human phys ch 8

Central Nervous System (CNS)

Brain and spinal cord; integrates information and sends commands.

Peripheral Nervous System (PNS)

Includes sensory (afferent) and motor (efferent) neurons that connect CNS to body.

Afferent Neurons

Carry sensory information from receptors to CNS.

Efferent Neurons

Carry motor commands from CNS to effectors (muscles, glands).

Somatic Motor Division

Controls voluntary movement via skeletal muscles.

Autonomic Division

Regulates involuntary activity of smooth and cardiac muscles.

Sympathetic vs. Parasympathetic

Divisions of autonomic system; differ by anatomy and neurotransmitters.

Enteric Nervous System

Intrinsic nervous system of the digestive tract.

Neurons

Electrically excitable cells that transmit information.

Dendrites

Receive incoming signals and increase surface area.

Axons

Carry outgoing signals to other cells.

Multipolar Neuron

Multiple dendrites and branched axon; most common.

Pseudounipolar Neuron

Cell body off to side of one long axon; used in sensory pathways.

Bipolar Neuron

One axon and one dendrite; found in retina and olfactory system.

Anaxonic Neuron

No visible axon, only dendrites; found in brain.

Interneurons

Found entirely within CNS; connect neurons.

Varicosities

Swellings along axons of efferent neurons that release neurotransmitters.

Nerve

Bundle of axons in PNS surrounded by connective tissue.

Sensory Nerves

Carry only afferent (sensory) signals.

Motor Nerves

Carry only efferent (motor) signals.

Cell Body (Soma)

Control center of neuron with nucleus and organelles.

Dendritic Spines

Small projections from dendrites involved in synaptic communication; dynamic.

Axon Hillock

Site on soma where action potentials are initiated.

Axonal Transport

Movement of materials from soma to axon terminal using motor proteins.

Kinesin-1 and Dynein

Motor proteins that transport cargo along microtubules.

Fast Axonal Transport

Moves vesicles and mitochondria quickly in both directions.

Slow Axonal Transport

Moves soluble proteins and cytoskeletal elements slowly.

Synapse

Junction between two neurons or neuron and target.

Presynaptic Cell

Neuron sending the signal.

Postsynaptic Cell

Cell receiving the signal.

Synaptic Cleft

Small gap between pre- and postsynaptic cells.

Chemical Synapse

Most common type in CNS; uses neurotransmitters.

Electrical Synapse

Less common; direct ion flow through gap junctions.

Growth Cone

Tip of growing axon; guides development to form synapse.

Neurotrophic Factors

Molecules supporting neuron growth and survival.

Glial Cells

Support cells in nervous system; outnumber neurons.

Schwann Cells

Myelinate axons in PNS; one cell per axon segment.

Oligodendrocytes

Myelinate axons in CNS; one cell to multiple axons.

Myelin Sheath

Insulating layer around axons that speeds up signal conduction.

Nodes of Ranvier

Gaps in myelin; allow saltatory conduction.

Satellite Cells

Support PNS neuron cell bodies in ganglia.

Astrocytes

CNS glia that support metabolism, form blood-brain barrier, and maintain ion balance.

Microglia

CNS immune cells that clean up debris; may contribute to neurodegenerative disease via ROS.

Ependymal Cells

Line ventricles in CNS; help produce and regulate cerebrospinal fluid.

Neuron Damage (Axon Severed)

Soma survives; distal axon degenerates unless regeneration occurs (mainly in PNS).

Ganglia

Clusters of nerve cell bodies in PNS.

Neuroepithelium

Stem cell layer in developing nervous system; gives rise to neurons and glia.

Nernst Equation

Predicts membrane potential for a single ion based on concentration gradient.

Resting Membrane Potential

Typically ~ -70 mV; slightly more positive than -90 mV predicted by K+ alone due to Na+ leak.

Goldman-Hodgkin-Katz (GHK) Equation

Calculates membrane potential considering multiple ions and permeabilities.

Depolarization

Membrane becomes less negative due to Na+ influx.

Hyperpolarization

Membrane becomes more negative due to K+ efflux or Cl- influx.

Ion Channels

Regulate movement of Na+, K+, Ca2+, Cl- across membrane.

Gated Channels

Open/close in response to signals like voltage or chemicals.

Conductance

How easily ions pass through a channel.

Ohm’s Law

V = IR; describes current flow in neuron.

Membrane Resistance

Resistance from the lipid bilayer.

Internal Resistance

Resistance from cytoplasm.

Graded Potentials

Local, variable-strength changes in membrane potential; lose strength with distance.

Action Potential

All-or-none long-distance electrical signal generated once threshold is reached.

Trigger Zone

Region (axon hillock/initial segment) where action potentials are initiated.

Excitatory Graded Potential

Depolarizes membrane, bringing it closer to threshold.

Inhibitory Graded Potential

Hyperpolarizes membrane, preventing action potential.

Subthreshold Potential

Graded potential that doesn’t reach threshold for firing action potential.

Suprathreshold Potential

Strong enough graded potential to trigger action potential.

Current Leak

Loss of charge through membrane, reduces strength of graded potentials.

Cytoplasmic Resistance

Hinders ion flow through neuron, weakening signals.

All-or-None Principle

Action potentials always occur fully if threshold is reached, otherwise not at all.