MOTOR SYSTEMS I and II

Extremes and lows of golgi tendon reflex

injury/muscle tear ; too relaxed

Alpha motor neuron function

innervate and cause contraction of skeletal muscle fiber

Where do axons of sensory neurons in stretch reflex extend to

spinal cord, directly synapsing with alpha motor neurons

Basic functional unit of nervous system reflex

reflex arc

Basic functional unit of nervous system

neuron

Stimulatory basal nuclei function

inhibits unecessary movements, fine tunes voluntary movement

Basal nuclei disorders

cerebral palsy, huntington & parkinson disease

Divisions of motor system

somatic (voluntary), autonomic (involuntary)

Function of motor system (of brain and SC)

balance, posture, trunk, head, limbs, eyes, facial expressions speech

Function of cerebral cortex

communicates with basal nuclei and cerebellum to plan, coordinate, execute movement

Upper motor neuron function

connect cortex to LMN via interneuron/directly

Lower motor neuron function

connects UMN to skeletal muscles

Where are cell bodies of UMN

motor area of cortex

Where are cell bodies of LMN

• ventral horn of spinal cord

• cranial nerve nuclei of brainstem

What are 3 basal nuclei

corpus striatum, substantia nigra (2 main), STN subthalamic nucleus

Structure of gyri in cerebellum

smaller

Cerebellum function

fine motor movement, balance, muscle tone, compares proprioceptive info with intended movement to maintain proprioception

What are group Ia and II afferent neurons

SENSORY neurons carrying info from muscle spindle receptor to spinal cord

Static length meaning

sustained length of muscle at any moment

Dynamic stretch

rate of change of length of muscle

Types of intrafusal muscle fiber

nuclear bag and chain

Nuclear bag fibers function

dynamic stretch

Nuclear chain fiber

static stretch

Polysynaptic reflex

reflex arc using 1 or more interneurons between sensory and motor neurons, allows more coordination between muscle groups

Bulbar reflexes

reflexes integrated in medulla oblongata

posture, body & head movement

Examples of bulbar reflexes

• automatic adjustment of limb and trunk for posture

• keeping head upright and aligned with body

Where does primary motor cortex (B4) receive input from

premotor area, sensory cortex, thalamus, cerebellum, basal ganglia

Location of premotor area

B6, anterior to primary motor cortex

Where does premotor area receive input from

sensory cortex, thalamus, basal ganglia

Other functions of premotor area (other than planning movement)

• stores programs of motor activity from past experience

• mirror neurons

• staging area before functions organized

Mirror neurons

mirrors behavior of another person found in premotor cortex and inferior parietal lobe

Where is prefrontal lobe located

next most anterior portion of brain (for personality)

Golgi tendon organs (description, location, function)

• Type of proprioceptive receptor located in tendon near tendomuscular junction

• Activated when tendon tension increases via muscle contraction or passive stretch

• Controls muscle contraction

• Surrounds tendon fasciculi (= bundle)

• Enclosed by delicate CT capsule

Muscle spindle

• Type of proprioceptor

• Located in belly of skeletal muscle

• provide info abt length of muscle

• Controls, tones posture of muscles (proprioception)

Basal nuclei

• groups of neuron cell bodies (gray matter) located deep inside brain (subcortical).

• prevent unwanted movement

• Neural circuits connect basal nuclei to each other + thalamus + cortex

• Inhibitory, stimulatory

Intrafusal muscle fiber function

• Location: Inside muscle spindle 

• Function: Sensory part of detecting speed, length of stretch of muscle (do NOT contribute to power of muscle contraction)

• Structure: Central region noncontractile (containing sensory endings), ends contractile (innervated by gamma motor neurons)

Gamma motor neuron

• Motor neurons innervating contractile ends of intrafusal muscle

• Adjust sensitivity of muscle spindle via contraction, to tighten sensory region

• Maintains sensory region’s alertness to stretching during contraction

• Works with alpha motor neurons (powering muscle) to upkeep function of spindle

Group Ia afferent neuron (primary ending)

• Wraps around chain and bag intrafusal fibers

• Detects both static length and dynamic stretch

• Rapidly adapting

• Crucial for stretch reflex

Group ii afferent neuron (secondary ending)

• Innervates nuclear chain intrafusal fibers

• Static length of muscle

• Slowly adapting

• Sends feedback to brain about proprioception

Joint receptors

• Sensory receptors in joint capsule, ligament

• Send info of joint position (pressure, tension, angle)

