Chapter 14: Nervous System: Spinal Cord & Spinal Nerves

Epidural space

Between the dura mater and the vertebral wall Contains adipose tissue (fat) and many small blood vessels Lumbar epidural is the largest- used for epidural anesthesia -knocks out just the lower spinal nerves

Nerve Connective Tissue Layers

Epineurium= covering peripheral nerve (whole nerve) Perineurium= around one fascicle -fascicle= collection of axons; contains blood vessels Endoneurium= covering the axon

Fast vs Slow Stimulus

Fast stimulus= involuntary response (reflux) Slow stimulus= voluntary response (no reflux)

Epidural anesthesia

Small catheter threaded into the posterior space between bone of lumbar vertebrae and dura mater Pain relief by blocking pain but preserving some motor functions -Duration and labor and delivery (obstetrical anesthesia)

Spinal Cord

Spinal cord begins at the end of the brain stem and continues down spine 3/4 the way until the cauda equina Spinal nerves (31): 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal Interior grey matter (butterfly) Exterior white matter Cauda equina "Horse's tail"= end of spinal cord at L1 or L2; bundle of nerves that extends beyond the spinal cord -carries nerve impulses to and from the legs Ratio of grey and white matter changes as you go down the spinal cord -more white matter (nerve fibers) at the top due to more signals (upper + lower signals)

Lumbar Puncture

Spinal tap Medical procedure performed to collect CSF for diagnostic purposes Hollow needle inserted into the subarachnoid space between L3-L5 CSF studied for infection, blood, or metabolic wastes

Sensory & Motor Regions of the Spinal Cord

*Dorsal root (sensory root)* of each spinal nerve consists an enlargement called the dorsal root ganglion that contains cell bodies of sensory neurons -Posterior *Ventral root (motor root)* of each spinal nerve consists of axons from motor neurons whose cell bodies are found within the gray matter of the spinal cord -Anterior *Posterior (dorsal) gray Horn* receives sensory information from somatic and visceral sensory neurons *Anterior (ventral) gray Horn* contains nuclei of somatic motor neurons *Lateral (intermediate) gray Horn* contains nuclei of visceral motor neurons

Spinal Cord Grey & White Matter

*Grey matter* in the center of the cord contains *interneurons and the cell bodies of motor neurons, axons, and dendrites* -impulse transmission *White matter* consists mostly of *glial cells and myelinated axons*; "wiring" -primarily carries information in spinal cord

Spinal nerve is a mix of

-Sensory -Motor -Autonomic fibers

Withdrawal Reflex

1. Arrival of pain stimulus and activation of pain receptor 2. Activation of sensory neuron- change the pain into an action potential (electrical signal); goes through the dorsal root 3. Action potential synapses in the spinal cord (CNS) onto: -interneuron: excitatory signal goes to the brain to become aware of the pain -motor neuron: electrical signal goes to the ventral root 4. Activation of a motor neuron; send signal to innervate skeletal muscle 5. Response by skeletal muscle effector; involuntary response by skeletal muscle that gets tissue away from the stimulus -Flexion

Reflex Arc

1. Arrival of stimulus and activation of receptor 2. Activation of a sensory neuron 3. Information processing in CNS 4. Activation of a motor neuron 5. Response by effector -Can be modified, complex

Sensory receptors

1. Exteroceptors= respond to stimuli arising outside the body. Sensitive to touch, pressure, pain, and temperature. Includes the special sense organs (eyes, ears, nose) 2. Proprioceptors= unconscious information recieved. Detect body position in space and movement. Located in the muscles, tendons, and joints inside the body and semicircular canals of the inner ear 3. Interoceptors= receive sensory information from inside the body. Detect internal body sensation. Examples:from the viscera (hollow organs), stomach pain, pinched spinal nerves, and deep skin inflammation.

Patellar Tendon Reflux

1. Fast stimulus: stretching the muscle spindle receptor on muscle tendon 2. Sudden increase in activity; activation of sensory neuron 3. Synapse onto motor neuron 4. Activation of motor neuron; carries to motor units in quadriceps group 5. Response of patellar tendon: produces an immediate increase in muscle tone and a reflective kick

Peripheral Flow of Sensory Information (Somatic)

1. From exteroceptors and proprioceptors of body wall & limbs from ventral ramus OR From exteroceptors and proprioceptors of back from dorsal ramus 2. Goes to the sensory neurons in the dorsal root ganglion 3. Through the dorsal root, travels to the somatic sensory area in the dorsal horn and synapse onto somatic sensory neurons VOLUNTARY

