nervous system and different parts of brain.pptx

nervous system

1. DIVISIONS OF NERVOUS SYSTEM 1. Central nervous system( brain + spinal cord) 2. Peripheral nervous system. CNS

2. PERIPHERAL NERVOUS SYSTEM 1. Somatic nervous system 2. Autonomic nervous system.

3. CLASSIFICATION OF NEURON Neurons are classified by three different methods. Depending upon the number of poles Unipolar neurons 2. Bipolar neurons 3. Multipolar neurons. B. Depending upon the function Motor or efferent neurons 2. Sensory or afferent neurons. C. Depending upon the length of axon. Golgi type I neurons Golgi type II neurons.

4. Depending upon the number of poles 1. Unipolar neurons are the neurons that have only one pole. From a single pole, both axon and dendrite arise. This type of nerve cells is present only in embryonic stage in human beings. 2. Bipolar Neurons with two poles are known as bipolar neurons. Axon arises from one pole and dendrites arise from the other pole. 3. Multipolar neurons are the neurons which have many poles. One of the poles gives rise to axon and all other poles give rise to dendrites.

5. DEPENDING UPON THE FUNCTION Motor or Efferent Neurons are the neurons which carry the motor impulses from central nervous system to peripheral effector organs like muscles, glands, blood vessels, etc. Generally, each motor neuron has a long axon and short dendrites. 2. Sensory or Afferent Neurons which carry the sensory impulses from periphery to central nervous system. Generally, each sensory neuron has a short axon and long dendrites.

6. DEPENDING UPON THE LENGTH OF AXON 1. Golgi Type I Neurons have long axons. Cell body of these neurons is in different parts of central nervous system and their axons reach the remote peripheral organs. 2. Golgi Type II Neurons have short axons. These neurons are present in cerebral cortex and spinal cord.

7. „ STRUCTURE OF NEURON Neuron is made up of three parts: Nerve cell body 2. Dendrite 3. Axon. Dendrites and axons are usually called nerve fibers.

8. Nerve cell body Nerve cell body is also known as soma or perikaryon . It is irregular in shape. Like any other cell, it is constituted by a mass of cytoplasm called neuroplasm , which is covered by a cell membrane. The cytoplasm contains a large nucleus, Nissl bodies, neurofibrils , mitochondria and Golgi apparatus. Nissl bodies and neurofibrils are found only in nerve cell and not in other cells.

9. DENDRITE „ Dendrite is the branched process of neuron and it is branched repeatedly. Dendrite may be present or absent. If present, it may be one or many in number. Dendrite has Nissl granules and neurofibrils . Dendrite transmits impulses towards the nerve cell body. Usually, the dendrite is shorter than axon. „ AXON Axon is the longer process of nerve cell. Each neuron has only one axon. Axon arises from axon hillock of the nerve cell body and it is devoid of Nissl granules. Axon extends for a long distance away from the nerve cell body. Length of longest axon is about 1 meter. Axon transmits impulses away from the nerve cell body.

10. basic functions of a neuron receive signals (or information). Integrate incoming signals (to determine whether or not the information should be passed along). Communicate signals to target cells (other neurons or muscles or glands).

11. Receptors Generally, receptors are classified into two types: Exteroceptors Cutaneous Receptors or Mechanoreceptors 2. Chemoreceptors 3. Telereceptors B. Interoceptors . Visceroceptors 2. Proprioceptors

12. Signal transduction

13. Reflex action Reflex action is a sudden and involuntary response to stimuli. It helps organisms to quickly adapt to an adverse circumstance that could have the potential to cause bodily harm or even death. Pulling our hands away immediately after touching a hot or cold object is a classic example of a reflex action . A reflex arc is a pathway that controls a reflex.

14. Different methods to classify reflexes Depending upon whether inborn or acquired 2. Depending upon situation – anatomical classification 3. Depending upon purpose – physiological classification 4. Depending upon number of synapse 5. Depending upon whether visceral

15. „ 1. DEPENDING UPON WHETHER INBORN OR ACQUIRED REFLEXES i. Inborn Reflexes or Unconditioned Reflexes ii. Acquired Reflexes or Conditioned Reflexes 2. DEPENDING UPON SITUATION – ANATOMICAL CLASSIFICATION Cerebellar Reflexes Cortical Reflexes Midbrain Reflexes Bulbar or Medullary Reflexes

16. 3. DEPENDING UPON PURPOSE – PHYSIOLOGICAL CLASSIFICATION i. Protective Reflexes or Flexor Reflexes ii. Antigravity Reflexes or Extensor Reflexes „ 4. DEPENDING UPON THE NUMBER OF SYNAPSE Monosynaptic Reflexes ii . Polysynaptic Reflexes 5. DEPENDING UPON WHETHER SOMATIC OR VISCERAL REFLEXES Somatic Reflexes ii. Visceral or Autonomic Reflexes

17. 6. DEPENDING UPON CLINICAL BASIS i . Superficial reflexes ii . Deep reflexes iii. Visceral reflexes iv . Pathological reflexes.

