Neuron Physiology

Nervous System Organization  CNS - Brain and spinal cord  PNS - Nerves and Receptors  Somatic  Autonomic - sympathetic and parasympathetic  Enteric - GI tract  CNS - Brain and spinal cord  PNS - Nerves and Receptors  Somatic  Autonomic - sympathetic and parasympathetic  Enteric - GI tract

Cells in Nervous Tissue  Glial cells - support cells (Schwann cells, Oligodendrocytes, Astrocytes, etc.)  Neurons  Structural - Multipolar, Bipolar, Unipolar  Functional - Sensory, Motor, Interneuron  Glial cells - support cells (Schwann cells, Oligodendrocytes, Astrocytes, etc.)  Neurons  Structural - Multipolar, Bipolar, Unipolar  Functional - Sensory, Motor, Interneuron

Neuroglia Smaller than neurons 5-50x more numerous Can multiply and divide Do not send action potentials

Neuroglia Astrocytes – Blood-brain barrier, may help form synapses, chemical balance Oligodendrocytes – Myelin sheaths in CNS Microglia – Phagocytes Ependymal Cells – Produce and circulate CSF, Blood-CSF barrier Schwann Cells – Myelin sheaths in PNS Satellite Cells – Structural support and exchange with cell bodies in PNS

Most of Brain and spinal cord Retina, inner ear, Olfactory area in brain Sensory neurons

Electrical signals  Graded potentials - short distance  Action potentials - short and long  Graded  Action  Membrane potential called resting membrane potential in excitable cells  Ion flow = electric current  Graded potentials - short distance  Action potentials - short and long  Graded  Action  Membrane potential called resting membrane potential in excitable cells  Ion flow = electric current

Ion Channels  Leakage channel  Voltage-gated channel  Ligand-gated channel (direct or indirect)  Mechanically-gated channel  Leakage channel  Voltage-gated channel  Ligand-gated channel (direct or indirect)  Mechanically-gated channel

Action potentials

Myelination

Propagation

Graded vs. Action potentials  Dendrites/Cell body  Ligand-gated/Mech- gated channels  Localized  Variable amplitude  Longer duration  Hyper- or depolarizing  No refractory period  Dendrites/Cell body  Ligand-gated/Mech- gated channels  Localized  Variable amplitude  Longer duration  Hyper- or depolarizing  No refractory period  Axon  Voltage-gated channels  Propagated  All or nothing  Shorter duration  Depolarizing then repolarizing  Refractory GradedAction

Synapses

Postsynaptic potentials  Excitatory (EPSP)  Depolarization  Action potential easier to generate  Inhibitory (IPSP)  Hyperpolarization  Action potential more difficult (membrane more negative than usual)  Excitatory (EPSP)  Depolarization  Action potential easier to generate  Inhibitory (IPSP)  Hyperpolarization  Action potential more difficult (membrane more negative than usual)

Summation  Integration of multiple inputs at trigger zone  Spatial - Multiple presynaptic neurons simultaneously  Temporal - Rapid and repeated stimulation from single presynaptic neuron  EPSPs  Threshold  Action potential  EPSPs  Threshold  Partial depolarization  Inhibitory  Excitatory = Hyperpolarization  Integration of multiple inputs at trigger zone  Spatial - Multiple presynaptic neurons simultaneously  Temporal - Rapid and repeated stimulation from single presynaptic neuron  EPSPs  Threshold  Action potential  EPSPs  Threshold  Partial depolarization  Inhibitory  Excitatory = Hyperpolarization

Neurotransmitters  Effects modified by stimulating or inhibiting:  Synthesis  Release  Receptor availability  Removal  Effects modified by stimulating or inhibiting:  Synthesis  Release  Receptor availability  Removal

Neurotransmitter Removal  Diffusion away from receptors  Enzyme degradation  Uptake via neurotransmitter transporters  Diffusion away from receptors  Enzyme degradation  Uptake via neurotransmitter transporters

Neural circuits  Functional groups of neurons  Types:  Simple series  Diverging  Converging  Functional groups of neurons  Types:  Simple series  Diverging  Converging

Gray and White Matter White matter = myelinated axons Gray matter = everything else! Unmyelinated axons Cell bodies and dendrites Neuroglia

Contrast: Ganglion – Collection of cell bodies in PNS Nuclei – Collection of cell bodies in CNS Tract – Bundles of axons in CNS Nerve – Bundles of axons in PNS

Nerves

Spinal Cord

Brain

Cerebrospinal fluid (CSF) Composition: Glucose, proteins, lactic acid, urea, ions, some WBCs Choroid plexuses and ependymal cells Protects from mechanical and chemical damage Circulates between ventricles and through subarachnoid space

Cerebrum Lateralized into hemispheres Cortex – outer gray matter Gyri – folds Sulci and fissures – grooves between gyri White matter Tracts between hemispheres, within the same hemisphere and between cerebrum and lower structures

Cerebrum

Lobes: Frontal – primary motor area, Broca’s area, Prefrontal cortex (mood, intellect, logic, personality, etc.) Parietal – Primary somatosensory area, gustation Temporal – Primary auditory area, olfaction Occipital – Primary visual area Insula

Lateralization

Basal Ganglia Regulates initiation and termination of movements Input from cortex, output to motor area Parkinson’s disease

Cerebellum Coordination of movements Posture and balance Corpora quadrigemina (coliculi)

Diencephelon Thalamus – Relay for sensory information; nuclei for movement control Epithalamus – pineal gland; emotional response to smells Hypothalamus – Controls ANS and pituitary; homeostasis; hormone production; body rhythms and behavioral patterns

Brain Stem Medulla oblongata – Relays information to and from brain; Reticular formation; Cardiovascular and respiratory centers Pons – Relay between cerebellar hemispheres; areas for breathing regulation

Autonomic Nervous System

What does it do? Regulation of smooth muscle, cardiac muscle and many glands Involuntary Sympathetic and parasympathetic

Dual Innervation Most organs receive innervation from both sympathetic and parasympathetic Autonomic tone = balance between divisions (regulated by hypothalamus)

Sympathetic responses E situations (Exercise, emergency, excitement, embarrassment) “Fight or flight” response includes: –Pupil dilation –Airway dilation –Increase in cardiac output and blood pressure –Reduced blood flow to kidney and GI tract –Increased blood flow to skeletal and cardiac muscle, liver, and adipose tissue –Increase in blood glucose level Longer lasting and more widespread effects than parasympathetic

Parasympath etic responses “Rest and digest” SLUDD –Salivation –Lacrimation –Urination –Digestion –Defecation Decreases in: –Heart rate –Airway diameter –Pupil diameter