BSC2085 Exam #4 “What You Should Know” 1 Lesson 16: The Spinal Cord and Nerves Describe the difference between the gray and white matter found in the spinal cord Gray Matter White Matter - Contains cell bodies of neurons, neuroglia, & unmyelinated axons - Surrounds central canal - Horns: Areas of gray matter on each side of spinal cord - Posterior, anterior, & lateral gray horns - Nuclei: Masses of gray matter within the CNS - Contains sensory & motor nuclei - Sensory nuclei = posterior/dorsal - Motor nuclei = anterior/ventral - Gray Commissure: Contain axons that cross from one side of the cord to the other - Contains large numbers of myelinated & unmyelinated axons - Divided into 3 columns - Posterior, anterior, & lateral white columns - Anterior White Commissure: A region where axons cross from one side of the spinal cord to the other - Each column contains tracts - Tract (Fasciculus): A bundle of axons in the CNS that is uniform in diameter, myelination, & conduction speed - All axons within a tract relay same type of info - Ascending Tracts: Carry sensory info to brain - Descending Tracts: Convey motor commands to spinal cord Explain the function of the gray horns of the spinal cord The gray horns contain the cell bodies of sensory & motor neurons and are organized into functional groups depending on the regions the motor neurons they contain control. Explain the function of the white columns of the spinal cord The white columns contain tracts, which are bundles of axons that relay the same type of information in the same direction. These tracts carry sensory information to the brain (ascending) and to convey motor commands to the spinal cord (descending). Describe the connective tissue layers covering the spinal nerves • Epineurium (outermost layer) o Dense network of collagen fibers • Perineurium (middle layer) o Connective tissue layer that divides the nerve into fascicles (bundles of axons) • Endoneurium (innermost layer) o Surrounds individual axonsBSC2085 Exam #4 “What You Should Know” 2 Describe the locations and function of the major nerve plexuses • Cervical Plexus o Consists of the ventral rami of spinal nerves C1-C5 o Branches innervate muscles of neck & extend into thoracic cavity Control diaphragmatic muscles o Phrenic nerve = major nerve of the cervical plexus Provides entire nerve supply to diaphragm o Other branches distributed to the skin of the neck & superior part of chest • Brachial Plexus o Innervates pectoral girdle & upper limb with ventral rami of spinal nerves C5-T1 o Nerves originate from trunks & cords Trunks: Large bundles of axons contributed by several spinal nerves Cords: Smaller branches that originate at trunks o Major nerves: Musculocutaneous nerve Median nerve Ulnar nerve Axillary nerve Radial nerve • Lumbar Plexus o Originates from lumbar segment of spinal cord o Contains axons from the ventral rami of spinal nerves T12-L4 o Supplies anterolateral abdominal wall, genitals, & lower limbs o Major nerves: Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve • Sacral Plexus o Contains axons from ventral rami of spinal nerves L4-S4 o Supplies buttocks, perineum, & lower limbs o Major nerves: Sciatic nerve • Fibular nerve • Tibial nerve Pudendal nerve Describe the five different patterns of neural circuits found in neuronal pools o 1. Divergence Spreads stimulation to many neurons or neuronal pools in CNS • Visual info goes to visual cortex & postural balance areas o 2. Convergence Brings input from many sources to single neuronBSC2085 Exam #4 “What You Should Know” 3 • Subconscious & conscious control of breathing o 3. Serial Processing Moves information in a single line • Relay of pain info o 4. Parallel Processing Moves same information along several paths simultaneously • Ex) Step onto nail, withdraw foot, shift weight, feel pain, scream o 5. Reverberation Positive feedback mechanism Functions until inhibited • May help maintain consciousness, muscle coordination, & normal breathing Lesson 17: Spinal Reflexes Explain what is a reflex and the components of the reflex arc. • Reflexes: Rapid, automatic responses to specific stimuli • Reflex Arc: The “wiring” of a single reflex o Begins at a receptor Either a specialized cell or dendrites of a sensory neuron o Ends at a peripheral effector Such as a muscle fiber or a gland cell Describe the five steps in a neural reflex. • Five (5) Steps in a Neural Reflex: o 1. Arrival of stimulus & activation of receptor Physical or chemical changes o 2. Activation of sensory neuron Graded depolarization – leads to action potential generation o 3. Information processing by postsynaptic cell Triggered by neurotransmitters o 4. Activation of motor neuron Action potential generated in motor neurons o 5. Response of peripheral effector Triggered by neurotransmitters cause skeletal muscle contraction Describe how reflexes are categorized. • Reflexes are classified on the basis of: o Time of development Innate Reflexes: Basic neural reflexes formed before birthBSC2085 Exam #4 “What You Should Know” 4 Acquired Reflexes: Rapid & automatic complex learned motor patterns o Type of motor response Somatic Reflexes: Control skeletal muscle contractions • Includes superficial, stretch, & deep tendon reflexes Visceral Reflexes: Autonomic reflexes that control actions of smooth & cardiac muscles, glands, adipose tissue • Consensual light reflex o Complexity of neural circuit Monosynaptic Reflex: Sensory neuron synapses directly on motor neuron • Only 1 synapse in reflex arc Polysynaptic Reflex: At least one interneuron between sensory neuron and motor neuron • Longer delay • Most reflexes are polysynaptic o Site of information processing Spinal Reflexes: Occur in spinal cord Cranial Reflexes: Occur in brain Explain the difference between monosynaptic and polysynaptic reflexes. What are some examples of these reflexes? What are the characteristics of polysynaptic reflexes? Monosynaptic Reflex Polysynaptic Reflex - Simplest reflex arc - Sensory neuron synapses directly on motor neuron - Only 1 neuron in reflex arc -
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