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Posterior median sulcus

shallow longitudinal groove on the dorsal surface of the spinal cord

Anterior median fissure

wide, deep crease along the ventral surface of the spinal cord

Where is gray matter greatest in spinal cord

In segments dedicated to sensory and motor control of the limbs

Spinal enlargements

Cervical- nerves to shoulders and upper limbs
Lumbar- pelvis and lower limbs

Conus medullaris

where the spinal cord tapers to a conical tip, which is at or inferior to the level of the first lumbar vertebrae (L1)

Filum terminale

anchors spinal cord and is a strand of fibrous tissue, originating at the conus medullaris and extending through the vertebral canal to the second sacral vertebra, ultimately becoming part of the coccygeal ligament

Dorsal root ganglia

contains sensory neuron cell bodies, each segment of the spinal cord is associated with a pair of these. The axons of the neurons form the dorsal roots. Bring sensory into spinal cord. Merges into spinal nerve - gray, unmyelinated

Ventral roots

Contains axons of motor neurons that extend into the periphery to control somatic and visceral effectors. Merges into spinal nerve

Spinal nerve

location where sensory and motor fibers unite, emerging from intervertebral foramina; distal to each dorsal root ganglion. Is considered a mixed nerve because contains afferent (sensory) and efferent (motor) fibers. 31 pairs associate w adjacent vertebrae. Spinal nerve T1 is below vertebra T1, cervical nerves take name of vertebra below it culminating in C8 so spinal nerve C1 is above the atlas
Co1 - coccygeal

Cauda equine

Horses tail - includes filum terminale, long ventral and dorsal roots of spinal segments L2-S5

Spinal meninges

a series of specialized membranes that provide physical stability and isolation, carry blood supply and provide shock absorption for neural tissues of the spinal cord. Blood vessels w/in deliver O2 and nutrients

Dura mater

thick, outermost layer of the meninges surrounding and protecting the brain and spinal cord
Layer of dense collagen fibers
Between it and walls of vertebral canal is epidural space
Is not extensively connected to spinal cord, but fuses w foramen magnum and blends w filum terminal to form coccygeal ligament- these connections prevent longitudinal movement

Arachnoid mater

The middle meninx (weblike) underlies the dura mater, threadlike projections anchor it to the pia mater
Outer surface is simple squamous epithelial layer called arachnoid membrane
Arachnoid trabeculae is a delicate network of collagen and elastic fiber. Subarachnoid space is where cerebrospinal fluid is. Lumbar puncture/spinal tap is into this space

Pia mater

thin, delicate inner membrane of the meninges
Meshwork of elastic and collagen fibers
Firmly bound to underlying neural tissue
Blood vessels servicing spinal cord run on surface of pia mater in subarachnoid space

Epidural space

separates the dura mater from the inner walls of the vertebral canal. Contains areolar tissue, blood vessels, adipose tissue padding
Anesthetics often injected here - epidural block

Coccygeal ligament

formed where the spinal dura mater tapers from a sheath to a dense cord of collagen fibers that ultimately blend with components of filum terminale

Subarachnoid space

a space in the meninges beneath the arachnoid membrane and above the pia mater that contains the cerebrospinal fluid


cerebrospinal fluid - in subarachnoid space - shock absorber, diffusion medium for dissolved gases, nutrients, chemical messengers and waste products
In the central canal of spinal cord

Denticulate ligaments

Lateral extensions of pia mater that pass through the arachnoid layer and attach to the internal surface of the dura mater • Function to anchor the spinal cord. Prevent lateral movement

Spinal anesthesia

anesthesia produced by injection of an anesthetic into the subarachnoid space of the spinal cord.


