Nervous System: Key Structures, Neuron Types, and Signal Transmission

CNS

Brain and spinal cord.

PNS

Cranial nerves, spinal nerves, ganglia.

Sensory nervous system

Detects stimuli and sends information to CNS.

Somatic sensory

Conscious input.

Visceral sensory

Unconscious input from organs.

Motor nervous system

Sends commands from CNS to muscles/glands.

Somatic motor

Voluntary muscles.

Autonomic motor

Involuntary control.

Synaptic knobs

Release neurotransmitters; at axon ends.

Retrograde transport

Moves material from axon terminal to cell body.

Anterograde transport

Moves material from soma to terminal.

Multipolar neuron

Many dendrites, one axon; most common type.

Bipolar neuron

One dendrite, one axon; found in sensory organs.

Unipolar neuron

Single process; sensory neurons.

Anaxonic neuron

Dendrites, no axon; local communication.

Interneurons

Association neurons; process info in CNS.

Myelination of PNS axons

Increases speed, protects axons.

CNS glial cells

Astrocytes - support, barrier; Ependymal - make CSF; Microglia - defense; Oligodendrocytes - myelinate.

PNS glial cells

Satellite - protect neuron bodies; Schwann - myelinate axons.

PNS regeneration steps

Degeneration → Tube forms → Debris cleared → Axon grows → Reconnect.

Action potential steps

Rest → Depolarize → Repolarize → Hyperpolarize → Rest.

Threshold reached

NaI channels open; depolarization starts.

Function of axon, dendrite, synaptic knob

Axon - sends; Dendrite - receives; Knob - releases.

Graded potential

Small, short change in voltage.

AP reaches synaptic knob

Ca²I enters, neurotransmitters released.

Neurotransmitters inducing EPSP

Excitatory.

Neurotransmitters inducing IPSP

Inhibitory.

Neuronal circuits

Converging - many to one; Diverging - one to many; Reverberating - loops; Parallel-after-discharge - multiple paths.