Ch 13 Spinal Cord Meninges surround brain sc

Ch 13 - Spinal Cord

Meninges- surround brain & sc -protection & nutrients 1. Dura mater – hard mother, outer SUBdural/Epidural space - space between dura mater and arachnoid mater -used to deliver anesthetic 2. Arachnoid mater – spider mother, thin, spiderwebby Subarachnoid space - this is the largest of the spaces between maters and this one is full of Cerebro. Spinal. Fluid (CSF) which bathes the spinal cord. -used for spinal taps (meningitis, MS, cancers) 3. Pia mater – delicate mother, attached directly to brain & s. c. , extensions that anchor the cord come off the pia matter and are known as "denticulate ligaments" Spinal Anesthesia- pg 422 http: //www. youtube. com/watc h? v=S 3 r 6 o. J 1 r. Eio

Meningitis • Infection of meningeal membranes by bacteria/virus • Infection causes inflammation = disruption to circulation of CSF = damage/death of neurons • Vaccinations can be given to prevent some forms of meningitis • Can be diagnosed by spinal tap • Highest risk group are children under 5, followed by individuals 1625 • Newest outbreak cause by steroid injections contaminated by a fungus

Spinal Cord regions 1. It is the link between the brain and the PNS. 2. pathway for sensory and motor impulses • (31 pairs) cervical spinal nerves have an extra set, C 8. All the others correspond to the number of vertebra in that particular spine. 1. Cervical- 8 pairs 2. Thoracic- 12 pairs 3. Lumbar- 5 pairs 4. Sacral- 5 pairs • 5. Coccygeal- 1 pair

Anatomical landmarks to know 1. 2 longitudinal depressions a. Posterior Median Sulcus - PMS b. Anterior Median Fissure - AMF 2. 2 enlargements of the spinal cord a. Cervical enlargement (biggest) - pectoral girdle – C 4 -C 8 b. Lumbar enlargement - supplies and innervates lower limbs 3. Conus Medullaris - L 1 - tapering end of the spinal cord proper 4. Cauda Equina - L 1 to sacrum - "Horse Tail" this is made up of bundles of nerves/axons 5. Filum Terminale - one terminal fiber which anchors the spinal cord to the end of the sacrum, comes off the cauda equina.

Internal Anatomy Grey matter - made up of unmyelinated axons, cell bodies of neurons, & neuroglia a. Dorsal Root - posterior - sensory nerves b. Dorsal Root Ganglion (contains sensory nerve cell bodies) c. Ventral Root - anterior - motor neurons "AMPS" anterior/motor and posterior/sensory *Spinal nerves start where the dorsal root ganglia and ventral root fuse or come together and join to become a mixed nerve/exit the spine at the intervertebral foramen.

1. Anterior Gray Horn: cell bodies of somatic motor neurons (anterior motor) 2. Posterior Gray Horn: cell bodies of somatic sensory neurons and visceral sensory neurons (posterior sensory) 3. Lateral Gray Horns cell bodies of autonomic nervous neurons 4. "grey & white commisures" - this is where nerve impulses cross over - remember that the right side of the brain deals with the left side of the body, etc. impulses cross over contralaterally at some point in the spine. - Central Canal in middle- contains cerebrospinal fluid

White Matter- Columns/Funiculi -has myelinated & unmyelinated 1. Anterior (efferent)- ascending and descending motor 2. Lateral (efferent)- ascending and descending motor 3. Posterior (afferent)- ascending sensory to brain Fascicle/Tracts-axons in each column which share functional & structural characteristics AMPS

Anatomy of Spinal Nerves • 3 layers of CT • Epineurium • Outermost layer • Consists of dense network of collagen fibers • Perineurium • Middle layer • Divide nerve into series of compartments which contain bundles of axons (fascicles) • Endoneurium • Innermost layer • Surround individual axons

Distribution of Spinal Nerves • Spinal Nerves: • Consist of dorsal root + ventral root • Branch to form pathways to destination • Includes motor and sensory nerves Dermatomes: a. each pair of spinal nerves controls a region of body surface sensation - the exception to this is C 1, which does not. b. from dorsal and ventral rami fibers c. damage to the spinal nerve results in loss of sensation to a region of skin d. this is a helpful diagnostic tool, sometimes pain is referred from one nerve to a corresponding region of skin.

