704_NEURO WK 1 Lec 2.pptx

Neuroanatomy and Neurophysiology Andrew Littmann, PT, PhD, MA, NZRP With contributions from and special thanks to Clifford Barnes, PhD, and Jean Marie Berliner, PT, DPT, PhD, NCS Objectives By the end of this session, the student will be able to: 1. Describe functional components of neuron anatom...

Neuroanatomy and Neurophysiology Andrew Littmann, PT, PhD, MA, NZRP With contributions from and special thanks to Clifford Barnes, PhD, and Jean Marie Berliner, PT, DPT, PhD, NCS Objectives By the end of this session, the student will be able to: 1. Describe functional components of neuron anatomy 2. Describe structure and function of supporting cells (glial cells) 3. Discuss neuronal transmission including propagation of action potentials, synaptic transmission, and pre-/postsynaptic activity influencing synaptic activity and reuptake of transmitters 4. Discuss excitation and inhibition at the synaptic level including generator potentials 5. Describe long-term potentiation and habituation Why is this important as a future Doctor of Physical Therapy? Neuron Anatomy Bipolar (retina) Pseudounipolar Multipolar (*sensory – (many no dendrites) dendrites, one axon) Multipolar (cerebellum) Interneuron Various Neuron Structures (Depend on function of neuron) A: Vagus nerve motor neuron B: Cerebellar olive neuron D:Layer 5 pyramidal neuron E: Purkinje cell F:  -motor neuron Dendritic “tree” • Blue color represents synapse points from afferent (incoming) neurons • Connection point known as “dendritic spine” How do neurons communicate? • Axon terminals interface at different locations on the neuron at the “synapse”. • Electrical impulse reaches the axon terminal and is converted to chemical via release of neurotransmitters (NT’s) from the presynaptic neuron into the synaptic cleft • NT’s bind to receptors on the postsynaptic neuron which triggers opening of ion channels, converting the nerve signal back to electrical. Synapse Types 1. Axosomatic (primarily inhibitory) • Synapses onto the soma or cell body 2. Axodendritic (primarily facilitatory) • aka Axospinous – synapse on dendritic “spine” 3. Axoaxonic • presynaptic inhibition (-) • presynaptic facilitation (+) • Whether a synapse is excitatory or inhibitory depends on the specific neurotransmitter (NT) Glial Cells (or “neuroglia”) • Schwann Cells • Form protective insulation layer over axons in the peripheral nervous system (PNS) known as Myelin • Fatty, non-conductive substance • Contributes to faster conduction of nerve impulses • Play essential roles in peripheral nerve • Development • Maintenance • Function • Regeneration of • Oligodendrocytes • Myelin forming cells of the CNS • One oligodendrocyte myelinates multiple axons • Most myelination in the CNS is completed by age 8 mos. but generally complete by 2 years • Astrocytes • Most abundant cells in the brain • “Astro” = star-shaped • Multiple functions • Neuron metabolism/nutrition • Support immune function • Maintain cellular environment • Blood-brain barrier Glial Cells (or “neuroglia”) Central Nervous System Peripheral Nervous System Support Cells: Glial Cells (or “Glia”) Oligodendrocytes form myelin in CNS One oligodenrocytemany axons Many Schwann cells one axon Schwann cell myelin impact on nerve signal transmission • Myelin • prevents loss of action potentials along the length of the axon • Notice difference in action potential speed Schwann cell myelin impact on nerve signal transmission Questions? To understand the complexity of the nervous system we need to consider: 1. Approximately 84-100 billion neurons in the brain (with 10-50x more glial cells) 2. Integration of  10,000 synapses on each neuron’s body, axon, dendrite profile 3. Neuron network (architecture) may contribute to convergent or divergent pathways 4. Different neurotransmitters (chemical communication) acting at different synapses • Does the transmitter result in a excitatory (more likely to fire) or inhibitory (less likely to fire) event 5. Distance away from the axon hillock for synapses on a single neuron 6. How excitatory is the signal at the initial segment of the axon hillock 7. Depending on the strength of the depolarization, how long does the neuron continue to fire action potentials (frequency) 8. And many others!! https://www.youtube.com/watch?v=YP_P6bYvEjE Intracellular fluid has high concentration of negatively charged protein molecules to produce a net negative intracellular electrical charge Ion Channels – the pathway of change 1. Modality-gated channels • Specific to sensory neurons • Respond to touch, pressure, stretch, temperature, chemicals, light, etc. 2. Ligand-gated channels • “ligand” molecule that binds to a site on a target protein • Open in response to a neurotransmitter binding to the surface of a channel receptor • When open, channels allow flow of electrically charged ions, resulting in voltage change in a small area of the neuronal membrane (local potential) • Example: ion channels on dendritic spine (axodendritic synapse) 3. Voltage-gated channels • Open in response an electrical potential (i.e. voltage) change on the cell membrane • Found at axon hillock and along the axon Voltage-gated channel example Key point of understanding! Action potential vs Local potential Action Potential • Nerve signal propagated along the axon (using voltage-gated channels) • All-or-none response • Unidirectional (axon hillock  axon terminals) • Leads to Neurotransmitt er release depends on Calcium Local Potential Another Local Potential Example: Receptor Potential No summation Spatial Summation Spatial Temporal Temporal Summation Firing frequency: our nerves communicate based on the rate of action potentials. Example: magnitude of muscle contraction is influenced by the frequency of action potentials (Muscle force output) Various firing rates of motor neurons on a muscle Basic forms of neural plasticity Excitatory neuron • Presynaptic facilitation • Axo-axonic synapse Inhibitory neuron • Presynaptic inhibition • Axo-axonic synapse Cellular forms of plasticity – Cellular learning Non-associative learning • Short-term, reversible response by a neuron in response to repeated exposure to a stimulus 1. Habituation • Synapse becomes less efficient with repeated exposure to a stimulus • causes decrease in release of excitatory neurotransmitters 2. Sensitization • Process by which a synapse becomes more efficient in response to a stimulus • Can be in PNS or CNS* • Example: release of prostaglandins inflammatory proteins) can make sensory neurons more sensitive to chemical or electrical (voltage) stimuli • Non-associative learning puppy training examples? Cellular forms of plasticity – Cellular learning Associative Learning • Experience-dependent plasticity • Long-term potentiation (LTP) • Persistent strengthening of synapses leading to long lasting signal transmission between neurons • Key component in development of human memory • Long-term depression (LTD) • Opposite of LTD • What might be a benefit of LTD? • Associative learning puppy training example? Think back to the patient, Holly: What signal was Holly’s muscles lacking shortly after GBS? (explain in terms of action potential firing rate) Why? (explain in terms of myelin and neurotransmitters)