Transcript central nervous system

CENTRAL NERVOUS SYSTEM
CH. 8
Central Nervous System
-- consists of brain and spinal cord
-- covered by meninges, bathed in CSF
-- Cerebral cortex – higher center
-- consists of gyri and sulci
-- four lobes: frontal, parietal, temporal, occipital
-- higher level thinking, interpretation
-- two hemispheres held together by the corpus callosum
-- Diencephalon – thalamus, hypothalamus, pituitary, epithalamus
(pineal gland)
-- Brainstem:
--midbrain – between diencephalon and pons
--hindbrain – pons, medulla oblongata
-- Cerebellum: “little brain”
All of these parts have their origins during embryogenesis
STRUCTURAL ORGANIZATION OF THE BRAIN
The brain begins as a hollow tube, and remains hollow.
5 Regions of the brain are formed during development.
The cavities of the brain are the ventricles.
Ventricles of the Brain
Ventricles are chambers that are filled with cerebrospinal fluid.
They are connected with the central canal that runs through the
spinal cord.
CEREBRUM
Outer part of cerebrum, the cerebral cortex, consists of gray matter.
Underneath is white matter, except for the gray basal nuclei.
Fig. 8.5 Shows the four lobes, precentral & postcentral gyri, central sulcus
Techniques for Visualizing the Brain
--MRI (Magnetic Resonance
Imaging)
-- uses a magnetic field to
make pictures of structures
inside the body.
--can see CSF, gray and white
matter
--shows structural abnormalIties. E.g. brain tumors, nerve
injury, damage caused by
stroke, bleeding, an aneurism
Techniques for Visualizing the Brain
--EEG (electroencephalogram)
-- electrodes on the scalp detect
synaptic potentials produced by
cerebral cortex
- Four types of wave patterns
- E.g Different waves happen at
different stages of sleep
- Deviations from normal patterns
are used to diagnose
- Epilepsy
- Confirm brain death in
someone with persistent coma
Techniques for Visualizing the Brain
--MRI AND EEG
-- Figure 8.8 Shows an MRI image of the brain, revealing the sensory
cortex.
-- the combination of the two techniques allows scientists to map
the parts of the brain that correspond with functional areas
of the body
Techniques for Visualizing the Brain
--Functional MRI visualizes
increased neuronal activity in the
brain indirectly, by the increased
blood flow.
--brain regions with the highest
metabolic activity receive the most
blood flow
-- e.g. the colors indicated in the
picture indicate increased blood
flow to the brain areas stimulated
when the subject views a screen
displaying images that change at
30 second intervals.
Can be used to look at growth of a tumor,
Determine how well the brain is functioning
after a stroke, learn where seizures are
located, diagnose Alzheimer’s
Techniques for Visualizing the Brain
--PET (Positron Emission Tomography); positrons are injected into the
blood; (electrons collide with positrons to release gamma rays, which
can be detected)
-- used to determine stages of cancer and patient responses to cancer
treatments
-- may detect early onset
-- used to study brain metabolism,
and drug distribution in the brain
--CT (Computed Tomography)
-- Xray tissues at different depth
-- generates a 3D image tissues
Maps of the Precentral and Postcentral Gyri
Basal Nuclei
Masses of gray matter located deep in the
white matter of the cerebrum; they relay motor
impulses from cortex to brainstem
Allows intended movements – CLICK HERE
Inhibits unintended movements – CLICK HERE
INJURY TO BASAL NUCLEI
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Tremors (while resting, not while moving)
Hypertonia – muscle rigidity (muscles will not stretch)
Delay in initiating movements
Clinical Examples: two neurodegenerative disorders:
– Parkinson’s Disease – exhibit shaking and lack of normal facial
expressions
• Due to deficiency of dopamine
• Dopamine activates other neurons in the basal ganglia that release other inhibitory
neurotransmitters
• Treatment: administering L-dopa (synthetic dopamine precursor)
– Huntington’s Disease (autosomal dominant)
• Degeneration of caudate nucleus
• Rapid involuntary movements of the limbs (writhing movements)
CEREBRAL CORTEX
• Cerebral dominance – (cerebral lateralization) - one side of the
brain complements the other (is not really dominant)
– Studies with people who had their corpus callosum cut showed that
different sides of the brain have specializations
– Majority of people are right-handed (>90% of
people). They use the left side of the brain.
