Presentation on theme: "The Spinal Cord and Spinal Nerves"— Presentation transcript:
1The Spinal Cord and Spinal Nerves Chapter 13The Spinal Cord and Spinal Nerves
2Functions of the nervous system Sensory (input):LightSoundTouchTemperatureTasteSmellInternal ChemicalPressureStretch
3Functions of the nervous system (cont’d) Integration:Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope).Motor (output):The response to the sensory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.
6The Spinal Cord & Nerves The spinal cord is part of the Central Nervous System.The spinal nerves are part of the Peripheral Nervous System.The lowest level of integration occurs in the spinal cord and peripheral ganglia.
12White Matter in the Spinal Cord Fibers run in three directions – ascending, descending, and transverselyDivided into three funiculi (columns) – posterior, lateral, and anteriorEach funiculus contains several fiber tracksFiber tract names reveal their origin and destinationFiber tracts are composed of axons with similar functions
14Spinal nervesThirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the headThey are named according to their point of issue8 cervical (C1-C8)12 thoracic (T1-T12)5 Lumbar (L1-L5)5 Sacral (S1-S5)1 Coccygeal (C0)
16Spinal Nerve structure Each axon is also called a “nerve fiber”These are covered by an endoneuriumThe endoneurium is made of areolar c.t.Fibers are bundled into “fascicles”These are covered by perineuriumThis is an extension of the outer layer of collagen fibersNerves are bundles of fasciclesEach nerve is covered by dense irregular tissue of collagen fibers
17Components of the Peripheral Nervous System Motor pathwaysLeave the spinal cord via the ventral nerve roots.Have multipolar cell bodies found in the gray matter.Carry motor impulses to skeletal muscle (somatic pathways) and to glands, smooth muscle, the heart, organs, etc (autonomic pathways).Are also called efferent pathways.
19Components of the PNS Sensory Pathways Enter the cord via the dorsal roots.Have unipolar cell bodies found in the dorsal root ganglia.Carry sensory inputs into the CNS via the central processes of their axons. They begin at the general sensory receptors of the skin (somatic sensory) and internal organs (visceral sensory).Are also known as afferent pathways.Special sense will be covered in Chapter 17
23Nerve plexusesFibers travel to the periphery via several different routesEach muscle receives a nerve supply from more than one spinal nerveDamage to one spinal segment cannot completely paralyze a muscle
36Neural CircuitsDivergent – spread information from one source to several destinations.Examples: visual input being processed at a conscious level (the horizon is tilting) and a subconscious level (I adjust my body so that I don’t fall over).Convergent – multiple sources of input into one neuron.Examples: conscious – I contract my rectus femoris to step over a pile of dog poop. Unconscious – my rectus femoris automatically contracts as the bus moves
37Neural Circuits Serial – a series of neurons in a sequence. Example: Pain pathwaysParallel – Divergence followed by serial.Example – reflexes that result in a complex series of responses simultaneouslyReverberation – positive feedback loopsExamples – many of the complex processes of the brain.
38Reflexes Rapid, automatic responses to stimuli. Can be visceral (e.g. swallowing) or somatic (“knee-jerk”).Have little variability
40Components of a reflex arc Stimulus activates a receptor.Impulse travels along a sensory pathway.Integration occurs in an integration center (most often in the CNS)Impulse then travels by a motor pathway.An effector responds.
