CH 12: 9-20-13 (BIO 181) Flashcards
the nervous system includes all ___ ____ in the body
neural tissue
____, ____ ___, ____ receptors, and nerves are all involved in the nervous system
brain, spinal cord, sensory receptors
nervous system divided into the ___ nervous system, and the ___ nervous system
central; peripheral
- includes the brain and spinal cord
- processing and coordinating of information
- sensory information (input) from inside and outside body
- motor commands (output) control activites of perpheral organs (skeletal muscles)
- higher functions of brain: learning, memory, emotion and intelligence
CNS
- includes all neurual issue outside the CNS
- deliver sensory information to the CNS
- carry motor commands to peripheral tissues and systems
- consists of nerves that are bundles of fibes with connective tussues and blood vessels and carry sensory information and motor commands via
- cranial nerves->connect to brain
- spinal nerves -> attach to spinal cord
PNS
___ and ____ divisions of PNS
afferent; efferent
- carries sensory information
- contains receptors and effectors
- receptors (source) detect changes or respond to stumuli, consist of neurons and highly specialized cells, complex sensory organs (eyes, ears)
- effectors (target) respond to efferent signals and consist of target cells and organs
afferent division (input) of PNS
- carries motor commands
- from CNS to PNS muscles and glands
- composed of the somatic and autonomic nervous system
efferent division (output) of PNS
nervous system in efferent division of PNS that controls skeletal muscle contractions (voluntary and involuntary muscles contractions)
somatic nervous system
nervous system in efferent division of PNS that
- controls subconscious actions: contractions of smooth muscle and cardiac muscle and glandular secretions
- sympathetic division has a stimulating effect
- parasympathetic division has a relaxing effect
autonomic nervous system
- the basic functional units of the nervous system
- specialized cells that control and monitor body activities and physiological functions
- sense changing conditions, process sensory input, and direct the body’s responses
- come in all shapes and sizes but all have certain characteristics in common.
neurons
- Contains nucleus and organelles
- Large nucleus and nucleolus (the brain of neuronal cells)
- Perikaryon (cytoplasm)
- Nuclear Pores (provides a route for the transferring of information)
- Mitochondria (produce energy)
- RER and ribosomes (produce neurotransmitters)
- Cytoskeleton consists of 3 types of filaments that give the cell structural support and enable some degree of motility/contractility
cell body (soma)
consists of 3 types of filaments that give the cell structural support and enable some degree of motility/contractility
• Together, these filiments keep the organelles suspended in the cytosol.
cytoskeleton
• _____and_____: resemble the microfilaments and microtubules seen in other cell types
Neurofilaments; neurotubules
bundles of neurofilaments that provide support for dendrites and axon
neurofibrils
- Dense areas of RER and ribosomes
* Make neural tissue appear gray (gray matter)
nissl bodies
- Highly branched projections from the soma
* Function in receiving information from extracellular environment, other cells, or other neurons
dendrites
- Single long processes extending from the soma
- Functions in sending out (or carrying) information to various targets
- Carries electrical signal (action potential)
- structure is critical to function
axon
- Contain synaptic terminals, which contain synaptic vessicles that are filled with neurotransmitters
- It is these neurotransmitters that, when released, affect the transmembrane potential of another cell
telondenria (collaterals)
- Cytoplasm of axon
* Contains neurotubules, neurofibrils, enzymes, organelles
axoplasm
- Specialized cell membrane of the axon
* Covers the axoplasm
axolemma
- Thick section of cell body
* Attaches to initial segment
axon hillock
• Attaches to axon hillock
initial segment
fine extensions of distal axon
telodendria
tips of telodendria
synaptic terminals
area where neuron communicated with another cell
synpse
all synapses involve ___ and ___ cells
presynaptic; postsynaptic
– Cell that sends message (information)
– Usually a neuron
– Releases chemicals to the postsynaptic cell
presynaptic
– Cell that receives message (information)
– Can be a neuron or any other type of cell
• The synapse can be anywhere on the receiving cell
postsynaptic
• Synapse between neuron and muscle
neuromuscular junction
• Synapse between neuron and gland
neuroglandular junction
- Is expanded area of axon of presynaptic neuron
* Contains synaptic vesicles of neurotransmitters
the synaptic knob (terminal buttons)
- are chemical messengers
- are released at presynaptic membrane
- affect receptors of postsynaptic membrane
- are broken down by enzymes
- are reassembled at synaptic knob
neurotransmitters
Neurons are Classified into____ Types – Based on_____
four; structure
- Found in brain and sense organs
- Typically Smaller than other neurons
- All cell processes look alike?……well, not really
- Dendrites and axons are difficult to distinguish
- Function is poorly understood
anazonic neruron
- Found in special sensory organs (sight, smell, hearing)
- Are small
- One dendrite, one axon
- Rare?
