Physiology Trans

PHYSIOLOGY day 1 second sem MAG ARAL NA TAYO SECOND SEM NA =) Reflexes- The basic unit of the of o f integrated neural activity

Consist of a sense organ and afferent neuron and one or more synapses in the central integrating station or in the synaptic ganglion. Then there is an efferent neuron and the e ffector or the effector organ/tissue. So those are the part of the reflex arc. In humans the connection between the afferent and efferent somatic neurons is generally in the brain or in the spinal cord. a) The afferent= neuron coming from the sense organ up to the central integrating system/ synapse. b) The efferent= neuron from the central integrating system up to the effector organ. * Afferent neuron enters neuron enters via the dorsal root or the cranial nerve and they have their c ell bodies in the dorsal root ganglion, or in some cases they are in the homologous ganglia of the cranial nerves, while the efferent fibers leave fibers leave the central integrating system via the ventral root. Thus, afferent enters via dorsal root; e fferent leaves via ventral root. Or they leave through the corresponding motor component of the cranial nerve. The principle that states that in the spinal cord, the dorsal roots are sensory and the ventral roots are motor is known as Bell-Magendie law.

Function of each component of the reflex arc: Impulses that are generated in the axons of the afferent and e fferent neurons, and in the muscles follow the all or none law/characteristics. law/characteristics. There are 3 junctions or junction like areas in the reflex arc where responses are usually graded and these are the receptor afferent neuron region, 1) the synapses, 2) the synapse between the afferent and efferent neurons, 3) and the neuromuscular junction.

At each of these points, a non-propagated potential which is proportionate to the magnitude of the incoming stimulus is generated, that’s why it is graded. The potential is in proportion to the size or magnitude of the incoming stimulus. The graded potential which serve to e lectronically depolarize the adjacent nerve or the muscle membrane and will set-up an all or none response; So even if the propagated potential is graded, the response is always an all or none response, thus it will either contract or not contract the muscle. The number of each action potential in the afferent nerve is proportionate to the magnitude of the applied stimulus at the sense organ. There is also a rough correlation between the magnitude of the stimulus and the frequency of the action potential in the efferent nerve but the connection between the afferent and efferent neuron is usually in the central

nervous system. And the activity in the re flex arc is modified by multiple inputs that are converging on the efferent neurons. 2 main types of reflexes 1) monosynaptic type ”monosynaptic arc” ex. Stretch reflex- when a skeletal muscle with an intact nerve supply is stretched, it will contract. The stimulus= that initiates the stretch reflex is stretching of the muscle The response= is contraction of the muscle *the most simple type of reflex

The sense organ in the muscle is t he muscle spindle, the impulses originating in the spindle are conducted to the central nervous system by means of fast sensory fibers that pass directly to the motor neurons that supply the same muscle. The neurotransmitter of this type of monosynaptic reflex at the central synapse is= glutamate Examples of simple monosynaptic reflexes are: 1) the knee-jerk reflex 2) the triceps extension at the elbow 3) the Achilles tendon= when tap will cause ankle jer k because of the contraction of the gastrocnemius muscle. 4) Stretched reflex of the masseter= when you tap the side of the face then there will be a stretch reflex that will be elicited in the masseter muscle. Structure of the muscle: Each muscle spindle consist of 2-10 muscle fiber that is enclosed to an c onnective tissue capsule called intrafusal fibers 2 types of intrafusal fibers in the muscle spindles 1) Nuclear bag fiber -contains many nucli in a dilated central area 2) Nuclear chain fiber -is tinner and shorter -lacks a definite bag -the ends connect to the sides of the nuclear bag fiber

*The ends of the intrafusal fibers are contract ile, whereas the central portions are not. There are 2 types of sensory endings that are present in each spindle 1) Primary “anuulo spiral ending” - These are the termination of rapidly conducting group of fibers of the afferent fibers that wrap around the center of the nuclear bag and the nuclear chain fibers. This are the termination of rapidly conducting groups, this is c alled the 1A fibers - End directly on motor neurons that supply the ext rafusal fibers of the same muscle.

2) Secondary “flower-spray ending” -termination of the group 2 sensory fibers, that are located nearer the ends of the intrafusal fibers but are only present in the nuclear chain fibers.

