4. THE SOMATOSENSORY SYSTEM
• SENSORY TRANSDUCTION: converting physical energy into a
neural signal
• RECEPTOR CELLS: specialized cells that carry out transduction
• GENERATOR POTENTIALS: local potentials that can trigger
action potentials
8. THE SOMATOSENSORY SYSTEM
All info in the NS is encoded as streams of action
potentials. So...
How does the brain keep the info organized and
divided based on
• Sensory system?
• Intensity stimulus?
• Location in the external world?
9. THE SOMATOSENSORY SYSTEM
• LABELED LINES: each nerve input to the brain reports
a particular type of information
• RANGE FRACTIONATION: each sensory receptor cell
specializes in one part of the range of intensities
• RECEPTIVE FIELD: the stimulus region and features
that affect the activity of a cell in a sensory system
11. THE SOMATOSENSORY SYSTEM
• ADAPTATION: loss of
sensitivity with constant
stimulation
– PHASIC RECEPTORS:
display adaptation
– TONIC RECEPTORS:
show slow or no
adaptation
15. THE SOMATOSENSORY SYSTEM
• PRIMARY SOMATOSENSORY CORTEX (S1):
postcentral gyrus; receives touch information
16. THE SOMATOSENSORY SYSTEM
• ASSOCIATION AREAS: process a mixture of inputs
from different sensory systems
• POLYMODAL NEURONS: allow for different sensory
systems to interact
• SYNESTHESIA: is a condition in which a stimulus in
one modality creates a sensation in another
20. PAIN
• PAIN: discomfort associated with tissue
damage
• NOCICEPTORS: receptors that respond to
stimuli that produce tissue damage
Why do animals NEED the sensation of pain?
21.
22. TRPV1:
• Detects painful heat
• Responds to capsaicin
• C FIBERS: small-diameter,
unmyelinated axons
create lasting pain
PAIN
TRPM3:
• Detects higher temperatures
• Doesn’t respond to capsaicin
• A DELTA (Aδ) FIBERS: large
myelinated axons register
pain quickly
25. • NEUROPATHIC PAIN:
– persists long after the
injury has healed
– Caused by damage to
the peripheral nerves
EX: Phantom Limb Pain
PAIN
26. Analgesia: the loss of pain sensation
1. Administration of Exogenous Opioids
– Opiate drugs bind to specific receptors in
the brain to reduce pain
– Epidural or intrathecal injections place
opiates directly into the spinal cord
PAIN
27. Analgesia: the loss of pain sensation
2. Activation of Endogenous Opioids:
– TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION
(TENS): stimulating nerves around the source of the pain
– PLACEBO EFFECT: relief of a symptom with a “sham”
treatment
– ACUPUNCTURE
PAIN
30. THE MOTOR SYSTEM
• MOVEMENTS:
– REFLEX: a simple, stereotyped, and unlearned response
– ACTS: complex, sequential behaviors
– MOTOR PLAN: set of muscle commands established
before the action occurs
32. Control mechanisms for movements:
• OPEN-LOOP CONTROL MECHANISM:
– Maximizes speed
– No external feedback
– Pre-programmed or BALLISTIC
• CLOSED-LOOP CONTROL MECHANISM:
– Maximizes accuracy
– Feedback information is obtained during the movement
– Corrections are made
THE MOTOR SYSTEM
34. Hierarchy of motor control
systems:
1. The skeletal system and
attached muscles
determine which
movements are possible
2. The spinal cord controls
skeletal muscles
3. The brainstem integrates
motor commands
THE MOTOR SYSTEM
35. Hierarchy of motor control
systems:
4. The primary motor cortex
initiates commands for
action
5. Nonprimary cortex is an
additional source of motor
commands
6. The cerebellum and basal
ganglia modulate activities
of these control systems, via
the thalamus
THE MOTOR SYSTEM
36. • TENDONS: connect muscle to
bone
• SKELETAL MUSCLES: used to
move the skeleton
THE MOTOR SYSTEM
37. • MOTOR NEURONS: located in the spinal cord &
brain stem – send axons to control muscles
• NEUROMUSCULAR JUNCTION: where the motor
neuron terminal and the muscle fiber meet
• ACETYLCHOLINE (ACh) : NT released onto muscle
fibers, causing contraction
• MOTOR UNIT: a motor neuron's axon and all of its
target fibers
THE MOTOR SYSTEM
39. PROPRIOCEPTION: info
about body movements &
position
PROPRIOCEPTORS:
1. INTRAFUSAL FIBERS: small
fibers within a muscle
spindle – respond to
stretch
1. GOLGI TENDON ORGANS:
receptors within tendons –
responds to muscle
tension
THE MOTOR SYSTEM
41. THE MOTOR SYSTEM
• STRETCH REFLEX:
contraction of a muscle in
response to a stretch
• In the spinal cord,
incoming sensory
information from muscle
spindles stimulates one set
of muscles and inhibits
their antagonists.
