introduction to the nervous system
DESCRIPTION
Introduction to the Nervous System. t o be copied. Nervous Tissue & Homeostasis. excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/1.jpg)
Introduction to the Nervous System
to be copied
![Page 2: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/2.jpg)
Nervous Tissue & Homeostasis
• excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue.
• together with endocrine system: responsible for maintaining homeostasis
![Page 3: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/3.jpg)
Differences in Nervous & Endocrine Control of HomeostasisNERVOUS ENDOCRINE• rapid responder• action potentials
• slow, prolonged response
• releases hormones
![Page 4: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/4.jpg)
Structures of the Nervous System• 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
![Page 5: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/5.jpg)
Functions of the Nervous System
• 3 basic functions:1. Sensory2. Integrative3. Motor
![Page 6: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/6.jpg)
Sensory Function• sensory receptors detect internal &
external stimuli• sensory (afferent) neurons carry this
sensory information to spinal cord & brain thru cranial & spinal nerves
![Page 7: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/7.jpg)
Integrative Function• integrate: process• nervous system takes information from
sensory neurons & processes that information, analyzes it, stores some of it & makes decisions for appropriate responses
• served by interneurons (connect 1 neuron to another neuron
• Perception:– conscious awareness of sensory stimuli– occurs in brain
![Page 8: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/8.jpg)
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 gland secreting
![Page 9: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/9.jpg)
Organization of the Nervous System
![Page 10: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/10.jpg)
Histology of the Nerrvous System
• 2 cell types1. Neurons2. Neuroglia
![Page 11: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/11.jpg)
Neurons • nerve cells that possess electrical
excitability:– ability to respond to a stimulus &
convert it into an action potential
– stimulus: any change in environment that is strong enough to initiate an action potential
![Page 12: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/12.jpg)
Action Potential• electrical signal that propagates
along surface of neurolema (membrane)– begins & travels due to movement of
ions between interstitial fluid & inside of neuron thru specific ion channels
– once begun it travels rapidly @ constant strength
![Page 13: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/13.jpg)
Parts of a Neuron
![Page 14: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/14.jpg)
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
![Page 15: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/15.jpg)
Nerve Fiber• general term for any neuronal
process or extension that emerges from cell body
• most neurons have 2:1. Dendrites2. Axons
![Page 16: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/16.jpg)
Dendrites • “little trees”• input portion of neuron• usually, short, tapering, highly
branched• their cytoplasm contains Nissl
bodies, mitochondria
![Page 17: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/17.jpg)
Axon • propagates action potentials – another neuron–muscle fiber– gland cell
![Page 18: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/18.jpg)
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
![Page 19: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/19.jpg)
![Page 20: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/20.jpg)
Parts of an Axon• axoplasm: cytoplasm of an axon• axolemma: plasma membrane of
axon• axon collaterals: side branches along
length of axon (most @ 90°)• axon terminals: axon divides into
many fine processes
![Page 21: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/21.jpg)
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
![Page 22: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/22.jpg)
Axonal Transport• 2 types:– for moving materials from cell body axon
terminals1. slow– 1-5 mm/d– replenishes new axoplasm to developing or
regenerating axons2. fast– 200 – 400 mm/d– moves materials to/from cell body• organelles or membranes needed in axon terminal
![Page 23: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/23.jpg)
Types of NeuronsFunctional Classification Structural Classification
• Sensory• Interneurons• Motor
• use # processes extending from cell body
1. Multipolar neurons2. Bipolar neurons3. Unipolar neurons
![Page 24: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/24.jpg)
Multipolar Neurons• several dendrites with 1 axon• includes most neurons in brain &
spinal cord
![Page 25: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/25.jpg)
Bipolar Neuron• 1 main dendrite & 1 axon• retina, inner ear, olfactory area of
brain
![Page 26: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/26.jpg)
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
![Page 27: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/27.jpg)
Unipolar Neuron
![Page 28: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/28.jpg)
Pyramidal Cells• in cerebral cortex of brain
![Page 29: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/29.jpg)
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
![Page 30: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/30.jpg)
Glial Cells of the CNS1. ASTROCYTES2. OLIGODENDROCYTES3. MICROGLIA4. EPENDYMAL CELLS
![Page 31: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/31.jpg)
Astrocytes • star-shaped• largest & most numerous of glial cells• functions: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
![Page 32: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/32.jpg)
Oligodendrocytes • “few trees”• smaller & fewer branches than
astrocytes• Functions:1. form & maintain myelin sheath on
axons in CNS2. 1 oligo. myelinates many axons
![Page 33: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/33.jpg)
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
![Page 34: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/34.jpg)
Ependymal Cells• single layer of cuboidal to columnar
cells• ciliated & have microvilli• function:1. line ventricles of brain & central canal
of spinal cord2. produce, monitor, & assist in
circulation of cerebrospinal fluid (CSF)3. form bbb
![Page 35: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/35.jpg)
Neuroglial Cells of the PNS• Schwann cells• Satellite cells
![Page 36: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/36.jpg)
Schwann Cells• functions:1. myelinate axons in PNS– 1 Schwann cell myelinates 1 axon
2. participate in axon regeneration
![Page 37: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/37.jpg)
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
![Page 38: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/38.jpg)
Myelination • myelin sheath: made up of
multilayered lipid & protein (plasma membrane) covering
• function:1. electrically insulates axon2. increases speed of nerve impulses
![Page 39: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/39.jpg)
Myelinated & Unmyelinated Axons
![Page 40: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/40.jpg)
Nodes of Ranvier• gaps in myelin sheath• 1 Schwann cell wraps axon between
nodes of Ranvier
![Page 41: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/41.jpg)
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
![Page 42: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/42.jpg)
Demyelination • loss of myelin sheath• see in disorders:–multiple sclerosis– Tay-Sachs– side effect of radiation therapy &
chemotherapy
![Page 43: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/43.jpg)
Gray Matter of the Nervous System
• contains:– neuronal cell bodies– dendrites– unmyelinated axons– axon terminals– neuroglia
![Page 44: Introduction to the Nervous System](https://reader035.vdocuments.mx/reader035/viewer/2022062812/568163a5550346895dd4acbe/html5/thumbnails/44.jpg)
White Matter of the Nervous System
• composed of:–myelinated axons