Physiology

S Krishna Kumar MD

CBS Publishers & Distributors Pvt Ltd

• New Delhi • Bengaluru • Chennai • Kochi • Kolkata • Lucknow • Mumbai
• Hyderabad • Jharkhand • Nagpur • Patna • Pune • Uttarakhand
 Dedicated to

“My Aunt Mrs Subbulakshmi Ammal who took care of me right from my 10 years of age”
 Preface
Dear Students,
With immense love and gratitude, I present to you the book “One Touch Physiology”. But before you start
going through this extremely useful work, it is essential to discuss with you the following specialties of this
book:
• High Yield is the word. This book is designed in such a way that it helps you to go through all the most
important areas you need to remember for your exams.
• MIMT: Maximum Information in Minimum Time. This book is loaded with whole lot of important
information presented in a concise way so that you can read and revise the entire content in short time.
• KISS: Keep It Simple & Significant. The language used while writing this book is simple one so that
anybody can easily understand the content. All the complex concepts are simplified.
• Prime Time Show: This book is very effective, especially when your exam is round the corner. (Prime
time). It will be so handy to you to go through all the important topics just before exams.
• Revision is the Key: Perhaps the single most important objective of this book is it helps you to REVISE
physiology effectively because important areas are covered concisely in a few pages.
• See and Learn: All the important images are given in the book. It helps you to tackle the image-based
questions in exams.
• Tables, Flowcharts & Must Know: Content is presented in the form of tables and flowcharts for effective
reading. Must know areas are highlighted for your convenience.
• Past Guides Our Future: All the questions asked in the recent exams are given with answers in this book.
Mastering Repeat topics and Repeat questions is an important trait of a successful candidate.
Although I have tried my level best to make this book error free, kindly do let me know in case you
come across any errors through my mail ID: tallboykk&gmail.com or through Instagram to my page @
krishnakumar_solaiappan
“All good things will happen at the right time. Have patience. Be well prepared and stay persistent and
consistent. Stay hopeful always”.
My good luck and best wishes are always there for you!

 Yours Lovingly
 S Krishna Kumar

 Contents
Preface ................................................................................................................................................................................................. vii

THEORY

1. General Physiology 3–3

1. Homeostasis ...................................................................................................................................................................... 3

2. Cellular Physiology 4–12

1. Cell Membrane (Plasma Membrane) ....................................................................................................................... 4
2. Endoplasmic Reticulum ................................................................................................................................................ 5
3. Golgi Apparatus .............................................................................................................................................................. 5
4. Lysosomes .......................................................................................................................................................................... 6
5. Peroxisomes (Microbodies) ........................................................................................................................................... 6
6. Mitochondria .................................................................................................................................................................... 6
7. Nucleus ................................................................................................................................................................................ 6
8. Marker Enzymes ............................................................................................................................................................. 6
9. Cytoskeletal Filaments .................................................................................................................................................. 7
10. Cell Junctions ................................................................................................................................................................... 8
11. Cellular Receptors ........................................................................................................................................................... 9
12. Membrane Transport .................................................................................................................................................... 9
13. Membrane Potentials ................................................................................................................................................. 11
14. Cellular Fluids ................................................................................................................................................................ 12

3. Nerve Muscle Physiology 13–20

1. Structure of a Neuron ............................................................................................................................................... 13
2. Parts of a Neuron along with their Characteristics ...................................................................................... 13
3. Classification of Neurons along with their Characteristics .......................................................................... 13
4. Myelin ............................................................................................................................................................................... 13
5. Nerve Action Potential .............................................................................................................................................. 14
6. Classification of Nerve Fibers .................................................................................................................................. 14
7. Nerve Injury .................................................................................................................................................................. 15
8. Skeletal Muscle .............................................................................................................................................................. 16
9. Neuromuscular Transmission and Excitation Contraction Coupling ....................................................... 16
10. Neuromuscular Blocking Agents and their Mechanisms of Action .......................................................... 17
11. Neuromuscular Junction and Diseases ................................................................................................................ 17
12. Muscle Contraction: Sliding Filament Theory .................................................................................................. 17
13. Length-Tension Relationship: Skeletal Muscle ................................................................................................. 18
x One Touch Physiology by Dr S Krishna Kumar

