DAT Biology: Nervous System

Neuron

Functional unit of the nervous system

Soma

Neuron cell body, nucleated region, integrating all the incoming electrical signals from the dendrites

Dendrites

Branch-like structures for receiving signals from neighboring neurons and converting them into electrical impulses

Myelin Sheath

Fatty insulation of the axon, accelerating action potential propogation

Axon

Process for sending signals to neighboring neurons, long-cable-like projection conducting electrical impulses (action potentials) away from the cell body toward other neurons/target cells

Axon Terminals

Site of synaptic signal transmission, branched endpoints of the axon releasing neurotransmitter molecules into the synaptic cleft to communicate with the next cell

Axon Hillock

Site of connection between the soma and the axon, cone-shaped, trigger zone, determines whether the summed signals are storng enough to generate an action potential

Nodes of Ranvier

Gaps in the myelin sheath, action potential can jump from gap to gap, where axon membrane is exposed and packed with ion channels allowing the electrical signal to be regenerated

Site of ion exchange in saltatory conductoin

Saltatory Conduction

The process where an action potential rapidly "jumps" from one node of Ranvier to the next, rather than traveling continuously down the axon, which speeds up transmission and conserves metabolic energy.

Myelin Sheath

Fatty, insulating layer wrapping around axon to electrically insulate it and prevent ion leakage, increasing speed of nerve signal transmission

Action Potential

Rapid change in the membrane potential that exists across a membrane, dictated by relative ion ratios in the intracellular/extracellular spaces, finishing at the axon terminal of the presynaptic neuron

Na+/K+, all or nothing (either has one or doesn’t)

Resting State

Prior to firing of the action potential, maintained around -70 mV

Voltage more negative inside the cell than outside

Pump 3 Na+ OUT of the cell for every 2 K+ pumped INTO the cell

Depolarization

Stimulated neurons depolarize IF the threshold potential is reached (-55 mV), causing some Na+ to flow back into the cell as voltage-gated Na+ channels open

Voltage-Gated Calcium Channels open (Ca2+ enters the cell), and large influx in Ca2+ triggers exocytosis of NTs; synaptic vesicles house NTs bind to the plasma membrane to initiate exocytosis

Repolarization

Transition from a more positive “depolarized” membrane potential back to a more negative “repolarized” membrane potential

Voltage-gated K+ channels open to allow K+ out of the cell, Na+ channels close and are inactive

Hyperpolarization

A membrane potential even more negative than the resting potential

Refractory Period

Phase where its either very difficult or impossible to trigger another action potential

Absolute Refractory Period

Impossible to trigger a second action potential

Na+ channels are inactivated as K+ channels continue to repolarize the membrane back to resting state from + charge

Relative Refractory Period

Very difficult to trigger a second action potential

Membrane potential drops below -40 mv and Na+ channels are closed but not inactivated

Synaptic Transmission

Transmission of chhemical signals from one neuron to another across an interneuron space called a synapse

Neurotransmitters (NTs)

Chemical signals generated in the presynaptic neuron and received at the postsynaptic neuron

Synapse

Space between two neurons, including the presynaptic and postsynaptic neurons

Presynaptic Neuron

Responsible for sending the signal and releasing neurotransmitters into the synaptic cleft via the axon terminal

Synaptic Cleft

Zone between two neurons, not including either neuron

Synaptic Vesicles

Responsible for the transport of neurotransmitters from the axon to the synaptic cleft

Postsynaptic Neuron

Responsible for signal reception and interacting with neurotransmitters

Neurotransmitters (NTs)

Messenger molecules released by presynaptic neuron and received by the postsynaptic neuron

Postsynaptic Ligand-Gated Ion Channels

Directly responsible for binding of free NTs at the postsynaptic neuron, where released NTs are received

Graded Potential

Local, short-lived change in membrane potential (depolarization or hyperpolarization) varying in strength and intensity and diminishing as it travels passively along the dendrites/soma toward the axon hillock

Excitatory Graded Potential

Graded depolarization (more positive) caused by Na+ influx (opens Na+ channels), pushing the membrane closer to the threshold making firing an action potential more likely

Inhibitory Graded Potential

Graded hyperpolarization (becomes more negative) caused by Cl- influx or K+ efflux (opens K+ channels), pushing membrane farther from threshold making firing an action potential unlikely,

Excitatory Neurotransmitters (ENTs)

Neurotransmitters invoking an excitatory response at the postsynaptic membrane, causing depolarization at synaptic membrane and pass on the action potential signal

Glutamate

Main ENT of the central nervous system

Dopamine

ENT involved in reward-motivated behavior (catecholamine)

Catecholamine

Class of neurotransmitters and hormones derived from tyrosine, consisting of dopamine, norepinephrine, and epinephrine (adrenaline)

Epinephrine and Norepinephrine

Involved in fight/flight response

Postsynaptic ENTs of the sympathetic nervous system, reroute blood towards most critical parts of body

Catecholamine

Acetylcholine

Most common neurotransmitter in muscular system, signaling muscle fibers by binding to ligand-gated sodium channels

Inhibitory Neurotransmitters (INTs)

Neurotransmitters invoking an “inhibitory” response at the postsynaptic membrane

Hyperpolarizes a cell at its synaptic membrane refrains from passing down the action potential

Gamma-Aminobutyric Acid (GABA)

Main INT of the CNS

Glycine

Another INT of the CNS

Seratonin

INT of the brain

Voltage-Gated Ca2+ Channels

This channel’s opening is responsible for the exocytosis of neurotransmitters into the synaptic cleft

Action potential works its way down axon to axon terminal, electric signal stimulates voltage gated calcium channels to open causing an influx of calcium into the cell, causing synaptic vesicles to undergo exocytosis to release neurotransmitters into synaptic cleft

