Central Nervous System PDF

Central Nervous System Dr. Nermeen Bastawy and Dr. somia mokabel Functional organization of CNS  Division of nervous system Nervous system is divided anatomically into: 1. Central nervous system (C. N. S) 2. Peripheral nervous system (P.N.S) 1. Central nervous sy...

Central Nervous System Dr. Nermeen Bastawy and Dr. somia mokabel Functional organization of CNS  Division of nervous system Nervous system is divided anatomically into: 1. Central nervous system (C. N. S) 2. Peripheral nervous system (P.N.S) 1. Central nervous system (C. N. S): - Formed of the brain and spinal cord. A. The brain: It is present inside the skull and it is formed of: 1. 2 cerebral hemispheres. 2. Cerebellum. 3. Brain stem consists of midbrain, pons, and medulla oblongata 4. Diencephalon including the thalamus, hypothalamus, and parts of basal ganglia B. Spinal cord: It lies inside the vertebral column and divided into 5 regions (31 segments): 1. Cervical region which is formed of 8 segments. 2. Thoracic region which is formed of 12 segments. 3. Lumber region which is formed of 5 segments. 4. Sacral region which is formed of 5 segments. 5. Coccygeal region which is formed of only 1 segment. 2. Peripheral nervous system (P. N. S): - It lies outside bony cavities and includes. A. Cranial nerves: They are 12 pairs which arise from the brain. A. Spinal nerves: They are 31 pairs each arises from a segment of spinal cord. Nerve fibers running in the spinal nerves may be: A- Sensory (afferent): - carry impulse towards the spinal cord - Enter the spinal cord through posterior root of the spinal nerve - The mother cells of these afferent Nerves are present in the posterior (dorsal) root ganglion - It is two types:  A) Somatic afferent From receptors in somatic structures as skin, skeletal muscles, joints.  B) Autonomic afferent Arising from receptors in the walls of the viscera as stomach, intestine, lungs, heart. B- Motor (efferent): - carry impulse away from the spinal cord - leave the spinal cord through anterior root of the spinal nerve - Their mother cells (A.H.C) for somatic (voluntary) motor or lateral horn cell (L.H.C) for autonomic (involuntary) motor N.B: - Cranial nerves are either sensory or motor or mixed nerves - All spinal nerves are mixed nerves N.B: - Some cranial nerves are afferent only (as optic nerve) - Others are efferent only (as hypoglossal nerve) - Some are mixed having afferent and efferent (as vagus nerve)  Reflex action: Def.: -It is the functional unit of nervous system. -It is involuntary useful action that occurs in response to a stimulus (reflex closure of the eyelids in response to a moving object in front of the eye/ reflex secretion of gastric juice on seeing or smelling food) -It is mediated through reflex arc.  REFLEX ARC It is the pathway of reflex action which is formed of: Receptor: It is a specialized structure very sensitive to minute changes outside or inside the body(stimuli) and informs the C.N.S about it. An afferent neuron: It carries impulses from the receptor to the C.N.S The center: Present in the C.N.S (anterior horn cell(AHC)/ lateral horn cell (LHC)) An efferent neuron: It carries impulses from the C.N.S to the effector organ An effector organ: It is the structure which produce the response, it may be skeletal muscle, a gland, smooth muscle or cardiac muscle. Types : according to the response (effector organ): 1 - Somatic reflex actions( include contraction of skeletal muscle)  They regulate the activity of the skeletal muscles as (Withdrawal reflex) when a pin pricks a hand, the arm is withdrawn quickly from the pin to protect the body against the harm of the pricking pin. 2 - Autonomic reflex actions  They regulate the activity of the non voluntary organs as contraction of cardiac muscle, smooth muscle or secretion of glands.  Somatic reflex arc Autonomic reflex arc Receptor The same The same Afferent The same The same Center anterior horn cell(AHC) lateral horn cell (LHC) Efferent one neuron Autonomic ganglia divide it into 2 neurons: a. Preganglionic fiber: starting from LHC to rely in autonomic ganglia b. Post ganglionic fiber which start from autonomic ganglia Effector Skeletal muscle smooth muscle/ the cardiac muscle/gland What is receptors? modified neurons or epithelial cells specialized to: The Sensory Rece 2- ptors (convert) the energy of the stimulus into electrical signals (impulses) that are then transmitted by afferent neurons to the CNS 1- Detect changes in external & internal environment (stimuli). Types of receptors  Classification of Receptors (by stimulus type) 1. Mechanoreceptors 2. Thermoreceptors 3. Pain receptors 4. Electromagnetic receptors 5. Chemoreceptors Functions of Receptors Detect the stimulus in the environment by absorbing energy. Converts the energy of the stimulus into electrical energy (transduction). Produces a receptor potential that may become an action potential.  Properties of receptors 1. Specificity Each receptor is specific to 1 type of stimulation 2. Excitability Receptor's response by generation of receptor potential & AP 3. Adaptation Decline of receptor potential magnitude and No of impulses emitted in spite of constant maintained application of the stimulus.  Regarding adaptation, receptors types are: Rapidly adapting R.(Phasic R) adapt rapidly to constant stimuli, but they discharge strongly ON/OFF Moderately adapting R. temperature, smell and taste receptors. Slowly adapting R. (non-adapting receptors) pain receptors, muscle spindles, baroreceptors Importance: keep the brain continuously informed  Somatic Sensations Mechano Thermo Pain Tactile sensation Cold Cutaneous pain Proprioceptive Warm Visceral pain sensation Musculoskeletal pain  Mechano. S. Tactile S. Propioceptive S. 1. Touch 1. Sense of position - Crude touch - Fine touch 2. Sense of movement 2. Stereognosis 3. Pressure 4. Vibration sense 5. Itch & tickling  Transmission of Somatic Sensation Types of Sensory Fibers Receptor B Sensory Afferents A,B,C Sp.cd 1st order neuron  Somatosensory cortex Somatosensory cortex is a part of your brain that receives and processes sensory information from the entire body S1 It is divided into 3 main areas: A. Somatic sensory area I (SSI) B. Somatic sensory area II (SSII) C. Association sensory area The somatic sensory cortex occupies Brodmann’s area 1, 2, 3, 5, 7 and 40. All are behind the central sulcus in the parietal S2 cortex. A- Somatic sensory area I:(SSI) Site: post central gyrus “area 1, 2, 3”. Characters of SSI: Receives from opposite side Shows spatial orientation i.e. different parts homunculus of the body are separately represented on SSI. body is represented upside-down except the face. The area of representation is directly proportional to the number of sensory receptors.  Functions of somatic sensory area I: 1. Receives fine touch/Stereognosis/Vibration/propio 2. Discrimination of weights/Temp 3. Localization of fast pain