# Quantitative model of jaw proprioception during active movements

> **NIH NIH F31** · JOHNS HOPKINS UNIVERSITY · 2024 · $54,774

## Abstract

PROJECT SUMMARY
Proprioception is an indispensable sense of the body’s position and movement in space. Fine motor control
depends on proprioceptors to monitor the mechanical consequences of motor actions. In particular, muscle
spindles are a class of primary proprioceptors that detect muscle length and stretch at the intrafusal fibers. The
signals generated by muscle spindles are complex with dynamical regulation of intrafusal fiber lengths via γ
motor neuron (fusimotor) activity. The interaction between feedforward mechanical signals at the muscle spindle
and descending motor commands at the parent muscle, especially in the context of naturalistic movements,
remains poorly understood. Opposing views disagree on whether muscle spindles passively sense muscle
length/stretch or actively process biomechanical signals based on motor commands to the muscle. Using the
unique advantages of rodent jaw proprioceptors in the hindbrain mesencephalic trigeminal (MeV) nucleus, I will
test the hypothesis that motor commands flexibly tune jaw muscle spindle coding in a context-dependent manner.
With experimental access to many levels of the jaw sensorimotor circuit, I will determine how feedforward
mechanical signals and descending motor commands interact at the primary proprioceptors. Aim 1 will find the
relationship between motor unit activity in jaw muscles and corresponding muscle spindle activity during passive
and active movements. Aim 2 will record muscle spindle activity with (a) external loads on the jaw and (b)
optogenetic decoupling of motor drives from muscle-driven motion. Aim 3 will provide an overarching framework
to model the jaw system as a feedback control loop. The proposed project investigates proprioceptive feedback
in craniofacial structures, electrophysiological mechanisms for controlling jaw function, and quantitative models
of the neural controller and muscles of the jaw. The immense training potential in this project lies in the application
of novel in vivo electrophysiology tools, well-designed use of optogenetics, and quantitative modeling rooted in
control theory. The proposed work has important implications in elucidating orofacial proprioception at the
primary receptors and understanding temporomandibular disorders and orofacial pain involving maladaptive
control of the jaw.

## Key facts

- **NIH application ID:** 10928726
- **Project number:** 5F31DE033256-02
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Jeong Jun Kim
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $54,774
- **Award type:** 5
- **Project period:** 2023-09-11 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10928726

## Citation

> US National Institutes of Health, RePORTER application 10928726, Quantitative model of jaw proprioception during active movements (5F31DE033256-02). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10928726. Licensed CC0.

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