General Anatomy 1

Lecture 01

The Skeletal System

Functions of Bones · Classification · General Features of Long Bone · Blood Supply

🦴 Overview

Composed of

Bones, cartilage & ligaments joined tightly → strong, flexible framework for the body

Cartilage

Forms most embryonic/childhood bones; in adults covers joint surfaces

Ligaments

Hold bones together at joints

Tendons

Structurally like ligaments but attach muscle to bone

⚙️ Functions of the Bones

Function	Description / Example
Support	Bones of legs, pelvis & vertebral column hold up the body
Protection	Enclose & protect brain, spinal cord, lungs, heart, pelvic organs & bone marrow (e.g. thorax protects heart/lungs, skull protects brain)
Movement (Locomotion)	Skeletal muscles attach to bones which act as leverage
Blood cell formation (Hemopoiesis)	Red bone marrow is the major producer of blood cells, including most immune cells
Electrolyte balance (Mineral storage)	Skeleton = main mineral reservoir — stores & releases calcium & phosphate
Triglyceride (Fat) storage	Yellow bone marrow stores triglycerides as a chemical energy reserve

📐 Classification — According to Position

Axial Bones

Bones forming the head, neck & trunk — skull, vertebral column, thoracic cage (sternum & ribs)

Appendicular Bones

Bones forming the upper & lower limbs

Part	Upper Limb	Lower Limb
Girdle	Clavicle & scapula	Hip bone & sacrum
Proximal segment	Humerus	Femur
Middle segment	Radius & ulna	Tibia & fibula
Distal segment	Carpus (8) · Metacarpals (5) · Phalanges (3 each, 2 for thumb)	Tarsus (7) · Metatarsals (5) · Phalanges (3 each, 2 for big toe)

🔷 Classification — According to Shape

Type	Description	Example
Long bones	Longer than wide; act as rigid levers for movement	Humerus, radius, ulna, femur, tibia, fibula, metacarpals/tarsals, phalanges
Short bones	Nearly equal in length & width	Carpals (wrist), tarsals (ankle)
Flat bones	Enclose/protect soft organs; broad surface for muscle attachment	Most cranial bones, ribs, sternum, scapula
Irregular bones	Shape doesn't fit other categories	Vertebrae; sphenoid & ethmoid (skull)
Pneumatic bones	Contain air-filled cavities	Frontal, maxilla (skull)
Sesamoid bones	Small bones within tendons	Patella (knee cap)

🧬 Classification — Structure & Development

Compact Bone

Dense, ivory-like — forms the cortex of bones

Cancellous Bone

Spongy-like — lies at ends of long bones, fills most irregular bones

Membranous Development

Intramembranous ossification — bone develops from membrane, e.g. flat bones

Cartilaginous Development

Intracartilaginous (endochondral) ossification — bone develops from cartilage, e.g. long bones

📏 Parts & General Features of a Long Bone

Diaphysis (Shaft): cylinder of compact bone enclosing the medullary cavity (filled with bone marrow); covered by fibrous membrane periosteum
Epiphysis (Ends): composed of spongy (cancellous) bone, covered by a layer of hyaline articular cartilage
Metaphysis: region of the shaft close to the growth cartilage plate
Epiphyseal growth plate (physis): cartilage between epiphysis & diaphysis in growing bone — site of increase in bone length; ossifies → epiphyseal line
Nutrient foramina: minute holes through which blood vessels penetrate the bone

Structural layers: Cortex (compact bone) → Medulla (spongy bone + red bone marrow, site of blood cell formation) → Medullary/marrow cavity (yellow bone marrow, fat storage) → Periosteum (covering membrane).

🩸 Blood Supply of the Long Bone

1 · Nutrient Artery

Main supply through the shaft via nutrient foramen

2 · Epiphyseal Artery

Supplies the epiphysis

3 · Metaphyseal Artery

Supplies the metaphysis

4 · Periosteal Artery

Supplies the outer cortex via the periosteum

SKELETAL SYSTEM

⚙️ Functions (6)

Support

Protection

Movement (leverage)

Hemopoiesis (red marrow)

Mineral storage (Ca, PO4)

Fat storage (yellow marrow)

📐 By Position

Axial: skull, vertebral column, thoracic cage

Appendicular: upper + lower limbs

🔷 By Shape (6 types)

Long — femur

Short — carpals

Flat — scapula

Irregular — vertebra

Pneumatic — frontal/maxilla

Sesamoid — patella

🧬 Structure & Development

Compact (cortex) vs Cancellous (spongy)

Intramembranous → flat bones

Intracartilaginous → long bones

🩸 Long Bone Parts & Supply

Diaphysis · Epiphysis · Metaphysis

Growth plate → epiphyseal line

Nutrient · Epiphyseal · Metaphyseal · Periosteal arteries

1

Composition

Skeletal system = bones + cartilage + ligaments. Tendons attach muscle to bone; ligaments attach bone to bone.

2

6 Functions

Support, Protection, Movement, Hemopoiesis, Electrolyte (mineral) balance, Triglyceride storage.

3

Red vs Yellow Marrow

Red marrow → blood cell formation. Yellow marrow → fat/triglyceride storage (energy reserve).

4

Axial vs Appendicular

Axial = head, neck, trunk. Appendicular = upper & lower limbs (girdle + 3 segments each).

5

6 Shapes

Long, Short, Flat, Irregular, Pneumatic, Sesamoid — each with a classic example (femur, carpals, scapula, vertebra, frontal, patella).

6

Compact vs Cancellous

Compact = dense, ivory-like, forms cortex. Cancellous = spongy, at ends of long bones & fills irregular bones.

7

Ossification Types

Intramembranous → flat bones (from membrane). Intracartilaginous → long bones (from cartilage).

8

Long Bone Parts

Diaphysis (shaft) + 2 Epiphyses (ends) + Metaphysis (between). Epiphyses covered by hyaline articular cartilage.

9

Epiphyseal Plate → Line

Growth plate = cartilage that allows lengthening; ossifies at maturity → becomes the epiphyseal line.

10

4 Blood Supplies

Nutrient, Epiphyseal, Metaphyseal, Periosteal arteries — each named for the bone region it supplies.

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Wrong: 0

The Human Skeleton — Axial skeleton (skull, vertebral column, ribs & sternum) shown in the center. Appendicular skeleton (limbs & girdles) on sides. 206 bones total in the adult.

General Features of a Long Bone — Diaphysis (shaft) = compact bone surrounding medullary cavity. Two Epiphyses (ends) = cancellous bone covered by articular cartilage. Epiphyseal plate = site of growth; ossifies to form epiphyseal line at maturity. Periosteum covers the shaft.

Classification of Bones by Shape — Long (femur) · Short (carpals) · Flat (scapula) · Irregular (vertebra) · Pneumatic (frontal sinus) · Sesamoid (patella).

