Chapter 12: Spinal Cord and Spinal Nerves

Grey Horns

- Grey matter subdivides into anterior, posterior, and lateral grey horns. -It is a site for integration (summing) of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs).

Erb-Duchene Palsy

- "waiter's tip" position - fall on shoulder - Loss of sensation along the lateral side of the arm -injury to the brachial plexus

Pia Mater

- Innermost layer - thin transparent connective tissue layer - consists of thin squamous to cuboidal cells within interlacing bundles of collagen fibres and fine elastic fibres - contains many blood vessels that supply nutrients and oxygen to the spinal cord

Anterior Median Fissure

- Divides spinal cord into left and right sides, penetrates white matter - Wide groove on anterior (ventral) side

Ventral (Anterior) Root

- Efferent - Axons of motor fibres - Conduct nerve impulses from CNS to effectors (muscles/glands)

Vertebral Canal

- Formed by vertebral column - Location of spinal cord -Provides sturdy shelter for the enclosed spinal cord.

Gray Commissure

- Forms crossbar of "H" in grey matter - Contains small space called central canal that extends entire length of spinal cord and contains cerebrospinal fluid

Polysynaptic Reflex Arc (Reciprocal Innervation)

- Involves more than two types of neurons and more than one CNS synapse - antagonist muscles must relax as part of reflex - sensory neuron also synapses with interneuron which can inhibit motor neuron to antagonistic muscle

Lumbar Plexus

- L1 to L4 - Supplies anterolateral abdominal wall, external genitals, & parts of lower limb -Is formed by the roots of spinal nerves L1-L4

Sacral Plexus

- L4 to L5 & S1 to S4 - Anterior to the sacrum - Supplies buttocks, perineum, & part of lower limb -Gives rise to the largest and longest nerve in the body--sciatic nerve

Arachnoid Mater

- Middle layer - Made of collagen fibres and elastic fibres (web-like)

Autonomic (Visceral) Reflexes

- Not consciously perceived - involve responses of smooth muscle, cardiac muscles, and glands - Output to viscera

Median Nerve Injury

- Numbness, tingling, and pain in the palm & fingers; inability to pronate forearm or flex fingers properly

Monosynaptic (Ipsilateral) Reflex Arc

- One sensory neuron synapses with one motor neuron - Controls muscle length - Contraction resists over-stretching, preventing injury - Brain controls muscle tone by adjusting sensitivity of muscle spindle sensors

Brachial Plexus

- Rami from C5 to T1 - Only nerve supply to shoulder & upper limb

Central Canal

A small space in the center of the gray commissure filled with cerebrospinal fluid.

What is a spinal tap?

Procedure that involves the use of a needle to withdraw CSF from the subarachnoid space. (lumbar puncture)

Ulnar Nerve Palsy

inability to abduct or adduct fingers

Wrist drop

inability to extend the wrist and fingers -injury to the brachial plexus

meningitis

inflammation of the meninges due to an infection.

myelitis

inflammation of the spinal cord

epidural block

injection of an anesthetic drug into the epidural space in order to cause a temporary loss of sensation.

Femoral nerve injury

injury to the femoral nerve which can occur in stab or gunshot wounds. -Is indicated by an inability to extend the leg and by loss of sensation in the skin over the anteromedial aspect of the thigh.

Dorsal (Posterior) Root

- Afferent - sensory axons and receptors, which conduct nerve impulses from skin, muscles, internal organs into CNS - contains swelling called dorsal root ganglion

Dermatomes

- Area of skin supplied by pairs of spinal nerves -provides sensory input to the CNS via one pair of spinal nerves or via the trigeminal nerve. - Some overlap between dermatomes - Overlap prevents loss of sensation if one of nerves damaged - Can use pattern of sensory loss to determine which nerves are damaged - Due to overlap, sensory anesthesia can require 3 spinal nerves be blocked

Reflex

- Automatic response to change in environment or stimulus that can be innate or learned

Epidural Space

- Between vertebral wall and dura mater - Contains padding of fat and connective tissue -is where epidural anaesthesia is injected.

Motor (Descending) Tracts

- Bundles of Axons that carry motor information AWAY FROM BRAIN - Continuous with motor tract in brain

Spinal Nerve Function

- Carry information brought into or sent from spinal cord - Path of communication between spinal cord and specific regions of bodies - Part of PNS - Bring info from muscles, glands, skin to CNS - Carries signals to effectors from CNS - Named by point of emergence from vertebral column (C1 for example comes out between occipital bone & atlas)

Stretch Reflex

- Causes contraction of skeletal muscle (the effector) in response to stretching of the muscle - Occurs via monosynaptic arc

Dorsal (Posterior) Root Ganglion

- Cell bodies of sensory nerves - Swelling on Posterior root

Tendon Reflex

- Controls muscle tension by causing muscle relaxation that prevents tendon damage - Both tendon & muscle are protected

Grey Matter

- Core of spinal cord shaped like letter "H" - Contains neuron cell bodies, dendrites, unmyelinated axons and neuroglia - gray matter on each side of spinal cord subdivided into regions called horns *(paired dorsal and ventral gray horns)

Posterior Median Sulcus

- Divides spinal cord into left and right sides, penetrates white matter - Narrow furrow on posterior (dorsal) side

