Lecture 12: Basics of Touch, Sensation of Movement and Pain

Flashcards covering the basics of touch, sensation of movement, and pain, including somatosensation, receptors, transmission, and integration.

Somatosensation

The ability to sense touch, pain, and itch, linking sensory input to behavior for survival.

Stimulus specificity

Spatial location of a stimulus, spatial discrimination, touch frequency, duration and intensity, skin history

Skin Types

Glabrous (non-hairy) and hairy skin, each with unique mechano-receptors conferring specific stimulus properties.

Shape and size of mechano-receptors

Influence what type of information they transmit and are sensitive to.

Meissner cells

Superficial cells responding to light vibration.

Merkel cells

Also superficial and they respond to pressure.

Pacinian cells

Deeper cells which respond to stronger inputs such as walking.

Mnemonic for skin receptor types

Cells with German names are superficial, the ones with Italian names are deeper

Piezo 1

ion channel allows for mechanical detection to be converted into action potential.

Piezo 2

Key transduction molecule in touch processing

Dorsal Root Ganglion (DRG)

area of the dorsal root where different functional populations of sensory neurons lie each individual touch afferent nerves will contain their cell bodies here.

Large cells in DRG

Large, myelinated Aβ fiber axons, allow us to feel broader sensations such as touch.

Small cells in DRG

Small, unmyelinated C fiber axons allow us to feel more specialised sensations such as pain take longer to process .

Dermatomes

Area innervated by each dorsal root ganglion (DRG).

Spinal Segments

Cervical- upper limbs,

Thoracic- trunk,

Lumbar- lower limbs,

Sacral- pelvic

Integration

Taking information from many different sources and creating a new code.

Receptive Fields

The area of skin that evokes action potentials when stimulated.

Somatosensory Circuits

Complex somatosensory ‘circuits’ are formed by sensory nerve fibres and dorsal horn neurons.

Duck-gait locomotor pattern

A locomotor pattern resulting from affected touch circuits in the spinal cord, leading to inaccurate spatial understanding.

Projection

Sensory information is transmitted from the dorsal horn to the brain by specialised ascending pathways

Ascending routes for touch

Direct, indirect, spino-cervical pathways.

Thalamic organization- medial lemniscal system

Touch and proprioceptive signals remain segregated throughout, relay information to the primary somatosensory cortex via the thalamus, upper body represented laterally and the lower body represented medially

Perception

signals maintain their anatomical organisation: map of body surface in cortex

Receptive Fields in the Brain

Receptive fields are large and convergent allows integration from individual touch receptors to recognize the overall shape of an object

Somatic Sensory Cortex Inhibition

Finger coordination is disrupted when synaptic transmission in the somatic sensory cortex is inhibited.

Touch

Constant feedback with the environment: maps are not fixed and static but constantly changing and dynamic.

anterolateral system

• pain, itch, temperature, and visceral information

• information is transmitted to the brain stem and the thalamus in the contralateral anterolateral system

what are the two projection pathways

dorsal column—medial lemniscal system

anterolateral system

receptive field complexity in the brain

• the neurons in S-I are at least three synapses beyond touch receptors in the skin.

• cortical inputs represent information processed in the dorsal column nuclei, the thalamus, and the cortex itself

• receptive fields in higher cortical areas are much larger than in the spinal cord, spanning functional regions of skin that are activated simultaneously during motor activity

• meaning that the receptive fields in the brain are much larger than those in the spine