BIOPSYCHOLOGY

LECTURE 7 — CENTRAL NERVOUS SYSTEM

Slides 27–62

Lecture 7’s final material expects you to understand how the nervous system develops from the neural tube and then be able to identify the major structures of the adult brain. The neural tube itself develops from the neural plate, which is formed from ectoderm. Lecture 7 Slides - The Central …

1. Neural plate → neural tube → major brain subdivisions

The basic developmental sequence is:

Neural plate → neural folds/groove → neural tube → brain + spinal cord

The rostral/anterior end of the neural tube becomes the brain, whereas more caudal portions form the spinal cord. The hollow interior of the neural tube remains important: it eventually becomes the ventricular system of the brain and the central canal of the spinal cord.

The three major early brain subdivisions are:

A major developmental feature is that the telencephalon expands tremendously and folds back over other brain regions, producing the large cerebral hemispheres.

Textbook connection: brain development

Your Chapter 4 summary gives five developmental processes that are important to distinguish:

Proliferation → Migration → Differentiation → Synaptogenesis → Myelination

Proliferation is production of new cells. Migration is movement of immature cells to their eventual locations. Differentiation is development of a particular cellular identity. Synaptogenesis is formation of synaptic connections. Myelination is the production of myelin around axons.

These overlap in time—they are not five completely separate periods.

A common misconception is that brain development simply means “making more neurons.” Development also requires neurons to migrate, differentiate, form appropriate connections, lose inappropriate connections, and become myelinated.

2. Ventricular system and cerebrospinal fluid

A ventricle is a fluid-filled compartment inside the brain.

The basic sequence to remember is:

Lateral ventricles → third ventricle → cerebral aqueduct → fourth ventricle → CSF circulation around brain/spinal cord

The lateral ventricles are associated with the cerebral hemispheres/telencephalon. The third ventricle lies near the diencephalon. The cerebral aqueduct runs through the midbrain. The fourth ventricle is associated with the hindbrain.

Choroid plexus

The choroid plexus is specialized tissue associated with the ventricles that produces cerebrospinal fluid (CSF).

CSF is important because it helps cushion and protect the CNS and provides a stable fluid environment.

Common pitfall

Do not confuse:

• Ventricle = space containing CSF.

• Choroid plexus = tissue that produces CSF.

• Central canal = continuation of the ventricular cavity within the spinal cord.

3. Meninges: protective layers of the CNS

The brain and spinal cord are surrounded by three meninges:

Dura mater → arachnoid layer → pia mater

From outside inward:

Dura mater is the tough outer layer.

Arachnoid is the middle layer and is associated with the CSF-filled space.

Pia mater is the delicate innermost layer closely associated with nervous tissue.

Memory order:

D-A-P = Dura, Arachnoid, Pia

4. Nuclei, tracts, ganglia, and nerves

This terminology is easy to mix up.

Inside the CNS:

• Collection of neuron cell bodies = nucleus/nuclei

• Bundle of axons = tract

Outside the CNS, in the PNS:

• Collection of neuron cell bodies = ganglion/ganglia

• Bundle of axons = nerve

So:

CNS → nucleus + tract

PNS → ganglion + nerve

5. Hindbrain

Medulla

The medulla is at the transition between the spinal cord and brain.

It controls essential physiological functions, including:

• Respiration

• Heart rate

Some cranial nerves also originate here.

Because these functions are necessary for survival, substantial damage to the medulla can have severe consequences.

Pons

The pons contains sensory and motor nuclei and contributes to communication among brain regions.

Your lecture also emphasizes serotonergic neurons associated with the raphe nuclei, whose axons project widely through the CNS.

Cerebellum

The cerebellum is attached to the brainstem and is crucial for:

• Coordination

• Timing

• Fine-tuning movements

• Motor learning

You will see this again in Lecture 8.

6. Midbrain

The midbrain can be divided conceptually into the tectum and tegmentum.

Tectum

The tectum includes:

Superior colliculus → vision

Inferior colliculus → audition

The colliculi are particularly involved in orienting and processing sensory information.

Do not reverse them:

Superior = visual

Inferior = auditory

The inferior colliculus will return in the auditory pathway in Lecture 11.

Tegmentum

Several important structures emphasized in the lecture are located here.

Periaqueductal gray — PAG

Important for pain responses and pain modulation.

This returns in Lecture 9 when discussing analgesia and descending control of pain.

Red nucleus

Associated with movement regulation.

It is connected to the rubrospinal system discussed in Lecture 8.

Substantia nigra

Contains important dopamine neurons and participates in movement through connections with the basal ganglia.

Ventral tegmental area — VTA

Also contains dopamine neurons, but is emphasized more for motivation and reward-related processes.

Reticular formation

Associated with processes such as sleep and arousal.

Major misconception

Do not treat every dopamine-containing region as performing the same function.

For this class:

Substantia nigra → movement

VTA → motivation/reward

7. Diencephalon: thalamus and hypothalamus

Thalamus

The thalamus is an important relay for information traveling to and from the cortex.

A major exam statement is:

Most sensory systems relay through the thalamus before reaching cortex, with olfaction as the major exception emphasized in this course.

That exception becomes extremely important in Lecture 10.

Hypothalamus

The hypothalamus regulates many homeostatic, motivated, autonomic, and endocrine functions.

Lecture examples include:

• Fight-or-flight-related responses

• Feeding

• Drinking

• Sexual behavior

• Stress hormones

• Growth-related hormones

• Thyroid-related hormonal regulation

One of its major functions is controlling the pituitary gland.

8. Pituitary gland: anterior versus posterior

This is explicitly listed on the Lecture 7 “Things to Know.”

The pituitary has two major parts:

Anterior pituitary

Posterior pituitary

But they communicate with the hypothalamus differently.

