Chapter 11 and 13a nervous tissue and cranial nerves

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Human Anatomy & Physiology, Sixth Edition

Elaine N. Marieb

PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky

1113a

Nervous System (11) and Cranial Nerves (13a)


Nervous System

The master controlling and communicating system of the body

Functions

Sensory input – monitoring stimuli occurring inside and outside the body

Integration – interpretation of sensory input

Motor output – response to stimuli by activating effector organs


Nervous System

Figure 11.1


Organization of the Nervous System

Central nervous system (CNS)

Brain and spinal cord

Integration and command center

Peripheral nervous system (PNS)

Paired spinal and cranial nerves

Carries messages to and from the spinal cord and brain


Sensory (afferent) division

Somatic afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain

Visceral afferent fibers – transmit impulses from visceral organs to the brain

Motor (efferent) division

Transmits impulses from the CNS to effector organs

Peripheral Nervous System (PNS): Two Functional Divisions


Somatic motor nervous system

Conscious control of skeletal muscles

Autonomic motor nervous system (ANS)

Regulates smooth muscle, cardiac muscle, and glands

Divisions – sympathetic and parasympathetic

Motor Division: Two Main Parts


The two principal cell types of the nervous system are:

Neurons – excitable cells that transmit electrical signals

Supporting cells – cells that surround and wrap neurons

Histology of Nerve Tissue


The supporting cells (neuroglia or glial cells):

Provide a supportive scaffolding for neurons

Segregate and insulate neurons

Promote health and growth

Supporting Cells: Neuroglia


Most abundant, versatile, and highly branched glial cells

They cling to neurons and their synaptic endings, and cover capillaries

Functionally they:

Support and brace neurons

Anchor neurons to their nutrient supplies

Guide migration of young neurons

Control the chemical environment

Astrocytes


Astrocytes

Figure 11.3a


Microglia – small, ovoid cells with spiny processes

Phagocytes that monitor the health of neurons

Ependymal cells – range in shape from squamous to columnar

They line the central cavities of the brain and spinal column

Help to circulate cerebrospinal fluid with cilia

Microglia and Ependymal Cells


Microglia and Ependymal Cells

Figure 11.3b, c


oligodendrocytes – branched cells that wrap around nerve fibers (axons) of neurons in the CNS to form a myelin sheath

Schwann cells – wrap around nerve fibers (axons) of neurons in the PNS to form a myelin sheath

satellite cells - surround neuron cell bodies in the PNS

Oligodendrocytes, Schwann Cells, and Satellite Cells

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3d, e

Oligodendrocytes and Schwann Cells


Structural units of the nervous system

Composed of a body, axon, and dendrites

Long-lived, amitotic, and have a high metabolic rate

Their plasma membrane functions in:

Electrical signaling

Cell-to-cell signaling during development

Neurons (Nerve Cells)


Neurons (Nerve Cells)

Figure 11.4b


Contains the nucleus and a nucleolus

Is the major biosynthetic center

Is the focal point for the outgrowth of neuronal processes

Has well-developed Nissl bodies (rough ER)

Contains an axon hillock – cone-shaped area from which axons arise

Nerve Cell Body (Perikaryon or Soma)


Armlike extensions from the soma

Called tracts in the CNS and nerves in the PNS

There are two types: axons and dendrites

Processes


Short, tapering, and diffusely branched processes

They are the receptive, or input, regions of the neuron

Dendrites of Motor Neurons


Slender processes of uniform diameter arising from the hillock

Long axons are called nerve fibers

Usually there is only one unbranched axon per neuron

Axons: Structure


Generate and transmit action potentials

Secrete neurotransmitters from the axonal terminals

Axons: Function


Whitish, fatty (protein-lipoid), segmented sheath around most long axons

It functions to:

Protect the axon

Electrically insulate fibers from one another

Increase the speed of nerve impulse transmission

Myelin Sheath


Formed by Schwann cells in the PNS and oligodendrocytes in the CNS

A Schwann cell:

Envelopes an axon in a trough

Encloses the axon with its plasma membrane

Has concentric layers of membrane that make up the myelin sheath

Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

Nodes of Ranvier: Gaps in the myelin sheath between adjacent Schwann cells

Myelin Sheath and Neurilemma: Formation


Myelin Sheath and Neurilemma: Formation

Figure 11.5a-c


Both myelinated and unmyelinated fibers are present

Myelin sheaths are formed by oligodendrocytes

Nodes of Ranvier are widely spaced

Axons of the CNS


White matter – dense collections of myelinated fibers

Gray matter – mostly nerve cell bodies (soma) and unmyelinated fibers

Regions of the Brain and Spinal Cord


Structural:

Multipolar — three or more processes

Bipolar — two processes (axon and dendrite)