14. Skeletal Muscle Fiber Types ..................................................................................................................................... 18

15. Cardiac Muscle .............................................................................................................................................................. 19
16. Smooth Muscle .............................................................................................................................................................. 19
17. Synaptic Potentials ..................................................................................................................................................... 19
18. Inhibition and Facilitation at Synapses .............................................................................................................. 19
19. Neurotransmitters ...................................................................................................................................................... 20

4. Neurophysiology 21–33
1. Sensory Physiology ...................................................................................................................................................... 21
2. Touch Receptors ........................................................................................................................................................... 21
3. Pain Receptors .............................................................................................................................................................. 21
4. Somatosensory Pathways ......................................................................................................................................... 22
5. Special Senses ................................................................................................................................................................ 22
6. Laws and Principles in Sensory Physiology ....................................................................................................... 26
7. Motor Physiology ......................................................................................................................................................... 26
8. Reflex ................................................................................................................................................................................ 27
9. Cerebellum ...................................................................................................................................................................... 27
10. Basal Ganglia ................................................................................................................................................................. 28
11. Thalamus ......................................................................................................................................................................... 30
12. Hypothalamus ............................................................................................................................................................... 30
13. Learning and Memory ............................................................................................................................................... 30
14. Language and Speech ................................................................................................................................................ 31
15. Cerebral Blood Flow ................................................................................................................................................... 31
16. Cerebrospinal Fluid ..................................................................................................................................................... 32
17. Electroencephalography Waves .............................................................................................................................. 32
18. Sleep ................................................................................................................................................................................. 32

5. Respiratory Physiology 34–45

1. Lung Airway Generations–Weibel’s Model of Airways ................................................................................. 34
2. Pulmonary Surfactant ............................................................................................................................................... 35
3. Mechanics of Breathing ............................................................................................................................................. 35
4. Muscles of Inspiration and Expiration ................................................................................................................. 36
5. Pressure Volume Relationship in Lung—The Concept of “Compliance” ................................................ 36
6. Pressure Volume Curves of Lung (PL), Chest Wall (PW),
Lung and Chest Wall Combined (PTR) .................................................................................................................. 36
7. Lung Volumes and Capacities ................................................................................................................................. 37
8. Ventilation and Perfusion ........................................................................................................................................ 38
9. Diffusion of Gases ......................................................................................................................................................... 40
10. Transport of Gases ...................................................................................................................................................... 40
11. Oxygen Transport ....................................................................................................................................................... 40
12. Transport of Carbon Dioxide .................................................................................................................................. 42
13. Regulation of Respiration ......................................................................................................................................... 42
 CONTENTS xi

14. Hypoxia and its Types ............................................................................................................................................... 44

15. Environmental Physiology ........................................................................................................................................ 44

6. Cardiovascular Physiology 46–58

1. Cardiac Potentials ....................................................................................................................................................... 46
2. Conduction System of Heart .................................................................................................................................. 47
3. Electrocardiogram (ECG) ......................................................................................................................................... 47
4. Cardiac Cycle ................................................................................................................................................................. 48
5. Cardiac Output ............................................................................................................................................................. 50
6. Coronary Circulation .................................................................................................................................................. 51
7. Vascular Physiology ..................................................................................................................................................... 51
8. Blood Groups and their Characteristics ............................................................................................................. 53
9. Characteristics of Blood Vessels ............................................................................................................................. 53
10. Hemodynamics ............................................................................................................................................................. 54
11. Blood Coagulation ........................................................................................................................................................ 55
12. Blood Pressure .............................................................................................................................................................. 56

