Transcript Parts of a Neuron

The
Biology of
Mind
Chapter 2
Parts of a Neuron
Dendrites
Dendrites: Branching
extensions at the cell body.
Receive messages from
other neurons.
Cell Body: Life support
center of the neuron.
Cell
Body
Axon
Terminals
Axon Terminals: Branched
endings of an axon that
transmit messages to other
neurons.
Axon: Long single
extension of a neuron,
covered with a myelin
[MY-uh-lin] sheath to
insulate and speed up
messages through neurons.
Parts of a Neuron – Summary
Action Potential – Summary
Figure 2.3
Refractory Period & Pumps
Refractory Period:
After a neuron fires
an action potential,
it pauses for a short
period to recharge
itself to fire again. It
pumps positively
charged sodium
ions back outside
the neuron.
Action Potential Properties
Threshold: Each neuron receives
excitatory and inhibitory signals
from many neurons.
When the excitatory signals
minus the inhibitory signals
exceed a minimum intensity
(threshold) the neuron fires an
action potential.
All-or-None Response: A strong
stimulus can trigger more
neurons to fire, and to fire more
often, but it does not affect the
action potentials strength or
speed.
Intensity of an action potential
remains the same throughout the
length of the axon.
How Neurons Communicate
Synapse [SIN-aps] a junction between the axon tip of the sending
neuron and the dendrite or cell body of the receiving neuron.
This tiny gap is called the synaptic gap or cleft.
Neurotransmitters are chemical messengers that traverse the
synaptic gaps between neurons.
When released by the sending neuron, neurotransmitters travel
across the synapse and bind to receptor sites on the receiving
neuron, thereby influencing whether it will generate a neural
impulse.
Neurotransmitters – Summarized
Reuptake
Neurotransmitters in
the synapse are
reabsorbed into the
sending neurons
through the process of
reuptake. This process
applies the brakes on
neurotransmitter
action.
Neurotransmitters
Table 2.1
Lock & Key Mechanism
Neurotransmitters bind to the receptors of the receiving neuron in
a key-lock mechanism.
The Nervous System
Figure 2.7
Kinds of Neurons – A Review
Sensory Neurons carry incoming information from the sense
receptors to the CNS.
Motor Neurons carry outgoing information from the CNS to
muscles and glands.
Interneurons connect the two neurons.
Interneuron Neuron
(Unipolar)
Sensory Neuron
(Bipolar)
Motor Neuron
(Multipolar)
Central Nervous System
The Spinal Cord and Reflexes
The spinal cord is an information highway connecting the
peripheral nervous system to the brain.
The neural pathways governing our reflexes, our automatic
responses to stimuli, illustrate the spinal cord’s work.
The Endocrine System
The Endocrine
System is the
body’s “slow”
chemical
communication
system.
Communication
is carried out by
hormones
synthesized by a
set of glands.
Pituitary Gland
The pituitary gland is called the “master gland.” The
anterior pituitary lobe releases hormones that regulate
other glands. The posterior lobe regulates water and salt
balance.
Other Endocrine Glands
The pituitary gland is called the “master gland.” The anterior
pituitary lobe releases hormones that regulate other glands. The
posterior lobe regulates water and salt balance.
The thyroid and parathyroid regulate metabolic and calcium rate.
Other Endocrine Glands
Adrenal glands consist of the adrenal medulla and the cortex. The medulla
secretes hormones (epinephrine and norepinephrine) during stressful and
emotional situations, while the adrenal cortex regulates salt and carbohydrate
metabolism.
Sex glands are located in different places in men and women. They regulate
bodily development and maintain reproductive organs in adults.
The Brain
Techniques to Study the Brain
A brain lesion experimentally destroys
brain tissue to study animal behaviors
after such destruction.
An electroencephalogram (EEG) is an
amplified recording of the electrical
waves sweeping across the brain’s
surface, measured by electrodes placed
on the scalp.
Computerized Axial Tomography (CAT
Scan) is a series of X-Ray photographs
taken from different angles and
combined by computer into a composite
representation of a slice through the
body. Also called a Computed
Tomograph (CT) Scan.
