CH 43 Nervous System

Neurons and Glia

Two types of nervous cells

Neurons

Cells that generate and conduct electrical impulses.

Cell Body

Region of neuron that contains cell’s organelles

Dendrites

Region of neuron that receives info and sends to cell body

Axon

Region of neuron that transmits action potential away from cell body

Axon Terminals

Region of neuron that releases neurotransmitters; synapse with other neurons or effector cells

Glia

Cells that don’t transmit electrical signals, but are more numerous than neurons

Microglia

Phagocytes of the central nervous systems, immune response

Macroglia

Supports neurons

Astrocyte

Type of glia cell that helps blood-brain barrier

Oligodendrocyte

Type of glia that wraps around multiple axons in CNS forming an insulating myelin sheath

Multiple Sclerosis

Demyelinating disease that destroys myelin sheaths in CNS

Schwann Cells

Type of glia that wraps around individual axons in peripheral nervous system forming and insulating myelin sheath

Ependymal Cells

Type of glia that lines ventricles in brain, produce cerebrospinal fluid

Resting Membrane Potential (RMP)

Electrical charge across plasma membrane of eukaryotic cells at rest, -60 to -100mV, interior is negative, due to unequal distribution of ions.

Ungated (leakage) ion channels

Ion distribution determined by this channel that is always open

Na+/K+ Pump

Ion distribution determined by this pump that requires ATP

Ca2+ & Cl

Ions highest in extracellular fluid

Gated Ion Channels

Allow facilitated diffusion of selected ions across a cell membrane. Requires a stimulus to open.

Mechanically-gated Channels

Open when cell membrane is physically distorted

Ligand (Chemically)-gated Channels

Open when ligand binds to channel proteins (neurotransmitters)

Voltage-gated Channels

Open/close in response to electrical changes across membrane, alter RMP, and only in neurons and muscle cells.

Graded Membrane Potential

Local Change in RMP

Graded Depolarization

If membrane potential becomes less negative

Graded Hyperpolarization

If membrane potential becomes more negative

Graded Potential

Proportional to magnitude of stimulus, decay as they spread, and can’t travel down axon but initiate APs which do.

Action Potentials (APs)

Sudden brief reversal of membrane polarity, initiated at axon hillock, travels 1-way along axon, all-or-nothing

Neurons & Muscle

The only cells that can generate APs

Undershoot (hyperpolarization)

Occurs because voltage-gated K+ channels close slowly, allowing more K+ to leave.

Na+/K+ Pump

This pump returns voltage to RMP

Voltage-Gated Na+ Channels

These channels cannot respond to another stimulus until their activation gates close & inactivation gates open

Refractory Period

Period of time that voltage-gated Na+ channels are unresponsive

Axon diameter, Degree of myelination, Temperature

Speed of AP along axon influenced by:

Synapse

Junctions between 2 neurons or between a neuron and an affector (muscle or gland)

Electrical Synapses

Action potentials spread directly via gap junctions. Rapid, proceed either direction. Common in invertebrates

Chemical Synapses

Presynaptic cell releases a neurotransmitter that affects changes in postsynaptic cell, less rapid, unidirectional. Common in vertebrates.

Acetylcholine

Neurotransmitter of CNS & PNS

Glutamine

Neurotransmitter of CNS, usually ecitatory

GABA

Neurotransmitter of CNS, usually inhibitory

Dopamine

Neurotransmitter of CNS, death of these neurons causes Parkinson’s

Serotonin

Neurotransmitter of CNS, mood enhancer, involved in sleep/wake cycles

Endorphins

Neurotransmitter of CNS & PNS, decreases perception of pain

Morphine & Opioids

Endorphin agonists (bind to endorphin receptiors & elicit the same response)

Naloxone (Narcan)

Endorphin antagonist, is used to reverse opioid overdose (bind to receptors w/out eliciting a response

Excitatory Postsynaptic Potential (EPSP)

Causes a graded depolarization, results from opening chemically-gated Na+ pumps

Inhibitory Postsynaptic Potential (IPSP)

Cased graded hyperpoarization usually results from opening chemically-gated K+ and Cl- channels

Type of neurotransmitter and Type of receptor on postsynaptic cell

Generation of ESPS and IPSP depends on:

Hillock

Summation takes place at a axons

Sponges

All animals have nervous system accept

Nerve Net

Type of nervous system that that is the simplest, in cnidarians

Ventral

Type of nervous system with a solid nerve cord and ganglia, in earthworms, squid

Brain & Dorsal

Type of nervous sytem with spinal cord (CNS & nerves (PNS). In vertebrates

Reflexes

Rapid, involuntary movement generated by stimulus; no participation from brain

Receptor, Sensory Neuron, Integration Center, Motor Neuron, Effector

5 Components of reflexes