7. Endocrine Physiology 59–75

1. Endocrine System ....................................................................................................................................................... 59
2. Classification of Hormones ....................................................................................................................................... 59
3. Role of Hypothalamus ................................................................................................................................................ 59
4. Pituitary Gland ............................................................................................................................................................ 59
5. Prolactin .......................................................................................................................................................................... 60
6. Thyroid Gland ............................................................................................................................................................... 61
7. Endocrine Pancreas .................................................................................................................................................... 63
8. Adrenal Gland .............................................................................................................................................................. 65
9. Aldosterone .................................................................................................................................................................... 65
10. Glucocorticoids—“Cortisol” ..................................................................................................................................... 66
11. Adrenal Sex Steroids ................................................................................................................................................. 67
12. Calcium Homeostasis .................................................................................................................................................. 67
13. Parathormone ............................................................................................................................................................... 67
14. Vitamin D ....................................................................................................................................................................... 68
15. Calcitonin ........................................................................................................................................................................ 68
16. Reproductive Physiology ........................................................................................................................................... 69
17. Placental Protein Hormone: Human Chorionic Gonadotropin (HCG) .................................................... 75
18. Lactation ......................................................................................................................................................................... 75

8. Renal Physiology 76–83

1. Structure of Kidney and its Functions ............................................................................................................... 76
2. Glomerular Filtration Rate ...................................................................................................................................... 76
3. Parts of Nephron ......................................................................................................................................................... 77
4. Free Water Clearance (CH2O) ................................................................................................................................. 80
5. Natriuretic Peptides ................................................................................................................................................... 81
6. Micturition ..................................................................................................................................................................... 81
7. Acid-Base Balance ...................................................................................................................................................... 82
xii One Touch Physiology by Dr S Krishna Kumar

9. Gastrointestinal Physiology 84–90

1. Functions and Structural Characteristics of Gastrointestinal Tract ....................................................... 84
2. Gastrointestinal Secretions ...................................................................................................................................... 84
3. Gastrointestinal Hormones ...................................................................................................................................... 86
4. Regulation of Food Intake ........................................................................................................................................ 87
5. Digestion and Absorption ......................................................................................................................................... 87
6. Absorption of Iron ....................................................................................................................................................... 88
7. Gastrointestinal Motility ........................................................................................................................................... 89
8. Colonic Flora .................................................................................................................................................................. 90
9. Dietary Fibers ................................................................................................................................................................ 90

10. Exercise Physiology 91–92

1. Types of Exercises and Sources of Energy for Muscles ................................................................................. 91
2. Cardiovascular Responses to Exercise .................................................................................................................. 91
3. Respiratory Responses to Exercise ........................................................................................................................ 91
4. Regulation of Body Temperature .......................................................................................................................... 91

LATEST QUESTION PAPERS

NEET PG 2023 ................................................................................................................................................................................95
NEET PG 2022 ................................................................................................................................................................................96
NEET PG 2021 ................................................................................................................................................................................97
INI-CET November 2023 ............................................................................................................................................................97
INI-CET May 2023 ........................................................................................................................................................................98
INI-CET November 2022 ............................................................................................................................................................99
INI-CET May 2022 ..................................................................................................................................................................... 100
INI-CET November 2021 ......................................................................................................................................................... 101
INI-CET July 2021 ..................................................................................................................................................................... 102
FMGE January 2024 .................................................................................................................................................................. 103
FMGE January 2023 .................................................................................................................................................................. 103
FMGE July 2023 .......................................................................................................................................................................... 104
FMGE June 2022 ......................................................................................................................................................................... 105
FMGE December 2021 .............................................................................................................................................................. 106
FMGE June 2021 ......................................................................................................................................................................... 106
 THEORY 13