Peripheral Neuropathies • Regional loss of sensory or motor function • Due to trauma or compression • Example: if your foot “falls asleep” Shingles • Caused by varicella-zoster virus (chickenpox) • After chickenpox, virus hides in neurons of spinal cord • Later in life, attacks neurons in dorsal roots of nerves = painful rash/blisters • Distribution of rash corresponds to dermatome nerves affected

Plexus- “braid” of nerves -a group of spinal nerves that do a specific job -Nerves do not go directly to the body structure they supply -from anterior rami -cervical, brachial, lumbar and sacral *Note: the Thoracic nerves are NOT A PLEXUS.

1. Cervical plexus C 1 -C 4 – head, neck, upper shoulders & chest Phrenic nerve- C 3 - C 5 -diaphragm

2. Brachial Plexus C 5 -T 1 -upper limbs and pectoral girdle. 5 major terminal branches: Axillary- armpit, shoulder Median- down the middle of the arm & hand Musculocutaneous – flexors of the arm Radial - along the radial bone, thumb, fingers 2 -3 Ulnar - along ulna, little finger

3. Thoracic nerves (Intercostals) • T 2 -T 12 remember, these are not a plexus, because they directly innervate each rib space Intercostal nerves - along each rib

4. Lumbar Plexus L 1 -L 4 - abs, external genitals, lower limbs Femoral Nerve -anterior thigh/leg, medial leg & foot Obturator nerve – adductors of leg Genitofemoral- middle thigh and genitals Ilioinguinal- genitals Iliohypogastric- abs & butt

5. Sacral Plexus • L 4 -S 4 - butt, perineum, lower limbs Sciatic nerve-posterior to femur, largest & longest nerve in the body, most of legs & even feet -2 divisions fibular/peroneal divison & tibial division Gluteal- butt

Neuronal pools • Interneurons (CNS) organized into function groups • May stimulate or depress parts of the brain/spinal cord • Five different ways organization takes place Divergence • Spread of info from one neuron/pool to several neurons/pools • Occurs when sensory neurons bring info to CNS • Allows for message to reach multiple places at the same time Convergence • Several neurons synapse on single post-synaptic neuron • Allow for control of same motor neurons both consciously and subconsciously Serial processing • Information relayed from one neuron to another in stepwise fashion • Occurs when sensory info is relayed from one part of the brain to another Parallel processing • Several neurons/pools process same info simultaneously • Divergence must take place first • Allows for responses to occur simultaneously Reverberation • Branches of axons extend back toward source of impulse to trigger further stimulation • Positive feedback loop • Help maintain consciousness, muscular coordination and normal breathing

1. Arrival of stimulus activates receptor 2. Sensory Neurons are activated and produce AP 3. Information processing in CNS AP = release of neurotransmitters which allow postsynaptic cell (interneuron or motor neuron) to process information 4. Activation of motor neuron releases neurotransmitters 5. Release of neurotransmitters leads to response by effector

Classification of Reflexes 1. Development • Innate reflexes • Genetically determined • Include chewing, suckling, tracking object with eyes, blinking when eyelash touched • Acquired reflexes • Learned motor patterns enhanced by repetition • Driving, walking, skiing 2. Response • Somatic reflexes • Involuntary control of skeletal muscle contractions • Include superficial and stretch reflexes • Provide rapid response that can be modified later by voluntary commands • Visceral (automatic) reflexes: Controls actions of smooth/cardiac muscles, glands, adipose tissue

Classification of Reflexes 3. Complexity • Monosynaptic: one synapse, little delay between stimulus and response • Polysynaptic: multiple synapses, longer delay between stimulus and response 4. Processing site • Spinal reflexes: Processing occurs in the spinal cord • Cranial reflexes: Processing occurs in the brain

Spinal Reflexes The Stretch Reflex • Most common monosynaptic reflex • Example: patellar reflex • • • Physician taps on patellar tendon Receptors in quadriceps are stretched Distortion of receptors stimulates sensory neurons This leads to reflex contraction of stretched muscle = kick Slow response can indicate defect with nerve conduction Patellar reflex helps with balance and walking, contracts muscle automatically when weight is put on feet during standing/walking

Spinal Reflexes Withdrawal Reflex • Type of polysynaptic reflex • Example: flexor reflex • Affects muscles of a limb • Occurs when you grab a hot pan • Grabbing hot pan stimulates pain receptors • Sensory neurons activate interneurons in spinal cord • Stimulate motor neurons in anterior gray horns • Result=contraction of flexor muscles that yanks hand away from stove • Inhibitory signals used to relax extensor muscles

Babinski Reflex • Babinski sign (positive Babinski reflex) • Occurs in absence of descending inhibition • Normal in infants/pathological in adults • If seen in adults = sign of damage to nerve paths connecting the spinal cord and brain • Plantar reflex (negative Babinski reflex): Stroking lateral sole of foot produces curling of the toes