Lecture 02

The Muscular System

Muscle Types · Construction · Naming · Classification · Action of Muscles

🐭 Origin of the Word "Muscle"

It is the diminutive of the Greek word MUS which means a mouse. The body & head of the mouse represents the belly; the tail represents the tendon.

🔬 Types of Muscle Tissue

	Skeletal	Smooth	Cardiac
Site / Distribution	Attached to skeleton	In internal viscera & blood vessels	Myocardium (heart wall)
Contraction	Voluntary	Involuntary	Involuntary
Nerve supply	Somatic	Autonomic	Autonomic
Shape	Tubular	Spindle-shaped	Tubular
Nucleus	Multinucleated	Single (uninucleate)	Single (uninucleate)
Striations	Present	Absent	Present
Branching	Not branched	Not branched	Branched & fuse together
Fatigability	Fatigues easily	Not easy to fatigue	No fatigability

🏗️ General Construction of a Skeletal Muscle

Belly (fleshy belly): the large fleshy portion of the muscle
Muscle attaches to bone via tendons (cord-like) or aponeuroses (broad & flat); a direct fleshy-to-bone connection is a "fleshy attachment"
Origin: the more fixed, usually proximal attachment
Insertion: the more mobile, usually distal attachment — moves towards the origin on contraction, producing joint movement

Connective tissue coverings (the "-mysium" family): Epimysium surrounds the entire muscle · Perimysium surrounds bundles (fascicles) of fibers · Endomysium surrounds individual muscle fibers.

🏷️ Naming of Skeletal Muscles

Basis	Example	Meaning
Shape	Deltoid	DELTA = Greek letter D, looks like a triangle
Number of origins (heads)	Biceps	BI = two, CEPS = head
Size	Adductor magnus	MAGNUS = great, large
Length	Adductor longus	LONGUS = long
Location	Biceps brachii / Biceps femoris	BRACHII = of the arm; FEMORIS = of the thigh
Function	Rotatores	ROTATORES = rotators (turn the vertebral column)

🧩 Classification — Arrangement of Fibers

Fibers parallel with the line of pull — e.g. Sartorius
Pennate fibers (feather-like), oblique to line of pull — uni-, bi-, multipennate (e.g. Extensor digitorum longus / Biceps brachii / Deltoid)
Oblique, non-pennate fibers — convergent (Pectoralis major) or circular (Orbicularis oris)
A muscle may have more than one fleshy belly (head) — e.g. Rectus femoris

🎯 Classification — Action of Muscles

Role	Description
Prime mover	Responsible for initiating a particular movement (e.g. Brachialis = prime mover of elbow flexion)
Antagonist	Opposes the action of the prime mover (e.g. Triceps opposes Brachialis during elbow flexion)
Synergist	Helps the prime mover by fixing its origin or stabilizing the joint it acts on
Fixator (stabilizer)	Steadies & eliminates unwanted movement in proximal joints while distal joints are active

⚡ Functions of the Skeletal Muscles

Movement of the body
Maintain body posture
Produce energy
Keep blood & lymph moving inside vessels
Protect internal organs
Stabilize the joints

MUSCULAR SYSTEM

🔬 3 Tissue Types

Skeletal: voluntary, somatic, striated, multinucleate

Smooth: involuntary, autonomic, spindle, uninucleate

Cardiac: involuntary, branched, no fatigue

🏗️ Construction

Belly → tendon/aponeurosis → bone

Origin (fixed) vs Insertion (mobile)

Epi-/Peri-/Endo-mysium coverings

🏷️ Naming Basis (6)

Shape, Number of origins, Size

Length, Location, Function

🧩 Fiber Arrangement

Parallel

Pennate (uni/bi/multi)

Oblique non-pennate (convergent/circular)

Multiple heads

🎯 Action Roles

Prime mover

Antagonist

Synergist

Fixator

1

Word Origin

"Muscle" ← Greek MUS (mouse). Belly = mouse body/head; Tendon = mouse tail.

2

Nerve Supply Rule

Skeletal = Somatic. Smooth & Cardiac = Autonomic.

3

Only Cardiac Branches

Cardiac muscle is the only type that is branched — fibers fuse together, single nucleus, never fatigues.

4

Origin vs Insertion

Origin = fixed (usually proximal). Insertion = mobile (usually distal) — moves toward origin on contraction.

5

-mysium Order

Epimysium (whole muscle) → Perimysium (fascicle/bundle) → Endomysium (single fiber) — outer to inner.

6

Biceps = 2 Heads

"BI-CEPS" = naming by number of origins, not shape. Compare Triceps (3 heads), Quadriceps (4 heads).

7

Pennate Muscles

"Pennate" = feather-like; fibers oblique to line of pull. Subtypes: unipennate, bipennate, multipennate.

8

Prime Mover vs Antagonist

Classic pair: Brachialis (prime mover, elbow flexion) ↔ Triceps (antagonist). They oppose each other's action.

9

Synergist vs Fixator

Synergist helps prime mover by stabilizing its origin. Fixator steadies proximal joints while distal joints move.

10

Tendon vs Aponeurosis

Both attach muscle to bone. Tendon = cord-like. Aponeurosis = broad & flat sheet.

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Structure of Skeletal Muscle — Epimysium surrounds the whole muscle · Perimysium surrounds fascicles (bundles) · Endomysium surrounds individual fibers. Tendon attaches muscle to bone.

Three Types of Muscle Tissue — Skeletal (striated, voluntary, multinucleated) · Smooth (non-striated, involuntary, spindle-shaped) · Cardiac (striated, involuntary, branched with single nucleus).

Fiber Arrangement in Skeletal Muscles — Parallel (Sartorius) · Convergent (Pectoralis major) · Circular/Sphincter (Orbicularis oris) · Unipennate / Bipennate / Multipennate (Deltoid).

Lecture 03

The Joints

Fibrous · Cartilaginous · Synovial Joints — Classification & Stability

🔗 Definitions

Joint (Articulation)

A point of contact between two or more bones

Arthrology

The science dealing with the study of joints

Two classification systems:
1) By nature of connecting substance → Fibrous (syn-desmosis) / Cartilaginous (syn-chondrosis) / Synovial (syn-ovial)
2) By range of movement → Synarthrosis (immovable) / Amphiarthrosis (slightly movable) / Diarthrosis (freely movable)

A. Fibrous Joints (Synarthroses)

Bones connected by fibrous tissue; joint has no cavity; no or very limited movement

Type	Description	Example
Sutures	Thin layer of fibrous tissue unites bones; no movement; some ossify in old age	Skull bones
Syndesmosis	Space between bones; fibrous tissue as a bundle (ligament) or sheet (interosseous membrane); slight movement	Inferior tibio-fibular joint
Gomphosis	Cone-shaped peg fits into a socket; no movement	Root of tooth in its bony socket

B. Cartilaginous Joints (Amphiarthroses)

Bones connected by cartilage (hyaline or fibrocartilage); no cavity; no/limited movement

