WEEK 3 Flashcards by Emma Wilson

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

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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.

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What are the roles of (i)muscle spindles (ii)Golgi tendon organs (iii)Joint receptors?

(i) Muscle length
(ii) Muscle tension
(iii) joint angle

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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

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What does an increase in impulse frequency do?

Intensifies the signal

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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

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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)

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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)

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What do sensory receptors do?

They act as transducers and convert sensory information into a digital code

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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)

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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

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What is a way that space is saved in the CNS?

multiple sensory neurons with overlapping fields project to a single ascending neurons

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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

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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

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What does adaptation do?

filters out on-going signals

which helps to emphasise changes

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What does the receptor field size determine?

the degree of detail that is sent to the CNS

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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

How is length monitoring of muscle fibres achieved?

Achieved by activation of both IA and II sensory fibres on BOTH bag & chain intrafusal fibre types

What is the purpose of stretch reflexes?

Act to minimise unexpected changes in muscle length

What is the function of the gamma motor neuron efferent?

- The central portion of muscle spindles are only sensitive over small change in length - So to prevent this, the spindle is adjusted to keep it in its most sensitive range - To do this, the CNS activates Gamma Motor Efferents to spindles IN CONCERT with alpha motor neuron activation of extrafusal muscle fibres

What are the 2 types of spindle fibres? Describe them.

``` Chain fibres: - IA = rate of change II = total length - most common - nuclei arranged in a chain in the central portion Bag fibres: - IA = rate of change ONLY - one or two per spindle - swelling in equatorial region that houses the nuclei ```

What are tendon jerk reflexes mediated by?

Muscle spindles | NOT the tendon

What is reciprocal innervation (of antagonist muscles)?

1. Influence of sensory nerve fibres from one (homonymous) muscle on motor neurons projecting to antagonist muscles 2. Effect: opposite to that of their own muscle 3. Relaxes the antagonist and facilitates shortening of the homonymous muscle 4. Requires involvement of local inhibitory neurons in the reflex onto the antagonist muscles

Describe what happens in voluntary contractions

When the voluntary signal for muscular contraction leaves the spinal cord, it goes to both intrafusal (via gamma MN's) & extrafusal muscle fibres (via alpha MNs) - which causes BOTH fibres to contract Therefore: the spindle ends shorten in concert with extrafusal fibres, keeping the central portion constant in length, meaning annulospiral endings detect no change in muscle length

What do unpredicted changes in muscle length cause?

A change in sensory nerve activity

What do muscle spindles monitor?

Muscle length Rate of change in length Duration change

What is the function of the Golgi Tendon Organ? What is their role within the reflex arc?

To monitor tension - it compliments the info from the spindles, in the CNS Provide reflex inhibition to motor neurons in whose tendon they are located (disynaptic reflex) - under normal use they regulate the amount of tension developed - under extreme conditions they protect the muscle & tendon from damage

When there is increasing tension in the tendon, what do the collagen fibres do?

They lock onto, and stretch the type IB fibres - increasing the generator potential - which speeds signal frequency

What is skeletal muscle contraction a combination of?

1. Alpha motor neuron mediated control 2. Gamma motor neuron mediated spindle fibre contraction - enabling accurate feedback 3. GTO mediated inhibitory feedback to alpha motor neurons

What does damage to the (i) peripheral nerves and (ii) Brain pathways do to reflex responses?

(i) reduction/loss of reflex response | (ii) exaggerated reflex response

Explain the reflexes involving special senses (ie the eye).

Rotatory Nystagmus - eye movements drive by moving visual images Post Rotatory Nystagmus - eye movements drive by the fluid movement in the semi circular canals of the inner ear The interpretation of movement within images is used to make postural adjustments - preserving balance

Describe Autonomic reflexes, giving 2 detailed examples.

Brought about by the activation of peripheral OR special sense organs (vision, hearing, balance, taste, smell) 1. OCULAR - when alarmed or excited - sympathetic NS activates radial muscles iris = DILATION - parasympathetic constricts pupil - focussing image on retina achieved by PS controlling ciliary muscles of eye (responsible for changing the shape of the lens) 2. CARDIOVASCULAR - BP determined by cardiac output & peripheral resistance of vascular beds - Sympathetic = inc HR (&force contraction) inc peripheral resistance (constricting small arterioles) - Parasympathetic = dec HR, less effect on peripheral resistance => Activation of Baroreceptors (by inc BP) do 2 things: (i) Depress tonic sympathetic activity to arterioles = dilation = drop peripheral resistance (ii) Inc vagal activity (PS) to heart = inc HR

What are conditioned reflexes? Name one example.

Form of subconscious learning when autonomic reflexes are altered E.g. salivation - conditioned response from ANS in response to auditory stimuli (dog, dinner, ding)