bipolar neurons
- Found in sensory organs of the PNS
- Have very long axons
- Fused dendrites and axon
- Cell body to one side
unipolar neuron
- Common in the CNS
- Include all skeletal muscle motor neurons
- Have very long axons
- Multiple dendrites, one axon
multipolar neurons
- Afferent neurons of PNS
* Originate at the periphery and terminate in the CNS
• Sensory neurons
- Efferent neurons of PNS
* Originate in the CNS and terminate at the effector organs (target)
• Motor neurons
- Association neurons
* All located in the CNS
• Interneurons
- Monitor internal environment (visceral sensory neurons)
- Monitor effects of external environment (somatic sensory neurons)
- Structure of sensory neurons
- Cell bodies are grouped in sensory ganglia
- afferent fibers extend from sensory receptors of the PNS to the CNS
• Functions of Sensory Neurons
carry instructions from CNS to peripheral effectors (targets)
• Via efferent fibers (axons)
Motor Neurons
• includes all somatic motor neurons that innervate skeletal muscles
• Somatic nervous system (SNS):
- visceral motor neurons innervate all other peripheral effectors
- e.g., smooth muscle, cardiac muscle, glands, adipose tissue
• Autonomic (visceral) nervous system (ANS):
• Motor neurons are grouped into
Ganglia (broad term = cluster of cell bodies)
• Neuronal cell bodies that make up the junction between_____ nerves originating from the CNS and autonomic nerves that innervate ___ organs
autonomic; peripheral
• Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia and then divide the axons into:
» preganglionic fibers
» postganglionic fibers
• Most interneurons are located in
brain, spinal cord, and autonomic ganglia
- Between sensory and motor neurons
* These comprise over 90% of all neurons
Interneurons
- Are responsible for Distribution of sensory information and Coordination of motor activity
- Are involved in higher functions: Memory, planning, learning
Interneurons
- Half the volume of the nervous system
- Many types of neuroglia in CNS and PNS
- These are the cells that support and protect neurons
neuroglia
- Cell with highly branched processes; contact neuroglia directly
- Form epithelium called ependyma
- Line central canal of spinal cord and ventricles of brain:
- secrete cerebrospinal fluid (CSF)
- have cilia or microvilli that circulate CSF
- monitor CSF
- contain stem cells for repair
Neuroglia in the CNS
• Ependymal cells
- large cell bodies with many processes
- Maintain blood–brain barrier (isolates CNS)
- Repair damaged neural tissue
- Guide neuronal development
- Control interstitial environment
- Absorb and recycle neurotransmitters
• Astrocytes (CNS)
• smaller cell bodies with fewer processes
• Processes contact other neuron cell bodies
• Wrap around axons to form myelin sheaths
(a membrane that wraps around the axon, giving it electrical insulation)
• Oligodendrocytes (CNS)
- Fewest and smallest of all microglia in the CNS
- Migrate throughout neural tissue
- Clean up cellular debris, waste products, and pathogens
• Microglia (CNS)
• Also called amphicytes
• Surround ganglia
• Regulate environment around neuron
– O2, CO2, and nutrient levels
• Satellite cells (PNS)
- Also called neurilemmocytes
- Form myelin sheath (neurilemma) around peripheral axons
- One Schwann cell sheaths one segment of axon:
- many Schwann cells sheath entire axon
- Participates in repair after injury
Schwann Cells (PNS)
- makes nerves appear white
* Nerves that are not myelinated appear gray
• Myelination
- internodes: myelinated segments of axon
- nodes
- gaps between internodes
- Extremely important in conduction
• Nodes of Ranvier
– 1 oligodendrocyte can myelinate
portions of several axons
– 1 schwann cell can only myelinate
one segment of a single axon
• myelin ____ myelinated axons
insulates
myelin _____ speed of electrical signals (action potentials)
increases
• Neurons perform all _______, information processing, and_____ functions of the nervous system
communication; control
preserve physical and biochemical structure of neural tissue and are essential to survival and function of neurons
neuroglia
• All plasma (cell) membranes produce____ signals by ion movements
electrical
