List, and describe, the classes of sensory receptors. (HINT: there is 5 types)
- Mechanoreceptors - tissue deformation
- includes stretch receptors, tactile receptors and hair cells of ear - Thermoreceptors - peripheral & core temp
- Pain receptors - pain & itch (& tickle)
- Chemoreceptors - chemicals in the blood
- OR chemicals in food by olfaction & taste - Photoreceptors - light via rods & cones
For each of the following state:(i) what they detect (ii) what fibres are involved (iii) their rate of adapting & activation threshold (iv) where they tend to be found
1. Free nerve endings 2. Merkel’s discs 3. Meissners corpuscles 4. Pacinian corpuscles 5. Ruffini corpuscles
- (i) detect pain (ii) C fibres (hot cold burning pain) and A delta fibres (sharp pricking pain) (iii) slow adapt, high activation threshold (iv)???
- (i) static touch & pressure (ii) A beta fibres (iii) slow adapt, low activation threshold (iv) w. Meissners (lips, genitals, extremities)
- (i)changes in touch & pressure/texture (ii) A beta fibres (in glabrous skin) (iii) rapid adapt, low acitvation threshold (iv) fingers, lips, areas high point discrimination)
- (i) high frequency vibration (ii) A beta fibres (iii) rapid adapt, low AT (iv) hands, feet, nipples
- (i) skin stretch (ii)?? (iii) slow adapt, low AT (iv) deep layers skin, tendons, ligaments (all skin types - main hands, fingers, soles feet.
What are the roles of (i)muscle spindles (ii)Golgi tendon organs (iii)Joint receptors?
(i) Muscle length
(ii) Muscle tension
(iii) joint angle
What does stimulating a nerve ending result in? How is modal info delivered to the brain?
APs to travel to the CNS
CNS distinguishes them by reading what their FINAL destination is
-topographic fashion
What does an increase in impulse frequency do?
Intensifies the signal
What is a generator potential?
Initiates impulses in sensory nerves
The larger the GP, the faster the frequency of impulses - and => increase in signal intensity
Discuss the generator potential amplitude.
- dependent on stimulus strength
- decreases with distance from the site of the origin (but the APs they initiate are self propagating)
How are GPs different from PSPs?
Unlike PSPs, GPs last as long as the receptor is stimulated
- and the amplification is determined directly by the intensity of sensory stimulation (NOT by NT concentration)
What do sensory receptors do?
They act as transducers and convert sensory information into a digital code
How do you measure receptor field size? What does the receptor field size indicate?
Measured using the two point discrimination test
A smaller receptor field size = better linear discrimination between stimuli (NOT sensitivity)
Why do not all areas of the body have high linear discrimination?
Higher linear discrimination needs more sensory neurons
- the torso (for example) does not need that much discrimination
- plus, the extra neurons would present a space problem in the spinal cord
What is a way that space is saved in the CNS?
multiple sensory neurons with overlapping fields project to a single ascending neurons
How does contrast enhancement work?
When a pin hits the skin, it innervates more than one sensory stimulus. But the secondary neuron for B (the most direct neuron to the point of contact of the pin) inhibits those around it, making the contrast between itself and the surrounding neurons larger. Making our bodies perceive the pain as strongest in one definite area
How does sensory information travel in the brain? Describe the relation of the level of discrimination and the brain.
Passes through the thalamus and on to the primary sensory cortex (post to central gyrus)
High discrimination = high proportion of space in cortex
What does adaptation do?
filters out on-going signals
which helps to emphasise changes
What does the receptor field size determine?
the degree of detail that is sent to the CNS
What are the main two characteristics which make axons differ from each other?
Myelination and diameter
Describe the characteristics of alpha motor neurons.
- axons of large diameter
- A alpha type fibres
- conduction 70-120 m/s
- innervate skeletal muscle
What does a motor unit consist of? How many fibres do large and small motor units innervate respectively?
motor neuron + muscle fibres it innervates
- smallest innervate 5-10 muscle fibres per neuron
- largest innervate less than 1000 muscle fibres per neuron
What does motor unit size depend on?
- The precision control required (small motor units give HIGH precision - eyes, fingers)
- Force of contraction required or a low precision (large motor units - postural or calf muscles)
What is the intensity of a muscle contraction graded by?
- Alterations in the frequency that any single motor neuron fires an action potential
- Recruitment of alpha motor neurons
- increased number motor units=increased tension
- smaller MN more readily excited (and vice versa)
Link the size of motor units to what muscle fibres they innervate and what effect they have on said muscle fibre.
Small motor units innervate slow oxidative muscle fibres, so can give low power but sustained effort
Larger motor units innervate fast glycolytic muscles fibres, so can give high power but fatigue quickly
What two ways can reflexes be classified?
- SEGMENTAL - reflex arc restricted to 1 or 2 spinal cord segments
- INTERSEGMENTAL - reflex arc involves a number of segments
What are the various components of the muscle reflex time? (HINT: there’s 5)
- Activation of sensory receptors
- Conduction from receptors -> CNS along nerve fibres
- Transmission across neuron - neuron synapse in CNS
- Conduction from CNS -> muscle along nerve fibres
- Activation of muscles contractile machinery
