Chapter 7 Flashcards
Central nervous system (CNS)
Brain and spinal cord
It receives and processes information from sensory organs and viscera to determine status of in/external environment
Peripheral nervous system
Efferent and afferent
Provide communication between central nervous system and Organs throughout the body
Afferent (senses)
Transmiss sensory from the organs to the central nervous system
Somatic senses- skin muscles and joints
Special senses-vision hearing equilibriums smell and taste
Visceral senses – fullness of stomach blood pressure and blood pH
Efferent (Innervate)
Transmit information from the central nervous system to organs in the periphery called effector organs
Muscles and glands
These neurons INNERVATE(effect) organs
Efferent divisions (Vol)
Somatic (Voluntary):
Motor neurons which regulate skeletal muscle contractions
Autonomic (involuntary):
Neurons that regulate the function of internal organs and other structures such as sweat glands and blood vessels
Autonomic nervous system
Parasympathetic (rest and digest) and sympathetic (fight or flight) has opposite effects on organs
Enteric nervous system
Intricate network of neurons in the Gastro intestinal tract that can function independently of the rest of the nervous system but communicates with the autonomic nervous system
Nervous system to main classes of cells:
Neurons(excitable cells) and glial cells
Glial cells
Account for 90% of the cells in the nervous system and provide various types of support to the neurons including structural and metabolic support
Three components of neurons
- Cell body
- Neural processes: Neurites and dendrites
- Axon
Cell body (Soma)
Nucleus Endoplasmic reticulum Golgi apparatus Free ribosomes Mitochondrion
Perform proteins synthesis and cellular metabolism
Cannot cellular divide
Undifferentiated or stem cells
in a few areas of the adult human brain neurons can develop by this
Dendrites
Branch from the cell body and receive input from other neurons at specialized junctions called synapses
Axon (collateral)
Receive information and send information
They can branch there by sending signals to more than one destination these branches are called collaterals
Action potential
Brief large changes in membrane potential during which the inside of the cell becomes positively charged relative to the outside
Axon hillock
The site where the axon originates from the cell body used for the initiation of action potentials
Axon terminal
Release neurotransmitter on arrival of an action potential. Carries signal to a post synaptic cell
2 axonal transport mechanisms (grade)
Anterograde transport-from cell body to the axon terminal (Kinesins)
Retrograde-Slow axonal transport and fast axonal transport
Fast and slow axonal transport
Both involved proteins including microtubules in a variety of neurofilaments
Slow: 0.5-40mm/day movement of mols in cytosol
Fast: 100-400mm/day movement of vesicles
Kinesins
Proteins that essentially walked down the microtubules, caring a vesicle with them (requires the ATP)
Leak channel (nongated channel)
Always open, Responsible for the resting membrane potential
Ligand gated channels (receive)
Open or close in response to the binding of a ligand to specific receptor in the plasma membrane
Densely located in dendrites and cell body (area that receive info)
Voltage gated channels
Open or close in responses to changes in membrane potential. Densely located in axon hillock, nodes of ranvier, axon
Sodium, calcium, or potassium Channel
Bipolar neuron
Sensory neurons with 2 projections (axon and dendrite)
Functions in senses of olfactory (smell) and vision
Subclass: pseudounipolar
Pseudo-unipolar
Axon and dendrites projections appear as a single process however the dendrite is a modified function like an Axon
Multipolar neuron
Have multiple projections from cell body; one projection axon and other dendrite
Three functional classes of neuron
Efferent neuron
Afferent neuron
Interneuron
Efferent neuron
From central nervous system to effector organs
Afferent neurons
Transmit info from either sensory receptors or visual receptors to the central nervous system for further processing
Most are pseudounipolar neurons-with somebody located in a ganglion outside CNS
Interneurons
99% of all neurons
Located entirely in central nervous system
perform all functions of the central nervous system including processing sensory information from afferent neurons, creating and sending out commands to affect your organs through efferent neurons, and carrying out complex functions of the brain
Pathways, tracts, or commissures (CNS)
Bundle of axons which travel together
Ganglia
Cluster of neurons
Nerves
Bundle of axons
Types of Glial cells
Astrocytes Microglia Oligodendrocytes Schwann cells (PNS) Ependymal cells
*all found in CNS
Myelin
Made by layers of the plasma membrane’s of oligodendrocytes and Schwann cells, insulate axons for rapid transmission of action potentials
Nodes of ranvier