42. Body muscles are controlled through two pathways:
1. PYRAMIDAL SYSTEM (M1)
• Cell bodies in the cerebral cortex & their axons, which pass
through the brainstem, forming the pyramidal tract to the
spinal cord
• Left and right pyramidal tracts each cross to the opposite side
2. EXTRAPYRAMIDAL SYSTEM
• Other axon pathways with tracts outside of the pyramids in
the medulla
• May pass to the spinal cord via specialized motor regions
THE MOTOR SYSTEM
43. THE MOTOR SYSTEM: Pyramidal System
• PRIMARY MOTOR CORTEX (M1): the precentral
gyrus is the apparent executive region for the
initiation of movement
45. • Are muscles or movements represented in M1?
• Both!
– Researchers recorded single M1 cells during a task—
many neurons encode muscle contractions
– More neurons, however, reacted to particular
movements, no matter what muscles were used to
perform them
THE MOTOR SYSTEM: Pyramidal System
46. Motor representations in M1 can change as a
result of training.
THE MOTOR SYSTEM: Pyramidal System
47. • NONPRIMARY MOTOR CORTEX: anterior to M1,
contributes to motor movements
1. SUPPLEMENTARY MOTOR AREA (SMA):
• Initiation of preplanned movement sequences
• Input from basal ganglia
• Modulates activity of M1
1. PREMOTOR CORTEX: activated when motor
sequences are guided by external events
THE MOTOR SYSTEM: Pyramidal System
49. Motor cortex damage can cause:
– PLEGIA: paralysis
– PARESIS: weakness of voluntary movements
– APRAXIA: inability to carry out movements, even
though no paralysis or weakness is present
THE MOTOR SYSTEM: Pyramidal System
50. • MIRROR NEURONS:
– Located in a subregion of premotor cortex (F5)
– Fire before making a specific movement AND when observing
someone else making that movement
THE MOTOR SYSTEM: Pyramidal System
52. BASAL GANGLIA:
– Help control the
amplitude and direction
of movement
– Important in:
• Initiating movement
• Movements
performed by
memory
THE MOTOR SYSTEM: Extrapyramidal
System
53. Cerebellum:
• Receives inputs from
sensory sources and
other brain motor
systems
• Guides movement
through inhibition and
fine-tunes skilled
movements
THE MOTOR SYSTEM: Extrapyramidal
System
54. Damage to extrapyramidal systems impairs
movement.
• Cerebellar damage:
– Abnormal gait, posture, and ATAXIA (loss of
coordination) of the legs
– DECOMPOSITION OF MOVEMENT: gestures that are
broken into segments
THE MOTOR SYSTEM: Extrapyramidal
System
55. Damage to extrapyramidal
systems impairs movement.
• PARKINSON’S DISEASE:
progressive loss of
dopaminergic cells in the
substantia nigra with slowed
movement
• HUNTINGTON’S DISEASE:
genetic disorder causes basal
ganglia damage, with excessive
THE MOTOR SYSTEM: Extrapyramidal
System
