Functional Organization of Nervous Tissue

Nervous System

Communication system including CNS and PNS.

Central Nervous System (CNS)

Comprises brain and spinal cord.

Peripheral Nervous System (PNS)

Includes nerves, ganglia, and receptors.

Neurons

Electrically excitable cells transmitting signals.

Glial Cells

Supportive cells with various functions.

Nerve

Bundle of axons outside CNS.

Cranial Nerves

12 pairs originating from the brain.

Spinal Nerves

31 pairs originating from spinal cord.

Ganglion

Collection of neuron cell bodies outside CNS.

Plexus

Network of axons and neuron cell bodies.

Homeostasis

Maintaining internal balance in the body.

Sensory Input

Monitoring internal and external stimuli.

Integration

Processing sensory input and initiating responses.

Motor Division

Transmits signals from CNS to effectors.

Somatic Nervous System

Voluntary control of skeletal muscles.

Autonomic Nervous System (ANS)

Involuntary control of smooth and cardiac muscles.

Sympathetic Division

Prepares body for physical activity.

Parasympathetic Division

Regulates resting functions like digestion.

Enteric Nervous System

Plexuses within the digestive tract.

Neuron Cell Body (Soma)

Contains organelles for typical cell functions.

Dendrites

Receive information from other neurons.

Axon

Conducts action potentials away from soma.

Axoplasmic Transport

Movement of materials within axons.

Sensory Neurons

Transmit action potentials toward CNS.

Motor Neurons

Transmit action potentials away from CNS.

Interneurons

Connect neurons within the CNS.

Multipolar Neurons

Most common type in CNS.

Bipolar Neurons

Found in retina and nasal cavity.

Oligodendrocytes

Form myelin sheaths around CNS axons.

Schwann Cells

Form myelin sheaths around PNS axons.

Myelinated Axons

Insulated axons speeding up signal transmission.

Unmyelinated Axons

Rest in Schwann cells, not wrapped.

Nodes of Ranvier

Gaps in myelin sheaths on axons.

Microglia

CNS macrophages responding to inflammation.

Ependymal Cells

Line brain ventricles and secrete CSF.

Astrocytes

Regulate extracellular fluid and form blood-brain barrier.

Nervous Tissue

Tissue responsible for transmitting electrical signals.

Degenerative Changes

Alterations in nerve structure following injury.

Axon Segmentation

Distal axon breaks into segments post-injury.

Macrophages

Cells that phagocytize myelin debris after injury.

Regenerating Axon

Axon that attempts to reconnect with target.

CNS Regeneration Limitations

Oligodendrocytes inhibit axon regeneration in CNS.

Gray Matter

Contains unmyelinated axons, cell bodies, and dendrites.

White Matter

Composed of myelinated axons for signal propagation.

CNS Nuclei

Clusters of neuron cell bodies in the CNS.

PNS Ganglia

Clusters of neuron cell bodies in the PNS.

Action Potentials

Electrical signals produced by cells for communication.

Membrane Potential

Voltage difference across a cell membrane.

Na+/K+ Pump

Active transport mechanism maintaining ion gradients.

Ion Concentration Gradient

Difference in ion concentrations across membranes.

Permeability Characteristics

Membrane's ability to allow ion passage.

Gated Ion Channels

Channels that open/close in response to stimuli.

Ligand-gated Channels

Open in response to ligand binding.

Voltage-gated Channels

Open in response to voltage changes.

Resting Membrane Potential

Potential difference in an unstimulated cell.

Equilibrium Potential

Charge difference at equilibrium across membrane.

Graded Potential

Localized change in membrane potential due to stimuli.

Threshold Potential

Minimum potential to trigger an action potential.

Depolarization

Decrease in membrane potential, making it less negative.

Hyperpolarization

Increase in membrane potential, making it more negative.

Summation of Potentials

Combining multiple graded potentials to reach threshold.

Leak Channels

Channels allowing passive ion flow across membranes.

Ionic Distribution

Arrangement of ions inside and outside the cell.

Summation

Combining multiple graded potentials for larger response.

Decremental Conduction

Magnitude decreases as graded potential spreads.

Action Potential

Neuronal signal triggered by reaching threshold.

Threshold

Membrane potential of -60 to -55mV required.

All-or-None Principle

Action potential occurs if threshold is met.

Depolarization Phase

Increased Na+ permeability leads to membrane potential rise.

Repolarization Phase

Increased K+ permeability returns membrane potential.

Afterpotential

Hyperpolarization following repolarization phase.

Absolute Refractory Period

No action potential can occur, regardless of stimulus.

Relative Refractory Period

Stronger-than-threshold stimulus can trigger action potential.

Action Potential Propagation

Constant magnitude, frequency varies with stimulus strength.

Subthreshold Stimulus

Insufficient to initiate an action potential.

Threshold Stimulus

Just enough to trigger an action potential.

Maximal Stimulus

Produces maximum frequency of action potentials.

Supramaximal Stimulus

Stronger than maximal, does not increase frequency.

Continuous Conduction

Action potential spreads along unmyelinated axons.

Saltatory Conduction

Action potential jumps between nodes in myelinated axons.

Node of Ranvier

Gap in myelin sheath where action potentials occur.

Speed of Conduction

Faster in myelinated axons due to saltatory conduction.

Synapse

Junction for communication between neurons.

Presynaptic Cell

Cell sending signal to the synapse.

Postsynaptic Cell

Cell receiving signal at the synapse.

Electrical Synapse

Bidirectional communication via gap junctions.

Chemical Synapse

Unidirectional communication using neurotransmitters.

Neurotransmitter

Chemical released to transmit signals across synapse.

Ligand-Gated Ion Channels

Open in response to neurotransmitter binding.

Synaptic delay

0.2-0.5 msec between AP arrival at axon terminal to NT effect on postsynaptic membrane

Synaptic fatigue

NT can't be recycled fast enough to meet demands from intense stimuli

Graded potential

Stimulation of neuron initiates a graded potential in the cell body, often resulting from opening of ligand-gated Na+ channels.

Depolarization at axon hillock

When the membrane potential reaches threshold, voltage-gated Na+ channels open allowing an influx of Na+.

Repolarization

Na+ channels become inactivated and K+ channels open, allowing K+ to move out of the cell.

Action potential propagation

The action potential at the axon hillock results in local currents, which bring the next area of the axon to threshold.

Synaptic communication

An action potential at the presynaptic terminal results in the release of neurotransmitters that will alter the activity of the postsynaptic cell.

Criteria to be considered a neurotransmitter

Must be synthesized by a neuron and stored within synaptic vesicles in presynaptic terminals; an action potential must stimulate its exocytosis in the synaptic cleft; it must bind to a specific receptor on the postsynaptic membrane; must evoke a response in the postsynaptic cell.

Ionotropic effect

Binding to ion channels.

Metabotropic effect

Binding to G-protein-linked receptors.

Acetylcholine (ACh)

Best understood and most common neurotransmitter.