Nervous Tissue Flashcards
What are the broad functions of nervous tissue?
Body’s control center and communication network
3 Broad Functions:
- Sense change in environment
- Integrates and interprets
- Responds if necessary
What are the divisions of the nervous system?
Central Nervous System
-Brain and Spinal Cord
Peripheral Nervous System
- Somatic
- Autonomic Nervous Systems
→Sympathetic and Parasympathetic Nervous systems
What are neuroglia and what are some examples?
Support cells for neurons within nervous tissue
Examples
- Oligodendrocytes = CNS
- Astrocytes = CNS
- Microglia = CNS
- Ependymal cells = CNS
- Schwann Cells = PNS
- Satelite Cells = CNS and PNS
What are the parts of the neuron pictured?
Cell Body
- nucleus
- nucleolus
- nissl substance
Dendrites
Axon
- axon hillock
- trigger zone
- axon collateral
- telodendrion
- synaptic knobs
What kinds of cells myelinate neurons in the CNS vs PNS? How does the myelin sheath differ?
CNS
- Oligodendrocytes
- each oligodendrocyte myelinates several nerve fibers inwards with centripetal myelination
PNS
- Neurolemmocytes
- schwann cells spiral repeatedly around single nerve fiber outwards with centrifugal myelination
Outer most layer of myelin sheath is neurilemma and surrounded by connective tissue calle endoneurium
What are the different types of neuron structures?
Unipolar Neurons (pseudounipolar)
- single process leading away from cell body
- carry signals to spinal cord for senses like touch and pain
Bipolar Neurons
- have one axon and one dendrite
- accessory sensory neurons including olfactory cells of nose
Multipolar Neurons
- most common
- most neurons of the brain and spinal cord
- motor neurons
How do impulses flow in neurons?
Dendrites carry infor to cell body
and
Axons carry info away from cell body
What are the different functional classifications of neurons?
Sensory Neurons
- also known as afferent (arriving)
- unipolar neurons
- from PNS to CNS
Association Neurons
- also known as interneurons
- interconnect incoming sensory pathways and outgoing motor pathways and amke decisions about information
- multipolar neurons and bipolar neurons in special sense pathways
Motor Neurons
- also known as efferent (exiting) neurons
- carry information primarily to muscle/gland cells, the effectors
- from CNS to PNS
What is a nerve fiber?
one process from one neuron
What is a nerve vs tract?
Nerve
-bundle of nerve fibers travelling through PNS
Tract
-bundle of nerve fibers travelling through CNS
What is a ganglion vs nucleus?
Ganglion
-collections of cell bodies in PNS
Nucleus
-collections of cell bodies in CNS
What is the difference between gray matter vs white matter?
Gray matter
-don’t travel far so unmyelinated
White matter
-myelinated fibers so faster and travel farther distances
What properties does communication by neurons depend on?
1. Electrical voltage, called resting membrane potential, across the cell membrane
- requires energy, ATP, to maintain
- Na+/positive outside and K+/negative inside
2. Neuronal cell membranes contain different ion channels that may be open or closed
-ion channels don’t require energy, facilitated diffusion
What is the resting membrane potential?
Buildup of ions on each side of the cell membrane
- creates a polarized membrane
- separation of charges creates potential energy
- resting membrane potential is -70mV
What factors contribute to the resting membrane potential?
1. Distribution of ions on either side of cell membrane
- extracellular fluid rich in Na+ and Cl-
- intracellular fluid rich in K+ and anions like negatively charged proteins
2. Relative permeability of cell membrane to the ions
- K+ and Cl- slightly more permeable than Na+
- impermeable to intracellular proteins
- There is a slow K+ leak w/not much of a Na+ leak
What are gated ion channels and what are the types?
Gated channels that open in response to specific stimulus
1. Chemically gated ion channel
- require ligand to bind to open/close channel
- normally found on dendrites of multipolar neurons
2. Voltage gated ion channel
- change in cell membrane potential open/close channel
- usually ligand gated channel starts voltage change
3. Mechanically and light gated channels
-mechanical stress or light opens/closes
What is the threshold stimulus?
Minimum change in resting membrane potential to initate action potential
-70mV to -55mV
What are the steps of an action potential?
- Depolarization
- Repolarization
- Refractory period
What is depolarization?
First step of action potential
- Threshold stimulus is reached
- Voltage gated Na+ channels open at site of stimulus
- Na+ influx through channel (-70 to +30mV)
- Positive feedback opens adjacent voltage gated Na+ channels
What is repolarization?
Second step of action potential
- Voltage gated K+ channels open
- K+ efflux from cell (+30 to -90mV)
- Hyperpolarization
- Na-K ATPase pumps restore ions to proper concentrations on either side of the membrane
What is the refractory period?
Time after action potential where another AP either can’t happen or is much more difficult to occur
1. Absolute refractory period
- voltage gated channels either opening/closing
- CANNOT have 2nd AP
2. Relative refractory period
- hyperpolarized membrane at -90mV
- AP CAN occur but need Suprathreshold stimulus
Explain the action potential.
Go through the positive feedback mechanism of an action potential.
What are the two types of conduction?
Continuous Conduction
- trigger zone to synapse
- propagation of the message
- one direction only
- 0.5 meters/sec
Saltatory Conduction
- myelin sheath
- nodes of ranvier
- 130 meters/sec
- conserves energy b/c only maintain membrane potential at nodes of ranvier
What is a synapse
A junction between two nerve cells
- integrate and filter information
- point where signals are either transmitted or inhibited
- there are presynaptic and postsynaptic neurons
How does a chemical synapse work?
- Arrival of action potential
- Voltage gated Ca2+ open = influx and signal neurotransmitter vesicles to fuse
- Synaptic vesicles rupture
- Neurotransmitter released
- Neurotransmitter diffusion
- Neurotransmitter binds receptor
- Postsynaptic potential created
What are the types of post synaptic potentials?
Inhibitory (IPSP) - hyperpolarizes postsynaptic membrane
-open Cl- channel to make cell more negative
Excitatory (EPSP) - facilitates postsynaptic membrane
What are the net effects of postsynaptic potentials?
1. Facilitation: bring closer to threshold but not reach
2. Summation (action potential): reach AP threshold
- Spatial: multiple neurons signaling one
- Temporal: one neuron signaling another one multiple times
3. Hyperpolarization (inhibition): make threshold harder to reach
How can neurotransmitters work?
Can be excitatory and/or inhibitory
-eg. epinephrine inhibits digestion but stimulates breathing
How are neurotransmitters removed from synaptic cleft so that its effects on the postsynaptic cell is limited?
- Diffusion away from the synapse
- Enzymatic degradation within the synapse
- Reuptake into the presynaptic neuron
What are the types of neuronal circuits?
- Simple series
- Diverging
- Converging
- Reverberating
- Parallel after-discharge