Posterior pituitary mechanism

Hypothalamic neuron → axon extends into posterior pituitary → neurohormone released directly into general circulation

The key idea is direct neural connection.

Anterior pituitary mechanism

Hypothalamus releases regulatory hormones → portal blood vessels → anterior pituitary endocrine cells → endocrine cells release additional hormones into general circulation

The key idea is:

Hypothalamus → portal circulation → anterior pituitary → systemic circulation

High-yield comparison

Common misconception

The pituitary is called the “master gland,” but that does not mean it operates independently. The lecture emphasizes that the hypothalamus controls it.

9. Telencephalon

Lecture 7 lists several major telencephalic components:

Cortex, internal capsule, commissures, basal ganglia, limbic system

Cerebral cortex and four lobes

Know the four major lobes:

Frontal lobe: movement, planning and higher-order functions.

Parietal lobe: includes primary somatosensory processing.

Temporal lobe: important for audition and other processes.

Occipital lobe: heavily associated with vision.

10. Precentral and postcentral gyri

Precentral gyrus

Located in the frontal lobe.

Contains the primary motor cortex, M1.

Important for movement.

Postcentral gyrus

Located immediately behind the central sulcus in parietal cortex.

Contains primary somatosensory cortex, S1.

Important for body sensation.

Memory:

PREcentral = motor

POSTcentral = somatosensory

11. Motor and sensory homunculi

A homunculus is the cortical representation of different body regions.

There is a:

• Motor homunculus in primary motor cortex

• Somatosensory homunculus in S1

The body is not represented according to physical body size.

Areas requiring especially precise movement or having dense sensory innervation receive disproportionately large cortical representations.

This is why the hands and face appear enormous on cortical homunculi.

12. Brodmann areas

Brodmann areas are numbered cortical regions based primarily on differences in cortical cellular organization or cytoarchitecture.

The lecture shows the classic division into 52 Brodmann areas.

The point is not necessarily to memorize all 52. The professor’s “Things to Know” says to know what a Brodmann area is.

13. Layers and columns of cerebral cortex

The neocortex contains six layers.

The lecture emphasizes pyramidal neurons, whose pyramid-shaped cell bodies are especially prominent in layers III and V.

Some regions are also organized into cortical columns.

A cortical column extends vertically through the layers and can act as a functional information-processing unit.

Do not confuse:

Layers = horizontal organization

Columns = vertical organization through multiple layers

14. Gray matter versus white matter

Gray matter contains relatively more:

• Cell bodies

• Dendrites

• Unmyelinated neural structures

White matter consists largely of:

• Axons

• Especially myelinated axons

The myelin gives the tissue its lighter appearance.

15. Major white-matter pathways

Corpus callosum

The corpus callosum is the major commissure connecting the left and right cerebral hemispheres.

Anterior and posterior commissures

Smaller bundles also connecting structures across the two sides.

Internal capsule

The internal capsule connects cerebral cortex with deeper parts of the brain and pathways leading toward the brainstem and spinal cord.

Common pitfall

Corpus callosum = hemisphere ↔ hemisphere

Internal capsule = cortex ↔ lower/deeper nervous-system structures

They are both white matter, but their connections are different.

16. Basal ganglia

Lecture 7 emphasizes:

• Caudate

• Putamen

• Globus pallidus

They form an interconnected system strongly involved in movement.

Your lecture also emphasizes strong connections with frontal cortex.

The caudate + putamen are often called the striatum, a term that becomes useful when studying Chapter 7 movement mechanisms.

The amygdala appears parenthetically on one basal-ganglia slide, but later slides emphasize it as part of the limbic system. For your studying, the core basal-ganglia structures highlighted repeatedly are the caudate, putamen, and globus pallidus.

17. Limbic system

The lecture associates the limbic system particularly with emotion, motivation, and learning.

Important structures include:

Amygdala: emotional processing; lecture also associates it with odor.

Hippocampus: learning.

Fornix: major pathway associated with the hippocampus.

Cingulate cortex/gyrus: attention and other functions.

Olfactory bulb: smell.

Hypothalamus: motivation, endocrine and homeostatic functions.

Mammillary bodies: included in the lecture's limbic diagram.

There is overlap among these systems. Brain structures rarely perform only one isolated function.

Lecture 7 — Things to Know checklist

You should be able to explain, not just recognize:

1. Neural plate → neural tube → major brain subdivisions.

2. Structures belonging to forebrain, midbrain and hindbrain.

3. Ventricular system and choroid plexus.

4. Meninges.

5. Hindbrain structures and functions.

6. Tectum versus tegmentum.

7. Thalamus versus hypothalamus.

8. Anterior versus posterior pituitary pathways.

9. Four cortical lobes.

10. Motor versus sensory homunculus.

11. Brodmann areas.

12. Gray versus white matter.

13. Internal capsule versus commissures.

14. Basal ganglia structures.

15. Major limbic structures.

LECTURE 8 — MOTOR SYSTEMS

The lecture presents movement as a hierarchical system. Skeletal muscles produce movement, the spinal cord directly controls skeletal motor neurons, the brainstem integrates motor commands, motor cortical regions generate higher-level commands, and the cerebellum and basal ganglia modify those motor systems through circuits involving the thalamus. Lecture 8 Slides - Motor Systems

18. Hierarchy of motor control

A simplified hierarchy is:

Cortical motor areas → brainstem/spinal motor systems → motor neurons → skeletal muscle

Meanwhile:

Basal ganglia + cerebellum → modulation of motor systems

The key concept is that movement is distributed across many levels.

The spinal cord is not simply a cable carrying cortex commands. It contains circuits capable of generating reflexes and coordinated patterns.

19. Somatic motor system and neuromuscular junction

The somatic nervous system controls skeletal muscle.

