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Neural Mechanisms of Mandibular Control: Mastication and Voluntary Biting

Erich S. Luschei, Louis J. Goldberg

10.1002/cphy.cp010227

Source: Supplement 2: Handbook of Physiology, The Nervous System, Motor Control

Originally published: 1981

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 General Features of Mandibular Motor System
1.1 Muscles of Mandible
1.2 Summary Neuroanatomy of Masticatory System
2 Mastication
2.1 Characteristics of Normal Mastication
2.2 Reflexes Possibly Involved with Chewing
2.3 Evidence Concerning Contribution of Jaw Reflexes to Mastication
2.4 Subcortical Mastication Pattern Generator
3 Initiation and Control of Mandibular Movements
3.1 Role of Sensorimotor Cortex in Mastication and Voluntary Jaw Movements
3.2 Peripheral Systems and Voluntary Isometric Jaw Muscle Contraction
3.3 Trigeminal Relationships in Cerebellum
4 Summary of General Conclusions
Figure 1. Figure 1.

Representation of main muscles of mastication of rhesus monkey (left) and domestic cat (right). Medial pterygoid, not shown for monkey, is located on medial side of mandible, parallel to and directly behind masseter.

Left from Luschei and Goodwin 161; right adapted from Turnbull 256
Figure 2. Figure 2.

Movement and jaw muscle activity pattern of a monkey chewing small pieces of monkey biscuit. Top traces, chewing on right side; bottom traces, chewing on left side. First chew, involving fracturing the piece of biscuit, is shown at far left. Right, movements during steady chewing (about 6–10 cycles after initial cycle). Note reversal of relative timing of right masseter and temporalis EMG when chewing on right and left. Top left trace (arrow), unloading response. Highest point of vertical position trace corresponds to jaws in occlusion (completely closed). Upward movement of horizontal position trace corresponds to movement toward animal's right side. Calibration bar to right of position traces represents 10 mm. Calibration bar to right of EMG traces represents 1.0 mV.

Data from C. R. Larson and E. S. Luschei, unpublished observations
Figure 3. Figure 3.

Spatial representation of jaw movements in frontal plane during steady chewing of pieces of monkey biscuit by 2 male rhesus monkeys with mature dentition. Chew patterns within each series are consecutive and are superimposed in pairs. Leftward is to animal's left, and rightward to animal's right. Movement is clockwise when chewing on left, and counterclockwise when chewing on right. Calibration bars represent 10 mm.

Data from C. R. Larson and E. S. Luschei, unpublished observations
Figure 4. Figure 4.

High‐speed record of transient suppression of EMG activity in jaw‐closing muscles (“unloading responses”) during fracturing of a piece of monkey biscuit. Record is an expansion of the period of time before and after the arrow in Fig. 2. The EMG and movement traces start during an earlier unloading response. As closing muscles become active again, about 10 ms after beginning of traces, jaw moves upward against a load. Slight upward deflection and fluctuation of the movement trace (1st arrow), caused by fracture of small piece of biscuit, is followed by transient suppression of activity in all jaw‐closing muscles. Subsequently, beginning at 2nd arrow, large piece of biscuit fractures and jaw moves rapidly up about 10 mm in less than 50 ms. Activity of all jaw‐closing muscles is suppressed during this rapid movement. About 10–15 ms after rapid movement stops, jaw muscles become active again, and jaw eventually begins to move upward toward occlusion. Very brief interval of time between mechanical transient associated with these fracturings and suppression of EMG (less than 10 ms) indicates that afferents having direct effects on jaw‐closing motoneurons are involved. Fluctuations on vertical position trace during unloading responses are caused by vibration of filament in tungsten light source of tracking device. Absence of significant response in digastric muscle, a jaw‐opening muscle, during the large, rapid, upward movement of jaw illustrates that jaw‐opening muscles do not have an effective stretch reflex. Calibration bar to right of position trace equals 10 mm at incisors. Calibration bar to right of EMG traces equals 1.0 mV, except for digastric EMG, for which it equals 500 μV.

Data from C. R. Larson and E. S. Luschei, unpublished observations
Figure 5. Figure 5.

Characteristic chewing patterns of 6 normal humans with normal occlusions during steady chewing of pieces of carrot. Initial chewing cycles have been deleted, but records shown on right or left are consecutive and are superimposed in consecutive pairs. Calibration bars equal 10 mm and apply to both vertical and horizontal movement.

Adapted from Milberg 177
Figure 6. Figure 6.

