Functional Divisions of the PNS and Neuronal Functions

These flashcards cover key concepts from the lecture on the functional divisions of the peripheral nervous system (PNS) and the anatomy and physiology of neurons.

What are the three functional divisions of the PNS?

Somatic, Autonomic, and Enteric Nervous Systems.

Define afferent vs efferent neurons.

Afferent carry sensory info to CNS; Efferent carry motor commands from CNS.

What is a neuron?

A complete nerve cell with cell body, dendrites, and axon.

What is the difference between a nerve and a tract?

Nerve = PNS axon bundle; Tract = CNS axon bundle.

Which neuroglia maintains the blood-brain barrier?

Astrocytes.

Which neuroglia is phagocytic in the CNS?

Microglia.

What is the role of ependymal cells?

Produce and circulate CSF in ventricles.

Which CNS glial cell myelinates multiple axons?

Oligodendrocyte.

Which PNS cell myelinates axons?

Schwann cell.

Can a single Schwann cell myelinate multiple axons?

No; it wraps around one axon segment only.

What is the resting membrane potential of a neuron?

Approximately –70 mV.

Which pump maintains resting potential?

Na⁺/K⁺ ATPase (3 Na⁺ out, 2 K⁺ in).

Why is the inside of a neuron negative at rest?

More K⁺ leakage out than Na⁺ in + trapped anions.

What causes depolarizing graded potentials?

Na⁺ influx through ligand-gated channels.

What causes hyperpolarizing graded potentials?

K⁺ efflux or Cl⁻ influx.

What is temporal summation?

Rapid, repeated stimulation by one neuron adds over time.

What is spatial summation?

Simultaneous stimulation by multiple neurons adds over space.

Where are sensory neuron cell bodies found?

Dorsal root ganglia.

What does the posterior column pathway carry?

Fine touch, vibration, and proprioception.

Where does posterior column decussate?

Medulla oblongata.

Damage to posterior column causes which side deficit?

Ipsilateral (below decussation).

What information does the spinothalamic pathway carry?

Pain, temperature, crude touch.

Where does the spinothalamic pathway decussate?

Spinal cord at entry level.

Damage to spinothalamic tract causes which side deficit?

Contralateral.

Which tract controls voluntary skeletal movement?

Corticospinal tracts (lateral and anterior).

Where does the lateral corticospinal tract decussate?

Medullary pyramids.

Where does the anterior corticospinal tract decussate?

Spinal cord level before synapsing.

Upper vs lower motor neuron locations?

Upper = motor cortex to spinal cord; Lower = anterior horn to muscle.

Somatic motor pathway uses how many neurons from CNS to effector?

One (lower motor neuron).

Autonomic motor pathway uses how many neurons from CNS to effector?

Two (preganglionic and postganglionic).