1. All lesions: spinal cord, tracts, UMNL, LMNL, Cerebellum, Basal ganglia, Thalamus, Hypothalamus, etc. 2. Structure and function of all parts of CNS. When you know the functions you'll need able to guess the connections 3. Site of secretion, functions, regulation of all hormones. When you know functions you'll know what happens for all endocrine hyper and hypo secretion syndromes. 5. Neuro muscular junction (very similar to synapse so read only one and extrapolate concepts), excitation contraction coupling, properties of muscle 6. Classification of neurons, properties of neurons

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CNS & Physiology - Quick Study Notes

1. CNS STRUCTURE & FUNCTION

Brain Parts - What They Do

Part	Job	Damage = ?
Medulla	Breathing, heart rate, BP, swallowing	Death (vital centers)
Pons	Relay to cerebellum, CN V/VI/VII/VIII	Facial palsy, hearing loss
Midbrain	Eye movements (CN III/IV), dopamine	Eye palsy, Parkinson's
Thalamus	Relay ALL senses to cortex (except smell)	Contralateral sensory loss
Hypothalamus	Temperature, hunger, thirst, hormones	Diabetes insipidus, obesity
Cerebellum	Coordination & balance	Ataxia, intention tremor
Basal ganglia	Smooth voluntary movement	Parkinson's / Huntington's
Frontal lobe	Motor + personality + speech (Broca's)	Weakness, personality change
Parietal lobe	Sensation + spatial awareness	Numbness, neglect
Temporal lobe	Hearing + memory + speech (Wernicke's)	Memory loss, aphasia
Occipital lobe	Vision	Blindness, visual field defects

Golden Rule for thalamus: It connects to everything → thalamic lesion = loss of ALL senses on opposite side of body.

2. SPINAL CORD TRACTS (Just 3 to Know)

DORSAL COLUMNS       → Fine touch, vibration, proprioception
                       Crosses at MEDULLA (ipsilateral ascent)

SPINOTHALAMIC        → Pain & temperature
                       Crosses at SPINAL CORD (1-2 segments above entry)

CORTICOSPINAL        → Voluntary movement
                       Crosses at MEDULLA (pyramidal decussation)

Trick: Pain crosses early (in cord). Touch crosses late (in medulla).

3. UMN vs LMN LESIONS

Feature	UMN (Brain/Cord)	LMN (Nerve/Muscle)
Tone	↑ Spastic	↓ Flaccid
Reflexes	↑ Brisk	↓ or absent
Plantar	Babinski (+)	Normal/absent
Wasting	Minimal	Severe
Fasciculations	No	Yes

One-liner: UMN = stiff, brisk, Babinski. LMN = floppy, wasted, twitching.

4. LESION PATTERNS

Pattern	Clue	Cause
Brown-Sequard	Ipsilateral motor loss + touch loss; contralateral pain/temp loss	Cord hemisection
Central cord	Bilateral pain/temp loss at level (cape distribution); motor spared initially	Syringomyelia
Posterior cord	Bilateral vibration/proprioception loss; motor/pain spared	B12 deficiency, syphilis
Anterior cord	Motor + pain/temp loss; vibration/touch spared	Anterior spinal artery infarct
Cauda equina	Flaccid, saddle anesthesia, incontinence	Below L1-L2

5. CEREBELLAR vs BASAL GANGLIA

	Cerebellum	Basal Ganglia
Signs	Intention tremor, ataxia, dysdiadochokinesia	Resting tremor, rigidity, bradykinesia
Tone	Hypotonia	Rigidity (lead-pipe/cogwheel)
Side	Ipsilateral	Contralateral
Disease	MS, alcohol, stroke	Parkinson's, Huntington's

Tremor trick: Intention (cerebellum) = tremor while MOVING. Resting (Parkinson's) = tremor at REST, stops when moving.

6. HORMONES (One Table per Gland)

Hypothalamus → Anterior Pituitary → Target

CRH → ACTH → CORTISOL (adrenal)
TRH → TSH  → T3/T4 (thyroid)
GnRH → LH/FSH → Estrogen/Testosterone (gonads)
GHRH → GH → IGF-1 (liver/all tissues)
Dopamine → INHIBITS Prolactin

Feedback: Target hormone always inhibits back up the chain (negative feedback).

