Chapter 12 Nervous Systems
Cranial nerves
12 pairs that emerge from the brain
Spinal nerves
31 pairs that protrude from the spinal cord
Sensory (afferent) division
conveys input into the CNS from receptors
Provides info from somatic senses and special senses
Sensory (afferent) division
Motor (efferent) division
transmit impulses from CNS to effector organs
divides into somatic nervous system (SNS) and the autonomic nervous system (ANS)
Motor (efferent) division
Somatic Nervous System (SNS)
voluntary with concious control of skeletal muscles
Autonomic Nervous System (ANS)
involuntary that regulates smooth and cardiac muscles and glands
Sympathetic and Parasympathetic division, Enteric Nervous System (ENS)
branches of the Autonomic Nervous System (ANS)
Enternic Nervous System
extensive network of neurons in the GI tract
helps regulate smooth muscles and glandcular activity in GI tract
Enternic Nervous System (ENS)
regulated by sympathetic and parasympathetic divisions
Enteric Nervous System (ENS)
Nervous System's functions
sensory, integrative, and motor
Sensory Function
sensory receptors monitor changes called stimuli, then sends info to brain and spinal cord
Integrative Function
Nervous system processes and interprets sensory input and decides whether action is needed (integration)
Motor Function
stimulates effectors through spinal and cranial nerves which makes muscles contract and glands secrete
cell body, dendrites, axon
Neurons
Cell body
metabolic center of neurons and contains a nucleus surrounded by cytoplasm and organelles
contains Fnodes bodies (free ribosomes and clusters of rough endoplasmic reticulum)
cell body
neuron inside cell bodies in CNS is called...
nuclei
neurons inside the cell bodies PNS are called...
ganglion
Dendrites
receiving or input portions on neurons
plasma membrane contain numerous receptors for binding chemical messengers from other cells
dendrites
information transferred is towards the cell body
dendrites
Axon
proprogates nerve impulses away from the cell bodies toward another neuro, muscle fiber, or gland
connected to cell body by axon hillock with the intial segment being the closest part to the axon hillock
Axon
nerve impulse begin at the junction of axon hillock and intial segment
triggered zone of axon
does not contain rough endoplasmic reticulum-can NOT produce proteins
Axon
Cytoplasm of axon is called..
axoplasm
plasma membrane of axon is called...
axolemma
branches protrude from axon are called...
axon collaterals
site of communication between neuron and another neuron or effector is called
synapse
Axon ends in many small processes are called...
axon terminals or telodendria
Axon terminals that swell at the ends are called...
synaptic end bulbs or varicosities
Synaptic end bulbs or varicosities contain...
neurotransmitters that can excite or inhibit other neurons, muscle fibers, or glands
Mulitpolar Neurons
most neuron in brain and spinal cord with several dendrites and on axon; motor neuron
Bipolar Neurons
found in special senses with one main dendrite and one axon
Unipolar Neurons
found in ganglia of spinal cord and cranial nerves with one axon and dendrites that are fused to one uninterrupted process
most function is sensory receptors and the trigger zone located at the juntion of dendrites and axon
Unipolar Neurons
Sensory (afferent) neurons
stimulus activates receptor, action potential is created in the axon and send TOWARDS CNS thru cranial or spinal nerves
Sensory (afferent) Neurons
unipolar structerd with receptors in dendrites or located as receptors that are separate cells
Motor (efferent) Neurons
action potential (AWAY) from CNS to effectors in the PNS through cranial or spinal nerves; multipolar structure
Interneurons (association) neurons
processes incoming sensory info and creates a motor reponse by activating motor neurons
Interneurons (association) neurons
mulipolar structure locates in the CNS between sensory and motor nerves
Neuroglia
not electrically excitable supporting cells in CNS and PNS that can multiply and divide and makes up half the volum of nervous system
Astrocytes
neuroglia in CNS
Astrocytes
processes contact capillaries, neurons, and thin membrane around the brain and spinal cord called pia matter
Fibrous astrocytes
long branches, in white matter
Protoplasmic astrocytes
have short branches, in gray matter
contain microfilament for strength to support neurons
Astrocytes