A neuromuscular junction (NMJ) is the synapse between a motor-neuron axon and a skeletal muscle fiber.

Motor neurons release acetylcholine, ACh, at the skeletal NMJ.

A muscle fiber normally receives input from one motor axon, although that axon can branch and innervate multiple muscle fibers.

One motor neuron plus the muscle fibers it innervates constitutes a motor unit.

A single motor-neuron action potential can cause a brief muscle contraction or twitch. Closely spaced activity can produce summation and eventually a sustained contraction. The lecture specifically contrasts single spikes producing twitches with summation producing sustained contraction. Lecture 8 Slides - Motor Systems

20. Three major sources of motor-neuron input

The lecture says lower motor neurons receive three major categories of input:

Spinal interneurons

Upper motor neurons

Muscle sensory receptors

That third category is crucial because movement constantly depends on proprioceptive feedback.

21. Proprioception

Proprioception is information about the position and movement of the body.

Two important proprioceptors:

Muscle spindle → muscle length/stretch

Golgi tendon organ → muscle tension

This distinction is extremely important.

22. Muscle spindle

A muscle spindle is located within a muscle and contains specialized intrafusal fibers.

It detects:

• Muscle stretch

• Length

• Change in length

Its sensory afferents include Ia afferent fibers.

When a muscle stretches, the spindle stretches too, increasing sensory activity.

23. Alpha motor neurons versus gamma motor neurons

Alpha motor neurons

Control the ordinary force-producing or extrafusal muscle fibers.

Their activation causes muscle contraction.

Gamma motor neurons

Control intrafusal fibers inside the muscle spindle.

Their purpose is not primarily to generate external force.

They adjust the spindle so it remains appropriately stretched and sensitive while the entire muscle contracts.

This solves an important problem.

Imagine an alpha motor neuron contracts a muscle. If the spindle simply became loose or “floppy,” it would stop detecting additional stretch.

Gamma activation contracts the intrafusal fibers and keeps the spindle taut, allowing Ia sensory fibers to remain responsive.

High-yield concept

Alpha = contracts main muscle

Gamma = maintains spindle sensitivity

24. Myotatic/stretch reflex

The myotatic reflex is a stretch reflex that helps maintain desired muscle length.

Classic example: knee-jerk reflex.

Sequence:

Muscle stretched → muscle spindle stretched → Ia afferent fires → enters spinal cord → excites alpha motor neuron → same muscle contracts

The core reflex can be monosynaptic because the Ia sensory neuron directly synapses with the alpha motor neuron supplying the stretched muscle.

25. Reciprocal inhibition

Movement requires coordination between antagonistic muscles.

If an extensor contracts, its antagonistic flexor often must relax.

During the stretch reflex:

Spindle afferent → activates motor neuron of stretched muscle

At the same time:

Spindle afferent → spinal inhibitory interneuron → inhibits motor neuron supplying antagonist

That is reciprocal inhibition.

Common misconception:

The entire knee-jerk response is not literally only one synapse. The direct activation of the agonist is monosynaptic, but inhibition of the antagonist requires an interneuron.

26. Golgi tendon organ and reverse myotatic reflex

The Golgi tendon organ (GTO) is located in the tendon and detects muscle tension.

High tension activates GTO afferents.

Through spinal circuitry, this can inhibit motor activity to the muscle.

Lecture functions:

• Protection from extreme overload

• Regulation of tension under ordinary conditions

So:

Muscle spindle → stretch/length

Golgi tendon organ → tension

Do not reverse them.

27. Spinal cord sensory versus motor organization

Another professor “Things to Know” item:

Sensory fibers enter dorsally.

Motor neurons leave ventrally.

Think:

Dorsal = sensory IN

Ventral = motor OUT

The spinal nerve itself is mixed, containing both sensory and motor axons.

28. Descending motor tracts

Lecture 8 divides them broadly into:

Lateral pathways

Especially important for voluntary control of distal musculature.

Includes:

• Corticospinal pathway

• Rubrospinal pathway

Ventromedial pathways

Especially important for posture and more axial/proximal control.

Includes:

• Vestibulospinal

• Tectospinal

• Reticulospinal

29. Corticospinal pathway

The corticospinal system begins in cerebral cortex and descends toward the spinal cord.

Key lecture sequence:

Motor cortex → descending fibers → cerebral peduncles/midbrain → medulla → fibers cross → spinal cord → ventral-horn motor systems

The crossing explains why a cerebral hemisphere predominantly controls the contralateral side of the body.

The textbook emphasizes the lateral corticospinal system particularly for precise limb movement, including fingers and hands.

30. Rubrospinal pathway

The rubrospinal pathway is associated with the red nucleus.

Lecture 8 associates it with voluntary/distal control and a somewhat more automatic contribution to movements such as gait.

It is also influenced by cortical projections.

Thus “brainstem motor pathway” does not mean “completely independent of cortex.”

31. Vestibulospinal and tectospinal systems

These belong to the broad ventromedial group.

Vestibulospinal system

Uses information from the vestibular system to help control:

• Balance

• Posture

• Head/body orientation

Tectospinal system

Associated particularly with the superior colliculus and helps produce automatic orienting movements of the head/neck in response to sensory events.

This links Lecture 7's superior colliculus to Lecture 8's motor system.

32. Reticulospinal systems

Lecture 8 distinguishes medial/pontine and lateral/medullary reticulospinal pathways.

They contribute especially to posture of the:

• Trunk

• Limbs

33. Primary motor cortex — M1

The primary motor cortex is in the precentral gyrus.

Its neurons contribute strongly to descending motor pathways.

Its organization is somatotopic, producing the motor homunculus.

But the textbook adds an important nuance: M1 does not simply encode one isolated muscle at a time. Many neurons participate in coordinated movements or movement outcomes.