• Transmembrane potential exists due to a difference in _____ and _____ gradients between the inside and outside of cells
chemical; electrical
- The transmembrane potential of resting cell
- The “reference point”
- (Typically –70mV)
resting potential
- Temporary, localized change in resting potential
* Caused by stimulus
graded potential
- Is an electrical impulse
- Produced by graded potential
- Propagates along surface of axon to synapse
action potential
- Releases neurotransmitters at presynaptic membrane
* Produces graded potentials in postsynaptic membrane
synaptic activity
• Response (integration of stimuli) of postsynaptic cell
information processing
• Concentration gradient of ions (Na+, K+)
• Selectively permeable through channels
• Maintains charge difference across membrane (resting potential –70 mV)
– Based on chemical and electrical forces
• Three Requirements for Transmembrane Potential
- Typical neuron is permeable to potassium and sodium (via leak channels that are always open)
- But, 25 times more permeable to______
potassium
• Outside cell
– Lots of____ and chloride
sodium
• Inside cell
– Lots of ____ and organic anions
potassium
- Chemical driving forces are pushing:
- ____ out
- ____in
K+; Na+
- Since the membrane is more permeable to K+
* K+ leaves cell ____ than Na+ enters
faster
- As a result, Electrical forces develop that want to push BOTH:
- Na+ ___ cell
- K+ ___ cell
into; into
pump maintains this resting potential
sodium/potassium
• The sum of chemical and electrical forces acting on a given ion
• Electrochemical Gradient
• The transmembrane potential at which there is no net movement of a particular ion across the cell membrane
• Examples
K+ = –90 mV
Na+ = +66 mV
So, the resting membrane potential is closer to the potassium equilibrium potential
• Equilibrium Potential
- Transmembrane potential ___ or ___
- In response to temporary changes in membrane permeability
- Resulting from opening or closing specific membrane channels
rises; falls
reference point
resting potential
more postitive
depolarization
more negative
repolarization
more negative than the resting potential
hyperpolarization
• Membrane permeability to Na+ and K+ determines changes in ____ potential
transmembrane
– are always open
– permeability changes with conditions
passive channels (leak channels)
– open and close in response to stimuli
– at the resting potential, most gated channels are closed
active channels (gated channels)
- Open in the presence of specific chemicals (e.g., ACh) at a binding site
- Found on neuron cell body and dendrites
chemically gated channels
- Respond to changes in transmembrane potential
- Have activation gates (open upon stimulation) and inactivation gates (close to stop Na+ influx)
- Characteristic of excitable membrane
- Found in neural axons, skeletal muscle, cardiac muscle
voltage-gated channels
- Respond to membrane distortion
* Found in sensory receptors (touch, pressure, vibration)
mechanically gated channels
• Transmembrane potential exists across
plasma membrane
• Cytosol (ICF) and extracellular fluid (ECF) have different
chemical/ionic balance
• The plasma membrane is
selectively permeable
• Changes in the Transmembrane potential occur
in response to chemical or physical stimuli
- Graded Potentials
* Action Potentials
two types of transmembrane potentials
- Also called local potentials
- Changes in transmembrane potential that cannot spread far from the site of stimulation
- Any stimulus that opens a gated channel produces a graded potential
- determine whether or not an action potential will occur
graded potentials
• Opening sodium channel produces graded potential:
– resting membrane exposed to chemical (Na+)
– sodium channel opens
– sodium ions enter the cell
– transmembrane potential rises (becomes more positive)
– depolarization occurs
Graded Potentials: The Resting State
- A shift in transmembrane potential toward 0 mV or becomes more positive:
- movement of Na+ through channel
- produces local current
- depolarizes nearby plasma membrane (graded potential)
- change in potential is proportional to stimulus
Graded Potentials: Depolarization
a ____ is produced by the spread of sodium ions inside the membrane.
