Chapter 12.6 & 13 Neural Integration and Spinal Cord

Postsynaptic potentials - most important determinants of neural activity are?

EPSP/IPSP interactions

EPSP

(excitatory postsynaptic potential) = depolarization

IPSP

(inhibitory postsynaptic potential) = hyperpolarization

EPSPs and IPSPs can combine through?

• Temporal summation

• spatial summation

  • Facilitation/inhibition

Mixed summation

Spatial Summation

Temporal summation

Inhibition

• GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob

• Reduces amount of neurotransmitter released when action potential arrives

Facilitation

• Activity at axoaxonal synapses increases amount of neurotransmitter released when action potential arrives

• Enhances and prolongs the effect of the neurotransmitter

Determination of the strength of a stimulus can be coded through?

Recruitment (more neurons fire) or by the rate of generation of action potentials are often used to interpret the signal

Neuronal pools

Functional group of interconnected neurons

Neural circuit patterns

• Divergence

• convergence

• Reverberation

• serial processing

• parallel processing

Localized enlargements provide innervation to limbs

• cervical enlargement

• lumbar enlargement

Conus medularis

Tapered conical portion of the spinal cord below lumbar enlargement

Filum terminale

fibrous tissue that supports the spinal cord below the conus medularis

Dura mater

Longitudinal collagen fibers

Arachnoid

• elastin and collagen fibers

• lined with simple squamous epithelium

• Subarachnoid space contains CSF

Pia Mater

• meshwork of elastin and collagen fibers

• Denticulate ligaments extend from pis mater to dura mater

White matter

Is myelinated and unmyelinated axons; exterior portion of the spinal cord

Gray matter

is cell bodies, unmyelinated axons and neuroglia; interior portion of the spinal cors

Nuclei

Are cluster of neuron cell bodies in the gray matter of the brain or spinal cord

Ganglia

are cluster of neuron cell bodies outside the CNS

Posterior gray horns

contains somatic and visceral sensory nuclei

Anterior gray horns

contains somatic motor neurons

Lateral gray horns

contain visceral motor neurons

Gray commissures

contain axons that cross froom one side to the other

Ascending tracts

relay information from the spinal cord to the brain

• sensory tracts

Descending tracts

carry information from the brain to the spinal cord

• motor tracts

Tracts

Are groups of nerve fibers carrying similar information to similar destinations. Anatomically, tracts are formed into columns, or fasciculi in the spinal cord

Ascending tracts

Carry sensory information toward the brain

• have three neurons in series. May have collaterals or connect to interneurons that go to other regions in divergent pathways

Descending tracts

Carry motor information from the brain

• have two neurons in series. May have collaterals or connect to interneurons that go to other regions in divergent pathways

first order neurons

Sensory neurons that deliver information to the CNS

• Cell bodies are in the dorsal root ganglia

Second order neurons

Interneurons in the CNS that synapse with axons from first order neurons

• they are in nuclei within the spinal cord or lower brain regions

• send axons to the thalamus

Third order neurons

Found in the thalamus

• if the sensation will reach conscious awareness (perceived) they send axons to the primary sensory area of the cerebral cortex (on the same side of the body)

• Collaterals go to other regions (sensory association areas, limbic system, other interpretation areas)

Somatic Sensory Pathways three major pathways carry sensory information, that are further subdivided

• posterior (dorsal) column pathways

  • Fasciculus gracilis

  • fasciculus cuneatus

• Anterolateral pathways (spinothalamic and others)

• Spinocerebellar pathways

Fasciculus gracilis

Carry information from inferior portion of the body

Fasciculus cuneatus

Carry information from superior portion of the body, upper limbs and neck

Second order neurons are in the nucleus gracilis or nucleus cuneatus within the medulla

They decussate and then relay information to the thalamus via a tract called the medial lemniscus

Anterolateral Pathway

Carries poorly localization sensations of crude (light) touch, pressure, pain, itchm and temperature

Second order neurons

are in the posterior gray horn of the spinal cord. Axons decussate in the spinal cord and ascend within the anterior and lateral spinothalamic tracts

Spinocerebellar pathway

Carries sensation to the cerebellum concerning proprioception

Proprioception

position of muscles, tendons and joints

Posterior spinocerebellar tracts

• uncrossed axons (ascend on the same side)

• Enter cerebellum via interior peduncle

Anterior spinocerebellar tracts

• mostly crossed but some uncrossed axons

• most crossed axons re-cross in the pons or cerebellum

Upper motor neuron

Cell body lies in the CNS processing center

Lower motor neuron

• Cell body located in the motor nucleus of the brain (for motor cranial nerves) or spinal cord and send axons to skeletal muscles

• Each lower motor neuron innervates a single motor unit and cause contraction of a muscle

Somatic Motor Pathways (3)

