phys exam comp 2

afferent neuron

carry signal from body to CNS

efferent/alpha motor neuron

carry signal to muscles from CNS

dendrites do what

receive information from preceding neuron

axon

transfers information from soma to the next cell

what is a synapse

the region where an axon terminal communicates with its postsynaptic target cell

describe the parts of a neuron form the input signal to the output signal

dendrites- soma with nucleus- axon hillock- axon with myelin sheath (usually)- presynaptic axon terminal- synaptic cleft- postsynaptic dendrite on postsynaptic neuron

point of communication between 2 neurons is deemed what

synapse

point of communication between a neuron and a muscle is deemed what

neuromuscular junction

point of communication between a neuron and other tissue is deemed what

neuroeffector system

functional classifications of neurons

sensory, motor, interneurons, projections

what are sensory/receptor neurons

sense changes in environment, internal or external and send the information to the CNS

what is a motor neuron

project information out of CNS to effector organs/tissue (skeletal, smooth, or cardiac)

what are interneurons

lie within a collection of cell bodies (nucleus in the CNS), local modulation of input and output, communication within an area of the CNS

what are projection neurons

projection from one area of CNS to another, communication between areas of CNS- often confused with interneurons

what is a unipolar cell

invertebrate neuron, one projection comes from the soma and splits into a dendrite and axon

what is a bipolar cell

Ex: retina

axon and cell body on opposite sides of the soma

what is a pseudounipolar cell

ex: ganglion cell of dorsal root

T-shaped junction: one branch extending peripherally to sensory receptors and the other extending centrally toward the spinal cord or brain

what is a multi-polar cell

ex: motor neuron of spinal cord, pyramidal cell of hippocampus

multiple projections coming from soma, usually multiple dendrites and a single axon

glial cells in PNS

schwann cells- myelin and secrete neurotrophic factors; one cell wraps around one neuron

glia in CNS and ratio of glial cells to neurons

oligodendrocytes, astrocytes, microglial

1.5:1

role of oligodendrocytes in CNS

forms myelin sheath, important for action potential conduction

one cell can surround many neurons

role of astrocytes in CNS

source of neural stem cells, secrete neurotrophic factors, help form blood-brain barrier, provide substrates for ATP, cleanup (of K+, water, and neurotransmitters), synaptic, transmission

looks like a star

role of microglial in CNS

5-20% of glial population, macrophage of the CNS, immune defense

role of ependymal cells in CNS

create barriers between compartments and are a source of neural stem cells `

role of satellite cells in PNS

support cell bodies

brain consumes how much of the body’s O2 supply to produce metabolic by-products

20%

Properties of blood vessels

made of vascular smooth muscle cells and endothelial cells, allows O2 to be taken to and CO2 to be removed from CNS, helps establish the blood-brain barrier

the forebrain consists of

cerebrum, basal nuclei, thalamus, hypothalamus

function of the cerebrum

higher sensory, perceptual, and motor functions

function of the basal nuclei

subcortical structures, motor control

functions of the thalamus

sensory relay to other part of the CNS, main integrating station

functions of the hypothalamus

integrative homeostatic area

function of the cerebellum

body balance, muscle tone, motor behavior

parts and functions of the brainstem

• midbrain, pons, medulla

• sends and receives information through cranial nerves

major regions of the CNS

forebrain, cerebellum, brainstem, spinal cord

grey matter

ventral and dorsal horn, contain primarily cell bodies, no myelin, so they look grey.

