Interesting Brain Facts

Brain Facts

• The adult human brain typically weighs around 3 pounds, equivalent to 1,300-1,400 grams.
• An adult human brain accounts for about 2% of the total body weight.
• By comparison, an elephant brain weighs about 6,000 grams.
• A cat brain weighs about 30 grams.
• The human brain has roughly 100 billion neurons.
• The octopus brain contains approximately 300 million neurons.
• The cerebral cortex has a surface area of about 2500 sq. cm, roughly 2.5 ft2.
• Maureen Weston holds the record for the longest time awake at 449 hours (18 days, 17 hours).
• Unconsciousness occurs 8-10 seconds after the brain's blood supply is interrupted.
• During early pregnancy, neurons multiply at a rate of 250,000 neurons per minute.
• An adult human cerebellum weighs 150 grams.
• The total volume of cerebrospinal fluid (CSF) ranges from 125-150 ml.
• The body produces approximately 400-500 ml of cerebrospinal fluid (CSF) daily.
• Cerebrospinal fluid is clear and colorless in its normal state.
• The human spinal cord contains about 13,500,000 neurons.
• The human spinal cord is 45 cm long in men, and 43 cm long in women.
• There are 1,000 to 10,000 synapses found in a "typical" neuron.

Nervous System Structure

• The nervous system includes the brain, spinal cord, and nerves.

Nerve Cell Composition

• There are around 100 billion neurons
• Glia support nerve cells; there are approximately 900 billion glia cells
• Glial cells include:
  • Astrocytes
  • Microglia
  • Ependymal cells
  • Oligodendrocytes
  • Schwann cells

Glial Cells Function

• Astrocytes are in the brain
• Ependymal cells line the fluid cavities in the brain.
• Oligodendrocytes form the myelin sheath around central nervous system (CNS) nerves.
• Schwann cells support peripheral nervous system (PNS) nerves and can be myelinated or unmyelinated.

Neuron Structure and Function

• Dendrites carry impulses to the cell body.
• Axons carry impulses to organs and extend the distance to supply organs.
• The cell body contains the nucleus and is located in the brain or spinal cord.
• Neurolemma is a thin membrane around the axon that functions in regeneration.
• Brain and spinal cord do not have neurolemma, so damage is permanent.

Myelin Sheath

• A myelin sheath insulates the neuron.
• The fatty covering is formed by Schwann cells.
• Nodes of Ranvier are gaps between Schwann cells.
  • Nodes of Ranvier serve relay 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.
  • The myelin sheath allows your brain to communicate with your toes in a few thousandths of a second.
• Insulation permits fine control over muscles.
• Babies cannot smile or move precisely at birth because the insulation for their nerve fibers is not completely developed.
• As insulation develops, children can smile and move with greater coordination and precision.

Multiple Sclerosis

• Multiple sclerosis involves deterioration of myelin sheath.
• Multiple sclerosis will slow or block messages between the brain and the body.
• Multiple sclerosis involves glia and not neurons.

Neuron Structural Classification

• Multipolar neurons are the majority of neurons and are interneurons or motor neurons.
• Bipolar neurons classifed as sensory neurons.
• Unipolar neurons are classified as sensory neurons.

Types of Neurons

• Sensory or afferent neurons receive stimulus and send info to brain and are unipolar and bipolar.
• Motor or efferent neurons carry signals from the brain to effector muscles.
• Interneurons connect sensory neurons with motor neurons and are multipolar.

Synaptic Transmission

• Electrical synapses use gap junctions for communication.
• Gap junctions can be found in cardiac and some smooth muscle.
• Chemical synapses involves synaptic knob, synaptic cleft, plasma membrane, and neurotransmitter.

Sodium-Potassium Pump

• Membrane potential is the difference in electrical charge across the plasma membrane.
• The resting membrane potential (MP) involves only sodium (Na+) slowly diffusing through channels; no action potential yet.
• The sodium/potassium (Na+/K+) pump uses active transport.
• It is embedded within the plasma membrane.
• It pumps sodium (Na+) out of the cell (neuron).
• It pumps potassium (K+) into the cell (neuron).
• The ratio of sodium to potassium is uneven, 3Na+ : 2K+.
• The imbalance is needed to maintain resting potential.

