4Organization of Spinal Nerves Every spinal cord segment:is connected to a pair of spinal nervesEvery spinal nerve:is surrounded by 3 connective tissue layersthat support structures and contain blood vessels
53 Connective Tissue Layers Epineurium:outermost layerdense network of collagen fibersPerineurium:middle layerdivides nerve into fascicles (axon bundles)Endoneurium:inner layersurrounds individual axons
6Peripheral Nerves Interconnecting branches of spinal nerves Surrounded by connective tissue sheaths
7How does the distribution pattern of spinal nerves relate to the regions they innervate?
8Peripheral Distribution of Spinal Nerves form lateral to intervertebral foramenwhere dorsal and ventral roots unitethen branch and form pathways to destination
9Nerve Plexuses Contain no synapses! For pre-midterm (Summarized in tables in text and lab guide):Know cord roots (“ventral rami,” actually) that contribute to the plexusKnow the names of the major peripheral nerves that each plexus gives rise to.3D Rotation of Peripheral Nerves and Nerve PlexusesPLAYFigure 13–9
25Development of Reflexes A reflex is a rapid, predictable motor response to a stimulus.Innate reflexes are unlearned and involuntaryAcquired reflexes are complex, learned motor patterns
26Nature of Reflex Responses Somatic: Reflexes involving skeletal muscles and somatic motor neurons.Autonomic (visceral) Reflexes controlled by autonomic neuronsHeart rate, respiration, digestion, urination, etcSpinal reflexes are integrated within the spinal cord gray matter while cranial reflexes are integrated in the brain.Reflexes may be monosynaptic or polysynaptic
28Components of a Reflex Arc 1. Activation of a Receptor: site of stimulus2. Activation of a Sensory Neuron: transmits the afferent impulse to spinal cord (CNS)3. Information processing at the Integration center: synapses (monosynaptic reflexes) or interneurons (polysynaptic) between the sensory and motor neurons.In CNSSpinal reflexes or cranial reflexes
29Components of a Reflex Arc 4. Activation of a Motor Neuron: transmits the efferent impulse to effector organ5. Response of a peripheral Effector: Muscle or gland that responds
32Stretch Reflexes1. Stretching of the muscle activates a muscle spindle (receptor)2. An impulse is transmitted by afferent fibers to the spinal cord3. Motor neurons in the spinal cord cause the stretched muscle to contract4. The integration area in the spinal cordPolysynaptic reflex arc to antagonist muscle causing it to to relax (reciprocal innervation)
34Stretch Reflex Example Patellar Reflex Tap the patellar tendonmuscle spindle signals stretch of musclemotor neuron activated & muscle contractsQuadriceps muscle contractsHamstring muscle is inhibited (relaxes)Reciprocal innervation (polysynaptic- interneuron)antagonistic muscles relax as part of reflexLower leg kicks forwardDemonstrates sensory and motor connections between muscle and spinal cord are intact.
35Tendon ReflexesMonitors external tension produced during muscular contraction to prevent tendon damageControls muscle tension by causing muscle relaxationGolgi tendon organs in tendon (sensory receptor)activated by stretching of tendoninhibitory neuron is stimulatedmotor neuron is hyperpolarized and muscle relaxesBoth tendon & muscle are protectedReciprocal innervation (polysynaptic)causes contractionMartini pg 443 states the receptor is unidentified; this is incorrect.
37Flexor Reflex Withdrawal reflex When pain receptors are activated it causes automatic withdrawal of the threatened body part.
38Flexor (Withdrawal) Reflex Is this a monosynaptic or a polysynaptic reflex?Is this an ipsilateral or a contralateral reflex?
39Crossed Extensor Reflex Complex reflex that consists of an ipsilateral withdrawal reflex and a contralateral extensor reflexThis keeps you from falling over, for example if you step on something painful. When you pull your foot back, the other leg responds to hold you up.
41Superficial Reflexes Elicited by gentle cutaneous stimulation Important because they involve upper motor pathways (brain) in addition to spinal cord neurons
42Superficial Reflexes Plantar Reflex Tests spinal cord from L4 to S2Indirectly determines if the corticospinal tracts of the brain are workingDraw a blunt object downward along the lateral aspect of the plantar surface (sole of foot)Normal: Downward flexion (curling) of toes
44Abnormal Plantar Reflex: Babinski’s Sign Great toe dorsiflexes (points up) and the smaller toes fan laterallyHappens if the primary motor cortex or corticospinal tract is damagedNormal in infants up to one year old because their nervous system is not completely myelinated.
49Visceral Reflex ArcReceptor Sensory neuron Processing center interneuron(s)1 or 2 visceral motor neuronsPre- and post-synaptic neurons (long reflex)Just a post-synaptic neuron (short reflex)
50Long ReflexesAutonomic equivalents (target visceral effectors) of polysynaptic somatic reflexesCoordinate activities of the entire organVisceral sensory neurons deliver information to CNS along dorsal roots of spinal nerves:within sensory branches of cranial nerveswithin autonomic nerves that innervate visceral effectors
51Short Reflexes Bypass CNS Involve 1 small part of target organ Involve sensory neurons and interneurons located within autonomic gangliaInterneurons synapse on ganglionic neuronsMotor commands distributed by postganglionic fibersControl simple motor responses with localized effects
52Case of the Woman with HT Name the two parts of the ANSDescribe the two major groups of receptors and their subtypes (and their usual ligands.)Distinguish between receptor stimulation and cell stimulation.Explain what “specificity” means when we are referring to a ligand’s specificity for receptors.Provide a background for studying examples of somatic and autonomic reflexes.
64The Lumbar Plexus Includes ventral rami of spinal nerves T12–L4 Major nerves:genitofemoral nervelateral femoral cutaneous nervefemoral nerve
65The Sacral Plexus Includes ventral rami of spinal nerves L4–S4 Major nerves:pudendal nervesciatic nerveBranches of sciatic nerve:fibular nervetibial nerve
66Summary: Lumbar and Sacral Plexuses Table 13-3 (1 of 2)
67Summary: Lumbar and Sacral Plexuses Table 13-3 (2 of 2)
68Medical Example: Poliomyelitis Polio means gray matterVirus causes inflammation of the gray matter in the anterior horn motor neurons.Results in paralysis which could kill a patient if it reaches the respiratory musclesPatients who recover have permanent weakness or paralysis in parts of the body (usually the legs)
69Lou Gehrig’s Disease Amyotrophic Lateral Sclerosis ALS is a genetic disease that causes progressive destruction of anterior horn motor neurons.Leads to paralysis and death within 5 years.Stephen Hawking has this disease.
70Medical Example: Shingles Post-Viral inflammation of the sensory nervesRash follows dermatomes.Notice it does not cross the midline.
71The Babinski Reflexes Normal in infants May indicate CNS damage in adultsFigure 13–19