Central Nervous System (CNS)

Brain and spinal chord

Peripheral Nervous System (PNS)

Nerves branching off of the CNS

Cerebral Cortex

Largest, outermost, deeply grooved portion of the brain (what you picture typically), made up of 4 regions—frontal, temporal, occipital, and parietal lobe

Frontal Lobe

Higher-level functioning, decision making, problem solving, attention and concentration

Temporal Lobe

Responsible for speech and hearing

Occipital Lobe

REsponsible for vision

Parietal Lobe

Responsible for spatial perception and sensation

Cerebellum

Responsible for the coordination of movement, independent of the cerebral cortex, between the occipital lobe and the brain stem

Brain Stem

Involved in the control of automatic functions (heart rate and signal relay), between cerebral cortex and spinal cord

Main Components: midbrain, pons, medulla oblongata, reticular formations

Midbrain

Responsible for the relay of senses to other parts of the brain

Pons

Responsible for the relay of messages between the forebrain, cerebellum, and medulla

Medulla Oblongata

Multi-functional part of the brain stem, responsible for controlling heart rate, breathing rate, blood pressure, and for sensing toxins

Reticular Formations

Neurons existing throughout the brainstem, responsible for corticol arousal and consciousness

Limbic System

Responsible for emotion, memory, learning, motivation

Main Components: thalamus, hypothalamus, hippocampus, amygdala

Thalamus

Brain’s relay center, relaying sensory and motor signals from the body to the brain, between the cerebrum and the midbrain

Hypothalamus

Responsible for the regulation of hormone secretion in the body

Hippocampus

Responsible for the consolidation of memory

Amygdala

Responsible for the emotional reaction to scents

Spinal Cord

Nervous tissue connecting the brain to the body, containing sensory (afferent) neurons and motor (efferent) neurons

Sensory (Afferent) Neurons

Relay signals to the spinal cord and eventually the brain via dorsal roots

Motor (Efferent) Neurons

Relay signals from the brain to the muscles via ventral roots

PNS Motor (Efferent) Neurons

Somatic Nervous System + Automatic Nervous System

Somatic Nervous System

Involved in voluntary motor action, including skeletal muscles

Automatic Nervous System

Involved in involuntary actions, including cardiac muscle, effector organs, smooth muscles

PNS Sensory (Afferent) Neurons

Mechanoreceptors, nociceptors, thermoreceptors, chemoreceptors, electroreceptors

Mechanoreceptors

PNS Sensory (Afferent Neuron) Responsible for reception of mechanical stimuli

Nociceptors

PNS Sensory (Afferent Neuron) Responsible for reception of pain stimuli

Thermoreceptors

PNS Sensory (Afferent Neuron) Responsible for reception of stimuli related to changes in temperature

Chemoreceptors

PNS Sensory (Afferent Neuron) Responsible for reception of chemical stimuli

Electroreceptors

PNS Sensory (Afferent Neuron) responsible for reception of light, electrical, and magnetic stimuli

Sympathetic Nervous System

Responsible for aiding the fight/flight response

Parasympathetic Nervous System

REsponsible for relaxing the body out fo a sympathetic state (rest and digest), effects occurring via the vagus nerve

Ganglion

Cluster of nerve cell bodies in the peripheral nervous system outside of the brain and spinal cord, site of synapsing between the preganglionic and postganglionic neurons

Preganglionic Neuron

Neuron coming from the CNS that enters the ganglia

Postganglionic Neuron

Neuron coming from the ganglia and exiting to the effector organs

Sympathetic Nervous System (Toward Effector Organ)

Contains Short preganglionic neuron and long postganglionic neuron, where acetylcholine is the neurotransmitter between them, and norepinephrine/epinephrine as NT from postganglionic neuron to effector organ

Parasympathetic Nervous System

Long preganglionic neuron, short postganglionic neuron, with acetylcholine as the sole neurotransmitter

Sympathetic Nervous System (Toward Blood Stream)

Stimulates adrenal medulla to release norepinephrine or epinephrine into the bloodstream

Acetylcholinesterase

Enzyme responsible for the rapid hydrolysis of acetylcholine to stop the propagation of a signal

Outer Ear

Responsible for taking in sound waves

Tympanic Membrane

Responsible for transferring sounds from the outer ear to the middle ear

Middle Ear

Responsible for carrying sound waves from the outer to inner ear

3 Bony Ossicles

Malleus, incus, stapes

Transfer and amplifies vibrations through the middle ear

Stapes

Responsible for transferring sound from the middle ear to the inner ear via the oval window

Inner Ear

Begin the transformation of sound waves into electrical impulses

Cochlea

Use fluid and hairs to convert mechanical signals into neural signals, known as transduction

Round Window

Membrane covered opening between the middle ear and inner ear, helping the cochlear expand and vibrate

Semicircular Canal

Uses fluid and hairs to convey information about a person’s movement

Cornea

Responsible for focusing light and protecting the eye, transparent

Iris

Controls the size of the pupil

Pupil

Controls the amount of light that enters the rest of the eye

Lens

Focuses the relevant image onto the retina

Retina

Located at the back of the eye and contains photoreceptors, and retinal photoreceptors can either be rods/cones

Rods

Responsible for vision in low light (greyscale)

Cones

Responsible for color perception in high light environments

Fovea

Retinal region with the highest concentration of photoreceptors, responsible for hgih acuity vision

Amacrine and Bipolar Cells

Transmits the info from the retinal rods/cones to ganglion cells of the optic nerve fibers

Optic Nerve

Bundel of axons transmitting visual info to the brain

Optic Disk

Eye’s blind spot, site of passage for the optic nerve heading towards the brain, no photoreceptors present