Unit IV: Coordination Impulse Transmission Ch. 11 – pgs 373-389 Ch. 14 – pgs 471-487

Review What is the CSF and what are the three functions it provides? Which way is caudal? Which is not a region the spinal nerves are named for? a.) cervical, b.) thoracic, c.) pelvic, d.) lumbar, e.) sacral How does the location of white and gray matter differ in the spinal cord compared to the cerebrum? The formation of the blood-brain barrier is stimulated by which glial cells? _____ are folds that increase surface. By increasing surface area, they allow for more ___________.

Initiation of Nerve Impulses Resting Membrane Potential ICF relative to ECF – electrical potential Polarized Requires use of ATP Created by Na+-K+ pumps ECF ICF Na+ channel K+ Na+ 145 mEq/L K+ 4 mEq/L Na+ 12 mEq/L K+ 150 mEq/L Large anions that cannot escape cell

Initiation of Nerve Impulses Action Potentials Na+ gate opens; K+ gate begins to open; depolarization begins Na+ gate closes; K+ gate opens fully; repolarization begins Both Na+ gate and K+ gate closed; repolarization complete.

Initiation of Nerve Impulses Types of gated channels: Chemical gated channel Voltage gated channel Extracellular fluid Plasma membrane Cytosol Gated channel (closed) Resting state Arrival of ACh Binding site Gated channel opens ACh Channel inactivated Channel closed Channel open Inactivation gate Activation

Initiation of Nerve Impulses Notes Threshold – Depolarization – Refractory period – Action Potentials – follow an All or Nothing Law are nondecremantal are irreversible Resting potential Graded Presynaptic neuron stimulus produces may produce Action potential Postsynaptic cell triggers Information processing Synaptic activity

Conduction of Nerve Impulses Notes Unmyelinated fibers – continuous propagation Myelinated fibers – ions exchanged only at nodes of Ranvier Saltatory propagation + + – – (a) (b) Na+inflow at node generates action potential (slow but nondecremental) Na+ diffuses along inside of axolemma to next node (fast but decremental) Excitation of voltage- regulated gates will generate next action potential here Action potential in progress Refractory membrane Excitable

Synaptic Transmission Chemical Synapse Structure Synaptic knob Synaptic vesicles Synaptic cleft 20-40nm gap Neurotransmitter receptors

Synaptic Transmission Synaptic delay (0.5 msec) Classes of Neurotransmitters Excitatory, inhibitory, neuromuscular junction 3 kinds of synapses: Excitatory cholinergic synapse = ACh Inhibitory GABA-ergic synapse = GABA Excitatory adrenergic synapse = NE

Excitatory Cholinergic Synapse Mitochondrion Acetylcholine Synaptic vesicle SYNAPTIC KNOB CLEFT POSTSYNAPTIC MEMBRANE Choline Acetate Acetylcholinesterase (AChE) ACh receptor CoA Acetyl-CoA Nerve signal opens voltage-gated calcium channels in synaptic knob Ca+ triggers release of neurotransmitter. ACh binds to sodium channel receptors producing a graded depolarization. ACh is broken down into acetate and choline by AChE. Choline is reabsorbed and used to synthesize new molecules of ACh. 1 2 3 4 5

Inhibitory GABA-ergic Synapse Nerve signal triggers release of neurotransmitters Receptors trigger opening of Cl- channels Postsynaptic neuron now less likely to reach threshold

Excitatory Adrenergic Synapse Acts through 2nd messenger systems (cAMP) cAMP has multiple effects binds to ion gate inside of membrane turn metabolic pathways on/off induces genetic transcription Its advantage is enzymatic amplification Presynaptic neuron Postsynaptic neuron Neurotransmitter receptor Norepinephrine Adenylate cyclase G protein – – – + + + 1 2 3 Ligand- regulated gates opened 5 ATP Na+ cAMP 4 Postsynaptic potential Multiple possible effects Enzyme activation 6 7 Metabolic changes Genetic transcription Enzyme synthesis

