Principles of Human Physiology I - Units 1 & 2

This set of vocabulary flashcards covers introductory physiology concepts, tissue types, homeostatic control, cell communication, and the fundamental structure and electrical signaling of the nervous system as discussed in Units 1 and 2.

Physiology

The study of the normal functioning of a living organism and its component parts.

Homeostasis

The maintenance of a relatively stable internal environment through a series of automatic control mechanisms that result in oscillation around a setpoint.

Acclimatization

An environmentally induced change in physiological function with no genetic change, such as adjusting to elevation changes.

Function

The ‘why’ of a physiological system, referring to why the system exists.

Mechanism

The ‘how’ of a physiological system, referring to how the system works at cellular and molecular levels.

Gap junctions

Direct cell-to-cell communication via protein channels called connexes that are capable of opening and closing.

Paracrine signal

A local chemical signal that diffuses through the immediate surrounding to communicate with neighboring cells.

Autocrine signal

A local chemical signal that acts on the same cell that secreted it.

Agonist

Any molecule that binds with a receptor and induces activity to create a response.

Antagonist

A molecule that binds to a receptor but produces no response and turns off or blocks activity.

Negative feedback

A homeostatic control mechanism where a change results in a response that returns the variable to its original value, keeping the system near a set-point.

Positive feedback

A non-homeostatic response that reinforces a stimulus, sending a variable further from its setpoint until an external signal turns it off.

Feedforward control

Reflexes that predict a change is about to happen and start a response loop in anticipation, such as salivation at the thought of food.

Soma

The cell body of a neuron which acts as the center of chemical processes to keep the cell functioning and alive.

Dendrites

Slender processes of a neuron that receive information and transmit electrical signals towards the soma.

Axon

A cytoplasmic extension of a neuron that transmits electrical signals away from the soma towards target cells.

Nuclei

Clusters of neuron cell bodies located within the Central Nervous System (CNS).

Ganglia

Clusters of neuron cell bodies located within the Peripheral Nervous System (PNS).

Tracts

Bundles of axons forming a pathway in the Central Nervous System (CNS).

Nerves

Bundles of axons forming a pathway in the Peripheral Nervous System (PNS).

Afferent neurons

Sensory neurons that receive information from receptor cells and transmit sensory information to the CNS.

Interneurons

Neurons located entirely inside the CNS that integrate information; they account for $96\%$ of all neurons.

Efferent neurons

Motor neurons that receive information from interneurons and transmit it to effectors such as muscles and glands.

Schwann cells

Glial cells in the PNS that wrap around axons to form a myelin sheath for electrical insulation.

Oligodendrocytes

Glial cells in the CNS that wrap around axons to form the myelin sheath.

Astroglia

Star-shaped glial cells in the CNS that contact blood vessels and neurons to help maintain the neuron microenvironment.

Microglia

Small, specialized immune cells in the CNS that remove damaged cells and foreign invaders.

Ependymal cells

Epithelial cells in the CNS that produce cerebral spinal fluid (CSF) and create a selectively permeable barrier between brain compartments.

Membrane potential

The relative difference in the number of cations and anions on either side of the cell membrane, measured in millivolts ($mV$).

Resting Membrane Potential

The charge difference between the inside and outside of a cell at rest, which is typically $-70\,mV$ for a neuron.

Equilibrium potential ($E_{ion}$)

The membrane potential that exactly opposes the concentration gradient of a specific ion, where electrical and chemical forces are equal and opposite.

Depolarization

A decrease in the membrane potential difference where the cell membrane potential becomes less negative.

Hyperpolarization

An increase in the membrane potential difference where the cell membrane potential becomes more negative.

Graded potential

A short-distance signal occurring in dendrites and cell bodies with an amplitude proportional to the strength of the triggering event.

Action potential

Identical, ‘all or nothing’ electrical signals that travel long distances along an axon without diminishing in strength.

Threshold potential

The minimum depolarization necessary to trigger an action potential, which is typically $-55\,mV$.

EPSP (Excitatory Post Synaptic Potential)

A depolarizing graded potential that brings the membrane potential closer to the threshold potential.

IPSP (Inhibitory Post Synaptic Potential)

A hyperpolarizing graded potential that moves the membrane potential farther away from the threshold potential.

Absolute refractory period

A period lasting approximately $1\,msec$ during which no action potentials can be triggered regardless of stimulus strength because $Na^+$ channels are inactivated.

Relative refractory period

A period following the absolute refractory period where a larger-than-normal (suprathreshold) stimulus is required to trigger an action potential.

Saltatory conduction

The process by which action potentials jump from one Node of Ranvier to the next along a myelinated axon.

Synapse

A point of cell communication consisting of a presynaptic axon terminal, a synaptic cleft, and a postsynaptic membrane.

Acetylcholinesterase

An enzyme found in the synaptic cleft that rapidly breaks down acetylcholine (ACh) into choline and acetyl CoA.

Autonomic division

The involuntary division of the PNS that innervates smooth and cardiac muscle, glands, and some adipose tissue using a two-neuron chain.

Somatic division

The voluntary division of the PNS that innervates skeletal muscle using a single neuron path.

Sympathetic branch

The branch of the autonomic division responsible for ‘fight or flight’ responses during physical activity and stress.

Parasympathetic branch

The branch of the autonomic division responsible for ‘rest and digest’ functions.

Neuroeffector junction

The synapse between a peripheral neuron and its effector or target tissue.

Varicosity

A swollen area on the axons of autonomic neurons that contains vesicles filled with neurotransmitter for release into the neuroeffector junction.