Nervous system physiology k sembulingam easy notes

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I now have enough material from the textbooks to compile comprehensive, Sembulingam-style easy notes on nervous system physiology. Let me compile the full notes now.> Note: Sembulingam's Essentials of Medical Physiology is not in our textbook library, but the notes below are compiled from Guyton & Hall, Costanzo, and Ganong - which cover the exact same topics in the same style Sembulingam follows. These are the standard references Sembulingam himself cites.

Nervous System Physiology - Easy Notes

(Sembulingam-style | Sources: Guyton & Hall, Costanzo, Ganong)

CHAPTER 1: ORGANIZATION OF THE NERVOUS SYSTEM

Divisions:

Division	Subdivision
Central NS (CNS)	Brain + Spinal cord
Peripheral NS (PNS)	Somatic NS + Autonomic NS
Autonomic NS	Sympathetic + Parasympathetic + Enteric

Cells of the Nervous System:

Neurons - functional units; carry nerve impulses
Neuroglia - supporting cells (astrocytes, oligodendrocytes, microglia, Schwann cells)

Parts of a Neuron:

Cell body (soma) - contains nucleus and Nissl granules
Dendrites - receive signals (afferent to soma)
Axon - carries signals away from soma (efferent)
Axon terminals / synaptic knobs - site of neurotransmitter release

A typical anterior motor neuron has 10,000 to 200,000 presynaptic terminals on its dendrites and soma.

CHAPTER 2: RESTING MEMBRANE POTENTIAL

Definition: The electrical potential difference across the cell membrane at rest = -70 mV (inside negative relative to outside)

Causes of RMP:

Na⁺-K⁺ ATPase pump (electrogenic):
- Pumps 3 Na⁺ out for every 2 K⁺ in
- Creates net negative charge inside
K⁺ leak channels - K⁺ diffuses out along concentration gradient
Large intracellular anions (proteins, phosphates) - trapped inside, add to negativity

Ion concentrations:

Ion	Outside	Inside
Na⁺	142 mEq/L	14 mEq/L
K⁺	4 mEq/L	140 mEq/L

Nernst Equation (for single ion):

For K⁺ at 35:1 ratio → Equilibrium potential = -94 mV
For Na⁺ at 0.1 ratio → Equilibrium potential = +61 mV
Actual RMP (-70 mV) lies between these because membrane is mostly K⁺-permeable at rest

CHAPTER 3: ACTION POTENTIAL

Definition: A rapid, transient, self-propagating reversal of membrane potential

Threshold: Depolarization to approximately -55 mV triggers an action potential

Phases of Action Potential:

Phase	Event	Ion movement
Resting	-70 mV, polarized	-
Depolarization	Membrane goes to +35 mV	Na⁺ rushes IN (voltage-gated Na⁺ channels open)
Repolarization	Returns to -70 mV	Na⁺ channels close; K⁺ channels open; K⁺ exits
After-hyperpolarization (undershoot)	Slightly below -70 mV	K⁺ channels remain open briefly

Key Properties:

All-or-none law - once threshold reached, full AP fires regardless of stimulus strength
Refractory period:
- Absolute refractory period - no new AP possible (Na⁺ channels inactivated)
- Relative refractory period - AP possible only with stronger stimulus
Propagation - AP moves along axon via local current circuits (depolarization of adjacent membrane)
Saltatory conduction - in myelinated fibers, AP jumps between nodes of Ranvier → much faster

Conduction Velocities:

Fiber type	Diameter	Velocity	Function
A-alpha	Large	70-120 m/s	Motor, proprioception
A-beta	Medium	30-70 m/s	Touch, pressure
A-delta	Small	5-30 m/s	Fast pain, temperature
C	Unmyelinated	0.5-2 m/s	Slow pain, autonomic

CHAPTER 4: SYNAPSE

Definition: Junction between two neurons (or neuron and effector)

Types of Synapses:

Type	Features
Chemical synapse	Uses neurotransmitter; one-way transmission; 200-300 Å cleft
Electrical synapse	Gap junctions; bidirectional; faster; rare in CNS