Peripheral Flow of Sensory Information (Visceral)

1. From interoceptors of body wall & limbs from ventral ramus OR from interoceptors of back from the dorsal ramus 2. Goes to sensory neurons in the dorsal root ganglion 3. Through the dorsal root, travels to the dorsal horn and synapse onto visceral sensory neuron OR 1. From interoceptors of visceral organs 2. Goes through rami communicantes 3. Goes to sensory neurons in the dorsal root ganglion 4. Through the dorsal root, travels to the dorsal horn and synapse onto visceral sensory neuron INVOLUNTARY

Peripheral Flow of Motor Commands (Somatic)

1. Somatic motor neurons in the ventral horn sends a signal via somatic nerves through ventral root to the spinal nerve 2. Goes through the ventral ramus to innervate skeletal muscles of body wall & limbs OR Goes through the dorsal ramus to innervate skeletal muscles of back VOLUNTARY

Peripheral Flow of Motor Commands (Visceral)

1. Visceral motor neurons in the ventral horn sends a signal via preganglionic fibers through ventral root to the spinal nerve 2. Goes through the white ramus (preganglionic) of the rami communicates 3. In the sympathetic ganglion, the preganglionic fiber synapses onto a postganglionic fiber neuron OR Goes through the sympathetic ganglion and sympathetic nerve via preganglionic fibers innervating abdominopelvic viscera 4. Through the sympathetic nerve, the postganlionic fibers innervate smooth muscle, glands, visceral organs in the thoracic cavity OR Through the gray ramus (postganglionic) the postganglionic fibers to the ventral ramus where it innervates smooth muscles, glands, etc. of body wall & limbs OR Through the gray ramus (postganglionic) the postganglionic fibers to the dorsal ramus where it innervates smooth muscles, glands, etc. of the back INVOLUNTARY

Plexus

Complex interwoven network of nerves 4 Major Nerve Plexuses: -Cervical (C1-C5) -Brachial (C5-T1) -Lumbar (T12-L4) -Sacral (L4-S4) *No thoracic plexus*

Spinal Meninges

Function: -Protecting the brain and spinal cord form mechanical injury -Providing blood supply to the skull and to the hemispheres -Providing a space for the flow of cerebrospinal fluid Dura mater "Tough mother"= toughest and outermost layer -protects and supports spinal cord Arachnoid mater= middle layer filled with a intricate "web" of collagen -shock absorption Pia mater= tender innermost layer -directly on the spinal cord

Peripheral Neuropathies

Generalized peripheral neuropathies affect the entire PNS -common diabetic neuropathy -uncommon Guillain-Barre syndrome Localized peripheral neuropathies (peripheral nerve palsies) are characterized by regional losses of sensory and motor function as a result of nerve trauma or compression -Brachial plexus birth palsy (Erb's palsy) -pressure palsies -radial nerve palsy -carpal tunnel syndrome -ulnar nerve palsy -sciatica

Subarachnoid space

In between the arachnoid layer and the pia mater -houses the brain's cisterns= pools of Cerebrospinal fluid (CSF) -contains cerebral arteries and veins. Area for spinal tap "lumbar puncture" -Lower back (below L3) is used to avoid damaging spinal cord

Dermatome

Localized area of skin supplied by sensory nerves that derive from a single spinal nerve root T4= Nipple line T10= umbilicus/ navel Clinically important to identify characteristic loss of sensation in specific areas of skin -damage to the spinal nerve or dorsal root ganglion can be identified -can indicate the level of motor loss Individual variability

Stretch Reflex

Muscle that is stretched, contracts reflexively 1. Stimulus: stretching of muscle stimulates muscle spindles 2. Activation of a sensory neuron 3. Information processing at motor neuron *No interneuron: MONOSYNAPTIC* 4. Activation of motor neuron 5. Response: Contraction of muscle -Posture: always swaying, reflux keeps us upright -FAST reflux

Spinal Cord injuries

Result of blunt trauma or penetrating trauma Dermatomes indicate the level of sensory and motor loss in a specific location Incomplete lesions= concussion, contusion, or compression without anatomical disruption of the spinal cord itself -Sacral sparing or intact sacral nerves indicates incomplete; return of function within 24 hours Spinal shock= period when all neurological activity below the level of injury is lost, including motor, sensory, reflux, and autonomic function due to disrupted cellular potassium ion flow; reflexes return after a few weeks