U6 Nervous System I Flashcards
Multiple Sclerosis (MS)
A potentially disabling disease of the brain and spinal cord (CNS) - the immune system attacks the protective sheath (myelin) that covers nerve fibers and causes communication problems between your brain and the rest of your body
CNS
central nervous system; down axial skeleton (brain & spinal cord)
PNS
peripheral nervous system; nerves leading to and from the CNS (12 cranial nerves + 31 spinal nerves)
Sensory Integrative Responsive
detection of internal or external changes to “decide” on a course of action for motor neurons
Afferent Neurons
carry information from sensory receptors of the skin and other organs to the central nervous system
Efferent Neurons
carry motor information away from the central nervous system to the muscles and glands of the body
Diff b/tw NERVOUS SYSTEM and ENDOCRINE SYSTEM
NERVOUS SYSTEM - transmits messages very fast (1-10 msec) using impulses and neurotransmitters; response stops when stimulus stops; prolonged stimulation = adaptation
ENDOCRINE SYSTEM - sends hormones into the bloodstream; takes more time to act; slow to adapt; last long after stimulation
Neurons (+ their structure)
masses of nerve cells that transmit information – dendrite, cell body, axon, myelin, node of ranvier
Neuroglial Cells
Provides support for neurons
Microglial Cells
Immune function; digests debris, kills bacteria
Oligodendrocytes
Makes myelin sheath that provides insulation around the axons (CNS ONLY)
Astrocytes
Connects blood vessels to neurons
Ependymal Cells
Forms membranes around tissue - produces cerebrospinal fluid (aka CSF)
Schwann Cells
Used to create the myelin sheath (same function as oligodendrocytes but found in the PNS ONLY)
Demyelination + MS
Nerves affected by MS lose their myelin sheath (called demyelination); messages not sent properly
White v Grey matter (brain)
White = myelinated
Grey = unmyelinated
Lesions
evidence of nerve cell damage in the brain or spinal cord - symptoms vary depending on the location of lesion (spinal cord = motor problems; back of brain = balance problems)
What happens during MS (auto-immune disorder)?
The immune system attacks and causes damage to oligodendrocytes. This makes it harder for the CNS to replace the damaged myelin. All of this leads to a loss of myelin, or demyelination. Without the myelin insulation, the axons, or nerve fibers, also get damaged.
Neuron Facts
- Longevity
- Do not divide
- High metabolic rate
- Newborns have unmyelinated nerve fibers (stimuli is coarse)
Action Potential Explained (Steps)
- Neuron membrane maintains resting potential
- Threshold stimulus is received
- Sodium channels open
- Sodium ions diffuse inward, depolarizing the membrane
- Potassium channels open
- Potassium ions diffuse outward, repolarizing the membrane
- The resulting action potential causes a local bioelectric current that stimulates the membrane.
- Wave of action potentials travel the length of the axon as a nerve impulse
Depolarization
Away from resting state (sodium ions moving inwards)
Repolarization
Towards resting state (potassium ions moving outwards)
Resting Membrane
Neg. potassium ions on the inside; Pos. sodium ions on the outside
Communication b/tw Neurons
Synapse = junction between 2 communicating neurons; Nerve Pathway = nerve impulse travels from neuron-neuron
How is a signal retrieved during neuron-neuron communication?
A neurotransmitter is released at the synaptic cleft to signal the next neuron – receptors on the other neuron’s dendrite receives info.
Excitatory Neurotransmitter
increase membrane permeability, increases chance for threshold to be achieved
Inhibitory Neurotransmitter
decrease membrane permeability, decreases chance for threshold to be achieved
Types of Neurotransmitters
ACH (muscle contraction), Dopamine (happy), Serotonin (sleep), Endorphins (pain reduction)
Agonist
molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does; substances that act as neurotransmitters and attach to certain receptors in the brain (e.g. Heroin)
Antagonist
molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron; attach to certain receptors in the brain but do not produce a response (e.g. Naltrexone)
Resting Membrane Potential
-70 millivolts
Voltage-Gated Channels
open and close in response to changes in membrane potential
Ligand-Gated Channels
open when a neurotransmitter latches onto its receptor
Mechanically-Gated Channels
open in response to the physical stretching of the membrane
Graded Potential
graded potentials are temporary changes in the membrane voltage
Threshold for Action Potential
-55 mV
Refractory Period
time where no other signals can happen
3 ways neurotransmitters can be inactivated:
- Degradation - enzyme changes the way the neurotransmitter looks so it cannot be recognized/remembered by receptors
- Diffusion - neurotransmitter moves away from the receptor
- Reuptake - neurotransmitter is sucked back up by the axon of the neuron that let it out
Modulatory Neurotransmitters
diffuse across a large area and are slow-acting
Issues w/ neurotransmitters:
- Neurons unable to create enough of a neurotransmitter
- Neurotransmitters reabsorbed too fast
- Too many neurotransmitters deactivated by enzymes
- Too much of a neurotransmitter is released
Direct Effects
mimics the neurotransmitter/similar in chemical structure
Indirect Effects
works by acting on synaptic receptors
What are ways we can manipulate an action potential to change the frequency of a signal?
When the intensity of the stimulus is increased, the action potential’s frequency of a signal increases