Type	Description	Example
Primary (Synchondrosis)	Connecting structure is hyaline cartilage; eventually ossifies	Epiphyseal plate (epiphysis↔diaphysis)
Secondary (Symphysis)	Bone ends covered by hyaline cartilage; connected by a flat disc of fibrocartilage; lies in median plane; allows limited movement	Pubic symphysis, intervertebral joints

C. Synovial Joints (Diarthroses)

Have a space between bones called the synovial cavity; wide range of movement
Classified according to: shape of articulating surfaces & axes of movement

Structure of a Synovial Joint

Bone ends covered by articular (hyaline) cartilage
Surrounded by two layers: outer fibrous capsule + inner synovial membrane
Capsule reinforced by ligaments; surrounded by muscles that produce movement
Cartilage inside the joint → called a meniscus
Synovial fluid: lubricates cartilage, allows free movement, nourishes cartilage/menisci/discs

🔄 Classification of Synovial Joints

Axes	Type	Mechanism	Example
Uniaxial	Hinge	Convex surface of one fits concave surface of another	Elbow joint
Uniaxial	Pivot	Pointed surface of one bone articulates with a ring formed by another bone + ligament	Superior radio-ulnar joint
Biaxial	Saddle	Articular surface of one is saddle-shaped; the other fits into the "saddle"	Carpometacarpal joint of thumb
Biaxial	Ellipsoid (Condyloid)	Convex oval projection of one fits oval depression of another	Metacarpophalangeal joints / Wrist
Multiaxial (Polyaxial)	Ball & Socket	Ball-like surface fits a cup-like depression	Shoulder & hip joints
Nonaxial	Plane	Articulating surfaces are flat or slightly curved	Intertarsal / intercarpal joints

🛡️ Stability of Synovial Joints

Shape of articular surfaces → determines what movements are possible
Number & position of ligaments → unite bones & prevent excessive/undesirable motion
Muscle tone & tendons crossing the joint

JOINTS

🦴 Fibrous (Synarthrosis)

Sutures — skull, no movement

Syndesmosis — ligament/membrane, slight movement

Gomphosis — tooth in socket

🦷 Cartilaginous (Amphiarthrosis)

Primary/Synchondrosis — hyaline, epiphyseal plate

Secondary/Symphysis — fibrocartilage, pubic symphysis

🦽 Synovial (Diarthrosis)

Synovial cavity + capsule + membrane

Meniscus, synovial fluid

Wide range of movement

🔄 By Axes/Shape

Uniaxial: Hinge, Pivot

Biaxial: Saddle, Ellipsoid

Multiaxial: Ball & Socket

Nonaxial: Plane

🛡️ Stability Factors

Shape of articular surfaces

Ligaments

Muscle tone & tendons

1

2 Classification Systems

By tissue type (Fibrous/Cartilaginous/Synovial) AND by movement range (Syn-/Amphi-/Di-arthrosis).

2

Gomphosis = Teeth Only

The only example of gomphosis is the tooth root fixed in its bony socket. No movement.

3

Synchondrosis Ossifies

Synchondrosis (hyaline cartilage, e.g. epiphyseal plate) eventually ossifies — temporary joint.

4

Symphysis = Midline

Secondary cartilaginous joints (symphysis) lie in the median plane — pubic symphysis, intervertebral discs.

5

Only Synovial Has a Cavity

Fibrous & cartilaginous joints have no cavity. Only synovial joints have a true joint (synovial) cavity.

6

Capsule = 2 Layers

Outer fibrous capsule + inner synovial membrane — reinforced by ligaments.

7

Meniscus

Cartilage found inside a synovial joint cavity is called a meniscus (e.g. knee joint).

8

Hinge vs Pivot

Both uniaxial. Hinge = convex-into-concave (elbow). Pivot = peg-in-ring (superior radioulnar).

9

Ball & Socket = Most Mobile

Multiaxial — ball-like surface in a cup-like depression. Shoulder & hip = most freely movable joints.

10

Plane Joint = Flat

Nonaxial; flat or slightly curved surfaces sliding past each other — intertarsal/intercarpal joints.

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Wrong: 0

Structure of a Synovial Joint — Articular (hyaline) cartilage covers bone ends · Fibrous capsule reinforced by ligaments · Synovial membrane lines the non-articular surfaces inside the capsule · Synovial fluid lubricates and nourishes the joint.

Classification of Synovial Joints — Uniaxial: Hinge (elbow) & Pivot (superior radio-ulnar) · Biaxial: Saddle (thumb CMC) & Condyloid/Ellipsoid (wrist) · Polyaxial: Ball-and-socket (shoulder, hip) & Plane (intercarpal).

Fibrous Joints — Sutures — Found between the bones of the skull. Dense fibrous tissue unites the bones. No movement (synarthrosis). Some fuse completely in old age. Example: coronal suture between frontal and parietal bones.

Lecture 04

The Skin & Fascia

Skin Structure · Appendages · Lines of Cleavage · Functions · Superficial & Deep Fascia

🧴 Structure of the Skin

A. Epidermis

Top layer; stratified squamous epithelium. Contains keratinocytes (keratin = "waterproof"), melanocytes (melanin → skin color & UV absorption), Langerhans cells (defend against microorganisms), Merkel cells (touch sensation)

B. Dermis

Deeper layer; dense fibroconnective tissue (collagen + elastic fibers) → strength, support, flexibility. Contains blood vessels, lymph vessels, sensory receptors, hair follicles & glands

🧷 Skin Appendages

Appendage	Parts / Details
Nail	Root (embedded, not exposed) + Body (exposed, free distal border) + Nail folds
Hair	Shaft (projects from surface) + Root + Follicle; Arrector pili muscle (sympathetic supply) makes hair stand vertical & compresses sebaceous glands
Sebaceous glands	Secrete sebum (oil); open into the hair follicle; absent in palms/soles; lubricate hair & soften skin
Sweat glands	2 types — see table below

	Eccrine Glands	Apocrine Glands
Number	More numerous	Fewer
Distribution	All over the body	Armpits & genital area
Duct opening	Opens at skin surface	Opens into hair follicle
Secretion	Clear (water & salt)	Contains fatty acids & proteins

✂️ Lines of Cleavage (Langer's Lines)

Collagen & elastic fibers in the dermis are arranged in parallel bundles
Langer's lines lie parallel to the collagen fibers of the dermis
Surgical importance: a cut parallel to the lines remains closed & heals well (less scarring); a cut across the lines gapes and scars more

⚙️ Functions of the Skin

Function	Details
A. Protection	Mechanical barrier, Chemical barrier, Biological barrier (against germs), Protection against UV radiation
B. Temperature regulation	Hot weather: sweating + widening of blood vessels (vasodilation) → heat radiation. Cold weather: narrowing of blood vessels (vasoconstriction) → heat storage
C. Absorption & Excretion	Absorbs fat-soluble vitamins (A,D,E,K) & some toxins; excretes water, salts, ammonia & urea via sweat
D. Synthesis of vitamin D	UV light activates a skin precursor → liver/kidney enzymes → calcitriol (active vitamin D)
E. 5th Sense	Sensory receptors transmit Pressure, Heat, Cold & Pain to the CNS

