NSCI 2101 Exam 3

somatomotor system

controls striated skeletal muscles responsible for voluntary movement

autonomic motor system

parasympathetic and sympathetic control of involuntary movements

• heart, blood vessels, digestive tract

upper motor neurons

neurons that originate in the cerebral cortex and send signals to lower motor neurons in the spinal cord to initiate voluntary movement

lower motor neurons

neurons that originate in the brainstem & spinal cord and directly innervate skeletal muscles that are responsible for executing voluntary movements

where are the somas of lower motor neurons located?

ventral horn of spinal cord and brainstem, cranial nerve motor nuclei

axon pathway of lower motor neurons

exit ventral root → merge with spinal nerves (AFTER dorsal root ganglion) → travel to target skeletal muscle

neuromuscular junction

neuron-muscle contraction site where synapses occur

type I muscle fibers

thin, low force, resistant to fatigue due to higher mitochondria

type IIa muscle fibers

thicker, immediate speed/force, moderate fatigue

type IIb muscle fibers

thick, fast, high force muscles that fatigue easily

muscle changes due to sustained exercise

increase in type I fibers (running=lean muscle)

muscle changes due to high intensity exercise

increase in type II fibers (bulky strength)

muscle contraction mechanisms

acetylcholine triggers Ca release → actin-myosin complex for contraction

Ach (acetylcholine) receptors

ligand gated ion channels. activation of these channels = depolarization

motor unit

a neuron and the muscle fiber it innervates

small motor units

fine control in hands and face

large motor units

coarse control in thighs/back

location of motor cortex

precentral gyrus of frontal lobe

function of motor cortex

voluntary movements (somatotopically organized)

damage to the motor cortex

leads to paralysis of specific muscle groups contralaterally

lower motor neurons are controlled by:

• local circuits

  • sensory neurons (reflexes)

  • spinal cord neurons

• upper motor neurons (voluntary control)

premotor cortex

involved in planning and executing movements

• somatosensory cortex

• thalamus

somatosensory cortex (in relation to somatosensory cortex)

integrates senses into movement planning

thalamus (in relation to the premotor cortex)

relays movement coordination

pyramidal tracts

• corticobulbar tract

• corticospinal tract

corticobulbar tract

a pyramidal tract that controls head and neck muscles via cranial nerves

• starts in premotor cortex

where does the corticobulbar tract originate?

primary motor cortex

corticospinal tract

a pyramidal tract that controls neck down

• lateral

• ventral

lateral corticospinal tract

crosses midline (decussation) for lower limb movements

ventral anterior coricospinal tract

projects bilaterally (doesn’t cross) to the body’s trunk

rubrospinal tract

non pyramidal tract that controls fine limb coordination

rubrospinal tract circuit

red nucleus → spinal cord

vestibulospinal tract

nonpyramidal tract that controls balance and head position

vestibulospinal tract circuit

vestibular nucleus → spinal cord

reticulospinal tract

nonpyramidal tract involved in posture control

reticulospinal tract circuit

reticular formation → spinal cord

tectospinal tract

nonpyramidal tract involved in head-eye coordination

tectospinal tract circuit

superior colliculus → cervical spinal cord

acetylcholine

neurotransmitter utilized by motor neurons to contract muscles

one neuromuscular junction..

per muscle fiber (1:1)

one motorneuron to…

several muscle fibers

one muscle fiber to…

only one motorneuron

basal ganglia

group of interconnected subcortical structures that process info for movement and decision making

striatum

in relation to basal ganglia. contains:

• caudate nucleus

• putamen

• nucleus accumbens

global pallidus

• external (GPc)

• internal (GPi)

substantia nigra

• pars compacta (SNc)

• pars reticula (SNr)

medium spiny neurons

neurons in the striatum that project to multiple structures of the basal ganglia

exciting the striatum has what effect?

