of action potentials

Primary Sensory Coding: Stimulus duration

Adaption = decrease in AP frequency in presence of constant stimulus

• Phasic receptors = adapt quickly - stop sending signals

• Tonic receptors = don’t adapt or adapt slowly - continue sending signals

  • Ex:

    • Smell = quick, bad sell = not quick

    • Taste = somewhat fast

    • Touch = quick adaptor (clothes)

Summary of Sensory and Receptors and Principles of Sensory Systems

• Receptors are sensitive to specific modalities

• Ascending pathways/circuits go through thalamus before relayed to cortex

• Processing in association areas can affect perception and memory

• Primay coding involves receptors transmitting info about stimulus type, location, intensity, and duration

General (somatic) senses - Types of receptors

Somatosensory:

• free nerve endings - uncapsulated, can penetrate into epidermis

  • can be phasic or tonic

  • can detect mechanical stimuli, temperature, pain, etc

  • ONE free nerve ending responds to ONE stimulus

• Merkel cells -

  • in strantum basale

  • send signals to free nerve endings

  • receptive field = small

  • very light touch

• Hair follicle receptor -

  • free nerve ending that is wrapped around the hair sheath

• Meissner corpuscle -

  • found in papillary layer, medium receptive field, encapsulated

• Pacinian corpuscle -

  • reticular dermis, large receptive field

Proprioception:

• muscle spindles -

  • inside skeletal muscle

  • send sensory (afferent) signals regarding state of muscle

• golgi tendon organs

  • send sensory (afferent) signals regarding state of muscle

Somatic Sensation and Proprioception

Receptors (afferent neurons) are unipolar neurons neurons with cells bodies in the DRG

General senses - Circuits Ascending Pathways

Specifc Ascending Pathways:

1. Affect neuron sends signal to spinal cord or brainstem

2. Ascending neuron decussates in the SPINAL CORD or MEDULLA

3. Projection neuron sends signal from THALAMUS to PRIMARY SOMATOSENSORY CORTEX

Contralateral = opposite side

Ipsilateral = same side

Primary Somatosensory Cortex

PARIETAL LOBE

• each hemisphere receives general sensory information from skin and joints/muscles from opposite side of the body

  • Touch

  • Temperature

  • Pain

  • Itch

  • Body position (proprioceptors)

The General Senses: Nocioceptors - how could you stop pain?

Nocioceptors = respond to extreme mechanical deformation, excessive heat and many chemicals

• Decrease stimulus

  • Ibuprofen

  • decreases activation of pathway

• Stop voltage-gated channels = block action potentials

• Increae uptake at synapses = decrease amount of NT in the synaptic space

• Non-pain stimulus = Inhibits afferent neuron

Referred Pain

Convergence of two receptors on one ascending pathway

General Sensory Systems Summary

Receptors

• can be free-nerve endings or encapsulated

• Most are unipolar neurons with cells bodies in DRG

• Receptor potentials in response to stimuli that trigger APs

Circuits

• Synapses in spinal cord and thalamus before related to cortex

• Can cause reflexes before stimulus perception occurs

• Decussation in spinal cord or medulla

Perception

• Somato-sensory cortex in parietal lobe

Gustation Chemoreceptors

Remember: special senses have a specific organ

• Gustation Chemoreceptors

  • Papilla = projections

  • Taste buds located on the side of papilla

Activation of Gustatory (Taste) Receptors:

Taste sensations:

• Sweet, sour, salty, bitter, umami

Tate Buds:

• Gustatory receptor cells

  • can be damaged easily bc they are more susceptible to the taste pore

• Supporting cells

  • basal cell = makes more cells

• Free nerve endings of afferent neurons

  • sent to cranial nerve

Signal Transduction in gustatory receptors

Chemicals enter cells through channels

• Sodium can diffuse straght into the receptors through channels

• Bigger chemicals need recetors to bind to and act through a secondary messenger system

