Transcript Brain Presentation1

Chapter Two
The Brain
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Made up of cells (neurons and glial cells)
Weight = 3 pounds
2 hemispheres (right and left)
The brain never sleeps
Neuron
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100 Billion cells
No two cells are identical
Few are produced after birth
Grow with stimulation creating more synaptic
connections
• Support by glial cells which 10 time more abundant
• Most reside in the brain but are found all over the
body
Glial Cell
• Support cell to the neuron
• Helps metabolism, respiration and
efficiency of the neuron
• In the peripheral nervous system glial
cells are called Schwann cells
• Often surround the neuron creating a
myelin sheath that greatly improves the
speed and efficiency of the neural impulse
Types of Neurons
• Sensory (or afferent) neurons: send information from
sensory receptors (e.g., in skin, eyes, nose, tongue, ears)
TOWARD the central nervous system.
• Motor (or efferent) neurons: send information AWAY
from the central nervous system to muscles or glands.
• Interneurons (Associative): send information between
sensory neurons and motor neurons. Most interneurons
are located in the central nervous system.
• Reflex Arc: Body to the spine back to the body before
ever reaching the brain
Receives
stimulation from
either sense
receptors or
other cells’
axons
Neuron Structure
The cell’s
life support
center
Small gaps
in the myelin
sheath of
nerve fibers
Executor of the
cell
Forms junctions with
other cells also
called terminal
knobs synaptic
buttons
Passes messages
away from the cell
body to other
neurons, muscles,
or glands
Insulates the axon
that speed neural
impulse
Difference between Axons and Dendrites
• Axons
• Take information away
from the cell body
• Generally only 1 axon per
cell
• More efficient if it has a
myelin sheath
• Branch further from the
cell body
• Dendrites
• Bring information to the
cell body
• Usually many dendrites per
cell
• No myelin insulation
• Branch near the cell body
Neural Impulse within the Neuron
• Electrical part of the electro-chemical impulse
• All or None Action Potential- There is either enough stimulation or
the neuron doesn’t fire
• Action Potential- Enough stimulation received from another cell that
causes the axon membrane to become permeable that opens gates that
causes depolarization (cell becomes positively charged) to occur that
allow positively charged particles (sodium ions) to enter the cell
• Neurons can fire up to 270 miles per hour helped by the diameter of
the axon and myelination.
• The cell needs only to reach –60 millivolts to fire and allow more
sodium to enter and cause the cell to reach +30 millivolts
• Then a refractory period begins where the cell can not fire in which
the cell repolarizes below –70 millivolts
• Resting Potential- Period when the cell is at –70 millivolts
• The cell can fire many times a second but it must rest between firings.
• When the cell is polarized it has no sodium ions in it and a negative charge.
Action Potential/
Depolarized
Refractory
Period
Resting Potential/
Polarized
Stimulus
Threshold
Neurotransmission
• Electrical transmission causes synaptic vesicles to release
neurotransmitters in the axon terminals
• The neurotransmitters leave the terminal and cross the synaptic space
to the near by dendrite receptor sites.
• The neurotransmitter bind to the receptor sites and triggers that
neuron to either fire or blocks it from firing
What happens at the Synapse
• Excitation neurotransmitter- Causes neurons to fire
• Inhibitation- Causes neurons not to fire
• Reuptake- Neurotransmitters that are not used are
retaken by the terminal buttons to be used again
• Enzyme Action- Breaks down neurotransmitters, that
are not used, to be recycled for later use
Neurotransmitters
• Acetycholine-Essential for movement- usually activates movement and
muscles (to contract), learning and memory
• Found especially in the PNS along with Norepinephrine
• Curare – blocks receptor site causing paralysis - lung contractions stop
• Botulism – blocks muscle contractions – used in Botox injections for wrinkles
• Rat studies show memory improvements with tissue transplants
• Loss linked to Alzheimer’s
• Dopamine- affects voluntary movement, attention, thought & memory
– Too much leads Psychosis – schizophrenia
– Too little leads to Parkinson’s
• Epinephrine and Norepinephrine are neurohormones which means they
can act like hormones are also referred to as adrenaline and
noradrenaline in the old nomenclature
• Norepinephrine- Emotional arousal, anxiety and fear – involved in the
activation of the sympathetic nervous system
• Seratonin- Sleep and emotional arousal; implicated in aggression
– Too low leads to depression and too high masked aggression
– High achievers or leaders tend to have higher levels of seratonin
– Tryptophan produces seratonin
Neurotransmitters