Action Potential

• Resting
• Depolarization
• Repolarization

Chemical Synapse Process

• Action potential received at the synaptic knob, Ca+2 channels open, and extracellular Ca+2 diffuses into the presynaptic cell
• Ca+2 triggers exocytosis of neurotransmitters from the vesicles in the knob
• Neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules in membrane of postsynaptic neuron
• Binding causes Na+ and K+ gates to open and create local potential
• Local potential moves towards the axon where action potential begins

Action Potential Mechanisms

• Resting Potential is at -70 mV.
• Stimulus then triggers Na+ channels to open, allowing Na+ into the cell, causing Depolarization.
• As threshold potential reaches -59mV, more Na+ influx occurs and the membrane is further depolarized.
• At action potential peak, Na+ gates close at +30 mV.
• K+ gates open, and K+ diffuses out, creating Repolarization.
• Brief period of hyperpolarization occurs due to too much K+ outflow; membrane potential restores with ions in resting position.
• During the refractory period which is the brief period where the membrane resists stimulation.
• For 0.5 ms after a threshold stimulus, the membrane will not respond to stimuli.

Threshold Stimulus and the All-or-None Response

• Stimulus have a certain minimum intensity to cause a neuron to fire - also known as the threshold of the neuron
• Smaller, or weaker stimuli won't provoke a response
• Stimulus open channels, and enough must be open to depolarize the membrane
• Increasing a stimulus above threshold does not result in a larger response is all-or-nothing.
• With all stimuli above threshold causing a neuron to fire, intensities of stimuli are detected using:
• Temporal summation - frequency of stimulation - a neuron fires more or less often, so 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, so 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

• There are more than 30 known neurotransmitters.
• They are classified by function and chemical structure- excitatory versus inhibitory.
• Function is determined by postsynaptic receptors.
• Neurotransmitter types:
  • Acetylcholine (Ach)
  • Amines
  • Neuropeptides

Neurotransmitter Classification

• Direct stimulation involves synaptic cleft, neurotransmitter, and neurotransmitter binding sites.
• Second messenger stimulation also involves synaptic cleft, neurotransmitter, and neurotransmitter binding sites.

Neurotransmitter: Acetylcholine (ACh)

• ACh is its own class of neurotransmitter.
• It is synthesized from acetate and choline.
• ACh junctions with motor effectors.
  • These include muscles and glands.
• ACh is found in many parts of the brain.
• It can be either Exhibitory or inhibitory
• ACh is involved in memory.
• Low Ach at NM junction causes Myasthenia Gravis.
  • Nerves cannot make muscles contract and do work with low Ach.
  • Muscular weakness and recessive disorder

Neurotransmitters: Amines

• Amines are synthesized from amino acids.
• Amines are found in various regions of the brain.
• It affects learning, emotions, and motor control.
• Neurotransmitters include:
  • Serotonin
  • Histamine
  • Catecholamines Dopamine Epinephrine Norepinephrine

Neurotransmitters: Serotonin

• Serotonin acts as a mostly inhibitory agent.
• It affects mood, emotions, and sleep.
• Low serotonin can cause depression or anxiety including mood disorder serotonin and or norepinephrine
  • Antidepressant/antianxiety drugs (SSRIs), make more of these neurotransmitters available to the brain
  • LSD binds to serotonin receptors, blocking the inhibitory effect, which leads to hallucinations (acid trip).

Neurotransmitters: Dopamine

• Dopamine is mostly inhibitory.
• It affects emotions, body temperature regulation, and water balance.
  • Low dopamine and norepinephrine is associated with ADHD.
  • Low dopamine has been linked to Parkinson's disease.
  • NM junction transmission results in a tremors
  • Is treated with L-dopa, which adds dopamine to the brain. However, too much L-dopa can result in schizophrenic-like symptoms.
  • High dopamine has been linked to schizophrenia.
  • Schizophrenia thought disorder and is incurable, but drug treatments control the disease.
  • Drugs treat schizophrenia by making less dopamine available to the brain.

Neurotransmitters: Epinephrine and Norepinephrine

• Epinephrine and Norepinephrine are inhibitory and excitatory.
• Epinephrine= hormone
• Norepinephrine = adrenaline

Neurotransmitters: Neuropeptides Endorphins

• Primarily inhibitory
• Works to block block pain.
• They block neurotransmitter receptor sites in the brain, which prevents sensory neurons from firing.
• Heroine, codeine, and morphine are chemically similar to endorphins and have the same effect.