Masses of gray matter in CNS - brain and spinal cord

Sensory nuclei

receive and relay sensory info from peripheral receptors. In spinal cord sensory nuclei are dorsal

Motor nuclei

issue motor commands to peripheral effectors. In spinal cord motor nuclei are ventral

Gray commissures

posterior and anterior to the central canal of spinal cord, contains axons of interneurons that cross from one side of the cord to the other before reach area of gray matter

Posterior gray horns

contain somatic and visceral sensory nuclei

Anterior gray horns

gray matter of spinal cord containing somatic motor nuclei (involved in motor control)

Lateral gray horns

contain visceral motor nuerons. Located only in thoracic and lumbar segments- not in cervical segment

Spinal White matter columns

Posterior, anterior and lateral

Anterior white commissures

cross over in the spinothalamic tract occurs in the spinal cord

Tracts aka fasciculi

bundles of axons in the white (myelinated) matter of the CNS that share common origins, destinations and functions and are uniform w respect to diameter, myelination and conduction
Ascending carry sensory info to brain
Descending carry motor commands to spinal cord


Specific bilateral region of skin monitored by a single pr of spinal nerves, some degree of overlap. Damage to spinal nerve or dorsal root ganglion will result in loss of sensation in that region of skin

Peripheral neuropathies

Regional losses of sensory and motor function most often from damage or compression
Example - when leg falls asleep

Spinal nerve layers

Perineurium- surround fasicles of axon bundles
Endoneurium - surround indiv axon


clusters of neuron cell bodies grouped together in the PNS


Collection of neuron cell bodies w a common function

Interneurons in CNS

Interpret incoming info and coordinate outgoing messages

Dimensions of spinal cord

18 inches long, 1/2 inch diameter

Subdural space

Between dura mater and arachnoid in spinal cord. Isn't usually a space. Dont confuse this w the subarachnoid space.

Spinal nerve layers

Epineurium, perineurium, endoneurium, Schwann cell, myelinated axon

Nerve plexuses

ventral rami merge with adjacent ventral rami to form a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location. Major plexuses include the cervical, brachial, lumbar, and sacral plexuses.


Outside the vertebral column, the nerve divides into branches. The dorsal ramus contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and sensory information to and from the skin and muscles of the back. The ventral ramus contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs.

Cervical plexus

Ventral rami of spinal nerves C1-C5
Phrenic nerve -diaphragm

Brachial plexus

Ventral rami of spinal nerves C5-T1 and C4, T2
Pectoral girdle and upper limbs
Complex - includes trunks then cords
Radial nerve- supination, thumb

Lumbar plexus, sacral plexus

Lumbar -T12 - L4
Sacral - L4-S4 - sciatic nerve

Neuronal pools

Smaller groupings of interneurons of the CNS forming functional groups of interconnected neurons (organizing to 20 billion interneurons)


A pattern of neural circuit in a neuronal pool
Spreads stimulation to many neurons/neuronal pools- broad distribution of specific input (diagram looks like a hierarchy)


A pattern of neural circuit in a neuronal pool
Several neurons synapse on a single post- synaptic neuron. Provides input to a single neuron from multiple sources (diagram looks like steams running into a river) Example breathing - controlled automatically and also can do voluntarily - two pathways to single action

Serial processing

A pattern of neural circuit in a neuronal pool
Relay from one neuron to another in a single line. Neurons/pools work sequentially. Example relay of sensory info from one part of brain to another

Parallel processing

A pattern of neural circuit in a neuronal pool
Several neurons/neuronal pools provide same info simultaneously. Looks like multiple patterns of divergence. Step on nail example- You yell, feel pain, move foot all at once


A pattern of neural circuit in a neuronal pool
Loop diagram. Is a positive feedback mechanism
Functions until inhibited or reach synaptic fatigue


Rapid automatic response to specific stimuli
Preserve homeostasis
Little variability
Follows homeostatic mechanism - receptor>integration center>effector
Neural reflex- sensory fibers deliver info from peripheral receptors to integration center (CNS) and motor fibers carry commands to peripheral effectors
Reflexes can be built on or modulated by highest levels of processing centers in the brain - once descending pathway serving 2 purposes

