Chapter 14 - Spinal Cord

Dura Mater

- 1 Layer - Stability - Extends between adjacent vertebrae and fuse with connective tissue around spinal nerves

Spinal Nerves

- 31 pairs of spinal nerves - Mixed nerves: sensory and motor - C1-C8 - T1-T12 - L1-L5 - S1-S5 - Co1

Hyperactive reflex

- Abnormally strong response - Possible damage in brain or spinal cord - Clonus: rhythmic oscillations between flexion and extension

Sacral Plexus

- Anterior Rami of spinal nerves L4-S4 - Immediately inferior to lumbar plexuses - Lumbosacral plexus - Innervates gluteal region, pelvis, perineum, posterior thigh, almost all of the foot and leg - nerves of anterior region innervate flexing muscles of lower limb - Posterior region innervate extending muscles of lower limb.

Intercostal nerves

- Anterior Rami of spinal nerves T1-T11 - Travel in intercostal space between two ribs - T12= subcostal (inferior to ribs not between) - Only T1 forms plexuses

Tibial Nerve

- Anterior division of sciatic nerve - Innervates hamstring, travels in posterior compartment of leg to supply the plantar flexors and toe flexors - Splits in the foot to lateral and medial plantar nerve

Extrafusal fibers

- Around muscle spindle - Innervated by alpha motor neurons

Sensory Pathways

- Ascending - Nerve signals transmitted by sensory receptors - Travel from spinal cord to the brain - Have primary, secondary, and sometimes tertiary neurons - Conduct info about limb proprioception and the sensations of touch, temperature, pressure, and pain

5 major Terminals of Brachial Plexus

- Axillary nerve - Median Nerve - Musculocutaneous nerve - Radial nerve - Ulnar nerve

Posterior Horns

- Axons of sensory neurons and cell bodies of interneurons

Epidural Space

- Between dura mater and vertebrae - Areolar connective tissue - Blood vessels - Adipose connective tissue - Epidural anesthetics

Anterior Funiculus

- Between gray horns and anterior median fissure - Interconnected by white commissure.

Posterior Funiculus

- Between posterior gray horns and posterior median sulcus

Gray Matter

- Centrally located in the spinal cord - Shaped like a butterfly - 4 components

5 subdivisions of Spinal cord

- Cervical - Thoracic - Lumbar - Sacral - Coccygeal - different parts of the spinal cord do not match up exactly with the vertebrae

Nuclei

- Collection of neuron cell bodies located within the CNS

Tectospinal tract

- Conduct motor commands away form superior and inferior colliculi in tectum of midbrain - help regulate positional changes of arms, eyes, head, and neck due to visual and auditory stimuli

Anterior Spinocerebellar Tract

- Conduct sensory signals form inferior part of trunk and lower limbs and enter cerebellum peduncles

Direct Motor Pathways

- Conscious control of skeletal muscle activity - Originates in Pyramidal cells of primary motor cortex - Axons project into brainstem or spinal cord - Two Tracts: Corticobulbar and Corticospinal tract

Lateral corticospinal tract

- Decussate within pyramids of medulla oblongata - Controlled skilled movements in the limbs

Primary Neurons

- Dendrites are part of the receptor - Reside in posterior root ganglia of spinal nerves - Axon projects to secondary neuron in CNS

Motor Pathways

- Descending - Transmit nerve signals that descend from the brain to the spinal cord and spinal cord to muscle or gland - Upper and lower motor neuron - Control effectors

Hypoactive reflex

- Diminished or absent - Possible damage to a segment of spinal cord - Possible muscle disease or damage at neuromuscular junction

Anterior Corticospinal tracts

- Do not decussate at the medulla but at anterior gray commissure of a spinal cord segment - Innervate axial skeletal muscle

Lateral Funiculus

- Each lateral side of the spinal cord

Pia Mater

- Elastic and Collagen fibers - Directly adheres to spinal cord - Supports blood vessels supplying spinal cord

Rootlets

- Extend from spinal cord - Form spinal nerves - Some form nerve plexuses

Arachnoid Space

- Filled with CSF

Phrenic Nerve

- From C4 and some axons of C3 and C5 - Travels through thoracic cavity to innervate the diaphragm

Gray Commissure

- Gray matter that surrounds central canal - Unmyelinated axons, communication between R and L gray matter

Tract

- Group or bundles of axons that travel together in the CNS

Anterior Horns

- House cell bodies of somatic motor neurons

Pathways

- How the CNS communicates with peripheral body structures - Either sensory nerve signals from receptors or motor nerve signals to effectors - Processing and integration occur along the pathways - Travel through white matter of spinal cord and connect CNS regions with spinal nerves

