Chapter 13: The Spinal Cord and Reflexes

Spinal Cord

Information highway connecting brain and lower body.

Spinal Nerves

31 pairs of nerves arising from the spinal cord.

Conduction

Nerve fibers transmit sensory and motor information.

Neural Integration

Spinal neurons process multiple inputs for output.

Locomotion

Central pattern generators coordinate walking movements.

Reflexes

Involuntary responses vital for posture and protection.

Cervical Enlargement

Thicker spinal cord area for upper limb nerves.

Lumbosacral Enlargement

Thicker area for pelvic and lower limb nerves.

Medullary Cone

Tapered end of the spinal cord.

Meninges

Three membranes enclosing the brain and spinal cord.

Dura Mater

Outer layer of the meninges, tough and protective.

Arachnoid Mater

Middle layer, adheres to dura and contains CSF.

Pia Mater

Delicate inner layer following spinal cord contours.

Epidural Space

Space between dura mater and vertebrae.

Subarachnoid Space

Contains cerebrospinal fluid (CSF) between arachnoid and pia.

Cerebrospinal Fluid (CSF)

Fluid cushioning the brain and spinal cord.

Lumbar Puncture

Procedure to sample CSF from the spinal canal.

White Matter

Myelinated axons carrying signals in CNS; surrounds gray matter

Gray Matter

Central core of spinal cord, butterfly-shaped.

Dorsal Horns

Pair of posterior horns in gray matter.

Dorsal Root

Carries sensory fibers to spinal cord.

Ventral Horns

Pair of thicker anterior horns in gray matter.

Ventral Root

Carries motor fibers from spinal cord.

Gray Commissure

Connects right and left gray matter sides.

Central Canal

Contains CSF, lined with ependymal cells.

Lateral Horn

Contains sympathetic neurons, visible from T2 to L1.

Funiculi

Three regions of white matter in the spinal cord. Contains neuron cell bodies, processes information.

Ascending Tracts

Carry sensory information up spinal cord.

Descending Tracts

Carry motor information down spinal cord.

Decussation

Crossing of midline in many tracts.

Contralateral

Origin and destination on opposite body sides.

Ipsilateral

Origin and destination on the same body side.

Gracile Fasciculus

Carries signals from lower body to brain.

Cuneate Fasciculus

Carries signals from upper body to brain.

Spinothalamic Tract

Carries pain and temperature signals to brain.

Spinoreticular Tract

Carries pain signals from tissue injury.

Spinocerebellar Tracts

Carry proprioceptive signals to cerebellum.

Upper Motor Neuron

Originates in cortex, controls lower motor neuron.

Lower Motor Neuron

Neuromuscular junction leads to muscle contraction.

Corticospinal Tracts

Control precise, coordinated movements from cortex.

Tectospinal Tract

Reflex turning of head to sights and sounds.

Reticulospinal Tracts

Control posture and balance muscles.

Poliomyelitis

Caused by poliovirus, destroys motor neurons.

Amyotrophic Lateral Sclerosis

Destroys motor neurons, causes muscle atrophy.

Nerve

Cord-like organ of bundled nerve fibers.

Mixed Nerves

Contain both afferent and efferent fibers.

Schwann Cells

Surround nerve fibers, forming myelin sheath.

Endoneurium

Loose connective tissue around individual nerve fibers.

Perineurium

Wraps bundles of nerve fibers into fascicles.

Epineurium

Dense tissue wrapping entire nerve.

Ganglion

Cluster of neurosomas outside the CNS.

Dorsal Root Ganglion

Contains sensory neuron cell bodies.

Cauda Equina

Bundle of nerve roots from L2 to S5.

Anterior Ramus

Innervates limbs and forms plexuses.

Posterior Ramus

Innervates skin and muscles of back.

Meningeal Branch

Innervates meninges and spinal ligaments.

Shingles

Localized disease from varicella-zoster virus reactivation.

Chickenpox

Common childhood disease caused by varicella-zoster virus.

Posterior root ganglia

Location where varicella-zoster virus remains dormant.

Cervical plexus

Nerve plexus supplying neck and diaphragm.

Brachial plexus

Nerve plexus supplying upper limb and shoulder.

Median nerve

Nerve associated with carpal tunnel syndrome.

Lumbar plexus

Nerve plexus supplying lower back and genitalia.

Sacral plexus

Nerve plexus supplying lower trunk and limbs.

Coccygeal plexus

Nerve plexus at the base of the spine.

Proprioception

Body position and movement information to the brain.

Somatic reflexes

Reflexes involving skeletal muscle contraction.

Dermatome

Skin area conveying sensory input to a spinal nerve.

Dermatome map

Diagram showing skin regions innervated by spinal nerves.

Somatic receptors

Receptors in skin, muscles, or tendons for reflexes.

Afferent nerve fibers

Carry sensory information to the spinal cord.

Integrating center

Synaptic contact point in spinal cord gray matter.

Efferent nerve fibers

Carry motor impulses to muscles from spinal cord.

Effectors

Muscles that execute the reflex response.

Muscle spindle

Stretch receptor in skeletal muscles monitoring length.

Extrafusal fibers

Muscle fibers generating force for movement.

Gamma motor neuron

Innervates intrafusal fibers to maintain muscle spindle tension.

Stretch reflex

Muscle contraction in response to stretching.

Knee-jerk reflex

Monosynaptic reflex tested by tapping the patellar tendon.

Reciprocal inhibition

Prevents antagonist muscles from opposing agonist contraction.

Flexor reflex

Withdrawal of limb from injurious stimulus.

Polysynaptic reflex arc

Pathway involving multiple synapses to reach muscle.

Crossed extension reflex

Extensor contraction in opposite limb during withdrawal.

Intersegmental reflex

Reflex input and output occur at different spinal levels.

Tendon organs

Proprioceptors in tendons monitoring tension.

Golgi tendon organ

1 mm long, monitors tension in tendons.

Complete transection

Total severance of spinal cord causing loss of function.

Paraplegia

Paralysis of both lower limbs.

Quadriplegia

Paralysis of all four limbs.

Paresis

Partial paralysis or weakness of limbs.