34. Premotor area — PMA

The premotor cortex/PMA contributes to planning and preparing movements, particularly movements directed toward external targets.

It uses information about:

• Target

• Current body position

• Desired movement

35. Supplementary motor area — SMA

The SMA is important for:

• Planning movements

• Organizing movement sequences

• Internally generated movement

Both PMA and SMA have somatotopic organization, but their role goes beyond simply producing muscle contraction.

36. Prefrontal and posterior parietal cortex

Lecture 8 includes both in motor planning.

Posterior parietal cortex: integrates sensory information and contributes to intention/preparation for movement.

Prefrontal cortex: contributes to planning, consequences and inhibition of inappropriate actions.

Useful sequence:

Posterior parietal → intention/sensory preparation

PMA/SMA → movement planning

M1 → motor command/execution

37. Basal ganglia versus cerebellum

This distinction is extremely important.

Basal ganglia

Lecture functions include:

• Initiating movements

• Controlling amplitude and direction

• Movements performed from memory rather than moment-to-moment sensory control

The textbook adds:

• Self-initiated movement

• Movement vigor

• Habit learning

• Reward-related learning

Cerebellum

Receives motor and sensory information and helps:

• Fine-tune movements

• Coordinate movement

• Correct errors

• Control timing

• Learn skilled movements

A useful distinction is:

Basal ganglia = selecting/initiating/scaling action

Cerebellum = timing/correction/precision

Neither structure directly acts as the final lower motor neuron to the muscle.

Lecture 8 — Major pitfalls

Do not confuse alpha and gamma motor neurons.

Do not confuse muscle spindle and Golgi tendon organ.

Do not say sensory signals leave through the dorsal root—sensory enters dorsally; motor exits ventrally.

Do not equate the cerebellum with movement initiation; its lecture emphasis is coordination and fine-tuning.

Do not assume PMA, SMA and M1 are interchangeable.

LECTURE 9 — SOMATOSENSATION: TOUCH AND PAIN

All sensory systems ultimately communicate using neural activity, but the concept of labeled lines explains how the brain distinguishes modalities: different sensory information travels along distinct pathways. Lecture 9 Slides - Somatosensat…

38. Sensory transduction

Sensory transduction means converting stimulus energy into a change in the electrical state of a sensory receptor.

A receptor first produces a graded generator/receptor potential.

If that electrical change becomes sufficient to reach threshold in the appropriate neuron, action potentials are produced.

39. Mechanoreceptors

Lecture 9 emphasizes several skin receptors. Lecture 9 Slides - Somatosensat…

Meissner corpuscles

• Lower-frequency vibration

• Lecture gives about 50 Hz

• Small receptive fields

• Useful for detecting changes in tactile stimulation and rough textures

Pacinian corpuscles

• Pressure/vibration

• Particularly higher-frequency vibration

• Lecture gives approximately 200–300 Hz

• Large receptive fields

Merkel discs

Respond especially to:

• Isolated points

• Fine spatial details/static touch

Ruffini corpuscles

Respond to:

• Stretching of skin

Free nerve endings

Respond to:

• Pain

• Heat

• Cold

40. Pacinian corpuscle transduction

A physical deformation of the Pacinian corpuscle changes the receptor membrane.

Sequence:

Pressure/vibration → deformation → mechanosensitive Na+ channels open → graded generator potential → threshold → action potential

Its layered physical structure also explains why it adapts quickly.

41. Sensory adaptation

Adaptation means the receptor or sensory system responds less strongly to a constant stimulus over time.

This is useful because the nervous system often cares more about changes than about an unchanging stimulus.

Example: clothes touching your skin are highly noticeable initially but become less noticeable.

The lecture also emphasizes central modulation: the brain can actively amplify or suppress sensory information.

42. Receptive fields and two-point discrimination

A receptive field is the area of sensory space that influences a particular receptor/neuron.

Small, densely packed receptive fields allow better spatial discrimination.

That is why fingertips show excellent two-point discrimination.

You need to connect:

High receptor density + small receptive fields → better ability to distinguish two nearby stimuli

Not simply “more sensitive receptors.”

43. Dermatomes

A dermatome is an area of skin providing sensory information primarily to a particular spinal-cord segment/spinal nerve.

Adjacent dermatomes overlap.

They are therefore not perfectly isolated strips.

44. Dorsal-column touch pathway — body

This pathway is one of the most important things to memorize in order.

Skin receptor → peripheral sensory neuron → dorsal root ganglion → dorsal root → ipsilateral dorsal columns → medulla/dorsal-column nuclei → axons cross → medial lemniscus → thalamus → primary somatosensory cortex S1

The crucial crossing point is:

Touch crosses in the medulla.

Before that crossing, body touch information ascends ipsilaterally.

45. Somatosensory pathway — face

For face sensation:

Face receptor → trigeminal nerve/CN V → pons → crossing → thalamus → S1

So the body and face do not enter the CNS through exactly the same route.

46. S1: primary somatosensory cortex

S1 is located in the postcentral gyrus.

It contains a somatotopic body representation—the sensory homunculus.

Different amounts of cortical area are devoted to different body regions based largely on sensory demands.

47. Somatosensory plasticity

The cortical map can change with experience.

The PowerPoint describes greater representation of fingers with extensive use—for example, string musicians.

The Chapter 4 summary extends this with cortical reorganization after loss of sensory input.

For example, if a finger is amputated, cortex that previously represented that finger can begin responding to neighboring fingers.

With a missing limb, adjacent representations may invade or strengthen within former limb cortex.

This helps explain phantom limb sensations: activation of reorganized cortex may still be interpreted by the brain as coming from the missing limb.