2. Anterolateral Pathway

- In anterior and lateral white funiculi of spinal cord - Anterior spinothalamic tract - Lateral Spinothalamic tract - Crude touch, pressure, pain, and temperature - Itch sensation

Crossed-Extensor Reflex

- In conjunction with withdrawal reflex - Usually lower limbs - Occurs in opposite limbs as withdrawal reflex - Sensory branches from sam signal cross to other side of spinal cord (contralateral) through gray commissure - Synapse with motor neurons for antagonistic muscles - Antagonistic muscles contract

Smaller nerves of Sacral Plexus

- Inferior gluteal nerve - Superior gluteal nerve - Posterior femoral cutaneous nerve - Pudendal nerve

Gamma Motor Neurons

- Innervate intrafusal muscle fibers - Detect changes within a muscle

Secondary Neuron

- Interneuron - Reside in posterior horn of spinal cord or brainstem nucleus - Axon projects to thalamus for conscious sensations - Project to cerebellum for unconscious proprioception - Synapses with the tertiary neuron

Tertiary neuron

- Interneuron - Resides within the thalamus (central processing and coding center) - Axon projects to the primary somatosensory cortex of parietal lobe

Lumbar Plexus

- L and R are formed from anterior Rami of spinal nerves L1-L4 - Main nerves: Femoral nerve and Obturator nerve - Smaller nerves: iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous.

Sciatic Nerve

- Largest and longest nerve - from both the anterior and posterior divisions of sacral plexus - From pelvis, through greater sciatic notch of os coxae into posterior region of thigh

Cervical Plexus

- Located deep on each side of neck - Immediately lateral to cervical vertebrae C1-C4 - Formed from spinal nerve C1-C4 - C5 not part of cervical plexus

Obturator Nerve

- Main nerve of anterior division - Through obturator foramen of Os Coxae to medial thigh - Innervates medial thigh muscles - Sensory nerve signal from superomedial skin of thigh.

Femoral Nerve

- Main nerve of posterior division - supplies anterior thigh muscle and iliopsoas - Sensory nerve signals from anterior and inferomeidal thigh and medial aspect of leg

Intrafusal Muscle Fibers

- Makes up muscle spindle - Lack myofilaments in their central regions, only contractile in distal regions

Stretch Reflex

- Monosynaptic - Monitors and regulates skeletal muscle length - Stretching of muscle reflexively causes contraction - muscle spindle, Intrafusal fibers, gamma motor neurons, Extrafusal Fibers

Cauda equina

- Nerve roots inferior to conus medullaris - Resembles horses tail - Filum terminale

Nerve Plexus

- Network of interweaving anterior Rami of spinal nerves - Damage to a single spinal nerve does not result in complete loss of innervation - Most thoracic spinal nerves and S5-Co1 do not form nerve plexuses

Denticulate Ligaments

- Paired, lateral triangular extensions of the spinal Pia Mater - Attaches to the Dura Mater - Help suspend and anchor spinal cord laterally

Filum Terminale

- Pia mater that helps anchor the conus medullaris to the coccyx

Withdrawal Reflex

- Polysynaptic - Initiated by painful stimulus - Nerve signal transmitted by sensory neuron to the spinal cord interneurons - interneurons stimulate motor neurons to flexor muscles - Flexor muscle contract

Common Fibular Nerve

- Posterior division of sciatic nerve - Supplies short head of biceps femoris muscle - Wraps around neck of fibula

Golgi Tendon Reflex

- Prevents muscles from tensing or contracting extensively - Polysynaptic reflex - Results in muscle lengthening and relaxation in response to increased tension at a golgi tendon organ

3. Spinocerebellar Pathway

- Proprioceptive info to cerebellum for coordinating body movement. - Anterior and posterior spinocerebellar tracts - Do NOT use tertiary neurons - Subconscious level

Reflexes

- Rapid, pre-programmed, involuntary reaction of muscles or glands to a stimulus

Lateral Indirect Pathway

- Regulates and controls precise, discrete movements and tone - Rubrospinal tracts from red nucleus in midbrain

Medial Indirect Pathway

- Regulates muscle tone and gross movements of head, neck, proximal limbs, and trunk. - Reticulospinal, Tectospinal, Vestibulospinal tracts

Reflex Properties

- Requires a stimulus to initiate a response - Rapid response requires few neurons are involved and synaptic delay is minimal - Pre-programmed response occurs the same way every time - Involuntary response requires no conscious intent or pre-awareness of reflex activity

Main Nerves of Sacral Plexus

- Sciatic nerve, - Tibial nerve - Common Fibular nerve - Deep Fibular Nerve - Superficial Fibular Nerve

Contralateral

- Sensory impulses from a receptor cross over through the spinal cord to activate effector organs in opposite limb.