3. NERVE MUSCLE PHYSIOLOGY

STRUCTURE OF A NEURON Neuron Characteristics

type
Bipolar • Have two types of processes that
neurons are functionally specialized-
dendrite and axon.
• Examples: Bipolar retinal neurons,
olfactory neurons
Pseudo • Are variants of bipolar cells in
unipolar which one end goes to the spinal
neurons cord and the other end goes to
peripheral skin
• Example: Dorsal root ganglion cell
Multipolar • Have single axon and many
neurons dendrites
PARTS OF A NEURON ALONG WITH THEIR • These are the most common types
CHARACTERISTICS of neurons in CNS
• Examples: Spinal motor neuron,
Parts of a Characteristics Purkinje cells of cerebellum,
neuron sympathetic ganglia
Cell body • Contains nucleus
• Metabolic center MYELIN
Nissl bodies • Rough endoplasmic reticulum of • Myelin insulates nerve fibers and fastens
neurons
conduction of impulses.
Dendrites • Receive information • Myelin speeds impulse conduction by permitting
• Has small knobby projections action potentials to jump between naked regions
called dendritic spines of axons called nodes of Ranvier. Such a type of
Axon hillock • Thickened area of the cell body nerve conduction is called Saltatory conduction.
Axon • Transmits propagated impulses • Myelin is a lipid protein complex. Lipid
to the nerve endings component is Sphingomyelin; and protein
Initial • Site where propagated action components are Myelin Basic Protein (MBP)
segment potentials are generated and Myelin Oligodendrocyte Glycoprotein
Nerve • Site where neurotransmitters are (MOG). Autoantibodies are directed against
endings stored and released these proteins in a demyelinating disorder called
multiple sclerosis.
CLASSIFICATION OF NEURONS ALONG WITH • Myelin is formed by oligodendrocytes in central
THEIR CHARACTERISTICS nervous system and Schwann cells in the
peripheral nervous system.
Neuron Characteristics • Oligodendrocyte can myelinate multiple neurons
type at a time but Schwann cell can myelinate only
Unipolar • Have a single process originating one neuron at a time.
neurons from the cell body. • Luxol fast blue: Special stain for staining myelin
• Example: Invertebrate neurons sheath.
Contd…
14 One Touch Physiology by Dr S Krishna Kumar

NERVE ACTION POTENTIAL

• Phase I: Local potential (-70 mV to -55 mV). Due to

slow sodium influx
• Phase II: Depolarization-Rapid sodium influx through
voltage gated sodium channels
• Phase III: Repolarization-Potassium efflux
• Phase IV: Hyperpolarization-Delayed closure of
potassium channels and also due to chloride influx
• Absolute refractory period (ARP): from firing level
(-55 mV) until repolarization is about one-third
complete. No stimulus, no matter how strong, will
not excite the nerve due to inactivation of sodium
channels
• Relative refractory period (RRP): Begins from the
remaining part of repolarization to the end of
action potential. Stronger than normal stimulus
(suprathreshold stimulus) produces action potential

CLASSIFICATION OF NERVE FIBERS

Erlanger and Gasser Classification

Fiber type Myelin present or Diameter (µm) Conduction Functions

absent velocity (m/s)

A α Myelinated 12-20 (Largest) 70-120 Proprioception; somatic

(Highest) motor

A β Myelinated 5-12 30-70 Touch, pressure

A γ Myelinated 3-6 15-30 Motor to muscle spindles

A δ Myelinated 2-5 12-30 Pain, temperature

B Myelinated <3 3-15 Preganglionic autonomic

C, dorsal root Unmyelinated 0.4-1.2 0.5-2 Pain, temperature

(Smallest) (lowest)

C, Sympathetic Unmyelinated 0.3-1.3 0.7-2.3 Postganglionic sympathetic

Lloyd Classification

Number Origin Fiber type

Ia Muscle spindle, annulo spiral ending A α
Ib Golgi tendon organ A α
II Muscle spindle, flower spray ending, touch pressure A β
III Pain and cold receptors A δ
IV Pain and temperature receptors C
 THEORY 15

NERVE INJURY

Sunderland Classification with its Equivalent Seddon Classification Terminology and Features

