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
In brain
Lines fluid cavities in brain
Forms myelin sheath; around CNS nerves
Supports PNS nerves; unmyelinated
Around peripheral nerve; myelinated
Nerve Cells: Glia
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 Unipolar
Majority of neurons Interneurons or motor neurons
Sensory neurons 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 Chemical Synapse
Synaptic knobSynaptic cleftPlasma membraneNeurotransmitter
Gap junctionsCardiac cells, some smooth muscle
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
• Membrane Potential – difference in electrical charge across the plasma membrane• Resting MP - Only Na+ slowly diffusing through channels; no action potential yet
Action Potential
Chemical Synapse1. RMP -70mV2. 3Na+ moves out/2K+ moves in down
the axon (action potential)3. Synaptic knob receives action
potential4. Ca+2 channels open to allow
extracellular Ca+2 to diffuse into presynaptic cell
5. Ca+2 triggers exocytosis of neurotransmitters from the vesicles in the knob
6. Neurotransmitters diffuse into synaptic cleft
7. Neurotransmitters bind to receptor molecules in membrane of postsynaptic neuron
8. Na+/K+ gates open and create local potential
9. Local potential moves towards axon where action potential begins to repeat process
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
Mechanisms To Produce Action Potential
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
• 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:AminesSerotonin
• 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:AminesDopamine
• Inhibitory and Excitatory
• Epinephrine = hormone
• Norepinephrine = adrenaline
• Cocaine increases the amount of and blocks the reuptake of dopamine, seratonin and epinephrine!
Neurotransmitters:AminesEpinephrine & Norepinephrine
• 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
Neurotransmitters:NeuropeptidesEndorphines
Myomas
• Glioma - common type of brain tumor that is usually benign but may still be life-threatening
• 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)
Pia Mater
Arachnoid Membrane
Dura Mater
Epidural Space
Subdural Space
Subarachnoid Space
sc vertebrate
Pia
Ara
chn
oid
Dur
a
Subarachnoid Space (contains CSF)
Subdural SpaceEpidural Space
Falx cerebri – extension of dura mater that extends vertically to separate two hemispheres
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 Brainstem– Midbrain– Cerebellum– Diencephalon– Cerebrum
BrainstemMedulla 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
BrainstemPons
• Between medulla and midbrain
• motor control and sensory analysis
• Regulate respiration
BrainstemMidbrain
• 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
DiencephalonThalamus
• 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
DiencephalonHypothalamus
• 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
DiencephalonPineal 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
relaxed wave
drowsy wave
deep sleep wave
EEG/ECGElectroencephalogram
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
PNSNerves
Somatic NSVoluntary
Effectors = skeletal muscles
Autonomic NSInvoluntary
Sympathetic Motor System
“Fight or Flight”
ParasympatheticMotor System
“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
• “Fight-or-Flight”• Allows body to
function under stress
Sympathetic Nervous System
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