Albia Dugger • Miami Dade College

Chapter 32Neural Control

Sections 7-12

32.7 The Peripheral Nervous System

• Peripheral nerves carry information though your body, to and from the central nervous system

• Nerves are bundled axons of many neurons

• Each axon is wrapped in a myelin sheath that increases the transmission speed of action potentials

Figure 32-13a p552

nerve fascicle (a number of axons bundled inside connective tissue)

blood vessel

axonmyelin sheath

the nerve’s outerwrappingA

Figure 32-13bcd p552

B “Jellyrolled” Schwann cells of an axon’s myelin sheath

unsheathed node

resting potentialaction potential

Na+

resting potential restored

axon

action potential

resting potential

resting potential

Na+K+

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Functional Subdivisions

• Somatic nervous system • Conducts information about the environment to the central

nervous system (involuntary)• Controls skeletal muscles (voluntary)

• Autonomic nervous system• Conducts signals to and from internal organs and glands

Functional Subdivisions

• The two divisions of the autonomic nervous system have opposing effects on effectors

• Sympathetic neurons are most active in times of stress or danger (fight-flight response)

• Parasympathetic neurons are most active in times of relaxation

Figure 32-14 p553

(most ganglia near spinal

cord)

midbrain medulla

oblongata

(all ganglia in walls

of organs)

pelvic nerve

sacral nerves (5 pairs)

lumbar nerves (5 pairs)

thoracic nerves (12 pairs)

cervical nerves (8 pairs)

Promotes erection, lubrication

Stimulates urination

Sympathetic Effects

Parasympathetic Effects

Constricts airways

Inhibits urination

Genitals

Bladder

Small intestine, large intestine

Adrenal gland

Increases heart rate Heart Decreases heart rate

Increases secretions and movements

Increases secretions to digestive tract

Liver, pancreas

Widens airways

vagus nerve

Airways

Stomach

Decreases secretion

Salivary glandsIncreases salivation Decreases salivation

Slows secretions and movements

Slows secretions and movements

Increases secretion

Slows secretions to digestive tract

optic nerve

Narrows pupilsWidens pupils Eyes

Organ

Increases secretions and

movements

Promotes ejaculation

Take-Home Message:What is the peripheral nervous system?

• The peripheral nervous system consists of nerves that extend through the body and relay signals to and from the central nervous system.

• Neurons of the somatic part of the peripheral system control skeletal muscle and convey information about the external environment to the central nervous system.

• The autonomic system carries information to and from smooth muscle and cardiac muscle, and to glands. Signals from its two divisions—sympathetic and parasympathetic—have opposing effects.

32.8 The Spinal Cord

• Spinal cord• Runs through the vertebral column and connects

peripheral nerves with the brain• Serves as a reflex center

• Central nervous system (CNS)• The brain and spinal cord

Protective Features

• Meninges• Three membranes that cover and protect the CNS

• Cerebrospinal fluid• Fills central canal and spaces between meninges• Cushions blows

Figure 32-15 p554

location of intervertebral disk

vertebra

spinal cord

spinal nerve

meninges(protectivecoverings)

dorsalventral

ANIMATED FIGURE: Organization of the spinal cord

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White Matter and Gray Matter

• White matter• Bundles of myelin-sheathed axons (tracts)• Outermost portion of spinal cord

• Gray matter• Nonmyelinated structures (cell bodies, dendrites,

neuroglial cells)

Dorsal and Ventral Roots

• Spinal nerves of the peripheral nervous system connect to the spinal cord at dorsal and ventral “roots”

• Sensory information travels to the spinal cord through a dorsal root

• Motor signals travel away from the spinal cord through a ventral root

Figure 32-16 p554

ventral horn (gray matter,including the cell bodiesof motor neurons)

ventral root (axonsof motor neurons thatrelay signals towardperipheral regions)

dorsal rootganglion (cellbodies ofsensory neurons)

dorsal root (axons ofsensory neurons thatrelay signals fromperipheral regions)

dorsal horn (gray matter,including interneuronsthat receive input fromsensory neurons)

white matter(myelinatedaxons)

Reflex Pathways

• A reflex is an automatic response to a stimulus, a movement or other action that does not require thought

• Examples: Stretch reflex, knee-jerk reflex, withdrawal reflex

• Spinal reflexes do not involve the brain

• Sensory signals flow to the spinal cord, which commands a response by way of motor neurons

Figure 32-17 p555

synapse of motor neuron with muscle cell

muscle spindle

STIMULUS Biceps stretches.

white matter

RESPONSE Biceps contracts.

gray matter

1

2

3

4

5

6

Take-Home Message: What are the functions of the spinal cord?

