What are the three overlapping functions of the nervous system
- Sensory input
- neural integration
- motor output
what is sensory input
transmitting impulses/signals from sense organs(receptors) to CNS for interpretation, function of PNS
what is neural integration
decision making, only happens in CNS
what is motor output
transmitting impulses (commands) from the CNS to effectors so that they can carry it on, function of PNS
describe how the nervous system is the main control and regulatory system of the body
The NS communicates electrically (with action potentials) and chemically (with neurotransmitters), to send messages quickly from the CNS (the brain and spinal cord) to the periphery of the body (skeletal muscles) and from the periphery of the body (receptors) to CNS
What are the parts of the nervous system that constitutes the CNS?
CNS: Brain (enclosed and protected by the cranium) and spinal cord (enclosed and protected by the vertebral column). Have somas of interneurons.
What parts of the nervous system constitute the PNS?
PNS: Nerves=a collection of nerve processes/axons (ex. spinal and cranial nerves) and ganglia=a collection of somas of neurons (like dorsal root ganglion). Has sensory (afferent) and motor (efferent division); somatic and visceral (autonomic) division. Have axons of sensory and motor neurons.
What are the different anatomical categories of the nervous system?
The Central Nervous System and The Peripheral Nervous System
What are the different functional categories of the nervous system? And examples of effectors?
- Autonomic (visceral)
- Motor (skeletal muscle, smooth muscle, cardiac muscle, glands)
Describe somatic division of the nervous system
this division mainly controls skeletal muscles of the body. It is voluntary.
Describe the autonomic division of the nervous system
(visceral motor division) It carries signals to internal organs (viscera) like glands, cardiac muscles, and smooth muscles. It is involuntary.
Identify the nervous system as a control system by naming nervous system elements
- Sensory receptors
- afferent pathway
- control center (in CNS)
- efferent pathway
Element of nervous system as a control system: Sensory receptors
- specialized structures that detect changes, aka stimuli or signals=sensory input (temperature, pressure, touch, etc.).
- Examples: the eyes, Merkel/tactile cells, ears, temperature and pain receptors (nociceptors), Pacinian, Meissner, hair receptor
Element of nervous system as a control system: afferent pathway
nerve pathway through which sensory input is transmitted to CNS from receptors. Formed by axons of sensory neurons.
Element of nervous system as a control system: Control Center
(In CNS) interneurons that analyze the sensory input and make a decision to respond to the change. Interneurons are also called association neurons.
Element of nervous system as a control system: Efferent pathway
nerve pathway through which motor output is sent away from CNS to effectors. Carried by axons of motor neurons.
Element of nervous system as a control system: Effector
Motor Output- carries out the decision. Examples: skeletal muscles contract; smooth muscle relaxes blood vessels; glands produce sweat.
what is the microscopic anatomy of nervous tissue?
Neurons and Glial cells (neuroglia)
What is the difference between neurons and glial cells?
- Neurons are structural units of the nervous system, large cells with dendrites and axons.
- Neuroglia are 10:1 to neurons. Help neurons do their jobs, highly mitotic.
What are the three fundamental properties of neurons?
excitability, conductivity and secretion.
Explain the excitability property of a neuron.
aka responsiveness, ability to respond to a signal/stimulus
explain the conductivity property of a neuron.
the ability to conduct an electrical signal (think axons)
explain the secretion property of a neuron
ability to produce and eliminate chemicals called neurotransmitters (think vesicles with neurotransmitters (NT) in axons
What are the three functional types of neurons?
sensory, interneuron/association neuron and motor neuron
Correlate the three functions types of neurons to the three overlapping functions of neurons.
- Sensory neurons conduct afferent/sensory information to CNS from receptors. Responsible for carrying sensory input.
- Interneurons make decisions. Are responsible for neural integration. Always in CNS.
- Motor neurons conduct efferent/motor information from CNS to effectors. Responsible for carrying motor output.
