spine nerves

Epineurium

—outermost; network of collagen fibers​

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Perineurium

—middle layer; separates nerve into ​

fascicles (axon bundles)​

Endoneurium

—innermost; surrounds individual ​

axons

Spinal nerves​

Pair of _______ emerges laterally from each spinal cord segment​

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Form by junction of anterior and posterior roots​

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All ______are mixed nerves​

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Peripheral nerves​

Form from branching and re-sorting of spinal nerves​

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All are mixed nerves (sensory and motor)​

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Same connective tissue layers as spinal nerves (continuous with each other)

Dermatome

—specific bilateral region of skin supplied by a single pair of spinal nerves​

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Peripheral neuropathies

—regional losses of neural function that affect dermatomes, often from nerve trauma, compression, various illnesses​

Shingles

—rash/symptoms occur along dermatomes​

Nerve plexuses​

Complex, interwoven networks of nerve fibers ​

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Formed from blended fibers of anterior/ventral rami of adjacent spinal nerves ​

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Allows multiple spinal nerves to supply the same structures​

Cervical plexus​

Brachial plexus​

Lumbar plexus​

Sacral plexus​

Four major nerve plexuses​

The cervical plexus ​

Includes anterior rami of spinal nerves C1–C5 ​

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Innervates scalp behind ear, neck, and diaphragm​

Major cervical plexus nerves​

Phrenic nerve—from C3–C5; controls diaphragm​

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Lesser occipital nerve​

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Great auricular nerve​

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Transverse cervical nerve​

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Supraclavicular nerves

The brachial plexus​

Innervates pectoral girdle, upper back, upper limb​

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Anterior rami of C5–T1 ​

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These rami first form three large trunks (superior, middle, and inferior trunks), and each trunk splits into divisions (anterior and posterior) ​

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Trunks re-sort their axons to form three cords (lateral, posterior, and medial cords)​

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Cords are named by their positions relative to the axillary artery​

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Most nerves of brachial plexus come off the cords; a few originate at the trunks​

Musculocutaneous nerve (lateral cord)​

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Median nerve (lateral and medial cords)​

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Ulnar nerve (medial cord)​

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Axillary nerve (posterior cord)​

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Radial nerve (posterior cord)

Major brachial plexus nerves​

The lumbar plexus ​

Includes anterior rami of spinal nerves T12–L4 ​

Major nerves​

Iliohypogastric nerve​

Ilio-inguinal nerve​

Femoral nerve​

Saphenous nerve​

Obturator nerve​

Genitofemoral nerve​

Lateral femoral cutaneous nerve

The sacral plexus​

Includes anterior rami of spinal nerves L4–S4 ​

Major nerves​

Sciatic nerve​

Fibular nerve (common fibular nerve)​

Tibial nerve​

Sural nerve ​

Collateral branches from fibular and tibial nerves form this nerve​

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Superior and inferior gluteal nerves ​

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Pudendal nerve ​

Main nerve of perineum​

Sensory​

From external genitalia of both sexes and the skin around the anus​

Motor​

External urethral sphincter and external anal sphincter​

Sensory neurons​

About 10 million; bring information into CNS (incoming)​

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Interneurons​

About 20 billion; located within CNS​

Interpret, plan, and coordinate signals coming in and out​

Motor neurons​

About 1/2 million; send commands from CNS out to peripheral effectors (outgoing)​

Neuronal pools​

Interneurons organized into functional groups of interconnected neurons​

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Each has limited input sources and output destinations​

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May stimulate or depress parts of brain or spinal cord​

Divergence

—spreads information from one neuron or neuronal pool to many​

Especially common in sensory pathways​

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Convergence

—several neurons synapse on a single neuron​

Example: subconscious and conscious control of the diaphragm in breathing—two neuronal pools synapse with the same motor neurons

Serial processing

—information moves along a single path, sequentially from one neuron or neuronal pool to the next​

Example: pain signals pass ______ through two neuronal pools to reach conscious brain​

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Parallel processing

—several neurons/neuronal pools process the same information at the same time ​

Example: step on a bee. Signals spread through several neuronal pools so you can shift your weight, lift your foot, yell in pain at about the same time​

Reverberation

—collateral branches of neurons extend back and continue stimulating presynaptic neurons​

Forms positive feedback loop; continues until synaptic fatigue or inhibition occurs​

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Examples: may maintain consciousness, breathing, muscle coordination

Neural reflexes​

Rapid, automatic responses to specific stimuli​

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Basic building blocks of neural function​

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A specific reflex produces the same motor response each time

Sensory receptor​

Sensory neuron​

Information processing in CNS ​

Motor neuron​

Effector

Five components of a reflex arc​

Stretch reflex​

Regulates skeletal muscle length throughout the body​

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Very rapid (large myelinated fibers)​

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Example: patellar reflex​

Calcaneal tendon reflex​

Biciptial reflex​

Tricipital reflex​

Brachioradialis reflex

intrafusal muscle fibers​

Are the receptors in stretch reflexes​

Made of bundles of small, specialized ____

gamma motor,gamma efferents​

Innervated by sensory and motor neurons ​

These motor neurons are called ____ neurons; their axons are called _____

extrafusal muscle fibers​

Muscle spindle is surrounded by _____

Maintain muscle tone and contract muscle​

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Postural reflexes​

Include both stretch reflexes (monosynaptic) and also complex polysynaptic reflexes​

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Maintain normal upright posture​

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Often involve multiple muscle groups (e.g., back and abdominal muscles)​

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Maintain firm muscle tone​

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Extremely sensitive receptors allow constant fine adjustments to be made as needed​

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Polysynaptic reflexes​

More complicated than monosynaptic reflexes​

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Interneurons can control multiple muscle groups​

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Produce either EPSPs or IPSPs, stimulating some muscles and inhibiting others​

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Examples​

Tendon reflex​

Withdrawal reflexes​

Crossed-extensor reflexes​

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Withdrawal reflexes​

Move body part away from stimulus (pain or pressure)​

Example: flexor reflex in limbs; pulls hand from hot pan ​

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Strength and extent of response depends on intensity and location of stimulus​

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Reciprocal inhibition​

For flexor reflex to work, stretch reflex of antagonistic (extensor) muscles must be inhibited (_____) by interneurons in spinal cord.​

When flexors contract, extensors relax​

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When extensors contract, flexors relax​

Ipsilateral reflex arcs​

Occur on same side of body as stimulus​

Stretch, tendon, and withdrawal reflexes​

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Crossed extensor reflexes

Coordinated with flexor reflex​

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Step on something sharp; before flexor reflex can lift injured foot, ______ straightens opposite limb to receive body weight, then flexor reflex can occur​

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Maintained by reverberating circuits

involve contralateral reflex arcs​

Occur on side opposite stimulus

Plantar reflex​

Normal in adults​

Stroke lateral sole, causes reflexive toe-curling​

Assess spinal segments L5-S1 and tibial nerve​

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The Babinski reflex​

Normal in infants​

May indicate CNS damage in adults​

Caused by loss of inhibition of toe extensors (stimulated by L4-S1 and deep fibular branch)