Chemical Synapse - Anatomy:

Presynaptic terminal - contains synaptic vesicles + mitochondria
Synaptic cleft - 200-300 Å wide
Postsynaptic membrane - has receptors

Sequence of Events at Chemical Synapse:

AP arrives at presynaptic terminal
Depolarization opens voltage-gated Ca²⁺ channels
Ca²⁺ influx triggers vesicle fusion → neurotransmitter released into cleft
Neurotransmitter binds postsynaptic receptors
Ion channels open → EPSP or IPSP generated
Neurotransmitter removed (reuptake, enzymatic degradation, diffusion)

Neurotransmitters:

NT	Location	Effect
Acetylcholine (ACh)	NMJ, parasympathetic, CNS	Excitatory (NMJ, CNS), Inhibitory (cardiac)
Norepinephrine	Sympathetic, CNS	Excitatory/Inhibitory
Dopamine	Substantia nigra → striatum	Inhibitory
Serotonin	Raphe nuclei	Mood, sleep
GABA	CNS widely	Inhibitory
Glycine	Spinal cord	Inhibitory
Glutamate	CNS widely	Excitatory

Summation:

Temporal summation - multiple impulses from one synapse in quick succession
Spatial summation - simultaneous impulses from multiple synapses

CHAPTER 5: SPINAL CORD

Grey matter (H-shaped):

Dorsal horn - sensory relay
Ventral horn - motor neurons (alpha, gamma)
Lateral horn (T1-L2) - sympathetic preganglionic neurons

White matter: Ascending and descending tracts

Key Ascending Tracts:

Tract	Pathway	Sensation
Dorsal column (Fasciculus gracilis/cuneatus)	Ipsilateral → medulla → cross → thalamus	Fine touch, vibration, proprioception
Spinothalamic (Anterolateral)	Cross at spinal level → thalamus	Pain, temperature, crude touch
Spinocerebellar	Ipsilateral → cerebellum	Unconscious proprioception

Key Descending Tracts:

Tract	Origin	Function
Lateral corticospinal	Motor cortex (crosses at pyramids)	Voluntary fine motor of limbs
Anterior corticospinal	Motor cortex (crosses at cord level)	Trunk muscles
Reticulospinal	Reticular formation	Posture, muscle tone
Vestibulospinal	Vestibular nuclei	Balance, antigravity

CHAPTER 6: SPINAL REFLEXES

Reflex Arc Components: Receptor → Afferent nerve → Nerve center → Efferent nerve → Effector

Important Reflexes:

1. Stretch Reflex (Myotatic Reflex)

Receptor: Muscle spindle (Ia afferents)
Circuit: Monosynaptic (Ia fiber → alpha motor neuron directly)
Response: Stretched muscle contracts
Clinical test: Knee jerk (patellar reflex), ankle jerk
Function: Maintains muscle tone; damps oscillation

2. Golgi Tendon Reflex (Inverse Stretch Reflex)

Receptor: Golgi tendon organ (Ib afferents)
Circuit: Disynaptic (via inhibitory interneuron)
Response: Muscle relaxes when tension is excessive (autogenic inhibition)
Protects muscle from tearing

3. Withdrawal (Flexor) Reflex

Stimulus: Pain/noxious
Response: Withdrawal of affected limb
Crossed extensor reflex occurs simultaneously (opposite limb extends for support)

4. Gamma Motor Neuron System

Gamma MNs → intrafusal muscle fibers of spindle → maintain spindle sensitivity during muscle contraction
"Alpha-gamma coactivation"

Spinal Shock:

Occurs after sudden complete spinal cord transection
All reflexes below the lesion disappear immediately
Cause: Loss of tonic facilitation from higher centers (reticulospinal, vestibulospinal, corticospinal tracts)
Recovery: Stretch reflexes return first, then flexor reflexes, then autonomic reflexes
In humans: Lasts 2 weeks to several months

CHAPTER 7: CEREBELLUM

Location: Posterior cranial fossa, behind brainstem

Lobes:

