Badal ganglia flowchart

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Basal Ganglia - Circuit Flowchart

Overview Diagram (Ganong's Review of Medical Physiology, 26th Ed.)

Basal ganglia principal connections - Ganong's

Solid lines = excitatory; dashed lines = inhibitory. ES = external segment; IS = internal segment; SNPC = substantia nigra pars compacta; SNPR = substantia nigra pars reticulata; PPN = pedunculopontine nucleus; DA = dopamine; Glu = glutamate.

Visual Flowchart (Direct vs. Indirect Pathways)

Basal ganglia direct and indirect pathway flowchart

Nuclei of the Basal Ganglia

Structure	Division	Neurotransmitter
Caudate + Putamen	Striatum (input nucleus)	GABA (medium spiny neurons); ACh (interneurons)
Globus pallidus, external (GPe)	Lenticular nucleus	GABA
Globus pallidus, internal (GPi)	Lenticular nucleus (output)	GABA
Subthalamic nucleus (STN)	Diencephalon	Glutamate
Substantia nigra pars compacta (SNpc)	Midbrain	Dopamine
Substantia nigra pars reticulata (SNpr)	Midbrain (output)	GABA

Inputs to Basal Ganglia (both excitatory - Glutamate)

Cerebral Cortex (widespread)  ──Glu──▶  STRIATUM
Thalamus (intralaminar nuclei) ──Glu──▶  STRIATUM

DIRECT PATHWAY (net excitatory to cortex - facilitates movement)

Cortex
  │ Glu (+)
  ▼
Striatum (D1 receptors; activated by DA)
  │ GABA (-)   [inhibits the inhibitor]
  ▼
GPi / SNpr  ←─── INHIBITED
  │ GABA (-)   [now reduced/less inhibition on thalamus]
  ▼
Thalamus  ←─── DISINHIBITED (more active)
  │ Glu (+)
  ▼
Motor Cortex  ←─── EXCITED

Net result: Movement facilitated ✓

Dopamine acts on D1 receptors in striatum → excites striatum → enhances the direct pathway.

INDIRECT PATHWAY (net inhibitory to cortex - suppresses unwanted movement)

Cortex
  │ Glu (+)
  ▼
Striatum (D2 receptors; inhibited by DA)
  │ GABA (-)   [inhibits GPe]
  ▼
GPe  ←─── INHIBITED
  │ GABA (-)   [normally inhibits STN - now this inhibition is lost]
  ▼
STN  ←─── DISINHIBITED (more active)
  │ Glu (+)   [strongly excites GPi]
  ▼
GPi / SNpr  ←─── MORE ACTIVE
  │ GABA (-)   [more inhibition on thalamus]
  ▼
Thalamus  ←─── INHIBITED
  │ Glu (+) ↓
  ▼
Motor Cortex  ←─── LESS ACTIVE

Net result: Movement suppressed ✗

Dopamine acts on D2 receptors in striatum → inhibits striatum → dampens the indirect pathway (i.e., dopamine overall reduces indirect pathway activity, which also facilitates movement).

HYPERDIRECT PATHWAY (fastest inhibitory - urgent brake)

Cortex ──Glu──▶ STN ──Glu──▶ GPi/SNpr ──GABA──▶ Thalamus suppressed

This bypasses the striatum entirely and provides the fastest inhibitory signal to stop movement.

Dopamine Summary Table

Receptor	Pathway	Effect of DA on Striatum	Net Effect on Motor Cortex
D1	Direct	Excites striatum	Facilitates movement
D2	Indirect	Inhibits striatum	Reduces inhibition → facilitates movement

Both D1 and D2 actions of dopamine work together to facilitate movement.

