The central nervous system is comprised of the brain and spinal cord and controls the body's responses by receiving sensory information. Neurons are electrically excitable cells that communicate via synapses. There are different types of neurons including afferent, efferent, and interneurons. The peripheral nervous system connects the central nervous system to organs and skin through nerves and is divided into the somatic and autonomic nervous systems. The autonomic nervous system regulates involuntary functions through the sympathetic and parasympathetic systems. The skin contains various receptors that detect temperature, pressure, pain and interact closely with the nervous, endocrine and immune systems.

1. Neurobiology

2.  The early central nervous
system begins as a
simple neural plate that
folds to form a neural
groove and then neural
tube. This early neural is
initially open initially at
each end forming
the neuropores. Failure of
these opening to close
contributes a major class of
neural abnormalities
(neural tube defects).

3. Aneuron or nerve cell is an electrically excitable cell that
communicates with other cells via specialized connections
called synapses.
A typical neuron consists of a cell body (soma), dendrites, and a
single axon.

4. Functional classification
 Afferent neurons convey
information from tissues
and organs into the central
nervous system and are also
called sensory neurons.
 Efferent neurons (motor
neurons) transmit signals
from the central nervous
system to the effector cells.
 Interneurons connect
neurons within specific
regions of the central
nervous system.

5. SYNAPSE
In the nervous system, a synapseis a structure that permits a neuron (or nerve cell) to
pass an electrical or chemical signal to another neuron or to the target effector cell.

6.  Neuron affects other neurons by releasing a
neurotransmitter that binds to chemical receptors. The
effect upon the postsynaptic neuron is determined by
the type of receptor that is activated, not by the
presynaptic neuron or by the neurotransmitter.
 A neurotransmitter can be thought of as a key, and a
receptor as a lock: the same neurotransmitter can
activate multiple types of receptors.
 Receptors can be classified broadly
as excitatory (causing an increase in firing
rate), inhibitory (causing a decrease in firing rate),
or modulatory (causing long-lasting effects not

7.  Holinergic neurons—acetylcholine. Acetylcholine is
released from presynaptic neurons into the synaptic
cleft. It acts as a ligand for both ligand-gated ion
channels and metabotropic (GPCRs) muscarinic
receptors. Nicotinic receptors are pentameric ligand-
gated ion channels composed of alpha and beta
subunits that bind nicotine.
 GABAergic neurons—gamma aminobutyric acid.
GABA is one of two neuroinhibitors in the central
nervous system (CNS), along with glycine. GABA has a
homologous function to ACh, gating anion channels
that allow Cl− ions to enter the post synaptic neuron.

8. :
Major neurotransmitters
 Amino acids: glutamate, aspartate, D-serine, gamma-
Aminobutyric acid (GABA),[nb 1] glycine
 Gasotransmitters: nitric oxide (NO), carbon monoxide
(CO), hydrogen sulfide (H2S)
 Monoamines: dopamine (DA), norepinephrine
(noradrenaline; NE, NA), epinephrine (adrenaline),
histamine, serotonin (SER, 5-HT)
 Trace amines: phenethylamine, N-
methylphenethylamine, tyramine, 3-iodothyronamine,
octopamine, tryptamine, etc.
 Peptides: oxytocin, somatostatin, substance P, cocaine

9. The central nervous system
 The central nervous
system (CNS) is comprised
of the brain and spinal
cord. The CNS receives
sensory information from
the nervous system and
controls the body's
responses. The CNS is
differentiated from the
peripheral nervous
system, which involves all
of the nerves outside of
the brain and spinal cord

10. Peripheral Nervous System
 The peripheral nervous
system (PNS) is the
division of the nervous
system containing all the
nerves that lie outside of
the central nervous
system (CNS). The
primary role of the PNS is
to connect the CNS to the
organs, limbs, and skin.
These nerves extend from
the central nervous
system to the outermost
areas of the body.

11.  The Autonomic Nervous System
 The autonomic system is the part of the peripheral
nervous system that's responsible for regulating
involuntary body functions, such as blood flow,
heartbeat, digestion, and breathing.
 In other words, it is the autonomic system that
controls aspects of the body that are usually not under
voluntary control. This system allows these functions
to take place without needing to consciously think
about them happening. The autonomic system is
further divided into two branches:
 Parasympathetic system: This helps maintain

13.  The skin is the most densely innervated organ in the
body and there is a close relationship between the skin
and the nervous system. Monodirectional and/or
bidirectional pathways exist in which the central and
peripheral nervous system, endocrine and immune
system, and almost all skin cells are involved.

14.  The interaction between peripheral nerves and
immune system is mediated by different types of
cutaneous nerve fibers which release neuromediators
and activate specific receptors on target cells in the
skin such as keratinocytes, mast cells, Langerhans
cells, microvascular endothelial cells, fibroblasts, and
infiltrating immune cells.

15.  These interactions influence a variety of physiologic
and pathophysiologic functions including cellular
development, growth, differentiation, immunity,
vasoregulation, leukocyte recruitment, pruritus, and
wound healing. Information is emerging about the
factors involved in these immunomodulatory
mechanisms. Recent findings have established a
modern concept of cutaneous neurobiology.

16.  Nerve bundles, together with arterioles and venules,
are found in great quantity in neurovascular bundles
of the dermis. Meissner corpuscles, found in the
dermal papillae, help to mediate touch and are found
predominantly on the ventral sides of the hands and
feet. Meissner corpuscles occur in greater abundance
on the hands, with greatest concentration in the
fingertips.
 Vater-Pacini corpuscles are large nerve-end organs
that generate a sense of pressure and are located in the
deeper portion of the dermis of weight-bearing
surfaces and genitalia. They also are found commonly

17.  SKIN RECEPTORS
 Types According to Function/ Stimulus Modality: 1.
Thermoreceptors – for temperature changes
 2. Mechanoreceptors – for mechanical stimulation.
 a) Tactile receptors – touch
 b) Baroreceptors – pressure
 c) Proprioceptors – distortion

18.  3. Nociceptors – for injuries leading to pain sensation.

19.  Types According to Morphology:
 1. Free nerve endings – nonmyelinated fibers that
enters the epidermis, extending as far as the stratum
granulosum.
 a) Merkel’s ending – free nerve ending attached to
modified epidermal cells, found in the stratum
germinativum layer.

20.  2. Encapsulated nerve endings
 a) Pacinian corpuscles – deep pressure
 b) Meissner’s corpuscles – touch
 c) Ruffini’s corpuscles – heat/warmth
 d) Krause’s corpuscles - cold

23. • Neuronal Control of Skin Function: The Skin as a
Neuroimmunoendocrine Organ
https://doi.org/10.1152/physrev.00026.2005

24.  FIG. 1. The skin as a neuroimmunoendocrine organ.
The skin is associated with the peripheral sensory
nervous system (PNS), the autonomous nervous
system (ANS), and the central nervous system (CNS).
1) Various stressors activate the
hypothalamus/hypophysisis within the CNS which
results in the 2) release of neuromediators such as
corticotropin-releasing hormone (CRH), melanocyte
stimulating hormone (MSH), pituitary adenylate
cyclase activating polypeptide (PACAP), or MIF, for
example. They may stimulate either the release of 3)
norepinephrine and cortisol from the adrenal glands

25.  Skin neuroendocrine system regulates global (A
and B) and local (B) homeostasis. In response to
noxious stimuli, the skin mounts progressive,
intensity-dependent, highly coordinated
responses.
 The generated signals travel through humoral or
neural pathways to reach the central nervous
system, immune system, and other organs.