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Origin of


Dr. Ravi Wijesiriwardana

Out Line:
Excitable Cells

Functional organization of Nervous system

Bioelectric phenomena at cellular level

Hodgkin and Huxley Model

Body surface potentials

A cell type is a classification used to distinguish between morphologically or phenotypically distinct cell forms within a species.
A multicellular organism may contain a number of widely differing and specialized cell types, such as muscle cells and skin cells
in humans, that differ both in appearance and function yet are genetically identical. Cells are able to be of the same genotype,
but different cell type due to the differential regulation of the genes they contain
Cells of Human Body:
Different Types of cells in the human body (based on tissue formation) Types of cells in human body (based on their function)
1.Bone cells (Osteocytes) They are the toughest body Cell as they are bound together by calcium and phosphate. 9. Conductive cells: Nerve cells, muscle cells come under this category. They have internal ability to conduct an
As you knows they give strength, support and frame-work to the body by enclosing organs in skeletal system electric impulse from region to other distant region in the body.
i.e bones. 10. Connective cells: Bone cells, blood cells come under this category. They help connect other cells and tissues.
2. Cartilage cells (chondrocytes) These cells are similar to bone cells but the surrounding material is just loose and 11.Glandular cells: These cells secretory cells. They form glands like pancreas,salivary glands etc and help
flexible compared to those of bone cells. Hence they are freely bendable. They are present in ear bone (hence ears in production of enzymes, hormones etc.
are fold-able), in between large bones to help them bend and move freely like in between two ribs, spinal bones, 12. Storage cells: Adipose cells, some liver cells etc act to store materials like fat for later use. This fat is consumed
joints etc. in time of starvation and also in excess cold temperatures.
3. Nerve cells: These cells are very long and have many branching at either ends. Their specialty is they never 13. Supportive cells: These are the cells which are present as support to adjacent cells. Ex: Glial cells in the brain
multiply in ones life time.They are present all over the body and are sometimes as long as few meters long. They and spinal cord help provide nourishment to the nerve cells and also protect them from shocks and trauma.
are human brain cells and are found in plenty in brain and the spinal cord and form the nervous tissue. 14. Special type of cells: These are specialized cells with important functions in the body. They are
4. Epithelial cell: These cells are very simple cells which form covering of other cells. These cells form covering a) Sperms: These cells unlike others are haploid (i.e. have only one set of chromosome). They are present only in
layers of all the organs and hence are preset in skin, scalp, respiratory tract, in the buccal cavity surface etc. Ex: Skin the males after puberty. These cells have a tail which enables them to swim and move in the female uterus. They
cells, mucous cells. have an enzyme namely hayaluronidase which helps them penetrate through uterine tissue and reach oocytes.
5.Muscle cells: These cells are of muscle tissue mostly long, large and have ability to contract and relax providing b) Oocytes: Cells are haploid and present in adult female genital system. They are also haploid like sperms. They
movements. They are three types as skeletal, cardiac and smooth muscles. start to form after puberty and continue so till the stage of menopause. They accept sperm cells to form zygote
(fertilized egg). This further grows in the uterus to form a baby.
6 Secretory cell: These cells as name indicates are secretory in nature. They form glands and secrete something
c) Stem cells: These are basic cells or parent cells which can differentiate into any cell based on the requirement.
important ex; pancreatic cells which secrete insulin, glucagon, salivary gland secrete salivary amylase, sebaceous
These stem cells in human body are given so importance due to their promising role in treatment of disorders in
gland secrete oil on the skin etc.They are found in all secretory organs.
7.Adipose cells: These are fat cells and are storage in nature to store fat. Especially seen in the soles, palms, bums
d) Rods & cones: These cells are in eye and have capacity to capture image color and light.
etc. They reduce friction to the body.
e) Ciliated cells: These cells are present as lining of respiratory tract, esophagus etc. and have a pointed thread like
8. Blood cells: These cells include RBCs, WBC, Thormbocytes etc. They are always motile and never stay in one
cilia which move in one particular direction to pass material.
place. They have limited life span and they never multiply to form new cells. Instead new cells are formed from
Human tissue types are again dependent on the types of cells involved in their formation.
other cells.
f) Blood cells: These are quite interesting cells and they are never attached to one another. Blood cells freely flow
in the liquid blood. Some of them are not alive (RBCs) while others have varied shapes like WBC, platelets (spindle
shape). Further these WBCs are of different types. Of them macrophages have ability to eat (gulp) any foreign
particle like bacteria in the body. Hence they are body defense cells.
There is no big difference in between cells of animals and humans while that of animal and plant cells have a lot
Types of cells in human body (based on their electrical excitability)