The Brain
Techniques to Study the Brain
A Positron Emission Tomography (PET) Scan is a visual
display of brain activity that detects a radioactive form of
glucose while the brain performs a given task.
Courtesy of National Brookhaven National Laboratories
Magnetic Resonance Imaging (MRI) uses magnetic fields and
radio waves to produce computer-generated images that
distinguish among different types of brain tissue. Top images
show ventricular enlargement in a schizophrenic patient. Bottom
image shows brain regions when a participants lies.
Thalamus
Brainstem
Reticular Formation is
a nerve network in the
brainstem that plays an
important role in
controlling arousal.
Reticular
Formation
Thalamus
Medulla
The Medulla [muhDUL-uh] is the base of
the brainstem that
controls heartbeat and
breathing.
The Thalamus [THALuh-muss] is the brain’s
sensory switchboard,
located on top of the
brainstem. It directs
messages to the sensory
areas in the cortex and
transmits replies to the
cerebellum and
medulla.
Cerebellum
The cerebellum, or “little brain,” is
attached to the rear of the brainstem.
It helps us judge time, modulate our
emotions, discriminate sounds and
textures as well as coordinate
voluntary movements and balance.
Amygdala and Hypothalamus
Thalamus
Hypothalamus
Pituitary Gland
Amygdala
Hippocampus
The Amygdala [ahMIG-dah-la] consists of
two lima bean-sized
neural clusters linked to
the emotions of fear
and anger.
The Hypothalamus lies
below (hypo) the
thalamus. It directs
several maintenance
activities like eating,
drinking, body
temperature, and
control of emotions.
The hypothalamus
helps govern the
endocrine system via
the pituitary gland.
The hippocampus
processes memory.
Without it, we cannot
process new memories
of facts and episodes.
The Cerebral Cortex
The cerebral cortex is the intricate fabric of interconnected neural
cells that covers the cerebral hemispheres like the bark of a tree. It
is the body’s ultimate control and information processing center.
Structure of the Cortex
Glial Cells
Neurons are like
queen bees…they
cannot feed or
sheathe (protect)
themselves.
Glial cells are
worker bees…they
provide nutrients
and insulating
myelin, guide
neural connections,
and mop up ions
and
neurotransmitters.
Structure of the Cortex
Frontal Lobe
Parietal Lobe
Temporal Lobe
Occipital Lobe
The frontal lobe is
involved in speaking and
muscle movements (motor
cortex) and in making
plans and judgments
The parietal lobe
integrates sensory
information from various
parts of the body and
includes the sensory
cortex.
The occipital lobe
includes the visual areas
which receive visual
information from the
opposite visual field.
The temporal lobe is
concerned with hearing,
memory, emotion, and
speaking.
Functions of the Cortex
The Motor Cortex is the area at the rear of the frontal lobes that
control voluntary movements.
The Sensory Cortex (parietal cortex) receives information from
skin surface and sense organs.
Association Areas
The sensory and motor cortexes
take up about one quarter of the
cerebral cortex.
Neurons in the other three
quarters are called association
areas. Association areas are
found in all four lobes of the
brain and are largest in humans.
Electrically probing these areas
does not trigger any observable
response, so mapping these areas
cannot be neatly done. This has
led to the erroneous claim that we
only use 10% of our brain (but
that would mean a bullet would
have a 90% chance of hitting an
unused area).
Our Divided Brain
Our brain is divided into two hemispheres.
For more than a century, clinical evidence has shown that the brain’s two sides
serve differing functions.
Lateralization (hemispheric specialization) is apparent after brain damage.
The left hemisphere processes reading, writing, speaking, mathematics, and
comprehension skills. In the 1960s, it was termed as the dominant brain.
Splitting the Brain
A commissurotomy is a procedure in which the two
hemispheres of the brain are isolated by cutting the connecting
fibers (mainly those of the corpus callosum) between them.
This surgery was done as a treatment for epileptic seizures.
Corpus Callosum
Martin M. Rother
Courtesy of Terence Williams, University of Iowa
Split Brain Patients
With the corpus callosum severed,
objects (apple) presented in the
right visual field can be named.
Objects (pencil) in the left visual
field cannot.
Divided Consciousness
“What did you see?”
“With your left hand, select
the object you saw from
those behind the screen.”