Voltage gated sodium and potassium channels that function in allowing ion movement across membrane
Resting membrane potential
Not receiving or transmitting signals, -70mV
Neurons range from -5mV to -100mV
Na+/K+ pump
Concentration gradient for sodium and potassium by transporting three sodium(+) ions out of the cell and to potassium(-)ions into the cell per ATP hydrolyzed
Electrogenic: Transports a net positive charge out of cell
Na and K balanced by
Na+ balances electrically by Cl-
K+ balanced electrically by organic anions (A-, proteins)
Equilibrium potential for potassium (Ek)
-94mV
Equilibrium potential for sodium (ENa)
+60mV
Potassium channels
There are more open potassium channels than sodium, 25 times more permeable to potassium
Neuron at rest
Neither sodium or potassium is at equilibrium, because the membrane potential is not equal to the equilibrium potential of each ion
Therefore electrochemical forces continually leak into cell and potassium continually leaks out
Membrane permeability
As the membranes permeability to a particular ion increases, the membrane potential moves closer to that ions equilibrium potential
Electrochemical force and mV
The electrochemical force is greater for the ion that is further away from its equilibrium
Hyperpolarization
A change in mem potential to a more negative value, more polarized
Inhibitory- take mem potential away from threshold
Depolarization
Change in mem potential to a less negative or positive potential, less polarized
Excitatory-bring mem potential closer to threshold to generate action potential
Repolarization
When mem potential returns to the resting membrane potential after depolarization
Graded potential
Small changes in membrane potential that occur when ion channels open or close in response to a stimulus acting on the cell
Decremental-Short range
Can Generate an action potential if they depolarize a neuron to threshold
Electrotonic conduction
Spread of voltage by passive charge movement in unmyelinated axons
ICF (+) ECF (-)
*diameter of axon determine speed of current (larger,faster)
Direction of graded potential 3 factors
Neuron
Stimulus
The opening and closing of ions
Can be excitatory(closer to threshold) or inhibitory (away from threshold)
Threshold
A critical value of membrane potential that must be met or exceeded if an action potential is to be generated
Action potential phases
Rapid depolarization
Repolarization
After-hyperpolarization
1st phase: Rapid depolarization
Mem potential changes from -70mV to +30mV
Dramatic increase of sodium approaches +60mV
2nd phase: Repolarization
Returns from +30mV to -70mV
Sodium intake decreases and potassium increases
3rd phase: After-hyperpolarization
Potassium permeability 5-15msec causes mem potential to rest at -94mV
Activation gates
Responsible for opening Of sodium channels during the depolarization phase of an action potential
Voltage gated
Inactivation Gates
Responsible for the closing of sodium channels during the repolarization phase of an action potential
Voltage gated
Sodium channel conformations
Closed but capable of opening
Open
Closed and incapable of opening
Closed but capable of opening
Inactivation gate open
Activation gate closed
Can be opened by depolarizing stimulus
Open
Both gates open
Occurs during depolarization phase
Closed and incapable of opening
Open activation gate, closed inactivation gate
Opens during repolarization
Subthreshold
A depolarization that is less than threshold
No action potential
Can open some Na+ channels
Suprathreshold
Greater than threshold
Elicits action potential
Does not increase in size as the strength of a suprathreshold increases
All or none principle
Whether a membrane is depolarized to a threshold or greater the amplitude of the resulting action potential is the same if the membrane is not depolarized to threshold
Refractory period
Period of reduced excitable
All or none principle
- Absolute refractory period: a second action potential cannot be generated in response to second stimulus
- Relative refractory period: possible to generate a second action potential but only in response to a stimulus stronger than that to reach threshold
Saltatory conduction
Specialized electrotonic conduction that propagates action potentials
Collateral
When an axon branches and this depends on the neuron
Factors of mem potential
Conc gradients of ions
Presence of ion channels in mem
Mechanically gated
open when physical forces such as stretching forces act on the membrane or the channel
Multiple sclerosis
Autoimmune disorder, degeneration of myelin sheath and attacks oligodendrocytes
Symptoms: Loss of muscle coordination Fatigue Numbness Vision degradation Loss of bladder/bowel control
Local anesthetics
Novacaine or Xylocaine
Blocks violated gated channels from sending info
Tetradotoxin (TTX)
Poison found in puffer fish gonads and liver
Blocks voltage gated channels
Deadly and create zombies
Dinoflagellates
Saxitoxin
Blocks voltage gated channels
Causes red tide
Cannot be destroyed by cooking
