chapter 12

🧠 1. Protection of the Brain

Four Ways the Brain Is Protected

  1. Bone (the skull)

  2. Meninges

  3. Cerebrospinal fluid (CSF)

  4. Blood–brain barrier

Meninges

Three Meninges (superficial → deep)

  1. Dura mater

  2. Arachnoid mater

  3. Pia mater

Locations

  • Dura mater – tough outer layer; attached to skull; forms dural folds and venous sinuses.

  • Arachnoid mater – middle layer; loose covering; has web-like extensions.

  • Pia mater – thin, delicate layer directly covering brain surface.

Which meninx forms venous sinuses?

  • Dura mater.

What is contained in the subarachnoid space?

  • CSF and blood vessels.

Subarachnoid space lies between:

  • Arachnoid mater and pia mater.

Arachnoid villi: location & function

  • Located in dural venous sinuses (especially superior sagittal sinus).

  • Function: Return CSF to venous blood.

Cerebrospinal Fluid (CSF)

Three functions of CSF

  1. Buoyancy – reduces brain weight by ~97%.

  2. Protection – cushions brain and spinal cord.

  3. Chemical stability – removes waste, regulates environment.

What structures form CSF?

  • Choroid plexuses.

Three components that form choroid plexuses

  1. Ependymal cells

  2. Capillaries

  3. Connective tissue (pia mater)

Where are choroid plexuses located?

  • In all four ventricles.

CSF Circulation (in order)

  1. Choroid plexuses of lateral ventricles

  2. → Lateral ventricles

  3. → Interventricular foramina

  4. → Third ventricle (more CSF added)

  5. → Cerebral aqueduct

  6. → Fourth ventricle (more CSF added)

  7. → Median and lateral apertures

  8. → Subarachnoid space

  9. → CSF circulates around brain & spinal cord

  10. → Arachnoid villi

  11. → Dural venous sinuses (reabsorbed into blood)

Blood–Brain Barrier (BBB)

Functions

  • Maintains stable brain environment.

  • Protects brain from toxins, pathogens, and fluctuations in blood chemistry.

Substances that CAN pass

  • Glucose, amino acids (via transporters)

  • Oâ‚‚, COâ‚‚, fats, alcohol, nicotine, anesthetics (lipid-soluble)

Substances that CANNOT pass

  • Most drugs, toxins, metabolic wastes, proteins, ions (unless transported), pathogens.

What glial cells help form BBB?

  • Astrocytes (their end-feet) + ependymal cells + tight junctions of endothelial cells.

đź©ş 2. Homeostatic Imbalances of the Brain

Define the following:

Concussion

  • Temporary, reversible brain injury; no permanent damage.

Contusion

  • Brain bruise; permanent tissue damage.

Subdural / Subarachnoid Hemorrhage

  • Subdural: bleeding between dura and arachnoid.

  • Subarachnoid: bleeding into subarachnoid space; affects CSF.

Cerebral Edema

  • Brain swelling due to water accumulation.

Ischemia

  • Reduced blood supply → lack of oxygen → tissue death.

Hemiplegia

  • Paralysis of one side of body (often from a stroke).

CVA (Stroke): cause & outcomes

  • Cause: blocked or burst blood vessel in brain.

  • Outcomes: death of brain tissue → paralysis, language deficits, death.

Transient Ischemic Attack (TIA)

  • Temporary blockage; “mini-stroke”; no permanent damage but warning sign.

Tissue Plasminogen Activator (tPA)

  • Clot-buster drug; reduces damage if given early in ischemic stroke.

Degenerative Brain Disorders

Alzheimer’s Disease

  • Progressive memory loss; plaques and tangles; neuron death.

Parkinson’s Disease

  • Loss of dopamine-producing neurons in substantia nigra; tremors, rigidity.

Huntington’s Disease

  • Genetic; excessive movements (chorea); degeneration of basal nuclei and cortex.

🧠 3. Higher Mental Functions

Brain Waves

What does an EEG show?

  • Electrical activity of brain neurons.

Four classes of waves

  • Alpha – relaxed, awake

  • Beta – mentally alert, concentrating

  • Theta – common in children; in adults may indicate frustration or abnormality

  • Delta – deep sleep (in awake adult → brain damage)

Epilepsy

  • Repeated seizures caused by abnormal electrical brain activity.

  • NOT caused by mental illness.

  • Can be triggered by injury, genetics, fever.

Consciousness

Three aspects

  1. Alertness

  2. Awareness of self and environment

  3. Responsiveness to stimuli

Syncope vs Coma

  • Syncope – fainting; temporary loss of consciousness.

  • Coma – extended unconsciousness; unresponsive.

Sleep & Sleep–Wake Cycles

Two major types of sleep

  1. NREM (non–rapid eye movement)

  2. REM (rapid eye movement)

Five stages of sleep (brief)

NREM 1

  • Light sleep; drifting; theta waves.

NREM 2

  • Deeper; sleep spindles; easily awakened.

NREM 3

  • Beginning of deep sleep; delta waves appear.

NREM 4

  • Very deep sleep; mostly delta waves; night terrors / sleepwalking occur.

REM Sleep

  • Dreaming; rapid eye movements; temporary paralysis; high brain activity.

Function of NREM 3 & 4

  • Restore body, tissue repair, energy conservation.

Result of REM deprivation

  • Moodiness, decreased concentration, hallucinations, memory problems.

Suggested function of REM sleep

  • Memory consolidation; problem solving; emotional stability.

Sleep Disorders

Narcolepsy

  • Sudden sleep attacks; abnormal REM intrusion.

Insomnia

  • Difficulty falling or staying asleep.

Sleep Apnea

  • Temporary cessation of breathing during sleep; frequent waking.

Language

Two areas involved

  1. Broca’s area – speech production

  2. Wernicke’s area – language comprehension

Which hemisphere?

  • Left hemisphere (in 95% of people)

Stroke damage:

  • Wernicke’s area: patient speaks fluently but nonsensical; cannot understand language (word salad).

  • Broca’s area: understands language but speech is slow, broken, difficult.

Function of corresponding areas in right hemisphere

  • Understanding emotion, tone, and nonverbal components of language.

Memory

Definition

  • The storage and retrieval of information.

Two stages

  1. Short-term memory (STM)

  2. Long-term memory (LTM)

Declarative Memory (facts)

  • Conscious learning of names, dates, words, facts.

  • Example: memorizing anatomy terms.

Nondeclarative Memory (implicit)

  • Automatic skills and emotional responses.

Three types + examples

  1. Procedural (skills) memory

    • Example: playing piano, typing.

  2. Motor memory

    • Example: riding a bike, walking.

  3. Emotional memory

    • Example: feeling fear when hearing a rattlesnake.

Three factors helping transfer STM → LTM

  1. Emotional state

  2. Repetition / rehearsal

  3. Association (connecting new info to existing knowledge)

Function of Hippocampus

  • Consolidates short-term → long-term declarative memory.

Destruction of Hippocampus

  • Inability to form new long-term memories (anterograde amnesia).

Where different memories are stored?

  • Procedural memory → Basal nuclei & cerebellum

  • Motor memory → Cerebellum

  • Emotional memory → Amygdala

Why can someone forget facts but still play piano or ride a bike?

  • Declarative memories depend on the hippocampus, but procedural and motor memories rely on the cerebellum, basal nuclei, and amygdala, which are intact, so skills remain even if facts are lost.