Neuro-Physiology Lecture Notes PDF

Neuro-Physiology LECTURE NO (1) Kamal Mohammad Assistant Professor of Physiology Sensory system Faculty Of Medicine Dept.Of Physiology  Control systems ▪ Nervous system: ▪ Endocrine system ✓Rapid control ✓Slow...

Neuro-Physiology LECTURE NO (1) Kamal Mohammad Assistant Professor of Physiology Sensory system Faculty Of Medicine Dept.Of Physiology  Control systems ▪ Nervous system: ▪ Endocrine system ✓Rapid control ✓Slow control ✓for short time ✓for long time  Nervous system (Anatomical divisions) 1- Central nervous system (CNS): (Lies inside bony cavities) ✓ Brain: lies inside the skull: a- cerebrum. b- Cerebellum. c- Brain stem: includes: Mid brain, Pons & M.Oblongata ✓ Spinal cord: Lies inside the vertebral column:  2- Peripheral nervous system (PNS): lies outside bony cavities: a- Cranial Nerves: 12 pairs arises from brain & brain stem. b- Spinal nerves: 31 pairs one from each spinal cord segments. Brain stem  Peripheral nerves types ▪ Sensory (Afferent): Carry sensory information to CNS via the posterior horn. ▪ Motor (efferent): Carry motor signals from the anterior horn. What the different between somatic & autonomic ?  Reflex Components 1- Receptor: specialized structure sensitive to changes in environment. 2- Afferent: carry sensory signals to CNS. 3- Center: in CNS 4- Efferent: carry signals to the effector organ. 5- Effector organ: The structure that produce the effect. Reflex arc The sensory system ❖ part of the nervous system. ❖ concerned with awareness of the external and internal environment. ❖ It consists of :- ✓ sensory receptors. ✓ neural pathways that conduct information from the receptors to the brain. ✓ Sensory cortex (parts of the brain responsible for receiving, processing and storing of these sensory information. Sensory Pathway Stimulus Sensory receptor (= transducer) Afferent sensory neurons CNS Integration, perception  Sensory receptors ❖ specialized structures present at the beginning of the sensory nerves. ❖ very sensitive to any change in the surrounding environment whether inside or outside the body.  Functions of receptors Sensory receptors act as :- Detectors. & Transducers.  Classification of sensory receptors Receptors can be classified according to the type of stimulus into: 1. Mechano-receptors: ❖ stimulated by mechanical compression or stretch of the receptor or the surrounding tissues e.g.: ▪ Touch receptors: ▪ Pressure receptors: ▪ Stretch receptors: ▪ Baroreceptors:  2. Thermal receptors: ❖ stimulated by change in the surrounding temperature and divided into :- ✓ Hot receptors ✓ Cold receptors  3. Pain receptors: ❖ stimulated by any stimulus which produces tissue damage (i.e. noxious stimulus).  4. Chemo-receptors: ❖ stimulated by chemical stimuli and divided into: ✓ External chemoreceptors e.g. taste and smell receptors. ✓ Internal chemoreceptors which are present in: ❖ Carotid and aortic bodies which are stimulated by changes in the chemical composition of blood e.g. CO2, O2 and H+.  5. Electromagnetic receptors: ❖ stimulated by electromagnetic waves of light. ❖ These receptors are present in the retina of the eye. Mechanism of action of receptors When the adequate stimulus is applied to its specific receptor. ✓ it causes opening or closing of ion channels leading to local depolarization of the membrane of the receptor. ❖ This condition known a receptor (generator) potential. ❖ If the receptor potential is strong enough. ✓ it leads to generation of an action potential in the first node of Ranvier which then propagates through the sensory nerve. Properties of receptors 1- Excitability: ❖ the ability of the receptors to respond to different types of stimuli (internal or external). ❖ Receptor acts as transducer by which stimulus is changed into nerve impulse. ❖ When the adequate stimulus comes in contact with its specific receptor, it produces receptor potential. Properties of receptor potential: 1- It is a graded potential. ▪ it is proportional with the intensity of the stimulus. ▪ it does not obey all or non rule. 2- It is of short duration (about 5 m. sec.) 3- It is not followed by refractory period. 4- It can be summated 2- Specificity: ❖ Each receptor is highly sensitive to a certain stimulus called the adequate stimulus. ✓ gives only one type of sensation. ❖ E.g. the retinal receptors are highly sensitive to light (electromagnetic stimulus) and give only the sensation of vision. 3- Adaptation: means gradual decrease in the rate of discharge from the receptors although the stimulus is still applied. ❖Adaptation is important to prevent sensory overload to the higher centers. ❖Also help to ignore the less important or unchanged stimuli.  