Chapter 12 Flashcards
Nervous System
Includes brain, spinal cord, and nerves.
Neurons
Cells for intercellular communication in nervous tissue.
Neuroglia
Supportive cells essential for neuron function.
Central Nervous System (CNS)
Brain and spinal cord; processes sensory data.
Peripheral Nervous System (PNS)
Nervous tissue outside CNS; connects to organs.
Enteric Nervous System (ENS)
Nervous system in digestive tract; 100 million neurons.
Afferent Division
Carries sensory information to the CNS.
Efferent Division
Carries motor commands away from the CNS.
Effectors
Target organs responding to motor commands.
Somatic Nervous System (SNS)
Controls voluntary and involuntary skeletal muscle.
Autonomic Nervous System (ANS)
Controls subconscious actions like heart rate.
Sympathetic Division
Stimulates ‘fight or flight’ responses.
Parasympathetic Division
Promotes ‘rest and digest’ functions.
Dendrites
: Short branches receiving signals from other neurons.
Axon
Long projection carrying signals away from cell body.
Axonal Transport
Movement of materials between cell body and axon terminals.
Anaxonic Neurons
Small neurons with similar processes; found in brain.
Bipolar Neurons
One dendrite and one axon; rare in special senses.
Unipolar Neurons
Fused axon and dendrites; most sensory neurons.
Multipolar Neurons
One axon and multiple dendrites; common in CNS.
Resting Membrane Potential
Voltage difference across a neuron’s membrane at rest.
Action Potential
Rapid change in membrane potential; signal propagation.
Synapse
Junction between neurons for signal transmission.
Neurotransmitters
Chemical messengers affecting postsynaptic membranes.
Information Processing
Integration and coordination of sensory and motor commands.
Cell Body (Soma)
Contains nucleus; maintains neuron function.
Dendritic Spines
: Fine processes on dendrites; increase surface area.
Axoplasm
Cytoplasm of axon; transports materials within neuron.
Perikaryon
Cytoplasm surrounding the nucleus in neuron.
Mitochondria
Produce energy for neuronal functions.
Somatic sensory neurons
Monitor external environment
Visceral sensory neurons
Monitor internal environment
Interoceptors
Monitor internal systems (e.g., digestive, urinary); Internal senses (stretch, deep pressure, pain)
Exteroceptors
Monitor external environment (e.g., temperature); Complex senses (e.g., sight, smell, hearing)
Proprioceptors
Monitor position and movement of skeletal muscles and joints
Motor neurons (efferent neurons)
Multipolar neurons that carry instructions from CNS to peripheral effectors via efferent fibers (axons)
Somatic motor neurons of SNS
Innervate skeletal muscles
Visceral motor neurons of ANS
Innervate all other peripheral effectors including smooth and cardiac muscle, glands, adipose tissue
Interneurons
Located between sensory and motor neurons; responsible for distribution of sensory information and coordination of motor activity
SAME
To distinguish between afferent and efferent: S - sensory, A - afferent, M - motor, E - efferent
Types of neuroglia in the CNS
Astrocytes, Ependymal cells, Oligodendrocytes, Microglia
Astrocytes
Have large cell bodies with many processes; maintain blood brain barrier, create framework for CNS, repair damaged tissue, guide neuron development
Oligodendrocytes
Cells with sheet-like processes that wrap around axons; produce multiple myelin sheaths that insulate myelinated axons
Ependymal cells
Line central canal of spinal cord and ventricles of brain; produce and monitor cerebrospinal fluid (CSF)
Microglia
Phagocytes that move through nervous tissue removing unwanted substances
White matter
Regions of CNS with myelinated axons
Gray matter
Regions of CNS that contains unmyelinated axons, neuron cell bodies, and dendrites
Satellite cells
Neuroglia of the PNS that insulate neuronal cell bodies
Schwann cells
Neuroglia of the PNS that insulate most axons
Myelin sheath
An electrically insulating layer wrapped around the axon that increases speed of action potentials
Nodes of Ranvier
Naked areas of the axons located between adjacent myelin internodes that contain a high concentration of voltage-gated Na+ channels
Cerebrospinal fluid (CSF)
Clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord
Neurodegenerative diseases
Diseases such as Huntington’s disease, Parkinson’s disease, and Alzheimer’s disease where astrocytes lose normal homeostatic functions
Phagocytosis
The process by which microglia remove cell debris, wastes, and pathogens
Internodes
Myelinated segments of axon
Schwann cells (neurolemmocytes)
Produce myelin sheath around axons, consisting of multiple layers that are tightly packed.