Identify the anatomical structure of a unipolar neuron
this neuron has ONE extension coming off the soma that divides into a dendrite and an axon
Identify the anatomical structure of a bipolar neuron
Has ONE dendrite and ONE axon. Rare.
Identify the anatomical structure of a multipolar neuron
Has MULTIple dendrites and ONE axon. Most common neuron.
What are the three structural types of neurons?
Unipolar, bipolar, and multipolar
describe the anatomical part of a neuron that receives the information?
Dendrites. Usually short and branching. Local potentials are usually created on dendrites and then travel to axon hillock. A neuron usually has multiple dendrites
describe the anatomical part of a neuron that integrates information
Soma –this part of the neuron contains the nucleus and other organelles
describe the anatomical part of a neuron that conducts the signal of a neuron
Axons. A neuron has one axon. The axon can have a myelin sheath(myelinated axons/fibers) or lack a myelin sheath (unmyelinated axons/fibers). Action Potential starts here
Where can you find unipolar neurons within the nervous system?
Seen in sensory neurons of dorsal root ganglion (outside CNS)
Where can you find bipolar neurons within the nervous system?
Found in sensory organs (smell and vision)
Where can you find multipolar neurons within the nervous system?
Found mostly in CNS
What are the types of glial cells found in the CNS?
- Ependymal cells
Types of glial cells found in the CNS: Describe the function of Oligodendrocytes.
form the myelin sheath in the brain and the spinal cord
Types of glial cells found in the CNS: Describe the function of Ependymal cells
line the cavities of the brain (ventricles) and spinal cord (central canal)
Types of glial cells found in the CNS: Describe the function of Microglia
phagocytize and destroy microorganisms, foreign matter, and dead nervous tissue(macrophages).
Types of glial cells found in the CNS: Describe the function of Astrocytes
participate in forming the Blood-Brain Barrier
What are the types of glial cells found in the PNS?
- Schwann cells
- Satellite cells
Types of glial cells found in the PNS: Describe the function of Schwann cells
these glial cells form the neurilemma and the myelin sheath around all PNS nerve fibers. (has to do with the exterior of PNS nerve fibers)
Types of glial cells found in the PNS: describe the function of satellite cells
provide support to neurons: electrical insulation and regulate chemical environment of neurons. (has to do with the interior of PNS nerve fibers)
Neurophysiology of Membrane potential
Across the plasma membrane of neurons and muscle cells, the voltmeter measures a voltage (from -40mV to -90mV). This potential difference in a resting cell is called a resting membrane potential (Vm) and the membrane is said to be polarized. This resting potential exists only across the plasma membrane
Neurophysiology of Voltage
measure of potential energy generated by separated charge (V or mV). It is the potential between two points. The greater the difference in charge, the higher the voltage
Neurophysiology of Current
flow of electrical charge from one point to another. Depends on voltage and resistance
Neurophysiology of Permeability
the ability to transport/allow solutes through a membrane. Ex: membrane is permeable to K and Na, but impermeable to negatively charged ions.
Describe the role of ion channels in the selective permeability of the membrane.
Solutes that cannot diffuse directly through the membrane will require channels to cross the membrane. When ion channels are open, these ions can pass through easily and the permeability is increasing. When ion channels are closed, solutes will not be able to pass through and the permeability will decrease.
Give an example of the role of ion channels in the selective permeability of the membrane.
Ex: in depolarization wave of AP, permeability to Na increases due to opening of additional voltage-gated Na channels, while during repolarization wave of AP, permeability to Na decreases, since the voltage gated Na channels are inactivated/closed
Identify and contrast possible relative concentrations that can be found within a neuron
- Anions- high ICF (stuck inside)Sodium- high ECF, low ICF
- Potassium- high ICF, low ECF
- Chloride- high ECF, low ICF
What is the difference between a concentration gradient and an electrical potential?
