Chapter 2Neural and Genetic Bases of Behavior

Overview of Nervous SystemOverview of Nervous System

Nervous System: an extensive network of specialized cells that carry information to and from all parts of the body

Neuroscience: deals with the structure and function of neurons, nerves, and nervous tissue

– relationship to behavior and learning

LO 2.1 What Are the Nervous System, Neurons, and Nerves?

An Overview of the Nervous SystemAn Overview of the Nervous System

Organization of the Nervous System

Organization of the Nervous System

Central(brain and

spinal cord)

Nervoussystem

Autonomic (controlsself-regulated action of

internal organs and glands)

Skeletal (controlsvoluntary movements of

skeletal muscles)

Sympathetic (arousing)

Parasympathetic (calming)

Peripheral

Nervous SystemNervous System

Central Nervous System (CNS)

–the brain and spinal cordPeripheral Nervous System (PNS)

–the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body

Central nervous system (CNS)Central nervous system (CNS)

– Spinal cord: slender, tube-shaped part of the (CNS) that connects the brain to the body via the peripheral nervous system The spinal cord transmits information from sensory

neurons to the brain, and from the brain to motor neurons that initiate movement.

The upper segments of the spinal cord control the upper parts of the body, while the lower segments control the lower body.

The spinal cord also controls some automatic, involuntary responses to sensory stimuli called reflexes.

ReflexReflex a simple, automatic, inborn response to a

sensory stimulus

Skinreceptors

Muscle

Sensory neuron(incoming information)

Motor neuron(outgoing information)

Brain

Interneuron

Spinal cord

Peripheral Nervous SystemPeripheral Nervous System

Peripheral nervous system (PNS): all nerves and neurons that are not contained in the brain and spinal cord but that run through the body itself

– divided into the:somatic nervous systemautonomic nervous system

LO 2.4 Somatic and Autonomic Nervous Systems

The Peripheral Nervous SystemThe Peripheral Nervous System

Peripheral nervous system: All the nerves located outside the brain and spinal cord.

– Its function—to connect the brain and spinal cord with the organs and tissues of the body.

– The peripheral nervous system is composed of two major divisions: The somatic/skeletal nervous system The autonomic nervous system

– Sympathetic nervous system– Parasympathetic nervous system

The Peripheral Nervous SystemThe Peripheral Nervous System

Somatic Nervous SystemSomatic Nervous System

Soma = “body” Somatic nervous system: division of the

PNS consisting of nerves that carry information from the senses to the CNS and from the CNS to the voluntary muscles of the body– sensory pathway: nerves coming from

the sensory organs to the CNS consisting of sensory neurons

LO 2.4 Somatic and Autonomic Nervous Systems

Somatic Nervous SystemSomatic Nervous System

Somatic Nervous System (cont’d)

– motor pathway: nerves coming from the CNS to the voluntary muscles, consisting of motor neurons

LO 2.4 Somatic and Autonomic Nervous Systems

Autonomic Nervous SystemAutonomic Nervous System

Autonomic Nervous System (ANS)

– division of the PNS consisting of nerves that control all of the involuntary muscles, organs, and glands; sensory pathway nerves coming from the sensory organs to the CNS consisting of sensory neurons

LO 2.4 Somatic and Autonomic Nervous Systems

Autonomic Nervous SystemAutonomic Nervous System

– sympathetic division (fight-or-flight system): part of the ANS that is responsible for reacting to stressful events and bodily arousal

– parasympathetic division: part of the ANS that restores the body to normal functioning after arousal and is responsible for the day-to-day functioning of the organs and glands

LO 2.4 Somatic and Autonomic Nervous Systems

Functions of the Parasympathetic and Sympathetic Divisions of the Nervous SystemFunctions of the Parasympathetic and Sympathetic Divisions of the Nervous System

The Endocrine System Communicates

by Secreting Hormones

The Endocrine System Communicates

by Secreting Hormones

The endocrine system is interconnected with—but not part of—the nervous system.

– consists of a network of glands that make and secrete hormones - chemical messengers.

– The pituitary gland (master gland), in the base of the brain, releases about 10 different hormones and is controlled by the hypothalamus.

– Other endocrine glands include the thyroid gland, the adrenal glands, and the gonads.

The Endocrine GlandsThe Endocrine Glands

The Endocrine GlandsThe Endocrine Glands

Pineal gland: endocrine gland located near the base of the cerebrum that secretes melatonin

Thyroid gland: endocrine gland found in the neck that regulates metabolism

Pancreas: endocrine gland that controls the levels of sugar in the blood

LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior

The Endocrine GlandsThe Endocrine Glands

Gonads: the sex glands that secrete hormones that regulate sexual development and behavior as well as reproduction

– ovaries: the female gonads

– testes: the male gonads

LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior

The Endocrine GlandsThe Endocrine Glands

Adrenal glands: endocrine glands located on top of each kidney that secrete over thirty different hormones to deal with stress, regulate salt intake, and provide a secondary source of sex hormones affecting the sexual changes that occur during adolescence

LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior

The Neuron The Neuron Neurons are specialized cells in the

nervous system that send and receive information throughout the body.

