Biological perspective

Aurelio | Lopez | Pablo |Rodas |Yao

Biological PerspectiveBiological Perspective

Nervous SystemA Network of cells that carries

information to and from all parts of the body

Neuroscience Life science concerned with the structure

and the functioning of the brain, neurons, nerves, and nerve tissues (All part of the

nervous system)Special focus on the relationship of behavior

and learning Santiago ramón y cajal (1887): Doctor who studied about brain tissue; theorized that the

nervous system is made up of individual cells

NeuronIt Receives and sends messages within the

Nervous System“Messenger of the body”

Makes up only 10% of the brain but there are millions of them!

Parts of the neuron

Dendrite (“Branch”) – receives messages from other cells

SOMA; cell body – dendrites attach to this, contains the nucleus and keeps the neuron alive and functioning

Parts of the neuronAxon – fiber attached to the soma/Cell body that carries out messages to other

cells• Does most of the travelling through the body• Coated by myelin sheaths and neurillema (aka

schwann’s membrane)

Parts of the neuronneurillema – surrounds both the axon and

the myelin sheath• Serves as a tunnel where damaged nerve

fibers can repair themselves• Axons in the brain and spinal cord don’t

have this.

Glial Cells

Gray fatty cells that compose 90% of the brain

It keeps neurons in place + lets them develop and work

Provides structural support – insulation• A Neuron’s message = electrical

Functions of the Glial Cells

Some Get nutrients to the neuronsOthers are in charge of Cleaning up dead

neurons The Communication with neurons and

other glial cells Act as insulators

Some affect the functioning of neurons and their structure, and “give birth” to

new neurons during prenatal development

What else do they do?They create myelin!

• Myelin: layer of fatty substance created by 2 types of glial cells

So, what does Myelin do?

It Creates a sheath around the axonwhich Protects it from damageMultiple sclerosis: damages the myelin sheath; leads to a loss of

function

So, what does Myelin do?

it Speeds up the neural message travelling down the axon

• HOW? Nodes of ranvier – they’re the periodic gap in the myelin sheaths of the axon; facilitate the rapid conduction of

nerve impulses

Nerves A “cable” of bundled-up myelin-coated axons

(The nerves are the ones in green)

Axon Terminal

Area at the end of the neuron where it meets another neuron

BUT ONE NEURON ALONE IS

MEANINGLESS!

Neural ImpulseElectrical and chemical transmission of

information from one neuron to another.

Neural Impulse

takes the same path all the timeProcess of conducting

information from a stimulus by the dendrite of one neuron and carrying it through the axon and

on to the next neuron.

So… What’s involved in the neural impulse?

IonsWe have both positively (+) and

negatively (-) charged particlesHowever, we’re only concerned with

the sodium (na+) and Potassium (K+) ions for the neural impulse

Ions inside are mostly negative, while ions on the outside are

mostly positive

Selectively Permeable Membrane

Outer membrane of the neuron is not impermeable

It Selectively allows some ions to pass through

HOW?It has pores that are only large

enough for small ions to pass through; the gates

Charge of the NeuronWhen the cell is at rest (not firing a neural impulse) it’s primarily negative

There are lots of positive sodium ions outside the membrane, while the ions

inside are negativeThey cluster around the membrane Difference in electrical charges =

electrical potential

Na-

Na-

Na-

Na-

Stimulus

Eventually, when the cell receives some stimulation from another cell

Dendrites activateThe particular gates are now open

which allow the sodium ions on the outside to rush into the cell

Action Potential

Causes the inside of the cell to become mostly positive; the

outside, mostly negativeThe Reversal of electrical charge

= action potential

Action Potential

When action potential gets to the end of the axon, the message is

transmitted to another cell

Repolarization

The neuron will now try to restore its charge by pumping out

the positively charged ions and bringing back the negative ones

All-or-noneNeurons are either firing at full strength, or does not fire

at allA strong message = fire more

quickly

The Synapse

End of the axon has several short fibers (axon terminals) with Calcium

ions nearbyAt the end of each terminal, there is a

synaptic knobIt has a number of saclike structures

in it called synaptic vesicles that contain neurotransmitters (chemical

inside a neuron that transmits messages)

The Synapse

Next to the synaptic knob, there’s a dendrite of another neuron

They don’t connect, but there’s a gap in between them called the synaptic

gap

The Synapse

The dendrite of the neighboring neuron contains locks called receptor

sitesShaped in a certain way that only a

particular molecule of a neurotransmitter can fit into it

The calcium stimulates the vesicles to move to the end of the knob

wherein they release neurotransmitters to the synapseThey’ll fit themselves into the

receptor sites, which activates the next cell

The Synapse

Neurons can also be turned on or off, depending on exactly what

synapse is being affectedTurn cells on (excitatory effect)Turn cells off (inhibitory effect)