18. The Action of Neuron Two neurons dominate the pathway, afferent nerves (receptor) and the efferent  nerves  (effector or excitor ). Firstly , it begins with receptor detecting the stimulus or a sudden change in the environment, where the instinct again has a role to play. The stimulus is received from a sensory organ. Then, the sensory neuron sends a signal to the relay neuron. This is followed with the relay neuron sending the signal to the motor neuron. Further, the motor neuron sends a signal to the effector. The effector produces an instantaneous response, for example, pulling away of the hand or a knee-jerk reaction. From the above explanations, it can be clearly summarized that the moment the afferent neuron receives a signal from the sensory organ; it transmits the impulse via a dorsal nerve root into the  Central Nervous System .  The efferent neuron then carries the signal from the CNS to the effector. The stimulus thus forms a reflex arc. In a reflex action, the signals do not route to the brain – instead, it is directed into the synapse in the spinal cord, hence the reaction is almost instantaneous.

19. Brainstem Brainstem is the part of brain formed by medulla oblongata , pons and midbrain . Brainstem contains ascending and descending tracts between brain and spinal cord. It also contains many centers for regulation of vital functions in the body.

20. Functions of Medulla oblongata Medulla oblongata or medulla is the lowermost part of brain. It is situated below pons and is continued downwards as spinal cord. Medulla forms the main pathway for ascending and descending tracts of the spinal cord Vasomotor center controls blood pressure and heart rate and Respiratory Centers maintain normal breathing Manages other automatic processes Some examples include coughing, sneezing, Deglutition center regulates the pharyngeal and esophageal stages of deglutition , Vomiting center induces vomiting during irritation or inflammation of gastrointestinal (GI) tract and maintaining balance. Salivatory nuclei control the secretion of saliva. Nerve connections . The vast majority of major nerves converge at spine , carrying signals to and from brain. It means those signals must pass through your medulla. Four of your 12 cranial nerves (which connect areas of throat and tongue directly to brain) pass through medulla.

21. Functions of Pons 1.Axons of pontine nuclei join to form the middle cerebellar peduncle or the brachium pontis . Pons forms the pathway that connects cerebellum with cerebral cortex. 2 . Pyramidal tracts pass through the pons 3 . Medial lemniscus is joined by the fibers of 10th, 9th, 7th and 5th cranial nerves in pons 4 . Nuclei of 8th, 7th, 6th and 5th cranial nerves are located in pons 5 . Pons contains the pneumotaxic and apneustic centers for regulation of respiration 6. It also contains the vestibular nuclei, which are already mentioned in medulla oblongata.

22. Functions of Midbrain Midbrain lies between pons and diencephalon . Through tectospinal tract, superior colliculus (part of midbrain) controls the movements of the eyes, head, trunk and limbs, in response to visual impulses. Efferent fibers from superior colliculus going to the nucleus of III cranial ( oculomotor ) nerve cause constriction of pupil during light reflex. Thus, it forms the center for light reflex. Superior colliculus also receives afferents from optic tract, which helps in the integration of optical and postural reflexes . Inferior colliculus (part of midbrain) is the center for auditory reflexes. Stimulation of this also produces reflex vocalization.

23. Control of muscle tone: Because of its connections with cerebellum, vestibular apparatus and skeletal muscle, the red nucleus plays an important role in facilitating the muscle tone. Control of complex muscular movements: Red nucleus controls the complex muscular movements. It plays an important role in the integration of various impulses received from many important areas of brain. Control of righting reflexes: Red nucleus is the center for all righting reflexes except optical righting reflexes Control of movements of eyeball: Through its efferent connections with nuclei of 3rd, 4th and 6th cranial nerves, red nucleus plays an important role in the control of ocular movements Control of skilled movements: Red nucleus plays an important role in controlling the skilled muscular movements by its connections with spinal cord and cerebral cortex.

24. Damping action refers to prevention of exaggerated muscular activity. This helps in making the voluntary movements smooth and accurate . Ballistic movements are the rapid alternate movements, which take place in different parts of the body while doing any skilled or trained work like typing, cycling, dancing, etc Servomechanism is the correction of any disturbance or interference while performing skilled work . Comparator function of the corticocerebellum is responsible for the integration and coordination of the various muscular activities.

25. Functions of cerebrum

26. FUNCTIONS OF BASAL GANGLIA CONTROL OF MUSCLE TONE CONTROL OF MOTOR ACTIVITY i. Regulation of Voluntary Movements ii. Regulation of Conscious Movements iii. Regulation of Subconscious Movements 3. CONTROL OF REFLEX MUSCULAR ACTIVITY 4. CONTROL OF AUTOMATIC ASSOCIATED MOVEMENTS 5. ROLE IN AROUSAL MECHANISM „ 6. ROLE OF NEUROTRANSMITTERS IN THE FUNCTIONS OF BASAL GANGLIA (for details consult jaypee )