Brain Facts

The adult human brain weighs about 3 pounds (1,300-1,400 g).

The adult human brain is about 2% of the total body weight.

The elephant brain weighs about 6,000 g.

The cat brain weighs about 30 g.

The human brain has about 100,000,000,000 (100 billion) neurons.

The octopus brain has about 300 million neurons.

The total surface area of the cerebral cortex is about 2500 sq. cm (~2.5 ft2)

The record for time awake is attributed to Mrs. Maureen Weston. She apparently spent 449 hours (18 days, 17 hours) awake in a rocking
chair.

Unconsciousness will occur after 8-10 seconds after loss of blood supply to the brain.

Neurons multiply at a rate 250,000 neurons/minute during early pregnancy.

The weight of an adult human cerebellum is 150 g.

The total volume of cerebrospinal fluid (CSF) is 125-150 ml.

A total of 400-500 ml of cerebrospinal fluid (CSF) is produced every day.

Cerebrospinal fluid is normally clear and colorless.

There are about 13,500,000 neurons in the human spinal cord.

The human spinal cord is 45 cm long in men and 43 cm long in women.

There are 1,000 to 10,000 synapses for a "typical" neuron.
Nervous System
Includes:
•Brain (CNS)
•Spinal Cord (CNS)
•Nerves (PNS)
Nerve Cells
• Neurons: 100 billion
• Glia: support nerve cells; 900 billion
– Astrocytes
– Microglia
– Ependymal cells
– Oligodendrocytes
– Schwann cells
Nerve Cells: Glia
In brain
Forms myelin sheath;
around CNS nerves
Around
peripheral
nerve;
myelinated
Lines fluid
cavities in
brain
Supports
PNS nerves;
unmyelinated
Nerve Cells: Neurons
•
Dendrites
–
•
carries impulse to cell body
axon
–
•
carries impulse to organ; extends the whole
distance to the organ that it supplies
cell body
–
–
•
has nucleus
usually located in brain or
spinal cord
neurolemma
–
–
–
thin membrane around axon
functions in regeneration
of neuron
brain and spinal cord
have no neurolemma therefore
damage is permanent
•
Myelin Sheath
• insulates the neuron
• fatty covering formed by Schwann cells
• Nodes of Ranvier
– gap between Schwann cells
– serves as points along the neuron for generating a signal
– signals jumping from node to node travel hundreds of times
faster than signals traveling along the surface of the axon.
– allows your brain to communicate with your toes in a few
thousandths of a second.
• Insulation permits the nervous system to exercise fine control over
muscles.
• The reason that babies cannot smile or move precisely at birth is
that the insulation for their nerve fibers is not completely developed.
As the insulation does develop in a child, they can smile and move
with greater coordination and precision.
• Multiple sclerosis
– deterioration of myelin sheath
– slows down or blocks messages between
your brain and your body
– involves glia and not neurons
Structural Classification of Neurons
Multipolar
Bipolar
Sensory neurons
Majority of neurons
Interneurons or motor neurons
Unipolar
Sensory neurons
Types of neurons
•
Sensory (afferent)
–
Receives stimulus and sends info to brain
–
Unipolar and bipolar
•
Motor (efferent)
–
Carries signal from brain to effector muscles
–
Multipolar
•
Interneuron
–
Connects sensory neuron with motor neuron; found in brain and spinal cord
–
Multipolar
Synaptic Transmission
Electrical Synapse
Gap junctions
Cardiac cells, some smooth muscle
Chemical Synapse
Synaptic knob
Synaptic cleft
Plasma membrane
Neurotransmitter
•
•
Membrane Potential – difference in electrical charge across the plasma membrane
Resting MP - Only Na+ slowly diffusing through channels; no action potential yet
Na+/K+ Pump
•
Active Transport
•
Embedded in plasma membrane
•
Pumps Na+ out of the cell (neuron)
•
Pumps K+ into the cell (neuron)
•
Ratio is uneven 3Na+:2K+
•
Need to keep a slight imbalance in
order to maintain resting potential
Action Potential
Chemical Synapse
1.
2.
3.
4.
5.
6.
7.
8.
9.
RMP -70mV
3Na+ moves out/2K+ moves in down
the axon (action potential)