Sunderland Equivalent Seddon Features

classification classification terminology
First degree Neuropraxia • Nerve in continuity
• Due to compression or ischemia
• Only local conduction block seen
• Spontaneous recovery in minutes
Second Axonotmesis • Injury to axon
degree • Encapsulating structures intact
• Wallerian degeneration occurs
• Recovery at 1-3 mm/day
Third degree Neurotmesis • Injury to axon
• Endoneurium disrupted, epineurium and perineurium intact
• Wallerian degeneration occurs
Fourth Neurotmesis • Injury to axon
degree • Endoneurium and perineurium disrupted, only epineurium
intact
• Wallerian degeneration occurs
• Requires surgical intervention for recovery
Fifth degree Neurotmesis • Injury to axon
• Disruption in all encapsulating layers
• Wallerian degeneration occurs
• Requires surgical intervention for recovery
16 One Touch Physiology by Dr S Krishna Kumar

SKELETAL MUSCLE

Sarcomere (Functional Units)

• Sarcomere—area between two Z lines

• I band—actin filaments (Thin filaments)
• A band—mainly myosin (Thick filaments)
• M line—runs exactly through center of A band
• H band—nonoverlapping part of myosin
• During muscle contraction—Z lines come
closer,. Length of H band and I band
decreases, A band length remains constant

Structure of sarcomere

• Titin
○ Largest known protein present in mammals
○ Muscle spring responsible for ‘‘Elasticity”
○ Connects Z line to the M line
• Nebulin
○ Runs along the length of actin
○ Regulates actin length
• Myomesin
○ Attach myosin to M line
Sarcomere proteins • Alpha actinin
○ Attach actin to Z line

Skeletal Muscle Proteins • Opening of Voltage gated Na+ channels-Sodium

influx leads to RMP change from -70 mV to
• Contractile Proteins: Actin and Myosin
-40 mV
• Structural Supporting Proteins: Titin, Desmin,
• Opening of Voltage gated Ca2+ channels-
Dystrophin
Calcium influx
• Regulatory Proteins: Tropomyosin and Troponin. • Exocytosis of Acetylcholine
○ Troponin C: Contains the binding sites for • Acetylcholine attaches to Nicotinic Ach receptor
Ca2+. in Post synaptic end muscle endplate
○ Troponin I: Inhibits the interaction of myosin • Sodium influx into motor endplate—Endplate
with actin. potential
○ Troponin T: Binds the troponin components • Endplate potential summates to produce action
to tropomyosin potential
• Relaxation Protein: SERCA pump: Takes up • Action potential activates Dihydropyridine
calcium ions leading to muscle relaxation Receptor (DHPR)
• DHPR and Ryanodine receptor are mechanically
NEUROMUSCULAR TRANSMISSION AND linked and opening of ryanodine receptor leads
EXCITATION CONTRACTION COUPLING to calcium release and actin myosin interaction
and muscle contraction
• RMP of Neuron is -70 mV • Muscle relaxation is brought about by reuptake
of calcium by SERCA pump
Contd…
Contd…
 THEORY 17

NEUROMUSCULAR JUNCTION AND DISEASES

Myasthenia Gravis Lambert Eaton

Myasthenia Syndrome
• Myasthenia • Lambert Eaton
gravis (MG) is Myasthenia
an autoimmune Syndrome (LEMS)
disease due to auto is a presynaptic
antibodies directed disorder
against nicotinic • LEMS is caused
acetylcholine by autoantibodies
receptors (AChRs). directed against
It is a postsynaptic P/Q-type calcium
disorder channels at the
• The cardinal features motor nerve
are weakness and terminals
fatigability of muscles • It is distinguished
NEUROMUSCULAR BLOCKING AGENTS AND but deep tendon from myasthenia
THEIR MECHANISMS OF ACTION reflexes are preserved gravis by two
Neuromuscular Mechanism of action • The amount of ACh important reasons.
blocking agent released per impulse One, LEMS have
normally declines on depressed or absent
Tetrodotoxin (source— Presynaptic voltage-gated repeated activity. It reflexes and two,
Puffer fish) sodium channel blocker is the reason behind high frequency
Dendrotoxin (source— Presynaptic voltage-gated decremental response repetitive nerve
Mamba snake) potassium channel blocker seen in repeated stimulation causes
Conotoxin (source— Presynaptic voltage-gated nerve stimulation in incremental response
Snail) calcium channel blocker myasthenia gravis in LEMS
called myasthenic
Botulinum Toxin Inhibits release of
fatigue.
Acetylcholine leading to
flaccid paralysis