Myomas (Brain Tumors)

• Glioma is a common type of brain tumor that is usually benign but may still be life-threatening.
• Glioblastoma multiforme is a highly malignant form of an astrocytic tumor.

CNS Outer Coverings

• Brain is covered with cranial bones
• Spinal cord is covered with vertebrate

CNS Inner Coverings- Meninges

• Dura mater (outer most layer, tough 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 separates dura mater and bony covering of brain and spinal cord and is a cushion of fat.
• Subdural space separates dura mater and arachnoid membrane and contains lubricating serous fluid.
• Subarachnoid space separates arachnoid and pia mater and contains cerebrospinal fluid (CSF).

Meningitis

• Meningitis: infection/swelling of meninges.
• Meningitis is caused by infection from viruses, bacteria, or other microorganisms and may also arise due to certain drugs or other diseases.
• Meningitis may be life threatening due to inflammation's proximity to the brain and spinal cord.
• Symptoms of meningitis are headache and neck stiffness, fever, confusion or altered consciousness, and inability to tolerate light or loud noises.
• A rash may presents, indicating a cause of meningitis, meningococcal bacteria.

Meningitis Diagnosis & Treatment

• Meningitis diagnosed by a spinal tap.
• Meningitis can be treated promptly with antibiotics or antiviral drugs.
• In some situations, corticosteroid drugs prevent complications from overactive inflammation.
• Meningitis can lead to serious long-term consequences or may be prevented by immunization.

Cerebrospinal Fluid (CSF)

• Offers cushioning
• Acts as circulating fluid
• Monitors internal environment changes
• Located in subarachnoid space and within cavities and canals of brain and spinal cord
• The average adult has 140 ml of CSF.

Hydrocephalus

• With hydrocephalus, a child has the "water head" and in unborn children, the drainage canal for CSF is blocked and fluids expand the brain.
• Children have oversized heads and are mentally retarded.
• hydrocephalus Accompanies other diseases (spina bifida, brain tumor, blood clots).
• It is a possible cause of coma or death.

Spinal Cord

• Located within the 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 into out of spinal cord.
• Interneurons are located in gray matter.
• Consists of a single mixed nerve on each side where dorsal and ventral nerve roots join.

Spinal Cord Makeup

• Gray matter extends the length of the spinal cord.
• Spinal cord consists of cell bodies of interneurons and motor neurons.
• Spinal reflex centers located here, has incoming sensory or outgoing motor.
• White matter surrounds gray matter and consists of axons.

Major Brain Regions

• Medulla oblongata
• Pons
• Midbrain
• Cerebellum
• Diencephalon
• Cerebrum
• All make up the Brainstem

Medulla Oblongata

• Considered the lowest part of the brainstem, attaches brain to spinal cord.
• Regulates the reticular formation for arousal an sleep, the (damaged=coma) and coordinates breathing, heart rate, and other activities of the gut.
• Coordinates swallowing, yawning, hiccuping, vomiting, coughing, and sneezing and injury often causes death.

Brainstem: Pons

• Located between medulla and midbrain with motor control and sensory analysis.
• Functions in respiration.

Midbrain

• Is above the pons, and below cerebrum.
• Functions in auditory and visual sensing, or muscular control.

Cerebullum

• Second largest part of brain.
• Contains numerous grooves and gyri and acts with the cerebral cortex to produce skilled movements (coordination).
• Controls skeletal muscles for balance, controls posture, subconscious level; and automatic processor and sends impulses to the cerebrum to coordinate movement.

Diencephalon

• Between cerebrum and midbrain
• Consists of:
  • Thalamus
  • Hypothalamus
  • Optic chiasma
  • Pineal body

Diencephalon: Thalamus

• Located between cerebral cortex and lower brain center with a role to perform major relay station for sensory impulses of emotions and complex reflex
• Conscious sensations like temperature, touch, and pain are detected at the cerebral cortex.

Diencephalon: Hypothalamus

• Located below the Thalamus.
• Links mind and body, it Regulates and coordinates autonomic activities,Synthesizes hormones secreted by [pituitary gland.
• Affects Water balance, Regulates appetite, and maintains normal body temperature.

Pineal Body

• Effects body's biological clocl and releases melatonin.