Synaptic knob receives action
potential
Ca+2 channels open to allow
extracellular Ca+2 to diffuse into
presynaptic cell
Ca+2 triggers exocytosis of
neurotransmitters from the vesicles
in the knob
Neurotransmitters diffuse into
synaptic cleft
Neurotransmitters bind to receptor
molecules in membrane of
postsynaptic neuron
Na+/K+ gates open and create local
potential
Local potential moves towards axon
where action potential begins to
repeat process
Mechanisms To Produce Action Potential
1.
Resting Potential (-70 mV)
2.
Stimulus triggers Na+
channels to open and allow
Na+ into cell (Depolarization)
3.
As threshold potential (-59mV)
is reached, more Na+ influx,
membrane depolarized more
4.
At action potential peak, Na+
gates close (+30 mV)
5.
K+ gates open, K+ diffuses out
(Repolarization)
6.
Brief period of
hyperpolarization (too much
K+ outflow), membrane
potential is restored with ions
in resting position
Refractory Period
• Brief period where membrane resists stimulation
• 0.5 ms after threshold, will not respond to stimuli
Threshold and All-or-None
•
•
•
•
•
stimulus must have a certain minimum intensity to cause a neuron
to fire - this is the threshold of the neuron
smaller, or weaker, stimuli do not provoke a response
the stimulus causes channels to open and there must be enough of
them opened to depolarize the membrane
increasing a stimulus above threshold does not result in a larger
response - this is all-or-nothing.
If all stimuli above threshold cause a neuron to fire, how do we
detect different intensities of stimuli?
–
–
–
temporal summation - frequency of stimulation - a neuron fires more or
less often. A warm object sends less frequent impulses to the brain
spatial summation - area of stimulation - more neurons fire
different thresholds - not all neurons have the same threshold. A warm
object may trigger only a few neurons while a hot object provides a
stimulus above the threshold of more neurons, causing them to fire
Neurotransmitters
• More than 30 known neurotransmitters
• Classified by function and chemical structure
– Excitatory vs. inhibitory
• Function determined by postsynaptic receptors
• Types
– Acetylcholine (Ach)
– Amines
– Neuropeptides
Neurotransmitters: Classification
Direct Stimulation
Second Messenger Stimulation
Neurotransmitters:ACh
• Acetylcholine is it’s own class
• Synthesized from acetate and choline
• Junctions with motor effectors
– Muscles, glands
•
•
•
•
Found in many parts of the brain
Excitatory or inhibitory
Involved in memory
Low Ach at NM junction causes Myasthenia Gravis
– Without this transmitter nerves cannot make muscles contract
and do work
– muscular weakness
– Recessive disorder
Neurotransmitters:Amines
•
•
•
•
Synthesized from amino acids
Found in various regions of brain
Affect learning, emotions, motor control
Neurotransmitters
– Serotonin
– Histamine
– Catecholamines
• Dopamine
• Epinephrine
• Norepinephrine
Neurotransmitters:Amines
Serotonin
•
•
•
•
•
Mostly inhibitory
Involved in mood, emotions, sleep
SSRIs: selective serotonin reuptake inhibitor
–
Drugs used to increase the extracellular level of the
serotonin by preventing its reuptake into the presynaptic cell, increasing the level
of serotonin in the synaptic cleft available to bind to the postsynaptic receptor.
Low seratonin causes depression or anxiety, Bipolar, OCD
–
mood disorder serotonin and or norepinephrine.
–
Antidepressant/antianxiety drugs (SSRIs) such as Effexor, Prozac, and Zoloft make more
of these neurotransmitters available to the brain.
•
http://www.youtube.com/watch?v=dSZNnz9SM4g
•
http://www.youtube.com/watch?v=GcQE1bN0mgQ
•
http://www.youtube.com/watch?v=9X88bMINXWs
–
Can not use for Bipolar…antidepressant cause mania and vise versa….usually use
Lithium
•
http://www.youtube.com/watch?v=_Y2uIfVUf5o
LSD binds to serotonin receptors and blocks the inhibitory effect which leads to hallucinations
