Nervous tissue

Sensory function

To sense changes in the internal and external environment though sensory receptors

Integrative function

To analyze the sensory information, store some aspects, and make decisions regarding appropriate behaviors

Motor function

To respond to stimuli by initiating action
-glands: secretions
-muscles: contract to cause movements

Parts of CNS

Brain and spinal cord

Parts of PNS

Everything else, connects body to spine and brain

Functions of CNS

-integrative function
-processing and control center, analyzing and consolidating incoming information and triggering the correct response
-storing sensory info, creating memories, emotions, and memories

functions of PNS

-sensory (after ent nerve fibers)
-motor (efferent nerve fibers)

Somatic (voluntary) nervous system

-part of PNS
-sensory neurons transmit information from receptors on the body surfaces, limbs, and special sense organs to the CNS
-motor neurons from the CNS to skeletal muscle tissue

Autonomic nervous system

-part of PNS
-autonomic sensory
-autonomic motor relays impulses from the CNS to the smooth muscle, cardiac muscle, and glands
-subdivided into sympathetic and parasympathetic

sympathetic nervous system

Fight or flight

parasympathetic nervous system

Rest and digest

Enteric nervous system

-brain of the gut
-involuntary sensory and motor neurons control GI tract
-neurons function independently of PNS and CNS

Neuroglia

-connective tissue around nerve
-support, protect, maintain neurons

Nerve

Bundle of neural axons

Soma

-cell body
-single nucleus with prominent nucleolus
-typical major organelles
-dendrites and axon branch off
-nissil bodies
-cytoskeleton that gives structure

Dendrites

-short, tapering, and highly branches
-radiates from the soma
-receive input from axons of other neurons
-sensory = serve as receptors

hillock

-an expanded area of the soma
-beginning of the axon
-nerve impulses arise at the junction of the axon hillock and the axon itself

axon

-a single process that arises from the hillock of the soma
-carries information to other neurons, muscles, glands, or lymphatic tissue
-contains a o plasm and it surrounded by a sheath called axolemma
-has mitochondria, microtubules, and neurofibrils
-no ER= no protein synthesis

Myelin sheath

-specific goal cells that wrap themselves around the axon
-nodes of ranvier are spaces between the sheath

Terminal arborizations

-branches of the axon
-their tips form expansions called synaptic knobs which synap with muscles and glands

Synaptic vesicles

-filled with neurotransmitters
-released in response to an action potentials in order to stimulate an adjoining neuron

Structural classification of neurons

Classified by the number of processes extending from the cell body fu

Functional classification of neurons

Classified by the direction the impulse is conveyed with respect to the CNS

Unipolar

-dendrites and a single axon extending as a fused process from their cell body
-function as sensory receptors, detecting various sensory stimuli (touch, pressure, pain)
-stimulation of the dendrite can trigger the neuron to fire an AP along the axon

Bipolar

-have one dendrite and one axon extending from their cell body
-found in retina of eye, inner ear, olfactory

Multipolar

Contain a number of dendrites and one axon

Sensory (afferent) neurons

-towards the CNS
-transport sensory information from skin, muscles, joints, sense organs, and viscera to CNS
-many unipolar in structure
-activated my receptors
-sense information from dendrites then send the information along

Motor (efferent) neurons

-away from CNS
-send motor nerve impulses to muscles and glands
-multipolar in structure
-conduct AP away from CNS

Interneurons

-connect sensory to motor neurons
-integrate sensory information from sensory neurons and elicit a motor response by activating appropriate motor neurons
-multipolar in structure

Neuroglia cells

-half the volume of the CNS
-smaller than neurons
-cells can divide
-do not generate AP
-hold nervous tissue together to provide structural and functional support

Gliomas

Rapid mitosis of Neuroglia cells in tumor formation

Astrocyte strucutre

-star shaped cells in CNS
-have multiple cytoplasmic processes that extend from body

Protoplasmic astrocytes

Many short branching processes (gray matter)

Fibrous astrocytes

Many long unbranched process (white matter)

Astrocyte function

-provide structural support
-passage for the exchange of nutrients between capillary blood and neurons
-form blood-brain barrier by covering blood
-metabolize neurotransmitters
-influence neuronal transmission
-learning and memory
-repair damaged neural tissue

Oligondendrocytes

-CNS
-forms myelin sheath around more than one axon
-exert inhibitory influence on axonal regrowth
-analogous to Schwann cells of PNS

Microglia

-CNS
-small cells with slender processes
-protective
-clear away dead cells, remove cellular debris, invading microorganisms, and damaged nervous tissue
-derived from cells that also gave rise to macrophages and monocytes