Reflex arc

the neural path of a reflex

Innate reflex

Reflex classification- developmental
Results from connections formed during fetal dev. EG - sucking, blinking when eyelash touched, w/drawing from hot object

Acquired reflex

Reflex classification- developmental
Learned- EX steering

Somatic reflex

Reflex classification- nature of response
Control skeletal muscles
Vital because they are immediate

Visceral reflex

Reflex classification- nature of response
Control activities of smooth muscles, cardiac muscles, glands, adipose tissue AKA autonomic reflexes

Spinal reflexes

Reflex classification- processing site
Processing in spinal cord

Cranial reflexes

Reflex classification- processing site
Processed in brain

Monosynaptic reflex

Reflex classification- complexity of circuit
Sensory neuron synapses directly on motor neuron
Lowest motor control interacting level - rapid, stereotyped and relatively inflexible

Polysynaptic reflex

Reflex classification- complexity of circuit
General characteristics
-Involves pools of Interneuron(s) between sensory and motor neuron. Results in longer delay between stimulus and response
Can produce EPSP or IPSP at CNS motor neuron
-Are intersegmental because interneurons pools extend across spinal segments and may activate muscles in many areas
-Reverberating circuits to prolong motor response- positive feedback
-Several reflexes may cooperate in coordinated response as in cross over reflex
-involve reciprocal inhibition - contract one muscle grp and inhibit opposing one

Stretch reflex

Example - patellar reflex
Monitors skeletal muscle length and tone. Receptors of stretch reflexes are muscle spindles which if stretched produce a sudden burst of activity the sensory neurons that monitor them and rapid motor response.
Postural reflex is a stretch reflex that maintains upright position (balance of muscles working in opposition)

Events of reflex arc

Generally removes or opposes original stimuli- is a negative feedback
1) arrival of stimulus and activation of receptor(eg sensory neuron, specialized cell) example- step on a nail) intero-, extero-, proprioceptors
2) activation of sensory neuron to transmit electrical impulses to grey matter of CNS. (An action potential along sensory neurons) Reaches spinal cord by dorsal root.
3) information processing in gray matter of CNS- an excitatory neurotransmitter released by the presynaptic membrane of the sensory neuron arrives at the POSTsynaptic membrane and and creates an EPSP
4) activation of motor neuron- action potential carried by axons of stimulated motor neuron in the ventral root of a spinal nerve
5)response in peripheral effector-

Types of polysynaptic reflexes

Tendon reflex - prevents tearing of tendon - greater tension on tendon, greater inhibitory effect on motor neuron
Withdrawal reflex - move body part away from stimulus - flexor reflex is example in which contraction of flexor muscle will yank body part away (and opposing muscles relax - reciprocal inhibition)

Ipsilateral reflex arc

Same side of body

Contralateral reflex arc

Opposite sides- sensory one side, motor opposite

Cross over extensor reflex

Step on nail w left foot pull it back (withdrawal/flexor reflex) AND react by jumping onto right foot. Stimulated side flexes, opposite side extends

Facilitation and inhibition

Facilitation that enhanced spinal reflexes - a single EPSP that does not depolarize the post synaptic neuron enuf to generate an action potential, but it is now more sensitive to excitatory stimuli (inhibition is opposite)

Reinforced reflexes

Reinforcement is facilitation that enhances spnal reflexes. Reinforced reflexes are too strong to consciously suppresses so testing them tells clinicians something about nervous system. Occurs when post synaptic neuron enters state of generalized facilitation due to chronically active excitatory synapses.

Babinski sign

In children causes toes to fan. (positive babinski sign) disappears in adults (toes will curl- negative Babinski sign) opposite results indicate CNS problem

Gray matter organization

From back to front
Sensory nuclei somatic
Sensory nuclei visceral
Motor nuclei visceral
Motor nuclei somatic

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