Neural Physiology

Anatomical organization One system – Two subdivisions CNS Peripheral

Anatomical organization Central (CNS) – Brain – Spinal cord – Function Integration of information Generation of memory Control of various systems Mental activity

Anatomical organization Peripheral – Sensory receptors Detection of various sensations – Nerves Conduits between sensory receptors and CNS – Ganglia Cluster of nerve cells located outside of the spinal cord – Plexus Network of neurons and axons located outside of the CNS

Anatomical organization Nerves – Cranial 12 pairs – Spinal 31 pairs

Afferent and efferent nerves – Afferent/sensory Transmission of signals from sensory receptors to the CNS Entry route – Dorsal horn of the spinal cord – Efferent/motor Transmission of information from the CNS to the organs – Motor neurons Transmission routre – Ventral horn of the spinal cord

Autonomic nervous system (ANS) Two divisions – Sympathetic – Parasympathetic Enteric (not exactly a division of the ANS) – Regulation of the GI tract function Plexuses

Neural tissue Neural cell – Generation and reception of neural signal Action potential Glial cells – Support and protection

Types of neurons Multipolar – Many dendrites – Single axon Bipolar – Single dendrite – Single axon Unipolar – No dendrite – Single axon

Glial cells within the CNS Functions – Fluid secretion and composition maintenance CSF by ependymal cells Brain fluid by astrocytes – Formation of barrier Blood-brain barrier by astrocytes – Response to inflammation Reactive astrocytes Microglia – Insulation of axon Myelin sheath by origodendrocytes

Glial cells in the PNS Schwann cells – Myelin sheath production Satellite cells – Support and protection of the cell body

Myelination Myelin sheath – Insulation of axon – Increased transmission speed Saltatory conduction from one node of Ranvier to the next – Greater the thickness of sheath, faster the conduction

Nerve tissue organization White matter – Bundles of myelinated axons Neural tracts Propagation of action potential from one area to the next – Neural cells and dendrites Gray matter – Bundle of unmyelinated axons – Neural cells and dendrites – Integration and relaying of signals

Transmission of neural signal Action potential – Exactly the same principle as the AP in the muscular system Propagation – Across the entire length of the axon One direction

Generation of action potential – Unmyelinated Same as muscle – Myelinated At node of Ranvier – Concentrated ion channels

Saltatory conduction

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Classification of nerve fiber Basis – Functional specialization Rapid transmission (motor neurons) = type A Homeostasis/ANS = type B and type C (unmyelinated) – Diameter of axon – Myelination

Rate of action potential conduction – Myelination Faster conduction AP generated only at node of Ranvier Effects of axon diameter – Larger the diameter, faster the conduction Greater surface area for Na channels

Synapse Junction between two cells – Communication Nerve cells Nerve cell and effector organs – Presynaptic Send signals – Postsynaptic Receive signals

Types – Electrical Rare (retina) Conduct signals via ion flow from one cell to the next – Connexon – Chemical Common Conduct signals via neurotransmitter

Steps of neural transmission 1.Arrival of action potential to the presynaptic terminal a.Increased flow of Ca ions 2.Release of neurotransmitter a.Increased intracellular Ca level 3.Binding of neurotransmitters to the Na channels a. Depolarization of postsynaptic membrane 4.Generation of local action potential 5.Propagation of action potential

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Neurotransmitters Classes – Acetylchorine – Biogenic amines – Amino acids – Purines – Neuropeptides – Gases

Neurotransmitter action – Specific receptor for the specific neurotransmitter – Response Stimulatory (AP generation) Inhibitory (hyperpolarization) Depends on types of receptors present on the cell

Regulation of neurotransmitter level Rapid removal – Acetylchorinesterase Removal of acetylchorine – Monoamine oxidase Removal of norepinephrine

Neuromodulator – Influence generation of postsynaptic action potential Presynaptic influence Postsynaptic influence – Affects type of neurotransmitter being released

Excitatory vs. Inhibitory postsynaptic potential Response of postsynaptic terminal to a neurotransmitter – Depolarization Excitatory postsynaptic potential Excitatory presynaptic neuron – Hyperpolarization Inhibitory postsynaptic potential – Increased K or Cl permeability Inhibitory presynaptic neuron

Presynaptic facilitation vs. inhibition Anoaxonic synapses – Affects release of neurotransmitter – Facilitation Increased release – Inhibition Decreased release

Summation Generation of action potential – One presynaptic AP is not enough Summation Temporal – Multiple AP from single presynaptic terminal Facilitation for AP generation by the subsequent Aps Spatial – AP from multiple axons

Generation of action potential – Excitatory vs. inhibitory stimulation Depends on summation of stimulation by these fibers

Importance of synapses within the CNS – Integration of information Sensory input must be strong enough to generate AP If not, ignored – Large amount of information entering the CNS Discarded

Neural pathway and circuit Convergent – Activation/inhibition of neural activity by combining various information Divergent – Simultaneous control of different system by a single neural input Circulatory – Repeated stimulation/inhibition of the same pathway by a single neural input Afterdischarge