Biology and Behavior

The Nervous system

• “Command center of the body

• controls what we think, how we feel, and how we move

What makes up the Nervous System?

Brain, Spinal cord, and nerves

What is the Nervous System divided into?

• Central nervous system (CNS)

• Peripheral nervous system (PNS)

Neurons

• Cells that receive, integrate, and transmit info to the nervous system

• Basic units of the system

3 types of neurons

1. sensory

2. motor

3. interneuron

What do neurons do?

Communicate with chemical signals through neural networks

Neurotransmitter

Chemical sent between neurons

How do networks develope?

Through repeated firing/communication

What do neurotransmitters do?

cause cells to “fire” AKA carry an electrical pulse

Cell Body

Info received by the dendrites from thousands of other neurons is collected and integrated

Axon

Once info is integrated in cell body, electrical impulses are transmitted along a long, narrow outgrowth

Dendrite

• Short, branchlike appendages that detect chemical signals from neighboring neurons

• Incoming signals can excitatory (make neuron fire) or inhibitory (prevent neuron from firing)

Myelin Sheath

• fatty material made up of glial cells

• Insulates axons to allow for faster movement

Nodes of Ranvier

Small gaps of exposed axon between segments of the myelin sheath, where action potentials take place

Terminal Buttons

Tiny bulblike structures at the end of axons that carry the neuron’s message into the synapse

Synapse

Chemical connections occur between neurons

• tiny gap between the axon of the “sending” neuron and the dendrite of the “receiving” neuron

Membrane

Fatty barrier covering the neuron

Semipermeable

Some substances can pass through

Ion channels

• Located along the membrane

• Allow ions to enter

• Regulates concentration of electrically charged molecules

Resting membrane potential

• The electrical charge of an inactive neuron

• Neurons are polarized (have an electrical charge)

• Charge inside is more negative than outside

Action potential (neuron firing) - in order for a neuron to fire…

It must be stimulated beyond a certain threshold

What can a strong stimulus trigger?

• More neurons to fire

• neurons fire more often

• does not affect action potentials strength or speed

What happens to the cell when a neuron fires?

electrochemical changes occur within the cell

All-or-nothing principle

• A neuron fires or does not fire

• same potency each time

• strength determines by how often a neuron fires

• stronger = more action potentials

What does action potential cause?

Causes channels in the cell membrane to open, allowing positively charged molecules to rush in

When do channels open?

When a region of an axon becomes depolarized

What happens to the intensity of an action potential as it goes down the length of the axon?

It stays the same

Depolarization

First domino falls

Propagation

The chain reaction that happens once the first domino falls

Resting membrane potential

A set up domino set

What does a neuron do before it can fire again?

The neuron resets to ensure forward movement of impulse

Refractory period

the time following an action potential during which a new action potential cannot be initiated

repolarization

reseting the dominos

Return to resting state

The dominoes are set up in original position agin

Neurotransmitters (NTS)

Chemicals that are made in the axon and stored in vesicles

What do neurotransmitters do?

Convey signals across the synapse

Presynaptic neuron

sends information

Postsynaptic neuron

receives information

Release of NTS

• Action potential reaches end of axon terminal

• NTS that are stored in vesicles are released into synapse

• “messenger” passes signal to the next neuron

Crossing the synapse

• NTS bind to receptors on the next neuron

• They bind to specific receptors on the postsynaptic neuron (next neuron)

• Binding opens ion channels on the postsynaptic neuron, which may trigger a new action potential if the signal is strong enough (excitatory) or inhibit it (inhibitory)

Reuptake

NTS “sucked” back into presynaptic terminal buttons

Enzyme deactivation

Enzyme destroys NTS in synapse

Auto reception

NTS binds to auto receptors in presynaptic neuron

• Presynaptic neuron monitors NT levels, inhibit further NT release when there is enough

Excitatory

increases likelihood of firing

• Acetylcholine

• Norepinephrine

• Glutamate

Inhibitory

decreases likelihood of firing

• dopamine

• serotonin

• GABA

• endorphins

Acetylcholine (Ach) function

• Voluntary movement

• memory

Dopamine function

• Movement

• Motivation

Glutamate function

memory

GABA (gamma-aminobutyric acid) function

Movement

Norepinephrine function

• sleep

• learning

• mood

Serotonin function

• mood

• appetite

• aggression

Endorphins function

• modulation of pain

Acetylcholine (ACh) disorder with malfunctioning

Alzheimer’s disease

Dopamine disorder with malfunctioning

• Schizophrenia (too much)

• Parkinsons’s (too little)

Glutamate disorder with malfunction

• Seizures

• neuron loss after strong

GABA (gamma-aminobutyric acid) disorder with malfunction

• Severe anxiety

• Huntington’s disease

• Epilepsy

Norepinephrine and Serotonin disorders with malfunction

• depression

• mood disorders

Endorphins disorder with malfunction

no established disorder