Sains Malaysiana 44(4)(2015): 593–597

Muscle Spindles Provide Servo-assistance to Jaw-closing Muscles for Chewing Hard Foods

(Otot Gelendung Memberikan Servo-Bantuan kepada Otot Rahang-Tutup untuk Mengunyah

Makanan Keras)

¹Dept. of Oral Biology & Biomedical Sciences, Faculty of Dentistry, University of Malaya

50603 Kuala Lumpur, Malaysia

²Division of Oral Physiology, Dept. of Oral Biological Science, Graduate Sch. of Med. and

Dent. Sci.Niigata University, Japan

Received: 30 April 2014/Accepted: 31 October 2014

ABSTRACT

The fundamental pattern of chewing induced by the network of neurons called central pattern generator has been reported to be modified by the information arising from the various oro-facial sensory receptors including muscle spindles of jaw closing muscles. The cell bodies of primary afferent neurons from these muscle spindles lie in mesencephalic trigeminal nucleus (MTN) in the brainstem. The aim of the study was to understand whether muscle spindles from jaw-closing muscles play any role in hard food chewing. Single neuronal discharge of muscle spindle afferents was recorded from the MTN simultaneous with jaw-movement and electromyograpic (EMG) activities of the left masseter (jaw-closing) muscle during chewing soft and hard foods (apple and pellet) in awake rabbits. Ten consecutive chewing cycles were taken for analysis. Discharge of nineteen muscle spindles from seven rabbits was successfully recorded. Muscle-spindle discharge was significantly higher during the closing phase of jaw-movement for the hard food chewing than for the soft food. The jaw-closing muscle EMG activity was significantly higher during hard food chewing compared to soft food. The spindle discharge was higher when the masseter muscle activity was greater for chewing hard food. Significant positive (r=0.822, p=<0.001) correlation was found between the difference of muscle activity between apple and pellet and the difference of spindle discharge between apple and pellet. Above findings suggest that the increase of spindle discharge during hard food chewing may play a role for facilitating jaw-closing muscle activities and thereby provides servo-assistance to jaw-closing muscles to compensate the hardness of food.

Keywords: Hard food; jaw-closing muscle; muscle spindles; neuronal discharge

ABSTRAK

Pola asas pengunyahan yang diaruhkan oleh rangkaian neuron yang dikenali sebagai penjana pola pusat telah dilapor boleh mengalami pengubahsuaian daripada maklumat yang diperoleh daripada pelbagai deria orofasial termasuk gelendung otot pada otot penutupan rahang. Jasad sel neuron aferen utama daripada gelendung otot ini, terletak di dalam ‘Mesencepholic Trgeminal Nucleus (MTN)’ di dalam batang otak. Tujuan kajian ini adalah untuk memahami sama ada gelendung otot dari otot-tutup rahang memainkan sebarang peranan dalam proses mengunyah makanan keras. Pelepasan neuron tunggal oleh gelendung otot aferen telah direkodkan dari MTN serentak dengan pergerakan rahang dan akitiviti elektromigram (EMG) bahagian kiri otot maseter (rahang-tutup) arnab sewaktu mengunyah makanan lembut dan keras (epal dan pellet). Dalam kajian ini, sepuluh kitar pengunyahan secara berturutan telah dipilih untuk dianalisis. Pelepasan 19 gelendung otot dari 7 ekor arnab telah berjaya direkodkan. Gelendung otot dilepaskan paling tinggi sewaktu fasa pergerakan rahang tutup untuk mengunyah makanan keras berbanding makanan lembut. Aktiviti EMG otot penutupan rahang adalah lebih tinggi dan signifikan semasa pengunyahan makanan keras berbanding dengan makanan lembut. Pelepasan gelendung otot adalah lebih tinggi semasa aktiviti otot masseter tinggi bagi jenis makanan keras. Keputusan yg diperoleh menunjukkan korelasi positif yang signifikan (r=0.822, p=<0.001) bagi aktiviti otot dan perbezaan pelepasan gelendong antara epal dan pellet. Hasil kajian menunjukkan pelepasan gelendung sewaktu pengunyahan makanan keras mungkin memainkan peranan untuk membantu aktiviti otot rahang-tutup dan seterusnya menyediakan servo-bantuan kepada otot rahang-tutup untuk mengkompensasi makanan yang berjenis keras.

Kata kunci: Makanan keras; otot gelendung; otot rahang-tutup; pengeluaran neuron

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*Corresponding author; email: zakir@um.edu.my