• Works with muscle spindles, golgi tendon organs for proprioception

Inhibitory basal nuclei function

1. Prevent antagonist muscle activity

2. Inhibit unwanted movement of trunk, limbs

3. decrease muscle tone (head, limbs, body) at rest

Comparator function of cerebellum pathway

1. voluntary movement initiated by action potentials descending to spinal cord and synapsing with LMN 

2. collateral branches from motor cortex to cerebellum which provide info of intended movement, input is entering from middle cerebellar peduncle

3. proprioceptive neuron cells send info about proprioception (proprioceptive neurons innervate joints, tendons, muscles) during actual movement

4. cerebellum compares intended to to sensory info

5. if difference detected - cerebellum sends action potentials to motor neurons in motor cortex and SC out from superior cerebellar peduncle

6. brainstem nuclei correct it as well

middle peduncle - motor plan from cortex - plan

superior peduncle - sensory info from body - reality

Stretch reflex

• Simplest

• Aka knee-jerk reflex/patellar 

• Muscle contraction in response to stretching force

• Maintains upright posture

• ligament below kneecap

Stretch reflex pathway

1. Muscle spindle detects stretch

2. Sensory send AP to SC

3. Sensory neurons DIRECTLY CONNECTED, synapse with alpha motor neurons receiving signals from UMN

4. Alpha motor neurons contracts quadriceps, WHILE:

5. Gamma motor neurons contract muscle spindle (AP from SC → muscle fiber of spindle)

Golgi tendon reflex description

1. Prevents contracting muscles from applying excessive tension to tendons

2. Feedback mechanism controlling muscle tension

Monkey bar example sa post quiz - golgi tendon reflex

Withdrawal reflex description

1. Flexor reflex (and also spinal cord reflex)

2. removes limb away from painful stimulus

3. polysynaptic

Withdrawal reflex pathway

1. nociceptors detect painful stimulus

2. Sensory neurons send AP to SC

3. Synapses with (excitatory) interneurons synapsing with alpha motor neurons

4. Alpha motor neurons contracts flexor muscles to pull away from stimulus

Sensory → interneurons → alpha motor 

Reciprocal inhibition

1. Opposing muscles reinforce withdrawal (reflex) by relaxing more (preventing contraction)

2. Allows coordinated contraction of flexor muscles and relaxation of extensor muscle

Crossed extensor reflex description

1. Occurs on opposite site of body (from stimulus) 

2. After withdrawal reflex occurs, crossed extensor reflex extends opposite side of body

3. Prevents falling (shifts weight to unaffected limb)

4. polysynaptic

Crossed extensor reflex pathway

1. During withdrawal reflex pathway, collateral branches of sensory neurons also synapse with excitatory interneurons crossing to opposite side of SC

2. Stimulates alpha motor neurons of extensor opposite limbs to contract

Spinal reflex

1. Reflexes where integration center is in SC

2. Doesn’t require brain to function

3. E.g. knee-jerk (tapping patellar tendon stretches muscle, causing contraction), withdrawal reflex (withdrawal happens thru spinal cord without brain feeling pain)

Sensory receptors of withdrawal reflex

nociceptors

regions of CNS and difficulty

SC - simple

brainstem - more complicated

cerebrum - most complicated

third order neuron

thalamus to primary somatosensory cortex

second order neuron + cell body

brainstem or SC to thalamus (DECUSSATION!)

cell bodies in: DORSAL HORN SC or BRAINSTEM NUCLEI

first order neuron + cell body

somatosensory receptor to brainstem or cerebellum

cell bodies in: DRG (outside SC, right before entering SC)

spinothalamic pathway

anterolateral column (decussation) → medulla oblongata → VPL thalamus → primary somatosensory cortex

level of decussation: DCML vs. spinothalamic

DCML: medulla oblongata

spinothalamic: anterolateral column SC

dorsal column medial lemniscus pathway

dorsal column spinal cord → 2ND ORDER NEURON CELL BODY: NUCLEUS GRACILIS AND CUNEATUS → medulla (DECUSSATION) → VPL thalamus → primary somatosensory cortex

free nerve ending + location

• pain

• itch

• temperature

• joint movement

• proprioception

more general

epidermis (stratum basale)

merkel disc + location

• superficial pressure

• light touch

stratum basale

hair follicle receptor + location

• light touch

• slight bending of hair

wraps around hair follicle in dermis

meissner corpuscle + location

• two point discrimination

• low frequency vibration

• fine discrimination

papillary dermis

ruffini end organ + location

• continuous pressure

• depression/stretch of skin

reticular dermis

pacinian corpuscle + location

• deep pressure

• deepest mechanoreceptor (reticular dermis and hypodermis)