The spindles have a motor nerve supply of their own, so these nerves are very fine, about 3-6 nanometers in diameter and they are called the Gamma efference, these are the motor nerve supply of the muscle spindles. The gamma efference of lexell, or sometimes called the small motor nerve system. The endings of this gamma efferent fibers have 2 types. 1) The motor-end plates ”plate endings” =are on the nuclear bag fibers 2) Trail endings- Ending that form extensive network =are on the nuclear chain fibers The spindles receive 2 functional type of innervations 1) dynamic gamma efference =terminates on the plate endings 2) static gamma efference =terminates on the trail endings Reaction time= the time between the application of stimulus and the r esponse

*in humans, the reaction time for the stretch reflex like the kneejerk is 19-24 milliseconds Central delay= the time taken for the reflex activity to traverse the spinal cord

*in humans, the central delay for kneeje rk reflex is 0.6-0.9 millisecond. The muscle spindles also make connections that cause muscle contractions via polysynaptic pathways, not only monosynaptic. The afference involve are usually the secondary endings. The group 2 fibers also make monosynaptic connections to the motor neuron, and make also small contribution to the stretch reflex. *Functions of muscle spindles: when the muscle spindles are stretch, the primary endings distorted ,and the receptor potential are generated, this will in return set -up an action potential in the secondary fibers at a frequency that is proportionate to the degree of stretching. The spindles are parallel with the extrafusal fibers, and when the muscles are possibly stretched, the spindles are also stretched. This initiates a reflex contraction of t he extrafusal fibers in the muscle. *The primary endings in the nuclear bag fiber and nuclear chain fibers are both stimulated when the spindles are stretched. When there is a stimulus of the gamma efferent system, this will cause the contractile ends of the intrafusal fibers to shorten and therefore it will stretched the nuclear bag portion of the spindle, deforming the annulo spiral ending, and this will initiate the impulse in the A1 fibers. There are Automatic controls of the gamma efferent discharge:

1) descending tract from a numbers of areas in the brain 2) anxiety = increase the discharge 3) Jandrassiks maneuver= pulling the hands apart when the flexed fingers are hook together, this will facilitate the kneejerk reflex. The kneejerk will be stronger when yo u perform the maneuver. Antagonist reflex= When a stretch reflex occurs, the muscle that antagonizes the act ion of the muscle that is involve will relax. Because there is a reciprocal innervation of the muscle.

Impulses in the A1 fibers from the muscle spindles of the protagonist muscle will cause post synaptic inhibition of the motor neurons of the antagonist muscle. The pathway mediating this effect is bisynaptic. There is also collateral from each of the A1 fibers that pass in the spinal cord to an inhibitory interneuron called Golgi bottled neuron, this neuron synapses directly on 1 of the motor neuron that supplies the antagonist muscle. *Inverse stretch reflex “autogenic inhibition”= up to a certain point, the harder a muscle is stretched the stronger is the reflex contraction, however when the tension is great enough, contraction will suddenly cease, and the muscle instead of contracting will relax. This relaxation in response to a very strong stretch is called the inverse stretch reflex. The receptor for this reflex is in the golgi tendon organ. This organ contains a netlike collect ion of nerve endings among the fascles of a tendon. The fibers in the golgi tendon organ makeup to the 1B group of rapidly myelinating sensory conduction nerve fibers. The 1B fibers will end in the spinal cord on the inhibitory interneurons that in turn will terminate directly on the motor neuron; but this nerve s coming from the golgi tendon organ will also connect with the excitatory connections in the mo tor neurons that supply the antagonist muscle.

Muscle Tone “tonus”= the resistance of a muscle to stretch. 1) Hypertonic ”spastic” muscle= resistance to stretch is very high, bec of the hyperactive stretch reflex -when the rate of gamma efferent discharge is high 2) Hypotonic ”flaccid” muscle= lacking tone, when the rate of gamma efferent discharge is low 3) Normotonic - between spasticity and flaccidity of muscle.

*Lenghtening reaction ” clast-knife effect” = reaction or response of spastic muscle to a lengthening stimulus. = when the muscle is hypertonic, the sequence of the moderate stretch muscle contraction, the strong stretch muscle relaxation is very cle arly seen. This sequence of resistance followed by a giving way of the resistance when a limb is m ove passively is called the clast-knife effect because of its resemblance to a closing of a pocket knife. Clonus= occurrence of regularly rhythmic contractions of muscle which is subjected to a sudden maintained stretched. More common in ankle so t he “ankle clonus” initiated by a brisk dorsiflexion of the foot and the always response here is a rhythmic plantar flexion of the ankle. The spindles of

the tested muscle are hyperactive and the blunt of the impulses from them discharges all at the motor neurons supplying the muscle at once.