- concentration gradient: concentration across plasma membrane due to selective permeability. (normally permeable to Na and K)
- electrical potential: voltage difference across membrane that depends on concentration gradient and selective permeability
Difference between constantly open and gated ion channels.
- Constantly open: are always open and allow ions to move in and out of the cell as long as the solute fits through the channel opening (reason why plasma membrane is normally selectively permeable to Na and K)
- Closed: these channels ONLY open in response to signals
What are the different types of gated ion channels?
Describe lingand-gated ion channels
open in response to chemicals attaching to them (ex: ligand-gated Na channels open in response to ACh)
Describe voltage-gated ion channels
open in response to voltage change (ex: voltage gated Na channels on the axon hillock open at threshold and generate an AP)
Describe mechanically-gated ion channels.
open in response to physical signals (like stretch)
What is the Vm in a cell?
Resting membrane potential: a difference in charge across the membrane
What is Vm dependent on with respect to Na/K pump
a)the concentration gradient of ions: more Na in ECF and less in ICF; more K in ICF and less in ECF; high concentration of anions in ICF and b) permeability of membrane to ions: permeable to Na and K and impermeable to anions
Describe the role of constantly open ion channels and Vm. With respect to the Na/K pump
Constantly open ion channels allow ions (K and Na) to pass through the plasma membrane due to their concentration gradient: Na diffuses into the cell and K diffuses out of the cell. Vm is maintained by the Na+/K+ pump that works continuously to actively move Na out of the cell and K into the cell.
What is the end result that constantly open ion channels achieve in the Na+/K+ pump?
- it maintains concentration gradient where theres more Na in ECF (positive charge on the outside of membrane) and more K in ICF (negative on the inside of the membrane due to large concentration of anions in ICF).
- Vm has a negative sign, because the inside of the membrane is negatively charged due to anions (stuck in the cell due to impermeability of membrane).
How are voltage-gated ion channels essential for the development of action potential?
- voltage-gated Na (fast) channels open first and cause depolarization wave of AP (Na rushes in and brings + charge)
- voltage-gated K (slower) channels open at peak of AP (when Na channels close). K moves out and takes away + charge causing repolarization. as well as a short hyperpolarization at the end of AP.
define threshold and its relationship to voltage-gated ion channels and generation of action potential.
Minimum electrical change required for voltage gated channels to open and generate an AP. Usually around -55mV. If threshold is not reached, voltage gated channels cannot open and an AP cannot be generated.
Voltage gated ion channels: Depolarization
Vm decrease. Inside of plasma membrane becomes less negative (closer to 0)
Voltage gated ion channels: Hyperpolarization
Vm increase. The inside of the plasma membrane becomes more negative (moves further from 0)
Voltage gated ion channels: Repolarization
return to a resting membrane potential (moves closer to original value)
what if there was an absence of a threshold in voltage-gated channels?
During action potential, voltage-gated channels (Na and K) will not open and these drastic changes in voltage (de-, hyper-, re-polariztion) repolarization not possible.
Describe sequence of events that must occur for action potential to be generated
- Chemicals attach to ligand-gated channels on dendrites and cause local potential
- local potential travels to axon hillcock (trigger zone)
- If local potential is strong enough to reach threshold at trigger zone, voltage-gated Na channels open
- Na ions rush into neuron and start depolariztion wave of AP
- Once Na channels are inactivated, voltage-gated K channels open fully and K exits neuron---> repolarization
- action potential (nerve signal) is conducted along axon. Unmyelated- slower conduction. Myelated- faster
what is an action potential
a nerve signal
Unmyelated axons conduct ______ than myelated axons
Describe the role of the sodium-potassium pump in making continued action potentials possible
The Na+/K+ pump allows for future action potentials by working continuously to maintain and restore the concentration gradient of a resting cell; more Na in ECF and more K in ICF. Which then allows for depolarization and repolarization of the next AP.
what is an absolute refractory period?
period of absolute resistance to stimulation = no stimulus will trigger an action potential.