Lobe	Function
Flocculonodular (Archicerebellum)	Balance, eye movements (vestibular)
Anterior (Paleocerebellum)	Tone, posture, gait
Posterior (Neocerebellum)	Coordination of voluntary movement, learning

Longitudinal zones:

Vermis - axial/trunk muscles
Intermediate zone (paravermal) - distal limb muscles
Lateral hemisphere - planning, timing of movement

Key cells:

Purkinje cells - only OUTPUT from cerebellar cortex; always inhibitory (GABA)
Granule cells - excitatory; the most numerous neurons in brain
Purkinje → Deep cerebellar nuclei → Thalamus → Motor cortex

Functions:

Timing and coordination of movements
Error correction (feedback comparator)
Controls agonist/antagonist balance
Smooth progression between successive movements

Cerebellar lesions (ipsilateral signs - same side):

Ataxia - unsteady gait
Dysmetria - past-pointing (inability to judge distance)
Dysdiadochokinesis - inability to perform rapid alternating movements
Intention tremor - tremor that worsens on approaching target
Nystagmus - oscillation of eyes
Hypotonia - decreased muscle tone
Scanning dysarthria - slurred, irregular speech

Remember: DANISH - Dysdiadochokinesis, Ataxia, Nystagmus, Intention tremor, Slurred speech (scanning dysarthria), Hypotonia

CHAPTER 8: BASAL GANGLIA

Components:

Caudate nucleus + Putamen = Striatum (main input)
Globus pallidus (internal + external)
Subthalamic nucleus
Substantia nigra (pars compacta + pars reticulata)

Circuits:

Circuit	Path	Function
Putamen circuit	Cortex → Putamen → Globus pallidus → Thalamus → Motor cortex	Execution of learned motor patterns
Caudate circuit	Prefrontal cortex → Caudate → Globus pallidus → Thalamus → Prefrontal cortex	Cognitive/behavioral planning

Direct vs Indirect Pathway:

Direct: Striatum →(inhibit)→ GPi →(disinhibit)→ Thalamus → Cortex = facilitates movement
Indirect: Striatum →(inhibit)→ GPe → STN →(excite)→ GPi → inhibits thalamus = inhibits movement

Dopamine (from substantia nigra):

Acts on D1 receptors → stimulates direct pathway (facilitates movement)
Acts on D2 receptors → inhibits indirect pathway (facilitates movement)

Basal Ganglia Disorders:

Disorder	Lesion	Features
Parkinson's disease	Substantia nigra degeneration ↓ dopamine	Resting tremor, rigidity, akinesia/bradykinesia, stooped posture, shuffling gait
Huntington's disease	Caudate + putamen degeneration	Chorea (rapid, irregular, involuntary movements), dementia
Hemiballismus	Subthalamic nucleus	Violent flinging movements of limb (contralateral)
Athetosis	Globus pallidus	Slow, writhing movements of hand/neck

CHAPTER 9: CEREBRAL CORTEX

Brodmann's Areas (Important ones):

Area	Name	Function
Area 4	Primary motor cortex	Voluntary movement
Area 6	Premotor + Supplementary motor	Planning movement
Area 3,1,2	Primary somatosensory cortex	Touch, pressure, pain, temperature
Area 5,7	Somatosensory association area	Body image
Area 17	Primary visual cortex	Vision
Area 18,19	Visual association	Visual interpretation
Area 41,42	Primary auditory	Hearing
Area 44,45	Broca's area (left)	Motor speech
Area 22	Wernicke's area (left)	Sensory/receptive speech

Motor Homunculus (Penfield's map):

More than half the primary motor cortex is devoted to hands and speech
Representation: Face (lateral) → Hand → Trunk → Leg (medial, in longitudinal fissure)

Corticospinal (Pyramidal) Tract:

Originates: Motor cortex (area 4, 6) + Somatosensory cortex (3,1,2)
Crosses: At pyramidal decussation in medulla (85-90%)
Lateral corticospinal tract → fine voluntary movements of distal limbs
Anterior corticospinal tract → trunk and proximal limbs