Signal transduction in gustatory receptors

• Receptor potentials occur when gustatory receptor is exposed to chemical

• Action potentials occur in afferent neuron

  • Gustatory cells depolarize and release NT

Sensitivity of Different taste receptors

Smaller threshold for action potential = more sensitive

• can be a warning sign to not eat

• bitter is most sensitive

Gustatory Pathway

Afferent neurons in cranial nerves

• → Medulla oblongota

  • → Thalamus

    • → Gustatory cortex

Olfaction (smell) - Chemorecptors

• Chemical binds dentrite of the olfactory receptor cell in cilia

• Axons group together to form olfactory nerve

• olfactory nerve goes through ethmoid bone

• olfactory nerve goes into the olfactory bulb

• GLOMERULI = bundle of nerves specific to odor molecule

• mitral cells connects to glomeruli and form the olfactory tract

OLFACTORY PATHWAY DOES NOT GO THROUGH THE THALAMUS

Signal transduction in olfactory receptors

• Receptor potentials occur when neuron is exposed to odorant molecules

• Action potentials occur if receptor potential is above threshold

• Around 400 different types of receptors

Processing of olfactory information

• Axons of olfactory neruons are found in olfactory nerves that go to the olfactory bulb

• Synapses occur in balls called GLOMERULI

• Each glomerulus processes info about one chemical

Olfactory Pathway

Olfactory receptor (afferent neuron)

→ Olfactory bulb

• → Olfactory cortex (perception of odors)

  • → Hypothalamus and Limbic regions (Physiological and emotional responses to odors)

DOES NOT GO THROUGH THALAMUS

Chemosensory Systems Summary

Olfactory

• Receptors =

  • Receptor potentials in response to stimuli that trigger APs

• Circuits =

  • Olfactory nerves synapse in olfactory bulb - goes directly to cortex

  • Each glomerulus processes a specific odor

• Perception =

  • Olfactory corte in temporal lobe connects to limbic system

Gustation

• Receptors =

  • Receptor potentials that cause graded release of NT to afferent neuron

• Circuits =

  • Gustatory receptors synapse on afferent neuron - goes through brainstem and thalamus

  • Decussation in medulla

• Perception =

  • Gustatory cortex in insula

Hearing and Equilibrium

• Mechanoreceptors sense vibration

• Found in the inner ear

Hearing = Cochlea

Equilibrium = Vestibule & Semicircular Canals

Pathways of sound wave-amplification

Amplification in middle ear as it goes through malleus, incus, stapes

• Air filled cavity

Sound Transduction

1. Tympanic membrane deflects

2. Middle ear bones move

3. Membrane in oval window moves

4. Basilar membrane moves

5. Membrane in round window moves

Cochlea - houses sensory receptors for hearing

• Scala vestibuli - filled with perilymph

• Cochlear duct - filled endolymph

• Scala tympani - filled with perilymph

  • Bailar membrane lines cochlear duct

  • Increases increases in thickness →

    • Thinner part detects high pitch, thick detects low

  • Hair cells on basilar membrane attached to tectorial membrane

  • When basilar membrane moves, the tectorial membrane forces the hair cells to intake potassium, causing a depolarization of the cells

  • Action potential sent to brain

Resonance

Different parts of the basilar membrane are sensitive to different frequencies

How sound energy is transduced to AP

Bending of the sterocilia opens ion channels - causes graded potentials

Auditory Pathway

Vestibulocochlear Nerve

→ Medulla (decusates)

• → Midbrain (reflexes)

  • → Thalamus

    • → Primary auditory cortex (perception) - temporal lobe

Threshold of Hearing

• Threshold for hearing is higher at lower frequencies

• Over 120 threshold of pain - can damage hair cells

Deafness

• Conduction deafness = conduction of sound wave from air → basement membrane

  • Something happens to hamper sound conduction of sound wave to fluid of inner ear

• Sensorineural deafness = damage from hair cells → afferent neurons

  • damage to neural structures in auditory pathway

Cochlear implant

Electrically stimulates afferent neurons, allowing signals to go to the brain

Hearing Summary

Receptors

• Receptor potentials that cause graded release of NT to afferent neuron

• The basilar membrane resonates at different frequencies to maximmaly stimulate particular hair cells