Cerebrum

• Contains:

  • Cerebral cortex
  • Cerebral tracts
  • Cerebral nuclei

• These all give four general functions

  • Consciousness
  • Language
  • Emotions
  • Memory

• Surfaces contains Gyri (bumps) and sulci (shallow grooves), and fissures are deep grooves

• The lobes in the fissures are:

  • 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 vs Inner surface of the cerebrum

• The Outer surface is made up of 6 layers of gray matter
• Largest and uppermost division of the brain and each hemisphere haves 4 lobes: Frontal, Parietal, Temporal, and occipital

Frontal Lobe

• Frontal lobe has multiple roles.
  • Prefrontal: personality, adjustment, foresight and imagination, and sense of self
  • Primary function; origination of of movement coordinated by Broca’s Area for speech production

Parietal Lobe

• The parietal lobe is an area that integrates sensory input with emotions and cognition
  • Touch as a primary sensation will occur before Proprioception sensation (proprioception is the subconscious awareness of body position in space).
    • If Lesions cause sensory the loss of the sensations or Proprioception.
  • A result can be; Receptive speech losses

Temporal Lobe

• Primarily deals with sounds, memory, and speech comprehension:
  • Cognition
  • Emotion
  • Memory
• Auditory control located at the temporal lobes while Wernicke's area governs the aspect to speech comprehension

Occipital

• The Occipital is in charge of visual processing as well the visual aspects for eye moment.

Limbic System

• Emotion, behavior, long term memory, and olfaction

  • Set of brain structures that forms the inner border of the cortex

  • It Includes:

    • Corpus callosum: connects left and right hemispheres
    • Hippocampus: long-term memory; cognitive maps
    • Amygdala: reward, fear, mating

Brain hemisphere

• Left-sided brain controls Language,
• Dominating hand movements
• Reasoning (logical functions)
• Controls Positive emotions
• Right:
  • Controls hearing
    • Dominating hand movements
    • Reasoning (logical functions), which are the:Spatial relationships
  • Nonsymbolic
  • Controls Positive emotion with Art and Spirituals function

EEG/ECG

• Electroencephalogram, can show brain activity and functions.
• Beta: awake state.
• Alpha: relaxed state.
• Theta: drowsy.
• Delta: deep sleep.

CNS Disorders

• Aphasia: loss of speech
• Hemiplegia, paraplegia, triplegia, quadriplegia: paralysis
• Cerebral palsy: crippling disease involving permanent damage to motor control areas of the brain
• Spastic paralysis
• CVA (cerebrovascular accident) also called Stroke: Cessation/hemorrhage of blood, which can cause neurological issues or damage
• Dementia, which often is due to:
  • Alzheimer’s- inherited usually onset around age 30-40
  • Huntington’s Disease (memory impacts later in age): affects memory in middle to late adulthood, causing cortex
• Lesions or can have impacts or origin from HIV and or AIDS
• Seizures: with Epilepsy

Nervous System Division Chart

• The nervous system is divided into the PNS and CNS.
  • The PNS is divided into Somatic nervous system with voluntary muscle control or the Autonomic nervous system with involuntary muscle movement
  • the Autonomic nervous system is broken down into the Sympathetic which is the “Fight or Flight” response, and the Parasympathetic system for “Rest and Repose”

Somatic Nervous System (SNS

• Skeletal muscles are somatic effectors.
• Transmits voluntary motor pathways outside of CNS.
• Neurotransmitter = ACh

Reflexes

• Reflexes - All motor pathways outside of CNS, acting as a resulting nerve impulse passing over reflex arc and an predictable response to stimuli: Autonomic reflexive (Visceral, Contraction, and Glands)
• Somatic Reflexes: Contraction.
• Somatic Reflexes Contracting skeletal muscles. Deviating form in certain conditions. Diagnostic and tool which often are the

Reflex Testing Includes

• patellar test :extension of lower leg
• Achilles reflex test : extension of foot
• Babinski (after 1.5 yrs means damage): Flexion of all toes
• Plantar test :flexion of all toes test
• Corneal wink when touch cornea
• Abdominal: stroke side of abdomen causes drawing in of abdominal wall

Autonomic Nervous System (ANS)

• Involuntary and Visceral body functions like Cardio, Respiratory, digestion and urogenital function, maintaining heart beat regulation
• Conducts nerve impulses from the CNS to autonomic effectors
• Two divisions:
  • Sympathetic
  • Parasympathetic

Sympathetic

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

Parasympathetic

• Feed-or-Breed” Response
• Rest-and-Repose
• Counteracts Sympathetic