– Left-handed people – most of them only write
with their left hand, but some do everything; they
use the right side
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THE DOMINANT HEMISPHERE (left)
Controls voluntary movement using the dominant hand (right) controlled by
the primary motor area
Senses are sent to the right side of the brain (primary sensory area)
Stereognosis using the dominant hand (right)
–
Mental construct through touch: being able to tell the difference between the feel of a
nickel and the feel of a dime. This is the way blind people feel Braille.
• Wernicke’s Language Comprehension area – located only in the dominant
hemisphere (left): this is how we convert writing we see into understanding
what the writing means; converting heard words into language we
understand
• Broca’s Speech Center – performance of speech (frontal lobe under the
primary motor area); injury from stroke (CVA) causes people to be unable to
speak, called aphasia
CLICK HERE FOR
• Mathematical Calculations. 3 + 5 x 4 = ?
BROCA’S APHASIA
• Learned reflexes and behaviors, e.g. driving a car
CLICK HERE TO SEE SOMEONE WITH WERNICKE’S APHASIA
THE SUBORDINATE HEMISPHERE
• Right side in 90% of the population
• Controls– Voluntary movement using the weaker
hand
– Stereognosis using the weaker hand
– Spatial relations and patterns (e.g.
what image do you see in the picture)
Recognizing patters
(foreground/background)
– Musical ability (playing an instrument; perfect pitch)
– Body sense (being coordinated; gymnasts, surgeons)
– Artistic/intuitive
FUNCTIONS NOT ASSOCIATED WITH A PARTICULAR HEMISPHERE:
Consciousness:
– Awareness of the environment (wakefulness), sensations,
perceptions, and self-cognition (humans) “Aware that you are
aware.”
e.g. your dog is aware, but not ‘aware he’s aware.’
– Social behaviors, moral and ethical reasoning
I’m aware that
I’m aware
I’m aware it’s
time to eat
Regions implicated as centers for emotion:
• Limbic system: aggregations of neuron cell bodies (green)
Aggression
Fear
Feeding
Sex
Goal-directed behavior
Exists in a circuit with
the hypothalamus.
• Studies have shown that
electro-shock of limbic system can function as a reward.
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Brain Regions Involved in Emotion
a) Yellow – orbitofrontal area of prefrontal cortex; blue-green:
cingulate gyrus of limbic system; b) insula is purple; anterior
cingulate gyrus of limbic system is blue-green, amygdala is red
EMOTION AND MEMORY: THE Prefrontal Cortex
• Phineas Gage (1823 - 1860) worked on the Vermont
railroad
• He drilled a hole through his head. Walked to the
doctor’s office; underwent serious personality
changes
• Here’s the video. Click HERE.
Memory: Hippocampus
• Required to take in memories and put them
into permanent storage in the cortex
• Removal of temporal lobe (which includes the
hippocampus) results in not
being able to form a new
memory.
Click here for video on H.M.
who had his hippocampus
removed
Alzheimer’s Disease
• The most common form of dementia
• Loss of brain weight/volume
• Loss of areas of the hippocampus
and cerebral cortex, of synapses
• Accumulation of “plaques” of proteins
SYNAPTIC CHANGES IN MEMORY
Glutamate binding to NMDA receptors causes Ca2+ to diffuse
into the cell, binds to calmodulin and activates a 2nd
messenger system. LTP: long-term potentiation is induced,
genes are activated by transcription factors.
DISORDERS OF THE CEREBRAL CORTEX
• VIRAL Encephalitis – a virus damages a particular area
• Cerebral palsy – damage to a motor area often due
to cerebral ischemia; symptoms: loss of control of
skeletal muscle
• Dyslexia – inability to properly read and write words
- skipping over a word while reading
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Mistaking b for d
Writing ‘was’ instead of ‘saw’
15% of children. More common in males
Hypothesis: lack of cerebral dominance OR injury OR congenital (from
birth)
DISORDERS OF THE CEREBRAL CORTEX
Cerebral Vascular Accident –
– Insufficient O2 to the brain (4 arteries to brain)
– Brain cells die – cerebral infarction (stroke)
• Could be due to cerebral thrombosis (blood clot)
• Could be due to cerebral hemorrhage (bleeding) due to
–High blood pressure OR
–Aneurysm (a bulging weak spot in a blood vessel)
– Symptoms: depend on which cells die
• Aphasia OR paralysis OR death
– Sometimes functions can be regained
(neuroplasticity)
DISORDERS OF THE CEREBRAL CORTEX
• Epilepsy –
– Increased electrical activity of the brain leads
to an altered state of consciousness
– Seizure – your consciousness has been seized
– Causes: metabolic/congenital; uremia (elevated urea in blood)
• Cretinism – A deficiency of thyroxin from birth
– Blood tests are now required in newborns
– Hypothyroid babies are put on synthroid (synthetic
thyroxin) so they don’t become mentally retarded
DIENCEPHALON
The diencephalon with the telencephalon (cerebrum)
constitute the forebrain, which is surrounded by the
cerebral hemispheres.