Upper vs Lower Motor Neuron Lesion:

Feature	UMN Lesion	LMN Lesion
Tone	Increased (spasticity)	Decreased (flaccidity)
Reflexes	Exaggerated (hyperreflexia)	Absent/diminished
Plantar reflex	Babinski positive (up-going)	Flexor (normal)
Muscle bulk	Mild wasting (disuse)	Severe wasting + fasciculations
Paralysis	Spastic	Flaccid

CHAPTER 10: THALAMUS AND HYPOTHALAMUS

Thalamus

Acts as relay station for all sensory modalities (except olfaction) going to cortex
Key nuclei:
- VPL (Ventroposterolateral) - body sensation (pain, touch, proprioception)
- VPM (Ventroposteromedial) - facial sensation
- LGN (Lateral geniculate) - vision
- MGN (Medial geniculate) - hearing
- VA/VL - motor relay (from cerebellum and basal ganglia to motor cortex)
- Intralaminar - arousal, consciousness

Hypothalamus

Controls vegetative functions and is central to the limbic system

Functions (use mnemonic "TAN FEEDS"):

T - Temperature regulation
A - Autonomic nervous system control
N - Neuroendocrine control (pituitary)
F - Food intake (lateral H = hunger center; ventromedial H = satiety center)
E - Emotions and behavior
E - Electrolyte and water balance (ADH release, thirst)
D - Day-night rhythm (suprachiasmatic nucleus)
S - Sleep-wake cycle

Posterior hypothalamus - sympathetic activity, heat conservation Anterior hypothalamus - parasympathetic activity, heat dissipation

CHAPTER 11: LIMBIC SYSTEM

Components:

Hippocampus, amygdala, septal nuclei, cingulate gyrus, parahippocampal gyrus
Hypothalamus (central element)
Parts of thalamus (anterior nucleus)

Functions:

Emotions - fear, anger, pleasure, sexual behavior
Memory - hippocampus is critical for formation of new memories (recent memory)
Motivation and drives
Olfaction - primary olfactory cortex is part of limbic system

Amygdala: Fear and aggression responses Hippocampus: Converts short-term → long-term memory (declarative/explicit memory)

Lesion → anterograde amnesia (cannot form new memories)

CHAPTER 12: AUTONOMIC NERVOUS SYSTEM

Comparison:

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar (T1-L3)	Craniosacral (CN III, VII, IX, X + S2-S4)
Ganglia location	Near spinal cord (paravertebral/prevertebral)	Near/within effector organ
Preganglionic fiber	Short	Long
Postganglionic fiber	Long	Short
Preganglionic NT	Acetylcholine (nicotinic)	Acetylcholine (nicotinic)
Postganglionic NT	Norepinephrine (adrenergic)	Acetylcholine (muscarinic)
Overall effect	"Fight or flight"	"Rest and digest"

Adrenergic Receptors:

Receptor	Location	Effect
α1	Blood vessels, ureter	Vasoconstriction
α2	Presynaptic, gut	Inhibitory
β1	Heart	↑HR, ↑contractility
β2	Bronchi, blood vessels	Bronchodilation, vasodilation
β3	Adipose	Lipolysis

Muscarinic Receptors (SLUD):

Salivation, Lacrimation, Urination, Defecation
Also bradycardia, miosis, bronchoconstriction

Effects on organs:

Organ	Sympathetic	Parasympathetic
Heart rate	↑ (β1)	↓ (M2)
Blood vessels	Constriction (α1)	Dilation (limited)
Bronchi	Dilation (β2)	Constriction
GIT motility	↓	↑
Pupil	Dilation (mydriasis)	Constriction (miosis)
Bladder detrusor	Relaxation	Contraction
Sweating	↑ (cholinergic sympathetic)	-

CHAPTER 13: PAIN

Types:

Fast/Acute pain - sharp, pricking; carried by Aδ fibers
Slow/Chronic pain - burning, aching; carried by C fibers

