Which 3 muscle types do we distinguish?
smooth
skeletal
heart
By which neuron is a skeletal muscle fiber innervated?
Each fiber by one α-motor neuron terminal
By which system is a skeletal muscle controlled?
somatic motor system
What are muscle spindles?
= specialized sensory structures within skeletal muscle
innervated by Ia sensory afferents
tell the CNS how stretched a muscle is
What´s the difference between extrafusal and intrafusal fibers?
Extrafusal fibers
innervated by α-motor neurons
move the limb
intrafusal fibers (located inside the muscle spindles)
innervated by γ-motor neurons
report muscle state, regulate sensitivity
—> α-motor neurons drive contraction, γ-motor neurons tune sensory feedback
What´s a motor unit? What is a motor neuron pool?
motor unit
1 α-motor neuron + all the muscle fibers it innervates
= contraction
motor neuron pool
all α-motor neurons + 1 single muscle e.g. biceps
Which 3 types of motor units do we distinguish?
slow
Fast-Fatigable (strongest)
Fatigue-Resistant
What´s the difference between upper and lower motor neurons?
Lower Motor Neurons
Upper Motor Neurons
α-motor neurons + γ-motor neurons
in ventral horn of the spinal cord + brain stem
motor cortex (areas 4 and 6) + brainstem
send signals to lower-motor neurons/interneurons
directly command muscle contraction by sending axons out of the CNS to innervate skeletal muscle fibers
usually no direct connection
—> descend through the spinal cord via tracts (corticospinal tract/vestibulospinal tract)
monosynaptic
descending tracts
generate muscles
initiate voluntary movements
regulate posture and locomotion
How does a monosynaptic reflex work?
Trigger: Sudden muscle stretch (e.g., a tendon tap)
Muscle stretch activates Ia afferents from muscle spindles.
Ia afferents directly excite α-motor neurons in the spinal cord.
The same muscle contracts to oppose the stretch.
e.g. knee-jerk reflex
How does a polysynaptic reflex work?
Trigger: Nociceptive (pain) input via Aδ or C afferents
e.g. The Flexor (Withdrawal) Reflex —> withdraw a limb from a painful stimulus
Aδ/C afferents enter the spinal cord
Excitatory interneurons activate ipsilateral flexor motor neurons
Inhibitory interneurons suppress ipsilateral extensors
Which other reflexes do exist?
Crossed-Extensor Reflex (polysynaptic)
—> protective withdrawal is coupled to postural stabilization
Reciprocal Inhibition: Coordinated Antagonist Suppression (polysynaptic)
reverse myotatic reflex (polysynaptic)
—> protects muscles from generating excessive force
What is the “final common pathway” of reflexes?
alpha motor neuron
Which part of the cortex are related to motor cortex? Which lobe? Gyrus? Brodmann´s area?
frontal lobe anterior the central sulcus
Area 4 = precentral gyrus
primary motor cortex
Area 6
secondary motor cortex
premotor area PMA
supplementary motor area PMA
Which functions do they have in general?
Area 4: primary motor cortex
—> execution of voluntary movements
Area 6: secondary motor cortex
—> planning of voluntary movements
PMA
—> proximal motor units
SMA
—> controls distal motor units
Which are the descending spinal tracts? What´s their function in general?
lateral pathways —> movement of the limbs
Corticospinal Tract (cortex)
Rubrospinal Tract (brainstem)
ventromedial pathways —> orientation, posture, balance (brainstem)
Vestibulospinal Tracts (balance + orientation)
Tectospinal Tract (balance + orientation)
Pontine Reticulospinal Tract (posture)
Medullary Reticulospinal Tract (posture)
What´s the main pathway for voluntary movements? + detailed pathway
Corticospinal Tract
motor cortex —> internal capsule and brainstem —> Fibers cross at the pyramidal decussation
—> controls precise voluntary movement, especially distal limbs
Where does the Rubrospinal Tract come from exactly?
brainstem —> nucleus ruber (Midbrain)
Vestibulospinal Tracts
Tectospinal Tract
Where do they come from? Which regions do they innervate?
