Ch. 12 Nervous Tissue and Neurophysiology Flashcards
What are the structural divisions of the nervous system?
1) Central nervous system CNS
Brain and spinal cord of dorsal body cavity, integration and control center (interpret sensory input and dictates motor output)
2)Peripheral nervous system. PNS
The portion of the nervous system outside the CNS, consist mainly of nerves that extend from the brain and spinal cord. Contains sensory and motor fibers. (spinal nerves two and from spinal cord - cranial nerves to and from brain)
- sensory (afferent) division
- motor (efferent) division
3) PNS - sensory division - the sensory division contains:
- somatic sensory fibers which convey impulses from skin, skeletal muscles and joint to CNS
- visceral sensory fibers which convey impulses from visceral organs to CNS
4) PNS - motor division - transmit impulses from CNS to effector organs, the muscles and glands. It contains two divisions, the somatic nervous system. (voluntary nervous system.) and the autonomic nervous system(involuntary nervous system)
What are the functions of the nervous system
Sensory input - information is gathered by millions of sensory receptors about internal and external changes
Integration - the nervous system processes and interprets the sensory input (reflexes)
Motor input - the nervous system activates effector organs (muscles and glands) and produces a response
Sensory (afferent) division
Somatic sensory fiber - convey impulses from the skin, skeletal muscle and joints to CNS
Visceral sensory fibers - convey impulses from visceral organs to CNS
Motor (efferent) division
Transmit impulses from CNS to effector organs (muscles and glands)
Two divisions
- somatic nervous system
- autonomic nervous system
Describe this somatic nervous system
The somatic nervous system is composed of somatic motor nerve fibers
- conduct impulses from CNS to skeletal muscle
- it is often referred to as a voluntary nervous system because it allows us to voluntary contract out muscles
Describe the autonomic nervous system
The autonomic nervous system consist of visceral motor fibers that regulate smooth muscle, cardiac muscle and glands
It is often referred to as the involuntary nervous system
Two functional subdivisions
- Sympathetic
- parasympathetic
Opposition to each other (one stimulates, the other inhibits)
Levels of organization in the nervous system
Identify the types of cells found in the nervous system
CNS
Astrocytes
Microglial cells
Ependymal cells
Oligodendcytes
PNS
Satelite cells
Schwann cells
Astrocytes
Most abundant glial cell of the CNS; physically support neurons
- Highly branched their process, clings to neurons, synaptic, endings and capillaries
Exchanges between capillaries and neurons
Guide migration of neurons and the formation of synopsis between neurons
Control chemical environment around neurons
Respond to nerve impulses and releases neurotransmitters
Participate in information processing in brain
Role in neuron-inflammation
Microglial cell
Defensive cells of the CNS - have phagocytic activity
Small, ovoid cells with thorny processes that monitor neurons
Sense and migrate toward injured neurons
Can transform to phagocytize microorganisms and neuronal debris
Ependymal cells
Line the cavities of the CNS where they form a permeable barrier between CSF and cells of CNS
Ependymal cells formed the epithelial lining of the ventricles of the brain and central canal of the spinal cord
They form a permeable barrier between cerebrospinal fluid (CSF) in the cavities and brain or spinal cord tissue
May be ciliated - help circulate CSF
Oligodendrocytes
Oligodendrocytes are moderately branch cells
Their processes wrap CNS nerve fibers, forming insulated Mylin sheets around thicker nerve fibers
Satellite cell
Surround and support neurons cell bodies in the PNS
- Function similar to astrocytes of CNS
Schwan cells (neurolemmocytes)
Surround all nerve fibers in the PNS and form the myelin sheath in thicker nerve fibers
- Function as Oligodendrocytes (Were they playing important role in nerve impulse transmission speed
- Vital to regeneration of damaged, peripheral nerve fibers
Neuron
Large, highly specialized cells that transmit impulses from one part of the body to another (main impulse transmitting cells of the nervous system)
Describe and identify the structure and function of neurons
Cell body
Nucleus
Dendrites
Axon
Axon hillock
Myelin sheath
Describe the two main functions of the myelin sheath
Function of the mylin sheet is to protect and electrically insulate the axon - increase speed of nerve impulses.
Because voltage gated ion channels are only found in the gaps, action potential seem to “jump” from gap to gap, rather than having to travel continuously down the axon
Myelinated fibers conduct nerve impulses quickly, whereas nonmyelinated fibers conduct impulses more slowly(dendrites are always nonmyelinated)
Describe how the myelin sheath is created and how this differs in the CNS and PNS
PNS - myelin sheath are formed by schwann cells
- wraparound axon in Jelly roll fashion
- One cell forms, one segment of myelin sheath
- The contents of the cytoplasm end up squeezed into a ridge.
