L21- Spinal chord

what are the 3 subdivisions of the somatosensory system

• cutaneous (skin) sensations

• visceral (internal organs and deep tissues)

• proprioception (position of limbs and body in space)

what are the functions of touch sense

• recognition and properties of things

• communication-social and intimate

• control of movement- source of feedback

describe sensory transduction

• receptor potential

• receptor potential magnitude depends on stimulus strength

define receptor potential

stimulus converted into graded electrical signals

describe action potential initiation

• if receptor potential exceeds threshold, the nerve fibre fires action potentials

• stimulus strength coded by firing rate or pattern

what is microneurography

properties of receptors can be studies by recording action potentials from single afferent nerves and mapping ‘receptive fields’ (the set of stimuli that evoke a response)

what generates force during external pertubation

extrafusal muscle fibres and alpha motor units

what sets a gain of spindle response during proprioception

intrafusal muscle fibres and gamma motor units

what divides the proprioception

a collagen/fibroblast sheath with a fusiform shape

how are muscles activated

as a result of action potentials arising at the neuromuscular junction causing release of ACh

what is a motor unit

a motoneuron and the muscle fibres it innervates

what is the Henneman size principle

small motor units are recruited before large motor units

• produce low force but are more fatigue resistant

describe the monosynaptic stretch reflex

• add load to muscle

• muscle and muscle spindle stretch as arm drops

• reflex contraction is initiated by muscle spindle which restores arm position

what is the function of spinal motoneurons

to recieve input from afferents and spinal interneurons as well as descending inputs from the brain

• represent the final common pathway of behaviour

what is the function of the Dorsal column pathway

fine touch/proprioception

what is the function of the spinothalamic pathway

pain/temperature

what is the function of the corticospinal pathway

voluntary movement

what are the myelinated wider afferents of proprioceptors

group 1a and 1b

what are the unmyelinated narrower afferents called

A delta and C fibres

• temperature/pain

what are the cutaneous mechanoreceptor afferents called

group 2 or A beta

what afferent is a muscle spindle (fusiform shape)

1a

what afferent is a golgi tendon organ spindle (measures tension)

1b

what is the contraction time of type 1 muscle fibres

slow

what is the oxidative capacity of type 1 muscle fibres

high

what is the diameter of type 1 muscle fibres

small

what is the resistance to fatigue of type 1 muscle fibres

high

what is the generating force of type 1 muscle fibres

small

what is the contraction time of type 2A muscle fibres

fast

what is the oxidative capacity of type 2A muscle fibres

high

what is the diameter of type 2A muscle fibres

medium

what is the resistance to fatigue of type 2A muscle fibres

moderate

what is the generating force of type 2A muscle fibres

moderate

what is the contraction time of type IIX muscle fibres

very fast

what is the oxidative capacity of type IIX muscle fibres

low

what is the diameter of type IIX muscle fibres

large

what is the resistance to fatigue of type IIX muscle fibres

small

what is the generating force of type IIX muscle fibres

very high