– Neurons are the nervous system’s building blocks.

A NeuronA Neuron

The nervous system contains 90 to 180 billion neurons (98.8 percent in the brain and 1.2 percent in the spinal cord).

Each neuron transmits information to about a thousand other neurons; there are trillions of different neural connections in the brain.

Structure of the NeuronStructure of the Neuron

Parts of a Neuron

– dendrites: branch-like structures that receive messages from other neurons

– soma: the cell body of the neuron, responsible for maintaining the life of the cell

– axon: long, tube-like structure that carries the neural message to other cells

LO 2.1 What Are the Nervous System, Neurons, and Nerves?

NeuronNeuron

Structure of a Neuron

There are three basic types of neurons:

There are three basic types of neurons:

Sensory neurons: send information from sensory receptors to the brain

Motor neurons: send commands from the brain to glands, muscles, and organs

Interneurons: connect other neurons to one another

Structure and Operation of the NeuronStructure and Operation of the Neuron

Neural CommunicationNeural Communication

Action Potential – a neural impulse; a brief electrical charge

that travels down an axon– generated by the movement of positively

charged atoms in and out of channels in the axon’s membrane

Threshold – the level of stimulation required to trigger a

neural impulse

Firing is all or none

Generating the Message: Neural ImpulseGenerating the Message: Neural Impulse

All-or-none: a neuron either fires completely or does not fire at all

The message is electrical To fire, the neuron must reach threshold Firing (or not-firing) messages come in

on the dendrites Firing is down the axon

The Neural Impulse Action PotentialThe Neural Impulse Action Potential

In the graph below, voltage readings are shown at a given place on the neuron over a period of 20 or 30 milliseconds(thousandths of a second). At first the cell is resting; it then reaches threshold and an action potential is triggered. After a brief hyperpolarization period, the cell returns to its resting potential.

ThresholdThreshold

Generating the Neural ImpulseGenerating the Neural Impulse

Ions: charged particles– inside neuron: negatively charged– outside neuron: positively charged

Resting potential: the state of the neuron when not firing a neural impulse

Action potential: the release of the neural impulse consisting of a reversal of the electrical charge within the axon– allows positive sodium ions to enter the cell

The Neural Impulse Action PotentialThe Neural Impulse Action Potential

Synapses: Points of Chemical Transmission between Neurons

Synapses: Points of Chemical Transmission between Neurons

– Axon terminal buttons contain round sacs called synaptic vesicles.

– When an action potential arrives, it causes these vesicles to release chemical messengers, called neurotransmitters, which travel across the synaptic cleft.

– These neurotransmitters fit into the receiving dendrites’ receptor sites, like keys fit into locks (based on molecular shape).

Synaptic TransmissionSynaptic Transmission

Synapses: Chemical Transmission between

Neurons

Synapses: Chemical Transmission between

Neurons

After locking into receptor sites, neurotransmitters either excite or inhibit firing of the receiving neuron.

Excitatory messages increase the probability of an action potential.

Inhibitory messages reduce the likelihood of neural firing.

Whether the neuron fires will depend on which type of message is in greater abundance.

Synapses: Chemical Transmission between Neurons

After neurotransmitters deliver their messages they are either:

– Repackaged into new synaptic vesicles in a process known as reuptake or

– Broken down by enzymes and removed from the synaptic cleft in a process called enzyme deactivation.

Synaptic Transmission—ReuptakeSynaptic Transmission—Reuptake

Synaptic Transmission— Enzyme Deactivation

Synaptic Transmission— Enzyme Deactivation

Chemical NeurotransmittersChemical Neurotransmitters

About 75 neurotransmitters have been identified, including: Acetylcholine (ACh): involved in muscle

contraction, cognition, and memory formation Dopamine (DA): controls large muscle

movements; influences pleasure and motivation Endorphins: important in the experience of

pleasure and control of pain Serotonin: involved in regulating emotional states

such as depression, sleep cycles and dreaming, aggression, and appetite

Agonists and AntagonistsAgonists and Antagonists

Neurotransmitter molecule

Receiving cellmembrane

Receptor site onreceiving neuron

Agonist mimicsneurotransmitter

Antagonistblocksneurotransmitter

Neuron CommunicationNeuron Communication

– agonists: mimic or enhance the effects of a neurotransmitter on the receptor sites of the next cell, increasing or decreasing the activity of that cell

– antagonists: block or reduce a cell’s response to the action of other chemicals or neurotransmitters

LO 2.2 How Neurons Use Neurotransmitters to Communicate