• Corticospinal & cortical bulbar pathway

• medial pathways

• lateral pathway

Basal nuclei and cerebellum monitor and adjust activity within these pathways

Facilitate or inhibit neurons

The corticospinal pathway (pyramidal system)

• Starts with pyramidal cells of the primary motor cortex

• Provides voluntary skeletal muscle control

Corticobulbar tracts

Terminate at cranial nerve nuclei

• control jaw, eye, face, some neck muscles

Corticospinal tracts

Synapse on motor neurons in the anterior gray horns of the spinal cord

• Visible along medulla as pyramids

Gracile Fasciculus/Cuneate fasciculus

• posterior

• in medulla

• Sensation of limb and trunk position and movment, deep touch, visceral pain, and vibration, below level T6

Spinothalamic

• lateral and anterior

• in spinal cord

• sensation of light touch, tickle, itch, temperature, pain, and pressue

Spinoreticular

• lateral and anterior

• spinal cord (some fibers)

• Sensation of pain from tissue injury

Posterior/Anterior(spinal cord) spinocerebellar

• lateral

• None of one of them and in spinal cord for the other

• Feedback from muscles (proprioception)

Lateral corticospinal

• lateral

• in medulla

• frin control of limbs

Anterior corticospinal

• anterior

• in spinal cord

• fine control of limbs

Tectospinal

• Anterior

• in midbrain

• Reflexive head turning in response to visual and auditory stimuli

Lateral reticulospinal

• lateral

• none

• Balance and posture; regulation of awareness of pain

Medial reticulospinal

• anterior

• none

• same as lateral reticulospinal

Lateral vestibulospinal

• anterior

• none

• balance and posture

Medial vestibulospinal

• anterior

• in medulla (some fibers)

• Control of head position

Dorsal roots contain

SENSORY AXONS

Ventral roots contain

MOTOR NEURONS

Nerve plexus

Complex interwoven network of nerves from different

spinal nerves made of mixed nerves (contain both

sensory and motor neurons)

Four large plexuses

Cervical plexus

Brachial plexus

lumbar plexus

Cervical plexus

Innervates neck, thoracic cavity, diaphragm, phrenic nerve

Brachial plexus

Innervates pectoral girdle and upper limbs

Lumbar plexus and sacral plexus

innervate the pelvic girdle and lower limbs, sciatic nerve

Reflex Arc

• Arrival of stimulus and activation of receptor

• Activation of sensory neuron (afferent pathway)

• Integration / Information processing (interneurons)

• Activation of motor neuron (efferent pathway)

• Response by effector (muscle or a gland)

Innate reflexes

Result from connections that form

between neurons during development (e.g. chewing, sucking,

tracking).

Acquired reflexes

Learned, and typically more

complex (e.g. driving skills, bell ringing and leave class, typing)

Cranial reflexes

Reflexes processed in the brain (startle reflex)

Spinal reflexes

Interconnections and processing events

occur in the spinal cord (e.g. knee jerk reflex)

Somatic Reflexes

• Control skeletal muscle

• They are imprecise and crude (e.g. the knee jerk reflex)

• Provide a rapid response (e.g. pull away from a hot

surface)

• Often modified by higher centers

Visceral reflexes

Control activities of other systems (e.g. blood pressure,

urination, defecation)

Monosynaptic reflex

Sensory neuron synapses directly on a motor neuron

(there is no interneuron)

Polysynaptic reflex

• At least one interneuron between sensory afferent and

motor efferent

• Because of synaptic delay, the more interneurons

there are the slower the reflex i.e. the longer delay

between stimulus and response

Stretch reflex

automatically monitors skeletal muscle

length and tone

• Patellar (knee jerk) reflex

sensory receptors are?

Muscle spindles

Postural reflexes

Maintains upright position

Muscle spindles

Specialized muscle regions used as sensory stretch receptors

Extrafusal muscle fibers

alpha (a) motor neurons

Intrafusal muscle fibers

gamma (y) motor neurons

Golgi tendon reflex

• prevents contracting muscles fromapplying excessive tension to tendons

• Produces sudden relaxation of the contracting muscle and activation of the antagonistic muscles

Reinforcement and inhibition

• brain can facilitate motor patterns based in spinal cord

• complex movements such as walking can work by having the brain initiate reflex movements

• Reinforcement

Reinforcement

Facilitation that enhances spinal reflexes

Spinal relexes can also be inhibited an example is?

Babinski relex replaced by the planter reflex

Planter reflex

Babinski sign

Withdraw and crossed extensor reflexes

• ipsilateral

• Contralateral

Flexor and Inhibitory Reflexes

Golgi Tendon organ

Muscle spindle relfec arches

Stretch Reflex (e.g. patellar reflex)

1

Phrenic nerve

2

Sciatic nerve

3

Cervical plexus

4

Brachial

5

Lumbar plexus