What is a relative refractory period?
period of relative resistance to stimulation = only a strong signal can trigger an AP
what is the physiological basis of the absolute and relative refractory periods.
- Absolute: when Na+ gates are inactivated and no movement of Na is possible. If Na cannot move across the membrane and enter the cell, no depolarization is possible, Cell cannot reach the threshold, which means no AP can be generated
- Relative: any time that K+ gates are still open and the cell is hyperpolarized. K is moving out of the cell and depolarization is possible, but only in response to a very strong signal.
Discuss the consequence of having an absolute refractory period.
AP is only able to travel one way, from the axon hillock to the synaptic knob, allowing the passage of signals from sensory to interneurons to motor neurons and not the other way.
Describe how local currents cause impulse conduction in unmyelinated axons
- In an unmyelinated axon, there are voltage-gated Na+ channels all along the length of the axon.
- The continuous wave of de- and re-polarization travels from one region of the membrane to the next (self-propagating AP)
- Called continuous conduction
What is saltatory conduction?
- This is a type of conduction seen with myelinated fibers/axons.
- saltatory = to jump, the signal moves very fast through the myelin sheath to the next node of Ranvier.
How do currents develop in saltatory conduction
- AP is only formed in the axon hillock and propagated by the voltage gated channels found in the Nodes of Ranvier
- the signal moves very fast through the myelin sheath to the next node of Ranvier.
how does axon diameter effect conduction velocity (speed of nerve impulse)?
a larger diameter will make an action potential travel faster along the axon because of less peripheral resistance.
how does a mylenated axon compare with an unmyelated axon and why?
an mylenated axon will conduct an AP (nerve signal) faster than an unmyelinated axon, since the signal can jump over the areas of the myelin sheath, called internodes
What structures have a role in an entire chemical synapse.
- Synaptic knob/axonal terminal
- Synaptic cleft
- Synaptic vesicles
- Presynaptic cells
- Postsynaptic cells
Structures of a chemical synapse: describe synaptic knob/axonal terminal
knob-like area that stores the neurotransmitters in synaptic vesicles and has voltage-gated Calcium channel that open in response to an AP to allow calcium ions to enter the axon terminal/synaptic knob
Structures of a chemical synapse: describe synaptic cleft
space between the pre- and post-synaptic neurons
Structures of a chemical synapse: describe synaptic vesicles
hold the neurotransmitters before they are released
Structures of a chemical synapse: describe presynaptic cells
cell before synapse
Structures of a chemical synapse: describe postsynaptic cells
cell after synapse
Structures of a chemical synapse: describe receptors
found on postsynaptic cell of synapse, bind the neurotransmitters, are ligand gated channels.
What are the differences between presynaptic and postsynaptic cells at a synapse
- Pre- cells that release neurotransmitters into synaptic cleft and send signal across synapse.
- Post- cells have receptors for neurotransmitters and process signal
Identify steps starting from AP arriving to release of neurotransmitter
- 1. A nerve signal (AP) arrives at the synaptic knob
- 2. Voltage-gated Ca2+ channels in the synaptic knob open
- 3. Calcium ions enter the synaptic knob (bc concentration in ECF is higher)
- 4. Ca2+ triggers exocytosis of the NT (Ach, Epi, substance P or other) from the synaptic vesicles into synaptic cleft
- 5. The neurotransmitter diffuses across the synaptic cleft
- 6. The neurotransmitter binds to ligand-gated channels on post-synaptic cell
- 7. These channels open and allow ions like Na+ or Cl- to enter the post-synaptic cell
- 8. As ions enter the post-synaptic cell, they depolarize or hyperpolarize the postsynaptic cell (creating a postsynaptic potential-IPSP or EPSP)
What 4 major groups are neurotransmitters classified into?