Agonists

Chemical substances that can mimic/enhance the effects of a

neurotransmitter on the receptor sites of the next cell

Antagonists

Chemical substance that blocks/reduces a cell’s response

to the action of other chemicals/neurotransmitters

BETA BLOCKERS: drugs used to control blood pressure by

blocking heart contractions which lowers the blood pressure

Neurotransmitters

Acetylcholine

Found at the synapses between neurons and muscle cells

Stimulates the contraction of skeletal muscles

Also found in hippocampus (brain area responsible for new

memory)If receptor sites are blocked =

paralysisIf too much released = death

Glutamate

It’s a Major excitatory neurotransmitter of the nervous

systemImportant role in learning and

memory formation

GABA (Gamma-aminobutyric acid)

Most common inhibiting neurotransmitter of the brain

Helps calm anxiety; it’s agonized by alcohol

Causes the general inhibition of the nervous system associated

with drunkness

SerotoninFound in the lower part of the

brainCan either be excitatory or inhibitory; depends on what

synapses are affectedAssociated with sleep, mood and

appetiteLow levels of serotonin have

been linked to depression

Dopamine

Also found in the brain; like serotonin, it can have different

effects depending on the locationControl of movement, sensations

of pleasureToo little released = parkinson’s

diseaseToo much released =

schizophrenia

Endorphin (Endogenous Morphine)

–Neural regulator or neural peptide (a neurotransmitter that directly controls

the release of other neurotransmitters) that controls pain

in the body.–The body halts production of this if

people take morphine or heroin, leaving them with no protection

against pain when the drug wears off (withdrawal).

• Leads to addiction

Cleaning up the synapse

–Neurotransmitters have to get out of receptor sites before the next

stimulation occurs–Reuptake: process where

neurotransmitters are taken back into the synaptic vessels

–Acetylcholine is not taken back

Cleaning up the synapse

–SSRI (Selective serotonin reuptake inhibitors)

–Blocks the reuptake of serotonin–Leaves more in the synapse to bond

with receptor sites–Elevates mood and lifts depression

Central Nervous System

• Consists of the brain and spinal cord

- Both are composed of neurons and glial cells that control life-sustaining functions,

thought, emotion, behavior.

Brain

• Makes sense of information received from the senses, makes decisions,

sends commands out to muscles and the rest of the body

Spinal Cord

• A long bundle of neurons that serves 2 vital functions for NS.

• Divided into two areas.– Outer section is composed of axons and

nerves (which appear white). Carries messages from the body to brain and vice-

versa; a message pipeline.– Inner section is composed of somas (which appear gray). It is a primitive “brain” that is

responsible for very fast, lifesaving reflexes.

Spinal Cord

• Damage to it was once thought permanent. Healthy brain cells only took over the

damaged ones.– It is now known that they can actually be

repaired by the body systems.– Scientists can implant nerve fibers from

outside the spinal cord into a damaged area and coax the damaged spinal nerves – The brain can also change itself by

adapting neurons to serve new functions when older ones die or become damaged.– Dendrites grow and new synapses are formed in at least some areas as people

learn new things

Reflex ARC: 3 types neurons

• Afferent/Sensory Neurons (“Afferent Accesses Spinal Cord”)

– Carries messages from senses to spinal cord

• Efferent/Motor Neurons (“Efferent Exits”)– Carries messages from spinal cord to

muscles and glands• Interneurons

– Connects Sensory and Motor Neurons–Makes up the inside of the spinal cord and

brain• This all happens very quickly. It allows for

very fast response times.

Neuroplasticity

• Lifelong ability of the brain to reorganize neural pathways based on new experiences• Ability of the brain to change with learning• Has a clear age-dependent determinant (the

younger the more plastic)• Occurs in the brain under 2 conditions:– Developmental plasticity and plasticity of

learning and memory– Compensation for lost function and

maximizing what is left• Environment plays a key role in influencing

brain rewiring

Stem Cells

• Repairs brain damage/disease.• Controversial as it comes from embryos• Recently, scientists have tried turning mice bone marrow cells into stem cells. • It is possible too that adult bone

marrow can be used.

Peripheral Nervous System

• Compromised of the nerves and neurons not contained in the brain and

spinal cord• Transmits information to and from the

central nervous system

Somatic Nervous System

• Controls the voluntary muscles of the body

• Carries sensory information and controls movement of the skeletal

muscles

Autonomic Nervous System

• Controls automatic functions of the body

• Automatically regulates glands, internal organs, blood vessels, pupil dilation,

digestion, and blood pressure

Parasympathetic Division

• Maintains body functions under ordinary conditions; saves energy

Sympathetic Division

• Prepares the body to react and expand energy in times of stress

Distant Connections: The Endocrine Glands


• GLANDS are organs in the body that secrete chemicals, some affect

functioning of the body but not all behavior, others have widespread

influence on the body and behavior.

