Download Unit 12 - Nervous System

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 _very fast!_.
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 _brain_____ and _body__. There
are three means of protection:
 Bones – _Cranium____ protects the brain; _Vertebrae____ protect the spinal cord
 Meninges - _3___ layers of tough, elastic tissue that _cushion______ the brain
and spinal cord.
 Cerebrospinal Fluid – Found between the meninges to provide _additional
cushioning__________
B. The Peripheral Nervous System or _PNS_______
The PNS is composed of _nerves_____, which are bundles of nerve cells. There are 2 divisions in
the peripheral nervous system.
 Somatic PNS – Regulates activities under _conscious_______ control, meaning
_brain_____ is involved. However, sometimes a response must occur very quickly. This is
known as a _reflex______. A reflex is processed directly in the _spinal cord_____,
although the brain becomes aware after the response has taken place.
 Autonomic PNS – Regulates activities that are not under conscious control such as
_breathing, heart rate, blood pressure_________________________.
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______ of 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 _sharper________ 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
_tympanum___________.
 Vibrations are then passed to three tiny bones →
o _malleus (hammer)______
o _incus (anvil)___________
o _stapes (stirrup)________
 The vibrations are transferred from the _stapes______ to another membrane known as
the _oval window__________.
 Finally, vibrations are converted to an electrical impulse in the _cochlea______, a snailshaped sensory structure filled with fluid and tiny hairs. These hairs are pushed back &
forth, producing electrical impulses.
 A 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 _spinal cord___ and
_brain______.
 Motor Neurons – Transmit impulses from the _brain__ and _spinal cord____ to the
_body______.
 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-tonode, 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.