NERVOUS SYSTEM

NERVOUS SYSTEM
Shri Vishnu College of Pharmacy (Autonomous)
Affiliated to Andhra Univ., Visakhapatnam; Approved by AICTE and PCI, New Delhi, and recognised by APSCHE
Prepared by
Grandhi Sandeep Ganesh
Dept. of Pharmacology

NERVOUS SYSTEM
DEFINITION
It can be defined as an organized group of
cells, called neurons, specialized for the
conduction of an impulse—an excited state—from
a sensory receptor through a nerve network to an
effector, the site at which the response occurs
The nervous system in human is made up of
brain, spinal cord, sensory organs and neurons
The nervous system maintains internal order
within the body by coordinating the activities of
muscles and organs, receives input from sense
organs, trigger reactions, generating learning and
understanding, and providing protection from
danger

CLASSIFICATION
Classification of Nervous
system

Central Nervous System (CNS):
It consists of the brain and the spinal cord, which act as the integrating and
command centers of the nervous system
They interpret incoming sensory information and issue instructions based on past
experience and current conditions.
Peripheral Nervous System (PNS):
It is the part of the nervous system outside the CNS.
They link all parts of the body by carrying impulses from the sensory receptors to
the CNS and from the CNS to the appropriate glands or muscles.
It consists mainly of the nerves that extend from the brain and spinal cord.
Cranial Nerves carry impulses to and from the brain.
Spinal Nerves carry impulses to and from the spinal cord.
CLASSIFICATION OF NERVOUS SYSTEM

SYNAPSE
 The junction between two neurons is called a
synapse.
 It is a specialized junction where
transmission of information takes place
between a nerve fibre and another nerve,
muscle or gland cell.
 It is not the anatomical continuation. But, it
is only a physiological continuity between
two nerve cells.

Structure
 A presynaptic ending that contains neurotransmitters, mitochondria and other cell
organelles
 A postsynaptic ending that contains receptor sites for neurotransmitters
 A synaptic cleft or space between the presynaptic and postsynaptic endings. It is
about 20nm wide
Functions
 The main function of the synapse is to transmit the impulses, i.e. action potential
from one neuron to another
 They allow integration, e.g. an impulse travelling down a neuron may reach a
synapse which has several post synaptic neurons, all going to different locations.
The impulse can thus be dispersed. This can also work in reverse, where several
impulses can converge at a synapse
SYNAPSE STRUCTURE AND FUNCTIONS

NEUROTRANSMITTERS
Neurotransmitters are chemical messengers that
transmit signals from a neuron to a target cell
across a synapse.
 Target cell may be a neuron or some other kind
of cell like a muscle or gland cell.
 Necessary for rapid communication in synapse.
 Neurotransmitters are packaged into synaptic
vesicles - presynaptic side of a synapse.

Synthesis: Neurotransmitters are synthesized by the enzymatic transformation of
precursors.
Storage: They are packaged inside synaptic vesicles.
Release: They are released from presynaptic terminal by exocytosis when calcium
enters axon terminal during an action potential Diffuse across the synaptic cleft to
the postsynaptic membrane.
Binding: They bind to receptor proteins.
Inactivation: The neurotransmitter is degraded either by being broken down
enzymatically, or reused by active reuptake.
STEPS IN NEUROTRANSMITTER PROCESSING

MENINGES
The meninges are three connective
tissue membranes that lie just
external to the brain and spinal cord

MENINGES
 CNS is covered by 3 membranes called meninges which are separated by 2
spaces called subdural & subarachnoid
 Meninges of brain are continuous with spinal meninges at foramen magnum. In
skull, dura is fused with periosteum of skull
 The meninges layers are
 Dura mater
 Arachnoid
 Pia mater

VENTRICLES OF THE BRAIN
Ventricles are the Communicating cavity
within the CNS that are lined by ependymal
cells, which produces, contains and
circulates CSF
The ventricular system comprises
1. Two lateral ventricles
2. 2. Single 3rd Ventricle
3. 3. Single 4th Ventricle and
4. 4. Single Terminal Ventricle
All of these are connected in series
via channels.