Common misconception

Plasticity does not automatically mean new neurons replaced the missing body part's neurons.

It can involve changed synaptic strength, unmasking of existing inputs, collateral sprouting, and reorganization of surviving networks.

48. Nociception and pain receptors

Nociceptors are sensory receptors responsive to potentially damaging stimuli.

Many are free nerve endings.

Lecture 9 emphasizes two fiber types.

C fibers

• Thin

• Unmyelinated

• Slow conduction

• Associated with longer-lasting/dull pain

The lecture associates TRPV1 receptors with C fibers.

TRPV1 responds to:

• Painful heat

• Capsaicin

Capsaicin activates a receptor that normally participates in detecting painful heat.

Aδ fibers

• Larger than C fibers

• Myelinated

• Faster conduction

• Associated with rapid/sharp pain

The lecture labels a high-temperature receptor TRP2 and associates it with Aδ fibers.

High-yield comparison

Aδ → fast, sharp pain

C → slow, lingering pain

49. Spinothalamic/anterolateral pain pathway

Pain and temperature take a different route from fine touch.

Sequence:

Nociceptor → dorsal root → dorsal horn → synapse → second-order neuron crosses in spinal cord → anterolateral/spinothalamic pathway → thalamus → cortical targets

The crucial distinction is:

Pain crosses in the spinal cord.

Compare:

Touch → crosses later in medulla

Pain/temperature → crosses early in spinal cord

This is one of the most likely pathway-confusion questions.

50. Pain neurotransmitters

Pain neurons use chemical signals including:

Glutamate

and for stronger/prolonged pain:

Substance P

The textbook summary also includes CGRP with stronger pain.

Substance P can also participate in inflammatory responses and promote surrounding tissue reactions.

51. Sensory versus emotional components of pain

Pain is not a single process.

Somatosensory/thalamic pathways contribute strongly to:

• Where is the pain?

• How intense is it?

Other structures—including:

• Anterior cingulate cortex

• Amygdala

• Hypothalamic circuits

contribute more to:

• Unpleasantness

• Emotion

• Motivation to escape the pain

Therefore, perception of pain intensity and emotional suffering from pain can partly dissociate.

52. Gate control theory of pain

The gate-control theory proposes that spinal-cord circuits can modulate whether nociceptive information continues strongly toward the brain.

Touch input can inhibit pain-transmission neurons.

That helps explain why rubbing an injured area sometimes reduces pain.

Simplified:

Pain fiber active → gate favors transmission

Competing large-fiber touch input → inhibitory spinal circuitry → reduced pain transmission

Descending brain pathways can also influence this gate.

53. Periaqueductal gray and descending pain control

Remember the PAG from Lecture 7.

The periaqueductal gray can activate descending pain-inhibitory mechanisms.

These systems can engage endogenous opioids and reduce pain transmission in the spinal cord.

This is a good example of why you should connect lectures instead of memorizing each lecture separately:

Lecture 7 PAG location/function → Lecture 9 pain inhibition

54. Types of pain relief

The Lecture 9 table divides pain relief into several categories.

Opiates

Bind opioid receptors, including receptors in the PAG and spinal cord.

Endogenous opioid chemicals such as endorphins can also reduce pain transmission.

Spinal block

Blocks pain signaling within spinal pathways.

Anti-inflammatory drugs

Reduce chemical inflammatory signaling at the site of injury.

Cannabinoids

The lecture table associates them with actions in:

• Spinal cord

• Nociceptor endings

TENS/mechanical stimulation

Large-fiber tactile/electrical stimulation can reduce pain transmission, consistent with gating mechanisms.

Placebo/cognitive mechanisms

Expectations and cognitive factors can recruit pain-control systems.

Lecture 9 — Core comparison

LECTURE 10 — SMELL AND TASTE

The chemical senses detect chemicals, but smell and taste use distinctly different receptor systems and pathways.

55. Olfactory epithelium

Olfaction = smell.

Olfactory receptor neurons are located in the olfactory epithelium of the nasal cavity.

Their cilia extend into mucus.

Odorant molecules interact with receptors located on those cilia. Your lecture emphasizes that vertebrates possess hundreds of olfactory receptor types and that individual receptor types differ in which chemicals activate them. Lecture 10 Slides - Smell and T…

56. Olfactory receptor transduction

This mechanism is explicitly important.

Olfactory receptors are metabotropic/G-protein-coupled receptors. Lecture 10 Slides - Smell and T…

Basic sequence:

Odorant binds receptor → G protein activated → intracellular signaling/second messenger → ion-channel activity changes → receptor depolarizes → action potentials

The critical distinction is that the odorant does not simply “become electricity.” Binding starts an intracellular signaling cascade.

57. Olfactory pathway

Know these structures:

Olfactory receptor cells → axons through cribriform plate → olfactory bulb → glomeruli → mitral cells → olfactory pathways → piriform cortex

The piriform cortex is the major primary olfactory cortex emphasized in the lecture.

Olfactory pathways also project strongly toward structures including the amygdala.

58. Glomeruli and pattern coding

Receptor axons converge onto structures called glomeruli in the olfactory bulb.

A single odor does not correspond to just one glomerulus.

Instead, odors are represented by patterns of activity across multiple receptors and glomeruli.

So:

Wrong idea: “one odor = one receptor.”

Better idea: “an odor generates a characteristic combination/pattern across receptors.”

59. Why olfaction is unusual

The lecture emphasizes:

Olfactory signals can reach primary olfactory/piriform cortex without first making the standard thalamic relay used by the other major sensory systems.

It also has relatively direct connections with the amygdala, which helps explain why smells can produce powerful emotional reactions.

Common misconception:

Do not turn this into “olfaction never interacts with the thalamus anywhere in later processing.” The exam-level point from the slides is that it does not make the usual thalamic stop before primary olfactory cortex.

