sensory and motor systems Flashcards
describe the organisation of the SS.
- all over the body
- tells us what body is up to and whats going on in the env
what sense is the SS most involved in?
movement
state the two types of skin we have.
hairy skin - relatively low sensitivity
glabrous - larger number of sensory receptors
what part of out body is most sensitive?
fingertips
state and describe the three main types of somatosensory perception.
nocioception - perception of pain and temperature
hapis - perception of fine touch and pressure
proprioception - perception of the location and movement of body
which type of SS perception has free nerve endings?
nociceptors
which type of SS perception has dendrite attached to hair, connective tissue or encased in capsule of tissue?
haptic
describe a rapidly occurring receptor.
body sensory receptor that responds briefly to the beginning and end of a stimulus on the body.
describe a slowly adapting receptor.
body sensory receptor that responds as long as a sensory stimulus is on the body.
describe the difference between slow and rapid receptors.
slow receptors signal the presence of a long sustained stimulus whereas rapid receptors give good responses to a repeated stimuli.
describe the dorsal-root ganglion neurone.
- the dendrite and axon are continuous and carry sensory information from the skin to the CNS via spinal cord.
- tip of dendrite is responsive to sensory stimulation
- each spinal cord segment has one dorsal-root ganglion on each side that contains many dorsal-root ganglion neurons.
- n the spinal cord, the axons of these neurons may synapse onto other neurones or continue up to the brain.
describe a similarity between proprioceptive and chaotic neurons.
they both carry information about location and movement and touch ad pressure, and have large, well-myelinated axons.
what type of axons do nociceptive neurons have?
small axons with little to no myelination.
deine deafferentiation .
loss of incoming sensory input usually due to damage to sensory fibres, also loss of any afferent input to a structure.
what is a consequence to deafferentiation?
loss sensation, simple actions are prolonged periods and require visual feedback, can not perform many daily tasks.
describe the dorsal spinothalamic pathway,
- carries haptic and proprioceptive info.
- axons from dorsal-root ganglion neurones enter spinal cord and ascend ipsilaterally until they synapse in dorsal column nuclei.
- axons from dorsal column nuclei cross over to the other side of brain and project up through the brainstem as part of pathway called medial lemniscus.
- axons synapse with neurones located in the ventrolateral nucleus of the thalamus, which project to the SS cortex and motor cortex.
describe the spinothalamic tract.
- carries nociceptive info.
- axons from dorsal-root ganglion neurones enter final cord and cross over right away and synapse onto neurones on contralateral side.
- axons from contralateral spinal cord then ascend to brain and join with other axons forming the medial lemniccus, synapsing with neurones located in the ventrolateral nucleus of the thalamus.
- neurones from the thalamus the project to the SS cortex.
true or false: spinal cord damage results in distinctive sensory losses to both sides of body.
true.
name a reflex.
monosynaptic reflex - require sone synapse between sensory input and movement.
define the vestibular system.
SS system that comprises a set of receptors in each inner ear that respond to body position and movement of head.
what do vestibular organs contain?
- three semicircular canals
- otolith organs
state the two functions of vestibular organs.
- tell us the position of body in relation to gravity
- signal changes in the direction and speed of head movements.
what happens when the head moves?
- fluid located within semicircular canals pushes against hair cells, causing bending of the clip located on top of hair cells.
- repsonds to ‘angular acceleration’
- bending of cilia leads to receptor potentials in the hair cells and APs in the cells forming the vestibular nerve.
- direction of cilia are bent determines whether the hair cells becomes depolarised or hyperpolarised.
when the head is tilted back and forth…
- the utride and succule also contain hair cells, which are embedded within a gelatine-like substance that contains small crystals of calcium carbonate called otoconia
- responds to ‘linear acceleration’
- when head is tilted, the gelatin and otoconia push against the hair cells, which alters the rate of APs in cells that form the vestibular nerve.
state the twi main SS areas in the cortex.
- primary -begins the process of constructing perceptions from SS information
- secondary- continues the construction, projects to frontal cortex.
describe penfields study?
- stimulated the cortex surface with large diameter electrodes and recorded patient responses, wanted to locate source of seizures.
what did penfields study suggest?
that there was a single SS homunculus.
describe Kaas study?
used small electrodes and precise recording techniques.
state the four separate SS homunculi.
area 3a: muscles
area 3b: skin
area 1: skin
area 2: joints, pressure
describe the hierarchal organisation.
- perceptions constructed from sensations depend on a hierarchal organisation.
- area 3a and 3b project to 1, which turn into2.
- each successive relay of info the size of the receptive field and synthesis of SS modalities increases.
- SS info is segregated and synthesised.
state effects of damage to the SS cortex.
- damage to primary results in impairment of pressure sensitivity, prop, hapsis and simple movements.
give evidence that reorganisation following damage is possible.
following damage to the arm, the cortex that was developed to the arm becomes sensitive to the face - ‘plasticity’.
state components of hierarchy.
- neocortex brainstem and spinal cord
- normally functions as a whole.
define hughlings-jackson.
conceived of NS as organised in successive layers, with higher levels controlling behaviour by acting through lower levels.
state the 1930s concept of the forebrain and initiation of movement.
action > feedback (action successful) > action.
describe 1950s concept of the forebrain and initiation of movement.
