chapter 10 central nervous system, spinal nerves, and cranial nerves

Chapter 10: Central Nervous System, Spinal Nerves, and Cranial Nerves

Vertebrae Spinal meninges

3 layers of connective tissue Dura mater Arachnoid mater Pia mater

Continuous with cranial meninges Cerebrospinal fluid (CSF)

Spinal Cord Protection and Coverings

External Cord Anatomy The spinal cord is located within the vertebral canal.

It is well protected. The vertebral ligaments, meninges, and CSFprovide additional protection.

The meninges (e.g., dura, arachnoid, pia) are three layers of connective tissue coverings that extend around the spinal cord and brain.

Spinal cord extends from the medulla oblongata, to the upper border of L2

(ending with the conus medullaris).

The roots of the spinal nerves or cauda equina, angle down the vertebral canal like wisps of flowing hair.

External Cord Anatomy

Internal Cord Anatomy The gray matter of the spinal cord contains

neuronal cell bodies,dendrites, unmyelinated axons, axon terminals, and neuroglia.

On each side of the spinal cord, the gray matter is subdividedinto regions called horns.

The white matter consists primarily of myelinated axons of neurons and is organized into white columns.

Each spinal nerve (and cranial nerve) contains layers of protective connective tissue coverings. Individual axons, whether myelinated or unmyelinated, are wrapped in endoneurium. Groups of axons with their endoneurium are arranged in bundles,called fascicles, each of which is wrapped in perineurium. The superficial covering over the entire nerve isthe epineurium.

Peripheral Nerves

Reflexes The pathway followed by nerve impulses that produce a

reflex is known as a reflex arc. Using the patellar reflex (knee jerk reflex) as an example, the basic components of a reflexinclude: 1) sensory receptor,2) sensory neuron, 3) integrating center, 4) motor neuron, and 5) effector.

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• Reflexes

The Human Brain The Human body uses only ~3 lbs. of tissue to process all

emotions, solve every equation, read every book, and take every breath

All these functions, andmany others, occurwithin the 100 billionneurons and 10 trillionneuroglia that comprisethe human brain

The human brain, compared to all other animals’ brains, is marked by the highest ratio of brain to body size － thought to directly correlate with our higher level of intelligence. Most of the expansion is manifest in man’s large cerebral

cortex. Especially expanded are the frontal lobes which are

associated with higher

(executive) functions such

as self-control, planning,

reasoning, and abstract thought.

The Human Brain

Parts of the Brain

Production and Flow of CSF CSF is a clear, colorless liquid that carries oxygen,

glucose, and other chemicals to neurons and neuroglia and removes their wastes and toxic substances.

CSF circulates through the subarachnoid space around the brain and spinal cord, and through cavities called ventricles.

The sites of CSF production are the choroid plexuses.

Production and Flow of CSF

Failure of CSF to form and drain normally results in a buildup of pressure called hydrocephalus. Hydrocephalus occurs with congenital

abnormalities, headinjury, meningitis, and episodes of bleeding into the brain.

Production and Flow of CSF

The Twelve Cranial NervesCranial Nerves

Cranial NervesCN I is the olfactory nerve (sense of smell).

Cranial Nerves CN II is the optic

nerve (sense of sight).

CN III, IV, and VI innervate the extraocular muscles that allow us to move our eyes. CN III also supplies motor

input to our eyelid muscles and facilitates pupillary constriction.

Cranial Nerves

Cranial Nerves CN V is the trigeminal nerve (the major

sensory nerve of the face). It has three large

branches, each of which supplies anarea of the face:ophthalmicmaxillarymandibular

Cranial Nerves CN VII is the facial nerve. It has 5 large

somatic branches which innervate the muscle of facial expression. It also carries some taste sensations (anterior 2/3 of tongue).

Paralysis of CN VII is called Bell’s Palsy and leads to loss of ability to close the eyes and impairment of taste and salivation.

Cranial Nerves

Cranial Nerves CN VIII is the vestibulocochlear nerve.

From the inner ear, the vestibular component carries information on balance, while the cochlear component enables hearing. Damage of CN VIII causes vertigo, ringing in

the ears, and/or deafness.

Cranial Nerves

Cranial Nerves CN IX is the glossopharyngeal nerve. This nerve

carries some taste sensations as well as ANS impulses to salivary glands and the mechanoreceptors of the carotid body and carotid sinus (senses changes in BP).

Cranial Nerves

Cranial Nerves CN X is the vagus

nerve (“the wanderer”), which carries most of the parasympathetic motor efferents to the organs of the thorax and abdomen.

Cranial Nerves CN XI is the spinal accessory nerve. This nerve

supplies somatic motor innervation to the Trapezius and Sternocleidomastoid muscles.

Cranial Nerves CN XII is the glossopharyngeal nerve. This is a very

large nerve (a lot of resources) to be devoted solely to the tongue—it takes a lot more coordination than you might guess to chew, talk, and swallow without injuring our tongue.

Midbrain The midbrain connects the pons to the diencephalon.

The anterior part consists of a pair of large tracts called cerebral peduncles.

Midbrain contains nuclei (e.g., red nuclei, substantia nigra).

Midbrain Red nuclei are reddish due to their rich blood supply and

iron. Axons from the cerebellum and cerebral cortex form synapses here and help coordinate muscular movements.

Nuclei of the substantia nigra are large and darkly pigmented. Loss of these neurons is associated with Parkinson’s disease.

Cerebrum The cerebrum consists of the cerebral cortex (an outer rim

of gray), an internal region of cerebral white matter, and gray matter nuclei.

The cerebrum provides us with the ability to read, write, and speak; to make calculations and compose music; to remember the past and plan for the future; and to create.

Cerebrum The cerebral cortex rolls and folds upon itself so that it

can fit into the cranial cavity. The folds are called gyri. The deep grooves between folds are fissures. The

shallow grooves are sulci.

The longitudinal fissure separates the cerebrum into right and left halves called cerebral hemispheres.

The central sulcus separates the frontal and parietal lobes. The precentral gyrus is located

immediately anterior to the central sulcus.

The postcentral gyrus is located immediately posterior to the central sulcus.

Cerebrum

Each cerebral hemisphere has four lobes that are named after the bones that cover them: frontal lobe, parietal lobe, temporal lobe, and occipital lobe.

Encircling the upper part of the brain stem and the corpuscallosum is a ring of structures on the inner border of thecerebrum and floor of the diencephalon that constitutes thelimbic system (limbic border).

The limbic system is sometimes called the “emotional brain” because it plays a primary role in a range of emotions, including pain, pleasure, docility, affection, and anger.

Limbic System

Cerebrum

Somatic Sensory Pathways

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• Somatic Sensory and Motor Pathways

Lateralization Brain controls opposite side of the body:

all sensory and motor pathways cross in CNS Left side of the brain controls right side of body Right side of brain controls left side of body

Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning

Right side more involved with spatial and pattern recognition and emotional content

Somatic motor pathways

Memory Process for storing and retrieving information Involves structural and functional changes Involves association areas, parts of limbic

system, and diencephalon Skill memory also involves cerebellum and

basal ganglia

Aging and the Brain Rapid brain growth during first few years of

life Due to increase in size of neurons and

proliferation of neuroglia Increase in development of dendritic branches

and synaptic contacts From early adulthood through

old age: Decline in brain mass Fewer synaptic contacts Some decrease in brain function

End of Chapter 10Copyright 2013 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.

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