Disease Correlations

Disease	Pathology	Effect on Pathways	Clinical Result
Parkinson's disease	SNpc degeneration → ↓ dopamine	Direct pathway ↓ (less excitation) + Indirect pathway ↑ (less inhibited)	Bradykinesia, resting tremor, rigidity
Huntington's disease	Striatal GABAergic neuron destruction (indirect > direct)	Indirect pathway fails first → STN under-active → GPi less active	Chorea (hyperkinesia), dementia
Hemiballismus	STN lesion	GPi under-active → thalamus disinhibited	Wild flinging movements of contralateral limbs

Key memory trick:

Direct pathway = Dopamine on D1 = Do move (facilitates)
Indirect pathway = Dopamine on D2 = suppresses the "No-move" pathway = net facilitation

Sources: Ganong's Review of Medical Physiology 26th Ed., p. 251; Costanzo Physiology 7th Ed., pp. 171-172

Liver anatomy

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I now have comprehensive material from multiple textbooks and excellent diagrams. Here is the complete liver anatomy overview:

Liver Anatomy

Gross Views - Anterior & Posterior

1. General Facts

Largest organ in the body; ~1.5 kg (~2% of body weight)
Located in the right upper quadrant, under the right hemidiaphragm, protected by the rib cage
Wedge/prism-shaped with the base to the right and apex to the left
Covered by visceral peritoneum (serosa) with underlying Glisson's capsule (fibrous connective tissue)
Unique in the body: can regenerate to 90-100% of its previous volume after resection

2. Lobes - Morphological vs. Functional

Morphological (surface anatomy) - 4 lobes

Lobe	Location	Landmark
Right lobe	Right side, large	Right of falciform ligament
Left lobe	Left side, smaller	Left of falciform ligament
Caudate lobe	Posterior (visceral surface)	Between IVC, ligamentum venosum, and porta hepatis
Quadrate lobe	Inferior (visceral surface)	Between gallbladder fossa and fissure for ligamentum teres

The falciform ligament does not represent the true functional division - this is a common misconception.

Functional (surgical) - 2 hemilivers

The true functional division is Cantlie's line - an imaginary plane from the IVC posteriorly to the gallbladder fossa anteriorly, through which the middle hepatic vein runs. This divides the liver into:

Right hemiliver (segments V, VI, VII, VIII)
Left hemiliver (segments I, II, III, IV)

3. Couinaud Segments (Surgical Anatomy)

Couinaud segments - Couinaud's 8 functional segments

Couinaud segments from Bailey and Love's Surgery

Each segment has its own independent blood supply (portal vein + hepatic artery), biliary drainage, and hepatic vein drainage - allowing surgical resection of individual segments.

Segment	Location	Notes
I	Caudate lobe (posterior)	Drains directly to IVC
II	Left lobe (superior-lateral)
III	Left lobe (inferior-lateral)
IV (IVa/IVb)	Left lobe (medial - quadrate)	IVa = superior, IVb = inferior
V	Right lobe (anterior-inferior)
VI	Right lobe (posterior-inferior)
VII	Right lobe (posterior-superior)
VIII	Right lobe (anterior-superior)

Dividing planes:

Middle hepatic vein = right/left hemiliver division
Right hepatic vein = right anterior / right posterior
Umbilical plane (falciform) = left medial (IV) / left lateral (II, III)
Portal plane = superior / inferior segments

Surgical resections:

Right hepatectomy = removes segments V, VI, VII, VIII
Left hepatectomy = removes segments II, III, IV
Left lateral segmentectomy = removes II, III

4. Ligaments & Peritoneal Reflections

Ligament	Description	Embryological remnant
Falciform ligament	Anterior, connects liver to anterior abdominal wall	Umbilical vein
Ligamentum teres (round ligament)	Free lower edge of falciform; runs to umbilicus	Left umbilical vein
Ligamentum venosum	On visceral surface, in fissure between left lobe and caudate	Ductus venosus
Left triangular ligament	Superior surface of left lobe to diaphragm	-
Right triangular ligament	Fixes right lobe to right hemidiaphragm	-
Coronary ligament	Reflection of peritoneum on posterior surface	-
Lesser omentum	Between stomach and liver; contains hilar structures in free right edge	-

5. Porta Hepatis (Hilum)

The porta hepatis is a transverse fissure on the visceral surface where structures enter/exit the liver.

