Nervous System: Nervous Tissue and Neurophysiology

Vocabulary practice flashcards covering nervous system anatomy, neuron cytology, glial cells, resting membrane potential, graded potentials, action potentials, and synaptic transmission from Chapter 12.

Sensory Nervous System (Afferent)

The functional division of the nervous system that carries signals towards the central nervous system by detecting stimuli from both internal and external environments.

Motor Nervous System (Efferent)

The functional division of the nervous system that transmits motor output from the central nervous system to effectors (muscles and glands) to elicit a response.

Somatic Sensory

The sensory component that detects stimuli we consciously perceive, including the five special senses.

Visceral Sensory

The sensory component that detects stimuli within internal organs and organ walls that we do not consciously perceive.

Somatic Motor

The motor component that transmits voluntary motor commands from the CNS to control skeletal muscles.

Autonomic Motor

The involuntary motor component that innervates cardiac muscle, smooth muscle, and glands, subdivided into sympathetic and parasympathetic divisions.

Central Nervous System (CNS)

The structural division of the nervous system composed of the brain (enclosed within the skull) and the spinal cord (enclosed within the vertebral canal).

Peripheral Nervous System (PNS)

The structural division of the nervous system consisting of nerves (bundles of axons) and ganglia (clusters of neuronal cell bodies) located outside the brain and spinal cord.

Ganglion

A cluster of neuronal cell bodies located in the peripheral nervous system.

Nerve

A bundle of axons surrounded by connective tissue located in the peripheral nervous system that carries sensory, motor, or both types of signals.

Mixed Nerve

A nerve that functionally contains both sensory and motor neurons.

Cranial Nerves

Nerves that structurally extend directly from the brain.

Spinal Nerves

Nerves that structurally extend directly from the spinal cord.

Excitability

A core characteristic of neurons defined as the ability to respond to a stimulus and initiate an electrical signal.

Conductivity

A core characteristic of neurons defined as the ability to propagate an electrical signal along the plasma membrane.

Extreme Longevity

A characteristic of neurons noting that most formed during development can survive and function throughout an individual's entire lifetime.

Loss of Mitotic Ability

A characteristic of mature neurons reflecting their inability to divide and form new cells via mitosis.

Dendrites

Short, tapering, unmyelinated processes branching off the neuronal soma that receive input signals and conduct them toward the cell body.

Soma (Cell Body)

The metabolic center of a neuron, defined by the presence of the nucleus and perikaryon cytoplasm, which controls protein synthesis and cellular metabolism.

Axon

A single, longer process extending away from the soma that propagates action potentials and ends at synaptic knobs.

Axon Hillock

The triangular cone-shaped region of the soma from which the axon originates and where action potentials are initiated.

Axolemma

The plasma membrane surrounding the axon of a neuron.

Axoplasm

The cytoplasm contained within the axon of a neuron.

Multipolar Neuron

A neuron structurally characterized by having multiple dendrites and a single axon extending from the cell body.

Bipolar Neuron

A neuron structurally characterized by having exactly two processes extending from the soma: one dendrite and one axon.

Unipolar Neuron

A neuron characterized by a single short process emerging from the soma that branches like a 'T' into peripheral and central axon branches.

Anaxonic Neuron

A neuron that possesses only dendrites and lacks an axon.

Interneuron (Association Neuron)

A multipolar or anaxonic neuron located entirely within the CNS that performs integrative functions; accounts for roughly $99\%$ of all neurons.

Chemical Synapse

A junction where a presynaptic neuron releases neurotransmitter molecules across a narrow synaptic cleft to bind receptors on a postsynaptic cell, causing a transmission delay of approximately $0.3\text{ to }0.5\,ms$.

Glial Cells (Neuroglia)

Non-excitable, supporting cells found in both the CNS and PNS that are smaller than neurons, lack a resting membrane potential, and are capable of mitosis.

Astrocytes

The most abundant star-shaped glial cells in the CNS that anchor neurons, form the blood-brain barrier (BBB), regulate extracellular ions and neurotransmitters, and form glial scars during repair.

Ependymal Cells

Ciliated glial cells lining ventricles and canals of the CNS that produce and circulate cerebrospinal fluid (CSF).

Microglial Cells

Phagocytic immune cells of the CNS that wander through neural tissue, detecting pathogens and engulfing cellular debris.

Oligodendrocytes

Glial cells in the central nervous system that wrap their cytoplasmic extensions around axons to form myelin sheaths.

