Transcript Nervous Tissue PPT

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Describe the organization of the nervous system.
Explain the three basic functions of the nervous
system.
Contrast the histological characteristics and the
functions of neuroglia and neurons.
Distinguish between gray matter and white matter.
Describe how a nerve impulse is generated and
conducted.
Explain the events of synaptic transmission and
the type of neurotransmitters used.
Somatic Nervous System (SNS)
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Sensory neurons conveys information from somatic receptors in head,
body wall, and limbs, and from receptors for special senses of vision,
hearing, taste, and smell to CNS
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Motor neurons conduct impulses from CNS to skeletal muscles only;
can be consciously controlled, voluntary actions
Autonomic nervous system (ANS)
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Sensory neurons convey information from autonomic sensory receptors,
located in visceral organs (stomach, lungs) to CNS
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Motor neurons conduct nerve impulses from CNS to smooth muscles,
cardiac muscles and glands; cannot be consciously controlled,
involuntary actions
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Two divisions of ANS are sympathetic division and parasympathetic
division; these divisions usually perform opposite functions
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“Fight-or-flight” responses  emergency actions (sympathetic)
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“Rest-and-digest” activities  GI tract activities (parasympathetic)
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Sensory functions _ (AFFECTORS)
Sensory receptors_ detect stimuli inside and outside
the body.
- Sensory or afferent neurons carry information from cranial to
spinal nerves into brain and spinal cord or visa versa
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Integrative functions _(LIKE A CONTROL CENTER)
Process sensory information by analyzing and storing
some of it and by making decisions for appropriate
responses
- Interneurons; have short axons that connect with neurons in brain,
spinal cord, and ganglion; are majority neurons in the body
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Motor functions _(EFFECTORS)
Respond the integrative decisions
- Motor of efferent neurons carry information from brain
toward spinal cord or out of brain to spinal cord into cranial or
spinal nerves
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Two types of cells
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Neurons
 unique functions of the nervous system; sensing, thinking,
remembering, controlling muscle activity, and regulating
glandular secretions
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Neuroglia
 support, nourish, and protect neurons and maintain
homeostasis in the intestinal fluid that baths neurons
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Three parts:
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Cell Body
 nucleus surrounded by cytoplasm; includes RER, lysosomes,
mitochondria, Golgi
 synthesizes cellular molecules needed for a neuron’s operation
Processes or extensions:
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Dendrites (“little trees”)
 multiple per single axon
 combined with cell body receiving and input parts of a neuron
 short, tapering, and highly branched, tree-branch array emerging
from cell body
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Axons_
 conducts nerve impulses toward another neuron, muscle fiber,
or gland cell
 long, thin, cylindrical projection that joins cell body at a cone-shaped
elevation
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STRUCTURAL CLASSIFICATION
Multipolar neurons: have several dendrites and one
axon; most in brain and spinal cord
 Bipolar neurons: have one main dendrite and one
axon; retina of the eye, inner ear, olfactory area of
brain
 Unipolar neurons: dendrites and one axon fused
together forming a continuous process that emerges
from cell body; begin in embryo as bipolar neurons;
most function as sensory receptors for touch,
pressure, pain, or thermal stimuli. Cell bodies of
most of this type located in ganglia of spinal and
cranial nerves.
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FUNCTIONAL CLASSIFICATION
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Sensory or afferent neurons: once sensory receptor activated,
these form an action potential in their axon that is conveyed
into the CNS through spinal and cranial nerves
 contain sensory receptors at their distal ends or are located just after
sensory receptors that are separate cells; most unipolar in structure
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Motor or efferent neurons: convey action potential away from
CNS to effectors (muscles and glands) in PNS through cranial
and spinal nerves
 Most are multipolar in structure
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Interneurons or association neurons: integrate incoming
sensory information from sensory neurons and then elicit a
motor response by activating appropriate motor neurons
 Located within CNS between sensory and motor neurons; most
multipolar in structure
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Smaller than neurons
5-50 times more numerous
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”glue” that holds nervous tissue together
do not generate or conduct nerve impulses
can multiply and divide in mature nervous system
in case of injury or disease multiply to fill in spaces
formerly occupied by neurons
Gliomas: brain tumors derived from glia called
gliomas; very malignant and grow rapidly
Myelin sheath, many-layered covering composed of lipids
and protein, surround the axons of most of our neurons.