Thalamus – contains 3rd
ventricle, a relay center
Epithalamus – contains the pineal
gland which secretes melatonin
Thalamus: The Waking Center (RAS: Reticular Activating System)
• The thalamus consists of masses of gray
matter in the center of the cerebral
hemispheres;
• All sensory information from the body
travels to the thalamus before going to the
cerebral cortex, except for olfactory
senses (smell). Smell goes directly to the cerebral cortex.
• Lets us tune out unimportant stuff, and tune in important stuff.
It’s a “sensory filter.” It alerts the cerebral cortex to relevant info.
(E.g. a mother is not awakened by noise except if it is her baby’s
cry).
Thalamus (cont.)
• Regulates levels of alertness and consciousness
– Sleep/wake states are controlled by opposing neurotransmitters in the
RAS
– Coma – we can’t be awakened or aroused at all
– Stimulated level of alertness – excited
– Hallucinations – we are in an extreme excited state
Thalamus (cont.)
• Drugs:
– CNS stimulants – increase alertness of the RAS (epinephrine, caffeine,
(which raises cAMP levels in the cell), amphetamines (mimic epi)
– Hallucinogens (LSD, psilocybin) overstimulate the RAS, alter the ability
of the RAS to filter sensory information into the cerebral cortex
– CNS depressants – slow down the RAS: alcohol, sedatives, inhibit
neuronal activity. Combining these  coma; injury of thalamus
interferes with the ability of information to get up to the cerebral cortex
• The limbic system is connected with the thalamus
– E.g. depression due to life events (which effect the limbic system) sends
signals to the thalamus and we may sleep a lot
– E.g. exciting news – may cause people to lose sleep
Thalamus (cont.)
• Student activity: propose a mechanism for narcolepsy,
the condition in which a person inappropriately falls
asleep during the day despite having enough sleep.
HYPOTHALAMUS is linked to the limbic system
• It’s linked to the pituitary gland by nerve fibers and blood vessels
(hypothalamic/pituitary portal system)
• Visceral Reflex Centers:
– Regulates temperature (thermoregulatory reflex center)
– Appetite/satiety reflex center:
Regulates blood sugar level (normal - 100mg/dL) “
– Osmoregulatory reflex center (regulates salt and water
balance: tonicity
should be 300 mOsm)
HYPOTHALAMUS (cont)
• Modulates the activity of visceral reflex centers in the
medulla oblongata: cardiovascular reflex center AND
vomiting reflex center
• Modulates the activity of the micturition reflex center
and a defacation reflex center. These are located in the
spinal cord.