Neurolemma
Outer surface of Schwann cell.
Membrane Potential
The difference in electric potential between the interior and the exterior of the cell, created by the difference in ion concentration.
Resting membrane potential
The membrane potential of a resting cell, typically -70 mV.
Graded potential
Temporary, localized change in resting potential caused by a stimulus.
Action potential
An electrical impulse produced by graded potential that propagates along the surface of the axon to the synapse.
Extracellular fluid (ECF)
Contains high concentrations of Na+ and Cl-.
Cytosol
Contains high concentrations of K+ and negatively charged proteins.
Electrochemical gradient
Sum of chemical and electrical forces acting on an ion across the membrane, a form of potential energy.
Sodium-potassium exchange pump
Powered by ATP, it maintains the concentration gradients of Na+ and K+ across the plasma membrane by ejecting 3 Na+ for every 2 K+ brought in.
Passive ion channels (leak channels)
Always open and their permeability changes with conditions.
Active ion channels (gated ion channels)
Open and close in response to stimuli.
Chemically gated ion channels
Open when they bind specific chemicals (e.g., ACh) and are found on cell body and dendrites of neurons.
Voltage-gated ion channels
Respond to changes in membrane potential and are found in axons of neurons and sarcolemma of skeletal and cardiac muscle cells.
Mechanically gated ion channels
Respond to physical distortion of membrane surface and are found in sensory receptors that respond to touch, pressure, or vibration.
Graded potentials (local potentials)
Changes in membrane potential that vary according to the size of the stimulus and cannot spread far from the site of stimulation.
Repolarization
When the stimulus is removed, membrane potential returns to normal.
Hyperpolarization
Results from opening K+ channels, where K+ moves out, increasing the negativity of the resting potential.
Chemical Stimulus
Change in membrane potential due to chemicals.
Depolarization
Membrane potential becomes less negative than resting.
Graded Potentials
Variable changes in membrane potential; localized effects.
All-or-None Principle
Action potential occurs fully or not at all.
Threshold
Membrane potential required to trigger action potential.
Voltage-Gated Na+ Channels
Channels that open at threshold, allowing Na+ influx.
Rapid Depolarization
Quick increase in membrane potential due to Na+ influx.
Inactivation of Na+ Channels
Closure of Na+ channels after peak depolarization.
Activation of K+ Channels
Opening of K+ channels leads to repolarization.
Repolarization Phase
Membrane potential returns to resting level after depolarization.
Temporary Hyperpolarization
Membrane potential briefly drops below resting level.
Local Currents
Passive spread of graded potentials in nearby areas.
Excitable Membrane
Membrane capable of generating action potentials.
Sodium Ion (Na+)
Positively charged ion crucial for depolarization.
Potassium Ion (K+)
Positively charged ion involved in repolarization.
Membrane Potential Change
Alteration in voltage due to ion movement.
Excitation Threshold Range
Threshold for action potential is -60 to -55 mV.
Restoration of Resting Potential
Membrane returns to -70 mV after action potential.
Voltage-Gated Channels
Channels that open/close in response to voltage changes.
Sodium ion
Positively charged ion crucial for action potentials.
Potassium ion
Positively charged ion involved in repolarization.
Refractory period
Time when membrane cannot respond to stimuli.
Continuous propagation
Slow action potential movement in unmyelinated axons.
Saltatory propagation
Fast action potential movement in myelinated axons.
Axon diameter
Larger diameter increases action potential speed.
Type A fibers
Myelinated, large diameter, fast (120 m/sec) transmission.
Type B fibers
Myelinated, medium diameter, intermediate speed (18 m/sec).
Type C fibers
Unmyelinated, small diameter, slow (1 m/sec) transmission.
Electrical synapses
Direct contact allowing rapid ion passage.
Chemical synapses
Signal transmission via neurotransmitters across synaptic cleft.
Cholinergic synapses
Release acetylcholine at neuromuscular junctions.
Excitatory neurotransmitters
Cause depolarization and promote action potentials.
Inhibitory neurotransmitters
Cause hyperpolarization and suppress action potentials.
Biogenic amines
Neurotransmitters like norepinephrine and dopamine.
Postsynaptic potentials
Graded potentials in response to neurotransmitter binding.
EPSP
Excitatory postsynaptic potential; graded depolarization.
IPSP
Inhibitory postsynaptic potential; graded hyperpolarization.
Axoaxonic synapses
Synapses between axons of two neurons.
Information processing
Integration of stimuli affecting action potential generation.