Effect of a single shock to the ipsilateral lingual nerve on membrane potential of a masseteric motoneuron (A) and on masseteric reflex (B). A and B were recorded in the same cat. A: resting potential, −55 mV, positivity upward. B: ordinate, reflex amplitude in percent of control; abscissa, time interval between conditioning (lingual nerve) and test (mesencephalic nucleus of V) stimulation. Time scales for A and B are the same. Voltage calibration in A is 3 mV.

From Goldberg and Nakamura 73
Figure 7. Figure 7.

Temporal relationship of activity of supratrigeminal interneurons and inhibitory postsynaptic potentials (IPSPs) in masseter motoneurons evoked by same peripheral stimuli in anesthetized cat. A, C illustrate spike discharges of right supratrigeminal inhibitory neuron evoked by stimulation of right lingual (5 × threshold) and masseteric nerve (10 × threshold, 3 pulses), respectively. Latencies of 1st spike were 2.0 ms in A and 6.8 ms in C. Stimulation of right lingual and masseteric nerve with same stimulation parameters as for A and C evoked IPSPs in a left masseteric motoneuron as shown in B and D, respectively, with onset latencies of 2.4 ms (B) and 7.3 ms (D). Thus, crossed IPSPs in masseteric motoneuron evoked from lingual and masseteric nerve were preceded by discharge of supratrigeminal inhibitory interneuron on stimulated side by 0.4 ms and 0.5 ms for lingual and masseteric nerve, respectively. Time base applies to A–D. Calibration in C applies to A and C, and that in D applies to B and D. Positivity shown upward in all records.

From Nakamura et al. 197
Figure 8. Figure 8.

Time course of suppression of monosynaptic masseteric reflex induced by stimulation of ipsilateral and contralateral lingual nerve in anesthetized cat; effect of midline section on contralaterally induced time course. A: each point represents amplitude, in percent, of masseteric reflex evoked by test stimulus to right mesencephalic nucleus and recorded from proximal end of severed right masseteric nerve. Mean amplitude of unconditioned masseteric reflex was 100%. Single‐shock conditioning stimuli were delivered to right (×) and left (•) lingual nerves before midline section, and to left lingual nerve after midline section (○). Conditioning interval is measured between lingual nerve and mesencephalic nucleus shock artifacts. B: recording of masseteric reflex from right masseteric nerve evoked by stimulation of right mesencephalic nucleus. First potential seen after artifact (a) is antidromic volley in masseteric nerve afferents evoked by stimulus to mesencephalic nucleus. Second potential is orthodromic masseteric reflex. C: complete suppression of masseteric reflex, as evoked in B, by a conditioning stimulus (b) to left lingual nerve. Each record is photographic superimposition of 10 oscilloscope sweeps.

From Goldberg 69
Figure 9. Figure 9.

Time course of jaw movement and frequency of firing of “low‐frequency” muscle spindle afferent from temporalis muscle in unanesthetized cat during eating (A) and lapping (B). Heavy dotted line is average movement estimated in 5 cycles. Scattered dots are superimposed instantaneous frequency points from the same 5 cycles. Vertical arrow indicates 25° of jaw movement in A and 10° in B. Note that upward movement of jaw (toward occlusion) corresponds to downward movement of position trace in this figure. This is opposite to vertical position traces of jaw movement shown in Figs. 2, 4, and 10 of this chapter.

From Cody et al. 37
Figure 10. Figure 10.

Responses of afferent from spindle located in anterior part of right masseter muscle of monkey chewing a piece of monkey biscuit. Top traces, unitary discharge of ending; sequence of dots, instantaneous frequency (Hz) triggered from preceding recorded action potential, whose vertical position gives reciprocal of interspike interval. Vertical and horizontal jaw position have same scale. Vertical trace, upward deflection indicates upward (toward closure) jaw movement; horizontal trace, upward deflection indicates movement to right. Calibration bars equal 10 mm at incisors (position traces) and 0.5 mV (unit). This unit was very insensitive to horizontal passive movements of mandible.

From Goodwin and Luschei 79
Figure 11. Figure 11.

Intracellular recording in jaw‐closing motoneurons of guinea pig during spontaneous rhythmic jaw movements. A: raster display of simultaneously recorded membrane potentials of jaw‐closing motoneuron (top trace) and digastric EMG (bottom trace). Note that hyperpolarization of jaw‐closing motoneuron is always associated with activity of digastric, a jaw‐opening muscle. One such hyperpolarization is shown on a higher‐speed record in C. B: response to electrical stimulation of tongue in same motoneuron and digastric muscle shown in A and C (each trace is photographic superimposition of 10 sweeps). D: same as in A, recorded from another animal during chewing on stick placed between molar teeth. Approximately first half of sweep 2 in D is shown in E at a higher gain and faster sweep speed. All calibration bars for digastric EMG recordings are 500 μV except for E, which is 200 μV. Raster displays in A, D illustrate continuous recordings during rhythmic jaw movements; however, a small part of record that occurs between end of 1 sweep and beginning of next is not shown.

