Lecture 9- Sensory and Motor Systems Flashcards
What is sensation?
• detection of sensory stimulus
• stimulus is a change in the external or
internal environments
Sensory stimuli include sight, sound, smell,
touch, pressure, taste, temperature, gravity,
position, pain etc.
What is perception?
• interpretation of the meanings of the
sensory stimuli
Where does both sensation and perception occur?
In the brain
What are the special senses and what regions of the brain are associated with each?
Taste, smell, vision, hearing & balance
• Each special sense organ projects to a specialized region of the brain. In the cerebrum, specialized region is called a primary sensory
cortex
taste - lower end of postcentral gyrus
smell - medial temporal (uncus) and orbitofrontal lobes
vision - occipital lobe
hearing - superior temporal lobe
equilibrium - mainly to the cerebellum
What are sensory receptors specialized to do? How are the classified?
-are specialized to respond to changes in their environment
Classified by:
- the type of stimulus they detect
- their body location
- their structural complexity
How can we classify sensory receptors by stimulus type?
• Mechanoreceptors
are sensitive to a mechanical force
(e.g. touch, pressure, vibration, stretch & itch)
• Thermoreceptors
are sensitive to temperature changes
• Photoreceptors
respond to light energy (the retina of the eye)
• Chemoreceptors
respond to chemicals in solution (molecules smelt or
tasted, or changes in blood chemistry)
• Nociceptors (noci = harm)
respond to potentially damaging stimuli that result
in pain
How we classify sensory receptors by location?
1) Exteroceptors (extero = outside)
- are sensitive to stimuli arising outside the body
- are located near or at the body surface
-include:
- touch, pressure, pain & temperature receptors (skin)
- receptors of special senses (vision, hearing etc.)
2) Interoceptors or Visceroceptors (intero = inside)
- are sensitive to stimuli within the body
- are located in the visceral organs & blood vessels
- monitor a variety of stimulii
(eg. chemical changes, tissue stretch, temperature)
3) Proprioceptors (propria = one’s own)
- are sensitive to internal stimuli
- located in skeletal muscles, tendons, joints,
ligaments & in connective tissue coverings
of bones & muscles
- eg. joint kinesthetic receptors
- equilibrium receptors of the inner ear are
sometimes included in this class
- constantly advise the brain of the body’s
movement and location in space
How can we classify sensory receptors based on complexity?
-Complex receptors are in the special sense organs
-Simple Receptors of the General Senses
• Tactile sensation (a mix of touch, pressure, stretch & vibration)
• Temperature
• Pain
• Muscle sense (provided by proprioceptors)
Anatomically, these receptors are
either free nerve endings
or encapsulated nerve endings
What is the somatosensory system?
the part of the sensory system serving the
body wall & limbs
• receiving inputs from exteroceptors &
proprioceptors
What do we mean when we say sensory integration?
-Combining the sensation with perception
What is the general organisation of the somatosensory system i.e. what are the three levels?
(1) sensory receptors
(2) ascending pathways
(3) cerebral neuronal circuits
What occurs in processing at the receptor level?
-Receptors: detecting stimuli
-Transduction: converting stimulus energy into changes in membrane potential in sensory axons
-Propagation: generating nerve impulses
What processing occurs at the circuit level?
-impulses delivered to the appropriate regions of the cerebral cortex for stimulus localization & perception
- or impulses delivered to the cerebellum
This is done via the ascending sensory pathways
What are the two pathways for somatic sensation?
Discriminative sensation via the dorsal column pathway
- fine touch/vibration
- conscious proprioception
- precise localization; only a few receptor types
Non-discriminative sensation via the Spinothalamic pathways
-pain
- temperature
- crude touch and pressure
What does the term dissociated sensory loss mean?
Two modes of sensation travel in different sensory pathways ——-> dissociated sensory loss means that damage is localised and has specific effects according to what specific pathway is damaged.
Describe how the dorsal column pathway works?
Refer to slide 15
How does the gracile tract and cuneate tract differ in the dorsal column pathways? Draw what these look like in a section of the spinal chord…
-Gracile tract carries impulses from lower limbs & inferior body trunk
-Cuneate tract transmits afferent impulses from upper limbs, trunk & neck (not present in spinal cord below T6)
-Look at slide 17 for diagram
Describe how the Lateral SpinoThalamic Pathway works
refer to slide 18
How does the lateral and anterior spinothalamic pathways differ according to function?