Circuits

• Synapses occur in the medulla, midbrain, and thalamus

• Can cause reflexes before stimulus perception occurs

• Decussation in medulla

Perception

• Auditory cortex in temporal lobe

Static Equilibrium

In the Vestibule:

• Macula of utricle

• Macula of saccule

  • Both situated perpendicular to each other

Otoliths =

• Stones that give density to membrane

Otolitic Membrane =

• Gelatenous

• Will “pull” on hairs when not flat

• Static = still

• Nerve fibers send signals of position

• Used to understand position of head in relation to gravity

Static Equilibrium - Explanation

• Nerve impulses generated in vestibular fiber (nerve)

• When hairs bend toward the Kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials

• When hairs bend away from the kinocilium, the hair cell hyper polarizes, inhibiting the nerve fiber, and decreasing the action potential frequency

Dynamic Equilibrium

Inside Semicircular Canal

1. Bone moves, fluid still

2. Fluid catches up with bone

3. Bone stops, fluid keeps going

• When the fluid moves, it pushes the Cupula

• Cupula is bent and ion channels are opened, altering electrical signals sent to the vestibular nerve

• Cupula will continue to be stimulated when fluid is slowing down after the bone stop moving due to inertia or fluid

Balance and Equilibrium

Information about the body’s position in space comes from three main sources and is fed into two major processing areas in the central nervous system

• Three main sources:

  • Vestibular Receptors

  • Visual Receptors

  • Somatic Receptors (skin, muscle, joints)

• Two major processing areas:

  • Cerebellum → CNS

  • VESTIBULAR NUCLEI (in brain stem)

    • → cranial nerves (PNS) for eye and neck movements

Activation of Vomiting (emetic) center

3 Sources Activate Vomit Center:

• Cortex (anxiety, anticipation) →

• Chemoreceptor trigger zone (toxins in blood) →

• Vestibular Center (motion) →

  • Histamine is the primary neurotransmitter in the brainstem that drives nausea and vomiting

  • Histamine attatches to Histamine receptors in the vestibular nuclei

VOMITING CENTER

• Sends signals to GI Tract

• GI Tract can also send signals to Vomiting Center

*No conscious perception in equilibrium

Equilibrium Summary

Receptors

• Hair cells in vestibule (static equilibrium) or semi-circular canals (dynamic equilibrium)

Circuits

• Synapses in brainstem for balance to vestibular center

• Inputs from vestibular center to other regions (like vomiting center)

Perception

• No direct cortical (cortex) region involved with perception

Accessory organs around the eye

• Eyebrows and eyelashes

• Eyelids (palpebrae)

• External eye muscles

• Conjunctiva = thin membrane over the sclera

  • Prevents debris from migrating to the back of the eye

• Lacrimal apparatus

Lacrimal Apparatus

Tears = Lacrimal Fluid

• Cleans and lubricates the eye

• Contains mucus, antibodies, and lysozyme

Structure of the eyeball

Fibrous Layer:

• Sclera

  • thick, white part of the eye

• Cornea

  • works with the lens to bend the light that hits the retina

Inner Layer:

• Retina

  • Composed of photoreceptors (rods and cones), Neurons, and Glial cells

  • Fovea = where light is focused

Vascular Layer:

• Iris

• Ciliary Body

  • produces aqueous humor

• Choroid

Vision

Optical Component

• focuses light onto receptor cells

Neuron Component

• transforms light stimulus to graded potentials and action potentials

Optics of vision

Refraction of light by cornea and lens

• Regulation of the amount of light entering the eye by the iris

Cornea

Transparent tissue that bends (refracts) light into the eye

Iris

Two separate muscles to control diameter of the pupil

• Sphincter pupillae muscle

  • Parasympathetic

  • Less light

• Dilator pupillae muscle

  • Sympathetic

  • More light

Lens

The lens can change shape

• ACCOMODATION = tauting or slac