Subdural Space

- Separates dura mater and arachnoid mater - Contains interstitial fluid

Flexor (Withdrawal) Reflex

- Step on tack, pain fibres send signal to spinal cord - Interneurons branch to multiple spinal cord segments (intersegmental reflex arc) - Motor fibres in segments activated - Multiple muscle groups activated to lift foot off tack

Dura Mater

- Superficial layer - dense irregular connective tissue - extends from foramen magnum to the 2nd sacral vertebra

White Matter

- Surrounds gray matter - Anterior/Posterior gray horns divide white matter on each side of cord into three specialized regions called columns: (1) Anterior (Ventral) White Columns (2) Posterior (Dorsal) White Columns (3) Lateral White Columns

Roots

- Two bundles of axons connect each spinal nerve to a segment of the cord - Spinal nerve axons enter/exit cord via this

Cervical Plexus

- Ventral rami of spinal nerves C1 to C5 - Supplies parts of head, neck, and shoulders - Phrenic nerve (C3-C5) keeps diaphragm functioning

Spinal Segment

- area of cord from which each pair of spinal nerves arises - appears to be segments because 31 pairs of spinal nerves emerge at regular intervals from intervertebral foramina (1 pair at a time) - naming of spinal nerve based on the segment they are located - 8 pairs of cranial nerves (C1-C8), 12 pairs of thoracic nerves (T1-T12), 5 pairs of lumbar nerves (L1-L5), 5 pairs of sacral nerves (S1-S5), 1 pair of coccygeal nerves (Co1)

Tracts (CNS)

- bundles of axons that form white matter columns - start/end in same place and carry similar information up/down spinal cord - have common origin/destination

Crossed Extensor Reflex

- contraction of muscles that extend joints in the opposite limb in response to a painful stimulus -helps you maintain balance.

Filum Terminale

- extension of pia mater that extends inferiorly, fuses with arachnoid mater and dura mater - "stabilizes spinal cord in canal" - anchors spinal cord to coccyx and stabilizes in canal

External Anatomy of Spinal Cord

- slightly flattened cylinder - extends from medulla oblongata - adult's 42-45 cm long & ~2cm diameter ENDS AT L2 - in newborns ENDS AT L4 - growth of cord stops at age 4 to 5

Functions of spinal cord/nerves

- spinal cord reflexes - integration of EPSPs and IPSPs - highway for upward and downward travel of sensory and motor information

Cauda Equina

-AKA: horse's tail - dorsal and ventral roots of lowest spinal nerves

Sensory (Ascending) Tracts

-Bundles of Axons that conduct sensory nerve impulses TOWARDS BRAIN - Continous with sensory tract in brain

Conus Medullaris

-Inferior to the lumbar - termination point for spinal cord - ends between L1 and L2 (lumbar vertebra)

Coccygeal Plexus

-formed by the anterior rami of S4-S5 and the coccygeal nerves. -Supplies a small area of skin in the coccygeal region.

Obturator nerve injury

-results in paralysis of the adductor muscles of the thigh and loss of sensation over the medial aspect of the thigh. -May result from pressure on the nerve by the fetal head during pregnancy.

5 Components of Reflex Arc

1. Receptor 2. Sensory Neuron 3. Integrating Center 4. Motor Neuron 5. Effector

4 Important Somatic Spinal Reflexes

1. Stretch 2. Tendon 3. Flexor (Withdrawal) 4. Crossed Extensor

Anterior White Commissure

Connects white matter of right and left sides of spinal cord

Subarachnoid Space

Contains shock absorbing cerebrospinal fluid; between arachnoid matter and pia matter -Is where spinal tap is performed.

Posterior Ramus

Goes to deep muscles/skin of back

Anterior Ramus

Goes to upper/lower limbs, skin of lateral & ventral surface of trunk

Cranial reflexes

Integration takes place in the brain stem rather than the spinal cord.

Somatic Reflexes

Involve output and contraction of skeletal muscles.

Diplegia

Is paralysis of both upper limbs or lower limbs

Lumbar Enlargement

One of two enlargements seen when spinal cord is viewed externally: - inferior - extends from T9 to T12 (thoracic vertebra) - nerves to and from lower limbs

Cervical Enlargement

One of two enlargements seen when spinal cord is viewed externally: - superior - extends from fourth cervical vertebra (C4) to first thoracic vertebra (T1) - arise nerves to and from upper limbs

Reflex Arc

Pathway followed by nerve impulses that produce a reflex

Endoneurium

The innermost layer-covers individual axon with in nerve.

Perineurium

The middle layer-covers fascicles

Epineurium

The outermost layer-covers the entire nerve

Meninges

Three protective, connective tissue coverings that encircle the spinal cord and brain: (1) Dura Mater, (2) Arachnoid Mater, (3) Pia Mater

Monoplegia

a paralysis of 1 limb only

paresthesia

an abnormal sensation such as burning, prickling, tickling resulting from a disorder of a sensory nerve.

Nerve Plexus

is a network of axons -They do not go directly to the body structures they supply. -They form networks on both the left and right sides of the body by joining with various numbers of axons from the anterior rami of adjacent nerves - Cervical, brachial, lumbar, and sacral are main plexuses

hemisection

is a partial transection of the cord on either the right or left side.

Quadriplegia

is paralysis of all 4 limbs

paraplegia

is paralysis of both lower limbs

hemiplegia

is paralysis of the upper limb, trunk, and lower on 1 side of the body.

Complete transection

means that the spinal cord is severed from 1 side of the other thus cutting all sensory and motor tracts.