Lecture - Nerve Tissue Flashcards
What is the synapse?
The area where one neuron’s synaptic bulb meets up with the target tissue (muscle cell, other neuron, etc.)
What is the microscopic gap between the pre-synaptic neuron and the target tissue?
Synaptic Gap
4 kinds of neural circuit
- Diverging
- Converging
- Reverberating
- Parallel after-discharge
One nerve fiber synapses with several post-synaptic cells, one motor neuron stimulates thousands of muscle fibers
Diverging circuit
What’s a converging circuit?
Several nerve fibers converge into one neuron, multiple neurons channeled to one area of brain
When do neurons stimulate each other in a linear sequence?
Reverberating circuit - some neurons send an axon collateral back to first neuron
What is the name for the brain and spinal cord?
Central nervous system
What is the peripheral nervous system?
All nerve tissues not in the brain and spinal cord
What is the PNS divided into?
- somatic nervous system (motor)
- autonomic nervous system: sympathetic and parasympathetic nervous systems
What are the 2 primary cell types in nervous tissue?
- Neuron - transmits nerve impulses
2. Glial cells - support cell (neuroglia)
Which 4 glial cells are in the CNS?
- Astrocytes
- Ependymal cells
- Oligodendrocytes
- Microglia
Which CNS glial cells constitute 90% of CNS tissue in some parts of the brain, are star shaped, support neurons, and form the Blood-Brain-Barrier (BBB)?
Astrocytes
What do the ependymal cells do in the CNS?
- cubodal epithelium w/no basement membrane
- line internal brain cavities
- create cerebrospinal fluid by filtering fluid out of teh choroid plexus
Which glial cells in the CNS form the myelin sheath?
Oligodendrocytes - like an octopus
Which glial cells in the CNS act as the immune system?
Microglia - phagocytize (eat) dead matter or debris and respond to infections
What 2 glial cells are in the PNS?
- Schwann cells
2. Satellite cells
Which cells form the myelin sheath in the PNS?
Schwann cells (one per)
What is the function of satellite cells in the PNS?
Unknown; surround neuron cell bodies
What is the structure of a nerve from the inside out?
- Endoneurium: surround each neuron on the outside of the myelin sheath
- Perineurium: surrounds each fascicle (bundle of nerves)
- Epineurium: surrounds the nerve as a whole
Which part of the reflex arch transmits a pain signal from the receptor to the CNS?
Sersory (afferent) neuron
What is a sensory receptor?
It is a receptor that receives information from the environment, like pain
Which neuron inside the spinal cord connects the sensory neuron with the motor neuron and processes information to make decisions about how to respond to stimuli?
Interneuron
Which neuron makes up 90% of the body’s neurons?
Interneuron
What is a motor (efferent) neuron?
A neuron that carries information from the CNS to muscles and glands
In the reflex arch, what contracts in an adaptive response to the original stimulus?
Muscles or glands
What is the name of the cell body of a neuron which contains the nucleus, endoplasmic reticulum, mitochondria, ribosomes, ect. ?
Soma
What is a dendrite?
The part of a neuron that receives the nerve impulse from the pre-synaptic neuron or responds to mechanical, electrical, or thermal stimulation
What is the name for the enlarged portion of the nerve axon where the cell body connects with the axon?
Axon hillock
What transmits action potential to the synaptic bulb?
The axon
What is the synaptic knob/bulb?
Enlargement at the end of the axon which contains neurotransmitters
What is the cell membrane around the axon called?
Axolemma
What is the outermost layer of a Schwann cell around the neuron called?
Neurilemma
What is the myelin sheath?
fatty substance surrounding neurons that speeds up impulse transmission
What is the name of the small gap between myelin sheaths, about 1 mm apart, where the axon is exposed to extracellular fluid?
Node of Ranvier
What is the tiny space between the pre-synaptic neuron and the target tissue?
Synaptic gap
What is the ER also known as when it is found in a neuron?