From Goldberg and Tal 76
Figure 12. Figure 12.

Membrane‐potential fluctuations in guinea pig jaw‐closing motoneuron during spontaneous rhythmic jaw movements before and after paralysis. A: top trace, intracellular record (2 M potassium citrate electrode); bottom trace, digastric muscle EMG record obtained during rhythmic chewing movements in anesthetized guinea pig. Intravenous injections of Flaxedil produced total muscular paralysis. Rhythmic membrane fluctuations continued after all movement had ceased. Note that spikes following each phase of hyperpolarization occur less frequently after paralysis and frequency of rhythm is slightly reduced. Essential features of rhythmic membrane fluctuations remain intact, however, after immobilization, as shown in B and C, which are taken from record shown in A, at a faster sweep and higher gain, before (B) and after (C) immobilization.

Data from Goldberg and Tal 75
Figure 13. Figure 13.

Response pattern of single unit recorded in face area of precentral cortex of monkey during production of controlled isometric bite response. A: representative trial. B: mean values of force, rectified EMG from temporalis muscle, and instantaneous unit firing rate as a function of time 1 s before and after beginning of bite response. Mean values were calculated from 50 consecutive trials with the animal producing bites of about the same magnitude. Responses aligned on beginning of force response. Force calibration bar represents 4.5 kg. The EMG calibration bar represents 50 μV, and firing rate (F.R.) calibration bar represents rate of 50 spikes/s. Time calibration at bottom right is 1 s.

From Hoffman 112
Figure 14. Figure 14.

Pre‐ and postoperative characteristics of force responses associated with reaction‐time bites in 3 monkeys with bilateral lesions of precentral cortex. Top and middle rows, animals with lesions in face area. Immediately after surgery, they bit on bite bar, but instead of producing a controlled low force (foreperiod response of reaction‐time task), they produced powerful phasic bites. After extensive training, they were able to produce foreperiod responses, but forces were far less steady than preoperative responses. Bottom row, animal with bilateral lesions in lateral precentral cortex. This animal never produced repetitive phasic biting seen in other animals, and foreperiod responses and reaction times were completely normal within a short period of time after retraining was started. Offset marks on trace below force record represent occurrence of visual reaction‐time stimulus.

Adapted from Luschei and Goodwin 162


Figure 1.

Representation of main muscles of mastication of rhesus monkey (left) and domestic cat (right). Medial pterygoid, not shown for monkey, is located on medial side of mandible, parallel to and directly behind masseter.

Left from Luschei and Goodwin 161; right adapted from Turnbull 256


Figure 2.

Movement and jaw muscle activity pattern of a monkey chewing small pieces of monkey biscuit. Top traces, chewing on right side; bottom traces, chewing on left side. First chew, involving fracturing the piece of biscuit, is shown at far left. Right, movements during steady chewing (about 6–10 cycles after initial cycle). Note reversal of relative timing of right masseter and temporalis EMG when chewing on right and left. Top left trace (arrow), unloading response. Highest point of vertical position trace corresponds to jaws in occlusion (completely closed). Upward movement of horizontal position trace corresponds to movement toward animal's right side. Calibration bar to right of position traces represents 10 mm. Calibration bar to right of EMG traces represents 1.0 mV.

Data from C. R. Larson and E. S. Luschei, unpublished observations


Figure 3.

Spatial representation of jaw movements in frontal plane during steady chewing of pieces of monkey biscuit by 2 male rhesus monkeys with mature dentition. Chew patterns within each series are consecutive and are superimposed in pairs. Leftward is to animal's left, and rightward to animal's right. Movement is clockwise when chewing on left, and counterclockwise when chewing on right. Calibration bars represent 10 mm.

Data from C. R. Larson and E. S. Luschei, unpublished observations


Figure 4.

