Transcript Neuroanatomy

Neuroanatomy
• Neuroanatomy refers to the study
of the parts and function of
neurons.
• Neurons are individual nerve cells
that combine to create the body’s
nervous system (communication
system).
• Neural Communication
Types of Neurons
• There are three types of neurons:
–Afferent Neurons
Neurons)
–Interneurons
–Efferent Neurons
(Motor Neurons)
(Sensory
•Afferent Neurons are
responsible for taking
information from the
senses TO the brain.
•Interneurons are located
in the spinal cord and
the brain, and are
primarily responsible for
processing information.
• Efferent Neurons are
responsible for taking
information FROM the
brain and the spinal cord
back to the rest of the
body.
• Most information travels from
the body, up the spinal cord, is
processed by the brain, sent back
down the spinal cord, and then
back to the body with behavior
instructions. The exception to
this general pathway is reflexes.
•Reflex behaviors are
controlled by the spinal
cord and brain stem
without any conscious
effort on behalf of the
upper brain.
• Can you not kick your leg out
when the patella nerve is
struck?
• Can you not contract your
pupil when a bright light is
shined in your eyes?
Parts of a Neuron
• A. Dendrites
–Thin, branching fibers attached to the
cell body that are lined with receptors
from which the dendrite receives
information from other neurons.
• B. Cell Body/Soma
–Contains the (C) nucleus and other
parts of the cell needed to sustain
life
C. Nucleus
• The function of the nucleus is to control the
activities of the cell
• D. Axon
–Wire-like structure ending in the
terminal buttons that extends from
the cell body and carries messages
towards the intended destination
(neuron, muscle, gland, etc.)
• E. Myelin Sheath
– An insulating, fatty covering around the axon
that speeds neural transmissions. Made of
Schwann cells.
– Axons that are myelinated appear white.
Known as “white matter.”
F. Schwann Cells
• Provide for the growth of the myelin sheath.
• G. Nodes of Ranvier
– Regularly spaced gaps in the myelin sheath
around an axon or nerve fiber. This is where
depolarization takes place.
• H. Terminal Buttons
–The branched end of the axon that
contains neurotransmitters
• I. Synapse
–The space between the terminal
buttons on one neuron and dendrites
of the next neuron
• Neurotransmitters
– Chemicals contained in the terminal
buttons that enable neurons to
communicate. Neurotransmitters fit into
receptor sites on the dendrites of neurons
like a key fits into a lock.
Neural Transmission
• In its resting state (resting potential
or polarization), a neuron is waiting
for input. Housed in the neuron are
positively charged potassium ions.
Outside are positively charged sodium
ions. They are kept separate by the cell
walls of the neuron.
• A neuron has a pre-set level of
stimulation that needs to be
met or exceeded in order for it
to pass the received impulses
on to the next neuron. This is
called a neuron’s threshold.
• If the threshold has been met or exceeded, a
chain reaction begins.
• With threshold being met, the cell becomes
depolarized. The cells walls open at the nodes
and allows positively charged ions into the
axon. This overwhelming positive charge causes
an electrical charge to form (an action
potential). At 120 meters per second, the
action potential travels to the terminal buttons
via the axon.
• If enough neurotransmitters have
been sent, the next neuron will
fire. If not, the message ends.
This is called the all-or-nothing
principle. There are no halfcharges or lesser messages sent.
• Action Potential
• Myelin and Action Potential
• At the terminal buttons,
neurotransmitters are released
into the synapse and passed
along to the dendrites of the
next neuron. These
neurotransmitters tell the
recipient what to do next.
• After a neuron fires its message,
there is a brief period of time before
it can fire again. This is called a
neuron’s refractory period.
• During the refractory period, excess
neurotransmitters are reabsorbed by
the sending neuron, called re-uptake,
as well as the cell becoming
polarized once again.
• Depending on what type of
neurotransmitter has been released,
the next neuron will react differently.
Since nerve cells are connected to
the brain, muscles, glands, etc., the
entire human body reacts different
depending upon what type of
neurotransmitter has been released.
• Part I
• Part II
• Part III
Neurotransmitters
• Neurotransmitters
Acetylcholine (ACh)
• Enables muscle action, REM
sleep, and memory
• Undersupply, as ACh-producing
neurons deteriorate, marks
Alzheimer’s disease
Dopamine
• This is the reward drug. After doing
something well, you “feel” good. Alos
plays a part in the motor control over
voluntary movements
• Excessive dopamine receptor activity is
linked to schizophrenia; a lack of
dopamine produces the tremors and
lack of mobility of Parkinson’s disease.
Serotonin
• Affects mood, hunger, temperature
regulation, sleep, and arousal
• Undersupply is linked to depression;
Prozac and other anti-depressants
raise serotonin levels.
Norepinephrine
• Helps to control alertness,
dreaming, waking from sleep,
reactions to stress
• Undersupply can depress mood.
GABA
• Neural inhibitor with a
tranquilizing effect.
• Undersupply linked to seizures,
tremors, and insomnia.
Glutamate
• Involved in memory
• Oversupply can overstimulate
the brain, producing migraines
or seizures
Endorphins
• Natural opiates (pain
killers) that are released in
response to pain and
vigorous exercise.
Endorphins
Epinephrine
• Adrenaline Burst of Energy
(small amounts in brain)
Drugs and Chemical Interactions with
Neural Transmission
• Some drugs that people put
into their bodies are classified
as agonists.
• Agonists may either speed up
the neural process, cause an
over-release or absorption of a
neurotransmitter, or block the
re-uptake process.
• After a neuron fires, if re-uptake
is blocked, the lingering
neurotransmitters in the synapse
will continue to be absorbed by
the receiving neuron until it is
gone.
• Therefore, a lingering feeling will
occur.
Examples of Agonists
• Cocaine – blocks the reuptake of dopamine
• MDMA (Ecstasy) –
excessive release of
serotonin
• Some drugs that people put into
their bodies are classified as
antagonists.
• Antagonists may slow or stop the
transmission of a neurotransmitter,
or they may bind themselves to
receptors on a neuron’s dendrite,
thus not allowing a message to be
passed on.
Examples of Antagonists
• Curare – a poison that stops the
flow of Ach – causes paralysis