POLYSYNAPTIC REFLEXES = there are multiple synapses =paths branches in a complex fashion, the number of synapses in each branch is variable. Because of the synaptic delay that is incard at each of this synapse, activity in the branches with fewer synapses will always reach the motor neuron first, then followed by the longer pathways. So this causes a prolonged bombardment of the motor neurons from a single stimulus and so with polysynaptic reflex, there is prolonged response. Some of the branched pathways turn back on themselves permitting activities to reverberate until it becomes unable to cause a propagated transsynaptic response and it dies out. Such pathway is called the reverberating circuit, which is common in the brain and spinal cord. Example of polysynaptic reflex: 1) Withdrawal reflex= typical reflex due to painful stimulus to skin. Response= is always contraction of a flexor muscle, and inhibition of the ex tensor muscle so that the part that is stimulated is flex and withdrawn to the stimulus. *When a strong stimulus is applied to a limb, the re sponse include in only flexion and withdrawal of the affected limb, but also an extension of t he opposite limb, this is called the cross-extensor response. *all withdrawal reflex is prepotent, meaning they pre ent the spinal pathway from any other reflex activity that is taking part at that moment so that the withdrawal reflex will be prioritize. Nociceptive stimuli= stimuli that is potentially harmful to the individual.

*A strong stimulus causes a prolong flexion and sometimes a series of flexion movements, and this prolong response is due to prolonged repeated firing of the motor neurons called the after discharge and is due to continued bombardment of the motor neurons by impulses arriving by complicated and circuitous pathways. The exact flexor pattern of the withdrawal reflex in a limb varies to the part of the limb that is stimulated. If the medial surface of the limb is stimulated, example the medial surface is stimulated, the response is abducted, but when in lateral surface, there will be adduction, so is is called the local sign. Fractionation= another characteristic of a withdrawal response =the fact that supra maximal stimulation of any of the sensory nerves from a limb never produces as a strong a contraction of the flexor muscle as that which is elicited by direct electrical stimulation of the muscle themselves.= even if the stimulus to a part of a limb is so strong/maximum response will not be stronger than what w e will elicit if we directly stimulate the nerve to that muscle. This means that each afferent input goes to only part of the motor neuron pool for the flexion of that partic ular extremity.

Occlusion= if all the sensory inputs are dissected out and stimulated 1 after the other, the sum of the tension that develop by stimulation of each is greate r than that which is produces by direct stimulation of the muscle.

Other examples of polysynaptic reflex are: 1) Abdominal reflex 2) cremasteric reflex General principles of all reflexes: 1) there should be an adequate stimulus= must be precise 2) the final common pathway= the motor neurons that supply the extr afussal fibers in the skeletal muscle are the efferent site of the reflex arc. All the neural influences affecting muscle contraction will ultimately funnel through them to the muscles. All reflexes will pass finally to the motor efferent neurons. 3) Central excitatory and inhibitory pathways= there are prolonged states in which the excitatory influences will overbalance the inhibitory influences or vice verse. I n the CNS either the inhibitory or the excitatory will prevail. When the central excitatory state is very strong, excitatory impulses will stimulate or it will radiate not only to the mini somatic areas of the spinal cord but also to the autonomic nervous system. * In chronically paraplegic patient, a mild noxious stimulus may cause in additional to prolonged withdrawal extension pattern will also cause not only withdrawal flexion or extension but will also cause urination, defecation and swelling, etc, this is called Mast reflex. 4) Habituation and sensitization = since reflex response are stereo type, there is a possibility that it can be modified by exper ience. Example: when often you put your finger in the fire, there will be a time that your threshold for that will increase that you won’t withdraw your finger even it is already burning.

Cutaneous, deep, and visceral sensation So the pathways for this sensation, the dorsal horn in the spinal cord are divided in the basis of histologic characteristics into laminas 1 up to 6: a) Lamina 1= is the most superficial b) Lamina 6= as the deepest c) Lamina 2 and part of 3 = make up the substantia genatinosa  (a highly stained area of the spinal cord near the top e ach dorsal horn)

3 types of primary afferent fibers 1) Large myelinated A Beta fibers= transmit impulses that are generated by mechanical stimuli. 2) Small myelinated A Delta fibers= some of which transmit impulses from cold receptors and nociceptors that mediate fasting; and some of which transmit impulses from mechanoreceptors. 3) Small unmyelinated C fibers= concern with pain and temperature sensation. But there are also C fibers that transmit impulses from mechanoreceptors.

