Chapter 2 Neural and Genetic Bases of Behavior

Overview 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 System

Organization of the Nervous System Central (brain and spinal cord) Nervous system Autonomic (controls self-regulated action of internal organs and glands) Skeletal (controls voluntary movements of skeletal muscles) Sympathetic (arousing) Parasympathetic (calming) Peripheral

Nervous System Central Nervous System (CNS) –the brain and spinal cord Peripheral 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) –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.

Reflex a simple, automatic, inborn response to a sensory stimulus Skin receptors Muscle Sensory neuron (incoming information) Motor neuron (outgoing information) Brain Interneuron Spinal cord

Peripheral 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 system  autonomic nervous system LO 2.4 Somatic and Autonomic Nervous Systems

The 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 System

Somatic 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 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 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 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 System

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 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 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 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 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 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 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?

Neuron

Structure of a Neuron

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 Neuron

Neural 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 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 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.

Threshold

Generating 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 Potential

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 Transmission

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—Reuptake

Synaptic Transmission— Enzyme Deactivation

Chemical 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 Antagonists Neurotransmitter molecule Receiving cell membrane Receptor site on receiving neuron Agonist mimics neurotransmitter Antagonist blocks neurotransmitter

Neuron 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