Slide set 4: Nervous system Flashcards
What is the general function of nervous system?
Along with the endocrine system, is to control and communicate
What are the 3 components pf nervous system?
brain, spinal chord, peripheral nerves
What are the 2 smaller “system” of nervous system?
- Central nervous system
- Peripheral nervous system
What are the parts, role of central nervous system? (CNS)
- Structural and functional center of entire nervous system
- Brain + spinal cord
- Integrates sensory information, evaluates it, and initiates an outgoing response
What are the parts/role of peripheral nervous system?
- Nerves that lie in “outer region” of nervous system
- Cranial nerves=> originate from brain
- Spinal nerves => originate from spinal cord
How is the nervous system also divided? What are the “categories” called?
According to types of organs they innervate.
Somatic vs Autonomic nervous system
How is the somatic nervous system divided?
- Somatic motor division: Carries information to the somatic effectors (skeletal muscles)
- Somatic sensory division: Carries feedback information to somatic integration centers in CNS from PNS
What is the difference between autonomic and somatic nervous system?
Autonomic=> without voluntary control
What is the afferent division and the efferent division
Afferent=> incoming message from visceral receptors
Efferent=> outgoing of ANS => carries information to the visceral effectors ( smooth and cardiac muscles and glands)
What are the 2 autonomic categories?
Sympathetic division
Parasympathetic division
What is the sympathetic division of the ANS efferent pathway?
it prepares the body to deal with immediate threats to the internal environment: produces fight-or-flight response
What is the parasympathetic division of the ANS efferent pathway?
Coordinates the body’s normal resting activities : something called the rest-and-repair division
What are some effect of the sympathetic control on the heart rate?
- Sympathetic branch of the ANS controls heart rate in emergency response-has and overall stimulatory effect
- When there is a need for greater blood flow
- Blood beats more forcefully and squeezes out more blood
- Has a vasoconstriction effect on blood vessels
What are some effect of parasympathetic control over the stomach?
- Distention of the stomach caused by the presence of food triggers parasympathetic reflexes
- increase secretion of gastric juice
- In response to presence of amino acids, Parasympathetic innervation causes gastrin (digestive hormone) secreted by mucosa in presence of food causes increased secretion of gastric juice
What are the 2 major cells of the nervous system?
- Neurons
- Glial cells
What are characteristics of neurons?
Are EXCITABLE cells that CONDUCT IMPULSES (functional cells) and are required for all nervous system activities
What are characteristics of Glial cells?
DO NOT conduct information, but support the functions of the neurons
What type of structure in neurons help transport small organelles? In what part of the cell is the transport more important?
Cytoskeleton :
- Microtubules and microfilaments as well as neurofibrils
They are a shuttle for small molecules and organelles
Axon transport
-motor molecules, move proteins on cytoskeleton. Highway for release at the synaptic knobs
What are the 4 types of glial cells of the central nervous system?
- Oligodendrocytes
- Microglia (modified immune cells)
- Astrocytes
- Ependymal cells
What are some characteristics of Astrocytes?
- Star-shaped
- Largest
- Most numerous
Cell extensions connect to both neurons and capillaries
Transfer nutrients from the blood to the neurons
Form tight sheats around brain capillaires, which with tight junctions between capilarru endothelial cells constitute the BLOOD-BRAIN-BARRIER (BBB)
What is the role of the blood-brain-barrier?
The BBB is the specialized system of capillary endothelial cells that protects the brain from harmful substances in the blood stream AND allow supply of the brain with required nutrients for proper function
How does BBB protect the brain?
BBB strictly limits transport into the brain through both physical (tight junctions) and metabolic (enzymes ) barriers
What are the 2 specialization that allows the BBB to function?
- Capillaries are specialized as they are held together by tight junctions => this acts as a barrier against molecules
- Second specialization involves the feet of the astrocytes
What is a tight junction?
- Occur in cells that are joined by “collars” of tightly fused material
- Molecules cannot permeate the cracks of tight junctions
- Important in the blood brain barrier in connecting endothelial cells
What is the role of astrocyte in BBB?
- Webs of astrocytes forms tight sheets around the brain’s capillaries => restrict the entrance of potentially harmful chemicals from the blood, while allowing entrance of essential nutrients
- This is a double barrier made up of astrocyte feet and the endothelial cells that make up the walls of the capillaries
What molecules can penetrate through the BBB?
- Lipid soluble molecules (ethanol, caffeine…)
- Glucose
- Liposomes (Liposome-A => spherical vesicle with a membrane composed of PHOSPHOLIPID BILAYER
What is a microglia?
- Macrophage of the brain
- Small, usually stationary cells
- Exception is in INFLAMED BRAIN TISSUE, where they ENLARGE , MOVE, and CARRY on phagocytosis to remove microorganisms and cellular debris
What are ependymal cells?
- RESEMBLE EPITHELIAL CELLS and form thin sheets that line fluid-filled cavities (cerbral-spinal fluid) in the CNS
- Have cilia
- Some produce fluid , others aid in circulation of fluid (reason why cilia)
What are oligodendrocytes?
