This document discusses the common terminal motor pathway which involves the anterior horn cell (A1) and its axon (the alpha motoneuron). It describes the major descending pathways that influence motor activity, including the corticospinal tract, rubrospinal tract, reticulospinal tract, and vestibulospinal tract. These pathways terminate on the alpha motoneurons and gamma motoneurons, which influence the muscle spindles. Afferent fibers from the muscle spindles and tendon organs provide feedback to complete the reflex loop.

1. Presented by
Dr Sadatinejad, Seyyed Mohsen,student of Medicine
from Iran,Kashan 19/12/2012

3.  Middle ear muscles : without any MS
Muscle Number of MS
Latissimus dorsi 400
soleus 400
abductor pollicis brevis 80
quadriceps 1300
medial gastrocnemius 150
extensor digitorum longus (EDL) 190
lumbrical
Muscle Density of MS (per gram)
lumbrical 12
soleus 0.4
EDL 3.7
 Motor units
 kind of extrafusal muscle fibers : “red” or slow fiber (Type I)

4. Afferent nerve fiber
(Proprioception)
 Ia: primery ending (annulospiral)
end to nuclear bag fibers
or Dynamic fiber
 II : secendary ending (flower-spray)
end to nuclear chain fibers
or Static fiber

5. Fig. 8.6. Responses of afferent fibers from a muscle spindle. A,
Length of muscle containing muscle spindle. Muscle length is
changed with various waveforms of stretch. B, Response of type
Ia afferent fibers from a primary ending of the muscle spindle. C,
Response of type II afferent fibers from a secondary ending of the
muscle spindle. Type Ia afferents respond to rapid stretch; type II
afferents respond to length.

6. Efferent Motor fiber
(Fusimotor fiber)
 γ motor neuron:
 Dynamic γ moto-neuron
innervate nuclear bag fiber
sensitivity of Ia fiber
 Static γ moto-neuron
innervate nuclear chain fiber
sensitivity of II fiber

7. (Negative )
Lenght Feedback

8. Strech Reflex
(Myotatic or Tendon Reflex)

9. Deep Tendon Reflexes
• Biceps brachii tendon reflex C5-6 (flexion of the elbow joint
by tapping the biceps tendon).
• Triceps tendon reflex C6-7 and C8 (extension of the elbow
joint by tapping the triceps tendon).
• Brachioradialis tendon reflex C5-6 and C7 (supination of the
radioulnar joints by tapping the insertion of the
brachioradialis tendon).
• Patellar tendon reflex (knee jerk) L2, L3, and L4 (extension
of knee joint on tapping the patellar tendon).
• Achilles tendon reflex (ankle jerk) S1 and 2 (plantar flexion
of ankle joint on tapping the Achilles tendon—tendo
calcaneus).

10. Muscle strength reflexes

12. Monosynaptic arch and Strech Reflex
(Ascending & Descending branch)
Unconscious Propericeotion
Cerebellum
conscious Propericeotion
Cerebral Cortec and Basal Ganglia

13. Conscious Propericeotion
Afferent Fiber
Post horn of 1
from Muscle DRG
Spindle 1 1 gray matter
Medulla
oblongata

14. Conscious Propericeotion
Afferent Fiber
Post horn of 1
from Muscle DRG
Spindle 1 1 gray matter
Medulla
oblongata

15. Unconscious Propericeotion
Afferent Fiber
Post horn of 1
from Muscle DRG
Spindle 1 1 gray matter
Medulla
oblongata

17. Sup peduncle
Cerebral Corex
Basal Ganglia RED Nucleus
Subsantial Nigra
RubroSpinal
Tract
Ant Horn Of
spinal cord
γ motor neuron

18. Sup peduncle
Dentothalamic tract
Controlateral
Ventrolteral (VL)
nucleus of Thalamus
Internal Capsule
(corona radiata)
Cerebral Cortex
(Primery Motor Area)
CorticoSpinal Tract
Ant.CorticoSpinal (Pyramidal Fiber)
20%
80%
Dicussation in spinal Segment Lat.
Cortico
Dicussation Of Pyramids Spinal