Neurolemmocytes (Schwann Cells)

Glial cells in the peripheral nervous system that wrap around axons to form myelin sheaths.

Satellite Cells

PNS glial cells that surround and insulate neuronal cell bodies within ganglia and regulate local nutrient and waste exchange.

Glioblastoma

The most common and aggressive malignant brain tumor in adults, arising from astrocytes, with an average survival time of $12\text{ to }15\text{ months}$.

Leak Channel

An ion channel in the plasma membrane that remains continuously open, allowing ongoing passive diffusion of a specific ion (such as $\text{K}^+$ or $\text{Na}^+$) down its concentration gradient.

Chemically Gated Channel

An ion channel (ligand-gated) that is normally closed at rest and opens briefly in response to the binding of a specific chemical neurotransmitter.

Voltage-Gated Channel

An ion channel that is closed at rest and opens briefly in response to changes in electrical charge (membrane potential) across the plasma membrane.

Receptive Segment

The functional neuronal region comprising dendrites and soma that features chemically gated channels, binds neurotransmitters, and produces graded potentials.

Initial Segment

The region at the axon hillock containing voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels where graded potentials undergo summation to initiate an action potential.

Conductive Segment

The length of the axon containing voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels along which action potentials propagate.

Transmissive Segment

The axon terminal containing voltage-gated $\text{Ca}^{2+}$ channels and $\text{Ca}^{2+}$ pumps that release neurotransmitters via exocytosis upon the arrival of an action potential.

Resting Membrane Potential (RMP)

The electrical potential difference across the plasma membrane when a neuron is at rest and unexcited, typically measured at $-70\,mV$ in neurons.

Sodium-Potassium ($\text{Na}^+/\text{K}^+$) Pump

An active primary transport protein that maintains the resting membrane potential by pumping $3\,\text{Na}^+$ out to the ECF and $2\,\text{K}^+$ into the ICF per $1\,\text{ATP}$ consumed.

Depolarization

A change in membrane potential that makes the cytosol less negative relative to the outside (moving closer to or above zero), typically caused by $\text{Na}^+$ influx.

Hyperpolarization

A change in membrane potential that makes the cytosol more negative relative to RMP, typically driven by $\text{K}^+$ efflux or $\text{Cl}^-$ influx.

Repolarization

The return of the membrane potential toward the polarized resting state following depolarization.

Graded Potential

A local, short-lived change in membrane potential occurring along the receptive segment that varies in amplitude (typically around $1\,mV$) based on the amount of neurotransmitter bound.

Excitatory Postsynaptic Potential (EPSP)

A depolarizing graded potential generated at the postsynaptic membrane caused by the influx of positive ions through chemically gated cation channels.

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarizing graded potential generated at the postsynaptic membrane caused by $\text{K}^+$ exiting through chemically gated $\text{K}^+$ channels or $\text{Cl}^-$ entering through chemically gated $\text{Cl}^-$ channels.

Threshold Potential

The critical membrane potential (typically $-55\,mV$) that must be reached at the axon hillock to trigger the opening of voltage-gated channels and initiate an action potential.

Summation

The additive integration of all incoming EPSPs and IPSPs occurring at the axon hillock (initial segment) to determine whether threshold is attained.

Action Potential

A rapid, all-or-none reversal of membrane potential from $-70\,mV$ to $+30\,mV$ and back to RMP, propagated along the conductive segment via sequential opening and closing of voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels.

Absolute Refractory Period

The time period during an action potential when voltage-gated $\text{Na}^+$ channels are either open or inactivated, making it completely impossible to generate another action potential regardless of stimulus strength.

Relative Refractory Period

The period immediately following the absolute refractory period during hyperpolarization when voltage-gated $\text{K}^+$ channels remain open, requiring a suprathreshold stimulus to trigger another action potential.

Continuous Conduction

The sequential propagation of an action potential along every unmyelinated segment of an axon.

Saltatory Conduction

The rapid propagation of an action potential along a myelinated axon where depolarization jumps between unmyelinated neurofibril nodes (nodes of Ranvier), requiring significantly less ATP.

Biogenic Amines (Monoamines)

A structural class of neurotransmitters consisting of modified amino acids, including dopamine, serotonin, noradrenaline, and adrenaline.

Neuropeptides

A structural class of neurotransmitters consisting of chains of amino acids, such as beta-endorphin and oxytocin.