- movement for skilled actions are performed quickly to rely on feedback.
- movements modules preprogrammed by the brain and produced as a unit or as ‘motor sequence’.
- as one sequence is executed, the next is prepared.
name the cortex’s in the frontal lobes.
PFC - planning
premotor - organises
primary - produces
animals with damage to premotor cortex cannot…
put motor sequences together.
describe what was found when measuring cerebral blood flow while performing various motor tasks.
- blood flow increases in primary SS and cortex when subject uses finger to push lever.
- blood flow increases in premotor cortex when subject performs a sequence of movements.
- blood flow increases in PFC, temporal and parietal cortex when subject uses a finger to find route around maze.
who worked to confirm the role of primary motor cortex in producing movements in humans?
Penfield.
describe the organisation of the motor cortex.
topographical organisation - neural spatial representation of body or areas of the sensory world perceived by a sensory organ.
- parts of a motor cortex that control the hands, fingers, lips and tongue are disproportionately larger than parts of the motor cortex that control other areas.
define homunculus.
- representation of the human body in the sensory or motor cortex.
explain findings fro Graziano’s work on monkeys.
- more precise stimulation in motor cortex
- movement categories have the same end regardless of the location of monkeys limb or its ongoing behaviour.
state the three types of organisations the motor cortex represents.
- part of body that is to be moved
- spatial location to which the movement is directed
- movements function
describe how motor-cortex damage affects movement with and without rehabilitation on monkeys.
without - hand area becomes smaller whereas elbow and shoulder become larger.
with -hand area of motor cortex retained its size and ability to move hand (forced and practice to move body part)
describe the corticospinal tract.
- bundle of nerve fibres directly connecting cerebral cortex to spinal cord.
- originates from layer V pyramidal neurons.
- branches at brainstem into opposite side lateral tract that controls movement of limbs and digits, and a same-side ventral tract tat informs movements of trunk.
define the lateral cortiospinal tract.
- branches at brainstem level, crossing over to opposite side of brain and spinal cord, moves digits and limbs on opposite side of body.
define the ventral cortiopsinal tract.
- remains on the same side of brain and spinal cord.
- moves the muscles of midline body on the same side of body.
state the two types of neurons in the spinal cord.
- interneurons project to motor neurons
- motor neurons project muscles of the body.
lateral loaded motor neurons project to the muscles that…
control the finger and hands.
intermediately located motor neurones project to muscles that control…
the arms and shoulders
the most medially located neurons project to…
muscles that control the tank.
limbs are arranged in pairs, name the pairs.
- extensor - away from trunk
- flexor - towards trunk
define quadriplegia
paralysis of the legs and arms due to spinal cord injury.
define paralegia
paralysis of legs due to spinal cord injury.
describe characteristics of motor cortex neurons
- planning and initiating movements
- code force of movement (neurons increase their rate and duration of firing in response to heavier weights)
- simple coding of movement direction (flexor vs extensor)
describe the basal ganglia.
- collection of subcortical nuclei within forebrain
- receives input from all areas of neocortex and limbic cortex
- project back to motor cortex
- allow us to adjust force of our movements
describe the volume hypothesis.
internal locus pallid us acts like a volume dial and projects to the thalamus, which projects to the motor cortex.
explain the two pathways in the basal ganglia.
direct - inhibitory effect on GPi, too much activity leads to overactivity in thalamus and amplified force of movement.
indirect - excitatory effect of GPi, too much activity leads to under activity in thalamus and reduced force of movement.
damage to the basal ganglia produces two main types of motor symptoms, describe these symptoms.
hyperkinetic symptom - symptom of brain damage that results in excessive involuntary movements e.g huntingtons
hypokinetic symptom - ““paucity of movement
describe huntingtons chorea.
- genetic disorder
- symptoms - excessive movements
- atrophy of caudate nucleus and putamen
- treatment - antipsychotics that block dopamine, anxiolytic/ anticonvulsant GABAergic drugs that increase inhibitory transmission.
describe hemiabllism.
- caused by stroke to the subthalamic nucleus (one part of body)
- results in involuntary, fast movements
- treatment: clozapine (dopamine blocker)
describe parkinsons.
- slow progressive disorder
- symptoms - slowness and stiffness of muscles
- loss of substantia nigra that send dopamine projections to putamen that controls movement and coordination
- treatment - L-dopa > dopamine precursor
what does dopamine to for parkinsons
increases activity in direct pathway neurones and decreased activity in indirect pathway.
- there is overactivity in indirect and underactivity in direct pathway.
can symptoms of parkinsons be restored?
study of mice:
- use 6-OHDA to lesion DA terminals in striatum
- use virus to express light sensitive ‘channel rhodopsin’ in only D1R-expressing neurones in lesioned area
- ontogenetic activation of D1R-expressing stratal neurones by shining blue light into striatum
= improvement in fine movement, decreasing freezing, increased locomotor activity.
what is involved in the cerebellum?
flocculus - small, dense lobe involved in eye movements and balance, inputs from vestibular system
two hemispheres - lateral parts and medial parts.
describe the three main motor functions.
- timing of movements
- maintaining movement accuracy - error connection, compares intended movement with actual movement and makes necessary adjustments
- motor associative learning - conditioned eye blink response, patients with cerebellar damage have trouble learning this response.