Ependymal cells

-CNS
-cuboidal to columnar cells
-single layer with microvilli and cilia lining the ventricles of the brain and central canal
-secrete and monitor cerebrospinal fluid (CSF)
-form semi-permeable barrier between CSF and interstitial fluid of CNS

Schwann cells

-PNS
-cells encircling PNS axons
-each cell produces part of the myelin sheath surrounding an axon
-helps regenerate neurons by guiding stimulation and growth

Satellite cells

-PNS
-flat cells surrounding neuronal cell bodies in peripheral ganglia
-structural support
-regulate exchanges of materials between neuronal cell bodies and interstitial fluid

Myelination

-multi-layer of protein covering
-insulates axon
-speeds up speed of nerve impulses
-made by Schwann cells (PNS) and oligodendrocytes (CNS) g

Ganglion

-cluster of cell bodies in the PNS
-closely associated with cranial and spinal nerves

Nucleus

Cluster of neuronal cell bodies in the CNS

Nerve

Bundle of axons in the PNS

Tract

Bundle of axons in CNS that interconnect neurons in the spinal cord and brain

Gray matter

-consists of unmylelinated axons, neurall cell bodies, dendrites, axon terminals, and supporting neuralgia
-gray because of nissil bodies
-spinal cord
-thin outer shell covers inside of brain

White matter

Consists of larger myelinated nerve fibers and blood vessels

Nerve fiber

formed by axon and myelin sheath

Nerve fascicle

-groups of nerve fibers packed with endoneurium (fibrous connective tissue that fills space within nerve fibers)
-wrapped in perineurium (tough membrane that encloses each fascicle)

Nerve

-cord like structure that transfers electrical signal to and from CNS
-contains nerve fascicles
-wrapped in epineurium (thick layer that surround each nerve and between spaces of fascicles)

Resting potential

What your nerves are without any stimulus (-70)

Ion channels

-allow specific ions to cross plasma membrane when open
-down electrochemical gradient (high to low)

Leakage channels

-randomly alternate between open and closed
-nerve cells have more K+ than Na+ leakage channels so membrane permeability to K+ is higher

Ligand-gated channel

-open and close in response to particular chemical stimuli (hormone, neurotransmitter, ion)
-ligand molecule open/closes itself by binding to channel or membrane protein activated messenger molecule to activate gate

mechanically-gated channel

-open/close with mechanical stimulation (vibration, pressure, tissue stretching)
-found in auditory receptors, touch receptors, internal organs

Voltage-gated channels

-opens in response to change in membrane potential (voltage)
-participate in generation of AP

Voltage-gated sodium channel

-activation gate closed at rest
-inactivation gate open at rest

Voltage-gated potassium channels

-only one gate
-opens to allow the flow of K+ ions through the channel
-closes to stop flow of K+ ion

Movement of cations through leakage channels

-predominant cation in extracellular fluid is Na+
-predominant cation in cystoscope rich is K+
-neuronal plasma membranes contain more K+ leakage channels than Na+
-causes inside of plasma membrane to be less positively charged
-causes outside to become more positively charged
-a difference in charge across the membrane is created and potential energy is produced

Trapped anions in the cytosol

-the large molecules (ATP and cytoplasmic proteins) cannot diffuse through membrane so anions build up which causes increase of negative inside charge

Maintenance of resting membrane potential through sodium-potassium pumps

-actively pump three Na+ ions out the cell, in exchange for two K+ ions into the cell
-remove three times more positivee ions from the cells than they bring in
-help maintain negative charge inside the neuron

Electrical signals in neurons

-graded potentials: local membrane changes only
-action potentials: can travel long distances

Depolarization

-graded potential causes plasma membrane to become less polarized
-due to an influx of positively charged ions

Hyperpolarization

-graded potential can cause plasma membrane to become more polarized
-due to an efflux of positively charged ions s

Summation

-Graded potentials combining with each other to become stronger
-decremental conduction: loses intensity and dies out

Action potential

-starts with graded potential
-graded potential depolarizes to -55
-threshold is -55 for action potential to be created

Action potential at rest

Inactivation gate of sodium channel is open and activation gate is closed so Na+ cannot get in

Action potential at depolarization

-graded potential reaches -55
-voltage-gated Na+ channels open and Na+ rushes into cell
-postive feedback process causes an increases in stimulus

Action potential at repolarizing

-30mV= K+ channel opening much slower than Na+ channel
-when K+ channels open, the Na+ have closed
-K+ outflow returns membrane potential to 70mV

