Physiology 1 Lecture Notes (PDF)

Neuro-Physiology LECTURE NO (1) Abdelmuhsin Hussien Mohamed Lecturer Of Physiology Introduction & Sensory Receptors Faculty Of Medicine - Dept.Of Physiology  Control systems  Nervous...

Neuro-Physiology LECTURE NO (1) Abdelmuhsin Hussien Mohamed Lecturer Of Physiology Introduction & Sensory Receptors Faculty Of Medicine - Dept.Of Physiology  Control systems  Nervous  Endocrine system: system  Rapid control  Slow control  for short  for long time 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.  Peripheral nerves types  Sensory (Afferent): - Carry sensory information to CNS via the posterior horn.  Motor (efferent): - Carry motor signals from the anterior horn.  Interneurones: - Connect each other & connect sensory & motor neurons  Control (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 (response). 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 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.  1. Receptors respond to the surrounding stimuli then send information to the CNS which play a role in:  Perception of all types of sensations  Regulation of all body functions.  Development of mental activity, learning, and memory.  2. Receptor is the starting points of all body reflexes.  receptors are essential for the proper functions of the nervous system as well as the other systems.  without receptors the nervous system becomes useless.  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. Thermo-receptors:  stimulated by change in the surrounding temperature and divided into :-  Warm receptors  Cold receptors 3. Pain receptors:  stimulated by any stimulus( energy) 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.  E.g. rods and cones of the retina Properties of receptors 1- Excitability:  the ability of the receptors to respond to adequate 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. Mechanism of receptors potential :- 1- When the adequate stimulus is applied to its specific receptor. 2- it causes opening or closing of ion channels leading to local depolarization of the membrane of the receptor( receptor or generator) potential. 3- If the receptor potential is strong enough to reach threshold leads to generation of an action potential in the first node of Ranvier which then propagates through the sensory nerve.  Properties of Receptor potential : 1- It is a graded potential. - it is proportional with the intensity of the stimulus. 2- It does not obey all or non law. 3- It is short duration 4- It is not followed by refractory period. 5- 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.  According to degree of adaptation the receptors are classified into :- a) Rapidly adapting receptors:- - e.g. light and touch receptors b) Moderately adapting receptors:- - e.g. thermal receptors, taste, smell. c) Slow adapting e. g proprioceptors for body position d) Not adapting receptors: - Never adapted at all - e.g pain receptors.  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.  ANY QUESTION THANK YOU Thank you