The Nervous system - sensory and motor physiology Flashcards
Give me two types of automatic motor activity ?
innate: breathing, contraction of smooth muscle in stomach
Voluntary motor activity :
learnt - sport, become automatic or nearly so but all include automatic postural component
voluntarily directed tasks: role of attention
regarding the stretch reflex whats the stimulus and receptor
stretch causing change in muscle length
receptor muscle spindle
whats the chemoreceptor reflex do in summary ?
associated with severe exercise
if P02 decreases in arterial blood, this detected by peripheral chemoreceptors which then leads to respiratory control centres inducing ventilation. same with Pco2, increase in H+ conc, detected by central chemoreceptors when its to do with cerebrospinal fluid.. down to respiratory control centres.. ventilation
what is sensation ?
a function of biochemical and neurological mechanisms that allow the receptor cells of a sensory organ to detect an environmental stimulus
perception ?
interpretation
What are the two types of sensory systems ?
somatosensory: touch pressure pain temperature special senses vision hearing balance (vestibular) taste smell
graded potential ?
Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none.
What is a sensory receptor ?
a sensory receptor is a free nerve ending or a specific structure that undergoes depolarisation in response to different kinds of physical stimuli, modalities
What does the adequate stimulus refer to ?
the stimulus is specific to that receptor and known as the adequate stimulus
what does the adequate stimulus cause ?
cation-permeable ion channels to open (which leads to the generation of action potentials via the receptor potential)
what is a receptor potential ?
change in membrane potential in response to a stimulus acting on a sensory receptor
what are graded potentials caused by ?
opening and closing ion channels, if greater than threshold, can generate action potentials
what must happen for action potentials to occur ?
Graded potentials must occur to depolarize the neuron to threshold before action potentials can occur.
what are the forms of energy that excite sensory receptors ?
mechanical - mechanoreceptors (baroreceptors, hair cells; muscle spindles)
thermal - thermoreceptors
light - photoreceptors
chemical - chemoreceptors (taste; chemical; odourants; blood pH)
noxious - nociceptors( pain receptors that respond to tissue damaging and potentially damaging stimuli i.e mechanical, thermal ,chemical
whats special about receptors ?
they are usually sensitive to one kind of stimulus, known as the adequate stimulus
are there free nerve endings in the skin ?
yes
what does muscle spindle detect ?
length detector
how do we hear ?
mechanoreceptors . hair cells in inner ear.. open K+ channels depolarisation..
photoreceptors .. modality
photons of light
chemoreceptors
chemical dissolved in saliva, chemicals dissolved in mucus, chemicals in extracellular fluid.. oxygen dissolved in plasma.. free hydrogen ions in plasma
warm receptors
30 to 43
cold receptors
35 to 20
what are the three types of mechanoreceptors ?
baroreceptors, osmoreceptors, hair cells
what do baroreceptors do ?
blood pressure.. modality is the stretch of specific blood vessel walls
osmoreceptors
osmolarity of extracellular fluid.. modality is the swelling or stretch of receptor cells
hair cells
sound.. sound waves
balance and equilibrium.. acceleration
what does the the depolarisation of sensory receptor represent ?
transduction (conversion of one energy form to another)
stimulus then
receptor
receptor then
change in the ionic permeability of afferent nerve ending
change in the ionic permeability of afferent nerve ending then
change in membrane potential of nerve ending (receptor potential)
change in membrane potential of nerve ending (receptor potential) then
generation of action potentials in afferent nerve terminal
generation of action potentials in afferent nerve terminal then
propagation of action potentials to CNS
propagation of action potentials to CNS then
integration of information by CNS
afferent neurone with receptor ending in periphery.. whats the other kind or receptors
receptor cells in periphery
in a muscle spindle what detects stretch
stretch sensitive channels in sensory nerves
what is adaptation
adaptation is a time dependent decrease in firing rate even though the stimulus is maintained
what does slowly adapting receptors tell you
•Provides information about the absolute size of the stimulus (firing rate is proportional to size of stimulus)
what happens to firing rate in slowing adapting receptors ?
•Firing rate reduces but is maintained throughout the duration of the stimulus
Rapidly/fast adapting:
- firing rate reduces or totally ceases
- Provides information about rate of change of stimulus
- Type I & II= reflects size of receptive field
Whats the key point regarding the rate of change and stretch of a stimulus ?
