Properties of polysynaptic arcs Series synaptic reflex arcs Several simple reflex arcs are united in series to give a chain of reflex arcs, e.g. flexor and extensor responses related to muscle tone. Convergent effector reflex arcs Two or more afferent neurons are in synaptic relation with only one efferent neuron. Hence, stimulation of many receptors […]
Properties of reflex arc One way conduction (Bell and Magendie law) The dorsal root fibres of the spinal cord are afferent (sensory), while the ventral root fibres are efferent (motor). The sensory impulses are centripetal (towards the CNS) and motor impulses are centrifugal (away from the CNS). Slow speed of conduction Slow build up of EPSP
Classification of reflex arc Components of reflex arc The neural circuit for reflex is referred to as reflex arc. Five components commonly make up a reflex arc. They are the receptor organ, sensory (afferent) neurons, interneurons in spinal cord or brain, motor neurons (efferent) and an effector organ (muscle or glands). Classification of reflex arcs
Reflexes A reflex is a specific, stereotyped, involuntary response to peripheral stimulation. The spinal cord is a reflex neural system and its activity is modified by influences transmitted from the brain via descending fiber system. The regulating system of the brain are informed of the reflex activity initiated within the spinal cord and is able
Spinal animal and Thalamic animal Spinal animal Spinal animal is prepared either transecting at the spinomedullary junction or by ligating both carotid arteries and the mid-vertebral artery to arrest the brain activities. Frog’s head behind the tympanic membrane is transected to separate spinal cord from the brain. Transection is to be done below the foramen magnum.
Gamma loop mechanism To initiate all somatic motor actions the influence of motor system upon gamma motor neuron is significant. The motor pathways depolarized dominantly gamma motor neurons which in turn initiate the contraction of intrafusal fibres of muscle spindle organ. These results in activation of group Ia afferent fibres. These fibres monosynaptically connect with
Demonstration of the motor control of the brain Motor control system of the brain is studied by removal of a particular portion and observing the alterations in the somatic motor activity. Decorticate preparation Decorticate preparation is demonstrated in cat or dog. In such preparations cerebral cortex with underlined white matter will be removed. Such animal
Pyramidal system and Major motor control Pyramidal and extra pyramidal system Descending (Motor) tracts of spinal cord consist of pyramidal and extra pyramidal system. Pyramidal system Pyramidal system controls the voluntary and fine motor movements in association with pyramidal motor cortex. This tract is well developed in primates and carnivores, but absent in birds and reptiles.
Descending tract of Spinal cord Cortico spinal tract Cortico spinal tract originates from the pyramidal (Betz) cells of the motor cortex‚ (60% from primary motor cortex and 40% from somasthetic motor cortex). Enter the internal capsule, pass through the cerebral peduncles, form the pyramids at he base of the medulla and then enter the spinal
Ascending tract of Spinal cord Dorsal spinocerebellar tract Dorsal spinocerebellar tract Occupies a portion of the lateral funiculus between the lumbar vertebrae and medulla. This fiber tract originates from the ipsilateral dorsal nucleus and ends within the ipsilateral cerebellar cortex. The fibers terminate in two regions of the cerebellar cortex. Conduction velocity of these fibers