- Smaller than astrocytes with fewer processes
- Hold nerve fibers together and produce MYELIN SHEATH in CNS
What is multiple sclerosis?
- Disorder of oligodendrocytes
- Auto-immune disease
- Most common disease in CNS
- Characterized by myelin loss and destruction
- Failure in nerve conduction
- Communication interupted
- Treatment, immune modulating , inflammation reducing
What is a Schwann cell?
- Glial cell
- Found only in PNS
- Functional equivalent of oligodendrocyte
- Support nerve fibers in some cases form MYELIN SHEATS. Gaps in the myelin sheats are called NODES OF RANVIER
- The myelin sheats and nodes of Ranvier are important for the CONDUCTION OF IMPULSES along nerve fibers
What are satellite cells?
- Glial cell
- Another type of Schwann cells that cover and support neuron cell bodies in PNS
- Do not form Myelin sheath
True or false
Schwann cells always form myelin sheaths
False
Some Schwann cells have only SUPPORTING ROLE and do not form the myelin sheath
What is myelin?
- Multiple layers of cell membrane
- Nucleus is pushed outside
What are the functional regions of a neuron?
- INPUT ZONE: receiving information at dendrites and cell body
- SUMMATION ZONE : axon hillock serves as the site where the nerve IMPULSES COMBINE and may trigger and ACTION POTENTIAL to be conducted along the axon
- CONDUCTION ZONE : axon- has voltage gated channels Na+ and K+
- Output zone: synaptic knobs of axon. Contains many Ca2+ channels. Nerve impulse trigger RELEASE OF NEUROTRANSMITTERS
What are the 3 functional classification of neurons?
AFFERENT (incoming-sensory) neurons: conduct impulses to SPINAL CORD OR BRAIN
EFFERENT (motor) neurons: Conduct impulses AWAY from SPINAL CORD OR BRAIN toward MYSCLES or GLANDULAR tissue
INTERNEURONS: lie ONLY WITHIN the CNS (brain and spinal cord): Conduct impulses from sensory neurons (afferent) to motor neurons
Describe the 3 steps of the reflex arc
- Sensory receptor send message to CNS
- Reaches interneuron
- Interneurons elicits outgoing (efferent ) response from motor neuron
Neurons are bundled into ____ in PNS and _____ in CNS
NERVEs in PNS => bundles of peripheral nerve fibers held together by several layers of connective tissue (each nerve contains axons bundled into FASCICLES)
TRACTS in CNS => bundles of nerve fibers are called tracts rather than nerves
True or false
Neurons are incapable of cell division
TRUE
- Neurons have limited capacity to repair themselves - PNS little or none in CNS
- Nerve fibres can be repaired if the damage is not extensive
What is the normal resting potential?
-70mV
What side of the membrane is positive/negative?
Outside: slightly positive
Inside: slightly negative
- slight excess of POSITIVELY CHARGED IONS on outside of the membrane and slight DEFICIENCY of POSITIVELY CHARGED IONS on inside of membrane
For what ion (Na+ or K+) is the membrane more permeable?
More permeable to K+
How is the membrane potential kept by the cell?
Membrane permeability+ membrane channels
- First mechanism that maintains RMP=> membrane channels which dictate membrane permeability
- Second mechanism: Active transport mechanism (sodium-potassium ATPase)
Na+/K+ pump contributes to the membrane potential by 3 Na+ out for every 2 K+ in
If the membrane potential is MORE negative than the RMP, it is called…
Hyperpolarization
If the membrane potential is LESS negative than the RMP, it is called…
Depolarization
What are the 3 types of gated channels?
- Mechanically gated: sensory neurons, physical trigger
- Chemical gated: most neurons, respond to ligand
- Voltage gated: cahnges in cell membrane potential
In a RMP which channel are open?
many of the K+ channels are open, but the Na+ are closed
Which way does potassium move?
More K+ inside, slowly diffuses out
What is the mechanism that produces an action potential?
An adequate stimulus triggers stimulus-gated Na+ channels to open, allowing Na+ to diffuse rapidly into the cell, producing a local depolarization
What channels open in case of excitation of a neuron?
Opening of additional Na+ channels, allowing the membrane potential to move toward zero (depolarization)- Action potential
What channels are open in case of INHIBITION of a neuron?
Inhibition of a neuron occurs when a stimulus triggers the opening of additional K+ CHANNELS , increasing the membrane potential by allowing K+ to diffuse out of th cells
- Excess of K+ outside the cell results in HYPOERPOLARIZATION due to increase in te membrane potential (makes it harder to stimulate)
What is the treshold potential?
The minimum magnitude of a voltage fluctuation that will trigger the opening of a VOLTAGE GATED channel
Typically -59 mV
What is a graded potential?
Potential that starts above treshold, but decreases in strenght when reaches summation zone… so doesn’t stimulate action potential
What is the action potential peak?
When reaches +30mV
What happens after peak action potential? How is it done?
Membrane begins to move back toward the resting membrane potential
- Achieved by opening of K+ channels , allowing outward diffusion of K+, this process is known as REPOLARIZATION
- BRIEF period of HYPERPOLARIZATION, because K+ channels reamin open as the membrane is returning to RMP
What is the refractory period?