(acid trip)
Neurotransmitters:Amines
Dopamine
•
•
•
•
•
Mostly inhibitory
Emotions, body temp regulation, water balance
Low dopamine (& norepinephrine) in ADHD/ADD
–
http://www.youtube.com/watch?v=5a0T9s_5_us
Low dopamine has been linked to Parkinson's disease
–
NM junction transmission results in a tremors
–
treated with the drug L-dopa which adds dopamine to the brain. Too
much L-dopa can result in schizophrenic-like symptoms
High dopamine has been linked to schizophrenia
–
thought disorder
–
incurable, but drug treatment often allows the disease to be
controlled.
–
Drugs used to treat schizophrenia, such as Thorazine, Haldol and
Clozaril make less dopamine available to the brain.
–
http://www.youtube.com/watch?v=nGqo7ZQc6Sg
Neurotransmitters:Amines
Epinephrine & Norepinephrine
•
•
•
Inhibitory and Excitatory
Epinephrine = hormone
Norepinephrine = adrenaline
•
Cocaine increases the amount of and
blocks the reuptake of dopamine,
seratonin and epinephrine!
Neurotransmitters:Neuropeptides
Endorphines
•
•
•
•
Mostly inhibitory
Act like opiates to block pain
Block neurotransmitter receptor sites in
the brain so neurons relaying messages
from sensory neurons don't fire
Heroine, codeine, and morphine are
chemically similar to endorphins and
have the same effect
Myomas
• Glioma - common type of brain tumor that
is usually benign but may still be lifethreatening
• Glioblastoma multiforme – highly
malignant form of an astrocytic tumor
CNS
• Outer Coverings
– Brain
• cranial bones
– Spinal Cord
• vertebrate
• Inner Coverings
– Meninges
• Dura mater
• Arachnoid membrane
• Pia mater
Meninges
• Dura Mater
– Outer layer
– Strong, white fibrous tissue
• Arachnoid Membrane
– Middle layer
– Delicate, cobwebby
• Pia Mater
– Inner layer (adheres to outer surface of brain and
spinal cord)
– Transparent
– Contains blood vessels
Meninges Spaces
• Epidural Space
– Between dura mater and bony covering of brain and
spinal cord
– Supportive cushion of fat
• Subdural Space
– Between dura mater and arachnoid membrane
– Lubricating serous fluid
• Subarachnoid Space
– Between arachnoid and pia mater
– Contains cerebrospinal fluid (CSF)
Falx cerebri – extension of
dura mater that extends
vertically to separate
two hemispheres
Epidural Space
Subdural Space
Dura Mater
Subarachnoid Space
Arachnoid Membrane
Pia
Arachnoid
Dura
Pia Mater
sc
vertebrate
Epidural Space
Subdural Space
Subarachnoid Space (contains CSF)
•
•
•
•
•
Meningitis
infection/swelling of meninges
caused by infection with viruses, bacteria, or other microorganisms
may also arise due to certain drugs or other diseases.
potentially life threatening due to the inflammation's proximity to the brain and
spinal cord; it is therefore a medical emergency
symptoms
– headache and neck stiffness
– Fever, confusion or altered consciousness
– inability to tolerate light (photophobia) or loud noises (phonophobia).
•
•
•
•
•
•
•
Sometimes, especially in small children, only nonspecific symptoms may be
present, such as irritability and drowsiness.
If a rash is present, it may indicate a particular cause of meningitis
(meningococcal bacteria
diagnosed by a spinal tap
must be treated promptly with antibiotics and sometimes antiviral drugs
In some situations, corticosteroid drugs can also be used to prevent complications
from overactive inflammation.
can lead to serious long-term consequences such as deafness, epilepsy,
hydrocephalus and cognitive deficit, especially if not treated quickly.
Some forms of meningitis may be prevented by immunization
CSF
• Provides supportive, protective cushioning
• Reservoir of circulating fluid
• Monitored by brain to detect changes in
internal environment
• Located in subarachnoid space and within
cavities and canals of brain and spinal
cord
• Average adult has 140ml of CSF
Hydrocephalus
• “water head”
• Sometimes in the unborn child, the drainage
canal for CSF becomes stopped up.