High‐speed record of transient suppression of EMG activity in jaw‐closing muscles (“unloading responses”) during fracturing of a piece of monkey biscuit. Record is an expansion of the period of time before and after the arrow in Fig. 2. The EMG and movement traces start during an earlier unloading response. As closing muscles become active again, about 10 ms after beginning of traces, jaw moves upward against a load. Slight upward deflection and fluctuation of the movement trace (1st arrow), caused by fracture of small piece of biscuit, is followed by transient suppression of activity in all jaw‐closing muscles. Subsequently, beginning at 2nd arrow, large piece of biscuit fractures and jaw moves rapidly up about 10 mm in less than 50 ms. Activity of all jaw‐closing muscles is suppressed during this rapid movement. About 10–15 ms after rapid movement stops, jaw muscles become active again, and jaw eventually begins to move upward toward occlusion. Very brief interval of time between mechanical transient associated with these fracturings and suppression of EMG (less than 10 ms) indicates that afferents having direct effects on jaw‐closing motoneurons are involved. Fluctuations on vertical position trace during unloading responses are caused by vibration of filament in tungsten light source of tracking device. Absence of significant response in digastric muscle, a jaw‐opening muscle, during the large, rapid, upward movement of jaw illustrates that jaw‐opening muscles do not have an effective stretch reflex. Calibration bar to right of position trace equals 10 mm at incisors. Calibration bar to right of EMG traces equals 1.0 mV, except for digastric EMG, for which it equals 500 μV.

Data from C. R. Larson and E. S. Luschei, unpublished observations


Figure 5.

Characteristic chewing patterns of 6 normal humans with normal occlusions during steady chewing of pieces of carrot. Initial chewing cycles have been deleted, but records shown on right or left are consecutive and are superimposed in consecutive pairs. Calibration bars equal 10 mm and apply to both vertical and horizontal movement.

Adapted from Milberg 177


Figure 6.

Effect of a single shock to the ipsilateral lingual nerve on membrane potential of a masseteric motoneuron (A) and on masseteric reflex (B). A and B were recorded in the same cat. A: resting potential, −55 mV, positivity upward. B: ordinate, reflex amplitude in percent of control; abscissa, time interval between conditioning (lingual nerve) and test (mesencephalic nucleus of V) stimulation. Time scales for A and B are the same. Voltage calibration in A is 3 mV.

From Goldberg and Nakamura 73


Figure 7.

Temporal relationship of activity of supratrigeminal interneurons and inhibitory postsynaptic potentials (IPSPs) in masseter motoneurons evoked by same peripheral stimuli in anesthetized cat. A, C illustrate spike discharges of right supratrigeminal inhibitory neuron evoked by stimulation of right lingual (5 × threshold) and masseteric nerve (10 × threshold, 3 pulses), respectively. Latencies of 1st spike were 2.0 ms in A and 6.8 ms in C. Stimulation of right lingual and masseteric nerve with same stimulation parameters as for A and C evoked IPSPs in a left masseteric motoneuron as shown in B and D, respectively, with onset latencies of 2.4 ms (B) and 7.3 ms (D). Thus, crossed IPSPs in masseteric motoneuron evoked from lingual and masseteric nerve were preceded by discharge of supratrigeminal inhibitory interneuron on stimulated side by 0.4 ms and 0.5 ms for lingual and masseteric nerve, respectively. Time base applies to A–D. Calibration in C applies to A and C, and that in D applies to B and D. Positivity shown upward in all records.

From Nakamura et al. 197


Figure 8.

Time course of suppression of monosynaptic masseteric reflex induced by stimulation of ipsilateral and contralateral lingual nerve in anesthetized cat; effect of midline section on contralaterally induced time course. A: each point represents amplitude, in percent, of masseteric reflex evoked by test stimulus to right mesencephalic nucleus and recorded from proximal end of severed right masseteric nerve. Mean amplitude of unconditioned masseteric reflex was 100%. Single‐shock conditioning stimuli were delivered to right (×) and left (•) lingual nerves before midline section, and to left lingual nerve after midline section (○). Conditioning interval is measured between lingual nerve and mesencephalic nucleus shock artifacts. B: recording of masseteric reflex from right masseteric nerve evoked by stimulation of right mesencephalic nucleus. First potential seen after artifact (a) is antidromic volley in masseteric nerve afferents evoked by stimulus to mesencephalic nucleus. Second potential is orthodromic masseteric reflex. C: complete suppression of masseteric reflex, as evoked in B, by a conditioning stimulus (b) to left lingual nerve. Each record is photographic superimposition of 10 oscilloscope sweeps.

From Goldberg 69


Figure 9.

Time course of jaw movement and frequency of firing of “low‐frequency” muscle spindle afferent from temporalis muscle in unanesthetized cat during eating (A) and lapping (B). Heavy dotted line is average movement estimated in 5 cycles. Scattered dots are superimposed instantaneous frequency points from the same 5 cycles. Vertical arrow indicates 25° of jaw movement in A and 10° in B. Note that upward movement of jaw (toward occlusion) corresponds to downward movement of position trace in this figure. This is opposite to vertical position traces of jaw movement shown in Figs. 2, 4, and 10 of this chapter.