🧵 The Fascial System

Fascia = a fibrous tissue network lying between the skin and the underlying muscles & bones
Composed of two layers: Superficial fascia (under the skin) & Deep fascia (deeply situated)

A. Superficial Fascia

Lies beneath the skin & attached to it; contains fat cells, blood vessels, nerves, lymphatics, and muscles (e.g. platysma)
Insulates the body & acts as an energy reserve
Gives the body its contour (shape)
Makes the skin slide over the deep fascia
Gives passage to blood vessels, nerves & lymphatics travelling to the skin

B. Deep Fascia

Tough, made of dense fibrous connective tissue
Investing layer: layer beneath skin & superficial fascia, envelops the entire body (third envelope)
Palmar & plantar aponeurosis: thickenings in the palm & sole
Retinacula: localized thickenings around the wrist & ankle
Intermuscular septum: tough membrane separating groups of muscles
Capsule: layer surrounding individual organs (e.g. kidney)
Loose areolar tissue: fascia filling among/around the organs

SKIN & FASCIA

🧴 Skin Structure

Epidermis: keratinocytes, melanocytes, Langerhans, Merkel

Dermis: collagen, elastic fibers, vessels, receptors

🧷 Appendages

Nail: root + body

Hair: shaft, follicle, arrector pili

Sebaceous (oil) glands

Sweat: Eccrine vs Apocrine

✂️ Langer's Lines

Parallel to collagen fibers

Cut parallel → heals well

Cut across → gapes/scars

⚙️ Functions (5)

Protection (4 barriers)

Temperature regulation

Absorption/Excretion

Vitamin D synthesis

5th sense

🧵 Fascia

Superficial: fat, vessels, platysma

Deep: investing layer, retinacula, aponeurosis, septum, capsule

1

Melanocytes

Produce melanin → gives skin its color AND absorbs damaging UV light.

2

Langerhans vs Merkel

Langerhans = immune defense. Merkel = touch sensation. Easy to confuse!

3

Arrector Pili = Sympathetic

Innervated by sympathetic nerves; contraction → hair stands up + compresses sebaceous gland (goosebumps).

4

Eccrine vs Apocrine

Eccrine: everywhere, opens to surface, watery. Apocrine: armpits/genitals, opens into follicle, fatty/protein secretion.

5

Surgical Incisions

Always cut parallel to Langer's lines for minimal scarring — classic exam point.

6

Temperature Control

Hot → sweat + vasodilation (heat loss). Cold → vasoconstriction (heat conservation).

7

Vitamin D Pathway

Skin (UV-activated precursor) → Liver → Kidney → Calcitriol (active vitamin D).

8

Platysma = Superficial Fascia

Unusual exception — the platysma muscle lies within the superficial fascia, not attached to bone like typical skeletal muscles.

9

Retinacula Location

Localized thickenings of deep fascia specifically around the wrist & ankle joints.

10

Capsule vs Areolar Tissue

Both are deep fascia types. Capsule = surrounds an individual organ (e.g. kidney). Loose areolar tissue = fills space among organs.

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Correct: 0

Wrong: 0

Structure of the Skin — Epidermis (outer, stratified squamous epithelium): contains keratinocytes, melanocytes, Langerhans cells & Merkel cells. Dermis (inner, dense fibroconnective tissue): contains blood vessels, nerves, hair follicles & glands.

Hair Follicle & Skin Appendages — Hair follicle = root + surrounding sheath. Sebaceous (oil) glands open into the follicle; secrete sebum. Arrectores pili muscles (sympathetic) cause hair to stand erect & squeeze sebum out. Sweat glands: Eccrine (all over body) & Apocrine (armpits, groin).

Cleavage Lines of Langer — Follow the direction of collagen fibers in the dermis. Surgical incisions parallel to Langer's lines → less retraction, minimal scarring. Incisions across the lines → wound gapes and leaves a prominent scar.

Lecture 05

The Cardiovascular System

The Heart · Blood Vessels · Circulations · Anastomoses

❤️ Overview

Blood is pumped by the heart around a closed circuit of vessels, again and again, through the various "circulations" of the body.

It Consists Of

The Blood · The Heart · A closed system of vessels (Arteries, Veins, Capillaries)

The Blood

Complex mixture of cells, water, proteins & sugars — 55% plasma (liquid) / 45% cells (solid)

🫀 The Heart — General Description

Four-chambered muscular organ, shaped & sized roughly like a closed fist
Lies inside the thorax, between the 2 lungs, superior to the diaphragm, and to the left of the midline

The Pericardium

Heart enclosed in a fibrous pericardium; inside lies the pericardial sac (serous membrane folded into 2 layers)
Visceral layer (inner) + Parietal layer (outer); space between = pericardial space

Layers of the Heart Wall (3)

Layer	Position
Epicardium	Outermost (= visceral pericardium)
Myocardium	Middle (muscular layer)
Endocardium	Inner

📐 External Features of the Heart

Roughly pyramidal / cone-shaped
Apex: blunt rounded end, tip of the pyramid; formed of the left ventricle; directed anteriorly, inferiorly & to the left

Anterior surface

Sternocostal surface

Inferior surface

Diaphragmatic surface

Posterior surface

The base

🔲 Chambers & Valves of the Heart

2 Atria: thin-walled chambers that receive blood from the veins
2 Ventricles: thick-walled chambers that pump blood out through the arteries

Valve Type	Location	Names
Atrioventricular ("cuspid") valves	Between atria & ventricles	Tricuspid (right), Bicuspid/Mitral (left)
Semilunar valves	At bases of vessels leaving the ventricles	Pulmonary & Aortic valves

⚡ Conducting System of the Heart

An intrinsic regulating system that initiates & distributes the cardiac impulse over the heart.