- ABSOLUTE refractory period=> Brief period during which a LOCAL area of a neuron’s membrane RESIST RESTIMULATION and WILL NOT RESPOND to a stimulus NO MATTER HOW STRONG
- RELATIVE refractory period=> time during which the membrane is repolarized and is restoring the resting membrane potential, the few miliseconds after absolute refractory period=> Membrane WILL RESPOND ONLY TO A VERY STRONG STIMULUS
How does propagation (conduction) of the AP happen?
The REVERSAL in polarity (from -70=> +30) causes electrical current to FLOW between the site of the action potential and the adjacent regions of membrane and triggers VOLTAGE-GATED Na+ channels in the next segment to OPEN, this next segment exhinits and ACTION POTENTIAL
Can an AP moves backwards?
No
The AP never moves backward, as a consequence of the REFRACTORY PERIOD which prevents restimulation
Where does the AP in myelinated fibres occur? How is the conduction called?
The AP occurs only at the nodes of Ranvier!
SALTATORY conduction
- Impulse regeneration leaps from node to node
How is conduction affected in demyelinated diseases?
Conduction slows when current leaks out of the previously insulated regions between the nodes
Describe the positive feedback loop of action potentials
- The fact that the POSITIVE CHARGE from DEPOLARIZATIOn trigger zone SPREADS to adjacent zones because the K+ is repelled by the Na and attracted by the negative charge of the adjacent RMP
- The spread to adjacent zone triggers MORE DEPOLARIZATION
- Can be considered a positive feedback loop
- Depolarization opens Na channels, Na enters causing more opening of Na channels
What are synapses?
Gaps where neurotransmitters are released
On what 3 structures can a neuron terminate?
muscle, gland or neuron
What is the most common type of synapse in the nervous system? where does it occur?
Chemical synapses
- occur where presynaptic cells release chemical transmitters across a tiny gap to the postsynaptic cell
What is the synaptic knob?
Tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that contains vesicles housing neurotransmitters
I am the space between a synaptic knob and the plasma membrane of a postsynaptic neuron, what am I?
Synaptic cleft
What are 3 arrangement of synapses?
Axodendritic: axon signals postsynaptic dendrite (common)
Axosomatic: axon signals postsynaptic soma -> cell body? genre ou il y a le noyeau (common)
Axoaxonic: axon signals postsynaptic axon=> may regulate action potential of postsynaptic axon
What are the 5 steps of synaptic transmission from pre to post-synaptic neuron?
- An action potential depolarizes axon terminal
- Depolarization opens VOLTAGE-GATED Ca 2+ channels and Ca 2+ ENTERS THE CELL
- Calcium entry triggers exocytosis of synaptic vesicle contents
- Neurotransmitter diffuse across the synaptic cleft and BINDS WITH RECEPTOR on the postsynaptic cell
- Neurotransmitter binding INITIATES A RESPONSE in the postsynaptic cell
What are some diseases related to defects/imbalance of neurotransmitters?
Alzheimers, depression, anxiety, Schizophrenia, Parkinson’s etc…
What are the 2 features of neurotransmitter classification?
- Function (determined by the post-synaptic receptor)
- Either excitatory or inhibitory - Chemical structure
True or false, a neurotransmitter can be excitatory as well a inhibitory in specific contexts
True!
ex: Ach
- Acetylcholine can be excitatory at muscle cells (nicotinic receptors), directly linked to ion channel
- Ach is inhibitory at cardiac muscle (parasympathetic input form cardiac inhibitory center of brain stem), slows heart rate acts by MUSCARINIC receptors
What are the 4 main chemical classes of neurotransmitters?
ACETYLOCHOLINE : junctions with motor effectors=> muscle and glands
- Also salivary and sweat autonomic sustem
- (excitatory in brain)
AMINES: exemple, monamines, such as serotonin- CNS inhibitory moods and emotions
AMINOACIDS: glycine=> spinal cord most common inhibitory neurotransmitter
OTHER small molecules : ex: nitric oxide which may be a signal from post to pre-synaptic neuron
Go see slide 78 and 79
Go
If a neurotransmitter binds to a chemically gated ion channel, the response will be _________________.
Rapid, short-acting fast synaptic potential
If a neurotransmitter binds to a G-protein coupled receptor, the response will be ____________
What neuro transmitter uses G-coupled prots?
Slow synaptic potentials and long-term effects
Norepinephrine
If a neurotransmitter uses the second messenger pathway, it will more like do what kind of action?
Modifies existing prots or regulate synthesis of new proteins
How is the action of a neurotransmitter terminated?
- TRANSPORTED BACK into SYNAPTIC KNOB (reuptake)
- METABOLIZED into INACTIVE compounds by enzymes
- Diffused and taken up by nearby glial cell
What is the structure of acetylcholine? What breaks it down?
- Unique chemical structure
- Acetate (acetyl coa ) with choline
Broken down by acetylcholine esterase (choline is brought back into axon terminal)
True or false,
Neurons can receive information from only one source
FAlse
can receive information from many sources
** SUMMATION OF THE POTENTIALS