CEREBRO SPINAL FLUID
 Cerebrospinal fluid ( CSF) is the clear, colourless
and transparent fluid that circulates through
ventricles of brain, subarachnoid space and
central canal of spinal cord.
 It is the part of extra cellular fluid (ECF).
 CSF is formed by choroid plexus, situated with
in the ventricles
PROPERTIES
 VOLUME: 150mL
 RATE OF FORMATION: 500-600 mL per
minute
 SPECIFIC GRAVITY: 1.005

CEREBRUM
Cerebrum is the largest part of the brain
located in the cranial cavity
It is divided into 2 parts, namely
Diencephalon (central core)
Telencephalon (cerebral hemisphere)
On the surface of cerebrum large size folds
can be seen
Depressions on the surface of cerebrum
are known as Sulci
Elevations between sulci is known as
Gyri

CEREBRUM
Surfaces of cerebrum
Three surfaces:
Superolateral surface: Between Superomedial border and inferolateral border.
Medial Surface: Between Superomedial and inferomedial border.
Inferior Surface: Between Inferolateral and inferomedial border.
Three borders:
Superomedial border: between superolateral and medial surface.
Inferolateral border: between superolateral and inferior surface.
Inferomedial border: between inferior and medial surface.
Three poles:
Frontal pole: Anterior most part of cerebrum (frontal lobe)
Occipital pole: Posterior most part of cerebrum (Occipital lobe)
Temporal pole: Anterior most part of temporal lobe

CEREBELLUM
 The cerebellum (Latin for little brain) is a
region of the brain that plays an important
role in motor control..
 It is located at the back of the brain,
underlying the occipital and temporal lobes
of the cerebral cortex
 The main parts two hemispheres vermis
Fissures primary fissure horizontal fissure (
prepyramidal fissure) posterior fissure
(posteroletral fissure)
 Lobes include anterior lobe, posterior lobe
and Flocculonodular lobe
 It consists of two parts outer grey matter
cerebellar cortex cerebellar nuclei inner
white matter

CEREBELLUM
Peduncles
Superior cerebellar peduncle : Connects to
midbrain. It Contains efferent fiber systems
extending to red nucleus and thalamus.
Middle cerebellar peduncle : Connects to
pons. It Contains fiber mass orginating from
pontine nuclei and represent continuation of
corticopontine tracts.
Inferior cerebellar peduncle : Connects to
medulla. It Contains spinocerebellar tracts and
connections to vestibular nuclei.

MID BRAIN
The midbrain develops from
mesencephalon. Cells within the midbrain
multiply continually and are compressed to
form cerebral aqueduct.
 Connects the pons and cerebellum with the
forebrain.
 It is about 0.8 inch in length
 The midbrain is traversed by a narrow
channel called cerebral aqueduct filled with
CSF.

Anterior surface
 Anteriorly, it presents two large bundles of
fibers, one on each side of the midline, called
crus cerebri
 The oculomotor nerve emerges from the
medial aspect of the crus of the same side
 The crus cerebri bounds the interpeduncular
fossa on either side.
MID BRAIN

MID BRAIN
 Posteriorly, the midbrain presents four rounded swellings called colliculi- One
Superior and inferior colliculi on either side.
 Each colliculus is laterally related to a ridge called brachium
 Superior and inferior brachium arises from respective colliculi
 Superior brachium connects the superior colliculus to lateral geniculate body
 Inferior brachium connects the inferior colluculus to medial geniculate body
 In the midline below the inferior colliculus, the trochlear nerve emerges which
then winds round the side of the midbrain to reach its ventral aspect

THALAMUS
Thalamus (Greek) means “inner chamber” or “meeting place”

THALAMUS
It acts as a relay station that modulates and coordinates the function of various
systems
Locus for integration, modulation and intercommunication between various
systems
Its has important motor, sensory, arousal, memory, behavioural, limbic and
cognitive functions
The largest source of afferent fibres to thalamus is cerebral cortex and cortex is
the primary destination for projection fibres from the thalamus

HYPOTHALAMUS
 Hypothalamus is described as “The Head ganglion
of the autonomic nervous system” by
“Sherrington”
 Stimulation of the hypothalamus produces
autonomic response
 It is a small bilateral structure extends from the
region of the optic chiasma to the caudal border of
the mammillary bodies
 It lies below the Thalamus
 Forms the floor and inferior part of the lateral
walls of the 3rd ventricle
 It is an integrative center for regulation of
cardiovascular system, body temperature, food and
water intake and endocrine secretion
 HT is only 0.3% of brain weight (10 gms)