1

SAN (Sinoatrial Node) — the pacemaker

2

AVN (Atrioventricular Node)

3

AV Bundle (Bundle of His)

4

Bundle branches (right & left)

5

Purkinje's fibers

🔄 Types of Circulation

Type	Pathway
Coronary	Circulation of blood in the arteries supplying the heart itself
Pulmonary	Flow of blood between the heart & lungs (oxygenation)
Systemic	Flow of blood between the heart & the cells of the body
Portal	Flow of blood between the digestive tract & the liver

🩸 Blood Vessels

	Arteries	Veins	Capillaries
Direction	Away from the heart	Towards the heart	Connect arteries to veins
Branching	Get smaller → arterioles; branches → "anastomosis"	Have tributaries; capillaries→small venules→larger venules→veins	—
Special feature	Distribute blood via branches	Some contain valves to allow flow against gravity	Thin walls allow passage of materials to/from cells

🔀 Anastomosis & Special Arteries

Anastomosis: "end to end" communication between neighboring vessels
Arterial anastomosis: artery to artery
Arterio-venous anastomosis: arteriole to venule
End arteries: arteries with no anastomoses — found in the retina & brain; sudden block → death of the tissue (infarction)
Wavy arteries: have a wavy/tortuous course, able to stretch — examples: Facial, Lingual, Splenic & Uterine arteries

CARDIOVASCULAR SYSTEM

🫀 Heart Layers

Pericardium: fibrous + serous (visceral/parietal)

Wall: Epicardium → Myocardium → Endocardium

🔲 Chambers & Valves

2 Atria (receive) + 2 Ventricles (pump)

AV valves: Tricuspid/Mitral

Semilunar: Pulmonary/Aortic

⚡ Conducting System

SAN → AVN → Bundle of His

Bundle branches → Purkinje fibers

🔄 4 Circulations

Coronary — to heart

Pulmonary — to lungs

Systemic — to body cells

Portal — gut to liver

🩸 Vessels & Anastomosis

Arteries (away) vs Veins (towards)

End arteries: retina, brain

Wavy arteries: facial, lingual, splenic, uterine

1

Blood Composition

55% plasma (liquid) + 45% cells (solid) — a quick number to memorize.

2

Apex = Left Ventricle

The heart's apex is formed by the left ventricle, pointing anteriorly, inferiorly & to the left.

3

Epicardium = Visceral Pericardium

The outermost heart wall layer (epicardium) is the same as the visceral layer of the serous pericardium.

4

Atria Receive, Ventricles Pump

Simple rule: Atria = thin-walled, receive. Ventricles = thick-walled, pump.

5

SAN = Pacemaker

The Sinoatrial Node (SAN) is the heart's natural pacemaker — first in the conduction sequence.

6

Portal Circulation

Unique pathway: blood flows from the digestive tract to the liver (not directly to the heart first).

7

End Arteries = No Backup

Retina & brain arteries have no anastomoses — a sudden block causes tissue death (clinically critical).

8

4 Wavy Arteries

Facial, Lingual, Splenic, Uterine — all need to stretch with movement/distension.

9

Veins Have Valves

Some veins contain valves to push blood against gravity back to the heart — arteries do not have valves (except semilunar at their origin).

10

Capillary Function

Capillaries connect arteries to veins; their thin walls allow exchange of materials with the cells.

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Internal Structure of the Heart — 4 chambers: Right & Left atria (thin-walled, receive blood) + Right & Left ventricles (thick-walled, pump blood). Valves: Tricuspid (right AV) · Bicuspid/Mitral (left AV) · Pulmonary & Aortic semilunar valves.

Circulations of the Body — Pulmonary: Right ventricle → Pulmonary artery → Lungs → Pulmonary veins → Left atrium. Systemic: Left ventricle → Aorta → Body → Venae cavae → Right atrium. Portal: GIT → Portal vein → Liver.

Conducting System of the Heart — SA Node (pacemaker) → AV Node → Bundle of His → Right & Left bundle branches → Purkinje fibers. This intrinsic system initiates and coordinates each heartbeat without external nerve input.

Lecture 06

The Lymphatic System

Lymph Formation & Transport · Lymphoid Tissue · Lymph Nodes · Thymus · Spleen

💧 Definition

Part of both the cardiovascular and immune systems
Reabsorbs & returns fluid escaped from blood vessels back to the venous system → heart
This fluid is called "the lymph" — Lympha = clear water

⚗️ Lymph Formation

Blood flows from arterioles → capillaries (rich in O₂ & nutrients)
Fluid escapes from the capillaries with O₂ & nutrients
Metabolism in cells → CO₂ & waste products, which diffuse back to the venous end of capillaries
The remaining fluid in intercellular spaces is reabsorbed by lymph capillaries → becomes lymph

🧪 Lymph Capillaries

Blind-ended tubes, slightly larger than blood capillaries
Pick up the extracellular fluid
Widely distributed except in: CNS, bone marrow, cornea & cartilage
Lacteals: special lymphatic capillaries in the villi of the small intestine; absorb fatty lymph (chyle) containing fats & fat-soluble substances

🚚 Lymph Transport

Sequence: Lymph capillaries → Lymph vessels → Lymph trunks → Lymph ducts → Subclavian veins

Duct	Drains
Right lymphatic duct	Right side of head/neck, thorax & right arm
Thoracic duct	The rest of the body (begins at cisterna chyli in the abdomen)

🧬 Lymphatic Tissue — 2 Main Types

	MALT (Mucosa-Associated)	Lymphatic Organs
Capsule	No capsule	Capsule present
Location	Connective tissue of almost all organs	Discrete organs
Role	Early detection of invaders	Filtration / immune maturation
Examples	Tonsils, Peyer's patches	Lymph nodes, Spleen, Thymus gland

🟢 Lymph Nodes

Collections of lymphoid tissue along the course of lymph vessels, arranged in groups
Filter the lymph from harmful organisms & cell debris
Afferent vessel: carries lymph towards the node
Efferent vessel: carries clean lymph away from the node to the venous system (added to plasma)

🦋 Thymus

Location: posterior to the sternum; divided into lobules
The only lymphoid organ that does NOT fight antigens — functions as a "T-cell academy", distinguishing "self" from "foreign" tissue
Produces hormone thymosin → stimulates lymphoid tissue maturation
Involutes after puberty

🫘 Spleen

Largest lymphoid organ
Located on the left side of the abdominal cavity, under the diaphragm
Supplied by the splenic artery & vein, entering/exiting at the hilum

Functions of the Spleen

Site of lymphocyte proliferation
Cleanses the blood from microorganisms
Stores breakdown products of old (worn out) RBCs for later reuse
Site of fetal erythrocyte production (till the 5th month of pregnancy)
Stores blood platelets

⚙️ Functions of the Lymphatic System

Return excess extracellular fluid to the CVS
Filter lymph from bacteria or cell debris
Lymphatic organs = sites for lymphocyte production, maturation & competency
Lymph contains lymphocytes that patrol different body regions
Transport digested lipids from intestinal lacteals

LYMPHATIC SYSTEM

💧 Formation

Arteriole → capillary → fluid escapes

Remaining fluid → lymph capillaries

Lacteals absorb chyle (fats)

🚚 Transport

Capillaries → Vessels → Trunks → Ducts

Right duct: head/neck/thorax/R arm

Thoracic duct: rest of body

🧬 Tissue Types

MALT: no capsule (tonsils, Peyer's)

Organs: capsule (nodes, spleen, thymus)

🦋 Thymus

T-cell academy, NOT antigen fighter

Thymosin hormone

Involutes after puberty

🫘 Spleen

Largest lymphoid organ

Filters blood, stores platelets

Fetal RBC production (<5 months)

1

Lympha = Clear Water

The word "lymph" comes from Latin lympha, meaning clear water.

2

No Lymphatics Here

Lymph capillaries are absent in: CNS, bone marrow, cornea, cartilage.

