Sensorimotor Function Quiz.text - - 6/8/99

QUESTION 1:  What is a motor program? ANSWER:  A motor program is a set
of "instructions" (not in a literal sense), or a "motor memory",
specifying the selection of muscles to use in a movement and the force
and timing of their contractions.

QUESTION 2:  What is the general name of the part of the cerebral cortex
which is involved in the planning of movement (amongst other things)?
ANSWER:  The association cortex.

QUESTION 3:  What are the three main phases of acquisition of motor
skill? ANSWER:  An initial COGNITIVE phase in which task requirements
are evaluated.  A second ASSOCIATIVE or MOTOR phase in which the skill 
is developed through repetition.  A final AUTONOMOUS phase in which the
movement becomes truly skilled and automatic.

QUESTION 4:  Define proprioception. ANSWER:  Proprioception is the sense
of where one's body parts are located in space.  It includes the sense
of movement of one's body parts, or kinaesthesia.

QUESTION 5:  Is proprioception very important in motor learning, or can
we generally do without it? ANSWER:  Proprioception is important in
learning of new movements.  Selective loss of proprioception due to
sensory nerve injury impairs motor learning although the motor system is
intact. Proprioception provides us with a sense of how the correct
movement should feel; this may be the key reason for its importance.

QUESTION 6:  How is a muscle like a spring? ANSWER:  A muscle in the
body (rather than an isolated muscle in a dish) increases in tension
when it is stretched and recoils when let go.  The muscle stretch reflex
helps to ensure that this occurs over a wide range of muscle lengths.

QUESTION 7:  How is a muscle NOT like a spring? ANSWER:  1.  Muscles do
not provide compressive tension, unlike springs.  2.  Muscle tension at
a given length can vary, depending on the degree of neural excitation
and reflex activity;  muscles are like springs of controllable and
variable stiffness.  3.  Muscles are also  "plastic". Unlike tension in
an ideal spring, tension in muscle is partly dependent on the prior use
of the muscle.  This is called thixotropic behaviour.

QUESTION 8:  Does learning a movement involving one group of muscles
(e.g. arm muscles) have any useful effect on performance of a similar
movement using another group of muscles (e.g. leg muscles)? ANSWER: 
Yes.  Motor programs are to some extent GENERALIZED - you can sign your
name with a pen held in the toes and the script has characteristics
similar to your normal signature.  Skills learned in one context may be
TRANSFERRED to a different context.

QUESTION 9:  What is a reflex movement? ANSWER:  A reflex is a
relatively reproducible innate motor response to a specific sensory
stimulus.  It is determined by neural connections formed during normal
neural development.  Don't confuse "reflex" with "highly-skilled".  The
term "conditioned reflex" refers to certain learned responses which are
based on innate reflex responses.

QUESTION 10:  What is a voluntary movement? ANSWER:  A voluntary
movement is a deliberate contraction of skeletal muscles, initiated for
the attainment of a goal or target.  It may be skilled or unskilled.

QUESTION 11:  Which brain structures are involved in the programming of
voluntary movement? ANSWER:  Well, probably the whole brain is involved
in the creation  of a new motor program!  The initiation of astored 
motor program probably requires mainly the cerebellum, basal ganglia, 
and association cortex.

QUESTION 12:  What will be the likely effect of a lower motor neuron
lesion on muscle tone?  Which side of the body will be affected by a
unilateral lesion? ANSWER:  Lower motor neuron lesions always result in 
HYPOTONIA on the same side as the lesion: skeleto-motor neurons only
excite skeletal muscle and always innervate ipsilateral muscles.

QUESTION 13:  What is the likely effect of an upper motor neuron lesion
on skeletal muscle tone?  Which side of the body is likely to be
affected by a unilateral lesion? ANSWER:  An upper motor neuron lesion
may result in HYPERTONIA because it may interrupt tonic descending
inhibitory pathways, causing RELEASE from inhibition.  However,
HYPOTONIA can also occur, due to release from tonic excitation.   In
addition, there may be effects due to neural plasticity.  It depends on
the site of the lesion and the may be different for different muscle
groups.  The side affected will depend on the precise site of the
lesion.  If it is at the level of the cortex or internal capsule the
hypertonia will be contralateral because the descending motor fibres
cross the mid-line below the level of the lesion.

QUESTION 14:  What happens to skilled motor control when somatic sensory
input is impaired? ANSWER:  Some well-learned skilled movements may be
hardly affected but others will be uncoordinated or clumsy - a problem
known as SENSORY ATAXIA.   Movements which normally depend on sensory
feedback e.g. doing up buttons, handwriting and gait, will be impaired.

QUESTION 15:  What is the overall effect on "anti-gravity" muscles of
tonic activity in descending pathways from the reticular formation and
vestibular nuclei? ANSWER:  The net effect is facilitatory i.e. tending
to maintain tone in the antigravity muscles and therefore helping to
maintain upright posture against the pull of gravity.

QUESTION 16:  Which limb and trunk muscles are regarded to have an
"antigravity" function?  [e.g. extensors or flexors?] ANSWER:  The
extensor muscles of the trunk and lower limbs and the flexor muscles of
the upper limb (excluding flexors of the hand, whose function has no
consistent relationship to the direction of gravity's pull!).