excitement of the thalamus

neurotransmitter involved in excitement of basal ganglia circuitry

glutamate via corticostriatal neurons onto medium spiny neurons

neurotransmitter involved in inhibition of outputs in basal ganglia

GABA

output of basal ganglia

GPi & SNr→ thalamus → cortex

input of basal ganglia

cortex → striatum

corticostriatal neurons

cortical projections to the striatum. involved in the input to basal ganglia

where do corticostriatal neurons project?

signals with glutamate onto medium spiny neurons in the striatum

cerebellum

involved in movement synergy, muscle tension/fluidity, balance, posture, motor learning, and attention/reward learning

lobes of cerebellum

• vermis (middle)

• hemispheres

cerebellar penduncles

pathways connecting the cerebellum to the brainstem

• superior

• middle

• inferior

superior cerebellar penduncle

connects to the midbrain

middle cerebellar peduncle

connects to the pons

inferior cerebellar peduncle

connects to the medulla

cerebellar cortex

made of folia

arbor vitae

white matter tracks of the cerebellum

cerebellar cortex layers

1. molecular layer: axons and dendrites

2. purkinje layer: purkinje cell bodies

3. granule layer: granule cell bodies

granule cells

sends axons to molecular layer

purkinje cells

neurons with extensive dendritic trees that are the only output of the cerebellum

inputs of the cerebellar cortex

• mossy fiber

• climbing fibers

mossy fibers

input cells of the cerebellum that contact granule cells

from where do mossy fibers receive input?

cerebral cortex, vestibular nucleus, spinal cord

climbing fibers

input cells of the cerebellum that contact ourkinje cells

from where do climbing fibers receive input?

olivary nucleus in the medulla

output of cerebellum

purkinje cells send axons to deep cerebellar nuclei

spinocerebellum

coordinates posture and movement corrections. receives proprioceptive info from spinocerebellar tracts and cranial nerves

processing of spinocerebellum

vermis & intermediate hemispheres → interposed nuclei → red nucleus → spinal cord

cerebrocerebellum

involved in learned movements. receives input from cerebral cortex via pontine nucleus

processing of cerebrocerebellum

lateral hemispheres → dentate nucleus → thalamus → cerebral cortex

vestibulocerebellum

maintains balance and coordinates head/eye movements. receives input from vestibular nuclei and nerve

processing of vestibulocerebellum

floculonodular lobe → fastigial nuclei & vestibular nuclei → spinal cord & cranial nerves

how are rhythmic patterns of locomotion generated?

central pattern generators

how are rhythmic patterns modulated for complex locomotion?

ascending and descending inputs onto CPGs

central pattern generators

network of neurons (in the spinal cord) that are capable of patterned firing w/o sensory feedback

flexors

muscles that bend the limb

extensors

muscles that straighten the limb

mutual inhibition

alternation between flexor and extensor muscles via excitatory and inhibitory interneurons

ipsilateral coordination

coordination between opposing muscles (flexors/extensors) on the same side of the body

contralateral coordination

coordination on the opposite side of the body

EphA4 gene

controls development of excitatory or inhibitory neurons interneurons when crossing the midline

what happens without the Eph4 gene?

excitatory neurons cross midline, causing contralateral excitation

involvement of sensory feedback on walking

modulates timing of steps, even when the brain is disconnected from movement control centers

mesencephalic locomotor region

in midbrain. releases glutamate to initiate CPG activity

1a afferents

detects proprioception from muscle spindles— detects stretch

1b afferents

detects proprioception from golgi tendon— detects contraction

golgi tendon organs

provides info on weight bearing— muscle load

muscle spindles

provides info on stage of walking (swing vs stance)

ascending pathways of locomotion

golgi tendon organs and muscle spindles

descending pathways of locomotion

mesencephalic locomotor region

which neurotransmitters initiate walking?

glutamate

which neurotransmitters modulate walking?

norephinephrine and serotonin

goal of eye movements

align foveae on objects of interest to maintain a clear, focused image

fixation

stabilizing gaze on particular point

saccades

rapid, conjugate eye movements to shift focus