3

Lacteals = Fat Absorption

Found in intestinal villi; absorb chyle (fatty lymph) — unique to the small intestine.

4

Afferent In, Efferent Out

Easy memory trick: Afferent = Arriving. Efferent = Exiting (clean lymph to venous system).

5

Thymus ≠ Antigen Fighter

Unique exam point — the thymus is the only lymphoid organ that does NOT fight antigens directly.

6

Thymosin

Hormone produced by thymus → stimulates maturation of lymphoid tissue (T-cells).

7

Spleen = Largest Lymphoid Organ

Located left side, under diaphragm; supplied by splenic vessels at the hilum.

8

Spleen's Fetal Role

Produces fetal erythrocytes (RBCs) up to the 5th month of pregnancy.

9

MALT vs Lymphatic Organs

Key distinguishing feature = capsule. MALT has none (tonsils, Peyer's patches); organs have one (nodes, spleen, thymus).

10

Right Duct vs Thoracic Duct

Right duct = small area only (right head/neck/thorax/arm). Thoracic duct = everything else, starting at the cisterna chyli.

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The Lymphatic System Overview — Returns excess interstitial fluid to the venous system. Two main ducts: Right lymphatic duct (right head/neck/arm/chest) + Thoracic duct (rest of body, begins at cisterna chyli). Lymph capillaries are blind-ended tubes absent in CNS, bone marrow, cornea & cartilage.

Lymph Node Structure — Afferent vessels carry lymph towards the node; efferent vessels carry clean lymph away. Act as filters preventing bacteria and toxins from reaching the bloodstream. Found in groups near proximal ends of regional vessels.

Lymphoid Organs: Spleen & Thymus — Spleen (largest lymphoid organ): located upper left abdomen under diaphragm; filters blood, stores platelets, site of fetal RBC production. Thymus: posterior to sternum; "T-cell academy" — distinguishes self from foreign; produces thymosin; involutes after puberty.

Lecture 07

The Respiratory System

Upper & Lower Respiratory Tract · Lungs · Pleura

🫁 Overview

Lungs contain "alveoli" or "terminal air sacs"
Gas exchange with blood occurs in the alveolar walls → respiratory zone
The rest of the structures act only as a passageway to conduct air to the lungs → conducting zone — they also purify, humidify & warm the air

Upper Respiratory Tract

Nose, Pharynx (throat)

Lower Respiratory Tract

Larynx, Trachea, Bronchi, Lungs

👃 The Nose

External nose: the only visible part of the respiratory system; air enters via 2 openings ("nostrils"); consists of cartilage & bones
Nasal cavity: separated by the nasal septum into 2 cavities

Functions of the Nose

Function	Mechanism
Passageway	For air
Cleans the air	Mucus membrane traps particles; tiny cilia move mucus backward to throat to be swallowed
Humidifies/warms air	3 bony projections ("conchae") on lateral wall — rich in blood vessels (warm) + secrete mucus (humidify)
Smell	Mucus membrane at upper nasal cavity has olfactory receptors
Resonance	Nose & paranasal sinuses are resonating chambers for the voice

Paranasal sinuses: hollow areas of skull bones opening into the nasal cavity; lined with mucus membrane (warming); make the skull lighter & the voice louder.

🗣️ Pharynx

Common opening for the respiratory & digestive systems
3 regions: Nasopharynx, Oropharynx, Laryngopharynx

🔊 Larynx & Epiglottis

Structure	Details
Larynx	Firm part felt in front of the neck; sits above the trachea; formed of cartilages; contains 2 vocal cords — vibration produces sound
Epiglottis	Part of the larynx; acts as a flap; keeps food from entering the air passage

🌬️ Trachea & Bronchial Tree

Starts at larynx, travels through upper thorax; ends at level T4/T5; about 10–12 cm long
Divides into 2 primary bronchi (one to each lung); bifurcation point = "carina"
Rests against the esophagus; kept open by C-shaped cartilage rings; posterior wall closed by muscle & connective tissue; lined by ciliated mucosa

Bronchial tree (like an upside-down tree): Bronchi → smaller → Bronchioles → smaller → Terminal bronchioles → give rise to Respiratory bronchioles

Alveoli: respiratory bronchioles terminate into alveolar ducts & sacs — the "respiratory exchange chambers" where O₂/CO₂ exchange occurs.

🫁 The Lungs

	Right Lung	Left Lung
Lobes	3 (Upper, Middle, Lower)	2 (Upper, Lower)
Fissures	Oblique + Horizontal	Oblique only
Special feature	—	Cardiac notch

Surfaces of Each Lung (lie within pleural cavities)

Apex

Up to the neck

Base

Rests on the diaphragm

Mediastinal surface

Contacts chest viscera; contains the hilum

Costal surface

Contacts the ribs

🌳 Lung Root (at the Hilum)

The root = bronchus + vessels entering each lung at the hilum:

Primary Bronchus
2 Pulmonary Veins — carry oxygenated blood from each lung to the heart
1 Pulmonary Artery — carries deoxygenated blood to each lung
Nerves
Lymph vessels

🎈 Pleura

A double membrane surrounding each lung
Parietal layer: lines the chest wall, diaphragm & chest viscera
Visceral layer: surrounds the lungs themselves
Pleural cavity: the cavity in between the 2 layers
Secretes fluid for lubrication (eases respiratory movement)

RESPIRATORY SYSTEM

👃 Upper Tract

Nose: cleans, warms, humidifies, smell, resonance

Pharynx: 3 regions, shared with GI

🔊 Larynx

2 vocal cords → sound

Epiglottis = flap, blocks food

🌬️ Trachea → Bronchial Tree

10-12cm, ends T4/5, carina

C-shaped cartilage rings

Bronchi → bronchioles → terminal → respiratory → alveoli

🫁 Lungs

Right: 3 lobes, 2 fissures

Left: 2 lobes, cardiac notch

Apex, Base, Mediastinal, Costal surfaces

🎈 Root & Pleura

Hilum: bronchus + 2 PV + 1 PA

Pleura: parietal + visceral + cavity

1

Respiratory vs Conducting Zone

Respiratory zone = alveoli (gas exchange). Conducting zone = everything else (passageway only).

2

Cilia Direction

Nasal cilia move mucus backward to the throat to be swallowed — not forward/outward.

3

Conchae Function

3 bony projections, rich in blood vessels (warm air) + mucus (humidify air).

4

Pharynx = Shared Tube

The pharynx is common to both respiratory & digestive systems — 3 regions: Naso-, Oro-, Laryngo-pharynx.

5

Carina = Bifurcation

The trachea divides into 2 primary bronchi at the carina — a key bronchoscopy landmark.

6

C-shaped Cartilage

Tracheal rings are C-shaped (incomplete posteriorly) — posterior wall closed by muscle, allowing the esophagus to bulge during swallowing.

7

Right = 3, Left = 2

Right lung has 3 lobes (extra space since heart is on the left); Left lung has 2 lobes + a cardiac notch to accommodate the heart.

