chapter 010

The Human Body in Health and Illness, 4th edition

Barbara Herlihy

Chapter 10: Nervous System: Nervous Tissue

and Brain

Lesson 10-1 Objectives

• Define the two divisions of the nervous system.

• List three functions of the nervous system.• Compare the neuroglia and neuron.• Explain the function of the myelin sheath.• Explain how a neuron transmits information.• Describe the structure and function of a

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Divisions of the Nervous System

• Central nervous system (CNS)

• Peripheral nervous system

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Functions of the Nervous System

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Types of Nervous Tissue

• Neuroglia or glia– Most abundant type – Support, protect, insulate, nourish, and generally

care for neurons

• Neurons– Do the communicating for the nervous system – Long shape makes them delicate

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Neuroglia

• Astrocytes• Ependymal cells• Microglia• Schwann cells • Oligodendrocytes

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Parts of a Neuron

• Cell body• Dendrites• Axon– Myelin sheath– Nodes of Ranvier– Neurilemma– Axon terminal

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Types of Neurons

• Sensory (afferent) neurons– Carry information from periphery toward the CNS

• Motor (efferent) neurons– Carry information from CNS toward periphery

• Interneurons– Found only in CNS; connect sensory and motor

nerves

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Nerve Impulses or Signals

• Electrical signals convey information along a neuron

• Also called action potential• Move along sensory or motor neurons

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The Action Potential

• Polarization: Resting state

• Depolarization: Stimulated state

• Repolarization: Return to resting

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Ionic Basis of the Action Potential

• Polarization– K+ leaks from neuron.– Determines resting

membrane potential

• Depolarization– Na+ rushes in.

• Repolarization– K+ rushes out.

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Why Action Potential “Moves”

• Action potential– Forms at axon’s

beginning– Regenerates along

axon’s length– Enters axon terminal – Releases ACh from

vesicles

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Increasing Action Potential’s Speed

• Myelin insulates axon.• Myelin exposes some

axonal membrane—nodes of Ranvier.

• Action potentials jump quickly from node to node, like a kangaroo.

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Communication across the Synapse

• ACh is – Secreted from neuron A – Diffused across synaptic cleft – Bound to receptors on neuron B

• Neuron B is activated.

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Lesson 10-2 Objectives

• Describe the four major areas of the brain.• Describe the functions of the four lobes of the

cerebrum.• Describe how the skull, meninges,

cerebrospinal fluid, and blood-brain barrier protect the central nervous system.

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Four Major Areas of the Brain

• Cerebrum• Diencephalon• Brain stem• Cerebellum

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Cerebrum: Four Lobes

• Frontal lobe• Parietal lobe• Temporal lobe• Occipital lobe

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Cerebrum: Markings

• Gyrus (convolution)• Fissures (sulci)– Central– Lateral– Longitudinal

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Frontal Lobe

• “ The executive” • Behavior• Personality• Motor control

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Frontal Lobe: Motor Activity

• Primary motor area– Precentral gyrus

• Frontal eye field • Motor speech area– Broca’s area

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Frontal Lobe: Motor Homunculus

• Shows percentages of frontal lobe devoted to body’s motor activities

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Other Cerebral Lobes• Parietal– Somatosensory area– Gustatory area

• Temporal– Auditory cortex – Gustatory area– Olfactory area

• Occipital– Visual cortex

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Functions Spanning Cerebral Lobes

• Speech areas– Span temporal, parietal and occipital lobes– Usually in left hemisphere– Wernicke’s area (helps translate thought into

speech)

• Association areas– Helps to interpret sensory information– Examples: Visual, auditory, somatosensory

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Diencephalon• Thalamus• Hypothalamus

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Brain Stem• Midbrain• Pons• Medulla oblongata• Vital center• Emetic center• Reflex center

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Cerebellum• Mediates

reflexes• Coordinates

motor activity• Evaluates

sensory input

Structures Spanning Brain Divisions• Limbic system– Emotional brain

• Reticular formation: Reticular activating system; sleep-wake cycle, consciousness, gaze center

• Memory areas– Immediate memory– Short-term memory – Long-term memory

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Protecting the CNS: Four Layers

• Bone• Meninges• Cerebrospinal fluid• Blood-brain barrier

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Protecting the CNS: Meninges

• Dura mater• Arachnoid mater– Subarachnoid space

• Pia mater

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Protecting the CNS: Cerebrospinal Fluid (CSF)

• Formed in ventricles by choroid plexus

• Circulates through subarachnoid space– From central canal of

spinal cord – From foramina

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Drainage of CSF

• Drainage of CSF must equal its production.

• Arachnoid villi project into dural sinuses filled with blood.

• CSF drains into blood and leaves the brain.

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Protecting the CNS: The Blood-Brain Barrier

• Made of special cells (astrocytes) within cerebral capillaries.

• Prevents some toxins from entering CNS from blood

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