L21 Sensation And Motor Control Flashcards
What are the subdivisions of the somatosensory system?
- Cutaneous sensations (skin)
- Visceral ( internal organs and deep tissues)
- Proprioception (positions 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
Why do sensory system require receptors?
They convert stimulus energy into action potentials
What is sensory transduction?
- the stimulus is converted into graded electrical signal (receptor potential)
- the receptor potential magnitude depends on stimulus strength
What happens if the receptor potential exceeds threshold?
The nerve fibre fires action potentials
What is stimulus strength coded by?
Coded by firing rate or pattern
How can properties of receptors be recorded?
By recording action potential from single afferent nerves and mapping ‘receptive fields’
Smaller set of nerves less myelin smaller diameter slower conduction
A beta
Type 2 axons
Cutaneous mechanoreceptors
Large set of nerves, large diameter, lots of myelination, fast conduction
Type 1a/1b
A alpha
Proprioception
What are the two main groups in Proprioception?
Muscle spindles - imbedded in the muscles
Golgi tendon organs
Outline extrafusal muscle fibres
Innovated by alpha fibres - large fibres
Generate force
Outline intrafusal muscle fibres
Gamma motor units - smaller than alpha motor units
Don’t really generate force
Set gain of spindle responses
They can detect whether the muscle has been stretched
How are extrafusal and intrafusal muscle fibres divided?
Divided by a collagen/fibrobast sheath with a ‘fuse form shape’
How are muscles activated?
Activated as a result of action potentials arising at the neuromuscular junction causing a release of Ach
What makes up a motor unit?
A motoneuron and the muscle fibres it innervates
Outline the Henneman Size Principle
Small motor units are recruited before large motor units
- these units produce low force but are more fatigue resistant
Outline the monosynaptic stretch reflex
- add load to muscle
- muscle and muscle spindle stretch as arm drops
- reflex contraction initiated by muscle spindle restores arm position
Where do spinal motoneurons receive input from?
- afferents
- spinal interneurons
- descending inputs from the brain
What is the dorsal column pathway responsible for?
Fine touch / Proprioception
What is the spinothalamic pathway responsible for?
Pain / Temperature
What is the coritcospinal pathway responsible for?
Voluntary movement
Which cutaneous receptors are located in the superficial area of the skin?
Meissner, merkel and free nerve endings
What do A-delta nerve endings detect?
Detect cold temperatures via bare nerve endings
Detect a sharp, initial pain via nociceptors
What do A-delta nerve endings detect?
Detect cold temperatures via bare nerve endings
Detect a sharp, initial pain via nociceptors
What do C-fibres detect?
Detects warm temperatures via bare nerve endings
Detects the burning/nagging pain via nociceptors
What do A-beta fibres transmit infomation about?
Info about pressure, vibration and flutter/stroking
Outline the pathway for a neurone that senses fine touch
Dorsal column pathway
- neurones project into the medulla where they first synapse
- leads into the thalamus where the second synapse occurs
- leads to the somatosensory cortex
Outline the pathway for a neurone that senses coarse touch
Spinothalamic tract pathway-also for nociception and temp
- the first synapse occurs in the spinal cord before crossing over
- continues through the medulla to the thalamus and somatosensory cortex