QUESTION 17:  What is spasticity? ANSWER:  Spasticity is a syndrome
which usually develops following an upper motor neuron lesion.  It
comprises paresis and a hypertonia characterized by velocity-dependent
resistance to stretch i.e. the resistance is most apparent in response
to rapid stretch.  In a typical stroke involving the internal capsule,
the hypertonia develops in upper limb flexors and lower limb extensors.

QUESTION 18:  What are the functions of the basal ganglia? ANSWER:  The
functions of the basal ganglia are by no means certain. They probably
include motor programming, sensory processing and as yet poorly
understood cognitive functions.  The major motor deficit in Parkinson's
disease is akinesia or bradykinesia, suggesting a role for the basal
ganglia in initiation of voluntary movements.

QUESTION 19:  What is akinesia?  How does it compare with paresis?
ANSWER:  Akinesia is an inability to initiate voluntary movements.  It
differs from paresis (partial paralysis) in that in akinesia movement
may still be possible  in response to sensory stimuli (as opposed to a
spontaneous or internally-generated movement).

QUESTION 20:  What are the most obvious signs of Parkinson's disease? 
Briefly describe them. ANSWER:  Akinesia/bradykinesia, rigidity and a
resting tremor.  The akinesia/bradykinesia is seen as a lack of
spontaneous movement including a lack of facial expression.  The
rigidity is described as "lead-pipe" and may have a "cog-wheel" property
i.e. it gives and grabs like a cogwheel in a clock, reflecting the
underlying fluctuations of the resting tremor.  The tremor is persistent
and most apparent in the hands.  It looks as if the patient is
"pill-rolling".

QUESTION 21:  What is the cause of Parkinson's disease? ANSWER: 
Degeneration of the substantia nigra and a consequence loss of
dopamine-releasing fibres which connect to the neostriatum (the main
part of the basal ganglia).  What causes this degeneration is unknown in
most cases.

QUESTION 22:  Which general functions of the brain are NOT affected by
cerebellar disease? ANSWER:  Sensory perception and the ability to
initiate movements are generally not affected. NOTE: cerebellar disease
may reduce the SPEED with which movements can be initiated, but it does
not cause paralysis or akinesia.

QUESTION 23:  What are the major effects of cerebellar disease? ANSWER: 
According to the classical view: ataxia, or difficulty with movement
coordination, and deficits in motor learning.  It was once thought that
the cerebellum had nothing to do with COGNITIVE function, but recent
clinical evidence suggests that the cerebellum coordinates our thinking,
as well as our movements.

QUESTION 24:  List the signs of neo-cerebellar disease. ANSWER:  Ataxia,
dysmetria, dys-diadocho-kinesia(!), decomposition of movement, intention
tremor, hypotonia, pendular knee-jerk reflex, scanning speech, explosive
speech.   Also, cognitive deficits (according to recent evidence).

QUESTION 25:  What is somatic sensation? ANSWER:  Somatic sensations are
those originating in the body, as opposed to the specialized sense
organs of the head (e.g. eye & ear).  They include touch, pressure,
warm, cold, vibration, pain, and proprioception.

QUESTION 26:  What are the posterior (=dorsal) columns? ANSWER:  The
posterior columns are the long nerve fibre tracts which are located in
the posterior region of the spinal cord, on either side of the midline. 
They carry somatosensory signals up the spinal cord to the brainstem.

QUESTION 27:  What are the functions of the posterior column somatic
afferent system? ANSWER:  The posterior column system is responsible for
discriminative ("fine") touch and pressure, vibration sense and
proprioception.  It enables precise localization of stimuli and accurate
judgement of stimulus intensity.

QUESTION 28:  What are the functions of the antero-lateral
(spinothalamic) somatic afferent system? ANSWER:  The anterolateral
afferent pathway is required for appreciation of pain, temperature,
tickle, itch and sexual sensations.  It also carries some signals
related to touch and pressure sensation; this function is relatively
poorly developed and is only apparent when the dorsal columns have been
injured.

QUESTION 29:  What are the effects of a unilateral lesion restricted to
the dorsal columns of the spinal cord? ANSWER:  Below the level of the
lesion and on the same side: impairment but not absence of touch and
pressure sensations (e.g. poor 2-point discrimination); loss of
vibration sense and loss of proprioception.  Some motor functions
dependent on somatic afferent feedback will be impaired (=sensory
ataxia).

QUESTION 30:  What are the effects on somatic sensation of a unilateral
lesion of the spinal cord, restricted to the antero-lateral quadrant of
the spinal cord? ANSWER:  Below the level of the lesion and on the
opposite side: loss of pain, temperature, tickle, itch and sexual
sensations.  Touch, pressure, vibration sense and proprioception are not
significantly affected.

QUESTION 31:  What are the effects of a lesion in the primary
somatosensory cortex? ANSWER:  Loss of discriminative capacity, but
retention of conscious appreciation of somatic stimuli: impaired
two-point discrimination, poor intensity discrimination, impaired
proprioception and astereognosis.  All effects are observed on the side
opposite to that of the lesion.

QUESTION 32:  What are the effects on somatic sensation of a lesion in
the somatosensory association cortex of the posterior parietal lobe?
ANSWER:  Somatosensory AGNOSIA affecting the side of the body opposite
to that of the lesion: astereognosis (an inability to recognise objects
by touch alone), sensory neglect (e.g. denial of the existence of body
parts)