Neurophysiology, Neuroanatomy

The brain is a combination of two types of cells, glial cells and neurons

The brain consists of 100 billion neurons and 1012 total cells

Cells in the brain that communicate with each other

Neurons are “born” early in life Limited regeneration

Provide support for neurons◦ Structure support◦ Metabolic and nutritional support

Can replace themselves Serve to clean up the brain, removes dead

tissue and foreign objects Play a large role in neural development May even be communicating with neurons Role is expanding with new research

Pyramidal neuron Purkinje neuron

Neurons communicate in two ways Electrical signal: within a neuron Chemical signal: between neurons Electrical signal is sent from one part of

the neuron to the other: The signal travels from the dendrite through the cell body to the axon◦ Dendrites receive the signal from another

neuron◦ Axons send the signal to other neurons

Chemical signal is sent from the axon of one neuron to the dendrite of another neuron

Neurons contain many ions and are charged

A- are large protein ions that always stay inside the cell

K+ is potassium. At rest it is mostly inside the cell

Cl- is chloride. It exists both inside and outside the cell

Na+ is sodium. It exists primarily outside the cell

When the cell is at rest (i.e., not doing anything), it has a charge of -70 mV. This is called the resting potential.

Because of the cell properties, many forces are acting on the cell.

1. Diffusion - substances tend to move from areas of high concentration to areas of low concentration.

2. Like charges repel each other and opposite charges attract

Charges stay the way they are because of the cell membrane. It is selectively permeable. It does this by ion channels.

Normally, membrane closes Na+ channels However, if the membrane is given an

electrical charge, it causes the membrane to lose some permeability

This opens the sodium channels If this electrical charge is large enough, the

flood gates will open Change in charge is potentiated down the

length of the neuron This wave of charge is called the action

potential

Once sodium has rushed in, the cell quickly regains its composure

Active process in which sodium is removed from the cell

Sodium is exchanged for potassium Requires metabolic activity Returns charge inside cell to -70 mV Refractory period

When the action potential reaches the terminal button, it causes a release of chemicals called neurotransmitters

These neurotransmitters are dumped into the synapse, the space between the axon of one neuron and the dendrite of another

Neurotransmitters come into contact with membrane of the other neuron

Receptors on the dendrite detect the neurotransmitter

NT binds to the receptor This causes a temporary change in the

membrane, allowing a little sodium inside the cell

This small charge is called the graded potential

This is passed on to the axon and it summates

When the sum of the potentials reaches the base of the axon, a sufficient charge may be present to cause an action potential.

Myelin – a layer of proteins that are wrapped around the axon.

Two functions: to protect the axon, and to speed up transmission

Without myelin, neural transmission is inefficient

Multiple Sclerosis – an autoimmune disorder in which the myelin is destroyed.◦ Fatigue, pain, motor disorders, cognitive

disorders, etc.

After the NT is initially released, the chemical must be removed

This is done in a couple of different ways◦ Biochemical breakdown of the NT◦ Reuptake: NT is pulled back into the presynaptic

button and packaged to be released again

Excitatory◦ Glutamate◦ Acetylcholine

Inhibitory – What does this mean?◦ GABA◦ Norepinephrine

Both◦ Dopamine◦ Serotonin

Psychopharmacology- the study of how drugs affect behavior

Nearly all drugs work by affecting neurotransmitter release

Prozac is an example of a SSRI – a selective serotonin reuptake inhibitor

Alcohol◦ Activates GABA receptors

Nicotine◦ Activates acetylcholine receptors◦ Changes overall number of ACH receptors

Cocaine / crack◦ Blocks reuptake of dopamine◦ Stimulates release of dopamine◦ Anesthetic effect on cells

Amphetamine / Methamphetamine◦ Similar to cocaine with no anesthetic effect

Heroin◦ Activates opiate receptors

Marijuana◦ Activates cannabinoid receptors (similar to opiate)

Ecstasy (MDMA)◦ Selectively destroys neurons that release

serotonin◦ Serotonin is dumped out when the cell dies

Central Nervous System: Includes Brain and Spinal Cord

Peripheral Nervous System: All other neural tissue. Specifically, the periphery. This includes muscles, the skin, and even the organs

PNS broken down into two parts1. Somatic nervous system: nerve fibers that

send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle.

