Spinal cord

spinal cord functions

conduction, neural integration, locomotion, reflexes

conduction

(Spinal Cord Fxn) Carries information up (sensory) and down (motor) the cord.

neural integration

(Spinal Cord Fxn) Pools of neurons receive input, integrate it, and execute a motor response.

locomotion

(Spinal Cord Fxn) Repetitive, coordinated contractions via central pattern generators (CPGs).

reflexes

(Spinal Cord Fxn) Quick, involuntary responses to stimuli.

meninges (sing. meninx)

Three connective tissue membranes: dura mater, arachnoid mater, pia mater.

dura mater

Outer, tough membrane of the meninges.

dural sheath

The dura mater around the spinal cord.

arachnoid mater

Middle layer of the meninges.

pia mater

Innermost, delicate membrane of the meninges, adhering to the spinal cord.

epidural space

Space between the dura mater and the vertebral bone.

subarachnoid space

Space between arachnoid and pia mater; contains CSF.

denticulate ligaments

Extensions of the pia mater that anchor the spinal cord to the dura mater.

lumbar puncture (= spinal tap)

Sampling of CSF below L1/L2.

spinal tract

Bundle of axons (nerve fibers) in the white matter; carries similar information.

ascending tract

Carries sensory information up the spinal cord.

descending tract

Carries motor information down the spinal cord.

spino- vs -spinal

Spino- indicates an ascending (sensory) tract (e.g., Spinothalamic); -spinal indicates a descending (motor) tract (e.g., Corticospinal).

ascending pathways

Sensory pathways.

conscious sensory input

Input that results in awareness of the stimulus (e.g., touch, pain).

1st order neuron

Neuron from the receptor to the cord/brainstem.

2nd order neuron

Neuron from the cord/stem to the thalamus.

3rd order neuron

Neuron from the thalamus to the primary cortex.

unconscious proprioception

Proprioceptive information sent to the cerebellum (does not reach consciousness).

gracile & cuneate fasciculi (= posterior columns)

Tracts carrying fine touch, pressure, vibration, and conscious proprioception.

fine touch, pressure, vibration

Sensory information carried by the gracile & cuneate fasciculi.

medulla > thalamus >cerebrum

Path for gracile & cuneate fasciculi/medial lemniscus.

medial lemniscus

Tract in the brainstem for fibers from the gracile/cuneate fasciculi.

spinothalamic tract

Carries pain, temperature, itch, crude touch.

pain, temperature, itch, crude touch

Sensory information carried by the spinothalamic tract.

gray horn > thalamus > cerebrum

Path for the spinothalamic tract.

spinocerebellar tract

Carries unconscious proprioception to the cerebellum.

pain of tissue injury

Stimulus that initiates a withdrawal (flexor) reflex.

gray horn >retic. form. > cerebrum

Pathway related to pain or general sensory input.

spinocerebellar tracts

Tracts carrying unconscious proprioception to the cerebellum.

unconscious proprioceptionss

Information about body position sent to the cerebellum.

gray horn > cerebellum

General pathway for spinocerebellar tracts.

descending pathways

Motor pathways originating in the brain.

upper motor neuron

Neuron with the soma in the cortex or brainstem.

cortex > stem or stem \>cord

Location/Path of the upper motor neuron.

lower motor neuron

Neuron with the soma in the brainstem or spinal cord that innervates the effector.

stem or cord > effector

Path of the lower motor neuron.

corticospinal (= pyramidal) tract

Descending pathway for voluntary movement.

voluntary movement

Function of the corticospinal tract.

primary motor cortex >tract

Origin/Path of the corticospinal tract.

tectospinal tract

Descending pathway for reflex head and eye movement.

sight/sound-triggered neck reflexes

Function of the tectospinal tract.

tectum > tract

Origin/Path of the tectospinal tract.

reticulospinal tracts

Descending pathways for posture and balance.

posture & balance; analgesia

Functions of the reticulospinal tracts.

reticular formation > tract

Origin/Path of the reticulospinal tracts.

vestibulospinal tracts

Descending pathways for balance and anti-gravity reflexes.

reflexes for counteracting body tilt

Function of the vestibulospinal tracts.

vestibular nuclei \rightarrow tract

Origin/Path of the vestibulospinal tracts.

nerve

A bundle of nerve fibers (axons) wrapped in connective tissue.

epineurium

Connective tissue that wraps the entire nerve.

fascicle

A bundle of nerve fibers within the nerve.

perineurium

Connective tissue that wraps a fascicle.

axon

The nerve fiber.

endoneurium

Connective tissue that wraps a single axon.

myelin sheath

Insulating layer around an axon.

functional nerve types

Sensory (= afferent) nerve, motor (= efferent) nerve, mixed nerve.

sensory (= afferent) nerve

Carries signals toward the CNS.

motor (= efferent) nerve

Carries signals away from the CNS.

mixed nerve

Contains both sensory and motor fibers.

ganglion (pl. ganglia)

A cluster of neurosomas (cell bodies) outside the CNS.

spinal nerve types

Cervical (C1-C8), Thoracic (T1-T12), Lumbar (L1-L5), Sacral (S1-S5), Coccygeal (Co).

rootlets

Small divisions that form a nerve root.

spinal nerve roots

The two proximal branches that merge to form a spinal nerve.

posterior (dorsal) root

Carries sensory fibers to the spinal cord.

posterior (dorsal) root ganglion

Contains the somas of sensory neurons.

anterior (ventral) root

Carries motor fibers away from the spinal cord.

spinal nerve ramus (pl. rami)

Branches distal to the spinal nerve (anterior, posterior, communicating).

posterior ramus

Innervates the muscles/joints in the back and the skin of the back.

anterior ramus

Innervates the anterior/lateral skin and muscles, and gives rise to nerve plexuses.

intercostal nerves

Anterior rami in the thoracic region (T2-T12).

communicating rami

Connect to the sympathetic chain ganglia.

meningeal branch

Reenters the vertebral canal to innervate meninges/vessels.

A meningeal branch is a vessel or nerve that supplies the meninges, the membranes surrounding the brain and spinal cord

nerve plexus

A web-like network of intersecting anterior rami.

somatic plexus

Plexus that serves the body (non-visceral).

cervical plexus

Formed by C1-C5; innervates neck and shoulders.

phrenic nerve

Major nerve from the cervical plexus (C3-C5); innervates the diaphragm.

brachial plexus

Formed by C5-T1; innervates the shoulder and upper limb.

radial nerve

Major nerve of the upper limb; injury causes crutch paralysis and wrist drop.

crutch paralysis

Damage to the radial nerve from pressure in the axilla.

wrist drop

Inability to extend the hand at the wrist due to radial nerve damage.

lumbar plexus

Formed by L1-L4.

sacral plexus

Formed by L4-S4.

sciatic nerve

Largest nerve in the body; from the sacral plexus.

sciatica

Pain extending down the leg along the course of the sciatic nerve.

coccygeal plexus

Formed by S4-Co1.

dermatome

A specific area of skin mainly supplied by a single spinal nerve.

cutaneous innervation

The supply of nerves to the skin.

reflex arc

The pathway of a reflex, involving five components.

components of a reflex arc

1) Sensory receptor, 2) Afferent nerve fiber, 3) Integrating center, 4) Efferent nerve fiber, 5) Effector.

sensory receptor

Detects the stimulus.

afferent nerve fiber(s)

Carries signals from the receptor to the CNS.

integrating center

Synapse(s) in the gray matter of the CNS.

efferent nerve fiber(s)

Carries motor signals from the CNS.

effector

Muscle or gland that carries out the response.