Neurobiology Terms

Neuron

Type of cell that receives and sends messages from the body to the brain and back (information only flows one way, from the dendrites into the soma and from the soma to the axon)

Central nervous system

CNS: made up of the brain (controls how we think, move and feel) and spinal cord (carries messages back and forth between brain and nerves in the body))

Peripheral nervous system

PNS: consists of nerves that branch out from the brain and spinal cord (communication network between CNS and body parts)

Afferent system

Sensory afferent division of the PNS, brings sensory information from body to CNS

Efferent system

Motor, carry signals from the brain to the PNS to initiate an action (move muscles / tendons)

Effector

Executive organ: muscles, glands: produce a specific response to a detected stimulus

Dendrites

Branched extension of a nerve cell, along which impulses received from another cell at synapses are transmitted to the cell body

Cell body (soma)

Where the nucleus of a neuron lies, and where proteins are made to be transported throughout the axon and dentrites

Axon hillock

Specialized part of the soma that connects to the axon

Axon

Long part of the neuron that transmits electrical impulses to other neurons (away from cell body)

Myelin sheath

Insulating layer, or sheath that forms around the axon, allowing for electrical impulses to pass quickly and efficiently

Schwann cell

Glial cells (hold cells in place and help them work) that form the myelin sheath around the axon

Node of Ranvier

Gap in the myelin sheath of an axon, between individual adjacent Schwann cells

Synapse

Place where a soma and a dendrite connect, allowing the soma to send information through the dendrite to the other neuron

Presynapse, presynaptic cell

A neuron that sends information to another neuron via a synapse (the cell that transmits the information is presynaptic)

Postsynapse, postsynaptic cell

A neuron receives information from another neuron via a synapse (the cell that receives the information is postsynaptic)

Synaptic cleft

Junction (they never touch), where neurons communicate with each other using chemical signals (neurotransmitters)

Terminal bulb (synaptic terminal)

End of an axon, where electrical signals are converted into chemical signals (neurotransmitters) and transferred to the soma by a synapse

Nerve fiber

Axon + myelin sheath, extension of a nerve cell that transmits electrical impulses

Nerve

Nerve fiber bundles that transmit impulses to the CNS and impulses from the CNS to the PNS

Potential difference

Difference of charge between two different spaces

Semipermeable membrane

Thin biological sheet of material that allows certain molecules to pass

Membrane potential

Potential difference between the extracellular an intracellular space

Resting potential

Membrane potential of a nerve cell at rest; it is negative (~-70mV, per definition negative on the inside and positive outside)

Concentration gradient

Describes the decreasing or increasing concentration of a substance between two areas

Electrical gradient

Describes the decreasing or increasing concentration of charge between two areas

Ion channel protein

Membrane proteins form a tube through which certain substances can pass: selectively but always through diffusion (according to electrical and concentration gradients)

Ion pump

Membrane protein, which transports substances against the concentration and/or electrical gradients, while consuming energy (ATP)

Nerve impulse

Signal transmitted along a nerve fiber, consisting of a wave of electrical depolarization that reverses the potential difference accross membranes

Action potential

Electrical impulse that travels the length of the axon and causes release of neurotransmitters in the synapses

Local stimulus response

When a cell in the axon notices a stimulus, it opens some voltage-gated Na+ channels

Depolarization

Rapid rise in potential when a high enough stimulus is detected, coinciding with the opening of more votage-gated Na+ channels

Repolarization

Potential doesn’t rise further, Na+ channels close and K+ channels allow an efflux of Ions, making the resting potential drop again

Hyperpolarization

When too many K+ Ions leave the cell, the resting potential difference becomes too low, but channels close and Na+/K+ pump makes the difference be in the normal range again

Refractory period

Period of time when no stimuli can be detected and no voltage-gated Na+ channels are open (sets a limit for the frequency of action potential to occur)

Ungated ion channel

A channel that is always open, allowing specific ions to pass

Voltage-gated ion channels

A certain change in voltage opens such a channel (voltage of an ion)

Ligand-gated ion channels

Ion channels open due to the binding of a small molecule (transmitter controlled Na+ channel)

Mechanically gated ion channels

Channels that open in response to the physical deformation of the receptor through touch or pressure

Tetrodotoxin

Neurotoxin of pufferfish that interferes with impulse transmission by blocking Na+ channels

Saltatory conduction

In myelinated axon: action potential can only form at node of Ravier, as the extracellular fluid only touches there and Na+ channels cannot open when covered by Schwann cells, local current travels from node to node

Continuous conduction

Conduction along a naked axon, where local current cannot travel as fast, and action potential is formed everywhere

Neurotransmitter

Chemical signaling molecule secreted by a neuron to affect another cell across a synapse

Synaptic vesicles

Organelles in a synapse that store and release NT through exocytosis

Chemical synapse

Junction where impulses are transmitted unidirectionally through the release of NT