Unipolar — single, short process

Neuron Classification


Comparison of Structural Classes of Neurons

Table 11.1.1



Table 11.1.2



Table 11.1.3


Functional:

Sensory (afferent) — transmit impulses toward the CNS

Motor (efferent) — carry impulses away from the CNS

Interneurons (association neurons) — shuttle signals through CNS pathways

Neuron Classification


Structure of a Nerve

Nerve – cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue

Connective tissue coverings include:

Endoneurium – loose connective tissue that surrounds axons

Perineurium – coarse connective tissue that bundles fibers into fascicles

Epineurium – tough fibrous sheath around a nerve


Structure of a Nerve

Figure 13.3b


Classification of Nerves

Sensory and motor divisions

Sensory (afferent) only – carry impulse to the CNS

Motor (efferent) only – carry impulses from CNS

Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve


Peripheral Nerves

Mixed nerves – carry somatic and autonomic (visceral) impulses

The four types of mixed nerves are:

Somatic afferent and somatic efferent

Visceral afferent and visceral efferent

Peripheral nerves originate from the brain or spinal column


The 12 Cranial Nerves

Twelve pairs of cranial nerves arise from the brain

They may have sensory, motor, or both sensory and motor functions

Each nerve is identified by a number (I through XII) and a name

Four cranial nerves carry parasympathetic fibers that serve muscles and glands


Cranial Nerves

Figure 13.5a


Summary of Function of Cranial Nerves

Figure 13.5b


Make up your own memory device!

I. O______________ VII. F_______________

II. O______________ VIII. V______________

III. O_____________ IX. G_______________

IV. T_____________ X. V________________

V. T______________ XI. A________________

VI. A_____________ XII. H_______________


Cranial Nerve I: Olfactory

Functions solely by carrying afferent impulses for the sense of smell

Arises from the olfactory epithelium

Passes through the cribriform plate of the ethmoid bone

Fibers run through the olfactory bulb and terminate in the primary olfactory cortex


Cranial Nerve I: Olfactory

Figure I from Table 13.2


Cranial Nerve II: Optic

Functions solely by carrying afferent impulses for vision

Arises from the retina of the eye

Optic nerves pass through the optic canals and converge at the optic chiasm

They continue to the thalamus where they synapse

From there, the optic radiation fibers run to the visual cortex


Cranial Nerve II: Optic

Figure II Table 13.2


Cranial Nerve III: Oculomotor

Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape

Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles

Parasympathetic cell bodies are in the ciliary ganglia


Cranial Nerve III: Oculomotor

Figure III from Table 13.2


Cranial Nerve IV: Trochlear

Functions primarily as a motor nerve that directs the eyeball

Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle


Cranial Nerve IV: Trochlear

Figure IV from Table 13.2


Cranial Nerve V: Trigeminal

Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

Composed of three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3)

Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3)


Cranial Nerve V: Trigeminal

Figure V from Table 13.2


Cranial Nerve VI: Abducens

Functions primarily as a motor nerve innervating the lateral rectus muscle

Fibers leave the inferior pons and enter the orbit via the superior orbital fissure

Figure VI from Table 13.2


Cranial Nerve VII: Facial

Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands; Sensory function is taste from the anterior two-thirds of the tongue

Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face

Mixed nerve with five major branches


Cranial Nerve VII: Facial

Figure VII from Table 13.2


Cranial Nerve VIII: Vestibulocochlear

Functions are solely sensory – equilibrium and hearing

Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border

Two divisions – cochlear (hearing) and vestibular (balance)


Cranial Nerve VIII: Vestibulocochlear

Figure VIII from Table 13.2


Cranial Nerve IX: Glossopharyngeal

Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland; Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx

Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat

Nerve IX is a mixed nerve with motor and sensory functions


Cranial Nerve IX: Glossopharyngeal

Figure IX from Table 13.2


Cranial Nerve X: Vagus

Motor - Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs; Sensory function is in taste

The only cranial nerve that extends beyond the head and neck

Fibers emerge from the medulla via the jugular foramen

The vagus is a mixed nerve


Cranial Nerve X: Vagus

Figure X from Table 13.2


Cranial Nerve XI: Accessory

Primarily a motor nerve:

Supplies fibers to the larynx, pharynx, and soft palate

Innervates the trapezius and sternocleidomastoid, which move the head and neck

Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord

The spinal root passes upward into the cranium via the foramen magnum

The accessory nerve leaves the cranium via the jugular foramen


Cranial Nerve XI: Accessory

Figure XI from Table 13.2


Cranial Nerve XII: Hypoglossal

Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

Fibers arise from the medulla and exit the skull via the hypoglossal canal


Cranial Nerve XII: Hypoglossal

Figure XII from Table 13.2

Chapter 11 and 13a nervous tissue and cranial nerves

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