Neural and Genetic Bases of Behavior

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Chapter 2Neural and Genetic Bases of Behavior
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Overview of Nervous System
LO 2.1 What Are the Nervous System, Neurons, and
Nerves?

• 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

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An Overview of the Nervous System
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Organization of the Nervous System
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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

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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.

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Reflex

• a simple, automatic, inborn response to a
  sensory stimulus

Brain
Sensory neuron (incoming information)
Interneuron
Motor neuron (outgoing information)
Muscle
Spinal cord
Skin receptors
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Peripheral Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems

• 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

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The Peripheral Nervous System

• Peripheral nervous system All the nerves located
  outside the brain and spinal cord.
• Its functionto 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

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The Peripheral Nervous System
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Somatic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems

• 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

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Somatic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems

• Somatic Nervous System (contd)
• motor pathway nerves coming from the CNS to the
  voluntary muscles, consisting of motor neurons

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Autonomic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems

• 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

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Autonomic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems

• 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

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Functions of the Parasympathetic and Sympathetic
Divisions of the Nervous System
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The Endocrine System Communicates by Secreting
Hormones

• The endocrine system is interconnected withbut
  not part ofthe 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.

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

• 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

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

• 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

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

• 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

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The Neuron

• Neurons are specialized cells in the nervous
  system that send and receive information
  throughout the body.
• Neurons are the nervous systems building blocks.

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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.

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

• 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

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Neuron
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Structure of a Neuron
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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

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Structure and Operation of the Neuron
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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 axons
  membrane
• Threshold
• the level of stimulation required to trigger a
  neural impulse
• Firing is all or none

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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

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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.
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Threshold
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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

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The Neural Impulse Action Potential
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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).

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Synaptic Transmission
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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.

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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.

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Synaptic TransmissionReuptake
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Synaptic Transmission Enzyme Deactivation
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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

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Agonists and Antagonists
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Neuron Communication
LO 2.2 How Neurons Use Neurotransmitters to
Communicate

• 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 cells response to
  the action of other chemicals or neurotransmitters