Electrical synapse

Behave as if post and pre synapse are one cell, local current can move freely (bidirectionally) between the two, interact through ions

Summation, spatial and temporal

Spatial: occurs when enough NT is built up from several presynapses to create action potential

Temporal: occurs when two or more impulses arrive in quick succession

Neural network

Connected artificial neurons that mimic brain function

Agonistic and antagonistic neurotoxins

Agonistic: increase synaptic transmission, mimics NT (nicotine) or interferes in NT breakdown (pesticides)

Antagonistic: decreases synaptic transmission, prevent release of NT (Botox) or blocks its action (curare)

Stimulus electrode

An instrument meant to stimulate the brain, spinal cord or nerves, using electricity

Stimulus threshold

Smallest amount of stimulation needed to elicit a response

All-or-none principle

Law that states that there will be a full response or none to a stimulus (if the stimulus is too low there will be no reaction, if it is higher than required, the same amount of action happens as for any sufficient voltage)

Local current

Diffusion of ions within axon that helps propagate action potential by making non polarized regions reach threshold value

Excitatory synapse

Increase likelihood by which an AP occurs in postsynapse by releasing certain NT

Inhibitory synapse

Decrease likelihood by which an AP occurs in postsynapse by releasing certain NT

Graded potential

Change in membrane potential that vary according to size of stimulus, if multiple presynapses work together or multiple stimuli arrive quickly they can cause AP

Recycling of NT

Transporter proteins remove NT from synaptic cleft or receptors and bring them back to synaptic vesicles for reuse

Five chemical groups of NT

Acetylcholine, Biogenic Amines, Amino acids, neuropeptides, gases

Spinal cord or spinal nerves

Tube-like structure that begins at brain stem and continues almost to the bottom of the spine, carry information from CNS to PNS

Grey matter

Consists of neuronal cell bodies (motor) (+ dendrites and unmyelinated axons), type of tissue in CNS

White matter

Large network of nerve fibers found in CNS

Dorsal horn and ventral horn of gray matter

Dorsal: receives sensory information via dorsal root

Ventral: contains interneurons and motor neurons

Dorsal and ventral root

Dorsal: carries sensory signals to CNS

Ventral: carries motor signals to PNS

Dorsal root ganglion

Structure between spinal cord and peripheral nerve that contains cell bodies of sensory nerve cells, involved in general transmission

Extensor and flexor

Extensor: increases angles between bones

Flexor: decreases angles between bones

Neuromuscular junction

Synaptic connection between terminal end of motor nerve and a muscle (skeletal, smooth or cardiac)

Knee jerk reflex

A reflex that comes from stimulation of patella which is felt by muscle spindles which trigger forward movement

Monosynaptic reflex

Stimulus and response take place in same organ

Reflex arc

Neutral pathway (connection) that controls a reflex

Muscle spindle

Stretch receptors that signal length change in muscles

Autonomic nervous system

Component of PNS that regulates involuntary physiological processes (heart rate, blood pressure, respiration, etc.)

Sympathetic and parasympathetic

Sympathetic: fight or flight

Parasympathetic: rest and digest

Enteric system

Gut feeling, second brain, located in gastrointestinal tract

Patella

Kneecap that helps keep quad muscles in place

Tendon = sinew

Tough band of connective tissue that connects muscles to bones

Ligament

Tough band of connective tissue that connects bones and keeps joints in place

Extraneous reflex

Fremdreflex

Camera obscura (pinhole eye)

Darkened box with a convex lens or aperture for projecting the image of an external object on the screen inside

Camera type eye

Camera obscura + convergin lens (convex lens) → our eye

cornea

Transparent part of the eye that covers the iris and pupil and allows light to enter inside

iris

Colored part of the eye that surrounds the pupil, regulates the amount of light entering by changing the size of the pupil

Aqueous humor

Fluid tat flows in and out of the front of the eye, keeps ocular pressure stable

Vitrious humor

Transparent tissue filling the eyeball behind the lens, sticks the retina at the back and makes eye keep its shape

sclera

White outer coating of our eye that prevents injury and keeps our eye in shape

choroid

layer of tissue in the middle layer of eye wall (between sclera and retina) filled with blood vessels to supply eye with nutrients and oxygen

retina

Light sensitive layer of tissue at the back of the eyeball, which converts images into electrical signals and sends them along the optic nerve to the brain

Ciliary muscle

Muscles that control the movement of the lens and pupil (if contracted the ligaments relax, making lens smaller; if relaxed the ligaments contract, streching lens)

Suspensory ligaments

Responsible for maintaining and supporting the lens, connected to lens and ciliary muscle

Fovea

Small depression in the retina where visual acuity is highest

Blind spot

Spot in the retina where the optic nerve connects, there are no light sensitive cones there, so you cannot see there

accommodation

Process to focus on objects at a certain distance

Presbyopia

Farsightedness due to age; lens not as elastic anymore, cannot round up itself when no pull on the suspensory ligaments