Lateral Spinothalamic Pathway
• Transmits impulses concerned with pain &
temperature to opposite somatosensory
cortex
Anterior Spinothalamic Pathway
• Transmits impulses concerned with crude
touch & pressure to opposite somatosensory
cortex
Do the Spinocerebellar Pathways contribute to conscious sensation? What is it’s function?
No
-Transmit information about muscle or tendon
stretch to the cerebellum, which use this
information to coordinate skeletal muscle
activity
-Responsible for unconscious proprioception
How do the spinocerebellar pathways work….
Refer to slide 23
How does processing at the perceptual level work?
Interpretation of sensory
input (stimulus location
and/or type)
• Depends on the locations
of the target neurons in
the sensory cortex
• Each sensory axon -
“labeled phone line”
telling brain “who” is
calling & from “where”
Go to one and complete questions on what damage to different parts of the spinal chord causes…
Answers on OneNote
Complete the flow chart showing the general organisation of the motor system…
OneNote
What is the hierarchy of motor control?
-Highest= Pre-motor cortex, Basal ganglia, Cerebellum. Known as the precommand/ pre-action level.
-Middle= primary motor cortex, brainstem. Known as the projection level.
-Lower= spinal cord, this is the segmental level. (think cut across spinal chord and organisation of gray matter within it: ventral horns are the motor neurons + interneurons, dorsal horns are the interneurons).
From motor neuron in the ventral horn what does it become?
axon fiber and then skeletal muscle fibers
Collectively these two are the motor unit
What are CPGs?
Central Pattern Generators (CPGs)
- the segmental circuits in the spinal cord that control
locomotion (eg. walking)
& other specific & oft-repeated motor activity
- consists of a network of local interneuron
and motor neurons, on both sides of the
spinal cord, that work together to generate
a rhythmic pattern of motor activity
- initiated and modulated by a “switch” –
brainstem command neurons,
particularly reticulospinal neurons
What does the projection level consist of? What neurons do what?
-primary motor cortex & brainstem
• Upper Motor Neurons in the primary cortical
motor areas & brainstem directly control the spinal cord
- The cortical motor areas produce the direct (pyramidal) system
- Brainstem motor areas oversee the indirect (multineuronal, extrapyramidal) system
What is the direct (Pyramidal) System also known as? Where does it originate?
-Corticospinal (Pyramidal) Tracts
-Origin is from the primary motor cortex
Complete the diagram on OneNote showing the somatopy of the internal capsule/ corticospinal tract…
Answers on OneNote
At the decussation of the corticospinal tract what is the percentage spilt for different sections?
-Lateral= 90%
-Anterior= 8%
-Uncrossed lateral= 2%
What is the primary functions of the corticospinal tracts?
-Regulating fast & skilled movements
-Controlling reflex motor output & modifying sensory input
What does damage to the corticospinal tract cause?
Damage to corticospinal tract at any level paralysis of target muscles
Clinical notes:
• If lesion above pyramidal decussation on right paralysis of left upper limb and lower limb muscles
• If lesion below the pyramidal decussation in the left lateral T10 spinal cord paralysis of left lower limb muscles.
What is the direct system between the brain and cranial nerves called?
Corticobulbar Tracts:
-bilateral synapses
-mainly contralateral side
What is the Indirect (Extrapyramidal) system? What are the major regions?
Motor axons arise from several brainstem nuclei
Indirect (Extrapyramidal) system
• Four major nuclei/regions are:
• Superior colliculus, located in tectum or
roof of midbrain
• Red nucleus in the midbrain
• Reticular formation in pons & medulla
• Vestibular nuclei in medulla
What are the four major pathways of the Indirect (Extrapyramidal) system?
Tectospinal tracts – move head & neck, visual input
Rubrospinal tracts – maintain muscle tone
Reticulospinal tracts – initiates CPG in spinal cord
Vestibulospinal tracts – maintain balance
What parts of the brain does the precommand level include/ what are their functions?
• Premotor cortex responsible for initiating plan for
next intended movement
• innervates Basal ganglia to
release brake to start a specific movement
innervates Cerebellum
• which precisely calculates the best way to achieve
coordinated synergistic movements across multiple
limb joints = sends this “blueprint” to the primary
motor cortex, which then starts the intended
movement
• also monitors muscle tone and balance
What is the consequence of stroke in the internal capsule?
Really bad relates to somatopy