60. Retronasal olfaction and flavor

Orthonasal smell

Odor comes from the external environment through the nostrils.

Retronasal smell

Volatile molecules from food in the mouth travel upward through the throat into the nasal cavity.

This is extremely important to flavor.

The lecture states that much of our ability to discriminate flavors depends on smell.

61. Taste versus flavor

Very important:

Taste = activation of taste receptor cells

Flavor = integrated perception combining taste + smell and additional oral sensations

Therefore:

A blocked nose may leave basic tastes intact while dramatically reducing flavor.

62. Five basic tastes

Know:

Sweet

Sour

Salty

Bitter

Umami

The lecture mentions research on additional candidates such as fat, starch, water and calcium, but its basic five-taste framework is the core one.

63. Taste receptor cells and taste buds

Taste receptors are modified epithelial/skin-like cells, not ordinary sensory neurons.

They have excitable membranes and release neurotransmitters onto neighboring gustatory neurons.

They are replaced approximately every 10–14 days according to the lecture.

Taste receptor cells are grouped into taste buds.

Taste buds are found within tongue structures called papillae.

Important papillae shown in your material include:

• Fungiform

• Foliate

• Circumvallate

64. The “tongue map” misconception

The old idea that one part of the tongue detects only sweet, another only bitter, etc., is incorrect for the material in your lecture.

Every region can detect the major taste qualities.

However, receptor distributions vary, meaning some regions or taste buds can be more sensitive to certain tastes.

65. General taste-cell mechanism

The shared logic is:

Tastant contacts receptor cell → receptor mechanism activated → cell depolarizes → neurotransmitter released → gustatory afferent neuron activated → signal travels to brain

What differs among tastes is how depolarization begins.

66. Salty transduction

Salt involves sodium.

Simplified lecture mechanism:

Na+ in food → Na+ enters taste receptor through ion channel → membrane depolarizes → transmitter release

So salty uses a relatively direct ion-channel mechanism.

67. Sour transduction

Sour corresponds to acids and therefore H+ ions.

The lecture mechanism shows H+ affecting potassium channels.

Simplified:

H+ → blocks/reduces K+ movement → positive charge accumulates → depolarization → transmitter release

Do not confuse sour with salty:

Salty → Na+ entry

Sour → H+ effect on channels

68. Sweet transduction

Sweet uses a metabotropic receptor.

The lecture specifically identifies a heterodimer consisting of:

T1R2 + T1R3

Binding initiates a G-protein/intracellular signaling pathway.

69. Umami transduction

Umami is associated especially with glutamate.

Its receptor is structurally similar to the sweet receptor but uses:

T1R1 + T1R3

Compare:

Sweet = T1R2 + T1R3

Umami = T1R1 + T1R3

That one-subunit difference changes what chemical the receptor responds to.

70. Bitter transduction

The PowerPoint illustrates metabotropic bitter signaling.

A detailed pathway shown is:

Bitter chemical → bitter receptor → G protein → phospholipase C → PIP₂ pathway → IP₃ → intracellular Ca²⁺ release → neurotransmitter release

The slide also illustrates that different bitter substances can influence ionic processes differently.

The main test idea is that bitter can use metabotropic/G-protein signaling, not simply sodium entering directly as in salty taste.

71. Supertasters

People differ in taste sensitivity.

Supertasters tend to have:

• More fungiform papillae

• Greater overall oral/taste sensitivity

Genes and hormones are among factors contributing to these differences.

72. Gustatory cranial nerves

This is worth memorizing by tongue region.

Anterior two-thirds of tongue

Chorda tympani branch of facial nerve — CN VII

Posterior one-third of tongue

Glossopharyngeal nerve — CN IX

Palate

Greater superficial petrosal branch of facial nerve — VII

Epiglottis/upper esophageal region

Superior laryngeal branch of vagus nerve — CN X

The lecture says gustation relies on multiple cranial-nerve pathways.

73. Trigeminal sensation is not the same thing as taste

The trigeminal nerve — CN V detects irritant/somatic sensations in the nose and mouth.

Examples:

• Capsaicin “burning”

• Irritation from ammonia

That is different from a basic taste.

Therefore, “spiciness” is not one of the five basic tastes in this lecture.

It is largely trigeminal/somatosensory.

74. Taste pathway to the brain

Core sequence:

Taste receptor → cranial nerve → nucleus of the tractus solitarius (NTS) in medulla → gustatory thalamus → insula/primary gustatory cortex

Additional areas receive taste-related information, including:

• Somatosensory cortex

• Amygdala

• Hypothalamus

• Orbitofrontal-related systems in the textbook summary

The somatosensory contribution helps process things like texture and oral tactile characteristics.

75. Specialist and generalist taste neurons

Some taste-responsive neurons are more selective or specialist.

Others respond to several taste categories and are more generalist.

Therefore, taste identity can depend on patterns of activity rather than every neuron acting as a strict “one taste only” labeled line.

76. Conditioned taste aversion

The lecture describes an especially strong form of learning:

Food/taste → illness → later avoidance of that food

A conditioned taste aversion can sometimes form after one trial.

Brain structures strongly involved in taste and aversion include:

• Insula

• Amygdala

• Hypothalamic PVN

Lecture 10 — Biggest pitfalls

Taste ≠ flavor.

Spiciness ≠ a basic taste.

Olfactory receptors ≠ glomeruli.

Olfaction does not follow the standard thalamus-before-primary-cortex pathway.

Sweet and umami share T1R3 but differ in their other receptor subunit.

Different tongue areas are not exclusive taste zones.

LECTURE 11 — THE AUDITORY AND VESTIBULAR SYSTEMS

The lecture begins with the general sensory logic:

Stimulus → receptor/transducer → electrical signal → neural processing.