Action potential at after-hyperpolarizing

-K+ gates are slow to prolong K+ movement
-if enough K+ leaves, it will reach -90
-K+ channels close and membrane potential returns to -70

Action potential at refractory period

-period of time where neuron cannot generate another action potential
-large fibers have shorter refractory period

Continuous conduction

-unmyelinated axons and in muscle fibers
-step-by-step depolarization of each portion of the length of the axolemma

Saltatory conduction

-depolarization only at nodes of Ranvier where there is a high density of voltage-gated ion channels
-current carried by ions flows through extracellular fluid from node to node

Speed of impulse propagation

-speed of nerve impulse is not related to stimulus strength
-factors are: myelination, axon diameter, temperature

A fibers

-largest
-myelinated
-brief refractory period
-sensory

B fibers

-medium
-myelinated
-longer refractory period

C fibers

-smallest
-unmyelinated
-long refractory period
-sensory
-autonomic motor

Graded vs action potentials

-origin: GP arise on dendrite, AP arise at trigger zone on hillock
-types of channels: GP- ligand or mechincally-gated, AP- voltage-gated
-conduction: GP- localized, AP- propagated
-amplitude: GP- depending on stimulus, AP- constant
-duration: GP- longer, AP-shorter
-polarity: GP- may be hyperpolarizing or excitatory, AP: consist of depolarizing follow by repolarizing
-refractory: GP- none, AP- yes

Synapse

Region where communication occurs between 2 neurons or between a neuron and effector cell

Presynaptic neuron

Carries signal toward synapse po

Postsynaptic neuron

Carries signal away from a synapse or an effector

Electrical synapses

-conduct directly between plasma membrane through gap junction
-located in CNS, cardiac muscles, visceral smooth muscle, smooth muscles, embryo
-fast communication
-direct path

Chemical synapses

-no touching- synaptic cleft
-axodendritic- from axon to dendrite
-axosomatic- from axon to cell body
-axoaxonic- from axon to axon
-synaptic delay- electrical impulse turns into chemical neurotransmitter, neurotransmitter flows through synaptic cleft

Excitatory postsynaptic potential

-depolarizing postsynaptic
-results from opening of ligand-gated Na+ channels
-postsynaptic cell is more likely to reach threshold

Inhibitory postsynaptic potential

-hyperpolarization potential
-results from opening of ligand-gated Cl- or K+ channels
-causes postsynaptic cell to become more negative
-less likely to reach threshold

Removal of neurotransmitter

-diffusion: move down concentration gradient
-enzymatic degradation: particular enzymes that break down the neurotransmitter
-uptake by neurons or glia cells: neurotransmitter transports, Prozac (serotonin reuptake inhibitor)

Spatial summation

Summation of effects of neurotransmitters released from several end bulbs onto one neuron

Temporal summation

Summation of effect of neurotransmitters released form 2 or more firings of the same end bulb in rapid succession onto a second neuron

Possible responses to summation

-IPSP > EPSP: hyperpolarized
-IPSP = EPSP: cancel each other
-impulse generated: threshold reached
-EPSP> IPSP: depolarization
-EPSP far > IPSP: depolarization may reach threshold

Neurotransmitters

-both excitatory and inhibitory are present in CNS and PNS
-grouped into acetylcholine, amino acids, bio genie amines, nitric oxide, neuropeptides

Neurotransmitter effects

-synthesis can be stimulated or inhibited
-release can be blocked or enhanced
-removal can be stimulated or blocked
-receptor site can be blocked or activated
-agonist: enhances transmitter effect
-antagonist: blocks action a

Acetylcholine

-released by many PNS neurons and some CNS
-excitatory on NMK
-inhibitory at others
-inactiveated by acetylcholinesterase

GABA

-amino acid
-inhibitory
-only in CNS
-in brain

Glycine

-amino acid
-inhibitory
-CNS
-used in 1/2 of neurotransmitters in the spinal cord

Glutamate

-amino acid
-excitatory
-most excitatory neurons in CNS
-most abundant excitatory neurotransmitter in nervous system

Norepinephrine

-biogenic amines
-excitatory and inhibitory
-CNS and PNS
-arosual, dreaming, awakenings from deep sleep

Dopamine

-biogenic amines
-excitatory and inhibitory
-CNS
-regulation of skeletal muscle tone and movement

Serotonin

-biogenic amines
-excitatory and inhibitory
-CNS
-control of mood, secondary perception, temperature regulation, appetite, and induction of sleep

Nitric oxide

-released by brain, neuromuscular, and neuroglandular synapses
-memory, learning, and vasodilation

Endorphins

-neuropeptide
-inhibitory
-CNS
-inhibit pain