Block 2 Human Physiology P225 IU

CNS

brain and spinal cord

PNS

Sensory, efferent neurons, somatic motor, autonomic: parasympathetic, sympathetic

Sensory neurons

Afferent neurons

Motor neurons

Efferent neurons

Somatic motor division

voluntary

autonomic division

involuntary

Dendrites

Projections coming out of the cell body, detect input signal

Cell body

integration center of neuron

nucleus

middle of the cell body

axon hillock

connects axon to cell body

Initial segment

beginning of axon between hillock and first myelin sheath

myelin sheath

lines the axon for faster communication

Collaterals

Extra axon branching off of main axon

axon terminal

End of the axon that is the beginning of the synapse

Synapse

presynaptic axon terminal (first axon), synaptic cleft (space between), postsynaptic dendrite

Axo-dendritic

axon connects to dendrite

Axo-somatic

axon connects to soma

axo-axonic

axon connects to axon

Dendodendritic

dendrite connects to dendrite

Neurotransmitter production

in the soma

Neurotransmitter transport

axonal transport

neurotransmitter storage

axon terminal

Slow axonal transport

cytoplasmic streaming

fast axonal transport

protein “walking”, anterograde and retrograde, vesicle recycling

Neurotransmitter secretion

axon terminal, exocytosis, vesicle recycling

Key factors determining resting membrane potential

K+ concentration gradient, K+, Na+ and Cl- resting membrane permeability

leak channels

always open, K+ goes out, Na+ goes in, counteracted by Na+/K+ ATPase pump

gated channels

chemical, mechanical, voltage, chemical and voltage are most common in neurons

Graded potential characteristics

input signal - change in membrane potential, location: dendrites and soma, type of ion channel: chemically, mechanically, occasionally voltage, ions involved: Na+ K+ and Ca2+. EPSP’s and IPSP’s

EPSP

Excitatory post-synaptic potential, causes depolarization

IPSP

Inhibitory post-synaptic potential, causes hyperpolarization

Graded potential characteristics: signal strength

variable, no minimum strength required, summation

Graded potential characteristics: Current flow

local, not propagated, decremental, spreads away from stimulus in all directions. towards trigger zone (axon hillock and initial segment), subthreshold - No AP. Suprathreshold - get AP

Action potential characteristics

type of signal, regenerative signal within the axon, location: axon hillock through axon terminal, type of ion channels: voltage gated, Ions involved: Na+ and K+ (some Ca2+)

action potential characteristics: signal type

EPSP’s only, no IPSP’s in action potentials

Action potential characteristics: signal strength

all or none, refractory period between action potentials: cannot sum

Action potential characteristics: current flow

one way flow, propagated, trigger zone to axon terminals

Action potential sequence: 1st half

Resting membrane potential, depolarizing graded potential: EPSP, EPSP to threshold, rapid depolarization: Na+ voltage gated channels, overshoot: Na+ voltage gated channels

Action potential sequence: 2nd half

repolarization: K+ voltage gated channels, hyperpolarization undershoot: K+ voltage gated channels, returning to resting membrane potential: K+ voltage gated channels, resting membrane potential

Voltage gated Na+ channels

closed, open, inactive. RMP - closed. Threshold - open. Threshold to equilibrium Na+ - open. At equilibrium Na + - inactive. Repolarization - closed

voltage gated Na+ and K+ channel feedback

Na+ voltage gated channel reinforced to completion (equilibrium of Na+) - positive feedback regulation. K+ voltage gated channel returns to RMP - negative feedback regulation.