CNS - myelin sheaths our formed by multiple flat processes of Oligodendrocytes not whole cells oligodendrocytes not whole cells
- Can wrap up to 60 axons at once
- myelin sheath gap is present
- No outer ridge of cytoplasm
Describe an identify the three “structural classifications” of neurons
Describe the three “functional classifications” of neurons
Functionally, neurons are grouped by the direction in which nerve impulse travels relative to CNS
SENSORY (afferent) (in) FUCK AROUND
- transmit impulses from sensory receptors towards CNS
- almost are all our unipolar
- Cell bodies are sensory ganglia located in the PNS
MOTOR (efferent) (out) FIND OUT
- Carry impulses from CNS to effectors
- multipolar
- most bodies in CNS
(except some autonomic neurons)
INTERNEURONS (association neurons)
- 99% of bodies neurons
- lay between motor and sensory neurons
- shuttle signals through CNS pathways
- are multipolar
- mostly confined in CNS
Explain what resting membrane potential is and how it’s maintained
Resting membrane potential is created by the differential permability of NA+ and K+ in the neurons plasma membrane. The extra cellular fluid (ECF) has a higher concentration NA+ than the intercellular fluid (ICF). The NA concentration is balanced by Cl- ions. The ICF has a higher concentration of K+ than the ECF. The concentration is balanced by negatively charged proteins, equalizing the two fluids inside and outside the cell.
The cell membrane is slightly permeable to NA+ (through leakage channels) and NA+ diffuses into the neuron down its concentration gradient. The cell membrane is 25X more permeable to K+ than NA+ (more leakage channels) and K+ diffuses out of the cell down its concentration gradient. Overall more K+ diffuses out than Na+ diffuses in which leaves a cell more negative inside the membrane than outside. (because of the negatively charged proteins) This is what establishes resting membrane potential.
Potential is maintained by NA+ & K+ pumps, which maintain the concentrate gradients for an NA+ & K+ by continually pumping back out of the cell and back into the cell (this creates the gradient so they can right back out)
Describe the two ways that membrane potential can be changed
Membrane potential can be changed by ion concentrations across the membrane and/or changes in membrane permeability to ions.
These can lead to depolarizations - a decrease in membrane potential, or hyperpolarizations - an increase in membrane potential
Differentiate between depolarization and hyperpolarization
Depolarization: there is a decrease in membrane potential (towards zero and above). the inside of the membrane becomes less negative than the resting membrane potential depolarization increase the probability of producing a nerve impulse
Hyperpolarization: in a hyperpolarization, there is an increase in membrane potential (away from zero). The inside of the cell becomes more negative than the resting membrane potential hyperpolarizations reduce the probability of producing a nerve impulse.
Describe a graded potential - what they are used for what triggers them were they occur and why are they so short-lived?
Graded potentials are short-lived, localized changes and membrane potential which can either be excitatory, (causing a depolarization) or inhibitory (causing a hyper polarization). They are short lived because the change in membrane potential is localized and decays overtime this is why graded potentials are signals only over short distances. This is because the ion channels involved in graded potentials are ligand-gated not voltage-gated (thus you don’t see the positive feedback mechanism or change in membrane). Potentials opens the next set of gates, etc.). They occur at dendrites or on the cell body. Graded potentials are triggered by some external stimulus that opens a ligand-gated or mechanically-gated ion channels usually a neurotransmitter. Typically graded to potentials occur before action potentials (if they are strong enough to trigger one).
Describe action potential
Action potentials are the principal means of long-distance neural communication.
They only occur in muscle cells and the axons of neurons and action potential a brief reversal of membrane potential with a change in voltage of 100mV.
Unlike graded potential action potential did not decay over distance.
Action potentials are triggered by membrane depolarization that reach threshold. Great potentials are responsible for the initial depolarization.
Describe the four steps of an action potential
- Resting potential. - all gated NA and K channels are closed only ligand-gated channels for NA+ K+ are open which maintains the resting membrane and potential.
- Depolarization - as local currents (graded potentials) depolarize the axon membrane voltage gated NA channels open and NA+ rushes into the cell. The influx causes depolarization more channels open , and the ICF becomes less negative. At threshold (-55 to -50mV) positive feedback causes opening of all NH channels and results in reversal of membrane polarity to +30mV.
- Repolarization - the slow inactivation gates of the of the NA channels began to close and membrane permeability to NA declines to resting levels. At the same time low-voltage gated K channels open and K exit the cell following its electrochemical gradient, and the interior of the cell becomes negative once again
- Hyperpolarization-after the repolarization of the membrane channels remain open, allowing excessive K to leave the cell. This results in the inside of the membrane more negative than the resting state. This causes a hyperpolarization of the membrane a (slight debt below resting voltage). At the same time NA channels begin to reset to the original position by changing shape to reopen their inactivation gates and close their activation gates.
Describe how an action potential is propagated down the axon why does it only go in one direction?
When any channels are open during a depolarization NA+ ions rush in once; inside the cause nearby regions of the neuron to become depolarized by moving laterally through the axon. This in turn causes the opening of more voltage-gated NA+ channels in those regions. Thus the NA+ channel activation moves in a wave like fashion - A.P. is propogated down the length of the axon to the synaptic terminals.
