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Proprioception and the Vestibular Sense
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Proprioception
– sense of the position and movement of our limbs and body
–
sensitive
to tension in muscles and angles of limbs at joints
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helps
maintain posture, move limbs and grasp objects
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Vestibular
sense – maintains balance through head position and movement
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semicircular
canals of inner ear responsive to rotational movement
> at base is cupula which has hair cells
protruding into it
> hair cells bend during acceleration causing
depolarizations or hyperpolarizations (depending on direction)
The Vestibular Sense
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Utricle
and saccule monitor head position
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receptors
covered with gelatinous mass embedded with calcium carbonate crystals (otoliths)
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when
head is tilted or moved the gelatinous mass with otoliths shifts bending cilia of the receptors (depolarizations; hyperpolarizations)
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utricle
for horizontal; saccule for vertical
–
responds
to acceleration – not steady speed movement
The Skin Senses
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Touch,
warmth, cold and pain
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Receptors
are free nerve endings or encapsulated endings
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Encapsulated
endings detect touch
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Messner's
corpuscles and Merkel's discs are located in superficial layers of skin and give brief vs. sustained responses, respectively
> texture, detail, movement
Receptors of the skin
The Skin Senses, continued
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Pacinian
corpuscles and Ruffini endings are deeper in skin
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detect
stretching
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Free
nerve endings detect warmth, cold and pain
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Some
areas (lips, face, fingers) have more receptors, therefore more sensitive
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Are
separate pathways for the different skin and body senses
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body
divided into dermatomes – distinct areas served by one spinal nerve
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Information
from skin senses travels to somatosensory cortex of parietal lobe
Dermatomes of the human body
Brain Areas for Skin Senses
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Primary
somatosensory (S-I) cortex contains a map of the body with different areas differentially sensitive (large areas of brain
for small area of body – lips)
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Cells
arranged in columns – single column responds to one area of body and one skin sense
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Some
cells are feature detectors for shape, orientation, texture, movement, etc.
Brain Areas for Skin Senses, continued
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Secondary
somatosensory cortex (S-II) receives input from right and left S-I (S-I is more lateralized)
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connects
to temporal lobe and hippocampus – determines whether stimulus will be remembered
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Posterior
parietal cortex combines input from various different sensory modalities
–
integrates
the body with the world
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coordinates
sensory information and motor behavior
The somatosensory and posterior parietal areas
Pain
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Three
types of pain receptors
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thermal
– respond to extreme heat and cold
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mechanical
– respond to extreme pressure and cutting
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polymodal
– respond to all of the above plus chemicals released
> chemicals include bradykinin, histamine,
prostaglandins,
Pain, continued
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Two
types of pain fibers
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large,
myelinated A-delta fibers – rapid transmission – sharp pain
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small,
lighly or even unmyelinated C fibers – slower transmission – dull, throbbing pain
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Pain
neurons in spinal cord release gultamate and substance P
Pain Relief
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Gate
control theory
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a
neural gate exists for pain perception – when open, feel pain; when closed; pain perception decreased
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emotion,
distraction and counterirritation may work by closing the gate
> use of transcutaneous electrical nerve
stimulation to decrease pain
Pain Relief, continued
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Endorphins
–
neurotransmitter/hormone
that acts at opiate receptors – reduces pain
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stress,
acupuncture & vaginal stimulation can also release endorphins
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released
by periaqueductal gray (PAG) and activate PAG neurons that travel down spinal cord inhibiting release of substance P
Phantom Pain
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Amputees
report vivid experiences of missing limbs – including pain
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Originally
thought to be due to nerve fibers that used to connect limb to brain
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May
be due to the brain tissue originally relegated to the missing limb being taken over by new functions (for arm it is usually
the face)
Muscles
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Three
types of muscles
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skeletal/striated
– move body and limbs
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smooth
muscles – internal organs, digestion
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cardiac
muscles – heart
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Made
up of many muscle fibers
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Muscle
fibers innervated by neurons at neuromuscular junction
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acetylcholine
is the neurotransmitter at all neuromuscular junctions
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Limbs
have antagonistic pairs of muscles for flexion and extension
Antagonistic muscles of the upper arm
Muscles and the Spinal Cord
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Spinal
cord coordinates reflexes
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stretch
reflex – patellar tendon reflex