Refractory periods

limit # of action potentials, forces one way propagation, type depends on Na+ voltage gated channel position, absolute and relative

Absolute refractory period

Cannot generate another action potential, Na+ voltage gated channels are open, they close during repolarization

Relative refractory periods

Na+ voltage gated channels are closed, only a larger than normal stimulus can stimulate a new action potential. Returning to RMP

Action potential propagation: trigger zone

initial segment, EPSP graded potential, voltage gated channels

Action potential propagation: Adjacent area

stimulated: depolarize, non-decremental

Action potential propagation: previous area

absolute refractory area, one directional flow

Rates of conduction

Diameter: larger diameter, less resistance, faster. Myelination: lipid insulation, much faster rates. Saltatory conduction, metabolic efficiency

Demyelination

CNS: heavy metal poisoning, multiple sclerosis. PNS: Guillain-Barre’ syndrome, copper deficiency

hyperkalemia

excess intake of K+, depolarizes membrane potential - makes it easier to get to threshold for an action potential

Hypokalemia

can happen with water toxicity, concentration gradient of K+ to move out of the cell, hyperpolarizes membrane potential, harder to stimulate action potential

Electrical Synapse

gap junction, direct transfer of action potential, bidirectional flow from point stimulation, CNS, cardiac muscle, smooth muscle

Chemical synapse

neurotransmitters, indirect transfer of action potential, one direction of flow, most of PNS, skeletal muscle

Neurotransmitters

direct effect on signal transmission: EPSP or IPSP. Paracrine agents: communication between pre and post synaptic cell. Autocrine agents: may provide self regulation or feedback to pre-synaptic cell

Neuromodulators

alters synaptic activity at pre or post synaptic cell

Ionotropic receptors

fast, ligand gated ion channels: ion specific. EPSP or IPSP

Metabotropic receptors

slow, G protein coupled receptor with 2nd messengers. EPSP or IPSP, intracellular response

Acetylcholine (nicotinic)

Cholinergic, ion channel receptor, skeletal muscle, autonomic neurons, CNS, agonist: nicotine, antagonists: curare

Acetylcholine (muscarinic)

Cholinergic, G protein coupled receptor, smooth and cardiac muscle, endocrine and exocrine glands, CNS, agonist: muscarine, antagonist: atropine

Norepinephrine

beta 1 and beta 3. G protein couple receptor, smooth and cardiac muscle, glands, CNS, adipose tissue, antagonists: alpha receptors: ergotamine, phentolamine, beta receptors: propranolol

Epinephrine

alpha 1, beta 2. G protein couple receptor, smooth and cardiac muscle, glands, CNS, adipose tissue, antagonists: alpha receptors: ergotamine, phentolamine, beta receptors: propranolol

Synapse Component Actions: Presynaptic Cell

Axon terminal, active zone, neurotransmitter vesicles. Voltage-gated Ca2+ channels, docking proteins, exocytosis of neurotransmitter

Synapse Component Actions: Synaptic cleft

interstitial space: ECF, Diffusion

Synapse Component Actions: Postsynaptic Cell

Postsynaptic density, neurotransmitter receptors, enzymes

Termination of neurotransmitter action: stop release

stop simulation, no action potentials

Termination of neurotransmitter action: remove

presynaptic cell re-uptake, enzyme degradation, AChE: acetylcholinesterase, diffusion away from cleft

Integration of Neural Information Transfer: Divergence

Spread message, one to many

Integration of Neural Information Transfer: Convergence

multiple message input, many to one

Integration of Neural information transfer: back talk

across synapse, neuromodulators, modifying what’s happening at axon terminal

Integration of Neural Information Transfer: Plasticity

mostly CNS, enhance or decrease synaptic activity, can regulate activity at a synpase

Integration of Neural Information Transfer: Stimulus strength

number of APs and frequency of APs. One EPSP can generate multiple APs by staying above threshold for long enough time, needs to be in relative refractory period to start another AP. Stronger EPSP can result in more frequent APs, a higher threshold means more likely to initiate AP and frequency of APs. More neurotransmitter release from stronger stimulus

