Download II. ORGANIZATION OF THE HUMAN NERVOUS

THE NERVOUS SYSTEM
I. NERVOUS SYSTEM FUNCTION - “I think; therefore, I am.” (pp. 897-900)
Responsible for maintaining _homeostasis_________ in the body by sending and receiving
information via _electrical___ impulses. The advantage to an electrical message system is
that it is _faster___.
II. ORGANIZATION OF THE HUMAN NERVOUS SYSTEM (pp. 787-791)
A. The Central Nervous System or _CNS___
Made up of the _brain____ and the _spinal cord__________. The spinal cord
acts as a “super highway” connecting the _body____ and _brain_____. There
are three means of protection:
1. Bones – _Cranium__ protects the brain; _vertebrae_____ protect the spinal cord
2. Meninges - _3___ layers of tough, elastic tissue that _cushions______ the brain
and spinal cord.
3. Cerebrospinal Fluid – Found between the meninges to provide further cushioning
B. The Peripheral Nervous System or _PNS____
The PNS is composed of _nerves___, which are bundles of nerve cells.
C. The Sensory Organs
(pp. 792-795)
1. Touch - Response to a _mechanical____ stimulus. The _skin____ is the largest
sensory organ. Sensory receptors detect pressure, pain, heat, cold.
2. Smell - Response to a _chemical_____ stimulus. Sensory receptor cells are
bathed in mucus and respond to different chemicals.
3. Taste - Response to a _chemical____stimulus. Sensory receptors called _taste buds____
are located on the _tongue___. Detect sweet, sour, salty, bitter.
4. Vision – Response to a _light___ stimulus.
 Cornea – Light first passes through the _cornea_____, a transparent, protective
covering which begins _focusing___ the light. The light then enters a chamber
filled then enters a chamber filled with watery fluid called the _aqueous
humor______.
 _Pupil____ - Hole that light passes through. The size of the pupil is controlled by
a ring of muscles known as the _iris___.
 _Lens____ - Completes focusing of the light ray. There is also a thick jelly-like
substance to help maintain the shape of the chamber known as the _vitreous
humor______.
 Retina – Nerve tissue at the back of the eyeball that converts light energy to an
_electrical impulse____. Made up of two types of cells:
o Rods - Cells that detect _shape & movement______; are stimulated
even in _dim___ light.
o Cones - Cells that detect _color____; provide a _sharp_____ image;
require _bright ____ light for stimulation.
 Optic Nerve - Transmits the impulse to the _brain___.
 Additional Structures
o Sclera - _”White of the eye”________; continuation of the _cornea____
o Choroid - Layer of blood vessels that _nourish_____ the eye.
5. Hearing - Response to a mechanical stimulation - _sound_____ waves.
 Sound waves first enter the outer ear and are funneled into the _auditory canal__.
 Causes vibrations of a membrane known as the _tympanic membrane_______ or
_eardrum______.
 Vibrations are then passed to three tiny bones →
o _hammer________________
o _anvil___________________
o _stirrup__________________
 The vibrations are transferred from the _stirrup____ to another membrane known
as the _oval window_______.
 Finally, vibrations are converted to an electrical impulse in the _cochlea_______,
a snail-shaped sensory structure filled with fluid and tiny hairs. These hairs are
pushed back & forth, producing electrical impulses.
 Nerve impulse is transmitted by way of the _auditory nerve_______ to the
_brain_____.
 The semicircular canals are also found in the ear. They play no role in hearing;
instead, they help maintain _balance______. The semicircular canals consist of
_3___ fluid-filled canals oriented at different angles to each other.
III. NERVE IMPULSE TRANSMISSION
The cells that make up the nervous system are known as _neurons_________. They are
_specialized______ cells capable of creating an _electrical______ impulse.
A. Types of Neurons – There are three types of neurons:
 Sensory Neurons – Transmit impulses from the _body____ to the _brain_____ and
_spinal cord______.
 Motor Neurons – Transmit impulses from the _brain___ and _spinal cord______ to
the _brain______.
 Interneurons - _Connection______ between sensory and motor neurons. Located
in the _brain____ and _spinal cord______ only.
B. Structure of a Neuron
 Dendrite – Short, branched extensions that first receive stimulus; act as _antenna,
detectors________
 Cell Body – Contains the _nucleus______. Site of _metabolic_____ activity.
Receives impulse from _dendrite______.
 Axon – Transmits impulses _away from the cell body______ to next cell. Usually a
long, single fiber with many small tips called _axon terminals_________.
 Schwann Cells – Wrap around the axons of many neurons to form insulating
layers known as a _myelin sheath_______; _insulate______ and _protect_____
the neuron. There are small gaps in the myelin sheath along an axon called
_nodes_____. The electrical impulse _hops___ from node-to-node, allowing
the impulse to _travel faster____.
C. Nerve Impulse Transmission
The _electrical____ impulse moves through the neuron in one direction → _dendrite____ →
_cell body___ → _axon_____ until it reaches an _axon terminal____. There is a small space
between the neuron and the next cell called a _synapse______. Chemicals known as
_neurotransmitters_______ are released to carry the impulse across the synapse to the
next cell.
IV. A CLOSER LOOK AT THE HUMAN BRAIN
A. Cerebrum
 _Largest____ part of the brain
 Composed of two _hemispheres_____ or sides.
 _Corpus callosum____________
o Connects the right and left hemispheres
o Maintains __communication___ between them
 Divided into regions called _lobes______; associated with specific functions
 Controls _conscious activities, intelligence, memory, emotions_________
B. Cerebellum
 Regulates _posture and balance______
 Coordinates _voluntary, skeletal___ muscle movement
C. Brain Stem
 Composed of the _pons, midbrain, and medulla oblongata________.
o Pons and midbrain act as _pathways____ connecting different parts of the
brain.
o Medulla oblongata controls _involuntary____ activities, such as
_breathing, heart rate, blood pressure___________
D. Thalamus
 _”Telephone Operator”___________
 Main location for _sensory processing____
E. Hypothalamus
 Controls many activities relating to _homeostasis____ such as _hunger, thirst, body
temperature_________
F. Glands in the Brain
Although the following glands are located in the brain, they are not part of the nervous
system. They are part of the _endocrine_____ system.
 Pituitary Gland - _”Master Gland”_____. Releases _hormones___ that regulate
other endocrine glands.
 Pineal Gland – Light-sensitive gland that secretes hormone called _melatonin___;
regulates _”internal clock”________.
V. DISEASES & CONDITIONS OF THE NERVOUS SYSTEM
(pp. 798-799)
A. Meningitis – Infection of _meninges_______. Symptoms include severe headache,
stiff neck, fever.
B. Alzheimer’s Disease – Disease of the elderly in which there is a build-up of protein plaques
on neurons in the _cerebrum_______. Results in progressive death of neurons.
Symptoms include memory loss, confusion, emotional disturbances.
C. Parkinson’s Disease – Disabling disease due to a decrease in _neurotransmitters________
which transmit impulses for movement. Results in tremors, muscle rigidity.
D. Multiple Sclerosis – Disease of young adults characterized by destruction of _myelin_____
_sheaths_____ of neurons. Normal nerve function is impaired. Symptoms include
numbness, muscle weakness, muscle fatigue, vision problems.