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 1.Channels that permit K+ to pass through remain open 2.K+ is pushed out of the cell, which reestablishes the original, resting state of the neuron SODIUM-POTASSIUM PUMP

Action Potential Regeneration The action potential regenerates itself along the axon, traveling down to the axon terminals.

Saltatory Conduction The impulses skip from node to node, thereby increasing the speed of the impulse. Nodes of Ranvier

Synaptic Transmission

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 Parietal lobe Temporal lobe Occipital lobe

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