The NA+ channels have a mechanism that avoids “back propagation” of the AP potential which could result in a confused signal. After opening the NA+ channels become inactivated as a potential becomes more positive and they cannot open again until they are “reset” by hyperpolarization at the end of an AP. This brief period of NA+ channel inactivation is called a refractory period, prevent bidirectional propagation of the AP constraining it to only go in one direction.
What are three functions of the nervous system
Sensory input- information is gathered by millions of sensory receptors about internal and external changes
Integration - The CNS processes and interprets the sensory input.
Motor output - The nervous system activates effector organs ( muscles and gland) and produces a response
Neuroglia
Cells which support neurons both functionally and structurally
Most common type of neuron
Multipolar
Rare type of neuron
Bipolar
Neuron found mainly in the PNS
Unipolar
Neuron which would connect to a muscle
Multipolar
Neuron which would be found in the retina of the eye
Bipolar
Neurons that connect impulses along afferent pathways to CNS
Unipolar
Describe the function of a synapse
Synopsis are junctions at mediate the information transfer
Synopsis connect one neuron, another neuron or neuron an effector cell (muscle or gland)
Identify the structure and function of a synapse
Describe the difference between pre-synaptic and postsynaptic neurons
Pre-synaptic neuron
The pre-synaptic neuron is the neuron conducting impulses toward the synapse
SENDS THE INFORMATION
Synaptic neuron (in PNS may be a neuron, muscle cell, or gland cell)
The post-synaptic neuron is the neuron transmitting electrical signals away from the synapse
RECEIVES THE INFORMATION
Describe how an action potential moves from a pre-synaptic neuron to a post-synaptic neuron
AP arrives at axon terminal
vaulted-gauges CA channels open allowing CA to enter the axon terminal
CA causes vesicles to fuse with terminal endings and release their products (neurotransmitters) via exocytosis
Neurotransmitters diffuse across the synaptic cleft
Neurotransmitters bind to ligand-gated channels, allowing ions to flow in/or out of the cell resulting in grated potential
Neurotransmitters are rapidly degraded or flushed away from the receptors
Differentiate between EPSP and IPSP ( i.e. graded potentials)
ESPS’s are a temporary depolarization of the postsynaptic membrane caused by the flow of positively charged ions into postsynaptic cell as revolved of a opening of a ligand-gated ion channels (by binding excitatory neurotransmitters for example) A postsynaptic potential is defined as EXCITATORY if it makes the neuron more likely to fire an action potential.
ISPS’s reduce the postsynaptic neurons ability to produce an action potential. They are caused by the binding of inhibitory neurotransmitters at inhibitory synapses - these hypopolarize the postsynaptic cell membrane by making it more permeable to K or CL ( ultimately making it more negative)
Summation
To influence the activity of a post-and optic neuron
Temporal summation
One or more presynaptic neurons transmit impulses in rapid-fire order
Spatial summation
Postsynaptic neuron stimulated simultaneously by large number of terminals at same time
Describe the summation in EPSP’s including temporal and spatial summation. Are ISPS’s also sensitive to summation
A single EPSP cannot induce an action potential. If many excitatory axon terminals fire upon the same postsynaptic, neuron (spatial summation) or if a small number of axon terminals fire rapidly (temporal summation) the probability of reaching threshold increases.
In this way, EPSP’s can summate or add together to influence the activity of a postsynaptic neuron. IPSP’s are also sensitive to summation.
List the neurotransmitters found in the nervous system
Acetylcholine
Biogenic amines (which include dopamine, norepinephrine, serotonin,histamine)
GABA
Glutamate
Endorphins
Nitric oxide
Acetylcholine
Acetylcholine is an EXCITATORY neurotransmitter at neuromuscular junctions in skeletal muscle. In cardiac tissue acetylcholine has INHIBITORY effect which lowers heart rate.
In the CNS it acts as a neural modulator alters the way the brain processes information.
Biogenic amines (which include dopamine, norepinephrine, serotonin, histamine)
The biogenic amines play major rules in learning emotions and mood most can be both excitatory and inhibitory, depending on receptor types
GABA
GABA is a principle inhibitory neurotransmitter in the brain. It is involved with cortical function, such as motor commission control, and vision. It may also play an anti-anxiety role. Alcohol mimics, GABA and binds to receptors = an agonist.
Glutamate
Glutamate is the main EXCIATORY neurotransmitter in the brain, it is important in cognition, memory, and learning
Endorphins
Endorphins are generally inhibitory they have many functions. They act as natural opiates to reduce pain perception.
Nitric Oxide
Can be excitatory or inhibitory
Important in vasodialation
Differentiate between neurotransmitters that act directly versus those act indirectly
Direct acting neurotransmitters - are those that find two and open ion channels are direct acting. they promote rapid responses by altering membrane potential (I.e. lead to the deep polarizations of hyperpolarizations)
Indirect acting neurotransmitters - are those that act through second messengers they do not bind to receptor to produce a direct response may influence the strength of synaptic transmission influence re-uptake of neurotransmitters module other neurotransmitter activity or membrane sensitivity to a neurotransmitter they generally have longer lasting affect, similar to hormones