For hearing, the stimulus is the sound wave and the receptor/transducer is the hair cell in the inner ear. Lecture 11 Slides - The Ear

77. Sound waves

Sound consists of changes in pressure—compressions and rarefactions traveling through a medium.

Two major properties are:

Amplitude/intensity

Related primarily to perceived loudness.

Measured in decibels, dB.

Frequency

Number of cycles per second.

Measured in Hertz, Hz.

Related primarily to perceived pitch.

The lecture also distinguishes a fundamental frequency, harmonics and timbre. Lecture 11 Slides - The Ear

78. Fundamental frequency, harmonics, and timbre

Fundamental

Basic frequency of a complex sound.

Harmonics

Frequencies that are multiples of the fundamental.

Timbre

Characteristic sound quality produced partly by the relative intensities of the harmonics.

Timbre helps explain why a piano and violin playing the same musical note do not sound identical.

79. Outer, middle and inner ear

Outer ear

Pinna → auditory canal

The pinna collects and alters sound depending partly on direction.

Middle ear

Tympanic membrane → malleus → incus → stapes

The ossicles transmit/concentrate mechanical energy.

The stapes communicates vibration to the oval window.

Inner ear

Includes the cochlea.

The cochlea contains the structures responsible for converting mechanical vibration into neural activity.

80. Complete mechanical pathway

Memorize this order:

Sound → pinna → auditory canal → tympanic membrane → malleus → incus → stapes → oval window → cochlear fluid movement → basilar membrane movement → stereocilia/hair cells → auditory nerve

81. Organ of Corti

The organ of Corti is the sensory structure located on the basilar membrane.

Important components include:

• Hair cells

• Supporting cells

• Auditory nerve endings

The basilar membrane forms the base of the organ of Corti.

The tectorial membrane interacts mechanically with the hair-cell stereocilia.

82. Tonotopy of the basilar membrane

Different frequencies produce maximal movement at different locations.

Base of cochlea

• Narrower

• Stiffer

• Near oval window

• Responds best to high frequencies

Apex

• Wider

• More flexible

• Responds best to low frequencies

Memorize:

HIGH = BASE

LOW = APEX

83. Hair-cell transduction — KNOW EVERY STEP

This is specifically listed on a “Things to Know” slide.

Step 1: basilar membrane moves

Sound produces a traveling mechanical wave in the cochlea.

Step 2: stereocilia bend

Movement between cochlear structures causes the stereocilia to bend.

Step 3: tip links change tension

Neighboring stereocilia are connected by tip links.

Movement in the excitatory direction pulls on the tip links.

Step 4: mechanically gated K+ channels open

This is unusual because cochlear endolymph has a high extracellular K+ concentration.

Opening the channel therefore permits K+ to enter the hair cell.

Step 5: hair cell depolarizes

Positive K+ entry depolarizes the receptor cell.

Step 6: voltage-gated Ca²⁺ channels open

Depolarization at the base activates voltage-gated Ca²⁺ channels.

Step 7: Ca²⁺ triggers neurotransmitter release

Synaptic vesicles release excitatory transmitter onto the auditory afferent.

Step 8: auditory nerve activity increases

The afferent neuron produces action potentials carried in CN VIII, the vestibulocochlear nerve.

Complete sequence:

Sound → basilar membrane → stereocilia bend → tip links pull → K+ channels open → K+ enters → hair cell depolarizes → Ca²⁺ channels open → neurotransmitter release → CN VIII action potentials

Opposite-direction bending

Bending stereocilia in the opposite direction reduces channel opening, hyperpolarizing the cell/reducing transmitter release.

Major misconception

The hair cell does not have to fire the auditory-nerve action potential itself.

Hair cell:

graded receptor potential + transmitter

Auditory neuron:

action potentials

84. Inner versus outer hair cells

Inner hair cells — IHCs

The lecture's major statement:

Inner hair cells carry information about the acoustic world to the brain.

Their afferent activity is crucial for actual auditory perception.

Outer hair cells — OHCs

Modify the mechanics of the cochlea.

They help:

• Amplify responses

• Sharpen frequency tuning

• Modify basilar-membrane mechanics

So:

Inner hair cells = information

Outer hair cells = amplification/tuning

The lecture also shows both afferent and efferent connections, meaning the brain can influence cochlear sensitivity rather than simply receiving sound passively.

85. Auditory pathway to cortex

Another sequence you should memorize exactly:

Cochlea/hair cells → vestibulocochlear nerve VIII → cochlear nucleus → superior olivary nucleus/complex → inferior colliculus → medial geniculate nucleus (MGN) of thalamus → auditory cortex/A1

The auditory system becomes substantially bilateral after the early brainstem stages.

This means each hemisphere eventually receives information influenced by both ears.

The inferior colliculus connects directly back to Lecture 7:

Inferior colliculus = auditory midbrain

86. Coding pitch: place coding

Place coding means pitch is represented by which portion of the basilar membrane and which hair cells are maximally activated.

High frequency:

base

Low frequency:

apex

This is especially important for higher frequencies.

87. Coding pitch: temporal/rate coding

Temporal coding represents frequency through the timing/rate pattern of auditory-neuron action potentials.

For relatively low frequencies, neurons can synchronize their firing with the sound wave.

The lecture diagram distinguishes temporal/rate coding especially below roughly 4 kHz from increasing reliance on place coding for higher frequencies.

The textbook adds the volley principle:

Different neurons can alternate their firing so that the population collectively represents a frequency greater than any single neuron's maximum firing rate.

Common pitfall

Place coding = WHERE

Temporal/rate coding = WHEN/HOW FAST

88. Coding intensity/loudness

Increasing sound intensity produces two important changes.

