Physiology Neuro

Electrical potential

The potential of separated electrical charges of opposite signs to do work if they are allowed to come together

Resistance

The hindrance to electrical charge movement

Resting membrane potential

The electrical potential difference across plasma membrane of an unstimulated cell

Equilibrium potential

Membrane potential at which the concentration and electrical forces on an ion are equal in magnitude and opposite in direction

Depolarized

A change to a less negative potential

Overshoot

A reversal in polarity such that a neuronal membrane becomes positive inside with respect to the outside of the cell

Repolarized

A return to the resting potential following a depolarization

Hyperpolarized

A change to a more negative potential

Threshold potential

The membrane potential at which an action potential is generate

All-or-none

Action potentials either occur maximally or they do not occur at all

Refractory period

The time during and immediately following an action potential when the membrane is absolutely or relatively refractory to initiation of a new action potential

Absolute refractory period

A second stimulus, no matter how strong, will not produce a second action potential

Relative refractory period

A second action potential can be triggered, but a larger stimulus is required to reach threshold

Unidirectional

Action potential only travels in one direction along the axon

Orthodromic

Action potential runs along axon away from the soma

Antidromic

Action potential runs along axon toward the soma

Electrotonic conduction

A non-propagated local potential, resulting from a local change in ionic conductance

Continuous conduction

Occurs in neurons with unmyelinated axons

Axon diameter

About one micrometer (µm)

Saltatory conduction

The method by which nerve impulses travel down a myelinated axon

Nodes of Ranvier

Gaps in the myelin sheath where ion channels are clustered on the axon

Internode

Portion of the axon between nodes of Ranvier (the myelinated segments)

Electrical synapse

Consist of gap junctions that allow current to flow between adjacent cells

Chemical synapse

Neurotransmitters stored in synaptic vesicles are released by a presynaptic axon terminal into the synaptic cleft, where they transmit the signal from a presynaptic neuron to an adjacent postsynaptic neuron at a region called a postsynaptic density

Active zones

Release regions where vesicles are docked on presynaptic membrane prior to activation

Postsynaptic density

The high density of membrane proteins in the postsynaptic membrane adjacent to an axon terminal

Synaptic cleft

Gap separating the presynaptic and postsynaptic neurons

SNARE proteins

Proteins that dock vesicles in active zones

Synaptotagmins

Proteins that cause a conformational change in SNARE proteins, leading to membrane fusion and neurotransmitter release

Ionotropic receptors

Receptors that are themselves ion channels

Metabotropic receptors

Receptors that indirectly influence ion channels through a G protein and/or second messenger

Excitatory postsynaptic potential (EPSP)

The electrical response (depolarization) in a postsynaptic cell at an excitatory chemical synapse

Inhibitory postsynaptic potential (IPSP)

Either a hyper polarization or a stabilization of the membrane potential at an inhibitory chemical synapse

Reuptake

Unbound neurotransmitters in the synaptic cleft are actively transported back into the presynaptic axon terminal for reuse

Temporal summation

Summed potential created by more than one EPSP and/or IPSP arriving at a single synapse on a postsynaptic cell membrane in quick succession

Spatial summation

Summed potential created by more than one EPSP and/or IPSP arriving together at different synapses on a postsynaptic cell membrane

Neurotransmitter inactivation

Diffusion away from synaptic cleft, enzymatic degradation, reuptake

Sensory system

A part of the nervous system that consists of sensory receptors that receive stimuli from the external or internal environment, the neural pathways that conduct information from the receptors to the brain or spinal cord, and those parts of the brain that deal primarily with processing the information

Sensory information

May or may not reach level of consciousness; if it does, it is called a sensation; awareness and understanding of a sensation are called perception

Sensation

Sensory information that reaches consciousness

Perception

Awareness and understanding of a sensation

Sensory receptors

Translate information from external and internal environments into graded potentials

Mechanoreceptors

Respond to mechanical stimuli, such as pressure or stretch, and are responsible for many types of sensory information, including touch, blood pressure, and muscle tension

Thermoreceptors

Detect sensations of cold or warmth

Photoreceptors

Respond to particular ranges of light wavelengths

Nociceptors

Respond to pain due to actual or potential tissue damage

Sensory transduction

The process by which a stimulus is transformed into an electrical response

Receptor potential

The graded potential produced by the opening or closing of ion channels in the sensory receptor

Adaptation

A decrease in receptor sensitivity, which results in a decrease in action potential frequency in an afferent neuron despite the continuous presence of a stimulus

Slowly adapting receptors

Maintain a persistent or slowly decaying receptor potential during a constant stimulus, initiating action potentials in afferent neurons for the duration of the stimulus

Rapidly adapting receptors

Generate a receptor potential and action potentials at the onset of a stimulus but very quickly cease responding

