PNS (Motor)

Motor cortex

The part of the cerebral cortex responsible for planning, controlling, and executing voluntary movements of the body. It sends signals to muscles through the peripheral nervous system.

• in frontal lobe

Pyramidal system

A collection of motor pathways that originate in the motor cortex and are involved in voluntary movement control, transmitting signals to spinal neurons.

• Cortiocospinal tract

• Corticobulbar tract

Corticobulbar tract

A pathway that carries signals from the motor cortex to the cranial nerves, responsible for voluntary movements of the face, head, and neck.

• descends towards brainstem

Lateral corticospinal tract

controls muscles in appendicular skeletal muscle

Ventral (anterior) corticospinal tract

controls muscles in axial skeletal muscle, influencing posture and balance.

Extrapyramidal tracts

Rubrospinal tract, reticulospinal tract, and vestibulospinal tract that are involved in involuntary and automatic control of muscles, reflex pathways

Alpha motor neuron- what is it, where are each parts located?

A type of motor neuron located in the spinal cord that directly innervates skeletal muscle fibers, causing muscle contraction.

• cell body in ventral (anterior) horns (grey matter)

• axon travels through ventral root, spinal nerve, peripheral nerves and terminates at the neuromuscular junction.

Dorsal horn

The dorsal horn is a region of the spinal cord that contains sensory neurons, receiving and processing sensory information from the peripheral nervous system before transmitting it to the brain.

Ventral horn

The ventral horn is a region of the spinal cord that contains motor neurons, which innervate skeletal muscles, playing a crucial role in motor control and voluntary movement.

Medial motor neurons

control axial muscles

Lateral motor neurons

control appendicular muscles

What spinal areas have enlarged gray matter and why?

The cervical and lumbar regions have enlarged gray matter because they contain a higher concentration of motor neurons that innervate the upper and lower limbs, respectively.

Sensory + motor innervation afferent route

1. sensory receptors

2. Dorsal ramus

3. Spinal nerve

4. Dorsal root

Sensory motor innervation efferent route

1. ventral root

2. spinal nerve

3. ventral ramus

Spinal plexuses

networks of fused ventral rami to innervate one body region

primary motor cortex

the region of the brain responsible for planning, controlling, and executing voluntary movements.

What do the primary motor cortex receive signals from

premotor, supplementary, and association prefrontal cortex.

Premotor cortex

• controls muscles responses to visual or sound cues

• stores motor memory

• planning of multi-step sequence of actions

Supplementary motor area

motor area is involved in the planning and coordination of movement, particularly in sequences of movements and bimanual coordination.

Association prefrontal cortex

ensure muscle movement behavior is appropriate (tourettes)

posterior parietal cortex

region that integrates sensory information for spatial awareness and guides movements.

Upper motor neuron

Brain to ventral horn (before synapse)

Lower motor neuron

Ventral horn to muscles (after synapse)

Direct pyramidal pathway

A neural pathway that directly connects the motor cortex to lower motor neurons in the spinal cord, facilitating voluntary movement control.

• motor cortex to skeletal muscle

Indirect pyramidal pathway

A neural pathway that connects the motor cortex to lower motor neurons via multiple synapses with intermediary neurons. It modulates voluntary movement through various brainstem structures.

• brainstem to muscle

Vestibulospinal tracts

• balance and posture

• bilateral and ipsilateral

Bilateral

refers to signals or functions that are transmitted or expressed on both sides of the body or through both hemispheres of the brain, ensuring coordinated activity.

Ipsilateral

refers to signals or functions that are transmitted or expressed on the same side of the body or brain, facilitating localized responses.

Tectospinal tracts

are involved in reflexive head and eye movements in response to visual and auditory stimuli, assisting with orientation.

Reflexive pathways

are neural circuits that mediate reflex actions, allowing for rapid and automatic responses to stimuli without direct involvement of the brain.

Somatic

involving skeletal muscle

Autonomic

involving smooth muscle

autonomic efferent pathway

• motor neuron → ventral root, travels from myelinated axon → synapses at ganglion → travels down unmyelinated, post synaptic axon → post ganglionic variosity

What happens when the eye encounters dim light?

• Sympathic nervous system is stimulated

• Central neuron synapses w/superior cervical ganglion of sympathetic chain

• Sympathetic postsynaptic neuron releases Norepinephrine, stimulates radical muscles to contract

• radical smooth muscle dilates pupils

What happens when the eye encounters bright light?

• Parasympathetic nervous system is activated

• Central neuron synapses with the Edinger-Westphal nucleus in midbrain

• Parasympathetic postsynaptic neuron releases Acetylcholine, causing circular muscles to contract

• Circular smooth muscle constricts pupils

Patellar stretch (knee jerk) reflex

• somatic reflex

• Activation of stretch receptors→ send afferent signal to spinal cord → synapse in spinal cord at motor neuron → motor neuron sends efferent signal to quadriceps muscle, causing contraction and leg extension.

