Physiology II: Somatosensory System 1 - Primary Sensory Neurones and their Modalities

The Somatosensory System can be subdivided into 3 parts: [blank_start]Exteroceptive Division[blank_end]: Registers cutaneous sensation by numerous receptors [blank_start]Proprioceptive Division[blank_end]: Monitors posture and movement via receptors in muscles, tendons and joints [blank_start]Enteroceptive Division[blank_end]: Reports upon the internal state of the body

Resting membrane potential is [blank_start]-90[blank_end]mV, whereras the resting potential of a neuron is [blank_start]-70[blank_end]mV.

A [blank_start]nociceptor[blank_end] is a receptor that responds to potentially damaging stimuli by sending 'threat' signals to the brain

[blank_start]Low threshold thermoreceptors[blank_end] mediate cold, cool, indifferent, warm and hot sensations [blank_start]Thermal nociceptors[blank_end] respond to extreme degrees of heat (both hot and cold) [blank_start]Chemical nociceptors[blank_end] responds to potentially damaging substances in tissue

Cutaneous afferent fibres in the fingertips are of a [blank_start]high[blank_end] density of innervation, each fibre having a [blank_start]small[blank_end] receptive field in order to allow a [blank_start]high[blank_end] acuity in terms of sensation.

Two point discrimination (spacial acuity) in higher in the [blank_start]finger tip[blank_end] but lower in the [blank_start]forearm[blank_end], due to the differing sizes of the afferent fibres' receptive fields.

As receptive field size increases, spatial acuity [blank_start]decreases[blank_end].

Which layer of the epidermis contains merkel cells?

[blank_start]Merkel cells[blank_end]: Sensitive to sustained pressure, texture and edges of objects [blank_start]Meissner corpuscles[blank_end]: Sensitive to stroking, flutter & low frequency vibration [blank_start]Pacinian corpuscles[blank_end]: Very sensitive to higher frequency vibration, act as event detectors during object manipulation [blank_start]Ruffini endings[blank_end]: Sensitive to shearing forces (e.g. drag)

Hairless skin is referred to as [blank_start]glabrous[blank_end] skin

[blank_start]Pacinian corpuscles[blank_end] are found in the subcutaneous tissues

The structure is called a ...

Each hair unit is innervated by free nerve endings that either wrap around the follicle or run parallel to it. Label these fibres below.