Unit 2: Neurobiology

Neurons, Brain, Body Systems

NeuroscienceHow does our brain organize and

communicate with itself?How does our brain allow us to

remember the lyrics to dozens of our favorite songs?

How do we remember exactly where we were and what we were doing when we heard about 9/11?

Neural Communication The basic building block of our body’s

communication is the neuron

The human brain has approximately 100 Billion neurons that communicate with each other and allow us to learn, remember, feel pain and function as human beings.

Parts of a Neuron

DendritesBushy, root-like parts of a cellReceive messages

(Neurotransmitters) from the sending

neuroni.e. the receiver

Soma (Cell Body) and Nucleus Contains nucleus and other life sustaining

parts of the cell In is resting state is -70 charged

AxonThe extension of a neuron“The sender”When the threshold is met

an electrical charge travels

down the axon

Myelin Sheath Fatty covering of the axon – “the

insulator” Speeds up the neural impulses Deterioration of the myelin sheath

causes

Multiple Sclerosis

Terminal Branches/Buttons Branched end of the axon containing the

neurotransmitters (the chemical messenger)

When the neuron fires, the terminal buttons release the NT into the synapse

Synapse (Synaptic Gap/Cleft)

Space between the terminal branches of one neuron and the dendrite of another

The gap is less than one billionth of an inch wide

Neurotransmitter The chemical messenger contained in

terminal branches that enable neurons to communicate

Fit into receptor

sites on dendrites

like a key to a lock

How Neurons Fire – the process

Neural communication is an electrochemical process. Electricity travels within the cell (down the axon) and the chemical (the neurotransmitter crosses the synapse to travel between cells). Electricity does not jump between neurons.

1.) In its resting state – the neuron is just hanging out and is at a -70 charge

2.) If enough + ions cross the cell membrane to change the charge to +50, the neuron has met its threshold and goes into action potential

3.) electricity travels down the axon 4.) terminal buttons release the NT 5.) the NT crosses the synapse and binds to the dendrites of the

receiving neuron 6.) the leftover NT is taken back up by the terminal buttons –

known as reuptake

Firing Neurons cont . . . Once a neuron fires it is in a refractory state and

cannot fire again until it pumps the + ions back out of the cell body and returns to a -70 resting state (i.e. it must re-load)

Firing is an “all or none" principle – if you meet the threshold, you fire

completely.

If you don’t, you don’t.

Neural firing takes place in

Fractions of a second

Neurotransmitters – the chemical messenger

Dozens of NT in your body – imbalances can cause problems

1.) Dopamine – controls movement, alertness, emotion – too much = schizophrenia, too little = Parkinson's

2.) Serotonin – affects mood, hunger, sleep, arousal – too little = depression

3.) Acetylcholine (Ach) – affects motor movement, learning, and memory – too little = Alzheimer's

4.) Endorphins – body’s natural pain killers

The Nervous System

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Central Nervous System

/ \

/ \

Brain Spinal Chord

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Peripheral Nervous System

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AutonomicSomatic

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/ \Sympathetic Parasympathetic

Afferent/Efferent Neurons

Afferent = Sensory Neurons – run from body to brain

Efferent = Motor Neurons – run from brain to body

Ex: I put my left hand on a warm stove. Afferent neurons in my left hand carry the message to the sensory cortex in my right brain. Efferent neurons from the motor cortex in my right brain, sends a message to move my left hand.

Peripheral Nervous System

Links the central nervous system with all other nerves in the body

Somatic Nervous System

Controls voluntary muscle movement

Autonomic Nervous System

Controls autonomic functions of our body (heart, lungs, organs, etc)Usually

operates

on its own

Autonomic is

Automatic!

Autonomic is divided into…..

Sympathetic NS: Excitatory - arouses

us for defensive action

Alert system of the body

Accelerates heart rate, blood pressure, breathing; slows digestion

Makes you alert and ready for action

Parasympathetic NS Calming system Returns body to

normal after stress passes

Lowers breathing, heart rate, constricts pupils

Reflexes – exception to the rule…. Message doesn’t go all the way back to the brain Sensory neurons carry the info to the spine and the

spine makes a motor command without the message getting all the way to the brain first Ex: knee; intense heat or cold

Brain Imaging…..

1.) Accidents and Injuries: If a part is damaged, we can deduce what it

controlled. – Phineus Gage

Brain Imaging

2.) Legions: Removal or destruction of part of the brain (brain

tumor). Deduces functions

Brain Imaging

3.) EEG - Detects brain waves

Brain Imaging

4.) CAT – Computerized Axial Tomography

3-D x-ray of brain

Shows

Structure, not

function

Brain Imaging

5.) Magnetic Resonance Imaging – MRI Uses magnetic fields to measure the density and

location of brain material Structure,

not function

Brain Imaging

6.) Positron Emission Topography - PET Lets researchers see what areas of the brain are most

active during certain tasks – shows function Measures how much of a certain chemical are used

in different parts

of the brain.