Posterior Pituitary (made in HYPOTHALAMUS, stored in posterior pituitary)

Hormone	Trigger	Action
ADH	↑ Osmolality, ↓ volume	Retains water (collecting duct)
Oxytocin	Cervical stretch, suckling	Uterine contraction, milk ejection

Adrenal Cortex - "GFR = Salt, Sugar, Sex"

Zone	Hormone	Key Action
Glomerulosa	Aldosterone	↑ Na+ retention, ↑ K+ excretion
Fasciculata	Cortisol	↑ Blood sugar, anti-inflammatory
Reticularis	Androgens	Sex drive in women

Quick Hyper/Hypo Patterns

Condition	Key Features
Hyperthyroidism	Weight loss, tachycardia, heat intolerance, anxiety, sweating
Hypothyroidism	Weight gain, bradycardia, cold intolerance, lethargy, slow reflexes
Cushing (↑ cortisol)	Central obesity, moon face, striae, hypertension, hyperglycemia
Addison (↓ cortisol + aldosterone)	Hypotension, hyponatremia, hyperkalemia, hyperpigmentation
Conn (↑ aldosterone)	Hypertension + hypokalemia + metabolic alkalosis
DI (↓ ADH)	Dilute polyuria, hypernatremia
SIADH (↑ ADH)	Water retention, hyponatremia

7. NEUROMUSCULAR JUNCTION (NMJ)

7 Steps (just chain them logically):

AP arrives → Ca²⁺ enters presynaptic terminal
→ ACh released (exocytosis, quantal)
→ ACh binds nicotinic receptor (motor end plate)
→ Na⁺ in / K⁺ out → End Plate Potential (EPP)
→ EPP spreads → muscle AP fires
→ AChE breaks down ACh → choline recycled

Key drugs:

Drug	Site	Effect
Botulinum toxin	Pre-synaptic (blocks ACh release)	Paralysis
Curare	Post-synaptic (blocks receptor)	Paralysis (used in anesthesia)
Neostigmine	Blocks AChE	↑ ACh action (treats MG)
Hemicholinium	Blocks choline reuptake	Depletes ACh

Disease shortcut:

Myasthenia Gravis = antibodies vs. post-synaptic receptor → fatigable weakness, worse with use, ptosis
Lambert-Eaton = antibodies vs. pre-synaptic Ca²⁺ channel → proximal weakness, improves with repeated use

8. EXCITATION-CONTRACTION COUPLING

Skeletal Muscle

AP → T-tubule depolarization
→ DHPR (voltage sensor) opens RyR1 on SR
→ Ca²⁺ released from SR
→ Ca²⁺ binds Troponin C
→ Tropomyosin moves → actin exposed
→ Myosin binds actin → cross-bridge cycling → CONTRACTION
→ Relaxation: SERCA pumps Ca²⁺ back into SR

Smooth Muscle (different!)

Ca²⁺ enters from outside (voltage-gated channels)
→ Ca²⁺ binds CALMODULIN (no troponin!)
→ Activates MLCK → phosphorylates myosin
→ Cross-bridge cycling → contraction

One-liner difference: Skeletal = troponin. Smooth = calmodulin. Cardiac = same as skeletal but Ca²⁺ entry triggers SR release (CICR).

9. NEURON CLASSIFICATION

By Function

Sensory = body to CNS
Motor = CNS to muscle/gland
Interneuron = CNS to CNS (99.9% of all neurons!)

By Shape

Multipolar = 1 axon + many dendrites (most neurons, motor neurons)
Bipolar = 1 axon + 1 dendrite (retina, ear)
Pseudounipolar = single process splitting in 2 (sensory/dorsal root ganglion)

By Fiber Speed (A→B→C = fast to slow)

Fiber	Speed	Function
Aα	Fastest (120 m/s)	Motor, muscle spindles
Aδ	Fast (30 m/s)	Sharp pain, cold
C	Slowest (1 m/s)	Burning pain, warmth

Clinical: Local anesthetics block C first (pain goes), motor last (Aα). Explains why you feel numb before paralyzed.

10. ACTION POTENTIAL (Properties)

Rest (-70mV) → Threshold (-55mV) → Na⁺ in (depolarize) → +30mV
→ Na⁺ channels inactivate → K⁺ out (repolarize) → -70mV
→ Afterhyperpolarization → return to rest

Property	Meaning
All-or-nothing	AP is always same size; frequency encodes intensity
Absolute refractory	No AP possible (Na⁺ channels inactivated)
Relative refractory	AP needs stronger stimulus (K⁺ channels still open)
Saltatory conduction	Myelinated = AP jumps node to node = fast

Demyelination (MS, Guillain-Barré): Slow or blocked conduction → neurological deficits.

MASTER CHEAT SHEET

TREMOR:     Moving = Cerebellum    |    Rest = Parkinson's
WEAKNESS:   Stiff+Babinski = UMN  |    Floppy+Fasciculations = LMN
SENSATION:  Dorsal column = touch/vibration (ipsilateral first)
            Spinothalamic = pain/temp (contralateral)
NMJ:        Pre-synaptic problem → Lambert-Eaton
            Post-synaptic problem → Myasthenia Gravis
MUSCLE:     Skeletal = Troponin C  |  Smooth = Calmodulin
HORMONES:   Know the axis → know the feedback → derive all syndromes

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