• high frequency vibration

• proprioception

reflex arc

neural pathway controlling reflex

monosynaptic reflex

• sensory neuron directly synapses with motor neuron

• NO interneuron

example of monosynaptic reflex

• muscle stretch reflex (e.g. knee jerk reflex)

examples of polysynaptic reflexes

• GT reflex

• flexor/withdrawal reflex

• crossed extensor reflex

• reciprocal inhibition

example of muscle stretch reflex

• knee jerk/patellar reflex

how is upright posture maintained

1. standing upright, begin to tip forward

2. postural muscles on posterior side stretched

3. stretch reflex initiated

4. postural muscles contract

golgi tendon reflex pathway

1. GTO reports excessive tension to POSTERIOR part of SC

2. sensory neuron synapses with INHIBITORY INTERNEURON in SC

3. interneuron inhibits ALPHA MOTOR NEURON from contracting muscle (in anterior SC)

4. causes muscle to relax

posterior vs. anterior part of SC

posterior - sensory

anterior - motor

effect of excitatory interneuron

excites next neuron

effect of inhibitory interneuron

blocks next neuron

brainstem function

1. respiration

2. cardiovascular

3. partial control gi function

4. stereotyped movement

5. equilibrium

6. eye movement (midbrain)

list 2 eticular nuclei

1. pontine reticular

2. medullary reticular

pontine reticular nuclei function

excites antigravity muscles

medullary reticular nuclei function

inhibits antigravity muscles

vestibular nuclei function

• associated with pontine reticular nuclei to control antigravity muscles

• excitatory signals to antigravity muscles via lateral and medial vestibulospinal tracts + controls these signals

• maintains equilibrium in response from vestibular apparatus

pontine reticular system function

• houses pontine reticulospinal tract

• excites antigravity muscles

where does the pontine reticulospinal tract terminate

ventral horn via medial anterior motor neurons

what muscles does the pontine reticulospinal tract excite

axial muscles (vertebral column muscles)

limb extensors

medullary reticular system function

• houses medullary reticulospinal tract

• counterbalances excitatory signals from pontine reticular system (avoids abnormal tension)

what inhibits medullary reticular system

higher systems to excite pontine system, causes standing

lower motor neuron lesion
- strength
- muscle bulk 
- reflexes

- special signs, symptoms

• weakness/paralysis

• severe atrophy

• hypoactive reflexes (both superficial, deep)

• fasciculations (visible twitching), fibrilations (invisible twitching), impairment (fine, gross movement) 

upper motor neuron lesion
- strength
- muscle bulk 
- reflexes

- special signs, symptoms

• weakness only

• mild, no atrophy

• hyperactive deep reflexes

• spasticity, babinski’s sign and clonus, widespread impairment

primary motor cortex

• NOT RESPONSIBLE FOR DESIGN OF PATTERN OF MOVEMENT but EXECUTES IT 

• EXCITES PATTERN OF SEPARATE MUSCLES

supplementary motor area

• B6

• bilateral movement

• finer motor control of arms, hands

what brodmann areas are prefrontal cortex

• 9

• 10

• 11

• 12

• foresight planning, initiate movement

function of direct pathways

• muscle tone, speed

• precision, skilled movement

function of indirect pathways

• less precise control

• body coordination, posture

list 2 lateral descending systems + function

• corticospinal and rubrospinal tract

• distal musculature

source of corticospinal tract

• betz cells neurons in primary motor cortex

• premotor/supplementary motor cortex

• somatosensory cortex

where does corticospinal tract decussate

medulla

where does corticospinal tract terminate

ventral horn of SC via interneurons and alpha motor neurons

function of corticospinal tract

precise movement of distal muscles of limb

where is rubrospinal tract located and originating in

tegmentum of midbrain, red nuclei

function of rubrospinal tract

• facilitates flexor muscles

• not significant in humans

list 3 medial system descending tracts + function

• reticulospinal 

• vestibulospinal

• tectospinal

for axial musculature (neck, upper back muscles)