Nissl substance/bodies
What is the axon filled with?
Cytoplasm filled with a carefully controlled concentration of ions
What is resting membrane potential?
When the inside of the axon is relatively negative compared to the outside, -70mV
What contributes to an axons internal negative charge?
Negatively charged proteins along with Potassium (K+)
What contributes to the positive charge outside of the axon?
Positively charged Sodium ions (Na+)
Is the axon permeable or impermeable to Na+ and K+?
It is mostly impermeable to Na+ and K+
What is a Potassium leak channel?
A channel that allows small amounts of K+ to leak out of the cell
What is a Sodium leak channel?
Allows Na+ to leak into the cell
What uses active transport to simultaneously pump 3 Na+ OUT of a cell and 2 K+ IN to a cell?
NAKA
What is a change in the membrane potential toward zero?
Depolarization
What is a change in membrane potential back toward the negative?
Repolarization
What is hyperpolarization?
A change in the membrane potential beyond the resting potential (below -70mV)
What is the refractory period?
The time during depol and repol where the neuron can’t fire
What is the threshold for action potential?
-55mV
What is the all-or-none principle?
The idea that the action potential only propagates if and only if the threshold is met
What causes the membrane potential to rise from -55mV to +35mV (depolarize)?
The opening of sodium voltage-gated channels and the rush of Na+ into the axon
What causes repolarization of the axon?
Voltage-gated Na+ channels closing and K+ channels opening
Why does the action potential usually drop to -72mV (hyperpolarize)?
K+ gates stay open longer than Na+ gates
How does the axon regain resting potential when it’s in hyperpolarization?
NAKA pump
What is the name for the movement of action potential down an axon?
Propagation or conduction
What is propagation an example of?
A positive feedback system
What is continuous conduction?
The movement of an action potential down an unmyelinated axon using propagation (depol-repol-depol-repol cycle)
How fast is continuous conduction?
Relatively slow, 2m/sec
What is the movement of an action potential down a myelinated axon?
Saltatory conduction
How does saltatory conduction work?
The neural impulse jumps from one node of Ranvier to the next, recharging at each node
How fast is saltatory conduction?
Fast; 120m/sec
How does synaptic transmission work?
Action potential at the synaptic bulb triggers release of calcium into axon which makes vesicles fuse with the membrane and release neurotransmitters into the synaptic gap. NTs bind with target tissue receptors
What are the 2 possible outcomes of a synaptic transmission?
- Target tissue excitation
2. Target tissue inhibition
Which NT activates skeletal muscle and autonomic nervous system neurons?
Acetylcholine
What does Norepinephrine do?
Role in sympathetic division of autonomous nervous system; dreaming, waking, elevates mood
Which NT is found in the brain’s “pleasure center,” elevates mood, and controls skeletal muscles?
Dopamine
Which NT has a role in relaxing the body during sleep and elevating mood (“comfy NT”)?
Serotonin
What is Glycine?
It is an inhibitory NT and an amino acid
What is GABA?
Inhibitor NT and amino acid
Which NT (also amino acid) is excitatory, involved in learning and memory?
Glutamate
What substance causes over-stimulation of Glutamate receptors?
Monosodium glutamate
Which neural circuit causes you to see the outline of the sun after you have looked away?
Parallel after-discharge circuit
What is the law of associative memory?
The brain’s ability to make memory with synapses
What is neural plasticity?
the ability of a neuron to disconnect and reconnect elsewhere
How many times do you have to see something to remember it?
7 times
What are brain tumors made of?
Glial cells
Which autoimmune disease attacks and scars the myelin sheaths causing motor and sensory deficits?
Multiple sclerosis
Neurologically, how does Ritalin work?
Unknown
In what 3 ways does the neuron remove NTs from the synapse?
- Diffusion - movement away from the gap
- Enzymatic breakdown - ex. acetylcholinesterase
- Reuptake into the pre-synaptic bulb