Information of Neural Information Transfer: temporal summation

Additive EPSP + EPSP, separated in time from the same synapse

Information of Neural Information Transfer: Spatial Summation

Additive EPSP + EPSP, separated by space but all at the same time

Integration of Neural Information Transfer: Inhibitory summation

EPSP + IPSP

Integration of Neural Information Transfer: Global Inhibition

No AP generated, all targets of the postsynaptic neuron are inhibited equally

Integration of Neural Information Transfer: Selective Inhibition

Some APs, an inhibitory neuron synapses on one collateral of the presynaptic and selectively inhibits one target

Integration of Neural Information Transfer: Presynaptic Factors

Neurotransmitter production, re-uptake, and breakdown. Amount of Ca2+ entering cell. Amount and rate of Ca2+ removed from cell or put into storage

Integration of Neural Information Transfer: Postsynaptic factors

enzyme activity: removal of neurotransmitter. Receptor up or down regulation. Receptor desensitization. Receptor agonists and antagonists. Alter signal action. Signal transduction pathway and signal amplification

Sensory Info: Conscious

Perceived, special senses and somatic senses, some proprioception

Sensory Info: Unconcious

not perceived, visceral, some proprioception, muscle length and tension

Sensory Info: System components

Stimulus, receptors (transduction), transmission (1st degree sensory neuron: PNS, 2nd degree sensory neuron: CNS decussation, 3rd degree sensory neuron: brain). Integration: cerebral cortex: conscious. Other areas of the brain: unconscious

Sensory Information: Receptors: Structure

Simple: free nerve ending. Complex: specialized receptor area. Specialized: non-neural receptor cells (gustation, vision, hearing, equilibrium). No AP needed in specialized receptors

Sensory Information: Receptors: Adequate stimulus

Chemoreceptors, Mechanoreceptors, Photoreceptors, Thermoreceptors, Nociceptors - pain

Sensory Information: Receptors: Function

Transduction. Stimulus energy converted to a change in the membrane potential. Receptor potential = graded potential (neuron vs specialized receptor cell). Ionotropic receptor (ion channel). Metabotropic receptor (second messenger opens ion channel)

Receptive Fields: 1st degree receptive field

large vs small, field overlap, 1st degree neuron convergence. Also a 2nd degree receptive field, and the 2 point discrimination test

Sensory Info: integration: unconscious

Spinal cord, brainstem, and hypothalamus

Sensory Info: integration: conscious

Cerebral cortex, perceptual threshold, filtering and habituation, CNS modification of threshold for perception, inhibitory modulation

Sensory Info: Integration: Olfaction

Olfactory cortex, limbic, hypothalamus

Sensory Info: integration: Vision

Midbrain → thalamus → visual cortex

sensory info: integration: Sound and taste

medulla → thalamus → auditory and gustatory cortexes

Sensory info: integration: Equilibrium

medulla → cerebellum and thalamus → cerebral cortex

Sensory Information: integration: Somatic senses

Spinal cord → thalamus → 1st degree somatosensory cortex

Sensory Info: sensory coding: Modality

Type of receptor and adequate stimulus, 5 submodalities of taste

Sensory info: sensory coding: labeled line coding

Location of integration determines perception

Sensory info: sensory coding: location of receptor field and labeled line coding

somatosensory and the homunculus, phantom limb pain, crosstalk among neurons, pitch and auditory cortex

Sensory Info: sensory coding: timing

interaural time difference

Sensory Info: sensory coding: population coding and lateral inhibition

number of receptors stimulated, 1st degree receptive fields, axoaxonic inhibition. enhances contrast and makes stimulus easier to perceive

Sensory info: sensory coding: population coding

number of receptors stimulated, receptor threshold low → need weak stimulus. Receptor threshold high → need strong stimulus

Sensory info: sensory coding: frequency coding

frequency of APs, tells how often one sensory neuron fires to one receptor

Sensory Info: sensory coding: Duration of stimulus

duration of sending APs, suprathreshold receptor potential, must persist into the relative refractory period