The Neural Control of Behavior

Chapter 5

Neurons The Basic Unit of the Mind NEURONS: single cells in

the nervous system that are specialized for carrying information rapidly from one place to another and/or integrating information from various sources

The human brain contains ~100 billion neurons and ~100 trillion synapses

The Human Nervous System

•CENTRAL NERVOUS SYSTEM: comprised of the brain and spinal chord•PERIPHERAL NERVOUS SYSTEM: the entire set of cranial and spinal nerves that connect the central nervous system (brain and spinal chord) to the body’s sensory organs, muscles, and glands.•NERVE: a large bundle containing the axons of many neurons. Located in the PNS, nerves connect the CNS with muscles, glands and sensory organs

Varieties of Neurons

SENSORY NEURONS: carry messages from a sensory organ (e.g. eyes, ears, nose, tongue and skin), through a nerve, into the brain and spinal chord.

MOTOR NEURONS: carry messages from the brain or spinal chord, through a nerve, to a muscle or gland

INTERNEURONS: exist entirely within the brain or spinal chord and carries messages from one set of neurons to another

Neuronal Structures SOMA: or cell body, contains

the nucleus and other cellular machinery

DENDRITES: thin, tube-like extensions that branch out of the soma and are specialized for receiving signals from other neurons

AXON: thin, tube-like extension from a neuron that is specialized to carry neural impulses to other cells

Neuronal Structures AXON TERMINAL : a swelling

at the end of the axon that is designed to release a chemical substance onto another neuron, muscle or gland cell

MYELIN SHEATH: a casing of fatty cells wrapped tightly around the axons of some neurons

Action Potentials

ACTION POTENTIAL: neural impulses; the all-or-nothing electrical bursts that begin at one end of the axon of a neuron and move along the axon to the other end

The Neuronal Membrane

CELL MEMBRANE: thin, porous outer covering of a neuron or other cell that separates the cell’s intracellular fluid from extracellular fluid

The Resting Potential

•The constant electrical charge that exists across the membrane of an inactive neuron

-70 millivolts

•A- and K+ inside

•Na+ and Cl- outside

Depolarization and Repolarization

DEPOLARIZATION

1. Action potential causes channels in the membrane to open

2. Na+ rush into the cell, making it more positive

3. Once it’s more positive inside than outside the cell, the channel closes

REPOLARIZATION

4. Channels that permit K+ to pass through remain open

5. K+ is pushed out of the cell, which reestablishes the original, resting state of the neuron

SODIUM-POTASSIUM PUMP

Action Potential Regeneration

The action potentialregenerates itself along the axon, traveling down to theaxon terminals.

Saltatory Conduction

The impulses skip from nodeto node, therebyincreasing thespeed of theimpulse.

Nodes of Ranvier

Syna

ptic

Tran

smiss

ion

Excitatory and Inhibitory Synapses

• Synapse at which the neurotransmitter increases the likelihood that an action potential will occur

• NT open Na+ channel depolarization• E.g. glutamate

Excitatory Synapse

• Synapse at which the neurotransmitter decreases the likelihood that an action potential will occur

• NT open Cl- or K+ channel hyperpolarization• E.g. GABA (gamma-aminobutyric acid)

Inhibitory Synapse

How Drugs Alter Synaptic Transmission

1. Act on the presynaptic neuron and either promote or inhibit neurotransmitter release

2. Act within the synapse to either promote or inhibit the process that terminates the action of the neurotransmitter

3. Act on postsynaptic receptors, either producing the same effect as the neurotransmitter or blocking the neurotransmitter from producing its normal effect

The Brain

Subcortical Structures: The Brain Stem and Thalamus

Spinal chord

Cerebellum

Thalamus

Medulla

Pons

Midbrain

The Cerebral Cortex

Frontal lobe

Parietallobe

Temporallobe

Occipitallobe

Somatosensory and Motor Cortex Maps

Asymmetry of the Cerebral Cortex

Our hemispheres behave contralaterally

Left hemisphere is specialized for language

Right hemisphere is specialized for nonverbal, visuospatial abilities