Coding

The conversion of stimulus energy into a signal that conveys the relevant sensory information to the central nervous system

Sensory unit

A single afferent neuron with all its receptor endings

Receptive field

The area of the body that leads to activity in a particular afferent neuron when stimulated

Recruitment

The “calling in” of receptors on additional afferent neurons

Acuity

The precision with which we can locate and discern one stimulus from an adjacent one

Two-point discrimination

The ability to discriminate between two adjacent stimuli

Lateral inhibition

Information from afferent neurons with receptors at the edge of a stimulus is strongly inhibited compared to information from afferent neurons at the center

Ascending pathways

Sensory pathways that project “up” to the brain

Second-order neurons

The interneurons upon which the afferent neurons synapse

Third-order neurons

Synapse with second-order neurons

Somatic sensation

Sensation from the skin, skeletal muscles, bones, tendons, and joints

Meissner’s corpuscle

Rapidly adapting mechanoreceptor, touch and pressure

Merkel’s corpuscle

Slowly adapting mechanoreceptor, touch and pressure

Free neuron ending

Slowly adapting, including nociceptors, itch receptors, thermoreceptors, and mechanoreceptors

Pancinian corpuscle

Rapidly adapting mechanoreceptor, vibration and deep pressure

Ruffini corpuscle

slowly adapting mechanoreceptor, skin stretch

Anterolateral pathway

Makes its first synapse between the sensory receptor neuron and a second neuron located in the gray matter of the spinal cord; immediately crosses to the other side; processes pain and temperature information

Dorsal column pathway

Neurons project through the white matter (dorsal columns of the spinal cord); ascend on same side and make the first synapse in the brainstem

Decussation

The crossing of nerve fibers

Spinothalamic tract

Sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory are of the thalamus

Retina

Forms the inner, posterior surface of the eye, containing numerous types of neurons, including photreceptors

Photoreceptors

The sensory cells of the eye

Outer segment

The tip of the photoreceptors composed of discs

Discs

Stacked layers of membrane that house the molecular machinery that responds to light

Inner segment

Part of the photoreceptors which contains mitochondria and other organelles and a synaptic terminal that connects the photoreceptor to other nuerons in the retina

Müller cells

Glial cells that take up about 20% of the volume of the retina; elongated, funnel-shaped cells that span the distance from the inner surface of the retina directly to the photoreceptors; provide metabolic support for retinal neurons, mediate neurotransmitter degradation, deliver light rays through the retinal layers directly to the photoreceptors

Pigment epithelium

Pigmented layer of the back of the retina that absorbs light rays that bypass the photoreceptors

Chromophore

Make up photopigments (retinal)

Opsin

Protein that makes up photopigments

Retinal

Chromophore that makes up photopigments

Guanylyl cyclase

Enzyme that generates a high concentration of cGMP, which acts as a ligand for a nonspecific cation channel

Cyclic GMP (cGMP)

Maintains outer segment ligand-gated cation channels in an open state, and a persistent influx of Na+ and Ca2+ occurs

Transducin

Activates the enzyme cGMP-phosphodiesterase to degrade cGMP

cGMP-phosphodiesterase

Degrades cGMP

Nerve fiber layer

The layer of axons that travel from ganglion cells in the inner retina through the optic nerve to terminate in the lateral geniculate

Ganglion cell layer

A layer of the retina that consists of retinal ganglion cells and displaced amacrine cells

Inner plexiform layer

Consists of synaptic connections between the axons of bipolar cells and dendrites of ganglion cells, contains the synapse between the second-order and third-order neuron in the visual pathway

Inner nuclear layer

Layer of inner granules of the retina made up of a number of closely packed cells, of which there are three varieties: bipolar cells, horizontal cells, and amacrine cells

Outer plexiform layer

Contains synapses among and between retinal photoreceptors, horizontal cells, and bipolar cells

Outer nuclear layer

Contains the cell bodies of photoreceptors, which point away from the light and therefore have photosensitive segments in the deepest layer

Photoreceptor layer

Contains photosensitive outer segments of rods and cones

Pigment epithelium

The pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells

Skeletal muscle

Composed of cylindrical, multinucleated muscle fibers (cells) derived from myoblasts

Muscle fiber

Skeletal muscle cell

Myofibrils

Filaments arranged in cylindrical bundles

Thick filaments

Made up of myosin molecules with extensions called cross-bridges that span the gap between thick and thin filaments

Thin filaments

Contain actin, troponin, and tropomyosin; anchored to the Z lines at each end of a sarcomere; free ends partially overlap the myosin-containing thick filaments in the A band at the center of the sarcomere

Myosin

Protein composed of two large polypeptide heavy chains and four smaller light chains that combine to form a molecule with two globular heads

Heavy chains

Form the core of a thick filament