From Cody et al. 37


Figure 10.

Responses of afferent from spindle located in anterior part of right masseter muscle of monkey chewing a piece of monkey biscuit. Top traces, unitary discharge of ending; sequence of dots, instantaneous frequency (Hz) triggered from preceding recorded action potential, whose vertical position gives reciprocal of interspike interval. Vertical and horizontal jaw position have same scale. Vertical trace, upward deflection indicates upward (toward closure) jaw movement; horizontal trace, upward deflection indicates movement to right. Calibration bars equal 10 mm at incisors (position traces) and 0.5 mV (unit). This unit was very insensitive to horizontal passive movements of mandible.

From Goodwin and Luschei 79


Figure 11.

Intracellular recording in jaw‐closing motoneurons of guinea pig during spontaneous rhythmic jaw movements. A: raster display of simultaneously recorded membrane potentials of jaw‐closing motoneuron (top trace) and digastric EMG (bottom trace). Note that hyperpolarization of jaw‐closing motoneuron is always associated with activity of digastric, a jaw‐opening muscle. One such hyperpolarization is shown on a higher‐speed record in C. B: response to electrical stimulation of tongue in same motoneuron and digastric muscle shown in A and C (each trace is photographic superimposition of 10 sweeps). D: same as in A, recorded from another animal during chewing on stick placed between molar teeth. Approximately first half of sweep 2 in D is shown in E at a higher gain and faster sweep speed. All calibration bars for digastric EMG recordings are 500 μV except for E, which is 200 μV. Raster displays in A, D illustrate continuous recordings during rhythmic jaw movements; however, a small part of record that occurs between end of 1 sweep and beginning of next is not shown.

From Goldberg and Tal 76


Figure 12.

Membrane‐potential fluctuations in guinea pig jaw‐closing motoneuron during spontaneous rhythmic jaw movements before and after paralysis. A: top trace, intracellular record (2 M potassium citrate electrode); bottom trace, digastric muscle EMG record obtained during rhythmic chewing movements in anesthetized guinea pig. Intravenous injections of Flaxedil produced total muscular paralysis. Rhythmic membrane fluctuations continued after all movement had ceased. Note that spikes following each phase of hyperpolarization occur less frequently after paralysis and frequency of rhythm is slightly reduced. Essential features of rhythmic membrane fluctuations remain intact, however, after immobilization, as shown in B and C, which are taken from record shown in A, at a faster sweep and higher gain, before (B) and after (C) immobilization.

Data from Goldberg and Tal 75


Figure 13.

Response pattern of single unit recorded in face area of precentral cortex of monkey during production of controlled isometric bite response. A: representative trial. B: mean values of force, rectified EMG from temporalis muscle, and instantaneous unit firing rate as a function of time 1 s before and after beginning of bite response. Mean values were calculated from 50 consecutive trials with the animal producing bites of about the same magnitude. Responses aligned on beginning of force response. Force calibration bar represents 4.5 kg. The EMG calibration bar represents 50 μV, and firing rate (F.R.) calibration bar represents rate of 50 spikes/s. Time calibration at bottom right is 1 s.

From Hoffman 112


Figure 14.

Pre‐ and postoperative characteristics of force responses associated with reaction‐time bites in 3 monkeys with bilateral lesions of precentral cortex. Top and middle rows, animals with lesions in face area. Immediately after surgery, they bit on bite bar, but instead of producing a controlled low force (foreperiod response of reaction‐time task), they produced powerful phasic bites. After extensive training, they were able to produce foreperiod responses, but forces were far less steady than preoperative responses. Bottom row, animal with bilateral lesions in lateral precentral cortex. This animal never produced repetitive phasic biting seen in other animals, and foreperiod responses and reaction times were completely normal within a short period of time after retraining was started. Offset marks on trace below force record represent occurrence of visual reaction‐time stimulus.

Adapted from Luschei and Goodwin 162
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Article Title: Neural Mechanisms of Mandibular Control: Mastication and Voluntary Biting
 

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Erich S. Luschei, Louis J. Goldberg. Neural Mechanisms of Mandibular Control: Mastication and Voluntary Biting. Compr Physiol 2011, Supplement 2: Handbook of Physiology, The Nervous System, Motor Control: 1237-1274. First published in print 1981. doi: 10.1002/cphy.cp010227