• Tracts of the spinal cord relay information between peripheral nerves and the brain. The axons involved in these pathways make up the bulk of the cord’s white matter. Cell bodies, dendrites, and neuroglia make up gray matter.

• The spinal cord also has a role in some simple reflexes, automatic responses that occur without conscious thought or learning. Signals from sensory neurons enter the cord through the dorsal root of spinal nerves. Commands for responses go out along the ventral root of these nerves.

ANIMATED FIGURE: Stretch reflex

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32.9 The Vertebrate Brain

• The brain is the main information integrating organ in the vertebrate nervous system – part of the CNS

• During development, the brain is organized as three functional regions: forebrain, midbrain and hindbrain

Development of the Human Brain

At birth

forebrain

hindbrain

midbrain

7 weeks 9 weeks

Brain Development and Evolution

• In all vertebrates, the embryonic neural tube develops into a spinal cord and brain

• The space inside the embryonic neural tube persists in adult vertebrates as a system of cavities (ventricles) filled with cerebrospinal fluid

Vertebrate Brains

Bird (goose)

Fish (shark)

midbrain

olfactory lobe

forebrain

hindbrain

Reptile (alligator)

Amphibian (frog)

Cerebrospinal Fluid

ventricle with cerebrospinal fluid

The Blood-Brain Barrier

• The blood–brain barrier controls the composition and concentration of cerebrospinal fluid and protects the CNS from harmful substances

• Tight junctions form a seal between adjoining cells of capillary walls

• Some toxins (nicotine, alcohol, caffeine, mercury) are not blocked

The Human Brain

• An average human brain weighs 1,240 grams (3 pounds)

• It contains about 100 billion interneurons, and neuroglia make up more than half of its volume

Hindbrain

• The medulla oblongata connects to the spinal cord – it governs heartbeat, breathing rate, and reflexes such as swallowing, coughing, vomiting, and sneezing

• The pons adjoins the medulla – it affects breathing and has connections to the midbrain

• The cerebellum has more neurons than other brain regions –it is involved in balance, motor skills and language

Midbrain and Brain Stem

• The midbrain in mammals is reduced – it plays an important role in reward- based learning

• Reflex behaviors are controlled by the brain stem (pons, medulla, and midbrain)

The Forebrain

• Cerebrum• Main processing center in humans, responsible for thought

and language• Divided into two hemispheres, coordinated by signals

across the corpus callosum• Each hemisphere deals with the opposite side of the body

The Forebrain

• Thalamus • Receives sensory signals, sorts them, and sends them to

the proper region of the cerebral cortex

• Hypothalamus• Center for homeostatic control of the internal environment• Regulates thirst, appetite, sex drive, and temperature• Interacts with the pituitary gland as a central control center

for the endocrine system

The Human Brain

Figure 32-21b p557

medulla oblongata

corpus callosum

midbrain

cerebellum

pons

thalamushypothalamus cerebrum

Functional Regions of the Human Brain

Take-Home Message: Describe vertebrate brain development and functional regions.

• The vertebrate brain develops from a hollow neural tube, the interior of which persists in adults as a system of cavities and canals filled with cerebrospinal fluid.

• Tissue of the embryonic neural tube develops into the hindbrain, forebrain, and midbrain. The hindbrain controls reflexes and coordination. The unique capacities of humans arise in regions of their enlarged forebrain.