19. Inferior C e r e b e l l a r peduncle
Reticular Lat.Vestibular Med.Vestibular
Formation nucleus nucleus
Reticulospinal VestibuloSpinal MLF
Tract Tract (med.longitudinal
Fasiculus)
↑Cranial III,IV,VI
↓Cranial XI to SCM
and Trapezious

20. CorticoTectal tract
SpinoTectal Tract
Substantial nigra
Med & Lat Geniculate RED Nucleus
Spinolivary Tract
TectoSpinal Dicussation OlivoSpinal Tract
Tract in brain Stem (Dicussation
in brain Stem)
Ant. Horn of
Spinal Cord

21. Common Terminal Moto r Pat hway
(A) The common terminal pathway of all centers involve d in moto r activity is the large
anterior horn cell ( A1) and its a xon (!-motoneuron. The central regions that influence
motor activity via descending pathways a re interconnecte d in many ways. The most
important af fe rent pathways ste m from the cereb ellum, which receives the impulses
of muscle receptors via the spinocereb ellar tracts (A2) and the stimuli of the cortex via
the corticopontine tracts (A3). The cereb ellar impulses are transmitte d via the
parvocellular part of the dentate nucleus ( A4) and the ventral lateral nucleus of thalamus
( A5) to the precentral corte x (area 4) (A6). The corticospinal (pyramidal) tract (A7 )
descends from area 4 to the anterior horn and gives of f collaterals in the pons ( A8) that
return to the cereb ellum. Additional cereb ellar impulses are transmitte d via the
emboliform nucleus ( A9 ) and the centromedian nucleus of the thalamus (A10) to the
striatum ( A11) and via the magnocellular part of the dentate nucleus (A12) to the red
nucleus (A13). From here f ib ers run in the central tegmental tract (A14) via the olive
(A15) back to the cereb ellum and in the rubroreticulospinal tract (A16) to the anterior
horn. Fib ers from the globose nucleus (A17) run to the interstitial nucleus of Cajal ( A18)
and from there i n the interstitiospinal fasciculus (A19) to the anterior horn. Finally, cere
b e llofugal f ib ers are relaye d in the ve stibular nuclei (A20) and in the reticular
formation (A21 ) to the vestibulospinal tract (A22) and the reticulospinal tract (A23),
respectively.The descending pathways can b e divide d into two groups according to their
ef fect on the muscles: one group stimulates the fle xor muscles , and another group
stimulates the e xtensor muscles. The corticospinal tract and the rubroret iculospinal
tract activate mainly the neurons of the flexor muscles and inhibit the neurons of the
extensor muscles. This cor responds to the functional importance of the corticospinal
tract for delicate and precise movements, especially those of hand and f inger muscles
where flexor muscles play an important role. In contrast, the f i b ers of the ve st
ibulospinal tract and the f i b ers from the pontine reticular formation inhibit the flexors
and activate the ex tensors. They b elong to a p hylogenetically old motor system that is
directe d against the ef fect of gravity and, thus, is of special importance for body posture
and balance. The peripheral f ib ers that run through the posterior ro ot into the anterior
horn originate from the muscle receptors. The af ferent f i b ers of the annulospiral
endings (A24 ) terminate with their collaterals directly on the !-motoneurons, while the f
ib ers of the tendon organs (A25) terminate o n interneurons. Many descending
pathways influence the !-neurons via the spinal reflex apparatus. They terminate on the
large !neurons and on the small "-neurons ( A26). Since the "-neurons have a lower
threshold of stimulation, they a re stimulate d f irst, which results i n the activation of
muscle spindles. The latter send their impulses to the !-neurons. Thus, the "-neurons and
muscle spindles have a starter function for voluntar y movements.
A27 Accessor y olive . A28 Skeletal muscles. A29 Muscle spindle.