Golgi tendon organ

A sensory receptor located at the junction of muscles and tendons, responsible for sensing muscle tension and preventing excessive force during contraction.

Spastic paralysis

• upper motor neuron injury

• ‘region of paralysis depends on location of injury

Contralateral spastic paralysis

weakness or loss of function on the opposite side of the body from the injury site.

• Results if corticospinal cord is injured above decussation in caudal medulla

Lower motor neuron injury

• ventral root neurons/ alpha motor neurons

• Only muscles innervated by that level of the spinal cord are affected

• same side of the body

• characterized by weakness, atrophy, and decreased reflexes in affected muscles.

Frontal lobe stroke symptoms

• loss of fine motor skills

Hemiplegia

is the total loss of movement on one side of the body, often resulting from a stroke or brain injury. It affects the side opposite to the injury and can cause significant impairment in mobility and function.

Ischemic stroke

lack of oxygen

Haemorrhagic stroke

occurs when a blood vessel in the brain bursts, leading to bleeding in or around the brain. This type of stroke can cause increased pressure on brain tissues and can be life-threatening.

Extrapyramidal systems

modulation of motor neurons in spinal cord that is not directly through pyramidal system, but through basal ganglia and cerebellum

Basal Ganglia

Deep gray matter

• promotes movement we want

• suppresses unwanted movements

Striatum (STR)

Part of the basal ganglia, the striatum is involved in coordinating movement and reward processing. It receives input from the cerebral cortex and is critical for motor control.

• Active during movement

GPe, GPi

The globus pallidus externus (GPe) and globus pallidus internus (GPi) are components of the basal ganglia that play a crucial role in regulating voluntary movement by inhibiting thalamic activity.

• active when muscles are at rest

STN

Modulates GPi in indirect pathway

• activates GPi (which is inhibitory)

SN

A nucleus in the midbrain involved in the production of dopamine, the substantia nigra (SN) plays a key role in movement control and reward pathways, and is often affected in Parkinson's disease.

Direct pathway

Promotes movement through disinhibition

1. Cortex sends glutamate (excitatory neurotransmitter) to STR

2. STR sends GABA (inhibitory neurotransmitter) to GPi, inhibiting its activity

3. Inhibits thalamus, thalamus releases glutamate to the cortex, facilitating movement by promoting motor signals.

disinhibition

Inhibiting inhibitory neuron activity, leading to increased excitation of target neurons.

Indirect pathway

Inhibits movement through excitation of inhibitory neurons.

1. cortex sends glutamate to STR, which in turn sends GABA to GPe, inhibiting it

2. GPe inhibition activates (reduces inhibition) of STN

3. reducing inhibition on STN leads to increased inhibition of GPi,

4. inhibites thalamus, thalamus sends less glutamase to cortex, less excitation to cortex

Role of SN in direct and indirect pathways

promotes direct pathway

inhibits indirect pathway

Dykinesia

involuntary muscle movements or spasms due to impaired regulation of motor control.

Akinesia

a condition characterized by the loss of voluntary movement

Hypokinesia

poor movements (Parkinsons)

Hyperkinetic

is a condition characterized by excessive movement or uncontrollable physical activity, often associated with disorders like dyskinesia.

Deep Brain Stimulation (DBS)

Treatment for Parkinson’s

• sends mild electrical impulses to STN and GPi

Cerebellum

is a brain structure located at the back of the skull, responsible for coordinating voluntary movements, balance, and motor learning.

• recieves proprioception info

• modulates thalamus

Recieves info from spinal cord and brainstem, sends it to thalamus, thalamus sends it to motor cortex

Cerebellar ataxia

is a neurological condition characterized by the lack of voluntary coordination of muscle movements, leading to unsteady movements and difficulty with balance.

• wide gait, tremor after movement

Where is decussation for the lateral corticospinal tract?

Decussation of the lateral corticospinal tract occurs in the medullary pyramids, where approximately 90% of the fibers cross to the opposite side before descending into the spinal cord.

Where is decussation for the anterior corticospinal tracts?

Decussation of the anterior corticospinal tract does not occur at the medullary pyramids; instead, these fibers typically cross at the level of the spinal cord where they exert their influence.

Spastic vs Flaccid paralysis

Spastic

• upper motor neuron injury

Flaccid

• lower motor neuron injury.

what type of paralysis depends on the location of the injury

spastic- if injured above decussation in medulla → contralateral paralysis

if injured below decussation → ipslateral paralysis