MUSCLE CONTRACTION: SLIDING FILAMENT THEORY

• ATP hydrolysis to ADP and Pi

Step 2
• Myosin head moves from 45° to 90°
• Myosin head contains ADP and Pi
Step 3
• In presence of calcium, actin and myosin
interacts
• Formation of crossbridge
Step 4
• ADP and Pi are released from myosin head
• Myosin head tilts back to 45° (Power Stroke)
Muscle contraction, sliding filament theory • Myosin head detachment from actin require
Step 1 a new molecule of ATP attachment to myosin
• Myosin head at 45° during resting state head
• ATP binding to myosin head activates myosin • After death—No ATP—No myosin head
ATPase detachment leads to RIGOR MORTIS
(Sustained Contraction)
18 One Touch Physiology by Dr S Krishna Kumar

LENGTH-TENSION RELATIONSHIP: SKELETAL MUSCLE

• Maximum tension generated by the muscle is between point B and C

• It corresponds to the sarcomere length of 2.2 micrometers.
• It Is at this segment BC where there is optimal overlap between actin and myosin
• On either side of BC, tension produced by the muscle decreases

SKELETAL MUSCLE FIBER TYPES

Characteristics of Skeletal Muscle Fibers

Characteristics Type I fibers Type II fibers

Type II a Type II b
Other names Slow oxidative Fast oxidative Fast glycolytic
glycolytic
Myoglobin content High High Low
Color Red Red White
Myosin ATPase activity Slow Fast Fast
Ca2+ pumping capacity Moderate High High
of SR
Diameter Small Large Large
Glycolytic capacity Moderate High High
Oxidative capacity High Moderate Low
Associated with motor Slow Fast resistant to Fast fatigable
unit type fatigue
Recruitment order First Second Third
Activities best suited for Maintaining posture, Endurance Walking Sprinting
type activities (running a
marathon)
Mitochondria Many Many Few
Capillaries Many Many Few
 THEORY 19

Motor Unit • Plasticity: If visceral smooth muscle is stretched,

it first exerts increased tension. However, if
• Each single motor neuron and the muscle fibers
the muscle is held at the greater length after
it innervates constitute a motor unit.
stretching, the tension gradually decreases.
• Motor unit innervates very few (three to six) This initial increase in tension later followed by
muscle fibers in muscles concerned with fine, decrease is called plasticity.
precise, graded movements like extra ocular
• Latch Bridge Mechanism: Smooth muscle can
muscles and hand muscles. In leg muscles, motor
be maintained in a prolonged state of partial
unit innervates up to 600 muscle fibers.
contraction (tonus) with very little use of
ATP. This is due to latch bridge mechanism in
Size Principle
which myosin cross-bridges remain attached to
• Small diameter slow type I fibers are always actin for some time after the cytoplasmic Ca2+
recruited first. They are followed by recruitment concentration falls.
of Type II a fatigue resistant fiber. • The type of neuromuscular junction in smooth
• Last to be recruited are the Type II b fast fatigable muscle wherein one neuron innervating multiple
fibers. smooth muscle cells is called synapse en passant.