HYPOTHALAMUS
Hypothalamic nuclei
 It is typically divided into 4 regions from rostral to caudal
 Pre optic area
 Supra optic area (anterior)
 Tuberal area (middle )
 Mamillary area ( posterior)

BASAL GANGLIA
 It is the Collection of masses of gray matter
situated within each cerebral hemisphere
 They are paired & located between thalamus
and white matter
 It Consist of 5 pairs of nuclei: These are
 Caudate nucleus
 Putamen
 Globus pallidus
 Substantia nigra
 Subthalamic nucleus

BASAL GANGLIA
Two main circuits are
 The Putamen Circuit For executing learned patterns of movement
 The Caudate Circuit For Cognitive Control of Sequences of Motor Patterns
 The term cognition means the thinking processes of the brain, using both
sensory input to the brain plus information already stored in memory. Most of
our motor actions occur as a consequence of thoughts generated in the mind, a
process called cognitive control of motor activity. The caudate nucleus plays a
major role in this cognitive control of motor activity.

FUNCTIONS OF BASAL GANGLIA
 Function in association with the corticospinal system to control complex patterns
of motor activity(cutting paper with scissors, hammering nails, shooting a
basketball through a hoop, passing a football, throwing a baseball etc.
 Cognitive control of motor activity e.g. if a person comes across a lion he will
subconsciously plan
 Turning away from the lion,
 Beginning to run, and
 Even attempting to climb a tree
 To Change the Timing and to Scale the Intensity of Movements
 A lesions of the posterior parietal cortex produce an inability to accurately
perceive objects through normally functioning sensory mechanisms, a
condition called agnosia.

REFLEXES
 The Reflex Arc is an automatic, rapid response to an adverse stimulus.
 Action is involuntary the brain is not involved in the event but may be informed
of it
 Many reflex actions are protective
 Some complex actions (swallowing, coughing and blinking) are coordinated by
reflexes.
Five Essential Components to the Reflex Arc
 Receptor – detects the stimulus
 Afferent (sensory neuron) – transmits impulses to the CNS
 Integration center – consists of one or more synapses in the CNS
 Efferent (motor neuron) – conducts impulses from integration center to an
effector
 Effector – muscle or gland cell, Responds to efferent impulses, Contraction or
secretion

TYPES OF REFLEXES
 Monosynaptic reflex – simplest of all reflexes
 Just one synapse
 The fastest of all reflexes
 Example – knee-jerk reflex
 Polysynaptic reflex – more common type of reflex
 Most have a single interneuron between the sensory and motor neuron
 Example – withdrawal reflexes

OLFACTORY NERVE
 Component: Sensory
 Function: Smell
 Origin: Olfactory receptor nerve cells
 Opening to the skull: openings in
cribriform plate of ethmoid

OPTIC NERVE
 Function: Vision
 Origin: Back of the Eyeball
 Opening to the skull: Optic Canal

OCCULOMOTOR NERVE
 Component: Motor
 Function:
 Raises upper eyelid
 Turns eyeball upward, downward and
medially
 Constricts pupil
 Accommodated the eye
 Origin: Anterior surface of the midbrain
 Opening to the skull: Superior orbital
fissure

TROCHLEAR NERVE
 Function: Assisting in turning eyeball
downward and laterally
 Origin: Posterior surface of the midbrain
fissure

TRIGEMINAL NERVE
 Component: Motor and sensory
 Function:
Opthalamic: sensory information from
the upper part of your face
Maxillary: sensory information from
the middle part of your face including your
cheeks, upper lip, and nasal cavity
Mandibular: It sends sensory
information from your ears, lower lip, and
chin. It also controls the movement of muscles
within your jaw and ear.
 Origin: midbrain and medulla oblongata

 Function: Lateral rectus muscle turns
eyeball laterally
 Origin: Medulla oblongata
fissure
ABDUCENT NERVE

 Component: Mixed
 Function:
 Muscles of the face and scalp
 Stapedius muscle
 Posterior belly of diagastric
 Opening to the skull: Interior acoustic
meatus, facial canal, stylomastoid
foramen
FACIAL NERVE