2. Autonomic nervous system – Controls the "insides" (the "viscera") of our body, like the heart, stomach and intestines - functions in an involuntary, reflexive manner - does things like constrict blood vessels, dilate pupils, and even makes our heart beat fast on a roller coaster, etc.-Has two components

- A. Sympathetic nervous system: - B. Parasympathetic nervous system

Sympathetic NS- Regulates “Fight or Flight”◦ Prepares the body during stressful situations ◦ Increases heart beat, blood pressure, speeds

breathing, slows digestive function Parasympathetic NS – Regulates "rest and

digest" ◦ Keeps the body running calmly◦ Shuts down the sympathetic NS when the

situation becomes less stressful

Spinal Cord: Two types of material, white matter (Axons) and grey matter (cell bodies)

Spinal cord relays sensory and motor information to and from the brain

Controls reflexes◦ Ex. Knee jerk reflex, pain reflex

Afferent neurons: neurons that send their signal TOWARDS the spinal cord

Efferent neurons: neurons that send their signal AWAY from the spinal cord

Reflex involves two neurons, one afferent and one efferent

Reflexive action takes place before it is sent to the brain

Allows for extremely efficient processing

3 major divisions1. Hindbrain:

Cerebellum; Pons; Medulla

2. Forebrain: Cortex, amygdala, hippocampus, thalamus, hypothalamus

3. Midbrain

Cerebellum: Extremely large area, millions of neurons◦ Responsible for coordination of movement◦ Plays a role in learning

Pons◦ Important for sleep and especially dreaming

Medulla◦ Controls all vital functions of the body including

breathing and heart rate

Thalamus◦ Primary relay station of the brain◦ Almost all sensory information passes through

before going elsewhere Hypothalamus

◦ Regulates autonomic nervous system◦ Regulates hormones, “4 F’s”; Feeding, Fighting,

Fleeing, and sexual behavior Amygdala

◦ Responsible for many aspects of emotion◦ Emotional learning

Hippocampus◦ Especially important for learning and memory◦ Resolving conflict

Cerebral Cortex◦ Does just about everything◦ Many think that the cortex is what makes

humans the way they are◦ Cortex is broken up into 4 lobes:

Frontal lobe: the front of the brain Temporal lobe: side, the temples Parietal lobe: kinda middle portion Occipital Lobe: very back

Frontal lobe◦ Important for planning◦ Thinking / decision making◦ Primary motor cortex: Generation of movement◦ Broca’s area: Production of Speech

Temporal lobe◦ Audition◦ Wernicke’s area: Language comprehension

Parietal lobe◦ Somatosensory function (touch, vibration, pain)◦ Combination of all senses with vision

Occipital lobe◦ Vision: Primary visual cortex

Brain is actually two different halves. It is split down the middle, with the right and left side being very similar to the other

The two hemispheres are connected by the corpus callosum: a bunch of axons

Each side of the brain controls the opposite side of the body. ◦ Ex. Moving right arm controlled by the left side of

the brain. Systematic differences in right vs. left. Most language and music on the left.

◦ Somewhat different for left-handed people The right hemisphere more involved with

visual imagery and creativity.

Sometimes the corpus callosum of a person is cut. It is often surgically cut in patients with severe epilepsy.

Allows for the study of the role of each hemisphere

Experiments have found crazy strange results

Many techniques can be used to study the brain of animals

Lesioning of the brain◦ Electrical lesions- electricity is passed through an

electrode until neurons die◦ Chemical lesions- inject chemicals like acid to kill

neurons Injection of drugs

In Vitro analysis: “In the Lab” – brain tissue is removed, isolated, and studied on its own. Individual neurons can be studied

In Vivo analysis: “In the Living” – the brain is studied in an intact animal

EEG: electroencephalogram – electrodes are placed on the scalp. ◦ It records the electrical activity of neurons.◦ Problem: It records from thousands of neurons at

a time; not very precise

“CAT” scan: Computerized tomography◦ Computer enhanced 3-D X-Rays◦ Not much resolution, still life

MRI: Magnetic resonance imaging – uses magnetic fields to get brain scans◦ Just get a picture

PET scan: Positron Emission Tomography– patients are injected with radioactive glucose.

The scanner tracks where the glucose moves to. This is used as an indicator of neural activity.

- Has problems: very expensive, resolution is fairly low.

Functional MRI (fMRI) – Registers changes in the metabolism of cells◦ Get 3-D picture of real time brain activity◦ Very expensive