what are neurons
- excitable cells
- carry electrical signals
- several types (classified based on structure and/or function)
- in response to a stimulus they rapidly propagate electrical signals in order to transmit info
what are glial cells (neuroglia)
- non excitable cells
- physical and biochemical support for neurons
- several types (classified based on location/function)
name and describe the glial cells found in the central nervous system
ependymal cells - create barriers between compartments
-> source of neural stem cells
astrocytes - source of neural stem cells
-> take up K+, water, neurotransmitters
-> secrete neurotrophic factors
-> help form blood brain barrier
-> provide substrates for ATP production
microglia (modified immune cells) - act as scavengers (for infection)
oligodendrocytes - form myelin sheaths
name and describe the glial cells found in the peripheral nervous system
schwann cells - form myelin sheaths
-> secrete neurotrophic factors
satellite cells - support cell bodies
explain the components of a neuron
- dendrites = receive incoming signal
- cell body (soma) = integrates information
- axons = carry outgoing information to axon terminal
- synapse = region where an axon terminal communicates with its postsynaptic target cell
- neuron = 1 cell
- nerve = bundle of axons from multiple neurons
describe the functional categories of neurons
- Sensory (afferent) neurons
->Carry information from receptors → CNS
->Detect stimuli (e.g., touch, light, sound, temperature)
-Interneurons (association neurons)
->Located within the CNS
-> Process, integrate, and relay information between sensory & motor neurons
->Most abundant type of neuron
-Motor (efferent) neurons
->Carry commands from CNS → effectors (muscles & glands)
->Enable responses such as movement or secretion
what are the structural categories of neurons
- pseudounipolar neurons have a single process called the axon, during development the dendrite fused with the axon
- bipolar neurons have 2 relatively equal fibers extending off the central cell body
- anaxonic CNS interneurons have no apparent axon
- multipolar CNS interneurons are highly branched but lack long extensions
-> a typical multipolar efferent neuron has five to seven dendrites, each branching four to six times
-> a single long axon may branch several times and end at enlarged axon terminals - different neural shapes reflect different functions
explain myelin formation
- schwann cell nucleus is pushed to outside of myelin sheath
- myelin consists of multiple layers of cell membrane
- each schwann cell forms myelin around a small segment of one axon
- node of ranvier is a section of unmyelinated axon membrane between 2 schwann cells
explain diseases of demyelination
- multiple sclerosis: autoimmune degeneration of CNS myelin; progressive
- guillain-barre syndrome: autoimmune degeneration of PNS myelin; sudden onset and usually temporary
- diseases of demyelination result in impaired conduction of electrical signals along the axon
-> loss of function depends on the neurons/nerve affected
what are electrical signals
- changes in membrane potential generated by the movement of ions
what are gated channels
- control ion permeability of the neuronal membrane
- mechanically gated
- chemically gated
- voltage gated
what are graded potentials
- depolarization or hyperpolarization
- excitatory vs inhibitory post synaptic potentials
- amplitude of response depends on strength of stimulus and density of receptor channels
- electrical signal travels as ionic charges (+ or -) diffuse through the cell
- signal loses strength with distance travelled
- increase stimulus; increase activation of channels
- increase channel density; increase sensitivity to stimuli
what are action potentials
- only depolarization
- all or none response depends on membrane reaching threshold potential
- high density of voltage gated Na+ channels required for this type of signal
-55mV for voltage gated sodium channel
overview of neuronal electrical signaling
- signal input in dendrites
- change in ion permeability
- generation of graded potential - graded potential spreads through soma
- reaches axon hillock where there is a high density of Na v channels
- if threshold reached, initiates action potential - action potential propagated/conducted along axon
- at axon terminal, action potential triggers neurotransmitter release
- neurotransmitter binds to receptors on postsynaptic dendrites/membrane
compare and contrast graded potential vs action potential: type of signal
GP- input signal
AP- regenerating conduction signal
compare and contrast graded potential vs action potential: occurs where
GP- usually dendrites and cell body
AP- trigger zone through axon
compare and contrast graded potential vs action potential: typed of gated channels involved
GP- mechanically, chemically gated or voltage gated
AP- voltage gated
compare and contrast graded potential vs action potential: ions involved
GP- Na+, Cl-, Ca2+
AP- Na+ and K+
compare and contrast graded potential vs action potential: type of signal
GP- depolarizing or hyperpolarizing
AP- depolarizing
compare and contrast graded potential vs action potential: strength of signal
GP- depends on initial stimulus, can be summed
AP- all or none phenomenon, cannot be summed
compare and contrast graded potential vs action potential: what initiates the signal
GP- entry of ions through gated channels
AP- above threshold graded potential at the trigger zone opens ion channels
compare and contrast graded potential vs action potential: unique characteristics
GP- no minimum level required to initiate
- 2 signals coming close together in time will sum
- initial stimulus strength is indicated by frequency of a series of action potentials
AP- threshold stimulus required to initiate
- refractory period: 2 signals too close together in time cannot sum
what is ohm’s law
V=IR -> I = V/R
- biological convention: current is the net movement of positive charges
- ion flow or current depends on the electrochemical gradient of the ion and the resistance that opposes the flow
what are the 2 sources of resistance to current flow in cells
- Rm, membrane resistance; varies with channels gating
- membrane normally good insulator; high Rm
- open channels allow ion flow; decrease Rm - Ri, internal resistance of cytoplasm
- depends on cytoplasm composition (constant)
- inversely related to cell diameter
- large diameter, lower Ri
-
Lecture 118
-
Lecture 240
-
Lecture 320
-
Lecture 421
-
Lecture 539
-
Lecture 620
-
Lecture 727
-
Lecture 820
-
Lecture 921
-
Lecture 10/1132
-
Lecture 1221
-
Lecture 1339
-
Lecture 1424
-
Lecture 1522
-
Lecture 1615
-
Lecture 1718
-
Lecture 1811
-
Lecture 1920
-
Lecture 2018
-
Lecture 2120
-
Lecture 2221
-
Lecture 2325
-
Lecture 2422
-
Lecture 2521
-
Lecture 2616
-
Lecture 2714
-
Lecture 2820
-
Lecture 2916
-
Lecture 30+3123
-
Lecture 3221
-
Lecture 3325
-
Lecture 3414
