Fundamentals of the Nervous System and Nervous Tissue

Nervous System

Master controlling and communicating system of body.

Electrical Signals

Rapid communication method used by nerve cells.

Chemical Signals

Molecules released for communication between cells.

Sensory Input

Information gathered about internal and external changes.

Integration

Processing and interpretation of sensory information.

Motor Output

Activation of muscles and glands producing responses.

Central Nervous System (CNS)

Brain and spinal cord; integration and control center.

Peripheral Nervous System (PNS)

Nervous system part outside CNS; consists of nerves.

Spinal Nerves

Nerves connecting spinal cord to body.

Cranial Nerves

Nerves connecting brain to body.

Sensory (Afferent) Division

Conveys impulses from sensory receptors to CNS.

Somatic Sensory Fibers

Transmit impulses from skin and muscles to CNS.

Visceral Sensory Fibers

Transmit impulses from internal organs to CNS.

Motor (Efferent) Division

Transmits impulses from CNS to effector organs.

Somatic Nervous System

Controls voluntary movements of skeletal muscles.

Autonomic Nervous System

Regulates involuntary functions of smooth and cardiac muscles.

Sympathetic Division

Prepares body for 'fight or flight' responses.

Parasympathetic Division

Promotes 'rest and digest' functions.

Neuroglia

Supportive cells in the nervous system.

Effector Organs

Muscles and glands responding to motor output.

Nervous tissue

Tissue composed of neurons and neuroglia.

Neurons

Excitable cells that transmit electrical signals.

Dendrites

Branching processes that receive signals from other neurons.

Cell body

Contains nucleus; integrates incoming signals.

Axon

Long process that transmits signals away from cell body.

Astrocytes

Most abundant glial cells; support and regulate neurons.

Microglial cells

Immune cells that monitor and protect neurons.

Ependymal cells

Line brain cavities; circulate cerebrospinal fluid (CSF).

Oligodendrocytes

Form myelin sheaths around CNS nerve fibers.

Satellite cells

Surround neuron cell bodies in PNS; support function.

Schwann cells

Form myelin sheaths around PNS nerve fibers.

Neuron cell body

Also called soma; contains nucleus and organelles.

Axon hillock

Cone-shaped area where axon meets cell body.

Axon terminals

Branches of axon that transmit signals to other cells.

Synapse

Junction between neuron and target cell.

Neurotransmitters

Chemicals that transmit signals across synapses.

Myelin sheath

Insulating layer that increases nerve impulse speed.

Anterograde transport

Movement of materials away from cell body.

Retrograde transport

Movement of materials toward cell body.

Nuclei

Clusters of neuron cell bodies in the CNS.

Ganglia

Clusters of neuron cell bodies in the PNS.

Tracts

Bundles of axons in the CNS.

Nerves

Bundles of axons in the PNS.

Multipolar neurons

Neurons with one axon and multiple dendrites.

Bipolar neurons

Neurons with one axon and one dendrite.

Unipolar neurons

Neurons with one T-like process; sensory function.

Sensory neurons

Transmit impulses from receptors to CNS.

Motor neurons

Carry impulses from CNS to effectors.

Interneurons

Connect sensory and motor neurons; mostly in CNS.

Membrane potential

Voltage difference across a cell's plasma membrane.

Resting potential

Membrane potential of a neuron at rest.

Action potentials

Rapid changes in membrane potential during signaling.

Resting Potential

Negative membrane potential when neuron is at rest.

Membrane Proteins

Maintain ion gradients across the neuronal membrane.

Ion Gradients

Concentration differences of Na+ and K+ across membrane.

Na+ Gradient

Higher concentration of sodium ions outside the cell.

K+ Gradient

Higher concentration of potassium ions inside the cell.

Membrane Permeability

More permeable to K+ than to Na+ at rest.

Na+/K+ Pumps

Use ATP to maintain Na+ and K+ gradients.

Graded Potentials

Short-distance signals in dendrites of neurons.

Action Potentials

Long-distance signals conducted along axons.

Gated Channels

Control ion movement across the neuronal membrane.

Voltage Gated Channels

Open/close based on changes in membrane potential.

Ligand Gated Channels

Open/close in response to chemical binding.

Depolarization

Decrease in membrane potential towards zero.

Hyperpolarization

Increase in membrane potential away from zero.

Threshold

Minimum membrane potential needed to trigger an AP.

Repolarization

Return to resting potential after depolarization.

All-or-Nothing Principle

APs occur fully or not at all.

Self-Propagation

APs propagate along the axon without decay.

Myelinated Axons

APs jump between nodes of Ranvier.

Frequency of Impulses

Indicates stimulus intensity to the CNS.

Refractory Periods

Time during which neuron cannot fire another AP.

Absolute Refractory Period

No new AP can be initiated regardless of stimulus.

Relative Refractory Period

A stronger stimulus can initiate a new AP.

Continuous conduction

Slow conduction in nonmyelinated axons along axolemma.

Saltatory conduction

Fast conduction in myelinated axons, ~30 times faster.

Myelin sheaths

Insulate axons, preventing charge leakage.

Voltage-gated Na+ channels

Found at myelin sheath gaps, generate action potentials.

Conduction Velocity

Speed of nerve impulse transmission, varies by fiber type.

Group A fibers

Transmit at 150 m/s; largest diameter, myelinated.

Group B fibers

Transmit at 15 m/s; intermediate diameter, lightly myelinated.

Group C fibers

Transmit at 1 m/s; smallest diameter, unmyelinated.

Presynaptic neuron

Neuron sending information toward the synapse.

Postsynaptic neuron

Neuron receiving information away from the synapse.

Axodendritic synapse

Connection between axon terminals and dendrites.

Chemical synapse

Involves neurotransmitter release and reception.

Electrical synapse

Neurons connected by gap junctions, less common.

Synaptic Transmission

Process of neurotransmitter release and reception.

VG Ca+2 channels

Open during action potential, allowing calcium influx.

Neurotransmitter (NT) removal

NTs cleared via reuptake, degradation, or diffusion.

Excitatory postsynaptic potentials (EPSP)

Depolarization that brings neuron closer to action potential.

Inhibitory postsynaptic potentials (IPSP)

Hyperpolarization that moves neuron away from action potential.

Temporal summation

Multiple signals in rapid succession at one neuron.

Spatial summation

Multiple signals from different neurons at one neuron.

Acetylcholine (ACh)

Neurotransmitter that can be excitatory or inhibitory.

ACh agonists

Substances that enhance ACh effects, e.g., spider venom.

ACh antagonists

Substances that block ACh effects, e.g., botulinum toxin.

Biogenic amines

Neurotransmitters including dopamine, serotonin, norepinephrine.

Dopamine

Involved in pleasure, part of reward system.