HUMAN SYSTEMS:
NERVOUS SYSTEM
& SENSE ORGANS
NERVOUS SYSTEM
THE NERVOUS SYSTEM

Need for communication

Communication is required for coordination

Gather information
Process information
Respond accordingly


THE NERVOUS SYSTEM

Nervous system has two parts (central and peripheral)


Central nervous system (CNS) – brain and spinal cord
Peripheral nervous system (PNS) – other parts of the nervous system

The CNS processes and responds to all messages coming from
the peripheral nervous system

The PNS connects all parts of the body to the CNS
It uses specialized structures called nerves to carry information
between body and CNS

THE NERVOUS SYSTEM
NEURONS
Nervous system is made up of cells known as
nerve cells or neurons
 Cell body, axon and dendrites
 Nerve cells are connected to each other

NERVES

A nerve is a collection of axons bundled together with
blood vessels and connective tissue

Nerves are found everywhere in the PNS

Most nerves have axons of both sensory neurons and
motor neurons
NERVES
PERIPHERAL NERVOUS SYSTEM



Sensory neurons – gather information
Special nerve endings called as receptors
Motor neurons – send impulses from brain and spinal
cord to other parts of the body e.g. muscle, sweat
glands etc.
PERIPHERAL NERVOUS SYSTEM



PNS has two types of motor neurons – somatic and
autonomic
Somatic - under conscious control (voluntary
movements such as writing, talking, smiling, or
jumping)
Autonomic - controls body functions that you do not
think about, such as digestion and heart rate



Maintain body’s functions in balance
Depending on the situation, the autonomic nervous system
can speed up or slow down these functions
The autonomic nervous system has two divisions: the
sympathetic nervous system and the parasympathetic
nervous system
PERIPHERAL NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM



The central nervous system receives information from
the sensory neurons
Then it responds by sending messages to the body
through motor neurons in the PNS
Made up of brain and spinal cord
BRAIN

Largest organ in the nervous system
Different parts perform different functions

Cerebrum






Largest part of the brain
Controls voluntary movements
It also allows to sense touch, light, sound, odors, taste, pain,
heat etc.
The cerebrum is made up of two halves, called hemispheres.
The left hemisphere directs the right side of the body, and
the right hemisphere directs the left side of the body
BRAIN
BRAIN

Cerebellum



The second largest part of your brain
and lies beneath the back of the
cerebrum
The cerebellum processes sensory
information from the body, such as from
skeletal muscles and joints
This allows the brain to keep track of the
body’s position
BRAIN

Medulla
 The medulla connects brain to the spinal cord
 Controls involuntary processes such as involuntary
breathing, the regulation of blood pressure and
heart rate
 Medulla constantly receives sensory impulses from
receptors in blood vessels and uses this
information to regulate blood pressure
 The medulla also sends impulses to the heart to
make the heart beat faster or slower
BRAIN
SPINAL CORD

Spinal cord






It is made of neurons and bundles of axons that pass impulses
to and from the brain
The spinal cord is surrounded by protective bones called
vertebrae
The axons in spinal cord allow the brain to communicate with
PNS
The axons of sensory neurons in skin and muscles carry
impulses to the spinal cord
The spinal cord relays these impulses to the brain
The brain interprets these impulses as pain, temperature, or
other sensations and responds to the situation
SPINAL CORD
SPINAL CORD
 Spinal
 May
cord injury
block information flow to and from the
brain
 Paralysis
SENSE ORGANS
SENSE OF TOUCH

Skin – integumentary system (which includes hair,
skin, nails)
Protect body from damage
Glands and receptors

Reflex

Skin and feedback mechanism
(Body temperature)


SENSE OF SIGHT



Eyes detect light and brain forms visual images
Cornea and retina
Mechanism of vision
SENSE OF SIGHT


Reacting to light – role if iris
Focusing light
SENSE OF HEARING





Sound and vibrations
Ear – outer, middle and inner
Outer ear
 Pinna and ear canal
Middle ear
 Tympanic membrane or ear drum
 Bones (hammer, anvil and stirrup)
Inner ear
 Cochlea and auditory nerve
 Fluid and balancing body
SENSE OF HEARING
SENSE OF TASTE





Taste is the sense that detects chemicals and to
distinguish flavors
The tongue is covered with tiny bumps called papillae
which contain taste buds
Taste buds contain clusters of taste cells, the receptors
for taste . They respond to dissolved-food molecules
Taste cells react to five basic tastes: sweetness (sugar),
sourness (lemon), saltiness (salt), savoriness (meats
and cheeses), and bitterness (some medicines)
When the brain combines information from all of the
taste buds, you taste a “combination” flavor
SENSE OF TASTE
SENSE OF SMELL






The receptors for smell are located on olfactory cells in the
upper part of your nasal cavity
An olfactory cell is a nerve cell that responds to chemical
molecules in the air. You smell something when the receptors
react to molecules that have been inhaled
The molecules dissolve in the moist lining of the nasal cavity and
trigger an impulse
Olfactory cells send those impulses to the brain, which interprets
the impulses as odors
Taste buds and olfactory cells both detect dissolved molecules
The brain combines information from both senses to give
sensations of flavor.
SENSE OF SMELL