Uses radioactive glucose

Brain Imaging

7.) Functional MRI

Combines the MRI

and the PET scan

Shows structure and function

Cerebral Cortex (CC)

It’s what you think of when you picture the brain: the gray, wrinkled surface of the brain

It’s a thin layer of densely packed neurons

Cerebral Cortex

Left Hemisphere Gets messages from

and controls the right side of the body

Logic Language Verbal Analytical

Right Hemisphere Gets messages from

and controls the left side of the body

Spatial Creative Emotionally intuitive

The Cerebral Cortex The left and right hemispheres look symmetrical – but they are

biologically the “odd couple” serving complementary functions Complex tasks

involve both

hemispheres

Corpus Callosum - band of fibers

Connecting left and right hemispheres

Split Brain Surgery – severe corpus

callosum – rare treatment for epilepsy

Dateline NBC – Growing Hope – Is Medical Marijuana a Viable Treatment for Epilepsy?

http://www.nbc.com/dateline/video/dateline-june-7-2015/2870103?onid=209511#vc209511=1

4 Lobes of the Brain

Frontal Lobe

Behind the eyes/forehead Involved in abstract thought, emotional

control, rational judgment (Phineus Gage) Contains

The Motor Cortex – sends out motor messages via efferent neurons

Broca’s Area (left frontal) – speech center

Parietal Lobe

Crown of the head

Contains the Sensory cortex – where afferent/sensory neurons carry information

The more sensitive the body area, the greater surface area assigned on the sensory cortex

Occipital and Temporal Lobes

Occipital –

Back of the head

Processes vision

Temporal – sides of head

over ears

Processes hearing

Wernicke’s Area – left temporal – language comprehension

Other Important Brain Parts…

Three subsections of the brain

Hindbrain

Within the hindbrain…

Hindbrain – consists of the top of the spine and base of brain – critical life functions Medulla: blood pressure, heart rate, breathing

Pons: just above medulla – critical in facial expressions

Cerebellum: located on the bottom, back side of the brain. Literally means “little brain.” Critical for balance and fine motor movements.

Midbrain

Just above spine. Very small in humans.

Reticular Formation: Finger shaped network of neurons – extends

throughout hindbrain to midbrain. Controls arousal and ability to focus attention.

Coma when malfunctions

Forebrain

ForebrainControls thought and reasonMost studied by psychologistsMuch bigger than the midbrain &

hindbrainWhat makes us

humans

Within the forebrain…..

Thalamus: sensory switchboard – relays all incoming sensory info except smell

Hypothalamus: “pleasure center” – regulates hunger, thirst, and sexual arousal. Also regulates the

entire endocrine

system via the

pituitary gland

Within the forebrain….

Amygdala: aggression and fear center. (Legion the amygdala in a monkey and he will be passive and docile)

Hippocampus: critical in forming episodic memories. Not fully formed until age 3. Smell is routed through the hippocampus.

Limbic System: the thalamus, hypothalamus, amygdala, and hippocampus all form the limbic system. Deals with aspects of emotion and memory.

Brain Plasticity

The brains ability to re-organize its neural connections after some type of damage, such that one part of the brain can develop the capacity to carry out a function it normally wouldn’t in a healthy brain.

Brain plasticity is inversely correlated with the age. The older you are the less plastic your brain is and the more difficult it is to overcome brain injury.

Genetics

Every human cell has 46 chromosomes in 23 pairs. Genetic material that makes up chromosomes is DNA.

Genetics

Dominant traits over-ride recessive

Genotype – every gene you are a carrier of

Phenotype – what actually manifests in your physical characteristics

Homozygous – having identical alleles for a single trait (BB, bb)

Heterozygous – having two different alleles for a single trait (Bb)

Dominant V. Recessive

Punnett Square

Twins….

Identical twins come from one fertilized egg that splits and share DNA.

Fraternal twins come two separate eggs fertilized by two separate sperm and are no more genetically similar than normal siblings.

Gender and X linked Disorders

Gender is determined by the 23rd pair of chromosomes. XX = girl, XY = boy

Female eggs always carry X. Male sperm carry X or Y and determine the gender of the baby.

X-linked disorders are carried on the X chromosome. Women are often the carriers and the disease manifests in their sons.

Muscular Dystrophy, color blindness, hemophilia

X Linked Disorders

Chromosomal Abnormalities

Turner’s Syndrome - Only one single X (girls). Cannot reproduce, short stature, webbed necks, abnormal sexual development

Klinefelters Syndrome – males, extra X (XXY), varied effects – minimal sexual development, extreme introversion, cannot reproduce

Down’s – extra chromosome on 21st pair. Causes mental retardation.