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patellar
tapped – stimulates muscle spindles in muscle – sends signal to spinal cord which sends signal to extensor muscle
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allows
maintenance of balance
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Golgi
tendon organs act to inhibit muscle – safety mechanism
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Spinal
cord contains central pattern generators that can be used without the brain
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produce
rhythmic pattern of motor activity (walking)
The patellar tendon reflex, an example of a stretch reflex
Brain Areas and Movement
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Motor
cortex contains primary motor cortex and two secondary motor areas
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supplemental
motor area and premotor cortex
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other
secondary motor areas are in cingulate cortex
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greater
amounts of brain tissue are dedicated to certain areas than others
> finer motor control (fingers)
Brain Areas and Movement, continued
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The
prefrontal cortex
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receives
input from posterior parietal lobe for motor planning
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is
activated before actual movement in monkeys during a delayed-match-to-sample task
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The
premotor cortex
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begins
programming a movement by integrating information needed for that movement
> cells respond to both visual and body
information
Brain Areas and Movement, continued
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The
supplemental motor area
–
responsible
for assembling movement sequences
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coordinates
sequencing between sides of body
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The
primary motor cortex
–
execution
of voluntary movements
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refines
direction, force and precision of movements
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receives
direct input from somatosensory cortex and posterior parietal lobe as well as secondary motor areas
Brain Areas and Movement, continued
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Basal
ganglia (caudate nucleus, putamen & globus pallidus)
–
smooth
movements via connections to thalamus
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receives
input from motor (primary & secondary) & somatosensory areas
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damage
leads to postural abnormalities and involuntary movements
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coordinates
complex sequences of movements and the learning of movement sequences
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implicated
in Parkinson's and Huntington's disease
The basal ganglia
Brain Areas and Movement, continued
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Cerebellum
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refines
movements, maintains balance, controls certain eye movements
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receives
input from vestibular system
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programs
order and timing of complex movements
> keeps smooth and coordinated
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necessary
for learning motor skills
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also
has functions in non-motor learning, attention and speed & time judgments concerning auditory and visual stimuli
Disorders of Movement
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Parkinson's
disease
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motor
tremors, rigidity, loss of balance and coordination, difficulty initiating movements
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caused
by deterioration of dopamine-secreting neurons in the substantia nigra of brain stem (sends signal to part of basal ganglia)
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cause
of the degeneration is unclear
> genetic mutations can lead to build up
of certain proteins that can lead to abnormal clumps in neurons (Lewy bodies)
Disorders of Movement, continued
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Parkinson's
disease
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industrial
chemicals, herbicides and pesticides also implicated
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disease
rate lower in coffee drinkers and smokers
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Treatments
for Parkinson's disease
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levodopa
(L-dopa)
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embryonic
stem cell transplantation
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surgery:
thalamotomy and pallidotomy
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electrical
stimulation of globus pallidus and cerebellum
Disorders of Movement, continued
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Huntington's
disease
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begins
with jerky movements, then involuntary movements such as fidgeting, limb movement, writhing and facial grimacing
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also
involves depression, personality changes, impaired judgement, and cognitive impairment
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degeneration
in striatum of basal ganglia and cortex
Disorders of Movement, continued
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Huntington's
disease
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probably
caused by build up of huntingin
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is
a single-gene disorder
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Treatments
for Huntington's disease
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fetal
striatum cell transplantation
Disorders of Movement, continued
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Myasthenia
gravis (MG)
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extreme
muscular weakness caused by reduced acetylcholine receptors
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acetylcholinesterase
inhibitors are effective temporarily (increase levels of acetylcholine at neuro-muscular junctions)
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thymectomy
can be effective as many patients have tumors on thymus gland
Disorders of Movement, continued
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Muscular
sclerosis (MS)
–
deterioration
of myelin in central nervous system
–
slowing
or elimination of neural responses; desynchronization of neural impulses
–
patient
experiences muscular weakness, impaired coordination, urinary incontinence and visual problems
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immune
system attacks the person's own myelin; may be due to earlier viral infections
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