Anatomy & Physiology
Nervous Tissue &Homeostasis
excitable characteristic of nervous tissue allows forgeneration of nerve impulses (action potentials) thatprovide communication & regulation of most bodytissue.
together with endocrine system: responsible formaintaining homeostasis
Differences in Nervous &Endocrine Control ofHomeostasis
NERVOUS
ENDOCRINE
rapid responder
action potentials
slow, prolongedresponse
releases hormones
Structures of the NervousSystem
total mass of 2 kg (~3% of total body mass)
Skull
Spinal Cord
Spinal Nerves
Cranial Nerves
Ganglia
Enteric Plexus
Special Senses & other Sensory Receptors
Major Structures of theNervous System
Functions of the NervousSystem
3 basic functions:
1.Sensory
2.Integrative
3.Motor
Sensory Function
sensory receptors detect internal & externalstimuli
sensory (afferent) neurons carry this sensoryinformation to spinal cord & brain thru cranial& spinal nerves
Integrative Function
integrate: process
nervous system takes information from sensoryneurons & processes that information, analyzesit, stores some of it & makes decisions forappropriate responses
served by interneurons (connect 1 neuron toanother neuron
Perception:
conscious awareness of sensory stimuli
occurs in brain
Motor Function
served by motor (efferent) neurons
carry info from brain/spinal cord effectors(muscle or gland) thru cranial or spinal nerves
results in muscles contraction or glandsecreting
Quick Quiz
What terms are given to neurons that carryinput spinal cord & brain?
What terms are given to neurons that carryoutput out of the brain & spinal cord?
Organization of the NervousSystem
Histology of the NervousSystem
2 cell types
1.Neurons
2.Neuroglia
Neurons
nerve cells that possess electrical excitability:
ability to respond to a stimulus & convertit into an action potential
stimulus: any change in environment thatis strong enough to initiate an actionpotential
Direction Action PotentialTravels
Action Potential
electrical signal that propagates along surfaceof neurolema (membrane)
begins & travels due to movement of ionsbetween interstitial fluid & inside ofneuron thru specific ion channels
once begun it travels rapidly @ constantstrength
Parts of a Neuron
Parts of Neuron: Cell Body
contains nucleus,cytoplasm, typicalorganelles,
+ Nissl bodiesclusters of RER
make materialsfor:
growth of neuron
regeneratedamaged axons inPNS
Dendrites
“little trees”
input portion ofneuron
usually, short,tapering, highlybranched
their cytoplasmcontains Nissl bodies,mitochondria
Axon
propagates action potentials
another neuron
muscle fiber
gland cell
Parts of an Axon
joins cell body @ cone-shaped elevation: axonhillock
part of axon closest to hillock = initial segment
jct of axon hillock & initial segment whereaction potential arises so is called the triggerzone
Parts of an Axon
axoplasm: cytoplasm of an axon
axolemma: plasma membrane of axon
axon collaterals: side branches along length ofaxon (most @ 90°)
axon terminals: axon divides into many fineprocesses
Synapse
site of communication between 2 neurons orbetween a neuron & effector cell
synaptic end bulbs: tips of some axon terminalsswell into bulb-shaped structures
synaptic vesicles: store neurotransmitter
many neurons have >1 neurotransmitter,each with different effects on postsynapticcell
Types of Neurons
FunctionalClassification
Structural Classification
Sensory
Interneurons
Motor
use # processesextending from cellbody
1.Multipolar neurons
2.Bipolar neurons
3.Unipolar neurons
Multipolar Neurons
several dendrites with 1 axon
includes most neurons in brain & spinal cord
Bipolar Neuron
1 main dendrite & 1 axon
retina, inner ear, olfactory area of brain
Unipolar Neuron
are sensory neurons that begin in embryo asbipolar
during development axon & dendrite fuse thendivide into 2 branches (both have characteristicstructure & 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 potentials
multiply & divide in mature nervous systems
glioma:
brain tumors derived from glial cells
very malignant, grow rapidly
Glial Cells of the CNS
1.ASTROCYTES
2.OLIGODENDROCYTES
3.MICROGLIA
4.EPENDYMAL CELLS
Astrocytes
star-shaped
largest & most numerous of glial cells
functions:
1.physically support neurons
2.assist in blood-brain-barrier (bbb)
3.in embryo: regulate growth, migration,&interconnections between neurons
4.help maintain appropriate chemicalenvironment for propagation of actionpotentials
Oligodendrocytes
“few trees”
smaller & fewer branches than astrocytes
Functions:
1.form & maintain myelin sheath on axons inCNS
2.1 oligo. myelinates many axons
Microglia
small cells with slender processes giving offmany spine-like projections
function:
1.phagocytes
remove cellular debris made during normaldevelopment
remove microbes & damaged nervous tissue
Ependymal Cells
single layer of cuboidal to columnar cells
ciliated & have microvilli
function:
1.line ventricles of brain & central canal ofspinal cord
2.produce, monitor, & assist in circulation ofcerebrospinal fluid (CSF)
3.form bbb
Neuroglial Cells of the PNS
Schwann cells
Satellite 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 neuronsin PNS ganglia
functions:
1.structural support
2.regulate exchange of materials betweenneuronal cell bodies & interstitial fluid
Myelination
myelin sheath: made up of multilayered lipid &protein (plasma membrane) covering
function:
1.electrically insulates axon
2.increases speed of nerve impulses
Myelinated & UnmyelinatedAxons
Nodes of Ranvier
gaps in myelin sheath
1 Schwann cell wraps axon between nodes ofRanvier
Myelin
amount increases from birth to maturity
infant‘s responses slower & less coordinated asolder child or adult in part because myelinationis a work in progress thru infancy
Demyelination
loss of myelin sheath
see in disorders:
multiple sclerosis
Tay-Sachs
side effect of radiation therapy & chemotherapy
Gray Matter of the NervousSystem
contains:
neuronal cell bodies
dendrites
unmyelinated axons
axon terminals
neuroglia
White Matter of the NervousSystem
composed of:
myelinated axons
