Lecture 11 Flashcards
How does the nervous system produce movement and respond to sensation?
- Functional anatomy of movement
- Basal ganglia and cerebellum
- Vestibular system
- Somatosensory system
Main components of the motor system
- Forebrain: initiating movement
- Brain stem: species-typical movement
- Spinal cord: executing movement
Main motor assisting brain regions
- Basal ganglia (forebrain): help to produce the appropriate amount of force
- Cerebellum (brainstem): regulate timing and accuracy
3 stages of movement execution
Planning: prefrontal cortex
Organisation: premotor cortex
Execution: primary motor cortex
Planning - prefrontal cortex
Specify goal and decide to execute a movement
Organisation - premotor cortex
Specify precise complementary movements needed to execute the plan (organise motor sequences)
- Preprogrammed set of movements produced as a single unit
Execution - primary motor cortex
Translate motor sequences into motor commands that produce specific movements (specialised in focal skilled movements)
Simple movement
Blood flow increased in the hand area of hte primary somatosensory and primary motor cortex when subjects used a finger to push a lever.
- M1 and S1
Movement sequence
Blood flow increased in the premotor cortex when subjects performed a sequence of movements
- M1 and S1
- Dorsal premotor
Complex movement
Blood flow increased in the prefrontal and temporal cortex when subjects used a finger to find a route through a maze
- M1 and S1
- Dorsal premotor
- Prefrontal (goal)
- Temporal (what)
- Parietal (how)
Hierarchical and parallel control organisation
H = prefrontal > premotor > primary motor
P = plan and execute multiple independent movements simultaneously
What does it mean that motor movements are spatially coded > somatotopic arrangement?
Body part relative sizes are disproportionate
- More extensive areas of M1 allow precise regulation of movements
Body parts are discontinuous
- Arranged different from those of our actual body
Corticospinal tract
- originates mainly in motor cortex layer V
- ends in anterior horn of spinal cord
- aka pyramidal tract, axon crossing in medulla (brain stem)
corticospinal tract - 2 descending pathways
- lateral corticospinal tract: crosses in medulla, brainstem
- ventral (anterior) corticospinal tract: uncrossed
lateral corticospinal tract
- crosses over to the contralateral side
- ends at the lateral region of the contralateral anterior horn
- distal musculature
- NB: mainly lateral interneurons and motor neurons
ventral (anterior) corticalspinal tract
- remains on the ipsilateral side
- ends in the medial region of the ipsilateral anterior horn
- proximal musculature
- NB: mainly medial interneurons and motor neurons
spinal cord
- neurons in the spinal cord form a butterfly structure
- in the middle is the central canal containing CSF
neuromuscular junction
the connection between the motor neurons of the spinal cord and the muscle fibres is called the
- neurotransmitter: acetylochile
- limb muscles are arranged in pairs: extensor and flexor
nuclei in the basal ganglia
- caudate nucleus
- putamen
- globus pallidus
- neucleus accumens
- subthalamic nucleus
- substantia nigra
movement issues connected to basal ganglia
hypokenetic - too little force
- paucity of movement (rigidity)
- parkinson (substantia nigra)
hyperkinetic - too much force
- excessive involuntary movement
- huntington’s disease (caudate & putamen)
cerebellum - movement
functions in the cerebellum mainly concern the timing and accuracy of movements - critical for acquiring and maintaining motor skills
cerebellum - somatotopic arrangement
- base (flocculus) - eye movements and balance
- medial - face and trunk
- lateral - limbs, hands, feet and digits
intention, action and feedback model
cerebellum compares intended action with actual action, calculates error and informs the cortex how to correct the movement
the vestibular system
the vestibular system is involved i the motor functions that allow us to maintain balance
- it is located in the inner ear and consists of 2 groups of receptors
2 vestibular groups
- semicircular canals
- otolith organs
semicircular canals
- 3 canals, 1 for each plane of movement (3D)
- contains vestibular hair cells
- filled with endolymph
- mead movements moves endolymph. bends the cilia and induces action potentials
- function: head orientation > detect head rotations
otolith organs
- utricle, saccule
- contains vestibular hair cells
- filled with jelly-like substance that contains small calcium carbonate crystals (otoconia)
- head tilting presses gelatin and otoconia against hair cells, bends the cilia and induces action potentials
- function: body orientation, detect gravity (tilt) and linear acceleration (translational movement)
the somatosensory system
somatic sensation is unique since it is distributed throughout the body.
- density of somatosensory receptors varies greatly throughout the body
3 receptor systems in the somatosensory system
nociception (irritation)
- pain, temperature, itch
hapsis (pressure)
- fine touch and pressure
proprioception (bodyawareness)
- perception of body location and movement based on stretch of muscles, tendons and join movement
rapidly adapting receptors
activate neurons when stimulation begins and ends - sends information about the stimulus onset and offset
slowly adapting receptors
activate neurons as long as the sensory stimulation is present - send information about whether the stimulus is still occurring
diameter and myelination of receptors
hapsis & proprioception = larger, well myelinated (faster)
nociception = smaller, less myelinated axons (slower)
posterior spinothalamic tract (dorsal)
- hapsis
- proprioception
- posterior/dorsal column (spinal cord to brainstem)
- crosses to contralateral side in brainstem
- via medial lemniscus to ventrolateral thalamus to S1
anterior spinothalamic tract (ventral)
- nociception
- anterior spinal cord (grey matter)
- crosses to contralateral side in spinal cord
- via medial lemniscus to ventrolateral thalamus to S1
monosynaptic reflex
- tapping patellar tendon stretches quadriceps
- stretch-sensitive sensory receptor synapses directly to a single motor neuron in the spinal cord
- motor neuron stimulates quadriceps to contract
pain gating theory
- attempts to explain the phenomenon that acute sharp pain can be diminished by rubbing or massaging of the painful spot
- might explain the pins and needles sensation - decreased blood flow deactivates large myelinated touch and pressure fibres, leaves small unmyelinated pain fibres unaffected
somatosensory cortex
somatotopic representation in the primary somatosenosry cortex is organised in four separate homunculi that respond to
- 3a, 3b
- 1
- 2
- receptive cells increase from back to front 3a,3b,1,2
unilateral spinal cord injuries
- ipsilateral loss of hapsis and proprioception
- contralateral loss of nociception