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The fibers mediating fine touch and proprioception (1  order neurons) will ascend or go to the dorsal column of the spinal cord up to the medulla where they synapse in the grassil and hunnate nucleus. The second order neuron from the grassil and hunnate nucleus and they will cross the midline and ascend in the medial lemniscuses to end in the ventral posterior nucleus and other related specific sensory relay nucleus o f the thalamus. This ascending system of neurons is called dorsal column or lemniscul system. Other touch fibers along with those mediating temperature and pain will also synapse on the neurons in the dorsal horn. The axons from these neurons will cross the midline again and they ascend in the anterolateral quadrant of the spinal cord and they form the anterolateral system of ascending fibers. In general:

a) Touch= is associated with the ventral spinothalamic tract b) Pain and temperature= is associated to the lateral spinothalamic tract *Although there is no rigid localization of function, but generally they follow this. There is a major input from the anterolateral system going to the mese ncephalic reticular formation, so sensory inputs activates the reticular activating system which maintains the cortex in the alert state. There are certain areas of the brain where these sensations are represented called cortical representation. From the specific sensory nuclei of the thalamus, the neurons will project into highly specific way into 2 somatic sensory areas of the cerebral cortex: 1) Somatic sensory area 1 or S1 = is in the post central gyrus 2) Somatic sensory area 2 or S2 = is in the wall of the sylvian fissure ( lateral cerebral sulcus) *The s1 will also project in the s2. This s1 correspond to the brodman’s area 1 and 2, etc based on their histologic characteristics. S1 corresponds to brodman’s area 1,2 and even 3. The arrangement of the thalamic fibers to s1 is such that the parts of the body are represented in a particular order along the post central gyrus. It is arranged/ represented is in an inverted manner. a) the legs are on top, b) head is at the lowest part of the gyrus. The size of the cortical representation also or the size of the cortical receiving area for impulses coming from a particular part of the body is represented is proportionate to the number of receptors in that part of the body. The legs and the hands are larger than the upper part of the body because there are more receptors in the extremities for sensory. *s2 is located in the wall of the sylvian fissure, and the head is represented at the inferior part of the post central gyrus and the feet at the bottom of the sylvian fissure. So the representation of the body part in the s2 is not as detailed as it is in the post central gyrus (s1). If there is an abrasion in:

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S1 causes: a) deficit in the position sense b) loss of ability to discriminate size and shape. c) deficit in sensory processing in s2 2) S2 causes: a) deficit in learning that is based on tactile discrimination. *no gross effect in the processing o f s1 Proprioception and fine touch is most affected by cortical lesions. Temperature sensibility are less affected Pain sensibility is only slightly affected

Principles that is followed in sensory physiology: 1) Each sense organ is specialized to convert 1 particular form of energy into an action potential in the sensory nerves. Example: stimulus to sight is light 2) Each modality has a discrete pathway to which going to t he brain, and the sensation that is perceived as well as the part of the body to which it is localized is de termined by a particular part of the brain that is activated. So the part of the brain that will be activated by the impulse will tell us what or where that stimulus came from. 3) The differences in the intensity of a given sensation are signaled in 2 ways: a) Changes in the frequency of the action potential in the sensory nerves b) Changes in the number of receptor that are activated 4) There is a punctuate representation of c utaneous sensation= there are fine parts of cerebral cortex that this particular sensations are represented.

Example: touch sensation is evoked from spots overlying the touch receptors, the same as pain and temperature sensation. So sensations are produce from st imulation of the skin only over the spots where the sense organs for these modalities are located. So when the part of the skin that is stimulated does not contain a pain recepto r there will be no pain sensation.

Touch- the most basic sensation Receptors: 1) Meissners and pacinian corpuscles= rapidly adapting receptors 2) Merkels disk and ruffini endings= slowly adapting receptors

*Most numerous in the skin of the fingers and lips; relatively scarce in the skin of the t runk. There are many receptors around hair follicles also in addition in those in the subcutaneous tissue of hairless areas. Group 2 sensory fibers that transmit impulses from touch receptors going to the central nervous system are 5 to 12 nanometers in diameter and they have conduction velocity of 30 to 70 meters per seconds. Some touch impulses are also conducted via the C fibers.

*Touch information is transmitted in both the lemniscal and anterolateral pathways. The information that is carried in the lemniscal system is concer n with the pain localization, special form, and temporal pattern of tactile stimul; while information in the spinothalamic tract is concerned with poorly localize gross tactile sensation.