The Biology of Mind Chapter 2. Parts of a Neuron Dendrites: Branching extensions at the cell body. Receive messages from other neurons. Cell Body: Life.
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The Biology of
Mind
Chapter 2
Parts of a Neuron Dendrites: Branching extensions at the cell body. Receive messages from other neurons.
Cell Body: Life support center of the neuron.
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.
Dendrites
Cell Body
Axon Terminals
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 CommunicateSynapse [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
ReuptakeNeurotransmitters in
the synapse are reabsorbed into the
sending neurons through the process of reuptake. This
process applies the brakes on
neurotransmitter action.
NeurotransmittersTable 2.1
Lock & Key MechanismNeurotransmitters bind to the receptors of the receiving
neuron in a key-lock mechanism.
The Nervous SystemFigure 2.7
Kinds of Neurons – A ReviewSensory 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.
Sensory Neuron(Bipolar)
Interneuron Neuron (Unipolar)
Motor Neuron(Multipolar)
Central Nervous SystemThe Spinal Cord and Reflexes
Figure 2.10 A Simple Reflex
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 SystemThe
Endocrine System is the body’s “slow”
chemical communicatio
n system. Communicatio
n is carried out by
hormones synthesized by a set of
glands.
Pituitary GlandThe 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 thyroid and parathyroid regulate metabolic and calcium rate.
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 GlandsAdrenal 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 BrainTechniques to Study the
BrainA 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 BrainTechniques 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.
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.
Courtesy of N
ational Brookhaven N
ational Laboratories
Brainstem The Medulla [muh-DUL-uh] is the base of
the brainstem that controls heartbeat and
breathing.
Reticular Formation is a nerve network in the brainstem that plays an important role in controlling
arousal.
The Thalamus [THAL-uh-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.
Medulla
Reticular Formatio
n
Thalamus
Thalamus
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.
Cerebellum
Amygdala and HypothalamusThe Amygdala [ah-
MIG-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.
Amygdala
Hypothalamus
Pituitary Gland
Thalamus
Hippocampus
The Cerebral CortexThe 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 CortexNeurons 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 neurotransmitte
rs.
Glial Cells
Structure of the CortexThe 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.
Frontal Lobe Parietal Lobe
Occipital Lobe
Temporal Lobe
Functions of the CortexThe 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.
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).
Association Areas
Our Divided BrainOur 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 BrainA 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
Ma
rtin M
. Ro
the
r
Courtesy of T
erence William
s, University of Iow
a
Split Brain PatientsWith 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.”
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