Mammalian Nervous System

Chapter 46

How Is the Mammalian Nervous System Organized?

Vertebrate nervous systems consist of a brain, a spinal cord, and peripheral nerves that extend throughout the body.

The central nervous system or CNS contains the brain and spinal cord.

The peripheral nervous system or PNS consists of the cranial and spinal nerves that connect the CNS to all tissues.

Figure 46.1 Organization of the Nervous System

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Figure 46.2 Development of the Human Nervous System (Part 1)

Figure 46.2 Development of the Human Nervous System (Part 2)

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Figure 46.2 Development of the Human Nervous System (Part 3)

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The three parts of the embryonic brain develop into structures in the adult brain.

The hindbrain becomes the medulla, the pons, and the cerebellum.Physiological functions, such as breathing and swallowing are

controlled by the medulla and pons.Muscle control is coordinated in the cerebellum.

The embryonic midbrain becomes structures that process visual and auditory information.

Together the hindbrain and midbrain are known as the brain stem.

The embryonic forebrain develops the central diencephalon and the surrounding telencephalon.

The diencephalon consists of the: Thalamus, which is the final relay station for sensory information Hypothalamus, which regulates physiological functions such as

hunger and thirst

The telencephalon consists of two cerebral hemispheres and is also called the cerebrum.

An evolutionary trend in which the telencephalon increases in size and complexity in vertebrates is telencephalization.

In humans, the telencephalon is the largest brain region and is involved in sensory perception, learning, memory, and behavior.

The spinal cord: Conducts information between brain and organs. Integrates information coming from PNS. Responds by issuing motor commands.

Anatomy of the spinal cord: Gray matter is in the center, and contains cell bodies of

spinal neurons. White matter surrounds gray matter and contains axons

that conduct information up and down the spinal cord. Spinal nerves extend from the spinal cord.

Spinal reflex: afferent information converts to efferent activity without the brain.

The knee-jerk reflex is monosynaptic: Stretch receptors send axon potentials through dorsal horn to

ventral horn, via sensory axons. At synapses with motor neurons in the ventral horn, action

potentials are sent to leg muscles, causing contraction.

Figure 46.3 The Spinal Cord Coordinates the Knee-Jerk Reflex

Structures in primitive regions of the telencephalon form the limbic system.

Amygdala: involved in fear and fear memory Hippocampus: transfers short-term memory to

long-term memory

Figure 46.4 The Limbic System

Cerebral hemispheres are dominant in mammals.Cerebral cortex – a sheet of gray matter covering each

hemisphere that is convoluted to fit into the skull Gyri: (sing. gyrus) ridges of the cortex Sulci: (sing. sulcus) valleys of the cortex

Figure 46.5 The Human Cerebrum (Part 1)

Figure 46.5 The Human Cerebrum (Part 2)

Regions of the cerebral cortex have specific functions.Association cortex is made up of areas that integrate

or associate sensory information or memories.Four cortical lobes: Temporal Frontal Parietal Occipital

Temporal lobe: Receives and processes auditory information Association areas of the temporal lobe involve:

• Identification• Object naming • Recognition

Agnosia: a disorder of the temporal lobe

Frontal Lobe: Central sulcus: divides the frontal and parietal lobes Primary motor cortex is located in front of the central

sulcus and controls muscles in specific body areas. Association areas involve:

• Planning• Personality

Parietal Lobe: Primary somatosensory motor cortex is located behind

the central sulcus; it receives touch and pressure information.

Association areas involve attending to complex stimuli.Contralateral neglect syndrome: an inability to recognize

stimuli on one side of the body when the opposite parietal lobe is damaged

Occipital Lobe: Receives and processes visual information Association areas involve:

• Making sense of the visual world• Translating visual experience into language

Autonomic Nervous System (ANS): the output of the CNS that controls involuntary functions

ANS has two divisions that work in opposition: one will increase a function and the other will decrease it.

Sympathetic and parasympathetic divisions are distinguished by anatomy, neurotransmitters, and their actions.

Sympathetic and parasympathetic divisions have different anatomy.

The sacral region contains preganglionic neurons of the parasympathetic region.

The thoracic and lumbar regions contain sympathetic preganglionic neurons.

Figure 46.10 The Autonomic Nervous System

Electroencephalogram (EEG): Measures activity of groups of neurons Records changes in electrical potential between

electrodes, over timeElectromyogram (EMG) records skeletal muscle

activity.Electrooculogram (EOG) measures eye movement.

Figure 46.14 Patterns of Electrical Activity in the Cerebral Cortex Characterize Stages of Sleep (1)

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Figure 46.14 Patterns of Electrical Activity in the Cerebral Cortex Characterize Stages of Sleep (2)

Language areas: Broca’s area located in the frontal lobe: damage

results in slow or lost speech but a person can read and understand language.

Wernicke’s area is in the temporal lobe: damage results in an inability to speak sensibly, as written or spoken language is not understood. A person may still be able to produce speech.

Angular gyrus: adjacent area essential for integrating spoken and written language

Figure 46.15 Language Areas of the Cortex (Part 1)

Figure 46.15 Language Areas of the Cortex (Part 2)

Figure 46.16 Imaging Techniques Reveal Active Parts of the Brain