• The fluid builds up and the pressure causes the
brain to expand like a balloon.
• Causes the child to have a very large head and
to be mentally retarded
• Accompanies diseases (spina bifida, brain
tumor, blood clots)
– Possible coma or death
Spinal Cord
•
•
•
•
Within spinal cavity (vertebral column)
Extends from foramen magnum to L1
Reflex center
Dorsal nerve root
– carries sensory info into spinal cord
• Ventral nerve root
– carries motor info out of spinal cord
• Interneurons – in s.c. gray matter
• Spinal nerve – single mixed nerve on each side
of s.c where dorsal and ventral nerve roots join
Spinal Cord
• Gray Matter
– Extends length of s.c
– Consists of cell bodies of interneurons and motor
neurons
– Spinal reflex centers located here
• Incoming sensory, outgoing motor
• White Matter
– Surrounds gray matter
– Consists of axons
Spinal Cord
Brain
• One of largest organs in adults
• 3 lbs
• 6 major divisions
– Medulla oblongata
– Pons
– Midbrain
– Cerebellum
– Diencephalon
– Cerebrum
Brainstem
Brainstem
Medulla Oblongata
• Lowest part of brainstem
• Attaches brain to s.c. just above foramen
magnum
• Reticular Formation – arousal, sleep
(damaged=coma) [Reticular Activating System]
• Controls breathing, heart rate and the activities
of the gut
• Coordinates swallowing, yawning, hiccuping,
vomiting, coughing and sneezing
• Injury often causes death
Brainstem
Pons
• Between medulla and midbrain
• motor control and sensory analysis
• Regulate respiration
Brainstem
Midbrain
• Above pons, below cerebrum
• Auditory and visual centers
• Muscular control
Cerebellum
• 2nd largest part of brain
• Numerous sulci (grooves) and gyri (raised area)
• Acts with cerebral cortex to produce skilled movements
(coordination)
• Controls skeletal muscles for balance
• Controls posture
• Subconscious level; automatic processor
• Impulses travel from cerebellum to cerebrum and muscles to
coordinate movement
Diencephalon
• Between cerebrum and midbrain
• Consists of
– Thalamus
– Hypothalamus
– Optic chiasma
– Pineal body
Diencephalon
Thalamus
• Major relay station for sensory impulses on their way to
cerebral cortex
• Sensations
– Conscious recognition of pain, temperature, touch
– Relay sensory info (except smell) to cerebrum
• Emotions of pleasant and unpleasantness
• Complex reflexes
Diencephalon
Hypothalamus
•
•
•
•
•
•
•
Below thalamus
Links mind and body
Regulates and coordinates autonomic activities
Synthesizes hormones secreted by pituitary gland
Water balance
Regulates appetite
Maintains normal body
temperature
Diencephalon
Pineal Body
• Regulates body’s biological clock
• Produces some hormones
– Melatonin
Cerebrum
•
Cerebral cortex, cerebral tracts, cerebral nuclei.
•
Four general functions
– Consciousness
– Language
– Emotions
– Memory
•
Gyri (bumps) and sulci (shallow grooves)
•
Fissures – deep grooves, divides lobes
– Longitudinal fissure – divides hemispheres
– Central sulcus – between frontal and parietal lobes
– Lateral fissure – between temporal and parietal lobes
– Parietooccipital fissure – between occipital and parietal lobes
•
Outer surface made up of 6 layers of gray matter
•
Largest and uppermost
division of brain
•
Right and left hemispheres
– Separated by corpus collosum
•
Each hemisphere has 4 lobes
– Frontal
– Parietal
– Temporal
– occipital
Parietooccipital
fissure
Lateral fissure
Frontal lobe
•
•
Prefrontal: Personality
– And adaptation of the personality to
events and experiences
– Foresight and imagination
– Sense of self
Frontal:
– main motor areas (originate movement that
is coordinated elsewhere)
– Broca’s Area: speech production
Parietal lobe
•
•
•
•
Principle sensory area
Touch
Proprioception
Lesions cause sensory
losses
• Involvement in cognition
• Receptive speech loss
Temporal
lobe
•
•
•
•
•
Cognition
Emotion
Memory
Auditory
Wernicke’s area: speech
comprehension
Occipital
lobe
• Vision
• Visual
processing