CARDIAC MUSCLE SYNAPTIC POTENTIALS

• Striated, Involuntary • Synaptic potentials can be excitatory postsynaptic

• Have Intercalated Disk-Cardiac Gap junctions potentials (EPSPs) or inhibitory post synaptic
• Connexins: Proteins present in Gap Junction potentials (IPSPs).
• Functional syncytium: cardiac muscle fibers • EPSP and IPSP can be fast or slow.
contract together all at the same time because • Fast EPSP: Due to influx of sodium or calcium
of the presence of Gap junctions (cell interior more positive).
• Calcium-induced calcium release (CICR): Calcium • Fast IPSP: Due to influx of chloride (cell interior
from extracellular source should come first more negative).
to release calcium from intracellular source in • Slow EPSP: Due to reduced potassium efflux (cell
cardiac muscle. interior more positive).
• Slow IPSP: Due to increase in potassium efflux
SMOOTH MUSCLE (cell interior more negative).
• Slow EPSP and IPSP are commonly seen in
• Involuntary
autonomic ganglia, cardiac and smooth muscles.
• Single unit and Multi unit—Single unit smooth
muscle has Gap junctions.
INHIBITION AND FACILITATION AT SYNAPSES
• Single unit smooth muscle is found in visceral
organs namely uterus, intestine, ureter and • Postsynaptic inhibition: Hyperpolarization is
urinary bladder. caused by the inhibitory neurotransmitters
• Multi-unit smooth muscle is found in iris, ciliary GABA and Glycine on a postsynaptic neuron.
body, epididymis, vas deferens, piloerector Also called afferent inhibition.
muscle of skin. • Presynaptic inhibition: Occurs at the presynaptic
• Blood vessels got both single unit and multi-unit terminals before the signal ever reaches the
smooth muscle in their walls. synapse by GABA. Also called lateral inhibition.
• No Z lines—equivalent is Dense bodies • Renshaw cell inhibition: Renshaw cells are
• Calmodulin—Calcium binding protein. No excited by a motor neuron. In turn, Renshaw
Troponin cells inhibit the same motor neuron which excites
it. Neurotransmitter involved is GLYCINE. Also
called “negative feedback inhibition”.
20 One Touch Physiology by Dr S Krishna Kumar

NEUROTRANSMITTERS

Some of the major neurotransmitters are as follows:

Acetylcholine • Functions as transmitter at—neuromuscular junction, autonomic ganglia,
and in postganglionic parasympathetic, basal forebrain complex, Ponto
mesencephalic cholinergic complex
• Involved in regulation of sleep-wake states, learning and memory
• Receptors: 2 types
• Muscarinic: (M1, M4, and M5-CNS), (M2-Heart), (M3-glands and smooth muscles)
• Nicotinic: (NM- neuromuscular junction), (NN- CNS and autonomic ganglia)
Norepinephrine • Location- locus coeruleus
• Activates reticular activating system
• Responsible for Awake arousal state
Dopamine • Location—Nigrostriatal system (motor movements), mesocortical system
(Ventral tegmental area nucleus accumbens for motivation and addiction) and
Tuberoinfundibular system (inhibits prolactin)
• Involved in addiction, reward
• Receptors: D1, D2, D3, D4, D5 (All are G Protein Coupled Receptors)
Serotonin • Present in highest concentration in blood platelets and in the gastrointestinal
tract
• Also, in midline raphe nuclei
• Responsible for Awake arousal state, platelet aggregation, peristalsis
Histamine • Location—posterior hypothalamus
• Responsible for awake arousal state
Glutamate • Major excitatory neurotransmitter in CNS
• Location—Hippocampus, Subthalamic Nuclei
• Important for learning and memory
GABA • Major Inhibitory neurotransmitter
• Causes hyperpolarization due to chloride influx leading to inhibition of neuronal
functions
Glycine • Both inhibitory and excitatory neurotransmitter
• Found in Renshaw cells in spinal cord
• Antagonist—Strychnine
Nitric Oxide • Gaseous neurotransmitter found in Hippocampus
• Role in learning and memory
Carbon Monoxide • Gaseous neurotransmitter produced by enzymatic degradation of heme by
heme oxygenase
• Role in learning and memory, pain processing, olfaction