Introduction to Pathophysiology and Cellular Basis of Disease Part 4

PERIPHERAL NERVOUS SYSTEM ● Cranial nerves - nerves that extend out from the brain ○ 12 pairs of cranial nerves (12 on both sides) ○ Some cranial nerves are entirely SENSORY ■ OLFACTORY I ■ OPTIC II ■ VESTIBULOCOCHLEAR VIII ● proprioception - inner ear, fluid that runs in multiple planes. Depends on what position your body is in, fluid shifts. Direction of fluid shift conveys to brain body position ○ Some are entirely MOTOR ■ OCULOMOTOR III ■ TROCHLEAR IV ■ ABDUCENS VI ■ FACIAL VII ■ ACCESSORY XI ■ HYPOGLOSSAL XII ○ Some are BOTH ■ TRIGEMINAL V ■ FACIAL VII ■ GLOSSOPHARYNGEAL IX ● Sensory - posterior ⅓ of tongue, tonsil, pharynx, middle ear ● Motor - stylopharyngeus, pharyngeal musculature ■ VAGUS X ● About 70% of the parasympathetic input to the body is conveyed through the vagus nerve (baseline, visceral function) ● Motor - pharynx, heart, lungs, bronchi, GI tract ● Sensory - heart, lungs, bronchi, trachea, larynx, pharynx, GI tract, external ear ● Spinal nerves - nerves that extend from spine ○ All but one pair of spinal nerves control both sensory and motor function ■ The exception at C1 (ALL SENSORY) ○ 31 pairs (31 on both sides) ■ ● ● ■ Meninges cover spinal nerve Spinal nerves are composed of fibers that run through: ○ VENTRAL ROOT - motor function ■ Controls skeletal muscle ■ Ventral = in front ○ DORSAL ROOT - sensory function ■ Dorsal root ganglia - Swelling at end of dorsal root ● Sensory neurons had strange shape to them - cell bodies were closer to axon terminal ● Ganglia is just all the cell bodies of sensory neurons Each set of spinal nerves responsible for diff region of body ● Sensory information towards spinal cord, motor commands away from spinal cord to muscles ● Dermatome map - maps out area of skin where sensation is conveyed by spinal nerve ● ● ○ Ex. shingles. Chicken pox → infected with virus (varicella). Even after you recover, most is eliminated, but some still remain in SPINAL CORD ○ If time of reduced immune function → varicella reemerges THROUGH A SPINAL NERVE ■ End up with region of lesions that conform to a dermatome ■ Common areas: middle of body (T9/10 on ONE SIDE. SHOULDN’T CROSS MIDLINE) ● If it crosses → not shingles ● Myotome map - maps muscle groups that are innovated by motor neurons coming out of each spinal nerve pair ○ Injury to a spinal nerve pair would cause impaired motor function in those corresponding muscle groups Ascending and Descending Tracts ■ ■ ■ ■ Vertebrae is made up of two different tissues: ● White matter (blue and green) ○ Composed of axon fibers. Myelination creates white color ○ Think of it vertically. Axons are either traveling UPWARD toward brain or DOWN the cord ● Gray matter ○ Cell bodies concentrate in gray matter (nuclear and cellular material creates the darker color) ○ Think of it in horizontal space. Cell bodies are literally sitting at a particular horizontal area within the spinal cord ○ Synapses/projections into and out of the gray matter Ascending tracks - sensory message move upward towards brain ● Present in DORSAL SURFACE (sensory) Descending tracks - efferent ● VENTRAL SURFACE ■ ● Gray matter: contains cell bodies of various efferent/afferent neurons ○ Towards dorsal surface = AFFERENT neuron’s cell body (ganglion root) comes in ■ SYNAPSES onto interneuron LOCATED IN DORSAL HORN. interneuron processes sensory info to diff places (ex. Crossing into white matter and moving up towards brain) ○ ○ In ventral = EFFERENT’s cell body ■ Cell body of Motor neurons. It will exit ventral horn and go and stimulate muscle ○ LATERAL HORN - where cell bodies belong to autonomic EFFERENT neurons ■ Controlled by autonomic system. Will project out to visceral organ to create effect ● Uses same pathway as ventral horn that motor neurons use ■ MOST CELL BODIES IN LATERAL HORN THROUGHOUT SPINAL CORD = SYMPATHETIC ■ DO NOT BECOME PART OF SPINAL NERVE WHEN VENTRAL ROOT AND DORSAL ROOT CONVERGES ● Diverges ○ When it diverges, what’s left is SYMPATHETIC CHAIN GANGLIA (structure of nerve fibers that runs lengthwise down vertebral column containing autonomic responses) Motor neuron pathway (ventral and dorsal roots) ■ Ex. Knee DTR. purely spinal. Doesn’t reach brain. Controlled by L2-L4 ● Vs. pain withdrawal reflex (hand on stove. pain). Sensory input must go to brain and sensory command must go back to hand ■ Initial stim: hammer on patellar ligament that’s connected to quad and pulls on quad (sensory fibers that wrap around skeletal muscle sense whenever there’s rapid stretching/tearing of muscle) → signals afferent impulses from stretch receptor to spinal cord (quad wants to oppose the stretching) → passes through dorsal root ganglia → synapses onto: ● Interneuron → interneuron synapses onto motor neuron serving antagonist muscle group (hamstrings) → goes to hamstring and causes INHIBITORY response → RELAX (allows it to