Excitable cells
Non-excitable Cells
Excitable Cells:
Electrochemical activities of certain class of cells produce changes in electrical potential difference between the inter and extra
cellular medium and generates all or nothing electrical pulse (action potential)
Nerve cells (sensory , motor and processing)
Motor cells (kind of actuators controlled by Pulse modulation )
Glandular cells ( also a Kind of actuator controlled by Pulse modulation)

very thin (7-15 nm) lipid-protein complex

transmembrane ion channels (pores) allow flow of ions across the membrane
like a leaky capacitor: a thin dielectric material acts as a charge separator
impermeable to intracellular protein and other organic anions
selectively permeable to sodium (Na+) potassium (K+) and chlorine (Cl-)ions
ion concentration difference across membrane creates a diffusion gradient
ions flow, creating an electric field that opposes flow, until an equilibrium is established
similar to p-n junction, ions flow by diffusion and create a potential difference which inhibits
further flow of charged ions
The CNS is made up of the brain and spinal cord

brain stem
The part of the brain that connects the spinal cord to the forebrain and cerebrum.
Part of the hindbrain in vertebrates. In humans it lies between the brainstem and
the cerebrum, and plays an important role in sensory perception, motor output,
balance, and posture.
spinal cord
A thick, whitish cord of nerve tissue that is a major part of the central nervous
system. It extends from the brain stem through the spine, with nerves branching off
to various parts of the body.
In humans it is the largest part of the brain and is the seat of motor and sensory
functions, as well as the higher mental functions such as consciousness, thought,
reason, emotion, and memory.
Brain Stem
The brain stem is connected to the underside of the brain. It consists of the midbrain, pons, and medulla. The midbrain is
found in between the hindbrain and the forebrain. It regulates motor function and allows motor and sensory information to
pass from the brain to the rest of the body. The pons houses the control centers for respiration and inhibitory functions. The
medulla also helps regulate respiration, as well as cardiovascular and digestive functioning.
The cerebrum, or the top portion for the brain, is the seat of higher-level thought. It is comprised of two hemispheres, each
controlling the opposite side of the body. Each of these hemispheres is divided into four separate lobes:
the frontal lobe, which controls specialized motor control, learning, planning, and speech;
the parietal lobe, which controls somatic or voluntary sensory functions;
the occipital lobe, which controls vision;
the temporal lobe, which controls hearing and some other speech functions.
In humans, the cerebellum plays an important role in motor control,
and it may also be involved in some cognitive functions such as
attention and language as well as in regulating fear and pleasure
The limbic system is the emotional brain made of deep gray Cingulate gyrus is involved with shifting thoughts, expressing
matter structures linked together by the fornix. The fiber tracts emotions through gestures and resolving frustration.
have the appearance of oval fibers and looks like the corpus
callosum but its not the same. The limbic system also includes The amygdala (fear and its sympathetic response) and
certain structures of the diencephalon: the anterior thalamus hippocampus (form and retrieve memories) reside very close
and hypothalamus. together.

The hypothalamus in the middle of all this stuff has a direct

between fearful stuff, memories and the autonomic nervous
system. Its a very strong anatomical connection.
Human Nervous system:
Neural Networks: Averagely 100 Billion Neurons each neuron
connects to surrounding neurons by 10,000 synapses.
Neuron :
Ion Channels and Membrane Voltage:
Membrane Voltage changes due to external stimuli due to the changes
Facilitated diffusion and transport
in the ion concentrations in the extra and itra celleular mediums.

Ion Pumps ( active channels use ATP Hydrolysis )

Ion Channels ( passive channels)

Ligand-gated channels (Ach GABA neurotransmitters are present)

Membrane Voltage-dependent channels

Action Potential :

Two states can be Identified

Resting state and action state.
Propagation of Action Potential:
OR Millman Equation
Resting Action
95% 16%

1% 80%

2% 2%

Propagation of Action Potential :
Hodgkin Huxley Model:
Axon Model
Voltage Clamp Measurement:
Hodgkin Huxley Model: Continued
Hodgkin Huxley Model: Continued
Channels consists of Gates:
Individual can be permissive or non permissive

n n

Steady state

Time constant

Hodgkin Huxley Model: Continued
Hodgkin Huxley Model: Continued
Hodgkin Huxley Model: Continued

t t
Note cable equation
Recording of Bioelectrical Phenomena:
Body surface electrodes measurements are used

Electrocardiogram (ECG)

Electroencephalogram (EEG)

Electroneurogram (ENG)


Electroretinogram (ERG)