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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 ft 2 ) 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 Forms myelin sheath; around CNS nerves

Nerve Cells: Glia

Lines fluid cavities in brain Supports PNS nerves; unmyelinated Around peripheral nerve; myelinated

• • • •

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 Majority of neurons Interneurons or motor neurons Sensory 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 + potential gates open and create local 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

Clozaril Thorazine, Haldol

make less dopamine available to the brain.

and – 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 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)

Epidural Space Subdural Space Subarachnoid Space

Falx cerebri

– extension of dura mater that extends vertically to separate two hemispheres Dura Mater Arachnoid Membrane 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 L 1 • Reflex center • Dorsal nerve root – carries sensory info

into

• Ventral nerve root – carries motor info

out

spinal cord 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) [ R eticular A ctivating S ystem] • 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

• 2 nd 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

• Below thalamus

Hypothalamus

• 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 Lateral fissure – between frontal and parietal lobes – 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 Lateral fissure Parietooccipital 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: comprehension speech

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

EEG/ECG Electroencephalogram

busy wave 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 Sympathetic Motor System “Fight or Flight” Involuntary Parasympathetic Motor 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

Sympathetic Nervous System

• “Fight-or-Flight” • Allows body to function under stress

ANS Neurotransmitters

• Norepinephrine (adrenaline) – Adrenergic fibers • release norepinephrine in

post

synaptic sympathetic neurons • Acetylcholine (ACh) – Cholinergic fibers • release ACh in

pre

synaptic sympathetic neurons • release ACh in

pre

and

post

neurons parasympathetic

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