• GABA- Inhibits brain excitability and anxiety
• Endorphines – Pain relief and elevation of mood heroin
and morphine act like endorphines
Common Drugs and their Interactions
• Depressants
– Alcohol- stimulates release of dopamine and depresses RAS
and possibly mimics GABA
– Valium – causes the release of GABA which causes relaxation
• Stimulants
– Cocaine – blocks the reuptake of dopamine causing heightened
elevation in mood – causes blood vessel constriction- used in
eye surgeries
– How drugs work
– Caffeine – slows reabsorption of NT by blocking enzymes
– Amphetamines- increases release of Dopamine and
norepinephrine and blocks reabsorption – in the past used for
weight loss – today used for narcolepsy and ADHD (Ritalin)
• Overdoses can lead to psychotic episodes lasting up to six months
Common Drugs and their Interactions
• Narcotics (Opiates)
– Heroin – stimulates the neuronal firing rate of dopamine
• Binds to endorphin receptor sites
• Tolerance occurs quickly
• Hallucinogenics
– Cannabis/Hash- May affect the release of a newly discovered
neurotransmitter Anandamide which may reduce stress and
pain
– LSD- (Psychedelics) Act on seratonin receptors
– Ecstasy- causes the release and blocks reuptake and depletes
the amount of seratonin in the brain
– PCP – stimulates both the sympathetic and peripheral nervous
system
Involuntary
movement
Body
Voluntary
Movement
Recovery
Action
The Autonomic Nervous System
Structure
Sympathetic Stimulation
Parasympathetic Stimulation
Iris (eye muscle)
Pupil dilation
Pupil constriction
Salivary Glands
Saliva production reduced
Saliva production increased
Oral/Nasal Mucosa
Mucus production reduced
Mucus production increased
Heart
Heart rate and force increased
Heart rate and force decreased
Lung
Bronchial muscle relaxed
Bronchial muscle contracted
Stomach
Peristalsis reduced
Gastric juice secreted; motility increased
Small Intestine
Motility reduced
Digestion increased
Large Intestine
Motility reduced
Secretions and motility increased
Liver
Increased conversion of
glycogen to glucose
Kidney
Decreased urine secretion
Adrenal medulla
Norepinephrine and
epinephrine secreted
Bladder
Wall relaxed
Sphincter closed
Increased urine secretion
Wall contracted
Sphincter relaxed
The Brain
• The brain has three regions we will
discuss in detail
– Cerebral Cortex
– Subcortex
– Limbic System
• The Brain is often divided up into
– Forebrain
– Midbrain
– Hindbrain
• The brain has two unique qualities
– Plasticity – the brain is malleable and
changes function after injury
– Corticalization- wrinkling of the brain
which increases its size
• Cerebral Cortex
– Frontal Lobe –thinking, planning, voluntary movement and control of
emotions and includes the motor cortex and the Broca’s region
– Occipital Lobe – organizes our visual information
– Parietal Lobe - Sensation reception includes the somatosensory
cortex
– Temporal Lobe – organizes our auditory information and includes the
Wernicke’s region
– Thalamus – relays information from the senses (except smell) to the
appropriate lobe and regulates attention, motivation and emotion
• Motor Cortex – handles voluntary movement Somatic Nervous
System
• Somatosensory Cortex – handles all of your sensations of touch from
your body
• Both systems partition off the cortex space based on the sensitivity
and fine motor skills of each part of the body
– A more sensitive part of the body has a large portion of the Somatosensory
cortex
Broca’s and Wernicke’s Regions
Broca's Area
• Broca’s Region
– If damaged speech production
is unattainable
– Located in the frontal lobe
Wernicke's Area
• Wernicke’s Region
– Jumbled speech and
incoherent sentences if
damaged
– Located in the temporal
lobe
Two Hemispheres of the Cerebral Cortex
Left Hemisphere
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Language
Math
Logic
Analytic side
• Spatial abilities
• Face
recognition
• Visual imagery
• Music
• Creative side
Split Brain Surgeries
• Corpus Callosum
– Connects the two hemisphere so they can directly communicate
– Epilepsy causes violent, uncontrollable neural firings across the
corpus callosum
– The CC is cut in severe cases which led to split brain research and
understanding of the roles of each hemisphere
• Cerebellum
Subcortex
– Recorded movement and balance
• Brain Stem – basic bodily function
Brain
Stem
– Medulla – heart and respiration functions
– Pons – Crossover point between other parts of the brain to the cerebellum
– Reticular Formation (RAS) – regulates sleep and attention
RAS
Limbic System
• Amygdala– regulates emotion esp. fear
• Hippocampus– consolidates memory from shortterm to long-term
• Hypothalamus– regulates the Autonomic Nervous
System and the Endocrine system Hypothalamus
– Homeostatic regulator including
temperature, blood pressure,
heartbeat, thirst, and hunger
• Pituitary Gland often referred to as
the master gland
CT Scans
• CT scans use a series of
X-ray beams passed
through the head.