8

Hilum Contents

At the hilum: 1 Bronchus + 2 Pulmonary Veins (oxygenated, to heart) + 1 Pulmonary Artery (deoxygenated, to lung) + nerves + lymphatics.

9

Pulmonary Vessels = Reversed

Unlike systemic vessels — pulmonary artery carries deoxygenated blood; pulmonary vein carries oxygenated blood.

10

Pleura = Double Membrane

Parietal (outer, lines chest wall) + Visceral (inner, on lung) + Pleural cavity (lubricating fluid) in between.

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The Respiratory System — Upper tract (above epiglottis): Nose → Pharynx (nasopharynx, oropharynx, laryngopharynx). Lower tract: Larynx (vocal cords, C4–C6) → Trachea (C-shaped cartilage rings, 10–12 cm) → Primary bronchi → Bronchial tree → Alveoli. Conducting zone = passageway; Respiratory zone = gas exchange.

Alveoli — Respiratory Exchange Chambers — Terminal bronchioles → Respiratory bronchioles → Alveolar ducts → Alveolar sacs. Gas exchange: O₂ enters blood capillaries; CO₂ exits. The extremely thin alveolar wall maximises diffusion efficiency.

The Lungs & Pleura — Right lung: 3 lobes (upper, middle, lower) — 2 fissures (oblique + horizontal). Left lung: 2 lobes (upper & lower) — 1 oblique fissure + cardiac notch. Pleura: double membrane — parietal (lines chest wall) + visceral (covers lung) — pleural cavity between them contains lubricating fluid.

Lecture 08

The Gastrointestinal System

Mouth · Pharynx · Esophagus · Stomach · Small & Large Intestine · Liver · Pancreas

🍽️ Overview

Digestive Tract

Mouth → Pharynx → Esophagus → Stomach → Small intestine → Large intestine

Digestive Organs (Accessory)

Teeth, Tongue, Salivary glands, Liver, Gall bladder, Pancreas

👄 The Mouth

Oral cavity: bounded externally by lips & cheeks
Vestibule: the space between lips/cheeks and the teeth
Separated from the nasal cavity by the roof of the mouth, formed of: Hard palate (bone), Soft palate (muscle), Uvula (finger-like projection from soft palate)

The Teeth

	Adults (32 teeth)	Deciduous / Milk Teeth (20 teeth)
Per half-jaw	2 Incisors (biting), 1 Canine (tearing), 2 Premolars (grinding), 3 Molars (crushing)	2 Incisors (central & lateral), 1 Canine, 2 Molars
Note	Last molar = "wisdom tooth"	Babies only — no premolars

👅 Tongue & Salivary Glands

Tongue: muscular organ covered with mucus membrane. Frenulum = fold attaching tongue's under-surface to floor of mouth. Papillae = rough dorsal projections, some carry taste receptors

Gland	Location	Duct Opening
Parotid (largest)	Anterior & inferior to the ears	Vestibule, opposite upper 2nd molar
Sublingual	Beneath the tongue, under mucosa of mouth floor	Many ducts, open under the tongue
Submandibular	Floor of mouth, medial to mandible	Single duct, opens under the tongue

Saliva contains bicarbonate and an enzyme that begins digestion of starch.

🔽 Pharynx & Esophagus

Pharynx: 3 parts (Naso-, Oro-, Laryngo-pharynx). No digestion occurs here — function = swallowing + air passage
Esophagus: muscular tube; passes from pharynx through thorax & diaphragm into the abdomen to join the stomach. Moves food via rhythmic peristalsis

🫃 The Stomach

Thick-walled, J-shaped organ; left side of abdomen, deep to liver & diaphragm
Continues with esophagus above, small intestine below

Functions of the Stomach

Reservoir & mixes the food
Starts digestion of protein & fats
Activates some enzymes
Destroys some bacteria
Makes intrinsic factor that absorbs vitamin B12
Absorbs alcohol & water

🌀 The Small Intestine

Extends from the pyloric sphincter to the ileocecal valve. 3 parts:

Part	Key Features
Duodenum	C-shaped, ~25cm; receives bile (via common bile duct) & pancreatic secretions (via pancreatic duct)
Jejunum	Proximal 2/5 of small intestine; larger lumen, more folds; fewer arterial arcades, longer vasa recta
Ileum	Distal 3/5; smaller lumen, fewer folds; more arcades, shorter vasa recta; has Peyer's patches; most absorption occurs here; empties into cecum via the ileocecal valve

🔄 The Large Intestine

~1.5 m long; begins lower right abdomen → ascends → crosses left to spleen → descends → terminates at anus
Divided into: Cecum, Appendix, Ascending/Transverse/Descending/Sigmoid colon, Rectum, Anal canal

Differs from small intestine

No villi · Has taeniae coli · Haustration (sacculation) · Epiploic appendages

Main role

Receives undigested food, absorbs water & electrolytes, passes feces out

🫘 Liver, Gall Bladder & Pancreas

Organ	Functions
Liver (largest gland, 4 lobes, upper right abdomen)	Makes bile · Detoxifies drugs/alcohol · Stores glycogen, vitamins (A,D,E,K), iron & cholesterol · Activates vitamin D · Fetal RBC production · Metabolizes absorbed nutrients
Gall bladder	Stores & concentrates bile; expels it into duodenum. Bile = yellowish-green fluid that emulsifies fats
Pancreas (mixed gland, posterior abdominal wall)	Endocrine: Islets of Langerhans → insulin & glucagon into blood. Exocrine: acini → pancreatic juice → duodenum

GASTROINTESTINAL SYSTEM

👄 Mouth & Teeth

Oral cavity, vestibule, palate

32 teeth (2-1-2-3 per half jaw)

3 salivary gland pairs

🔽 Pharynx & Esophagus

Pharynx: no digestion, just passage

Esophagus: peristalsis

🫃 Stomach

J-shaped, left side

Intrinsic factor → B12

Starts protein/fat digestion

🌀 Small Intestine

Duodenum: bile + pancreatic juice

Jejunum: proximal 2/5

Ileum: distal 3/5, Peyer's patches

🔄 Large Intestine & Accessory Organs

No villi, taeniae coli, haustra

Liver: bile, detox, storage

Pancreas: endocrine + exocrine

1

Tooth Formula

Adults: 2 incisors, 1 canine, 2 premolars, 3 molars per half-jaw = 32 total. Babies: no premolars = 20 total.

2

Parotid = Largest

The parotid gland is the largest salivary gland; duct opens opposite the upper 2nd molar.

3

No Digestion in Pharynx

The pharynx's only role is swallowing & air passage — no digestion happens there.

4

Intrinsic Factor

Made by the stomach; essential for absorption of vitamin B12 in the ileum.

5

Jejunum vs Ileum

Jejunum = proximal 2/5, larger lumen, fewer arcades/longer vasa recta. Ileum = distal 3/5, Peyer's patches, most absorption.

