Sensory and motor pathways Flashcards
what is a receptive field?
the space occupied by a sensory receptor that can elicit a response to a stimulus.
what is lateral inhibition?
the capacity of an excited neurone to reduce the activity of its neighbours. this helps to sharpen sense perception.
a stimulus will stimulate some neurones greater than others depending on the position of the stimulus in a receptive field. a highly stimulated neurone will activate interneurones that inhibit excitation of laterally positioned cells. this creates greater contrast between the receptive fields and allows the brain to recognise where the stimulus is coming from
what do hair follicle receptors sense and what is their fibre type?
sensation- motion, direction
fibre type- type II (A beta)
what do meissner corpuscles sense and what is there fibre type?
sensation- tap, flutter (5-40 Hz)
fibre type- type II (A beta)
what do pacinian corpuscles sense and what is their fibre type?
sensation- vibration (60-300Hz)
fibre type- type II (A beta)
what do Merkel cells sense and what is their fibre type?
sensation- touch- pressure
fibre type- type II (A beta)
what do Ruffini corpuscles sense and what is their fibre type?
sensation- skin stretch/ slippage
fibre type- type II (A beta)
what do free nerve endings sense and what is their fibre type?
sensation- nociception- pain, heat
fibre type- type III (A delta) or type IV (C)
what is the difference between rapid adapting and slow adapting receptors?
rapid adapting- respond to the application/removal of a stimulus, transient, phasic, vibratory stimuli, fail to respond to maintained stimuli e.g meissners corpuscles, some hair follicle receptors, pacinian corpuscles
slow adapting- encode stimulus intensity, active for duration of stimulus, e.g Merkel cells, some hair follicle receptors and Ruffini corpuscles
what are the areas of the brain involved in decision and planning of movement?
the association cortices (parietal, pre-frontal, pre-motor and frontal) and the basal ganglia
what is the function of the basal ganglia in the planning of movement?
inhibits inappropriate movement s and allows appropriate movements
what are the areas of the brain are involved in the execution of movement?
primary motor cortex and the corticobulbar and corticospinal tracts
how is ongoing movement controlled?
movement leads to consequences which need to be adjusted and needs to be adjusted in near-real time speed. however ongoing sensory feedback is too slow to be helpful for this. therefore the brain feeds a copy of the motor output into an internal stimulation of the body in order to generate a stimulated outcome of movement (state estimate)quickly and accurately. the actual sensory outcome is compared to the stimulated sensory outcome to produce a discrepancy signal which indicates the difference between the actual and stimulated outcome. this signal is used to contribute to the fine tuning of ongoing movement and used to improve the accuracy of the internal stimulation. the cerebellum is responsible for this internal stimulation.
what are the ascending and descending pathways of the spinal cord?
ascending- dorsal column, posterior and anterior spinocerebellar tract, anterolateral system (including the spinothalamic tract)
descending- lateral corticospinal tract, rubrospinal tract, reticulospinal tracts, anterior corticospinal tracts, vestibulospinal tract
what is the pathway of the Dorsal column- medial lemniscus system?
the first order neurone enters through the dorsal root and accents in the ipsilateral dorsal column either in the cuneate fasiculus (from upper limb) or gracile fasiculus (lower limb). the neurone terminates in the dorsal column nuclei in the medulla (cuneate or gracile nuclei) and synapses with a second order neurone. this decussates to the contralateral side in the medulla and ascends in the medial lemniscus to synapse in the thalamus. the third order neurone projects from the thalamus to the sensory cortex
what is the dorsal column medial lemniscus pathway responsible for sensing?
discriminative (fine touch), pressure, vibration, proprioception
what is the pathway of the anterolateral system?
first order neurone enters through dorsal root and synapses with a second order neurone in the spinal cord which decussates to the contralateral side before ascending in the spinothalamic tract to synapse in the thalamus.
the third order neurone projects from the thalamus to the sensory cortex.
what is the anterolateral system responsible for sensing?
non-discriminative tacile touch
pain
temperature
what are the spinocerebellar tracts responsible for?
sub-conscious proprioceptive information. feedbacks to cerebellum to aid balance and fine movement adjustments
what is a motor unit?
a motor neurone and the skeletal muscle fibres innervated by that motor neurones terminal axons
what is the significance of small and large alpha motor neurones motor neurones?
small motor neurones innervate relatively few muscle fibres and form motor units that generate small forces.
large motor neurones innervate larger, more powerful motor units
what are the types of motor unit?
slow motor unit- contract slowly and generate small forces. they are resistant to fatigue and are important for activities which require sustained contraction- maintaining posture
fast- fatiguable- large motor units the generate more force that are easily fatigued. important for brief exertions
fast fatigue-resistant- lie between the two, intermediate size, slower than FF but much more resistant to fatigue and produce much more force that slow.
slow motor units recruited first then larger ones
what occurs at a neuromuscular junction?
axon terminal depolarises causing ca to enter the terminal causing vesicles containing neurotransmitter to fuse with the membrane and release neurotransmitter into the synaptic cleft. neurotransmitter binds to receptors on the muscle fibre causing Na/K channels to open and the fibre is depolarised causing contraction.
what Are upper and lower motor neurones?
upper motor neurone- connects brain to lower motor neurone
lower motor neurone- connects LMN to muscle