wraps around capillaries and secretes chemicals to maintain the selective permeablity of neurons and prevent entrance of harmful chemicals
Astrocytes
in embryo, secretes chemical to regulate growth, migration, and connections amoung brain neurons
Astrocytes
Astrocytes
helps maintain chemical environment for nerve impulses-serves as an conduit for substance between neurons and capillaries
Oligodendrocytes
neuroglia of CNS
responsible for formation and maintenance of myelin sheath around axons of neurons in the CNS
Oligodendrocytes
Myelin Sheath
multi-layered covering lipid and protein that covers axons
insulates axon and increase speed of nerve impulses transmission
Myelin Sheath
Microglial Cells (microgalia)
neuroglia of CNS
Small cells that give off spiney projections that removes cellular debri, damage tissue, and microbes
Microglial Cells (microgalia)
Ependymal Cells
Neuroglia of CNS
cubodial to columnar cells arranged in a single layer and possess microvilli and cilia
Ependymal Cells
lines ventricles of the brain and centrl canal of spinal cord and produces and assist in circulation of cerebrospinal fluid; forms the blood-brain barrier
Ependymal cells
Schwann Cells
neurogalia of PNS
forms myelin sheath around axon and particpates in axon regeneration
Schwann Cells
each cell myelinates a single axon and encircles neurons of PNS
Schwann Cells
Satellite Cells
neuroglia of PNS
surrounds the cell body of neurons of PNS ganglia and provides structural support
Satellite Cells
regulates exchange of materials between neuron cell bodies and interstitial fluid
Satellite Cell
Metabotropic ceptors
contains neurtransmitter, do NOT have ion channels
G protein in membrane opens or closes the ion channel or activates another molecule in the cystol which opens or closes the ion channel
Metabotropic receptors
Ionotropic receptors
cotains a neurostramitter binding site and an ion channel
when correct neurotransmitter binds to receptor, the ions channels opens allowing ions to enter to poduce an EPSP or IPSP
Ionotropic receptors
Axon diameter
affects AP propagation because larger the axon, the faster the propagation due to large surface area
Amount of Myelination
affects AP propagation due to AP travels faster along myelinated axons
Temperature
affects AP proganation bc AP travels at slower speeds at cooler temps
much faster than continous conduction
Saltatory Conduction
Salatory Conduction
AP generated by myelinated axon, electric current flow through extracellar fluid from one node to the next causing the next node to depolarize and an AP at second node
appears like "jumping" from one node to another down the entire length of axon
Salatory Conduction
Oligodendrocytes-CNS, Schwann Cells-PNS
produce myelin
Nodes of Ranvier
gaps in myelin sheath found at intervals in the rapid impulse conduction fround in myelinated axons
no myelin sheath and has voltage gated channels so Na+ and K+ ions flow across the membrane
Nodes of Ranvier
Nuclei
clusters of cell bodies in the CNS
Ganglia
collection of cell bodies outside of the CNS in the PNS
Tracts
bundle of nerve fibers in the CNS
Nerve
bundle of nerve fibers in PNS
White Matter
collection of myelinated fibers (tract)
Gray Matter
composed of unmyelinated axons, dendrites, cell bodies, axon terminals, and neuroglia
Resting Membrane Potential
like voltage stored in a battery where the flow of charged particles occurs
Polarized
cell that has a membrane potential
Action potential
nerve impulse
Depolarizing phase
negative membrane potential become less negative, reaches zero, then becomes more postive
first gate channel that opens the voltage-gated Na+ which allows Na+ ions to rush into the cell
Depolarizing Phase
Repolarizing Phase
membrane potential is restored to the resting value of -70mv
second channels to open are voltage gated K+ channel which allows K+ ions to flow out
Repolarizing Phase
Hyperpolarizing Phase
after repolarizing phase, the membrane potential becomes more negative that the resting level-occurs when K+ channels remain open
Threshold
when depolarizing reaches the level of -55mv and AP occurs
All or none prinicipal
the AP is formed from a threshold stimulus, it either occurs completely or not at all
Refactory Period
time after an AP begins when an excitable cell cannot produce another AP in reponse to a normal threshold stimulus
Sodium-Potassium Pump
restores ionic distribution back to resting conditions
small inward Na+ leak and outward K+ leak is offset
Sodium-Potassium pump