Cessation of the Signal Stop signal in presynaptic neuron Mechanisms to “turn off” the signal diffusion of neurotransmitter into ECF synaptic knob reabsorbs neurotransmitters degradation of neurotransmitters in synaptic cleft Acetylcholinesterase Adrenalate cyclase

Postsynaptic Potentials Excitatory postsynaptic potentials (EPSP) a positive voltage change = more likely to fire Inhibitory postsynaptic potentials (IPSP) a negative voltage change = less likely to fire Summation – net postsynaptic potentials Temporal Summation Initial segment Threshold reached ACTION POTENTIAL PROPAGATION FIRST STIMULUS SECOND Spatial Summation TWO SIMULTANEOUS STIMULI ACTION POTENTIAL PROPAGATION Threshold reached

Peripheral Nervous System Consists of spinal and cranial nerves Sensory (afferent) Division Somatic Sensory Division Visceral Sensory Division Motor (efferent) Division Somatic Motor Division Visceral Motor Division (Autonomic Nervous System) Sympathetic Division Parasympathetic Division Enteric Division

Motor Division Autonomic vs. Somatic Reflex Arcs 1. ANS = 2 neurons from CNS to effectors preganglionic neuron - cell body in CNS postganglionic neuron - cell body in peripheral ganglion

Motor Division Autonomic vs. Somatic Reflex Arcs 2. Autonomic effectors function in absence of stimulation 3. Autonomic stimulation can be excitatory or inhibitory 4. Autonomic control is usually involuntary 5. Autonomic effectors are smooth and cardiac muscle, glands 6. Autonomic integrative center in hypothalamus

Autonomic Nervous System Sympathetic Division Origin in thoracolumbar region Short preganglionic fibers, long postganglionic fibers Synapses at paravertebral ganglia 17 postganglionic neurons for every preganglionic neuron Mass activation “Fight or Flight” Associated with adrenal glands Stimulate the release of neurotransmitters

Sympathetic Efferent Pathways PONS Eye Salivary glands Heart Lung Liver and gallbladder Stomach Spleen Pancreas Large intestine Small Adrenal medulla Kidney Urinary bladder Scrotum Penis Uterus Ovary Inferior mesenteric ganglion Superior mesenteric Celiac ganglion Cardiac and pulmonary plexuses T1 L2 Spinal cord Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) Sympathetic chain ganglia Preganglionic neurons KEY Post-Ganglionic neurons Sympathetic Efferent Pathways

Autonomic Nervous System Parasympathetic Division Origin in craniosacral region Long preganglionic fibers, short postganglionic fibers Synapses at terminal ganglion 2 postganglionic neurons for every preganglionic neuron Specific and local effects “Rest and Digest”

Parasympathetic Efferent Pathways Spinal cord S2 S3 S4 Uterus Ovary Penis Scrotum Liver and gallbladder Stomach Spleen Pancreas Large intestine Small Kidney Urinary bladder Rectum Eye Salivary glands Heart Lungs Hypogastric plexus Inferior mesenteric Celiac plexus Cardiac plexus Vagus nerve (X), which provides about 75% of all parasympathetic outflow PONS Otic ganglion Submandibular ganglion Ciliary ganglion Pterygopalatine ganglion III VII IX Lacrimal gland Preganglionic neurons KEY Ganglionic neurons

Innervation Dual Innervation Antagonistic Effect Cooperative Effects Brain Dual Innervation Antagonistic Effect Cooperative Effects Parasympathetic fibers of oculomotor nerve (III) Sympathetic fibers Superior cervical ganglion Ciliary ganglion Spinal cord Cholinergic stimulation of pupillary constrictor Iris Adrenergic stimulation of pupillary dilator Pupil Sympathetic (adrenergic) effect Parasympathetic (cholinergic) effect Pupil dilated Pupil constricted

Innervation Control without dual innervation Some targets receive only sympathetic fibers Sympathetic tone Artery 1 Sympathetic nerve fiber 1 Strong sympathetic tone 2 2 Smooth muscle contraction 3 Vasomotor tone 3 Vasoconstriction (a) Vasoconstriction 1 1 Weaker sympathetic tone 2 2 Smooth muscle relaxation 3 3 Vasodilation (b) Vasodilation