Posterior Spinocerebellar Tract

- Sensory signal from lower limbs, parts of the trunk and upper limbs and enter cerebellum through inferior cerebellar peduncles

Dermatomes

- Specific segment of skin supplied by a single spinal nerve - All spinal nerves except C1 are associated with a Dermatome - Can indicate potential damage to one or more spinal nerves

Viscerosensory Pathways

- Stimuli received from the viscera

Muscle Spindle

- Stretch receptor

Indirect Motor Pathways

- Subconscious or unconscious (reflexive) level of response from midbrain - Modifies or controls the pattern of somatic motor activity - Inhibit or excite lower motor neurons innervating muscle

Spinal Cord meninges

- Surround and protect spinal cord - Continuous with the cranial meninges - Spaces between have clinical significance

Conus Medullaris

- Tapering end of the spinal cord - Official end of spinal cord proper

Process of Golgi Tendon Reflex

- Tendon stretches causes increased tension - Golgi Tendon organ is activated - Transmit nerve signals to interneuron - Inhibits alpha motor neuron in same muscle - Associated muscle relaxes

Brachial Plexus

- network of nerves that supple the upper limb - Formed by anterior rami of spinal nerves C5-T1 - Innervates pectoral girdle and the entire upper limb of one side

Somatosensory pathways

- stimuli received from skin, muscles, and joints

3 Major Types of Somatosensory Pathways

1. Posterior Funiculus-Medial Lemniscal 2. Anterolateral Pathway 3. Spinocerebellar Pathway

Steps of Reflex Arc

1. Stimulus activates receptor 2. Nerve signal travels through sensory neuron to CNS 3. Information from nerve signal is processed in integration center by interneurons and transmitted to motor neuron 4. Motor neuron transmits a nerve signal to an effector 5. Effector responds to nerve signal from motor neuron

Adult Spinal Cord

3/4 in diameter 42-45 cm in length - Extends from the brain, through the vertebral canal and ends at the L1 vertebra

Reflex arc

Begins at a receptor in PNS, communicates with CNS and ends at a peripheral effector - May be ipsilateral or contralateral

Arachnoid Mater

Between Dura mater and Pia mater - Potential space in life, found in tissue preparations

Ipsilateral

Both receptor and effector organs of the reflex are on same side of spinal cord Ex: muscles in L arm contract to pull your left hand away from a hot stove

White Matter

External to Gray matter - 3 Regions called Funicules

Corticospinal Tract

From cerebral cortex, through brainstem and form pyramids of medulla oblongata - Continue into spinal cord to synapse on lower motor neurons in anterior horn of spinal cord - 2 components: lateral & anterior

Cortiocobulbar Tract

From facial region of motor homunculus - Axons extend to brainstem cranial nerve nuclei - Do NOT pass through spinal cord - Involved in cranial nerves NOT spinal nerves

Reticulospinal tract

From reticular formation of brain - Helps control unskilled reflexive movement for posture and balance

Referred Visceral pain

Pain from one organ is mistakenly referred to a dermatome - Ex: appendicitis causing pain to the T10 dermatome (umbilicus region)

1. Posterior Funiculus-Medial Lemniscal

Projects through spinal cord, brainstem and thalamus and terminates with cerebral cortex - Posterior Funiculus: Tracts in the spinal cord - Medial Lem: Tracts in the brainstem - Conducts sensory info concerned with proprioceptive (balance and posture) info about limb position and discriminative touch, precise pressure, and vibration sensations

Golgi Tendon organ

Sensory nerve endings within a tendon or near a muscle-tendon junction.

Lateral Horns

T1-L2 regions - Contain cell bodies of autonomic motor neurons that innervate cardiac muscle, smooth muscle, and glands

Decussate

To cross over

Outermost to Innermost Spinal Cord Meninges

Vertebrae - Epidural Space - Dura mater - Subdural space - Arachnoid mater - Subarachnoid space - Pia mater

Vestibulospinal tract

Vestibular nuclei of brainstem - Regulate muscular activity that helps maintain balance in sitting, standing and walking

Contralateral

relationship to opposite side

Ipsilateral

relationship to same side