Chemical Synapse
one-way to transfer info from a presynaptic neuron to a postsynaptic neuron
AP cant conduct across the synpatic cleft so neurotransmitter are released by presynaptic neuron, it diffuses across synaptic cleft and binds to receptors of postsynaptic neuron
Chemical synapse
main cations and anions of neurons
main cation in cystol is K+ w/ phosphates and amino acids being main anions
K+ leak channels are more numerous than Na+ channels
causes negativity of resting membrane potential
anions inside cells are attached to nondiffusable molecules which doesnt allow anions to follow K+ out of cells
causes of negativity of resting membrane potential
3 Na+ ions are pumped out at the same time 2 K+ ions are pumped in
causes of negativity of resting membrane potential
Origin (graded potential)
arise mainly in dendrites and cell bodies
Origin (AP)
arises at trigger zone and propagate along axon
Type of Channel (GP)
ligand-gated or mechanically gated ion channels
Type of Channel (AP)
voltage-gated Na+ and K+
Conduction (GP)
decremental (not propagated); permit communicatio over short distances
Conduction (AP)
Propagated and this permits communication over longer distances
Amplitude (GP)
depending on strength of stimulus, varies form less than 1mv to more than 50mv
Amplitude (AP)
all or none, about 100mv
Duration (GP)
typically longer, ranging from several milliseconds to several mins
Duration (AP)
shorter, ranging from 0.5 to 2 milliseconds
Polarity (GP)
maybe hyperpolarizing or depolarizing
Polarity (AP)
allows consists of depolarizinf phase followed by repolarizing phase and return to resting membrane potential
Refactory Period (GP)
Not present; summation can occur
Refactory Period (AP)
Present; summation cannot occur
Leak channel
gated channel that randomly opens and closes; located in nearly all cells, dendrites, cell bodies axons of all types of neurons
Ligand-gated Channel
gated channels that open in response to binding of ligand stimulus; located in dendrites and cell bodies of interneurons and motor neurons, pain receptors
mechanically-gated channels
open in resposne to mechanical stimulus such as touch, pressure, vibration or tissue stretching; located in dendrites of some sensory neurons, touch, pain, and pressure receptors
Voltage-gated channel
open in response to voltage stimulus (change in membrane potential); located in axons of all types of neurons
Synapse Structures
voltage-gated Ca++ channels..synaptic vessicles..neurotransmitter..synaptic cleft..neurotransmitter receptors..postsynaptic potential
Electrical Synapse
AP conducted thru membrane of adjacent cells thru gap junctions that connect the cystol of the 2 cells, ions flow from one cell to the next , the AP passes from cell to cell
faster than chemical synapse and are common in cardiac and smooth muscle
Electrical Synapse
Chemical Synapse
presynaptic neuron converts an electrical impulse into a neurtransmitter which then is converted nack to an electrical signal by the postsynaptic neuron
one-way to transfer info from a presynaptic neuron to a postsynaptic neuron
Chemical synapse
Spatial Summation
stimuli occur at different locations of the postsynaptic membrane at the same time
Temporal Summation
due to stimuli that occurs at the same loaction of the postsynaptic memebrane at different times
around 24-48hrs after injury to an axon, Nissl bodies break into fine granular masses
Chromatolysis (PNS neuron repair)
third to fifth day, axon distal to injury becomes swollen and myelin shealth deteriorates
Wallerian Degeneration (PNS Neuron Repair)
Regeneration tube (PNS Neuron repair)
formed when Schwann cells on either side of injured area multiply by mitosis and grow toward each other
tube guides the growth of the new axon from proximal and distal, in time Schwann cell will for a new myelin sheath
Regeneration tube (PNS Neuron repair)
ions flows thru each adjacent segment creating AP down the axon, threshold is reached Na+ ions flow into cell across membrane and resting potential is depolarized and
AP is intiated, polarity reversal of inital patch of membrane changes permeabilty of adjacent patch and positive ions flow toward negative, Na+ channel open in adjacent patch causing it to depolarized, this will continue down axon
Continuous conduction
Continuous Conduction
unmyelinated axons and muscle fibers
involves continuous depolarization and repolarization of adjacent segments of the membrane
Continuous Conduction