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Figure 2.27 Proprioceptive Reflex Control of Muscle Tension

Interaction of the muscle spindle and Golgi tendon organ during passive stretch of a muscle (panel A) and during a contraction (panels B and C).

A. Afferent inhibition

From extensor spindle receptor (Ia, II fibers)

From flexor (Ia, II fibers)

Axoaxonic presynaptic inhibitory synapse -

To extensors

B. Stretch reflex

(reciprocal inhibition)

Axoaxonic presynaptic inhibitory synapse -

To extensors

Renshaw Cell

To extensors To flexors

From extensor spindle receptor (Ia, II fibers)

Axosomatic or axodendritic inhibitory synapse

Excitatory synapse

To extensors To flexors

C. Recurrent inhibition

D. Tendon organ reflex

Renshaw cells

Collaterals

To synergistic muscles

Renshaw cells

Collaterals

To synergistic muscles

Recurrent Inhibition

From extensor tendon organ (Ib fibers)

Inhibitory synapse Excitatory synapse

From extensor tendon organ (Ib fibers)

Inhibitory synapse Excitatory synapse

To extensors To flexors

E. Flexor withdrawal reflex

Nociceptive fibers

Ipsilateral flexion

Inhibitory synapse

Excitatory synapse

To extensors To flexors

Nociceptive fibers

Inhibitory synapse

Excitatory synapse

To extensors To flexors

Inhibitory Synapse

Contralateral extension

Excitatory synapse Inhibitory synapse

To extensors To flexors

Contralateral extension

Excitatory synapse Inhibitory synapse

To extensors To flexors

Figure 2.28 Spinal Reflex Pathways

Summary of the spinal reflex pathways.

Mesencephalon (cerebral peduncles)

Spinothalamic tract

Mesencephalon (cerebral peduncles)

Spinothalamic tract

Lower part of medulla oblongata-

Reticular formation

Lateral Cervical Nucleus

Fasciculus gracilis Fasciculus cuneatus

Dorsal (posterior) spinal root ganglion

Lateral cervical nucleus Spinocervical tract

Cervical part of spinal cord

Lumbar part of spinal cord

Figure 2.29 Somesthetic System of the Body

Cerebral cortex: postcentral gyrus

Posterior limb of internal capsule

Ventral posterolateral (VPL) nucleus of thalamus

Lower part of medulla oblongata-

Reticular formation

Fasciculus gracilis Fasciculus cuneatus

Dorsal (posterior) spinal root ganglion

Cervical part of spinal cord

Lateral spinothalamic tract: pain, temperature -

Ventral (anterior) spinothalamic tract: touch, pressure

Lumbar part of spinal cord

Proprioception, position

Touch, pressure, vibration

Pain, temperature

Large myelinated fibers

Small myelinated and unmyelin-ated fibers

Lateral cervical nucleus Spinocervical tract

Figure 2.29 Somesthetic System of the Body

Pain, temperature, and pressure sensations below the head ultimately are conveyed to the primary somatosensory cortex (postcentral gyrus) by the anterolateral system (spinothalamic and spin-

sations to the thalamus (ventral posterolateral nucleus), whereas the lateral cervical system mediates some touch, vibratory, and proprioceptive sensations (blue and purple lines show these dual oreticular tracts). The fasciculus gracilis and cuneatus of the spinal pathways). Ultimately, these fibers ascend as parallel pathways to lemniscal system convey proprioceptive, vibratory, and tactile sen- the thalamus, synapse, and ascend to the cortex.

Sensory Pathways: II

neurophysiology

Pons

Spinocervical Tract

^ Cerebral cortex: ^ postcentral gyrus

Ventral posteromedial (VPM) nucleus of thalamus Internal capsule

Midbrain (cerebral peduncles)-

Ventral trigeminal lemniscus

Pontine reticular formation

Pons

Dorsal trigeminal lemniscus Trigeminal mesencephalic nucleus Trigeminal motor nucleus Principal sensory trigeminal nucleus Touch, pressure Pain, temperature Proprioception

Trigeminal (semilunar) ganglion

Ophthalmic n.

Maxillary n.

Sensory root and

Motor root of mandibular n.

Medullary reticular formation

Spinal trigeminal tract

Spinal trigeminal [

nucleus

Cervical part of spinal cord

Facial (VII) n. Vagus (X) n. Dorsolateral fasciculus (of Lissauer) Substantia gelatinosa (Iamina II)

Figure 2.30 Somesthetic System of the Head __

Nerve cells bodies for touch, pressure, pain, and temperature in the head are in the trigeminal (semilunar) ganglion of the trigeminal (CN V) nerve (blue and red lines in figure). Neuronal cell bodies mediating proprioception reside in the mesencephalic nucleus of CN V (purple fibers). Most relay neurons project to the contralateral VPM nucleus of the thalamus and thence to the postcentral gyrus of the cerebral cortex, where they are somatotopically represented.

Somatotopic Representation

Levels of principal dermatomes

C5 Clavicles

C5, 6, 7 Lateral parts of upper limbs

C8, T1 Medial sides of upper limbs

C6 Thumb

C8 Ring and little fingers

T4 Level of nipples

T10 Level of umbilicus

T12 Inguinal or groin regions

L1, 2, 3, 4 Anterior and inner surfaces of lower limbs

L4 Medial side of great toe

51, 2, L5 Posterior and outer surfaces of lower limbs S1 Lateral margin of foot and little toe

52, 3, 4 Perineum

Figure 2.31 Dermatomes

Sensory information below the head is localized to specific areas of the body, which reflect the distribution of peripheral sensory fibers that convey sensations to the spinal cord through the dorsal roots (sensory nerve cell bodies reside in the corresponding dorsal root ganglion). The area of skin subserved by afferent fibers of one dorsal root is called a dermatome. This figure shows the dermatome segments and lists key dermatome levels used by clinicians. Variability and overlap occur, so all dermatome segments are only approximations.

A. Eyeball

Suspensory ligament

B. Section through retina

Lens

Ciliary body

Suspensory ligament

Lens

Axons Nursing

Ciliary body

Optic nerve

Retina Choroid Sclera Fovea

Optic nerve

B. Section through retina

Scleral Nerves

Inner limiting membrane

Axons at surface of retina passing via optic nerve, chiasm, and tract to lateral geniculate body

Ganglion cell

Müller cell (supporting glial cell)

Amacrine cell Bipolar cell Horizontal cell Rod Cone

Pigment cells of choroid

Rod Cone Distribution

Figure 2.32 Visual Receptors

D. Rod in light

Photons of light

Synaptic ending fully polarized Synaptic bar

Synaptic ending fully polarized Synaptic bar

Nucleus

Nucleus

Lumirhodopsin

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Responses

  • Aaron
    What is the lateral cervical nucleus?
    8 years ago
  • krystian graham
    Where is the cervical tract in the body?
    8 years ago

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