Nervous System: Histology and Physiology Overview

Nervous System Function

Control and regulation through sensory, integration, motor.

Sensory Input

Afferent signals from receptors to CNS.

Information Processing

Integration and decision-making within the CNS.

Motor Output

Efferent signals to muscles, organs, glands.

Central Nervous System (CNS)

Includes brain and spinal cord.

Peripheral Nervous System (PNS)

Comprises nerves outside the CNS.

Somatic Nervous System

Voluntary control of skeletal muscles.

Autonomic Nervous System (ANS)

Involuntary control of internal organs.

Sympathetic Division

Prepares body for 'fight or flight' response.

Parasympathetic Division

Promotes 'rest and digest' activities.

Neurons

Excitable cells transmitting nerve impulses.

Cell Body (Soma)

Contains nucleus and organelles of neuron.

Dendrites

Receive incoming signals to the neuron.

Axon

Transmits outgoing signals from neuron.

Synapse

Connection point between two neurons.

Neurotransmitters

Chemicals released at synapses for communication.

Ependymal Cells

Produce and circulate cerebrospinal fluid (CSF).

Astrocytes

Provide structural support and nutrient supply.

Oligodendrocytes

Form myelin sheaths in the CNS.

Schwann Cells

Form myelin sheaths in the PNS.

Myelin Sheath

Insulating layer around axons for faster conduction.

Nodes of Ranvier

Gaps in myelin sheath aiding saltatory conduction.

Gray Matter

Contains neuron cell bodies and dendrites.

White Matter

Contains myelinated axons in CNS.

Wallerian Degeneration

Process of distal axon disintegration after injury.

Resting Membrane Potential

Measured at -70mV, inside more negative.

Action Potential

Long-distance nerve impulse with high current.

Electrochemical Gradient

Positive charge outside cell membrane.

Graded Membrane Potentials

Local, short-lived changes in membrane potential.

Depolarizing Potential

Membrane potential moves toward 0mV.

Hyperpolarizing Potential

Membrane potential moves below -70mV.

Action Potentials

Long-distance nerve impulses with brief polarity reversal.

Threshold Stimulus

Minimum stimulus required to trigger action potential.

Resting State

Na+ channels closed, membrane at -70mV.

Rapid Depolarizing Phase

Na+ influx reverses potential to +30mV.

Repolarizing Phase

K+ efflux resets membrane potential.

Refractory Periods

Altered sensitivity to stimuli post-action potential.

Absolute Refractory Period

No further stimulation possible during depolarization.

Relative Refractory Period

Stronger stimulus needed during repolarization.

Propagation

Action potential moves along axon membrane.

Continuous Propagation

Unmyelinated fibers transmit impulses at 1m/s.

Saltatory Propagation

Myelinated fibers transmit impulses rapidly between nodes.

Axon Diameter

Larger diameter increases conduction speed.

Type A Fibers

Large, myelinated fibers; 120mps speed.

Type B Fibers

Smaller, myelinated fibers; 15mps speed.

Type C Fibers

Smallest, unmyelinated fibers; 1mps speed.

Electrical Synapse

Rapid communication via gap junctions.

Chemical Synapse

Neurotransmitter diffusion across synaptic cleft.

Neurotransmitter

Chemical messenger affecting post-synaptic receptors.

EPSP

Excitatory post-synaptic potential; depolarizing effect.

IPSP

Inhibitory post-synaptic potential; hyperpolarizing effect.

Summation

Combination of EPSPs to reach action potential threshold.

Facilitation

Increases likelihood of reaching action potential threshold.

Inhibition

Decreases likelihood of reaching action potential threshold.

Neuromodulator

Chemical altering neurotransmitter effects or release.

Acetylcholine

Neurotransmitter involved in memory and muscle activation.

GABA

Inhibitory neurotransmitter and neuromodulator.

Serotonin

Inhibitory neuromodulator affecting mood and anxiety.

Multiple Sclerosis

Autoimmune disease damaging myelin sheath.

SSRIs

Medications increasing serotonin for anxiety and depression.