HYPOTHALAMUS (cont)
• HOMEOSTASIS: It adjusts the activity of the various
visceral organs to match the physical activity and energy
requirements of the person (via descending autonomic
fiber tracts, and the autonomic motor neurons)
• It also secretes two hormones: ADH and oxytocin
– These are neurotransmitter/hormones
Midbrain and Hindbrain (brain stem)
MIDBRAIN – between pons and diencephalon
1) Nigrostriatal system – dopamine sent from
substantia nigra to basal nuclei (control of skeletal
muscles; degeneration results in Parkinson’s)
2) Mesolimbic system – dopamine sent from Ventral
tegmental area to nucleus accumbens (emotional reward)
The Midbrain
• Contains Visceral Reflex Centers:
– Salivation Reflex Center – initiates salivation
– Tearing Reflex Center – controls tearing, incl. when we get something in
our eyes
– Oculomotor reflex center – regulates pupil size; regulates tracking and
focusing of our eyes. When we change from near to distant vision,
there’s a change in the size of the pupils. They’re constricted when we
look at something close; wide when we’re looking far away
HINDBRAIN
1) pons:
contains respiratory control
centers; relay center
2) cerebellum:
motor coordination
3) medulla oblongata,
which contains visceral
control centers
Medulla Oblongata
Reflex centers
– Cardiovascular reflex center regulates blood pressure
– Respiratory reflex center regulates CO2 and O2 levels and pH
• Whenever CO2 accumulates, it can combine with water
• CO2 + H2O  H2CO3 (carbonic acid. Therefore a buildup of
CO2 causes respiratory acidosis)
- Coughing reflex center (a rapid forced exhalation)
- Sneezing reflex center (a forced exhalation out the nose)
- Swallowing reflex center (deglutition)
- Vomiting reflex center. (anti-emetic drugs suppress
electrical activity of the vomiting reflex center
Medulla Oblongata (cont)
-- Vestibular reflex center – receives information from the v.c. nerve
from the cochlea and otolith organs
-- receives visual information from the eyes, tracking of
eyes when spinning
-- receives info about spatial orientation, balance,
equilibrium
-- receives info from peripheral proprioceptors (e.g.
stretch receptors w/in muscle spindles).
--sends out messages to through somatic motor neurons to
contract skeletal muscles, effects posture
-- sends out messages to the oculomotor reflex center in the
midbrain (which controls the size of the pupils; controls eyeball
movement by controlling the extrinsic eye muscles while we spin or
rotate. This causes our eyes to move in the direction we’re spinning in
(tracking or nystagmus). These signals also go to the vomiting reflex
center, causing motion sickness.
Clinical Issues
• Vertigo – a person experiences spinning even though they’re not
spinning. A clinical problem if the person is not really spinning.
• Motion sickness – requires drugs that slow down electrical activity
in the vestibular reflex center/vomiting reflex center
• Nystagmus – eyes drift in direction of spinning with a rapid return in
the opposite direction. This is a clinical problem if the person is not
really spinning.
• The medulla oblongata is the region of the brain least affected by
general anesthesia. Thankfully.
CEREBELLUM
• Means “small brain”/ unconsciously coordinates voluntary motor
activity.
• It receives sensory information from the vestibular apparatus
• It receives sensory information from peripheral proprioceptors (in
joints and tendons) and stretch receptors
• It activates signals along the extra-pyramidal tract to activate
somatic motor neurons to control skeletal muscles.
• The cerebrum wants to move a body part  the cerebellum deals
with the details of how to move the body part.
Injuries to the CEREBELLUM
• Cerebellar Ataxia – a loss of coordination;
• Intention tremors – tremors during movement
• Dysarthria – hesitant and slurred speech; it
Seems like the person is drunk.
• Decomposition of voluntary movements
INTENTION TREMOR
CONTROL OF SKELETAL MUSCLE ACTIVITY
• BASAL nuclei (inhibit)  MIDBRAIN
• CEREBELLUM (excitatory)  MIDBRAIN
• CEREBRAL CORTEX  MIDBRAIN  INVOLUNTARY
(extrapyramidal tract) 
SOMATIC MOTOR NEURONS  SKELETAL MUSCLE
CEREBRAL CORTEX (PRIMARY MOTOR AREA)  VOLUNTARY
PATHWAY, PYRAMIDAL TRACTS  SOMATIC MOTOR NEURONS
(Excitatory or inhibitory); needed for fine motor control
ASCENDING/DESCENDING SPINAL CORD TRACTS
- Carry information from sensory organs up the spinal cord
to the brain
- Naming: Ascending start with spino- and end with the
name of the brain region where they end. Descending
begin with the brain region and end with spinal.
- Ascending – carry sensory information
- Descending – corticospinal, pyramidal tracts(motor),
extrapyramidal motor tracts
CRANIAL NERVES (PNS)
See table 8.6
12 pairs
designated by Roman Numerals
most are ‘mixed’ (sensory and motor)
Those associated with sensory are sensory only. Their
cell bodies are located in ganglia near the sensory
organ
SPINAL NERVES
31 pairs
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
these are mixed
REFLEX ARC
Does not directly involve
the brain
A sensory neuron synapses
with a motor neuron.
Or, a sensory neuron
synapses with an
association
neuron and then a motor
neuron.
An easy way to study
nervous system function.