414 Classifications of Reflexes By early developmentBy type of motor responseBy complexity of neural circuitBy site of information processing
42Development How reflex was developed: innate reflexes: basic neural reflexesformed before birthacquired reflexes:rapid, automaticlearned motor patterns
43Response Nature of resulting motor response: somatic reflexes: involuntary control of nervous systemsuperficial reflexes of skin, mucous membranesstretch reflexes (deep tendon reflexes) e.g., patellar reflexvisceral reflexes (autonomic reflexes):control systems other than muscular system e.g., glands smooth muscle and cardiac muscle
44Complexity Complexity of neural circuit: monosynaptic reflex: sensory neuron synapses directly onto motor neuronpolysynaptic reflex:at least 1 interneuron between sensory neuron and motor neuron
45Processing Site of information processing: spinal reflexes: occurs in spinal cordcranial reflexes:occurs in brain
47Monosynaptic Reflexes Have least delay between sensory input and motor output:e.g., stretch reflex (such as patellar reflex)Completed in 20–40 msec
48Muscle Spindles The receptors in stretch reflexes Bundles of small, specialized intrafusal muscle fibers:innervated by sensory and motor neuronsSurrounded by extrafusal muscle fibers:which maintain tone and contract muscle
53The Tendon Reflex Prevents skeletal muscles from: developing too much tensiontearing or breaking tendonsSensory receptors unlike muscle spindles or proprioceptors
54Withdrawal ReflexesMove body part away from stimulus (pain or pressure):e.g., flexor reflex:pulls hand away from hot stoveStrength and extent of response:depends on intensity and location of stimulus
55Reflex Arcs Ipsilateral reflex arcs: Crossed extensor reflexes: occur on same side of body as stimulusstretch, tendon, and withdrawal reflexesCrossed extensor reflexes:involves a contralateral reflex arcoccurs on side opposite stimulus
575 General Characteristics of Polysynaptic Reflexes Involve pools of neuronsAre intersegmental in distributionInvolve reciprocal inhibitionHave reverberating circuits:which prolong reflexive motor responseSeveral reflexes cooperate:to produce coordinated, controlled response
58The Babinski Reflexes Normal in infants May indicate CNS damage in adultsThe Babinski ReflexesFigure 13–19
59Spinal Cord Trauma: Paralysis Paralysis – loss of motor functionFlaccid paralysis – severe damage to the ventral root or anterior horn cellsLower motor neurons are damaged and impulses do not reach musclesThere is no voluntary or involuntary control of muscles
60Spinal Cord Trauma: Paralysis Spastic paralysis – only upper motor neurons of the primary motor cortex are damagedSpinal neurons remain intact and muscles are stimulated irregularlyThere is no voluntary control of muscles
61Spinal Cord Trauma: Transection Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cutParaplegia – transection between T1 and L1Quadriplegia – transection in the cervical region
63PoliomyelitisDestruction of the anterior horn motor neurons by the poliovirusEarly symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexesVaccines are available and can prevent infection
65Amyotrophic Lateral Sclerosis (ALS) Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tractSymptoms – loss of the ability to speak, swallow, and breatheDeath often occurs within five yearsLinked to malfunctioning genes for glutamate transporter and/or superoxide dismutase
66Some Famous Victims of ALS Lou GehrigSteven Hawking,renowned physicist
67Axonal degeneration of motor neurons evident in lateral corticospinal (pyramidal) pathways, especially in the loss of myelinated fibers of the corticospinal tracts
68SUMMARY (1 of 7) General organization of nervous system: CNS, PNSGross anatomy of spinal cord:enlargements, dorsal and ventral roots, filum terminale, conus medullaris
69SUMMARY (2 of 7) Afferent (sensory) and efferent (motor) fibers Structures and functions of spinal meningesGray matter and horns of spinal cord
70SUMMARY (3 of 7) White matter and columns (tracts) of spinal cord 3 layers in spinal nervesDistribution (rami) of spinal nerves:white, gray, dorsal, ventral
71SUMMARY (4 of 7) 4 major nerve plexuses: cervical, brachial, lumbar, sacralNeuronal pools and neural circuit patterns:divergence, convergence, serial, parallel, reverberation
72SUMMARY (5 of 7) Reflexes and reflex arcs Classifications of reflexes: innate vs. acquiredsomatic vs. visceralcranial vs. spinalmonosynaptic, polysynaptic, or intersegmental
73SUMMARY (6 of 7) Characteristics of monosynaptic reflexes: stretch reflex, postural reflex, muscle spindlesCharacteristics of polysynaptic reflexes:tendon, withdrawal, flexor, and crossed extensor reflexes