6

Duodenum Receives 2 Ducts

Common bile duct (bile) + Pancreatic duct (pancreatic juice) both empty into the duodenum.

7

Large Intestine ≠ Villi

Large intestine has no villi (unlike small intestine) — instead has taeniae coli, haustra, epiploic appendages.

8

Bile = Fat Emulsifier

Made by liver, stored/concentrated in gallbladder, emulsifies fats in the duodenum.

9

Pancreas = Mixed Gland

Endocrine (islets → insulin/glucagon) + Exocrine (acini → pancreatic juice via pancreatic duct).

10

Liver = Largest Gland

4 lobes; makes bile, detoxifies, stores vitamins/glycogen/iron, activates vitamin D, metabolizes nutrients.

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The Gastrointestinal System — Digestive tract: Mouth → Pharynx → Oesophagus → Stomach (J-shaped, left abdomen) → Small intestine (Duodenum 25cm · Jejunum 2/5 · Ileum 3/5) → Large intestine (1.5m: Caecum · Colon · Rectum · Anal canal). Accessory organs: Liver (largest gland) · Gallbladder · Pancreas (mixed gland).

Jejunum vs Ileum — Jejunum: wider lumen, more internal folds (plicae), fewer arterial arcades, longer vasa recta. Ileum: smaller lumen, fewer folds, more arcades, shorter vasa recta, Peyer's patches (lymphoid nodules). Most digested material is absorbed in the ileum.

The Large Intestine — Begins at ileocaecal valve, ends at anus. Parts: Caecum + Appendix → Ascending colon → Transverse colon → Descending colon → Sigmoid colon → Rectum → Anal canal. Unique features vs small intestine: Taeniae coli · Haustra (sacculations) · Epiploic appendages · No villi. Function: absorb water & electrolytes, pass faeces.

Lecture 09

The Nervous System

CNS · PNS · Spinal Nerve · Autonomic Nervous System

🧠 Function of the Nervous System

The master system that controls & communicates all body systems together.

Step	Description
1. Sensory input	Sensory receptors detect stimuli from inside & outside the body
2. Integration	Nervous system interprets & processes sensory input, decides what should be done
3. Motor output	Effects a response by activating muscles or glands

🔬 Structure — Cellular Level

1 · Neurons (Nerve Cells)

Structural & functional unit of the nervous system; specialized in transmitting nerve impulses; each has a cell body + processes (dendrites & axon)

2 · Neuroglia (Supporting Cells)

Accessory "nerve glue" cells — physiological support, protection & insulation in CNS & PNS. There are 10× as many neuroglia as neurons

🏛️ 1. Central Nervous System (CNS)

Consists of the Brain + Spinal Cord

Component	Details
Brain	Lies within the skull; formed of cerebrum, cerebellum & brain stem (midbrain, pons, medulla)
Spinal Cord	Lies in upper 2/3 of vertebral canal; continuous above with medulla; outer white matter + inner gray matter; provides 2-way conduction; gives exit for 31 pairs of spinal nerves

Meningeal Coverings (outer → inner)

Dura mater (outer)
Arachnoid mater (middle)
Pia mater (inner)

Subarachnoid space (between arachnoid & pia) contains cerebrospinal fluid (CSF).

🌐 2. Peripheral Nervous System (PNS)

Includes cranial & spinal nerves; divided into Somatic & Autonomic nervous systems
Cranial nerves: 12 pairs — carry information to/from the brain
Spinal nerves: 31 pairs — carry information to/from the spinal cord

Spinal Nerve — 2 Roots

Root	Function
Ventral root	Motor (efferent)
Dorsal root (+ DRG)	Sensory (afferent)

⚖️ Autonomic Nervous System

	Sympathetic	Parasympathetic
Nickname	"Fight or Flight"	"Rest and Digest"
Division	Thoracolumbar	Craniosacral
Dominant when	Stress — anger, fear, anxiety, exercise	Relaxed (non-stress) states — normal organ function

NERVOUS SYSTEM

⚙️ 3-Step Function

Sensory input

Integration

Motor output

🔬 Cell Types

Neurons: cell body + dendrites + axon

Neuroglia: 10× more numerous, support cells

🏛️ CNS

Brain: cerebrum, cerebellum, brain stem

Spinal cord: 31 pairs of nerves

Meninges: Dura, Arachnoid, Pia

🌐 PNS

12 cranial nerve pairs

31 spinal nerve pairs

Ventral root (motor) / Dorsal root (sensory)

⚖️ Autonomic NS

Sympathetic: thoracolumbar, fight/flight

Parasympathetic: craniosacral, rest/digest

1

3-Step Process

Sensory input → Integration → Motor output. The classic functional sequence of the nervous system.

2

Neuroglia >> Neurons

There are 10× as many neuroglia (support cells) as neurons in the nervous system.

3

CNS = Brain + Spinal Cord

Simple but essential: CNS consists of only the brain & spinal cord — everything else is PNS.

4

Meninges Order

Outer → Inner: Dura → Arachnoid → Pia (mnemonic: "DAP"). CSF is in the subarachnoid space.

5

31 Spinal Nerve Pairs

Spinal cord gives exit to 31 pairs of spinal nerves; cranial nerves = 12 pairs (don't mix these numbers up).

6

Ventral = Motor

Easy rule: Ventral = Voluntary/motor (efferent). Dorsal = sensory (afferent), with the DRG.

7

Sympathetic = Thoracolumbar

Sympathetic outflow originates from thoracic & lumbar spinal segments — fight or flight.

8

Parasympathetic = Craniosacral

Parasympathetic outflow originates from cranial nerves & sacral spinal segments — rest & digest.

9

White vs Gray Matter

In the spinal cord: outer = white matter (myelinated tracts), inner = gray matter (cell bodies) — opposite arrangement to the brain.

10

Brain Stem = 3 Parts

Brain = Cerebrum + Cerebellum + Brain stem (which itself = Midbrain + Pons + Medulla).

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Organisation of the Nervous System — CNS: Brain (cerebrum, cerebellum, brainstem: midbrain + pons + medulla) + Spinal cord (upper 2/3 of vertebral canal, 31 pairs of spinal nerves). PNS: 12 cranial nerve pairs + 31 spinal nerve pairs. Meninges: Dura mater (outer) · Arachnoid mater (middle) · Pia mater (inner). CSF in subarachnoid space.

The Neuron — Structural & functional unit of the nervous system. Composed of: Cell body + Dendrites (receive signals) + Axon (transmits impulse away from cell body). Supporting cells = Neuroglia (10× more numerous); provide support, protection and insulation in CNS & PNS.

Spinal Nerve & Autonomic NS — Spinal nerve formed by: Dorsal root (sensory/afferent + DRG) + Ventral root (motor/efferent). Autonomic NS: Sympathetic "Fight or Flight" = thoracolumbar division, dominant in stress. Parasympathetic "Rest & Digest" = craniosacral division, dominant in relaxed states.