white matter

fiber tracts, collection of myelinated axons

T/F: the spinal cord runs the entire vertebral column in adults

false

regions of the spinal cord

• cervical (C)- 8 segments

• thoracic (T)- 12 segments

• lumbar (L)- 5 segments

• sacral (S)- 5 segments

dorsal roots connect to

afferent (sensory) information

ventral roots connect to

efferent (motor) information

what secretes CSF in the brain and its purpose

choroid plexus

buffer brain from mechanical and acceleration-deceleration injury, fills 4 compartments

what does the choroid epithelium do

acts as a blood-CSF barrier

where are the resting potentials in a myotactic reflex

muscles cells, afferent sensory neurons, synaptic terminal, inner neuron

where are the action potentials in a myotactic reflex

in the sensory afferent neuron

what is an excitable tissue

they have the potential to produce an action potential because of their ability to propagate electrical signals rapidly in response to a stimulus

what is electricity

a form of energy resulting from the existence of charged particles, either statically as an accumulation of charge or dynamically as a current

what is transmembrane voltage

voltage difference across the membrane

what is the definition of voltage

an electromotive force or potential difference expressed in volts

membrane potential (Vm) is proportional to

the separation of positive and negative ions

by convention the outside of the cell membrane is how many mV

zero

definition of resting membrane

a special case of Vm where the cell is not active, the inside is more negative than the outside

• due to a difference in (+) and (-) ions in the area CLOSE to the membrane, ACROSS the membrane

definition of depolarization

decrease in membrane potential, aka a decrease in the potential difference across the membrane

• when Vm becomes less negative or closer to zero (the potential difference decreases)

definition of hyperpolarization

an increase in membrane potential, aka an increase in the potential difference across the membrane

• when Vm becomes more negative or further from zero (the potential difference increases)

when a cell acts as a capacitor, it

stores charge

what ion has the largest driving force to cross the cell membrane at Vr values

Ca²⁺

Na-K pump purpose and how many K/Na go in/out?

created some charge difference across membrane

2 K in, 3 Na out with the help of ATP

how can passive diffusion of k and Na lead to development of negative membrane potentials

K will move out to the cell, taking its (+) while leave behind a negatively charged impermeant anion that they are typically attached to inside the cell (like proteins or amino acids). Na will go into the cell taking its (+) in. Because there are a lot more leaking K channels on the cell membrane, the influx of Na into the cell does not counterbalance the efflux of K out of the cell, leading to a negatively charged membrane potential

what is the name of the equation is used to find the equilibrium potential and what is it?

Walter Nernst Potential

E_K = -61.5 logK_in/K_e for potassium, they can switch for other ions

what is the equilibrium for K

-95 mV

what is the equilibrium for Na

+62 mV

Why is Vr so close to E_K

There are more leaking K channels than Na leaking channels

what is driving force

where the ion wants to be, determines the direction of ionic current flow and the magnitude of current flow

• V_m - E_ion

driving force of K and Na

K: -65 - -95= 30

Na: 62- -65= 120

what is the equation used to predict voltage changes in a cell caused by conductance changes

goldman-hodgkin-katz

• Ca is not included because it is tightly regulated

what does P’ equal in the goldman-hodgkin-katz equation and what are the values for K, Na, and Cl

relative permeability of the ions across the cell membrane. 100, 1, 10

functions of an action potential

information delivery/encoding, rapid information transmission over long distances, initiators of cell responses (like muscle contraction and secretion)

threshold voltage is about how many millivolts positive to resting potential

15

Action potential properties

initiated by depolarization, have “constant” amplitude, constant conduction velocity, cannot summate- coded by frequency not amplitude

ohms law

V=I*R, guides the magnitude of Vm change

threshold is the point at which the

inward Na current outweighs the outward K current

threshold depolarization first opens ___ and then after a delay, _____ open

voltage gated Na channels, voltage gated K channels

describe action potential depolarization

once at threshold, Na activation gates open, Na conductance is increases, more Na enters depolarizing further bring the membrane potential closer to Na equilibrium, the Na inactivation gate closes because they are time sensitive, then the activation gate closes and delayed K channels open

describe action potential repolarization

there is a delay in the opening of voltage dependant K channels (triggered by depolarization) and stay open as long as the cell is depolarized- not time dependent, K leaves the cell due to an increase is conductance and driving force. The inactivation of Na channels also contribute.

what happens when the extracellular concentration of Na is reduced

there would be less of a driving force for Na to get into the cell and lowers the peak height of the action potential

what happens when the extracellular concentration of K is reduced