• ENDOCRINE GLANDS secrete chemicals called hormones into bloodstream; affect behavior and emotions by

influencing the activity of the brain and by controlling muscles and organs such

as heart, pancreas, and sex organs.


• pituitary gland• pineal gland• thyroid gland• Pancreas• Gonads

• adrenal glands

Peeking Inside the Brain

• It is impossible to tell the function of a brain structure if it is dead.

• A scientist can’t even be sure what the brain tissue looks like in the skull.

Clinical Studies• Study animals or people with brain

damage- Animals: May damage deliberately, then are tested. Or the area can be electrically

stimulated• Deep lesioning: insertion of a thin, insulated wire into the brain, then a

current is sent that destroys the brain cells at the tip of the wire

• ESB (Electrical Stimulation of the Brain): stimulation of brain tissue with milder current; causes neurons to react as if

they’ve received a message

EEG (Electroencephalograph)

• Record electrical activity of neurons below skull with EEG machine

• Small metal disks (electrodes) are placed on the skin covering the skull using a jelly-like substance to help

conduct. The electrodes are wired to a computer (older ones connected to

graphing machines)


• Output: Waves that indicate sleep, seizures, tumors, etc. It also determines

which areas of the brain are active during reading, writing, speaking, etc.• Alpha waves: Regular, slower waves -

relaxation• Beta waves: Irregular, fast waves -

waking activity• Theta waves: Drowsiness and sleep

• Delta waves: Large, slow waves - Deep stage of sleep


• ICA (Independent Component Analysis): Allows identification of individual

signals• ERP (Event-Related Potential): Results

of multiple presentations of a stimulus are measures and averaged; hence an

electric potential–May be used to follow Alzheimer’s, and lie

detection

CT Scan (Computed Tomography Scan)

• X-ray of the brain that maps “slices” of the brain by computer

• Can show stroke damage, tumors, injuries, abnormal structure

• Good for imaging brain structure especially if there is metal in the body

MRI Scan (Magnetic Resonance Imaging)

• Magnetic field that can create a 3D image of the brain and display “slices”

of it• More detailed than CT Scan

• Strongly not recommended if the person has metal in their body

PET Scan (Positron Emission Tomography)

• Sees brain in action• A radioactive glucose is injected in the

brain, and the computer detects which parts of the brain are using them up. It

projects it on a monitor.–Why glucose? It is the “fuel” of the brain.

• Uses colors - lighter areas are active and darker ones inactive

FMRI (Functional Magnetic Resonance Imaging)

• A form of MRI where the computer tracks changes in oxygen levels of

blood. It is placed on top of the picture of the brain

• By combining images, a “movie” can be made

• More detailed than PET Scans

Parts of the brain

Medulla

• Part of the hindbrain that relays messages between the cerebellum and

the cortex

Pons

• Part of the hindbrain that relays messages between the cerebellum and

the cortex

Reticular Formation

• A system of nerves running from the hindbrain and through the midbrain to

the cerebral cortex• Controls arousal and attention

Hippocampus

• Plays a role in our learning, memory and ability to compare sensory

information to expectations

Pituitary Gland• Regulates other endocrine glands

Hypothalamus• Part of the forebrain that regulates the amount of fear, thirst, sexual drive, and

aggression we feel.

Corpus Callosum• Connects left and right hemispheres of

the brain

Cerebral Cortex• Controls complex thought processes

Thalamus• Part of the forebrain that relays

information from sensory organs to the cerebral cortex

Paul Broca

• Case: (1861) a Man lost ability to speak after a head injury

• Later, after the post mortem autopsy, broca was able to demonstrate that the

cause of the man’s deficit lay in the damage to a specific point in the brain• Proof of this localization of function

(connecting a specific behavior to a specific brain area)

Henry Molaison

-Removal of Both Medial Temporal Lobes (Loss of hippocampus, amygdala, and perirhinal cortex)- Severe anteroggrade amnesia

Phineas Gage

The Accidental Neuroscience

Pioneer

So what happened?

John Martyn Harlow• Phineas Gage’s Doctor

• Arrived an hour after Gage was brought to the hospital

• Did all he could to find out what caused Gage’s changes in behavior.

• “No Longer Gage”

• Continued to study Gage’s skull long after he died.

Biological Perspective• The tamping iron

hit the frontal lobe of Gage’s brain causing changes in personality.

• From a mild mannered man, Gage turned into “fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom)”-Dr. John Martyn Harlow.

Biological perspective

Education

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