- Acetylcholine (Ach)
- Catecholamines (Epinephrine and Norepinephrine)
- Neuropeptides (substance P)
- Amino acids (GABA)
how are the receptors for neurotransmitters related to opening chemically-gated ion channels
Receptors are ligand-gated channels. These channels will only open when the NT binds to the receptor. Each receptor is specifically built to only bind a a specific neurotransmitter.
What happens when a NT binds to its specific receptor in regards to opening chemically-gated ion channels?
Ligand-gated channels open. They can be Na channels or Cl channels. Once open, channels allow ions to enter the postsynaptic cell and depolarize= excite (if Na+) or hyperpolarize=inhibit (if Cl-) the postsynaptic cell.
What is a Cholinergic synapse
synapse in which acetylcholine (Ach) is the neurotransmitter
what is the relationship between a neurotransmitter and its receptor in a cholinergic synapse?
- Present in motor neurons responsible for activating skeletal muscles
- Ach binds to ligand-gated Na+ channels on postsynaptic cell to allow Na+ to enter the cell and depolarize it (EPSP)
- post-synaptic neuron is excited and is more likely to reach the threshold and “fire” (generate an AP to send along to next neuron)
What is a GABAergic synapse
this synapse uses amino acid (GABA) as neurotransmitter
what is the relationship between a neurotransmitter and its receptor in a GABAergic synapse
- Present in motor neurons responsible for activating skeletal muscles
- GABA binds to ligand-gated Cl- channels on the post-synaptic cell to allow Cl- to enter the postsynaptic cell and hyperpolarize it (IPSP)post-synaptic neuron is inhibited and is less likely to reach the threshold and “fire” (generate an AP to send along to next neuron)
What is EPSP
Excitatory postsynaptic potential (EPSP) – graded depolarization will bring a normal Vm closer to the threshold
What is IPSP
Inhibitory postsynaptic potential (IPSP) – graded hyperpolarization will bring a normal Vm farther away from the threshold
Explain how movement of sodium, potassium and chloride ions across the postsynaptic cell membrane can excite or inhibit a neuron.
- Sodium is main role. If it can make it into membrane-->depolarization (closer to threshold).
- K ions leaving cell (take + charge)--> Repolarization
- Cl- enter thru ligand-gated channels--> negative charge--> hyperpolarization (away from threshold)
- Opening of K+ channels allows K to leave making inside more negative--> hyperpolarization. Until Na/K pump reestablishes concentration gradient
Explain temporal summation of synaptic potentials
ONE presynaptic neuron stimulates ONE postsynaptic neuron multiple times within a brief period of time. All EPSPs in the postsynaptic neuron add up (summation) and ARE more likely to reach the threshold. The postsynaptic neuron is more likely to fire.
Explain spatial summation of synaptic potentials
MULTIPLE presynaptic neurons stimulate ONE postsynaptic neuron. All EPSPs add up (summation) and ARE more likely to reach the threshold. The postsynaptic neuron is more likely to fire.
describe characteristics of local potentials
- (graded potentials) Localized changes in membrane potential.Need chemical neurotransmitters and depend on ligand-gated channelsgraded-magnitude varies in size, reversible, travel short distances, decrease in size/strength as they travel, excitatory (EPSP) or inhibitory (IPSP)
describe characteristics of action potentials
- more pronounced change in membrane potential with a reversal and total amplitude of about 100 mV.
- If local potential is strong at trigger zone, threshold (-55 mV) is reached, voltage-gated channels open and neuron “fires” (generates an AP)
- all-or-nothing law-if threshold is reached there is a full AP; if threshold is not reached, there is no AP, irreversible, travel a long distance, don’t decrease in size/strength as they travel, which means they have the same voltage at end of axons as they had in the beginning of axon
What is one common excitatory neurotransmitter in the CNS
Ach and epinephrine (Epi)
What is one common inhibitory neurotransmitter in the CNS.
amino acid - (GABA)