FSG 280 2021 lecture 5. Neurophysiology.

Neurophysiology.

1. UNIY!IIIT!IT YAM PIUOIIA UNIYEIIITY OF PRETORIA YUNIIESITHI YA PRETORIA FSG 280 Neurophysiology Lecture 5 Dr Y Hlophe [email protected] Department of Physiology, University of Pretoria

2. Study unit 2.6 Autonomic and Somatic motor control Human Physiology an integrated approach chapter 11

3. Autonomic Nervous System ANS is part of the nervous system responsible for homeostasis Regulates body temperature Fluid and electrolyte balance Blood pressure Innervates visceral organs Heart Lungs Glands (sweat and salivary) Blood vessels Bladder Includes enteric nervous system in gastrointestinal tract Contains sensory, inter and motor neurons Contains as many neurons as spinal cord

4. Autonomic Nervous System ANS has two divisions Sympathetic (excitatory) Parasympathetic (inhibitory) Each has a preganglionic and a postganglionic division Antagonistic effect

5. Sympathetic Division Sympathetic nervous system (prevail during stress) Nerve fibres leave CNS With spinal nerves (T1-L2) Thoracolumbar outflow Preganglionic fibres synapse in paravertebral ganglia Preganglionic fibres release acetylcholine Postganglionic fibres release norepinephrine

6. Sympathetic Division Adrenergic receptors (G protein- coupled receptors; 2 nd messenger activity): Alpha Alpha1 (muscle contraction) Alpha2 (smooth muscle relaxation) Beta ( differ in catecholamine affinity) B1 (norepinephrine + epinephrine) B2 (sensitive to epinephrine) B3 (sensitive to norepinephrine)

7. Sympathetic Division

8. Sympathetic Division There are preganglionic neurons whose axons terminate directly on the effector organ (target tissue) Adrenal gland Adrenal Medulla acts as a sympathetic ganglion Pre-ganglionic neuron synapses with chromaffin cells (in adrenal medulla) They in turn release neurotransmitter into blood vasculature Norepinephrine/Noradrenalin Epinephrine/Adrenalin Necessary during Exercise Stressful situations

9. Parasympathetic Division Parasympathetic nervous system (prevail during rest) Leave CNS Cranial nerve III, VII, IX, X Spinal nerves Sacral nerves (S2-S4) Craniosacral outflow Vagus (X cranial nerve) Supplies thorax

10. Parasympathetic Division Preganglionic fibres synapse terminal ganglia Release Ach Postganglionic fibres release Acetylcholine ( Ach) Enzyme activity Acetylcholinesterase

11. Neurotransmission

12. Neurotransmission

13. Neurotransmission A number of autonomic neurons do NOT secrete norepinephrine nor acetylcholine Nonadrenergic neurons Noncholinergic neurons Substance P Somatostatin Nitric oxide ATP Vasoactive intestinal peptide (VIP) Synapse between postganglionic autonomic neuron and target cell Neuroeffector junction Autonomic postganglionic axons at distal endings (enlarged and swollen) Varicosity Contains vesicles filled with neurotransmitter Can be assigned to either the sympathetic or parasympathetic branch according to where their preganglionic fibres leave the CNS.

14. Autonomic Nervous System

15. Neurotransmission Direct agonists and antagonists Bind target receptor to either Block/mimic neurotransmitter action Direct antagonist Beta blockers Indirect agonists and antagonists Alter secretion, reuptake and degradation of neurotransmitters Indirect agonist Cocaine Cholinesterase inhibitors Serotonin reuptake inhibitors

16. Somatic Motor Division

17. Somatic Motor System

18. Motor System Single efferent neuron Leaves CNS via ventral horn towards target tissue (Skeletal muscle) Synapse of somatic motor neuron on muscle fibre = neuromuscular junction Somatic efferent neuron vesicles release acetylcholine (Ach) Ach taken up by nicotinic Ach receptors Acetylcholine esterase inactivates Ach (by degrading it) The esterase is in high concentration at cholinergic nerve ending Inhibits contraction of skeletal muscles

19. Motor Cerebral Cortex Precentral gyrus , posterior section of the frontal lobe . Site of primary motor cortex

20. Motor Homunculus Coronal section through the Precentral gyrus

21. Upper and Lower Motor Neurons References: http://www.kenzanweb.com/upper-and-lower-motor-neurons

22. Somatic Motor System Motor pathway From CNS to muscles All motor tracts in CNS are directed towards: Lower motorneurons All motor neurons involved in the CNS motor tracts are called: Upper motorneurons

23. Direct (pyramidal/corticospinal) pathway

24. Controls movement of axial muscles (of the trunk), oblique and rectus muscles Somatic Motor System

25. Corticospinal pathway Lateral corticospinal pathway Voluntary movement Anterior corticospinal pathway From the cerebral cortex, descending to the thalamus, brain stem and finally spinal cord Fibres that end in the brain stem ( corticobulbar tracts ) Mainly from motor head muscles (larynx, tongue, of eye movement )

26. Indirect (extrapyramidal/extracorticospinal) pathway Includes motor pathways not part of the pyramidal pathway Upper motor neuron (UMN) originate in deep nuclei in the cerebrum not the cerebral cortex UMN does not pass through the pyramids The system includes: Rubrospinal Vestibulospinal Reticulospinal Tectospinal tracts Regulate: Axial muscles that maintain balance and posture Muscles controlling course movement of the proximal portions of limbs Head, neck and eye movement Involuntary movement

27. Cerebellum Vestibulocerebellum: Concerned with equilibrium and eye movement Spinocerebellum: Receives proprioceptive input from the body I nteracts with medial and lateral descending systems C rucial for motor execution Cerebrocerebellum: Interacts with the motor cortex in planning and programming movements Reference: Functional divisions of the cerebellum. Principles of Neural Science 4th ed.McGraw-Hill,2000.

28. Basal Ganglia Five divisions of the Basal Ganglia: Caudate nucleus Putamen Globus Pallidus Subthalamic nucleus Substantia nigra Neurons in the Basal Ganglia discharge before movements begin Dopaminergic, cholinergic and GABAergic system travel from the striatum to the substantia nigra Involved in planning and programming of movement Striatum Lenticular nucleus