Chapter 12 - Nervous System Flashcards
What are the divisions of the nervous system?
- Central Nervous System (CNS) - brain + spinal cord
- Peripheral Nervous System (PNS) - cranial + spinal nerves
a. Somatic NS (SNS) - activates skeletal muscle –> causes movement
b. Autonomic NS (ANS) - regulates smooth + cardiac muscle, and glands
- —Sympathetic NS - fight or flight; active states
- —Parasympathetic NS - homeostasis; passive states
What is the neural network of the digestive system called? Where is it located?
Is this system under the direction of the brain?
- Enteric Nervous System - located in the mesentery between small + large intestines
- NOT under direction of the brain
What are different types of glial cells? What job does each of them perform?
CNS:
- Oligodendrocytes - produce myelin sheath
- Astrocytes - maintains blood-brain barrier; converts glucose –> lactate; responds to injury; metabolizes neurotransmitters; balances K+ ions
- Microglia - immune protection; dedifferentiation (can replace oligodendrocytes; like stem cells)
- Ependymal cells - form CSF + help it circulate
PNS:
- Schwann cells - produces myelin sheath
- Satellite cells - protect neuron cell bodies w/ support + nutrition
Why is it impossible for neurons to undergo mitosis (cell division)?
Neurons are amiotic because they have no centrioles (organelles required for cell division).
What are the parts of a neuron?
- Dendrites - “trees”; receive input
- Soma (cell body) - contains the nucleus + nissl bodies (granules of rough ER needed for protein synthesis)
- Axons - conducts impulses
- —-Axon hillock - “trigger zone”; triggers ACTION POTENTIAL
What part of the neuron is most important for generation of a nerve impulse?
Axon
—-Axon hillock –> ACTION POTENTIAL
What is a Resting Membrane Potential + what is its typical voltage?
Resting Membrane Potential - occurs when a cell is polarized (has more positive ions on the outside, ECF, than the inside)
—has many K+ leakage channels (K+ leaves cell, negative ions stay on the inside, ICF)
Typical Voltage: -70mVolts
What are Local Potentials?
Local Potential (LIGAND GATED CHANNEL):
- Graded Potential - small deviation in the resting membrane potential due to hyperpolarizing/depolarizing of a neuron by neurotransmitters (Chemical ligand-gated channels)
- —Hyperpolarization - make nerve more negative (inhibitory); Cl-
- —Depolarization - make nerve less negative (excitatory); Na+
- —Summation - “magic number”; -55mVolts triggers ACTION POTENTIAL
What are the steps of an Action Potential + what is the threshold voltage?
Action Potential (VOLTAGE GATED CHANNEL): 1. Action Potential - triggered by axon hillock (local potential ---> action potential) Voltage: -55mVolts A. Depolarization -Na+ channels open -20,000 Na+ ions enter -Membrane loses electrical charge -Na+ gates close Voltage: +30mVolts B. Repolarization -K+ gates open -K+ ions pass outwards (positive ions leave ICF) -Negative charge created Voltage: -77mvolts
What are two ways that an Action Potential can be conducted down an axon?
Continuous conduction (slower) + Saltatory conduction (faster)
What occurs when an Action Potential reaches a synaptic knob?
- Electrical synapses
- CNS
- Action potential jumps from one neuron’s presynaptic neuron to another’s postsynaptic neuron (dendrites) - Chemical synapses
- Calcium ions rush inward
- Synaptic vesicles release neurotransmitters to the synaptic cleft
What occurs during excitatory synaptic transmission?
Ex: Cholinergic synapse (Acetylcholine)
- Arrival of nerve signal –> opens Ca+ gates
- Ca+ enters synaptic knob –> triggers exocytosis of acetylocholine
- Empty vesicle drops back in knob (to be refilled)
- Acetylocholine diffuses across synaptic cleft –> binds to ligand regulated gates
- Na+ spreads across ICF (causes change in postsynaptic potential) –> makes cell less negative (DEPOLARIZING)
What occurs during inhibitory synaptic transmission?
Ex: GABA
- Arrival of nerve signal –> opens Ca+ gates
- Ca+ enters synaptic knob –> triggers exocytosis of GABA
- Empty vesicle drops back in knob (to be refilled)
- GABA diffuses across synaptic cleft –> binds to ligand regulated gates
- Cl- spreads across interior (causes change in postsynaptic potential) –> makes cell more negative (HYPERPOLARIZING)
What ion excites a neuron?
Na+
What ion inhibits a neuron?
Cl-