1. Increased firing rate

Stronger stimulation causes auditory neurons to fire more rapidly.

2. Recruitment of more neurons

Greater basilar-membrane movement spreads across a broader region.

Therefore more hair cells/auditory neurons become active.

So louder sound is represented by:

higher firing rates + larger neural population

89. Sound localization

The brain compares information from the two ears.

Several cues are important.

Interaural time differences

A sound reaches the nearer ear slightly earlier.

Particularly useful for lower-frequency sounds.

The superior olive is an important early site for binaural comparisons.

Intensity difference / sound shadow

For higher-frequency sound, the head blocks some acoustic energy.

The farther ear receives weaker sound.

Therefore:

high-frequency localization → intensity difference/sound shadow

Pinna cues

The shape of the pinna changes frequencies differently depending on whether sound comes from:

• Above

• Below

• Front

• Behind

This helps resolve locations that simple left-versus-right comparison cannot fully distinguish.

Memory shortcut

Low frequency → timing

High frequency → intensity/head shadow

90. Hearing loss

The lecture describes three major categories.

Conductive hearing loss

Problem in the:

• Outer ear

• Tympanic membrane

• Middle ear/ossicles

Sound is not efficiently transmitted to the cochlea.

Sensorineural hearing loss

Damage involving:

• Hair cells

• Cochlea

• Auditory nerve

Possible causes discussed include genetics, infection, drugs and loud sounds.

Central/cortical hearing loss

Damage to central auditory brain systems.

Can affect the ability to recognize or interpret sounds.

91. Tinnitus

Tinnitus is persistent perceived ringing or similar auditory sensation without the corresponding external sound.

It often occurs with auditory-system damage.

The textbook connects some cases conceptually to neural reorganization after sensory loss, somewhat like phantom-limb phenomena.

92. Cochlear implants

A cochlear implant bypasses normal damaged cochlear transduction and uses electrical stimulation to activate auditory nerve fibers.

Conceptually:

Microphone detects sound → processor analyzes sound → electrodes stimulate auditory nerve at cochlear locations → neural signals travel toward brain

It is therefore not simply “a louder hearing aid.”

A hearing aid primarily amplifies acoustic sound.

A cochlear implant converts sound information into electrical stimulation of auditory neurons.

93. Vestibular system

The final part of Lecture 11 shifts from hearing to equilibrium and head movement.

The vestibular apparatus is located in the inner ear near the cochlea.

Important structures:

• Three semicircular canals

• Utricle

• Saccule

• Ampulla

• Hair cells

94. Semicircular canals

There are three canals oriented in different planes.

Lecture orientations correspond to:

• Pitch/nodding

• Yaw/shaking head

• Roll/tilting

When the head accelerates:

Head movement → fluid movement in canal → stereocilia in ampulla deflected → hair cells alter activity → vestibular nerve signal

The canals are particularly important for rotational/angular acceleration, not simply a head being motionless at an angle.

95. Utricle and saccule

The textbook adds the otolith organs.

The utricle and saccule contain hair cells associated with small calcium-carbonate structures called otoliths.

They contribute to detection of:

• Head tilt

• Linear acceleration/deceleration

High-yield distinction:

Semicircular canals → rotation

Utricle/saccule → tilt + linear acceleration

96. Vestibular pathway

Vestibular information travels through the vestibular portion of CN VIII.

Many fibers reach the vestibular nuclei in the brainstem.

Some also project strongly toward the cerebellum.

From vestibular nuclei, information is distributed to motor systems controlling:

• Posture

• Head

• Neck

• Eyes

This connects Lecture 11 to Lecture 8's vestibulospinal tract.

97. Vestibulo-ocular reflex — VOR

The VOR keeps vision stable while the head moves.

Example:

If your head rotates to the right, the reflex causes your eyes to move appropriately in the opposite direction so that your gaze can remain on the same object.

Simplified circuit:

Semicircular canal → vestibular nerve → vestibular nucleus → ocular motor pathways → eye muscles

The lecture emphasizes that this is a fast reflex with very few synapses.

Your professor specifically says to know the vestibular nucleus, but not to worry about memorizing all the individual ocular-motor nuclei shown in the figure.

98. Vestibular postural reflexes

Vestibular information also influences descending motor systems.

Simplified:

Vestibular receptor → CN VIII → vestibular nucleus → vestibulospinal pathways → spinal motor neurons → postural muscles

This automatically helps keep the body and head stable.

99. Motion sickness

The lecture discusses sensory conflict theory.

Motion sickness can occur when sensory systems provide contradictory information.

For example:

Vestibular system signals movement

while

visual system signals relative stability

The mismatch can contribute to nausea and motion sickness.

MASTER PATHWAYS TO MEMORIZE

These five sequences are especially valuable because they force you to understand mechanisms instead of isolated definitions.

MOST IMPORTANT CROSS-LECTURE CONNECTIONS

Thalamus versus olfaction

Most sensory information in these lectures uses a thalamic relay on the way to primary cortex. Olfaction is the major exception emphasized by your professor.

PAG

Lecture 7: midbrain structure

Lecture 9: descending pain modulation

Inferior colliculus

Lecture 7: auditory structure of midbrain tectum

Lecture 11: major auditory pathway relay

Superior colliculus

Lecture 7: visual midbrain structure

Lecture 8: contributes to tectospinal/orienting motor control

Basal ganglia

Lecture 7: anatomy

Lecture 8: movement initiation/scaling, learned/habitual movement

Cerebellum

Lecture 7: hindbrain anatomy

Lecture 8: timing, correction, coordination

Lecture 11: receives vestibular information

S1 plasticity

Lecture 9: somatosensory map can change.

Chapter 4: experience, amputation, or sensory loss can reorganize cortical representations.

COMMON EXAM TRAPS