The rate of adaptation varies in different types of receptors according to their functions as follow:-  a) Rapidly adapting receptors:- ▪ These receptors adapt rapidly (within seconds) and completely. ▪ i.e. stop discharge while the stimulus is still applied. ▪ e.g. touch receptors. b) Slow adapting receptors ▪ These receptors adapt also completely but after a relatively longer time. ▪ e.g. taste and smell. c) Not adapting receptors: ▪ Never adapted at all ▪ e.g pain receptors its protective mechanism.  Mechanism of adaptation: The adaptation of the receptors is not due to their fatigue, the following are possible causes: 1. Gradual closure of the Na+ channels. 2. Gradual ↓ of the excitability of the first node of Ranvier. Skin receptors 41 ⚫ Tracts: it is collection of nerve fibers inside the CNS have the same origin, termination and functions divided into i. Ascending tracts ii. Descending tracts ❖ Ascending tracts: These are tracts that carry impulses to the sensory areas of the cerebral cortex include: 1. Spinothalamic tracts 2. Dorsal column ⚫ Spinothalamic tracts Carry. a. pain b. tickle and itch c. Sexual sensation d. Crude touch e. Temperature ⚫ Dorsal column a. Fine touch b. Vibration c. Position sensation d. Pressure Figure 10.15 Spinothalamic Dorsal column sensations sensations  Sensory cortex ⚫ The cerebral cortex is divided into 2 large hemispheres, each of which contains frontal, parietal, temporal and occipital lobes ⚫ The central fissure separate the frontal and parietal lobes ⚫ The lateral fissure separates both the frontal and parietal from temporal lobe ⚫ The surface of each lobe is formed of elevations called gyri separated by depressions called sulci ⚫ Sensory cortex: ⚫ Receives the ascending impulses through the sensory tracts, and then gives perception about type, site and strength of stimulation The sensory cortex divided into i. Somatic sensory area I (area SI) ii. Somatic sensory area II (area SII) ⚫ Somatic sensory area I ⚫ Located at the postcentral gyrus ⚫ Is the final destination of the sensory pathways projecting from the thalamus. ❖ Characters of area SI 1. Receive sensation mainly from the opposite side of the body 2. The body is topographically presented in an inverted manner  Chapter 21 ⚫ Cerebral Cortex Figure 21-1. p. 688. 3. The area of representation of each part is proportionate to the number of receptors in this part and not to its size e.g. the lips and fingers occupy a much greater area than that occupied by the trunk 4. The area of representation are changeable e.g. if a finger is amputated, the areas specialized for the neighboring fingers expand and occupy that of the lost finger  Somatic sensory area II ⚫ It receive signals from a) Somatic sensory area I and other sensory areas (e.g. the visual and auditory area) b) The thalamic nuclei c) The brain stem ⚫ Functions of area SII: ⚫ It potentiate the functions of area SI  Functions of the Somatosensory cortex Somatosensory cortex: 1. Spatial recognition: a. Localization of the site of stimulus b. Two-point discrimination The minimal distance by which two touch stimuli must be separated to be perceived as separate. 2. Recognition of intensity of stimuli 3. Stereognosis: The ability to recognize objects by touching them without looking at them. Coding of sensory information's ▪ It the ability of the nervous system to detect modality (type), locality (site) & intensity of sensation in spite of that all sensation reach the CNS in the form of action potential.  Discrimination of modality (type) of sensations ▪ The higher centers can discriminate the modality of sensations by the following 3 factors:- a) Specificity of the receptors: b) Specificity of the sensory pathway: c) Termination in a specific area in the cerebral cortex:  Somatic sensory tracts Spinothalamic tracts Dorsal column ww w.al lteb fam ily.c om  Discrimination of locality (site) of sensation ▪ Each receptor (or group of the same receptor) is connected through a separate pathway to a certain point in the cerebral cortex. ▪ Stimulation of this point in the cerebral cortex (or any where in the pathway) projects the sensation to the location of the receptor. ▪ This is known as " The law of projection". ▪ Law of projection is clear in patients whose limb are amputated. ▪ Who may feel severe pain in the phantom limb due to irritation of the sensory nerves at the site of amputation.  Discrimination of intensity of sensation ▪ The higher centers can discriminate the intensity of sensation by: a) Varying the number of stimulated receptors: ▪ Strong stimulus stimulates a large number of receptors and produces a strong sensation, while the weak stimulus stimulates a few receptors and produces a weak sensation. b) Varying the rate of discharge from each receptor: ▪ Strong stimulus increases the rate of discharge from each receptor and produces a strong sensation, while the weak stimulus decreases the rate of discharge and produces a weak sensation. Any question Knowledge THANK YOU itself is power Thank you