Sensation Flashcards
What does somatosensory mean?
From the body
What are the types of peripheral somatosensory receptors?
- Muscle spindles (stretch, rate of movement)
- Golgi tendon organs (tension)
- Joint receptors (stretch, rate of movement)
- Cutaneous receptors
What are the 3 types of cutaneous receptors?
- Thermal (temp)
- Nociception (pain)
- Mechanoreceptors (light/firm touch, vibration)
What are the types of mechanoreceptors?
- Pacinian corpuscles
- Merkel’s disks
- Meissner’s corpuscles
- Ruffini endings
- Lanceolate endings
What is the difference between myotome and dermatome?
Myotome: Muscles innervated by one nerve root
Dermatome: Area of skin innervated by one nerve root
What does postural control require?
- Sensory info coming in
- Processing of info at an automatic/cognitive level
- Activating muscles an appropriate amount for the environment/task
- Ability to rapidly modify the response
- Learning & memory
What is the thalamus and where is it located?
Major processing centre of the brain, in the diencephalon
What somatosensory information is relayed to the somatosensory cortex via the thalamus?
Conscious sensation of touch, pressure, pain, temperature, vibration and proprioception
What somatosensory information is relayed to the cerebellum via the brainstem?
Unconscious sensation, e.g. position, movement
How does the visual system work?
- Photoreceptors respond to light
- Sensory info transmitted via optic nerve
- Medial optic nerve fibres cross at optic chasm
- Lateral optic nerve fibres remain on same side, forming optic tract
- Optic tract carries info to lateral geniculate nucleus in thalamus
- Info transmitted to primary visual cortex in occipital region
What are the afferent and efferent functions of the visual system?
Afferent: Provide sight & info about posture & body movement
Efferent: Eye movements
How can you test the afferent and efferent function of the visual system?
Afferent: Test pupillary reflexes, Snellan chart, visual fields
Efferent: Test eye movements
What does the vestibular system monitor?
Monitors changes in head position, movement and direction of gravity
Where are the vestibular system receptors located?
Within the inner ear
- Utricle
- Saccule (vertical/linear displacement, gravity)
- Semicircular canals (direction, acceleration)
How is sensory info from the vestibular system transmitted?
By vestibular nerve to vestibular nuclei within brain stem and cerebellum
What is the function of the vestibular system?
- Stimulates reflexes for equilibrium and gaze stabilisation
- Coordinates balance
- Contributes to positioning of head, postural adjustments, autonomic function & consciousness
How can the vestibular system be tested?
- Vestibular evoked myogenic potentials (clicking sound while holding head up)
- Neck muscle activity
- Caloric test (response to water in ears)
- Eye movements
- Rotations tests
What are muscles spindles composed of?
Intrafusal muscle fibres (3 types):
- Static nuclear bag
- Dynamic nuclear bag
- Nuclear chain (less elastic)
What are the two types of afferent neurons in muscle spindles?
Group Ia & Group II (cell bodies in dorsal root ganglion)
Where are group Ia afferent neurons located and what do they detect?
Wrap around the middle of IF muscle fibres (bag and chain)
Sense rapid change in muscle length
Where are group II afferent neurons located and what do they detect?
Wrap around the area just off the middle (mostly chain)
Less responsive to stretc
What type of efferent neurons are located in muscle spindles?
Gamma motor neurons (dynamic & static)
How does reciprocal innervation occur in a pain withdrawal reflex?
- Afferent neurons conduct action potentials from receptors to spinal cord
- Synapse with excitatory interneurons (withdrawal reflex)
- Collateral branches of afferent neurons synapse with inhibitory interneurons
- Inhibitory interneurons synapse with alpha motor neurons
- Alpha motor neurons relax extensor muscles (reciprocal)
What are the 3 ascending sensory spinal cord pathways?
- Dorsal column/medial lemniscus
- Anterolateral/spinothalamic
- Spinocerebellar
What sensations and receptors are associated with the dorsal column?
Sensations: Fine touch, pressure, vibration, conscious proprioception
Receptors: Sensitive mechanoreceptors
What sensations and receptors are associated with the spinothalamic tract?
Sensations: Pain, crude touch, temp
Receptors: Nociceptors, mechanoreceptors, thermoreceptors
What sensations and receptors are associated with the spinocerebellar tract?
Sensations: Unconscious proprioception
Receptors: Golgi tendon organs, muscle spindles
How is the spinocerebellar tract different from the other 2 spinal cord pathways?
No 3rd order neuron, does not cross sides of the spinal cord
What is the 1st order neuron for all 3 ascending sensory pathways?
Dorsal root ganglion
Where does the dorsal column cross to the other side of the spinal cord?
At the 2nd order neuron, the nucleus cuneatus in the medulla
Where does the spinothalamic tract cross to the other side of the spinal cord?
At the 1st order neuron, the DRG
What is myelin and where is it produced?
- A sheath made of a lipid layer that surrounds axons and facilitates fast signal conduction
- Produced by Schwann cells in PNS
What do myelinated nerves (type A) transmit?
Large fibres: Motor function, proprioception, touch, pressure, pre-ganglionic signals
Small fibres: Pain, temperature, crude touch
What do unmyelinated nerves (type C) transmit?
Small fibres: Slowly transmit pain, touch, pressure, post-ganglionic signals
What are the types of sensory neuron fibres?
- A-alpha (I)
- A-beta (II)
- A-delta (III)
- C (IV)
What does the Nottingham assessment test?
Light touch Pressure Pinprick Temperature Tactile localisation Bilateral simultaneous touch Kinaesthetic sensation Stereognosis
What are the indications for neurological examination?
- Spinal symptoms extending past the point of shoulder or buttock crease
- Reports of altered sensation/weakness in the limbs
What does neurological examination screen for?
- Nerve conduction loss
- PNS vs CNS involvement
- Nerve root vs peripheral nerve injury/compression
- Neural sensitisation
What are the causes of nervous system disorders?
- Trauma
- Vascular disorders
- Infections
- Degeneration
- Structural disorders
- Other, e.g. tumours
What are the injury-related sensation changes in the spinal cord, nerve root and peripheral nerve?
Spinal cord: Bilateral, non-dermatomal
Nerve root: Unilateral, dermatomal
Peripheral nerve: Unilateral, peripheral nerve
What are the injury-related strength changes in the spinal cord, nerve root and peripheral nerve?
Spinal cord: Bilateral, non-myotomal
Nerve root: Unilateral, myotomal
Peripheral nerve: Unilateral, peripheral nerve
What are the injury-related reflex changes in the spinal cord, nerve root and peripheral nerve?
Spinal cord: Bilateral increased, non-myotomal, +ve Babinski, clonus
Nerve root: Unilateral decreased, myotomal, -ve Babinski, clonus
Peripheral nerve: Unilateral decreased, peripheral nerve, -ve Babinski, clonus
What is the nervi nervorum?
Nerve of the nerve, contained within the perineurium and epineurium
What are 3 types of traumatic peripheral nerve injuries?
- Neuropraxia
- Axonotmesis
- Neurotmesis
What are the 2 types of pain?
Nociceptive: Pain signal transmitted to CNS following tissue injury
Neurogenic: Pain generated by nerve due to nerve injury