• The images are then
developed on sensitive
film.
• This method creates crosssectional images of the
brain
• Shows the structure of the
brain, but not its function.
Computed Tomography Scan
(CT Scan)
Pet Scan
Positron Emission Topography
• A scanner detects radioactive
material that is injected or inhaled to
produce an image of the brain.
• Commonly used radioactivelylabeled material includes oxygen,
fluorine, carbon and sugar.
• When this material gets into the
bloodstream, it goes to areas of the
brain that use it.
• When the radioactive material
breaks down, it gives off a neutron
and a positron.
MRI Scans
• MRI uses the detection
of radio frequency
signals produced by
displaced radio waves
in a magnetic field.
• It provides an
anatomical view of the
brain.
Magnetic Resonance Imaging
Endocrine System –Secretes Hormones
• Pituitary– master gland, regulates growth and
stimulates milk for nursing
• Dwarfism and giantism
• Pineal- (Melatonin)
– Regulates sleep cycle
• Thyroid- (Thyroxin)
– Regulates metabolism rate
• Hypo- underproduction-lethargic
• Hyper- overproduction- hyperactive
• Adrenal- (Adrenaline –Epinephrine)
– Stimulates the body into action and
responds to stress
• Pancreas- (Insulin)
– Regulates blood sugar and insulin levels
and regulates hunger
• Gonads- (Testosterone and Estrogen)
– Ovaries- regulates female sexual
behavior and female characteristics
– Testes- regulates male sexual behavior
and male characteristics
Pineal
Gland
GHB and the Brain
Although GHB can be made in the laboratory, it is also produced
normally in the brain through the synthesis of a neurotransmitter called
GABA. Some of the greatest concentrations of GHB are found in the
substantia nigra, thalamus and hypothalamus. When GHB is ingested by
a user, it affects several different neurotransmitter systems in the brain:
•GHB can increase acetylcholine levels.
•GHB can increase serotonin levels.
•GHB can reduce dopamine activity, especially in the basal ganglia.
This action is probably the result of the inhibition of the release of
dopamine from synaptic terminals. Some studies show that GHB first
inhibits the release of dopamine, then causes the release of dopamine.
The effect on the dopamine system may depend on the dose of GHB.
•GHB can activate GHB receptors and GABA receptors on neurons
in the brain.
GHB was first developed as a general anesthetic, but because it did not
work very well to prevent pain, its use as an anesthetic declined. The
observation that GHB may cause the release of growth hormone led
some people, especially athletes and body-builders, to take it because
they thought it would increase muscle development. At the time, GHB
was available as a dietary supplement and as such was not regulated by
the US Food and Drug Administration. In 1990, after numerous reports
that GHB caused illness, the FDA began investigating the drug. It is now
classified as an illegal substance. Research is being conducted to
investigate the use of GHB in the treatment of the sleep disorder called
narcolepsy.
GHB has been grouped with other drugs in the "date-rape drug" category
such as Rohypnol, because it can be slipped easily into a drink and given
to an unsuspecting victim, who often does not remember being assaulted.
GHB is especially dangerous when combined with alcohol.
LSD was first synthesized from a fungus that grows on rye and
other grains. In 1938, Albert Hofmann working in the Swiss
pharmaceutical company called Sandoz, produced LSD for the
first time. He was hoping that this new drug could be used to
stimulate circulation and respiration. However, the tests he
conducted were all failures and he forgot about LSD for 5 years.
In 1943, Hofmann accidentally ingested (or somehow absorbed) a
bit of LSD and experienced some of the psychedelic effects of this
chemical: dizziness, visual distortions and restlessness. A few
days later he prepared 0.25 mg of LSD in water and drank it. He
again experienced the mood and thought altering effects of LSD.
Effects of LSD on the Nervous System
LSD is water soluble, odorless, colorless and tasteless - it is a very powerful drug - a dose as small as a single grain of salt (about 0.010 mg) can
produce some effects. Psychedelic effects are produced at higher doses of about 0.050-0.100 mg. The effects of LSD depend on a user's mood
and expectations of what the drug will do and last several hours. The behavioral effects that LSD can produce include:
•Feelings of "strangeness"
•Vivid colors
•Hallucinations
•Confusion, panic, psychosis, anxiety
•Emotional reactions like fear, happiness or sadness
•Distortion of the senses and of time and space
•"Flashback" reactions - these are the effects of LSD that occur even after the
user has not taken LSD for months or even years.
•Increases in heart rate and blood pressure
•Chills
•Muscle weakness