stretch so quad can kick) ● Motor neuron serving quad (wants quad to not tear/stretch) → goes to quad and causes EXCITATORY response → CONTRACTION (reverses/resists the stretch) ■ ● ■ What’s missing? Interneuron that received SENSORY input will ALSO branch into white matter and move up information to alert the brain Ex. say a pt has spinal cord injury to T6 and no message/signal can get past it (efferent/afferent). Below T6 PARALYSIS ● Would Knee DTR still work? ○ Yes because it doesn’t require any input from brain. PT CANNOT WATCH THOUGH AUTONOMIC NERVOUS SYSTEM ● The targets of ANS: smooth muscle that lines vasculature and viscera ○ Controls function of cardiac muscle ○ Controls function of both exocrine (secrete shit out to epithelial system) and endocrine glands (secrete into bloodstream) ○ ANS: parasympathetic (baseline function for ANS) and sympathetic responses (fight/flight) ■ Each arm has EFFERENT AND AFFERENT neurons ● Afferent - relaying to brain baseline/ongoing conditions of visceral function (BP, HR, RR, etc) ● Basic organization of ANS (symp/parasymp) ○ EFFERENT ARM ■ Two cells and two synapses ■ First cell body resides in CNS (preganglionic neuron) → synapses onto second cell (postganglionic neuron) that sits outside CNS somewhere in a peripheral ganglion (collection of cell bodies/synapses/axon fibers that sit outside CNS) → postganglionic neuron sits inside one of the peripheral ganglion and synapses onto target cell (organs) ● ● SYMPATHETIC NERVOUS SYSTEM ○ Preganglionic neuron’s cell body sits in spinal cord (SPECIFICALLY in LATERAL HORN of spinal cord between levels T1-L3) → project out towards SYMPATHETIC GANGLIONIC CHAIN for the FIRST SYNAPSE onto postganglionic neuron (which is called the PARAVERTEBRAL GANGLIA-bc it runs down both sides of vertebral column) ■ Exception to this: some preganglionic cell pass through and make FIRST SYNAPSE at PREVERTEBRAL GANGLIA (postganglion cells are more distal than sympathetic chain), consists of: ● Celiac ganglion ● Hypogastric plexus ■ All postganglionic cells project to target cells (organs) ○ EXCEPTION TO 2 CELL, 2 SYNAPSE ARRANGEMENT ■ ENDOCRINE PORTION OF THE SYMPATHETIC NERVOUS SYSTEM ● Preganglionic cell of sympathetic system extend FROM SPINAL CORDand directly innervate the adrenal medulla (inner portion of the adrenal gland) ● ● Adrenal medulla releases hormone, EPINEPHRINE into bloodstream and that targets organs PARASYMPATHETIC NERVOUS SYSTEM ○ Structure is 2 cell 2 synapse, but location is different, ○ Preganglionic cell bodies sit in ■ MIDBRAIN and MEDULLA → extend out of brain through CRANIAL NERVES (3, 7, 9, 10) KNOW!!! ● Vagus nerve is important for parasympathetic nervous system, branches out both sides, conveys 70% of parasympathetic nervous system ■ Originate SPINAL CORD T12-L1 (SACRUM) ● Leave vertebral column within the sacral portion between SACRAL LEVEL 2-4 ○ These affect the function of: ■ Bladder function ■ Anal sphincter function ○ Postganglionic cells are very small and distal, some close to target organ ■ Ex. cardiac plexus. Located near aortic arch of heart, extends out of the heart ● ● NEUROTRANSMITTERS OF ANS ○ Acetylcholine ■ Anything that releases ACh = cholinergic ○ Norepinephrine ■ Anything that releases NE = adrenergic ○ Parasympathetic ■ Preganglionic cell synapses and releases ACh to NICOTINIC RECEPTOR (N2 RECEPTOR) close to target cell → N2 Rec releases ACh to MUSCARINIC RECEPTOR (M RECEPTOR) ○ Sympathetic ■ 1) Pregang cell synapses and releases ACh to N2 REC at peripheral neurons → postgang synapses to target cell at ALPHA and BETA adrenergic receptors and releases NE ● Alpha 1 rec - receptors predominantly on SMOOTH MUSCLE of vasculature (BLOOD VESSELS of organs) ○ ● ● ● ● vasoCONSTRICTION, DILATATION OF INTESTINAL (relaxation), contracts sphincter of bladder ■ Blood vessels of SMOOTH MUSCLE → BETA 2 RECEPTORS Beta 1 rec - receptors found on CARDIAC MUSCLE ○ INCREASE IN: ■ HR, contraction strength, Beta 2 rec ○ receptors found on bronchioles in lungs ■ vasoDILATION ○ Receptors found on bladder ■ When Epinephrine and NE → smooth muscle wall of BLADDER WILL RELAX ● ■ 2) Adrenal medulla. Pregang synapses to adrenal medulla and releases ACh to N2 REC → adrenal medulla releases neurotransmitters into bloodstream Targets of innervation for both para/sympathetic ○ Both systems usually target same organs. Usually have antagonistic effects on the target ■ EXCEPTION: ● SYMPATHETIC ○ Kidney is only innervated by symp ○ AUTONOMIC TONE → the volume of stimulation being supplied to target organ ■ Both systems provide some degree of tone to all organs. DON’T EQUAL IN STRENGTH. ● RESTING - more parasympathetic tone than symp ● STRESS - more symp tone than parasymp Parts of brain that controls EFFERENT commands to organs ○ Hypothalamus and brainstem ■ ■ ● Hypothalamus: heat, water balance, appetite/feeding Brainstem: urinary, respiratory, cardiovascular control