Key point: Rate of change and strength of stimulus coded by frequency of APs
What do type 1 and type 11 receptor potentials depend on ?
axon diameter and size of receptive field
lare receptive field ?
two points perceived as one point
small receptive field ?
two points perceived as two points
what comes out of the golgi tendon organ ?
1b afferents from golly tendon organ
what are the two main ascending tracts ?
dorsal column system and antero-lateral system(spinothalamic), plus spinocerebellar (to cerebellum from spinal cord) afferent projection
dorsal column system properties
• Dorsal column system: touch and pressure
– Large diameter afferents therefore fast conduction velocity
– Intensity and localisation of mechanical stimulus (touch / pressure; movement against skin; position sense)
– High degree of discrimination
antero-lateral system (spinothalamic) properties
Antero-lateral system (spinothalamic): pain & temperature
– Smaller diameter afferents, therefore slower conduction velocity
– Touch and pressure but less localised, thus poor stimulus discrimination
– Temperature and noxious information
describe the dorsal column system ?
Dorsal column system:
Ascends ipsilateral to stimulus in dorsal columns to DC nuclei in medulla; cross to contralateral side in medial lemniscus and ascend to thalamus, synapse and ascend to sensory cortex.
spinothalamic system ?
Spinothalamic system:
Neurons may ascend few segments in Lissauer’s tract but form synapses with 2nd order neurons in dorsal horn (SG), cross to opposite side of cord and ascend in anterolateral quadrant of cord to thalamus and synapse to ascend to sensory cortex
what are the main type of motor system descending tracts ?
Corticospinal (pyramidal) - cortical origin
- Reticulospinal - brainstem origin
- Vestibulospinal
what do skilled movements require ?
postural reflexes and programmes and multiple sensory inputs: Visual
•Muscle receptors
•Joint receptors
•Vestibular (inner ear and brainstem)
•Cutaneous and pressure receptors of body parts providing support)
where do ascending pathways convey signals to ?
sensory cortex which somatotopically organised
what do motor programmes interact with ?
sensory feedback. motor system: goal directed movements
what do motor actions result from?
Motor actions: result from integration of reflexes (spinal cord circuits) and motor programmes
what do descending pathways do ?
Descending pathways: efferent pathways from cortex and brain stem for the control of posture and voluntary/goal directed movement
what receptors are found in the skin ?
Pacinan corpuscles which are found in the skin and are activated by mechanical stimuli, they are expecially sensitive to vibration.
give me two receptors that appear as free nerve endings?
thermoreceptors in the skin and noxious receptors in the skin
what is the dorsal column- leminiscal system associated with ?
the ability to localize and estimate the intensity of a mechanical stimulus, with pressure sensation, with movement against the skin and with position sense.
Thermal and noxious information ascends via this route.
anterolateral system
what does the thalamus project to
the somatosensory cortex
what is the somatosensory homunculus
The somatosensory homunculus is a distorted map of the peripheral sensory surface
what regions are large in the somatosensory cortex
finger and mouth regions
what is the size of the cortical region associated with a particular peripheral area related to
the density of receptors in that peripheral area
which areas have excellent spatial discrimination
areas that are densely innervated
what initiates movements
they may be reflex in origin or due to central programmes that can be influenced by sensory feedback
what are motor centres involved in ?
‘Motor centres’ involved in the control of movement are distributed throughout the CNS and a hierachical order is apparent.
what are goal directed movements controlled by ?
the motor system
give me three examples of higher motor centres
basal ganglia, cerebellum and motor cortex
there are interconnections between certain motor centres as well as input from centres involved in processing sensory information. what are receptors ?
proprioceptors - these are receptors that provide information about the position and movement of limbs; they are found in muscles and joints cutaneous receptors (information from those in the soles of the feet being of particular importance in the control of posture)
vestibular apparatus
which pathways are involved in the control of posture
These pathways
are involved in the control of truncal and proximal limb muscles; hence they are involved in the control of posture.
where does the pyramidal tract orientate from
descending pathway. originates from cerebral cortex, in particular from that area known as the motor cortex where the cells of origin are often known as “upper motoneurons.
how is the primary motor cortex organised ?
somatotopically organized
Again, body parts are not represented in the cortex in proportion to their size.
More cortical control is required by those parts with the greatest repertoire of movements
