NEUR100: Exam 3

On a basic level, how does sensory information travel to the brain? (3 steps)

1) Sensory receptors in skin

2) Travel up spinal cord

3) Cross contralaterally in the medulla

Where does sensory information cross contralaterally?

In the medulla

When does pain information cross contralaterally?

Right away

All sensory information, except for ___ and ___, is sent to the brain contralaterally. (2)

olfaction, gustation

Where is sensory information sent? (+3)

Afferent —> up to the brain

(1) Primary Sensory Cortices, (2) Secondary Sensory Cortices, (3) Association Area

Where is motor information sent? (+4)

Efferent —> down to the muscles

(1) Motor Association Cortex, (2) Secondary Motor Cortex, (3) Primary Motor Cortex, (4) Muscles

What is processed by the primary somatosensory cortex?

Somatic sensations

Where does information pass in the primary area of the somatosensory pathway?

Information from 3a, 3b, and 1 —> 2

Area 3a; Somatosensory Pathway

Muscles

Area 3b; Somatosensory Pathway

Skin (slow)

Area 1; Somatosensory Pathway

Skin (fast)

Area 2; Somatosensory Pathway

Joints (pressure)

Who originally proved phantom limb syndrome was an issue in the brain?

Sylas Mitchell

Because the injuries were so frequent and prevalent, what events does Kean say have benefitted neuroscience?

Wars

How is the somatosensory cortex impacted when the body is damaged?

Brain recognizes to account for damage —> phantom limb syndrome

What is phantom limb syndrome?

• Body area damaged

• Adjacent area of brain will take over

• Person still feels sensation in that area

What happens if the second somatosensory cortex is damaged?

• Impacts how movements are performed

• Apraxia

What is apraxia?

Inability to complete a plan of action accurately

What is the somatosensory association cortex responsible for, and what happens if it is damaged?

• Integrates sensory and visual information into a “whole”

• Lesion can result in neglect

What is the function of the motor association cortex?

Plans complex behavior and movements

The prefrontal cortex receives information from ___ areas, integrates/processes it, then sends it to the ___ ___ ___.

sensory; motor association cortex

What is the function of the secondary motor cortex?

Organizes movement sequences

What are mirror neurons involved in?

Imitation of task or thinking of task

What is the function of the primary motor cortex?

Produces specific movements (fine motor movements)

What happens if the secondary motor cortex is damaged?

Difficulty organizing a sequence

What happens if the primary motor cortex is damaged?

• Difficulty holding things using precision/pincer grip

• Difficulty w/ skilled movements

Can damage to the motor pathway be rehabilitated?

Lesion/deficit can be rehabilitated

When digits area was lesioned in primary motor cortex, what happened with vs. without rehabilitation?

• Without rehabilitation, area controlling hands = smaller, elbow/shoulder = bigger

• With rehabilitation, area controlling hands = larger

Do any areas other than the motor cortex impact movement?

Yes, the cerebellum and basal ganglia also impact movement.

Cerebellum

• Topographically organized

• Receives input from the cranial nerves, the cerebral cortex, and the pons

• Impacts aim and timing

What happens when there is damage to the cerebellum?

• Disrupts timing and movement execution

• Doesn’t abolish movements

• Doesn’t impact continuous movements

Basal Ganglia

• Initiates movements

• Receives input from the cerebral cortex

• Responsible for learning new movements

What happens when there is damage to the basal ganglia?

• Difficulty learning new motor movements

• Can’t convert new movements into automatic responses

How did Water Hess discover the role that the brainstem plays in the motor pathway?

• Water Hess stimulated the brainstem → innate movements

• Fear response

Locked-in Syndrome

• Damage to brainstem

• Patient awake

• Paralysis of muscles

How does motor information travel from the brain to the body (efferently)?

Corticospinal Tracts

Lateral Corticospinal Tract

Precise movement of hands and feet

Medial Corticospinal Tract

Controls trunk for posture, bending, and walking

Neuromuscular Junction

Synapse between a motor neuron axon and a muscle fiber

Where is acetylcholine released, and where does it bind to?

Released into the neuromuscular junction; binds to receptors on the muscle

Flexor Motor Neurons

Moves limb in towards the trunk

Extensor Motor Neurons

Moves limb away from the trunk

Proprioceptor

• Detects position or movement of a part of the body

• Detects stretch and tension of muscles and sends information to brain

Mechano- and thermosensitive ion channels activate due to changes in ____ ___ or ___.

membrane stretch; temperature

Temperature Receptors

• Convert energy into action potentials

• Responsible for you feeling pain, hot, warm, cold

• Can also be activated by certain chemicals (like capsaicin)

How are transient receptor potential (TRP) ion channels activated?

• Activated by temperature change

• Each TRP channel has a unique firing threshold

• Each member of the TRP family is activated in a graded fashion to their “ideal” temperature

• The more activated, the hotter/colder the stimulus = tells you “Caution!”

What are the two categories of thermal receptors?

Those that respond to warmth, and those that respond to coolness

T/F: Some receptors respond to both temperature and chemical input.

True

TRPV1 Vanilloid Receptors

• Activated by moderate heat or capsaicin

• Allow for influx of Na+ and Ca2+

Why do TRPV1 vanilloid receptors sense capsaicin?