•This results in depolarization of adjacent portions of the plasma membrane – and this continues
local current
- The transmembrane potential is most affected at the site of stimulation – and this affect decreases with distance
- The effect spreads passively via local currents
- Whether the membrane depolarizes or hyperpolarizes in response to a given stimulus, depends on the nature of channels that are involved in the membrane itself
- The strength of the response is determined by the strength of the stimulus
graded potentials
• When the stimulus is removed, transmembrane potential returns to normal resting potential
repolarization
- Here, the stimulus causes the opening of K+ channels
- When K+ channels open, positive ions move OUT of the cell (not in)
- This Increases the negativity of the resting potential
- Opposite effect of opening a sodium channel
- But when stimulus is removed, potential returns to rest
hyperpolarization
• The effect of _______ depends on WHERE they happen:
• At cell dendrites or cell bodies:
– trigger specific cell functions
– e.g., exocytosis of glandular secretions
• At motor end plate:
– releases ACh or other neurotransmitters into synaptic cleft
Graded Potentials
- Propagated changes in transmembrane potential
- Affect an entire excitable membrane
- Link graded potentials at cell body with motor end plate actions
action potential = nerve impulses
• A graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential
( -70 mV) to threshold level of voltage-gated sodium channels (–60 to –55 mV)
• Initial stimulus must reach threshold!
• If a stimulus exceeds threshold amount:
– the action potential is the same
– no matter how large the stimulus
• Action potential is either triggered, or not!
• All-or-none principle
Resting State Prior to Action Potential
- Na+ activation gate = closed
- Na+ inactivation gate = open
- K+ gate = closed
- Step 1: Depolarization to threshold
- Step 2: Activation of Na+ channels
- Step 3: Inactivation of Na+ channels, activation of K+ channels
- Step 4: Return to normal permeability
Four Steps in the Generation of
Action Potentials
- From beginning of action potential to the return to resting state
- During this time, the membrane will not respond normally to additional stimuli
refectory period
- Sodium channels open or inactivated
* No action potential possible
absolute refractory period
- Membrane potential almost normal
* BUT, Very large stimulus can initiate action potential
• Relative refractory period
- The movement of action potentials that have been generated in axon hillock
- This travels along the entire length of the axon
- Consists of a series of repeated actions, NOT passive flow (as we saw in graded potentials)
• Propagation
- Continuous propagation: ______ axons
* Saltatory propagation: ______ axons
unmyelinated; myelinated
unmyelinated axon propagation is very ____, repeats in ___ like fashion (tiny steps)
slow; chain
- Faster and uses less energy than continuous propagation
- Myelin insulates axon and prevents continuous propagation
- Local current “jumps” from node to node
- Thus, Depolarization occurs only at nodes (rather than along the entire length of the axon in tiny steps)
Saltatory Propagation along Myelinated Axon
• Axons behave like electrical cables, so the speed at which action potentials are propagated are determined by
axon diameter and mylenation
» Large axon =___ propagation
» Small axon = ___ propagation
fast; slow
» Myelinated axons =____ propagation
» Unmyelinated axons = ___ propagation
fast; slow
• The most important information (vision, balance, motor commands) is carried by
large-diameter, myelinated axons
- Are transmitted from presynaptic neuron
- To postsynaptic neuron (or other postsynaptic cell)
- Across a synapse
• Action potentials (nerve impulses)
- Direct physical contact between cells
- Are locked together at gap junctions (connexons)
- Allow ions to pass between cells
- Produce continuous local current and action potential propagation
- Are found in areas of brain, eye, ciliary ganglia
• Electrical Synapses
- Signal transmitted across a gap by chemical neurotransmitters
- Are found in most synapses between neurons and all synapses between neurons and other cells
- Cells not in direct contact
- Action potential may or may not be propagated to postsynaptic cell, depending on
- Amount of neurotransmitter released
- Sensitivity of postsynaptic cell
• Chemical Synapses