and visual
association
• Involved in
eye movement
Limbic System
•
•
emotion, behavior,
long term memory, and
olfaction
Set of brain structures
that forms the inner
border of the cortex
– Corpus callosum:
connects left and
right hemispheres
– Hippocampus:
long-term memory;
cognitive maps
– Amygdala:
reward, fear,
mating
Left
Hemisphere
•
•
•
•
Language
Dominating hand movements
Reasoning (tangible data)
Positive emotion
Right
Hemisphere
•
•
•
•
Hearing
Touch
Spatial relationships
Nonsymbolic data
– Art
– Spiritual
– Negative emotions
busy wave
EEG/ECG
Electroencephalogram
relaxed wave
drowsy wave
deep sleep wave
CNS Disorders
•
Aphasia
– loss of speech
•
Hemiplegia, paraplegia, triplegia, quadriplegia
– paralysis
•
Cerebral palsy
– drippling disease involving permanent damage to motor control areas of the brain
•
Spastic paralysis
–
–
–
•
altered skeletal muscle performance in muscle tone involving hypertonia; it is also referred to
as an unusual "tightness", stiffness, or "pull" of muscles
lack of inhibition results in excessive contraction of the muscles, ultimately leading to
hyperflexia (overly flexed joints)
Presents in multiple sclerosis and other CNS disorders
CVA (cerebrovascular accident) aka Stroke
– cessation or hemorrhage of blood causing neuronal damage
•
Dementia
– Alzheimer’s: inherited form of dementia (early signs around age 30-40)
– Huntington’s Disease: affects memory in middle to late adulthood, causing cortex
lesions
– AIDS
•
Seizures
– Epilepsy
PNS
Nerves
Somatic NS
Voluntary
Effectors = skeletal muscles
Autonomic NS
Involuntary
Sympathetic
Motor System
Parasympathetic
Motor System
“Fight or Flight”
“Rest and Repose”
Somatic Nervous System
• Contraction of skeletal muscles
• Skeletal muscle = somatic effector
• All voluntary motor pathways outside of
CNS
• Neurotransmitter = ACh
Reflexes
• All voluntary motor pathways outside of CNS
• Reflexes
– Action resulting from nerve impulse passing over a
reflex arc
– Predictable response to stimuli
– Autonomic Reflex
• Visceral
• Contraction of smooth or cardiac muscle
• Secretion of glands
– Somatic Reflex
• Contraction of skeletal muscles
Somatic Reflexes
• Contraction of skeletal muscles
• Reflexes deviate from normal in certain conditions
• Reflex testing is valuable diagnostic tool
– Patellar Reflex: extension of lower leg
– Achilles Reflex: extension of foot
– Babinski Reflex: extension of big toe
• Present until age 1.5
• If present after, indicates damage to corticospinal fibers
– Plantar Reflex: flexion of all toes and slight turning in of foot
– Corneal Reflex: wink when touch cornea
– Abdominal Reflex: stroke side of abdomen causes drawing in of
abdominal wall
Knee-Jerk (Patellar) Reflex
Autonomic Nervous System
• Involuntary/Visceral body functions
– Cardio, resp, dig, urogen
• Maintain homeostasis by: regulating heartbeat,
smooth muscle contraction, glandular secretions
• Conduct impulses from CNS to autonomic
effectors
• Two divisions
– Sympathetic
– Parasympathetic
Autonomic Conduction Pathway
Parasympathetic
Nervous System
• “Feed-or-Breed”
• “Rest-and-Repose”
• Counteracts
Sympathetic
Sympathetic
Nervous System
• “Fight-or-Flight”
• Allows body to
function under stress
ANS Neurotransmitters
• Norepinephrine (adrenaline)
– Adrenergic fibers
• release norepinephrine in postsynaptic sympathetic
neurons
• Acetylcholine (ACh)
– Cholinergic fibers
• release ACh in presynaptic sympathetic neurons
• release ACh in pre and post parasympathetic
neurons
Norepinephrine
• Affects visceral effectors by binding to
adrenergic receptors
– Alpha receptor: blood vessels constrict
– Beta receptor: blood vessels dilate
• Inhibiting action of norepinephrine
– MAO (monoamine oxidase): enzyme that
breaks up norep that are taken up by synaptic
knobs
ACh
• Binds to cholinergic receptors
– Nicotinic receptors
– Muscarinic receptors
• Inhibiting action of Ach
– acetylcholinesterase