HONORS ANATOMY & PHYSIOLOGYCHAPTER 11

Fundamentals of the

Nervous System

Functions of the Nervous System

3 overlapping functions:1. Sensory input

monitor changes in & outside of body information gathered called sensory input which is

carried to #2 on afferent nerves

2. Integration processing & interpreting sensory input

3. Motor output activation of effector organs (muscles or glands) to

cause a response called motor output which is carried on efferent nerrves

Divisions of the Nervous System

1. Central Nervous System(CNS) Brain Spinal Cord

2. Peripheral Nervous System (PNS) Sensory neurons: specialized endings to detect a

particular sense Motor neurons:

Somatic: CNS skeletal muscle (voluntary) Autonomic:1. Sympathetic2. Parasympatheric

Organization of the Nervous System

Histology of Nervous Tissue

very cellular, ~20% extracellular material2 cell types:1. Neurons

excitable (respond to stimuli) able to transmit electrical impulses (action

potentials)

2. Neuroglia: supporting cells

Parts of Neuron: Cell Body

contains nucleus, cytoplasm, typical organelles,

+ Nissl bodies clusters of RER make materials

for: growth of neuron regenerate

damaged axons in PNS

Dendrites

“little trees”input portion of

neuronusually, short,

tapering, highly branched

their cytoplasm contains Nissl bodies, mitochondria

Axon

propagates action potentials another neuron muscle fiber gland cell

Parts of an Axon

joins cell body @ cone-shaped elevation: axon hillock

part of axon closest to hillock = initial segment

jct of axon hillock & initial segment where action potential arises so is called the trigger zone

Parts of an Axon

axoplasm: cytoplasm of an axonaxolemma: plasma membrane of axonaxon collaterals: side branches along length

of axon (most @ 90°)axon terminals: axon divides into many fine

processes

Synapse

site of communication between 2 neurons or between a neuron & effector cell

synaptic end bulbs: tips of some axon terminals swell into bulb-shaped structures

synaptic vesicles: store neurotransmitter many neurons have >1 neurotransmitter,

each with different effects on postsynaptic cell

Types of Neurons

Functional Classification

Structural Classification

SensoryInterneuronsMotor

use # processes extending from cell body

1. Multipolar neurons2. Bipolar neurons3. Unipolar neurons

Multipolar Neurons

several dendrites with 1 axonincludes most neurons in brain & spinal cord

Bipolar Neuron

1 main dendrite & 1 axonretina, inner ear, olfactory area of brain

Unipolar Neuron

are sensory neurons that begin in embryo as bipolar

during development axon & dendrite fuse then divide into 2 branches (both have characteristic structure & function of an axon)

1 branch ends with dendrites (out of CNS)2nd branch ends in axon terminal (in CNS)cell bodies of most found in ganglia

Unipolar Neuron

Purkinje Cells

found in cerebellum

Pyramidal Cells

in cerebral cortex of brain

Neuroglia (Glia)

~50% vol of CNS“glue”do not generate or propagate action

potentialsmultiply & divide in mature nervous systemsglioma:

brain tumors derived from glial cells very malignant, grow rapidly

Glial Cells of the CNS

1. ASTROCYTES2. OLIGODENDROCYTES3. MICROGLIA4. EPENDYMAL CELLS

Astrocytes

star-shapedlargest & most numerous of glial cellsfunctions:1. physically support neurons2. assist in blood-brain-barrier (bbb)3. in embryo: regulate growth, migration, &

interconnections between neurons4. help maintain appropriate chemical

environment for propagation of action potentials

Oligodendrocytes

“few trees”smaller & fewer branches than astrocytesFunctions:1. form & maintain myelin sheath on axons in

CNS2. 1 oligo. myelinates many axons

Microglia

small cells with slender processes giving off many spine-like projections

function:1. phagocytes

remove cellular debris made during normal development

remove microbes & damaged nervous tissue

Ependymal Cells

single layer of cuboidal to columnar cellsciliated & have microvillifunction:1. line ventricles of brain & central canal of

spinal cord2. produce, monitor, & assist in circulation of

cerebrospinal fluid (CSF)3. form bbb

Neuroglial Cells of the PNS

Schwann cellsSatellite cells

Schwann Cells

functions:1. myelinate axons in PNS

1 Schwann cell myelinates 1 axon

2. participate in axon regeneration

Satellite Cells

flat cells that surround cell bodies of neurons in PNS ganglia

functions:1. structural support2. regulate exchange of materials between

neuronal cell bodies & interstitial fluid

Myelination

myelin sheath: made up of multilayered lipid & protein (plasma membrane) covering

function:1. electrically insulates axon2. increases speed of nerve impulses

Myelinated & Unmyelinated Axons

Nodes of Ranvier

gaps in myelin sheath1 Schwann cell wraps axon between nodes

of Ranvier

Myelin

amount increases from birth to maturity infant‘s responses slower & less coordinated

as older child or adult in part because myelination is a work in progress thru infancy

Demyelination

loss of myelin sheathsee in disorders:

multiple sclerosis Tay-Sachs side effect of radiation therapy & chemotherapy

Gray Matter of the Nervous System

contains: neuronal cell bodies dendrites unmyelinated axons axon terminals neuroglia

White Matter of the Nervous System

composed of: myelinated axons