Contents of the hepatoduodenal ligament (right free edge of lesser omentum):

Anterior right:   Common bile duct / hepatic duct
Anterior left:    Proper hepatic artery
Posterior:        Portal vein
Also:             Lymphatics, autonomic nerve plexus

Memory aid - "VAN" from posterior to anterior, right to left: Portal Vein (posterior) → Hepatic Artery (anterior left) → bile duct/Nduct (anterior right)

6. Blood Supply - Dual

The liver receives ~1,350 mL/min of blood (27% of resting cardiac output):

Source	Contribution	Vessel	O₂ contribution
Portal vein	80% flow	From superior mesenteric + splenic veins (behind neck of pancreas)	~50% O₂
Hepatic artery	20% flow	Branch of coeliac trunk	~50% O₂

Portal pressure = ~9 mmHg; hepatic vein pressure = ~0 mmHg → very low resistance

Arterial variants (important surgically):

Right hepatic artery may arise from superior mesenteric artery (replaced right hepatic artery)
Left hepatic artery may arise from left gastric artery (replaced left hepatic artery)

7. Venous Drainage

Three main hepatic veins drain into the IVC just below the diaphragm:

Vein	Drains
Right hepatic vein	Segments VI, VII (posterior right)
Middle hepatic vein	Segments IV, V, VIII; runs in Cantlie's plane
Left hepatic vein	Segments II, III (middle + left often share a trunk)

Segment I (caudate) drains directly into the IVC via short hepatic veins
A variable number of inferior short hepatic veins drain directly from the liver to the anterior IVC wall

8. Biliary Drainage

Bile canaliculi (between hepatocytes)
      ↓
Canals of Hering
      ↓
Bile ductules
      ↓
Right & Left hepatic ducts (emerge at porta hepatis)
      ↓
Common hepatic duct (CHD)
      ↓ ← cystic duct (from gallbladder) joins here
Common bile duct (CBD)
      ↓
Ampulla of Vater → Duodenum (2nd part)

9. Microanatomy - Liver Lobule

The basic functional unit is the liver lobule (50,000-100,000 in the human liver):

Cylindrical structure, several mm long, 0.8-2 mm diameter
Centered on a central vein (drains to hepatic vein)
Hepatocyte plates radiate outward like spokes
Periphery: portal tracts (triads) containing portal venule, hepatic arteriole, bile ductule
Blood flows inward: portal triad → hepatic sinusoids → central vein
Space of Disse - between endothelial lining and hepatocytes; allows free exchange of plasma proteins; drains to lymphatics
Kupffer cells - resident macrophages lining sinusoids; phagocytose bacteria and debris

Functional unit (acinus of Rappaport):

Zone 1 (periportal) = highest O₂, first affected by toxins
Zone 2 (mid-zone)
Zone 3 (centrilobular) = lowest O₂, first affected by ischaemia, site of alcoholic damage

10. Key Functions (Summary)

Glucose metabolism (glycolysis, gluconeogenesis, glycogenolysis)
Synthesis of clotting factors (I, II, V, VII, IX, X, XI), albumin, angiotensin
Bilirubin formation and conjugation
Drug/hormone metabolism via cytochrome P450
Urea formation from protein catabolism
Storage of vitamins A, D, E, K, B12 and glycogen
Removal of gut endotoxins (via Kupffer cells)
Immune function (mononuclear phagocyte system)

Sources: Bailey and Love's Short Practice of Surgery 28th Ed., pp. 1213-1215; Gray's Anatomy for Students 4th Ed., pp. 401-402; Guyton and Hall Medical Physiology, pp. 851-852

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