“Endovanilloids” involved in pain response to injury

TRPM8 Receptors

• Detects cold (below 28 C)

• Also responds to menthol

Why do we construe mint as cool temperature?

TRPM8 receptors respond to both cold and menthol

Desensitization

Diminished responsiveness w/ repeated or continual exposure

Nociceptors

• Cutaneous and subcutaneous receptors specialized for the detection of harmful (noxious) stimuli

• Typically free nerve endings

Free Nerve Endings

Hairy and glabrous skin

What are the three ways nociceptors detect intense stimuli?

1) Touch (pressure, stretch, pinch)

2) Temperature (TRPV receptors)

3) Chemicals (irritants found in garlic, horseradish, wintergreen oil, etc.)

What are the two types of pain?

1) Early perception of pain (sharp pain) = first (initial) pain —> travels via myelinated axons

2) Later, dull ache or burning sensation = second (longer lasting) pain —> travels via unmyelinated axons

What are the four main areas of the pain pathway?

(1) Site of injury —> (2) Spinal cord —> (3) Brainstem and (4) Thalamus

What detects an acute injury at its site?

Nociceptors in the periphery

At the site of injury, what sends high speed signals to the spinal cord (dorsal horn)?

Myelinated fibers

What happens during first pain in the spinal cord?

Reflexive withdrawal (i.e., you pull your hand back before you realize it)

Interneurons in the spinal cord connect ___ input (___ horn) and ___ output (___ horn) neurons to process information.

• Sensory input (dorsal horn)

• Motor output (ventral horn)

What happens during second pain in the spinal cord?

Sends information up to brain to further process/assess the pain

How do neurons travel up to the thalamus, and how does this play a role in pain?

• Spinothalamic tract —> thalamus

• From here we begin to send information to various parts of the cortex to inform our experience

Where does the thalamus project to (4), and what is significant about these areas?

1) Anterior Cingulate Cortex

2) Prefrontal Cortex

3) Amygdala

4) Hippocampus

Significance: all areas believed to be involved in emotional reaction to pain

What part of the brain was activated when experiencing “hurt feelings”?

Anterior Cingulate Cortex

How do opiates provide pain relief?

Binding to opioid receptors in the periaqueductal gray

What are the natural pain relievers that opiates mimic?

Endorphins — endogenous pain relievers (endogenous = internal origin)

Taste

Sensations evoked by solutions in the mouth that make contact with receptors in the tongue and mouth

What two qualities does taste reflect, and how is this useful?

1) Pleasant qualities

2) Nutritive qualities

Usefulness: indicates whether food is safe to eat

Papillae

Bumps on tongue that contain taste buds

Taste Buds

Sensory receptors that transduce taste information

How often do taste buds regenerate?

Every 1-2 weeks

Microvilli

Projections on the tip of the receptor cell that extend into the taste pore

Where do substances bind for taste?

On the microvilli

Taste buds consist of groups of how many receptor cells? How are these specialized neurons arranged?

Groups of 20-50 receptor cells; arranged like the segments of an orange

What does sour taste indicate?

Potentially toxic

What does bitter taste indicate?

Potential poison

What does umami taste indicate?

Savoriness/MSG; proteins to repair tissue

What does salty taste indicate?

Physiological processes and energy source

What does sweet taste indicate?

Energy source

What stimuli do Type I taste receptors respond to?

Salty

What stimuli do Type II taste receptors respond to?

Sweet, bitter, umami

What stimuli do Type III taste receptors respond to?

Sour

Tastants are stimuli that can be tasted. Tastants are broadly divided into two categories:

1) Made up of small charged particles; travel via ion channels through the membrane — Salty & Sour

2) Detected by G-Protein coupled receptors (GPCRs) — Bitter, Sweet, & Umami

Bitter (hint: activation of ___ activates __)

Activation of T2PR receptors activates G-Protein signaling cascades

Umami (hint: flavor, activated by, activation of ___ activates ___)

• Savory

• Activated by glutamate and other amino acids (MSG)

• Activation of T1R receptors (R1 + R3) activates G-Protein signaling cascade

Sweet (hint: evoked by, activation of ___ activates ___)

• Evoked by sugars

• Activation of T1R receptors (R2 + R3) activates G-Protein signaling cascade

What is miraculin?

A glycoprotein that has a carbohydrate group attached

What receptors does miraculin bind to?

T1R2-T1R3 (sweet) receptors

On a basic level, how does miraculin make you perceive sweet?

Sour receptors are active, yet the stimulation of sweet receptors by the miraculin in the presence of the acids make you perceive sweet

What impacts how we taste?

Number of taste buds

When do taste buds decline?

As we age (after age 50)

What is ageusia, and what causes it?

• Inability to taste

• Caused by damage to either taste buds or cranial nerves

Supertasters

• Genetically linked

• 6x as many taste buds

• 25% of population

What kind of paper is used to test if a person is a supertaster?

Propylthiouracil (PROP)

How do taste buds send information to the brain?

Via cranial nerves

What are the three cranial nerves involved in taste?

1) Facial Nerve (VII)

2) Glossopharyngeal Nerve (IX)

3) Vagus Nerve (X)

The facial nerve (VII) is responsible for taste in…

…anterior 2/3 of tongue

The glossopharyngeal nerve (IX) is responsible for taste in…

…posterior 1/3 of tongue