ANIMATION: Ion concentrations

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ANIMATION: Sagittal view of a human brain

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ANIMATION: Regions of the vertebrate brain

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32.10 The Human Cerebrum

• Each cerebral hemisphere is divided into frontal, temporal, occipital and parietal lobes

• Cerebral cortex• Outermost gray matter of the cerebrum• Controls voluntary activity, sensory perception, abstract

thought, language and speech • Distinct areas receive and process signals

Figure 32-22 p558

Broca’s area

occipital lobe (vision)

temporal lobe (hearing, advanced visual processing)

frontal lobe (planning of motor movements, aspects of memory, inhibition of unsuitable behaviors)

primary somatosensory cortex

parietal lobe (visceral

sensations)

primarymotorcortex

Wernicke’sarea

Functions of the Cerebral Cortex

• Specific areas of the cerebral cortex correspond to specific body parts or functions

• The body is spatially mapped out in the primary motor cortex, which controls skeletal muscles

• The primary somatosensory cortex at the front of the parietal lobe receives sensory input from the skin and joints

• Areas for sound, odor, language (Wernicke’s area), and vision are located in specific parts of the cortex

The Primary Motor Cortex

Take-Home Message: What are the functions of the cerebral cortex?

• The cerebral cortex controls voluntary activity, sensory perception, abstract thought, and language and speech.

32.11 Emotion and Memory

• The limbic system (emotional-visceral brain) governs emotions, assists in memory, and correlates organ activities with self-gratifying behavior such as eating and sex

• The limbic system Includes the hypothalamus, hippocampus, amygdala, and cingulate gyrus

Limbic System Components

hippocampus

(olfactory tract)

cingulate gyrus thalamus hypothalamus

amygdala

Making Memories

• The cerebral cortex receives information and processes some of it into memories

• Memory forms in stages• Short-term memory lasts seconds to hours• Long-term memory is stored permanently• Skill memory involves the cerebellum• Declarative memory stores facts and impressions

• Emotions influence memory retention

Sensory stimuli, as from the nose, eyes, and ears

Temporary storage in the cerebral cortex

SHORT-TERM MEMORY

Input forgotten

Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage

LONG-TERM MEMORYInput irretrievable

Recall of stored input

Stepped Art

Figure 32-25 p559

Take-Home Message:

What is the cerebral cortex?

• The cerebral cortex, the outer layer of gray matter, has areas that receive and integrate sensory information. It also controls conscious thought and actions.

• The cerebral cortex interacts with the limbic system, a set of brain structures that collectively affect emotions and contribute to memory.

Video: Targeting Alzheimer’s Disease

32.12 Neuroglia—The Neurons’ Support Staff

• Neuroglial cells (neuroglia) act as a framework that holds neurons in place

• In a developing nervous system, neurons migrate along highways of neuroglia to reach their final destination

• The main neuroglia of the peripheral nervous system are Schwann cells, which produce the myelin that insulates peripheral nerves

Four Main Types of Neuroglia

• Neuroglial cells make up the bulk of the brain

• The adult brain has four types of neuroglial cells• Oligodendrocytes make myelin sheaths• Microglia have immune system functions• Astrocytes stimulate formation of the blood-brain barrier,

take up neurotransmitters, assist in immune defenses, release lactate, and synthesize nerve growth factor

• Ependymal cells line brain cavities

Neuron and Astrocytes

Neuroglia in Disease

• Multiple sclerosis (MS) is an autoimmune disorder that arises when white blood cells attack and destroy the myelin sheaths of oligodendrocytes

• Guillain-Barré syndrome occurs when the immune system attacks and breaks down the myelin of peripheral nerves

• in Alzheimer’s disease, microglia and astrocytes take up and break down beta-amyloid that forms plaques in the brain

Brain Tumors

• Unlike neurons, neuroglia continue to divide in adults, and can be a source of primary brain tumors (gliomas)

• Tumors can also arise from epithelial cells in the meninges or endocrine glands of the brain, such as the pituitary

• Most tumors that originate in the brain are not cancer – however, even a benign tumor can pose a serious threat

Take-Home Message: What are neuroglia and how do they affect health?

• Neuroglial cells make up the bulk of the brain. They provide a framework for neurons, insulate neuron axons, assist neurons metabolically, and protect the brain from injury and disease.

• Because neuroglia have essential roles in assisting neurons, diseases that impair neuroglia impair the function of the nervous system.

• Unlike neurons, most types of neuroglia continue to divide. Thus, neuroglia can be a source of brain tumors.