Nervous Tissue Lecture Notes

A comprehensive set of vocabulary flashcards covering the anatomical divisions, cellular structures, neuroglia types, membrane potentials, and synaptic activities described in the Chapter 12 lecture on Nervous Tissue.

Central nervous system (CNS)

The anatomical division consisting of the brain and spinal cord responsible for integrating, processing, and coordinating sensory data and motor commands.

Peripheral nervous system (PNS)

All nervous tissue outside the CNS that delivers sensory information to the CNS and carries motor commands to peripheral tissues.

Afferent division

A functional division of the PNS that carries sensory information from receptors in peripheral tissues and organs to the CNS.

Efferent division

A functional division of the PNS that carries motor commands from the CNS to effectors such as muscles, glands, and adipose tissue.

Somatic nervous system (SNS)

A component of the efferent division that controls skeletal muscle contractions through both voluntary and involuntary (reflex) actions.

Autonomic nervous system (ANS)

Also known as the visceral motor system, it provides involuntary control over smooth muscle, cardiac muscle, adipose tissue, and glands.

Enteric nervous system (ENS)

A network of neurons in the walls of the digestive tract that coordinates local visceral reflexes without instructions from the CNS.

Perikaryon

The cytoplasm surrounding the nucleus within the cell body (soma) of a neuron.

Nissl bodies

Dense areas of RER and ribosomes in the perikaryon that appear gray in color and are responsible for protein synthesis.

Axon hillock

The thickened region of the cell body that attaches to the initial segment of the axon.

Anterograde transport

The movement of materials from the cell body to the axon terminals, powered by the protein kinesin.

Retrograde transport

The movement of materials from the axon terminals toward the cell body, powered by the protein dynein.

Multipolar neurons

Neurons with one long axon and two or more dendrites; these are the most common type in the CNS and include all PNS motor neurons.

Interoceptors

Sensory receptors that monitor internal systems such as the digestive and urinary tracts and detect stretch, deep pressure, and pain.

Proprioceptors

Sensory receptors that monitor the position and movement of skeletal muscles and joints.

Astrocytes

The most numerous CNS neuroglia that maintain the blood-brain barrier (BBB), provide structural support, and regulate the interstitial environment.

Oligodendrocytes

CNS neuroglia with cytoplasmic extensions that wrap around axons to form the lipid-rich myelin sheath.

Ependymal cells

Cells that line the central canal of the spinal cord and ventricles of the brain, producing and monitoring cerebrospinal fluid (CSF).

Microglia

The smallest and least numerous CNS neuroglia that clean up cellular debris, wastes, and pathogens via phagocytosis.

Schwann cells

Also called neurolemmocytes, these PNS neuroglia form the myelin sheath or indented folds of plasma membrane around peripheral axons.

Wallerian degeneration

A process in the PNS where the axon distal to an injury site degenerates, while Schwann cells form a path for new growth.

Resting membrane potential

The membrane potential of an unstimulated, resting cell, characterized by an inner surface that is more negative than the outer surface, typically at $-70\,mV$ in neurons.

Sodium–potassium exchange pump

An active transport mechanism powered by ATP that moves $3\,Na^+$ out of the cell and $2\,K^+$ into the cell to stabilize the resting potential.

Equilibrium potential

The membrane potential at which there is no net movement of a particular ion; for $K^+$ it is $-90\,mV$ and for $Na^+$ it is $+66\,mV$.

Voltage-gated ion channels

Channels that open or close in response to changes in membrane potential, characteristic of axons and sarcolemma.

Depolarization

A shift from the resting membrane potential toward a less negative potential, often caused by $Na^+$ entry into the cell.

Threshold

The membrane potential, typically between $-60\,mV$ and $-55\,mV$, required to trigger an action potential.

All-or-none principle

The concept that any stimulus large enough to reach threshold will trigger a standard action potential that propagates the entire length of the axon.

Absolute refractory period

The time during which the membrane cannot respond to further stimulation because voltage-gated sodium channels are already open or inactivated.

Saltatory propagation

The rapid movement of an action potential along a myelinated axon where the local current jumps from node to node.

Type A fibers

The largest myelinated axons that transmit sensory and motor information to and from the CNS at high speeds.

Synaptic delay

A delay of $0.2\,ms\text{ to }0.5\,ms$ between the arrival of an action potential at the axon terminal and its effect on the postsynaptic membrane.

Acetylcholinesterase (AChE)

The enzyme responsible for breaking down acetylcholine ($ACh$) in the synaptic cleft.

Excitatory postsynaptic potential (EPSP)

A graded depolarization of the postsynaptic membrane that moves the membrane potential closer to threshold.

Temporal summation

The integration of effects from a single synapse by receiving two or more depolarizing stimuli in rapid succession.

Spatial summation

The integration of effects that occurs when stimuli arrive at the same time but at different locations on the postsynaptic membrane.