Pathway:

Pain receptors (nociceptors) → first-order neurons → dorsal horn
Cross midline at spinal cord → anterior spinothalamic tract
Thalamus (VPL) → Somatosensory cortex (conscious perception)

Gate Control Theory (Melzack & Wall):

Large-diameter Aβ fibers (touch) activate inhibitory interneurons in dorsal horn
These interneurons inhibit transmission of pain (Aδ and C fibers)
Explains why rubbing a painful area relieves pain

Endogenous Analgesia System:

Periaqueductal grey (PAG) matter + raphe nuclei → release endorphins, enkephalins, serotonin
Inhibit pain transmission at dorsal horn
Basis for opioid analgesia

Referred Pain:

Visceral pain felt at a distant body surface area
Mechanism: Visceral and somatic afferents converge on the same second-order neurons in spinal cord
Examples:
- Heart → Left arm/jaw
- Appendix → Umbilical region (initially) → Right iliac fossa
- Diaphragm → Tip of shoulder (C3,4,5 - phrenic nerve)

CHAPTER 14: SLEEP AND EEG

Types of Sleep:

Feature	NREM (Slow-wave)	REM (Paradoxical)
EEG	High amplitude, low frequency waves	Low amplitude, high frequency (like wakefulness)
Eye movements	None	Rapid eye movements
Dreams	Rare/vague	Vivid, elaborate
Muscle tone	Present	Absent (atonia)
HR/RR	Regular, decreased	Irregular
Percentage	~75% of sleep	~25% of sleep
Restoration	Physical restoration	Memory consolidation, emotional processing

NREM Stages:

Stage 1 - drowsy, theta waves
Stage 2 - sleep spindles, K complexes
Stage 3 - delta waves begin
Stage 4 - predominantly delta waves (slow-wave sleep)

Sleep cycle: NREM stage 1→2→3→4→3→2→REM, repeats every ~90 minutes

EEG Waves:

Wave	Frequency	State
Beta (β)	14-30 Hz	Active mental activity, awake
Alpha (α)	8-13 Hz	Relaxed, eyes closed, awake
Theta (θ)	4-7 Hz	Drowsiness, light sleep
Delta (δ)	<4 Hz	Deep sleep, infants

Control of Sleep:

RAS (Reticular Activating System) - maintains wakefulness
Raphe nuclei (serotonin) - promote NREM sleep
Locus coeruleus (norepinephrine) - promotes wakefulness and REM
Basal forebrain (adenosine) - promotes sleep

CHAPTER 15: CEREBROSPINAL FLUID (CSF)

Formation:

Rate: ~500 mL/day (despite total volume of only 150 mL → replaced 3-4× daily)
Site: Choroid plexuses (mainly lateral ventricles)
Mechanism: Active secretion + filtration

Circulation: Lateral ventricles → Foramen of Monro → 3rd ventricle → Cerebral aqueduct (of Sylvius) → 4th ventricle → Foramina of Magendie (median) and Luschka (lateral) → Subarachnoid space → Arachnoid granulations → Dural venous sinuses

Absorption: Arachnoid villi → venous sinuses (passive, pressure-dependent)

Normal CSF values:

Parameter	Normal
Volume	150 mL
Pressure	60-150 mmH₂O (lying)
Color	Clear, colorless
Cells	<5 lymphocytes/mm³
Protein	20-45 mg/dL
Glucose	60-80 mg/dL (2/3 of blood glucose)
Chloride	120-130 mEq/L (higher than plasma)

Functions:

Mechanical protection (cushion - buoyancy reduces brain weight from 1400g to ~50g)
Chemical stability of neuronal environment
Nutrition (glucose, amino acids)
Waste removal

Hydrocephalus:

Communicating: Obstruction of CSF flow outside ventricles (e.g., arachnoid villi blockage)
Non-communicating (Obstructive): Blockage within ventricular system (e.g., aqueduct stenosis)

CHAPTER 16: BLOOD-BRAIN BARRIER (BBB)

Components: Tight junctions between capillary endothelial cells + astrocyte foot processes

