NERVOUS SYSTEM

NEURON STRUCTURE & FUNCTION

Dendrite (receptors receive signals, dendritic spines increase S.A.) 📬

Axon

Cell Body (soma) Has all organelles a reg. cell (nucleus, E.R. synthesizes NT's)

Synapse- presynaptic & postsynaptic

axon hillock (where action potential begins)

carry signal outward

N.T.'s synthesized into cell body are sent to the axon terminal for release into the synapse

Fast: carried along microtubule

Slow: moves through cytoplasm

AfmsJ

Types of Neurons

Interneurons Primarily in CNS, link neurons together

Motor (efferent neurons) send motor info out to muscle. send info from CNS to PNS

Sensory (afferent neurons) respond to sensory stim (temp, touch) bring info from PNS to CNS

GLIAL CELLS white matter)- support cells for neurons

myelin forming cells

Oligodendrocyte (CNS)

Neurolemmocytes (Schwann cells) (PNS) a single cell forms myelin around 1 axon

myelin (phospholipid insulates the cell & allows for saltatory conduction

unmyelinated portions of axons

CNS

PNS

Satellite cells [provide support for ganglia (clusters of neuron cell bodies)

microglia immune cells of the CNS (phagocytize debris) small, found in cerebral spinal fluid (CSF)

astrocyte provide neurons w/ nutrients (glucose,) form part of the blood brain barrier, regulate ion conc. in extracellular space. Neurotransmitter uptake & release. (v important)

BBB- composed of capillaries (selectively permeable due to tight junctions) It regulates the substances that can enter the brain.

Ependymal cells- epithelial cells that the ventricles in the brain and the central canal of the spinal cord. Have cilia that beat to move the cerebral spinal fluid (CSF) around.

Neurons (excitable tissues that propagate on electrical signals)

NERNST equation

GOLDMAN-HODGKIN-KATZ (GHK) equation

calculates a mem. potential for a single ion

E ion= 61/z log ([ion] out/ [ion] in)

calculates membrane potential considering ALL ions that can cross the mem.

Vm= 61 log (all of [ion] out added / all of [ion] in added)

types of polarization

Depolarization neurons become more positive inside. Gains (+) charge or Loses (-) charge.

Repolarization membrane returns to resting potential

Polarization membrane has a charge associated with it (+ outside, - inside)

Hyperpolarization neuron becomes more (-) inside than it was at a resting mem. potential. Gains (-) charge or Loses (+) charge

HOW DOES MEM. PERMEABILITY CHANGE?

ACTION POTENTIAL

NEUROTRANSMITTERS

Neurotransmitter Release

Inactivation of Neurotransmitters

  1. Ca++ triggers exocytosis of vesicles containing nt
  1. NT is released and travels across synapse
  1. Voltage gated Ca++ channels open and Ca++ enters the neuron
  1. NT binds w/ receptor on post synaptic neuron and initiates response
  1. Action potential reaches axon terminal and depolarizes it

REUPTAKE

ENZYME DEGRADATION (i.e. AChE)

DIFFUSION

Common N.T.'s

Excitatory N.T.

Acetylcholine (ACh)

Inhibitory N.T.

released onto muscles --> muscle contraction synthesized by choline + acetyl coA. Broken down by AChE.

Broken down by nicotinic & muscarinic receptors

Glutamate (aa nt) receptors NMDA & AMDA

GABA

Glycine (aa nt)

Amine N.T.'s

Epinephrine (E)

Norepinephrine (NE)

Dopamine (DA)

  1. Action potential begins
  1. AP reaches axon terminal & DEPOLARIZES it, voltage gated Ca++ enters neuron triggering exocytosis of vesicles containing NT
  1. NT is released & travels across the synapse binding w receptor on post synaptic neuron initiating a response
  1. Voltage gated ion channels (Na+) opens
  1. EPSP's continue to charge summates (spatially or temporally) until potential @ axon hillock becomes -55mV
  1. EPSP begins (mem. potential ⬆ bc of Na+)
  1. excitatory n.t. (glutamate) binds to receptors on post synaptic neuron. Ligand gated channel opens and Na+ enters
  1. post synaptic neuron @ rest (-70 mV)

Gated ion channels open or close

ligand-gated Na+ on dendrites

voltage-gated Na+ channels @ axon hillock & along axon

How does NT release lead to an AP?

EPSP = excitatory post-synaptic potential. To have an EPSP it must become more (+)

IPSP = inhibitory post synaptic potential inhibits an action potential from happening