Nervous System
Nerve Cells
Neuron  designed to respond to surrounding environment
Axons and Dendrites
•Small branches called dendrites receive chemical or electrical input
from the body. Neurons have many dendrites
•Large branches are called axons, or nerve fibers, which carry
information away from the cell in the form of a nerve impulse.
Neurons commonly have only 1 axon
•Nerves are simply bundles of axons. Axons are surrounded by a
“Band-Aid” of cells called Schwann Cells. Multiple layers of these
cells create a sheath, or covering, around the axon called a myelin
sheath.
•The myelin sheath, allows for the super-fast conduction of nerve
impulses. Nerves that are mylenated appear white. Mylenated nerves
are used to send signals over long distances.
•Unmylenated nerves appear gray (like gray matter in the brain) and
are often used for processing nerve information
Typical Nerve Cell (Neuron)
Neurons in 3 dimensional space
Nerve Communication
•Neurons communicate to each other by sending chemical signals to
one another. These chemicals are called neurotransmitters.
•Neurotransmitters leave one neuron, travel through a small
intercellular space, to another neuron. That space is called a
synapse.
•At the end of each neuron is a receptor that monitors the internal
condition of the body
•Receptors transmit information down the dendrite, to the cell body.
Information is processed and sent out of the axon, away from the
neuron
• The nervous system consists of millions of communicating neurons,
neurotransmitters, receptors, and synapses.
Neurotransmitter Release
Neuron Clusters
Conduction of a Nerve Impulse
•Nerve impulse in a human travels more than 600 feet per second
• Resting nerve cells tend to have lots of negatively charged proteins
in them, and therefore have a negative charge to them (-65mv).
•Resting nerve cells also have lots of potassium inside the cell.
•They also have lots of Sodium just outside the cell
Action Potential
1. Action Potentials describe how a nerve impulse is generated and
conducted throughout the body
2. The nerve cell is stimulated by an electric current, change in pH, or
a pinch, causing an action potential
3. Upon stimulation, Sodium gates in the nerve cell membrane open
and sodium rushes into the cell. This rush of positive ions causes
the cell’s charge to rise and spike (from -65mv to +40mv). This
process is called depolarization.
4. After the initial rush, the sodium gates close (stopping sodium
movement) and potassium gates open. Potassium then rushes out
of the cell. The loss of these positive ions causes the cell to return
to its resting charge (-65mv). This is called repolarization.
5. Eventually, the sodium which rushed into the cell and the
potassium which rushed out of the cell are pumped out of the cell
(Na) and into the cell (K). This is done by the sodium potassium
pump.
6. During this time the nerve is in its refractory period.
Action Potential
Divisions of the Nervous System
Central Nervous System Brain and spinal cord
Peripheral Nervous System  All other parts of the body
Somatic Nervous System Nerves that are controlled
voluntarily
Autonomic Nervous System Nerves that are controlled
involuntarily
Types of Neurons
•Sensory Neuron  Neurons with receptors on the end. Send
signals to the brain.
•Motor Neurons  Carry nerve impulses to from the brain to
your muscles
•Interneurons Reside in the brain and spinal cord. Connect
sensory neurons to motor neurons
Parts of the Brain
• Brain Stem contains the medulla oblongata and the pons.
Located at junction of brain and spinal cord
• Medulla Oblongata contains clusters of neurons that control
heartbeat, respiration, and blood pressure. Also contains neurons
that control reflexes like swallowing, coughing, hiccups, and
vomiting
• Pons Means “bridge”. Mostly aids in sending messages from MO
to spinal cord. Also has limited tactile, visual, and auditory
function
Diencephalon
• Hypothalamus Maintains Homeostasis; Regulates hunger, thirst,
body temperature, and sleep. Hypothalamus also controls the
pituitary gland (growth)
• Thalamus: Post office of the brain. Receives incoming messages
from the spinal cord and processes the information, sends the
information to the appropriate part of the brain
Cerebellum and Cerebrum
Cerebellum
2 portions separated by the brain stem
Cerebellum functions in skeletal muscle coordination; maintaining
balance and posture. Receives information from the inner ear
Cerebrum
Surface area of the brain
Area of the brain devoted to consciousness.
4 surface areas: Frontal, Parietal, Temporal, and Occipital
Frontal Lobe: formation of conscious thought; thinking
Parietal Lobe: Sensations: Pain, pressure, touch
Temporal Lobe: Hearing and smelling
Occipital Lobe: Visual Processing
Other Interesting Parts of the Brain
Corpus callosum Part of the frontal lobe that splits into right and left
sides. Over excitation of CC can cause epileptic seizures.
Limbic System Lies below the cerebrum in the frontal lobe.
Controls emotions such as love, anger, sadness, guilt, etc... Also
controls sense of memory (long and short term)
Destruction of neurons in the limbic system leads to Alzheimer’s
disease
Most hallucinogenic drugs affect neurons in the limbic system