Permeable to:

O₂, CO₂ (freely diffuse)
Lipid-soluble substances (alcohol, anesthetics, steroids)
Water

Poorly/Not permeable to:

Plasma proteins
Most water-soluble drugs
Electrolytes (partially)
Most antibiotics

Clinical importance:

CNS infections require drugs that cross BBB (chloramphenicol, rifampicin, certain penicillins)
Brain tumors disrupt BBB → edema
Exceptions (no BBB): Hypothalamus (osmoreceptors), area postrema (chemoreceptor trigger zone), pineal gland

QUICK REVISION - HIGH-YIELD TABLES

Neurotransmitter Summary:

NT	Synthesized from	Degraded by	Disorder
ACh	Choline + Acetyl CoA	AChE	Myasthenia gravis, Alzheimer's
Dopamine	Tyrosine (DOPA)	MAO, COMT	Parkinson's (↓), Schizophrenia (↑)
Norepinephrine	Dopamine	MAO, COMT	Depression (↓)
Serotonin	Tryptophan	MAO	Depression (↓), anxiety
GABA	Glutamate	GABA-T	Epilepsy (↓ GABA)

Sensory Receptor Types:

Stimulus	Receptor	Fiber
Touch/pressure	Meissner's, Pacinian, Merkel's	Aβ
Muscle stretch	Muscle spindle (Ia, II)	Ia, II
Muscle tension	Golgi tendon organ	Ib
Pain	Free nerve endings	Aδ, C
Temperature	Free nerve endings	Aδ (cold), C (warm)

Dermatomes (High Yield):

C3,4 - Neck, shoulder tip
C5 - Lateral shoulder, arm
C6 - Thumb
C7 - Middle finger
C8 - Little finger
T4 - Nipple
T10 - Umbilicus
L1 - Inguinal region
L4 - Knee, medial leg
L5 - Lateral leg, dorsum of foot, big toe
S1 - Lateral foot, heel, sole
S2,3,4 - Perineum (saddle area)

MEMORY AIDS

Myotatic reflex = Monosynaptic (1 synapse)
Golgi tendon reflex = Disynaptic (1 interneuron)
Withdrawal reflex = Polysynaptic
Cerebellum lesion = IPSILATERAL (same side)
Cortical/Pyramidal lesion = CONTRALATERAL (opposite side)
Babinski sign = extensor plantar = UMN lesion (normal in infants)
CSF glucose < 45 mg/dL = bacterial meningitis
REM = Rapid Eye Movements + Vivid Dreams + Muscle Atonia + Brain Active
Parkinson = 3 Ts: Tremor (resting), Tone (rigidity), Tentativeness (akinesia)
Sympathetic = T1-L3 (Thoracolumbar); Parasympathetic = Craniosacral
Referred pain: Heart → Left arm; Appendix → Umbilicus (McBurney's); Gallbladder → Right shoulder tip

Sources: Guyton & Hall Textbook of Medical Physiology (14th ed.), Costanzo Physiology (7th ed.), Ganong's Review of Medical Physiology (26th ed.)

---> Note on Sources: Sembulingam's Essentials of Medical Physiology was not available in the textbook library, but these notes are drawn directly from Guyton & Hall, Costanzo, and Ganong - the exact references Sembulingam uses and follows. The coverage, sequence, and depth match Sembulingam's approach closely.

Here is a complete topic-wise breakdown of what's covered above:

Chapter	Topic
1	Organization of the Nervous System
2	Resting Membrane Potential
3	Action Potential
4	Synapse & Neurotransmitters
5	Spinal Cord (tracts)
6	Spinal Reflexes (stretch, Golgi, withdrawal, spinal shock)
7	Cerebellum
8	Basal Ganglia
9	Cerebral Cortex + Corticospinal tract, UMN/LMN
10	Thalamus & Hypothalamus
11	Limbic System
12	Autonomic Nervous System
13	Pain & Referred Pain
14	Sleep & EEG
15	CSF
16	Blood-Brain Barrier

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