Lecture 9- Sensory and Motor Systems

Question 1

What is sensation?

Answer 1

• 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.

Question 2

What is perception?

Answer 2

• interpretation of the meanings of the
sensory stimuli

Question 3

Where does both sensation and perception occur?

Answer 3

In the brain

Question 4

What are the special senses and what regions of the brain are associated with each?

Answer 4

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

Question 5

What are sensory receptors specialized to do? How are the classified?

Answer 5

-are specialized to respond to changes in their environment
Classified by:
- the type of stimulus they detect
- their body location
- their structural complexity

Question 6

How can we classify sensory receptors by stimulus type?

Answer 6

• 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

Question 7

How we classify sensory receptors by location?

Answer 7

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

Question 8

How can we classify sensory receptors based on complexity?

Answer 8

-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

Question 9

What is the somatosensory system?

Answer 9

the part of the sensory system serving the
body wall & limbs
• receiving inputs from exteroceptors &
proprioceptors

Question 10

What do we mean when we say sensory integration?

Answer 10

-Combining the sensation with perception

Question 11

What is the general organisation of the somatosensory system i.e. what are the three levels?

Answer 11

(1) sensory receptors
(2) ascending pathways
(3) cerebral neuronal circuits

Question 12

What occurs in processing at the receptor level?

Answer 12

-Receptors: detecting stimuli
-Transduction: converting stimulus energy into changes in membrane potential in sensory axons
-Propagation: generating nerve impulses

Question 13

What processing occurs at the circuit level?

Answer 13

-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

Question 14

What are the two pathways for somatic sensation?

Answer 14

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

Question 15

What does the term dissociated sensory loss mean?

Answer 15

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.

Question 16

Describe how the dorsal column pathway works?

Answer 16

Refer to slide 15

Question 17

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…

Answer 17

-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

Question 18

Describe how the Lateral SpinoThalamic Pathway works

Answer 18

refer to slide 18

Question 19

How does the lateral and anterior spinothalamic pathways differ according to function?

Answer 19

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

Question 20

Do the Spinocerebellar Pathways contribute to conscious sensation? What is it’s function?

Answer 20

No

-Transmit information about muscle or tendon
stretch to the cerebellum, which use this
information to coordinate skeletal muscle
activity
-Responsible for unconscious proprioception

Question 21

How do the spinocerebellar pathways work….

Answer 21

Refer to slide 23

Question 22

How does processing at the perceptual level work?

Answer 22

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”

Question 23

Go to one and complete questions on what damage to different parts of the spinal chord causes…

Answer 23

Answers on OneNote

Question 24

Complete the flow chart showing the general organisation of the motor system…

Answer 24

OneNote

Question 25

What is the hierarchy of motor control?

Answer 25

-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).

Question 26

From motor neuron in the ventral horn what does it become?

Answer 26

axon fiber and then skeletal muscle fibers
Collectively these two are the motor unit

Question 27

What are CPGs?

Answer 27

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

Question 28

What does the projection level consist of? What neurons do what?

Answer 28

-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

Question 29

What is the direct (Pyramidal) System also known as? Where does it originate?

Answer 29

-Corticospinal (Pyramidal) Tracts
-Origin is from the primary motor cortex

Question 30

Complete the diagram on OneNote showing the somatopy of the internal capsule/ corticospinal tract…

Answer 30

Answers on OneNote

Question 31

At the decussation of the corticospinal tract what is the percentage spilt for different sections?

Answer 31

-Lateral= 90%
-Anterior= 8%
-Uncrossed lateral= 2%

Question 32

What is the primary functions of the corticospinal tracts?

Answer 32

-Regulating fast & skilled movements
-Controlling reflex motor output & modifying sensory input

Question 33

What does damage to the corticospinal tract cause?

Answer 33

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.

Question 34

What is the direct system between the brain and cranial nerves called?

Answer 34

Corticobulbar Tracts:
-bilateral synapses
-mainly contralateral side

Question 35

What is the Indirect (Extrapyramidal) system? What are the major regions?

Answer 35

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

Question 36

What are the four major pathways of the Indirect (Extrapyramidal) system?

Answer 36

Tectospinal tracts – move head & neck, visual input
Rubrospinal tracts – maintain muscle tone
Reticulospinal tracts – initiates CPG in spinal cord
Vestibulospinal tracts – maintain balance

Question 37

What parts of the brain does the precommand level include/ what are their functions?

Answer 37

• 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

Question 38

What is the consequence of stroke in the internal capsule?

Answer 38

Really bad relates to somatopy