module 2 - nbl 356

where does the extrapyramidal (indirect) system originate?

in specific nuclei in brainstem and travel to spinal cord

what tracts are included in the extrapyramidal system? (4)

rubrospinal, reticulospinal, vestibulospinal, and tectospinal tracts

rubrospinal tract

only extrapyramidal tract involved in voluntary movements

what are the rest of the extrapyramidal tracts involved in?

unconscious control of balance, posture, coordination, locomotion, and reflexes

origin of reticulospinal tract

reticular formation (located in midbrain, pons, and medulla)

what does the reticulospinal tract include?

ascending pathways to the cortex and descending pathways to the spinal cord

what is the reticulospinal tract responsible for?

descending tract - postural control and locomotion

2 tracts under reticulospinal tract

potine and medullary: originate in pons or medulla

axons of pontine and medullary tracts

somatic axons in these synapse on local interneurons and lower motor neurons

what axons/neurons does the reticulospinal tract have?

autonomic and somatic

origin of vestibulospinal tract

vestibular nuclei in pons and medulla

where does the vestibular nuclei receive info from?

receive info thru vestibulocochlear nerve about changes in orientation of head and relay motor commands thru tract

function of motor commands of vestibulospinal tract

alter muscle tone, extend, and change position of limbs and head to support posture and maintain balance

origin of tectospinal tract

tectum (superior colliculus) in midbrain

what is the tectospinal tract involved in?

reflex postural movements of head in response to visual and auditory stimulus

what does the tectospinal tract coordinate/control?

coordinates head and eye movements and controls head and neck movements

superior coliculus (2)

receives afferent inputs from visual nuclei; then, projects to cranial nerve motor nuclei in midbrain and pons and 1st cervical segments of SC

origin of rubrospinal tract

magnocellular red nucleus in midbrain

what is the rubrospinal tract involved in?

voluntary muscle control of limbs

termination of rubrospinal tract

terminates by synapsing w/interneurons in SC and terminates primarily in cervical and thoracic portions (upper limbs)

what is the rubrospinal tract responsible for?

large muscle movement regulation flexor and inhibiting extensor tone and fine motor control

size of rubrospinal tract in humans

small and rudimentary

upper motor neurons in extrapyramidal tracts

located in nuclei in brainstem and extend axons, form tracts in SC, and synapse on spinal INs and LMNs in SC ventral horn

2 tracts in lateral system

lateral corticospinal and rubrospinal tracts

location of meduallary reticulospinal tract

lateral

location of pontine reticulospinal tract

medial

tracts in ventromedial/medial system (4)

anterior/ventral/medial corticospinal tract; reticulo-, vestibulo-, and tecto- spinal tracts

dorsal and ventral roots

lie on outermost lateral dorsal and ventral regions of SC

axons of dorsal and ventral roots

where sensory axons enter (dorsal) and motor axons exit (ventral)

what regions are the dorsal and ventral horns

gray matter regions

what does gray matter region contain? (5)

contain neuronal cell bodies, dendrites, synapses, gray matter astrocytes, and blood vessels

what does white matter region include? (4)

ascending/sensory tracts and descending/motor tracts that contain myelinated axons, oligodendrocytes, white matter astrocytes, and blood vessels

secondary sensory neurons

in the SC, the neurons that relay sensory info

where are somatic and visceral secondary sensory neurons located?

dorsal horn; visceral in lower region and somatic in upper region

where are spinal INs and somatic MNs located? (2)

ventral horn; both in region called lateral horn

primary sensory neuron cell bodies (somatosensory neurons)

located in dorsal root ganglion and synapse and transmit sensory info to secondary sensory neurons located in dorsal horn

where are cell bodies of LMNs located?

in the ventral or lateral horn

all spinal nerves are

mixed nerves

mixed nerves

axons from sensory and motor, somatic and visceral neurons will merge and be located in each of the spinal nerves

major regions of SC (posterior to anterior) (5)

cervical, thoracic, lumbar, sacral, coccygeal

vertebral column and meninges

serve to protect and cushion SC and allow flow of CSF around it

cervical and lumbar are located where

diameter is larger than in other regions

what do cervical and lumbar regions contain?

higher gray matter bc more spinal INs, LMNs, and secondary sensory neurons

what do cervical and lumbar regions control? (2)

areas that have high degree of innervation; ex: arms-hands and legs-feet

2 types of spinal INs in ventral horn

excitatory (glutamatergic) and inhibitory (glycinergic-GABAergic)

2 types of LMNs of somatic motor system

alpha and gamma

all LMNS are

cholinergic

where are alpha and gamma MNs located?

ventral horn

axons of alpha and gamma MNs

axons exit SC thru ventral root

alpha and gamma MNs travel

in spinal nerves to innervate skeletal muscles

alpha MNs innervate

extrafusal muscle

what does extrafusal muscle involved in?

in muscle contraction that lengthens or shortens muscles that produce force and does work to produce movement

gamma MNs (2)

innervate intrafusal muscle (muscle spindle); involved in muscle tone

muscle spindle (2)

sensory receptor that sends info ab muscle stretch back to SC; this info is to ensure muscle tension is maintained and protects muscles from damage

gamma MNs induce

contraction or relaxation of spindle that maintains size and tension of muscle spindle so it can act as accurate sensor

what do muscle cells contain?

protein filaments of action and myosin that slide past one another, producing a contraction that changes both the length and shape of the cell

what are muscle cells responsible for? (3)

maintaining and changing posture, locomotion, and movement of internal organs such as contraction of heart

tendons

most skeletal muscles are attached to bones by bundles of these collagen fibers

muscle fiber =

muscle cell (myofiber)

muscle fibers

individual contractile units w/in muscle

a single muscle contains

many muscle fibers

when are individual muscle fibers formed?

during development from fusion of undifferentiated immature cells, called myoblasts, to long, cylindrical, multi-nucleated cells

what does a motor unit consist of?

single alpha LMN and all muscle fiber it innervates

motor pool

all motor units w/in a muscle

when is movement generated?

when UMN and spinal INs synapse an alpha LMN, which activates motor unit, causing coordinate contraction

many movements and reflex arcs involve

coordinated contraction in 1 muscle and inhibited contraction in opposing muscle

flexors

decrease angle around joint

extensors

increase angle around joint

when flexer contracts,

opposing extensor relaxes and vice versa

reason for flexor and extensor opposing contraction/relaxation (3)

muscles wont work against each other, prevents muscle strain and injury, and ensures muscle contraction can produce finely tuned movement

what does a motor pool include?

all alpha LMNs that innervate a single muscle; LMNs that innervate all types of muscle fibers including all types of fast and slow twitch fibers

where are somatic LMNs located?

in ventral horn

location of neurons that control flexors and extensors

flexor neurons are located above extensor neurons

2 lateral SC systems

cortico- and rubro- spinal tracts

what do the 2 lateral SC systems control?

voluntary movement of distal muscles in arms-hands and legs-feet