 Two Functions:
(1) insulates the axon
(2) increases the speed of nerve impulse conduction
The amount of myelin increases from birth to maturity
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Clusters of Neuronal Cell Bodies
 Ganglion: cluster of neuronal cell bodies
located in PNS
 Nucleus: cluster of neuronal cell bodies in CNS
Bundles of Axons
 Nerve: bundle of axons located in PNS; cranial
nerves connect brain to periphery and spinal
nerves connect spinal cord to periphery
 Tract: bundle of axons located in CNS; tracts
interconnect neurons in spinal cord and brain
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White matter: myelinated and unmyelinated axons of many
neurons which is white in color; also has blood vessels
Gray matter: neuronal cell bodies, dendrites, unmyelinated
axons, axon terminals, and neuroglia white is grayish pink in
color; also has blood vessels
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AKA  nerve impulses
Two features of plasma membrane needed for action potentials in
muscle fibers and in neurons
 existence of resting membrane potential
 presence of specific types of ion channels
Membrane potential difference in the amount
of electrical charge inside and outside plasma
membrane.
 membrane that has potential is polarized
Resting membrane potential  voltage difference between the inside
and outside of a plasma membrane when not responding to a stimulus,
in muscle fibers and neurons
 voltage created by flow of ions
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Two types of ion channels:
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Leakage channels allow small but steady stream of ions
to leak across the membrane
Gated channels  open and close on command
Voltage-gated channels are used to generate and
conduct action potentials; open in response to a change
in membrane potential
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Action potential (AP) or impulse generates rapidly occurring events that
decrease and increase the membrane potential and eventually restore it to
its resting state
Ability of muscle fibers and neurons to convert stimuli into action
potential is called electrical excitability.
Stimulus in cell’s environment changes resting membrane potential; if
stimulus causes cell to depolarize to a critical level; called a threshold
(about -55mV) then an action potential arises
Two main phases:
 Depolarizing phase- rapidly occurring events that decrease and
eventually reverse polarization of membrane, makes inside more
positive than outside; Na+ ions move into cell
 Repolarizing phase- membrane polarization is restored to resting state;
Na+ ions move back out cell restoring charge to original state
Depolarizing
phase
Repolarizing
phase
Reversal of
polarization
Threshold
Stimulus
6After-hyperpolarizing phase
7.Resting
membrane
potential
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Also called propagation
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Way cells communicate information from one part of
body to another
Nerve impulses travel from where they arise, usually
axon hillock, along axon to axon terminal
Positive feedback process
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Continuous conduction
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Step-by-step process; impulses travel a short
distance in 10 milliseconds
Occurs in unmyelinated axons (muscle fibers)
 Have smallest diameter
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Saltatory conduction
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Impulses leap from one node of Ranvier to the next
Occurs in myelinated axons
 Have largest diameter
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How synapses neurons communicate with other
neurons or with effectors through a series of events
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neuron sending the signal is called the presynaptic neuron
neuron receiving the signal called the postsynaptic neuron
 A synaptic cleft separates the presynaptic and postsynaptic
neurons
Neurotransmitters
Different neurotransmitters are found in synaptic vesicles. These
different neurotransmitters have different effects.
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Essential neurotransmitters are removed in order to restore
normal synaptic function
Three ways:
 Diffuse away from synaptic cleft (out of reach of receptors)
 Destroyed by enzymes
 Actively transported back into neuron (reuptake)