 Function:
 Vestibular – Saculae, saccule,
semicircular canals – positions of
head
 Cochlear – Organ of Corti - hearing
 Opening to the skull: Interior acoustic
meatus
VESTIBULOCOVHLEAR NERVE

 Component: Mixed
 Function:
 Motor: Assists swallowing
 Sensory: Taste, tongue and pharynx
 Opening to the skull: Jugular foramen
GLOSSOPHARYNEGEAL NERVE

 Function:
 Heart and great thoracic blood vessels
 Larynx, trachea, bronchi and lungs
 Alimentary tract from pharynx to
splenic flexure of colon
 Liver, kidney, pancreas
VAGUS NERVE

 Function:
Cranial root
 Muscles of soft palate
 Muscles of pharynx
 Muscles of larynx
Spinal root
 Sternocleidomastoid and trapezius
muscle
ACCESSORY NERVE

 Function: Muscle of tongue
 Opening to the skull: Hypoglossal canal
HYPOGLOSSAL NERVE

Action Potential
Na+
ACH
Acetylcholinesterase
Na+
Preganglionic neuron
Nicotinic
Receptor
PARASYMPATHETIC GANGLIONIC SYNAPSE

Action Potential
Na+
ACH
K+
G
Postganglionic neuron
Muscarinic
Receptor
PARASYMPATHETIC ORGAN SYNAPSE

Action Potential
Na+
ACH
Na+
Preganglionic neuron
Nicotinic
Receptor
SYMPATHETIC GANGLIONIC SYNAPSE

Action Potential
Na+
NE
Postganglionic neuron
Adrenergic
Receptor
SYMPATHETIC ORGAN SYNAPSE

Summary of parasympathetic neurons and
synapses
• Preganglionic neurons
• Long
• Synapse with postganglionic
• neurons at or near organ
• Release acetylcholine (ACH) to activate
nicotinic receptors on postganglionic
neurons
• Postganglionic neurons
• Short
• Synapse on the target organ
muscarinic receptors on the target organ
Summary of sympatheticneurons and
synapses
• Preganglionic neurons
• Short
• Synapse with postganglionic
• neurons near spinal cord
nicotinic receptors on postganglionic
neurons
• Postganglionic neurons
• Long
• Synapse on the target organ
• Release norepinephrine to activate adrenergic
receptors on target organs
ANS SUMMARY

• Sympathetic Stimulation (Fight or Flight)
– ↑HR, BP,blood flow
– Diffuse distribution (more than one organinnervated)
• Parasympathetic Stimulation (Rest & Digest)
– Maintaining homeostasis
– Discrete distribution/activation
• Role of CNS
– Reflex Arcs : Afferent input ~ hypothalamus, medulla oblongata,and
spinal cord ~ efferent reflex impulse via ANS
– Emotions:
• Innervation by ANS
– Dual
– Only sympathetic (adrenal medulla, kidney, pilomotor muscles,and
sweat glands)
FUNCTIONS

Branch Type Location
TypicalAgonist
Drugs
Sympathetic
(adrenergic)
α1
Most vascular arterioles, Sphincters of bladder Norepinephrine
& GI tract, Iris dilator Epinephrine
TypicalAntagonist
Drugs
Phenoxybenzamine
Phentolamine
Prazosin
α2 GI tract, presynaptic sympathetic neurons Yohimbine
β1 Heart muscle, Salivary glands, Fat cells
Clonidine
Epinephrine
Norepinephrine
Isoproteronol
Dobutamine
Epinephrine
"Beta blockers"
Propranolol
Metoprolol
β 2
Bronchioles of lung, Arterioles of skeletal
muscles, brain and lungs, Bladder wall, GIT
Epinephrine
Isoproteronol
Albuterol
"Beta blockers"
Propranolol
Butoxamine
Parasympathetic
(cholinergic)
M Bronchioles of lung, Sweat glands Iris
constrictor
Heart muscle, Sphincters of bladder & GI tract Acetylcholine
Atropine
Scopolamine
N Neuromuscular junctions, Autonomic ganglia
Muscarine
Carbachol
Acetylcholine
Nicotine
Carbachol
Curare

NERVOUS SYSTEM

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