Neurological consideration for movement- Sensory feedback

Question 1

What is perception?

Answer 1

Perception- the processes of obtaining information about the internal and/or external environment from sensory stimulation:

It can be an unconscious process.

Relies on specialised nerve cells (e.g. receptors) that convert mechanical, visual, acoustic or chemical energy (the stimulus) into a neural signal.

It brings information to the brain (afferent signals) for controlling, planning or deciding.

It’s often multimodal (integrates multiple senses at the same time)

It can be modulated by the CNS (e.g. how much the sensor responds to a stimulus)

Involves motor behaviour- move to perceive and perceive to move

Question 2

What is sensation?

Answer 2

Perception is different than sensation.

Sensation is the activation of sensory receptor cells at the level of the stimulus. Perception is the central processing of sensory stimuli into a meaningful pattern. Sensation provides the input for perception. Not all sensations are perceived.

Question 3

What is a sensory neuron made up of?

Answer 3

Sensory neuron: (enter the spinal cord via the dorsal root, collects information from receptors and brings it to the CNS)

Cell body- contains nucleus and cell machinery, lie in the dorsal root ganglia

Axon- carries impulses away from the cell body into the spinal cord, can continue up the spinal cord to the brain

Peripheral fibre- carries impulses from the dendrites to the cell body

Central terminal branches- make connections with motor neuron dendrites or connector neurons in the spinal cord

Dendrites- carries impulses from the sensory receptors to the peripheral fibre

Question 4

What are sensory receptors, exteroceptors and interoceptors?

Answer 4

Sensory receptors- cells or organs that are selective in their response to different types of stimuli, they absorb energy and convert it into a neural signal.

Exteroceptors- located at or near a body surface, respond to signal coming from the environment, including 5 senses

Interoceptors: visceroceptors- impulses from viscera (internal organs), proprioceptors- impulses related to movement or position

Question 5

What are different types of sensory receptors?

Answer 5

Photoreceptors- sensitive to light

Mechanoreceptors- sensitive to mechanical inputs (e.g. force, pressure)

Chemoreceptors- sensitive to chemical substances (e.g. smell)

Thermoreceptors- sensitive to thermal energy (e.g. heat)

Nociceptors- can fall in more than one of these categories (sensitive to pain)

Question 6

What are phasic and tonic sensory receptors and what are proprioceptors?

Answer 6

The stronger the stimulus, the higher the firing rate in the afferent axon. Response tends to decrease over time if stimulus stays constant.

Phasic- if decline is fast
Tonic- if decline is slow

Proprioceptors- located in muscles, tendons and joints. Stimulated by motion- their response depends on the magnitude, direction and the rate of change of the body movement.

Question 7

What are muscle spindles?

Answer 7

Located in muscle belly

Lie parallel and between muscle fibres

Sensitive to length change

When stretched, a sensory nerve sends impulses to CNS, which activates the motor neurons via a reflex action causing muscle to contract

Stimulate muscle to produce force to resist stretching

Question 8

What are intrafusal muscle spindle fibres?

Answer 8

Sensory fibres are classified into 4 main groups: I (largest diameter), II, III and IV (smallest diameter)- conduction velocity is governed by this diameter

Primary ending (annulospiral- AS)- responsible mainly for phasic response (quick changes in fibre length), but also tonic (static) stretch. They also provide information about the velocity of the stretch

Secondary ending (flower-spray- FS)- register only tonic (static) stretch

The length of the intrafusal muscle spindle fibres can change so that they can function at all muscle fibre lengths- this is controlled by y-MN (like an a-MN, but connected to spindles)

y-MN (gamma motor neuron), a-MN (alpha motor neuron)

Question 9

What is the Golgi Tendon Organ?

Answer 9

Located at the musculo-tendinous junction (between muscle and tendon)

Sensitive to tension

Type Ib sensory fibre

When stretched they cause muscle to relax

GTOs and muscle spindles function together to protect the muscles for excessive

Question 10

What are the 2 joint proprioceptors?

Answer 10

Paccinian Corpuscles:
Located around joint capsules, ligaments and tendon sheaths.
Activated by rapid joint angle changes and by changes in intra-articular pressure.
Detect joint angle change, intraarticular pressure change and vibration.

Ruffini Endings:
Located in deep layers of skin or within the joints.
Detect joint angle change and constant intraarticular pressures.
Activated by joint angle change, but also recognise constant pressure- slow/very little adaptation.

Question 11

What are neck receptors and labyrinthine proprioceptors?

Answer 11

Neck receptors:
Maintenance of equilibrium of the head is due to joint receptors C1-C3 (cervical).
Sensitive to the angle between body and head.

Labyrinthine proprioceptors:
Labyrinths recognise orientation and the movements in the head.
Consists of cochlea, 3 semicircular canals, utricle and saccule.
3 semicircular canals at 90 degrees to each other.

Question 12

What is the stretch reflex?

Answer 12

A reflex is a motor response developed in the CNS after sensory input is received.

The stretch reflex (effect of muscle spindles)- positive effect on muscle force, when stimulated causes muscles to contract and generate force to resist stretch.

Receptor- muscle spindle (sensitive to stretch)
Effect on agonist- positive or excitatory=more force
Effect on antagonist- negative or inhibitory=less force

Question 13

What is the tendon stretch?

Answer 13

The Golgi tendon reflex (effect of GTO)- negative effect on muscle force, when stimulated causes muscle to relax and produce less force to reduce tension.

Receptor- GTO (sensitive to force)
Effect on agonist- negative or inhibitory=less force
Effect on antagonist- positive or excitatory=more force

Question 14

What is the withdrawal and cross extensor reflex?

Answer 14

Withdrawal reflex:
Receptor- pain and tactile
Effect- withdraw leg
How- positive or excitatory effect on hamstrings

You would fall over if the withdrawal reflex occurred on its own.

Cross extensor reflex: (works with the withdrawal reflex)
Receptor- pain and tactile
Effect- weight support on contralateral limb
How- positive or excitatory effect on quadriceps

We are born with reflexes, but lose some when we grow: moro reflex, grasp reflex, step reflex, rooting and sucking reflex.