brain stem
—> vestibular nuclei of the medulla
—> superior colliculus (optic tectum) of the midbrain
—> balance and orientation
—> head, neck, and postural reflexes
Pontine Reticulospinal Tract
Medullary Reticulospinal Tract
—> pontine reticular formation located in the pons
—> medullary reticular formation located in the medulla
—> posture
—> regulate whole-body motor state
summary
Which pathways exist? Where do they come from? Where do they end?
lateral pathways
cortex —> corticospinaltract
brainstem —> red nucleus (Midbrain) —> rubrospinal tract
ventromedial pathways (all from brainstem)
pontine reticular formation (Pons) —> Pontine Reticulospinal Tract
medullary reticular formation (Medulla) —> Medullary Reticulospinal Tract
superior colliculus/optic tectum (Midbrain) —> Tectospinal Tract
vestibular nuclei (Medulla) —> Vestibulospinal Tracts
= end in spinal cord
Which belong to the extrapyramidal system?
all descending motor pathways except the corticospinal (pyramidal) tract
Are PD and HD extrapyramidal or pyramidal diseases?
extrapyramidal disorders because they affect the basal ganglia, NOT the corticospinal tract (which would cause spastic paralysis)
What is the entry point to the basal ganglia?
striatum = nucleus caudatus + Putamen
What is known as the motor loop of the basal ganglia?
Cortex PFC+motor cortex+sensory cortex—> Striatum —> Globus pallidus —> Thalamus (VLo-Kern) —> Cortex, especially supplementary motor area (SMA) = BA6
= Initiating Deliberate Movements
(basal ganglia in Striatum and Globus pallidus)
Which role does the Cerebellum play?
—> doesn't initiate movement, but it fine-tunes
The cerebellum calibrates movement
Receives input from spinal cord, brainstem and cortex
Compares intended movement with sensory feedback
Outputs via deep cerebellar nuclei
Refines timing, precision, coordination and motor learning
What is the motor loop of the lateral cerebellum?
motor cortex (BA4,6) + sensory cortex —> Pons —> pontine nuclei —> Cerebellum on the opposite side
—> compares the intended goals of movements (relayed from the cortex) with the current body position (relayed from the spinal cord)
—> deep cereballar nuclei —> ventral lateral nucleus (VLc) of the thalamus —> primary motor cortex 4
Which are the “cerebellar signs”?
—> Cerebellar disease disrupts movement accuracy, not basic strength
Ataxia
Dyssynergia
Dysmetria
Intention tremor
What are the general dysfunction patterns of
basal ganglia
cerebellum
corticospinal tract
brainstem pathways
hypo-/hyperkinesia
ataxia, dyssynergia, dysmetria, intention tremor
weakness, spasticity, Babinski
postural/gait instability
What should you keep in mind about proprioception in muscle spindels/Golgi tendon?
Muscle spindles
Golgi tendon
embedded within skeletal muscles (intrafusal fibers, innervated by γ-motor neurons)
between muscle fiber and tendon
detect length
detect tension
use Ia afferents
use Ib afferents
trigger monosynaptic stretch reflex
trigger polysynaptic reverse myotatic reflex
excitation of α-motor neurons
inhibition of α-motor neurons
= relaxation
in parallel
in series
What links electrical excitation to mechanical contraction?
Ca²⁺
Motor neuron activates the muscle fiber
Depolarization spreads through T-tubules
The sarcoplasmic reticulum releases Ca²⁺
Ca²⁺ binds troponin
Actin-myosin interaction generates contraction
Ca²⁺ reuptake into SR allows relaxation
Zusammengefasst:
Which pathways do we distinguish? Where do they come from?
Which of these pathways are extrapyramidal?
all except corticospinaltract
What is false when evolving PD or HD
What is Tetraplegia?
= loss of movement and control in both the arms and the legs due to an interruption of the motor signals descending from the brain to the spinal cord
= damage to upper motor system
Last changed6 days ago
