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Physiology 232 BMS Dr/Nahla Yacout 2016/2017 Nervous system & its function Classification of nervous system Brain Parts of the brain & the function of each part Spinal cord & spinal nerves Meninges & cerebrospinal fluid Peripheral nervous system Components of PNS Functional classification of PNS Neurons Structure of neurons Classification of neurons (Structural & functional) Action potential & its steps The nervous system is the master controlling & communicating system of the body Every thought, action & emotion reflects its activity Its cells communicate by signals, which are rapid & specific, & usually causes immediate responses 1. It monitors the changes occurring inside & outside the body………This gathered information is called (Sensory input) 2. It interprets this sensory input & decides what should be done at each moment …………… (Integration) 3. It causes a response……………(Motor output) (By activating effector organs) Ex: When you are driving, & see a red light ……… Sensory input Your nervous system integrates this information (Red means stop) ……….. Integration Your foot will go to the break ……….. Motor output w Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Consists of the nerves that extend from the brain (Cranial nerves) & spinal cord (Spinal nerves) The brain constitutes about one fiftieth of the body weight & lies within the cranial cavity Parts of the brain: Midbrain Cerebrum Pons (Brain stem) Cerebellum Medulla oblongata Cerebrum: Is the largest part of the brain Is divided into right & left cerebral hemispheres by longitudinal cerebral fissure Deep in the brain the hemispheres are connected by nerve fibers (White matter) The superficial part of the cerebrum is composed of the nerve cell bodies (Grey matter) Each hemisphere is divided into lobes: Frontal – Parietal – Temporal - Occipital Hypothalamus: Functions: 1. Controls the hormone secretion from pituitary gland 2. Control of appetite & thirst 3. Control of body temperature Pons Is placed infront of the cerebellum, below the midbrain & above the medulla oblongata Pons differ from the cerebrum in that: In cerebrum: White matter lies deeply – Grey matter lies on the surface In pons: Grey matter lies deeply – White matter lies on the surface Deep within the hemispheres, there are masses of grey matter, including, Thalamus & Hypothalamus Thalamus: Sensory input from the organs is transmitted to thalamus before reaching the cerebrum Medulla oblongata: Extends from the pons above & is continuous with the spinal cord below It contains the vital centers as: Cardiac center Respiratory center Reflex centers of vomiting, coughing, swallowing Cerebellum: Is placed behind the pons Functions: Important in voluntary muscular movement & balance of the body Is the elongated, cylindrical part of the central nervous system, which is placed inside the vertebral canal It is surrounded by meninges & cerebrospinal fluid There are 31 pairs of spinal nerves, that are named according to the vertebrae with which they are associated 8 cervical – 12 thoracic – 5 lumbar – 5 sacral 1 coccygeal The spinal cord is the link between the brain & the rest of the body Nerves carrying impulses from the brain to various organs pass though the spinal cord & then they leave the cord & passes to the organ they supply Sensory nerves from the organs to the brain pass upwards through the spinal cord Some activities of the spinal cord are independent of the brain, called (Spinal reflexes) Consist of three elements: Sensory neurons Connector neurons Motor neurons Example: The pain impulse initiated by touching a hot surface with the finger is transmitted to the spinal cord by sensory nerves This will stimulate many connector & motor neurons in the spinal cord, which results in contraction Are 3 membranes covering the brain & spinal cord Named from outside to inside: Dura matter Arachnoid matter Pia matter Dura & arachnoid matters are separated by space called: Subdural space Arachnoid & pia matters are separated by space called: Subarachnoid space (This space contains cerebrospinal fluid) Is a clear fluid that is present in the subarachnoid space It consists of: Water Mineral salts Proteins Glucose Urea Creatinine Functions of CSF: 1. Supports & protects the brain & spinal cord 2. It maintains constant pressure around brain & spinal cord 3. It keeps the brain & spinal cord moist Cranial nerves (12 pairs) Carry impulses to & from the brain Spinal nerves Carry impulses to & from the spinal cord 31 pairs of spinal nerves that are named according to their point of exit from the spinal cord Cervical (8 pairs) Thoracic (12 pairs) Lumbar (5 pairs) Sacral (5 pairs) Coccygeal (1 pair) Functional classification of PNS Sensory (Afferent) division Consists of nerves that carry impulses to the CNS from the whole body Motor (Efferent) division Consists of nerves that carry impulses from the CNS to the whole body (Effector organs as: glands, muscles) Motor (Efferent) division Somatic NS (Voluntary) Consists of somatic motor nerves that conduct impulses from CNS to skeletal muscles (Voluntary muscles) Autonomic NS (Involuntary) Consists of motor nerves that conduct impulses from CNS to smooth muscles (Involuntary muscles) & cardiac muscles Neurons They are the structural & functional units of the nervous system They are highly specialized cells that conduct messages in the form of impulses from one part of the body to another Amitotic Have no ability to divide – no ability to be replaced if destroyed Have high metabolic rate Require continuous supply of nutrients & oxygen Structure of neurons 1. 2. 3. 4. Cell body (Soma) Dendrites (Transfer the messages towards the cell body) Axon Myelin sheath (Sheath around neurons to protect them) Myelinated neurons……..Conduct impulses rapidly Unmyelinated neurons…….Conduct impulses slowly Classification of neurons Structural Multipolar neurons Bipolar neurons Unipolar neurons Functional Sensory (Afferent) Motor (Efferent) Interneurons (Association) Multipolar Many processes extend from the cell body Unipolar One process extend from the cell body Bipolar Two processes extend from the cell body (One fused dendrite, & the other is an axon) Sensory Transmit impulses from organs to CNS Interneurons Lie between sensory & motor neurons Motor Transmit impulses away from CNS to the effector organs (Muscles, glands) Components of reflex action: 1. Receptor……Site of stimulus action 2. Sensory neuron……Transmits impulses to the CNS 3. Integration center……Is always in CNS 4. Motor neurons…….Transmit impulses from CNS to effector organs 5. Effector…….Muscles or glands that respond to the impulses (By contraction or secretion) Nerve Is a part of the peripheral nervous system It consists of parallel bundles of axons (Some myelinated & some not) enclosed by connective tissue Sensory Carry impulses to CNS Motor Carry impulses away from CNS (to organs) Mixed Carry impulses to & from CNS Action potential Neurons are highly irritable (responsive to stimuli) When a neuron is stimulated, an impulse is generated & conducted along the neuron …….. This response is called (Action potential) Membrane ion channels Membrane contains variety of proteins that act as ion channels These ion channels are selective to the type of ion it allows to pass Ex: (Potassium ion channel allows only potassium ions to pass) When these ion channels open, ions diffuse quickly across the membrane from area of high concentration to area of low concentration Resting membrane potential Inside the membrane is more negative than outside (This state is called Resting membrane potential) Why?????? The membrane is very slightly permeable to sodium in comparison to potassium & SO…..Potassium ions diffuse out of the cell more easily than sodium ions can enter the cell & SO……The easy flow of potassium out of the cell causes the cell to become more negative inside than outside Depolarization Inside of the membrane becomes less negative Hyperpolarization Inside of the membrane becomes more negative 1. Resting state: Na+ & K+ channels are closed 2. Depolarization: Na+ channels open & K+ channels still closed & so……Na+ ions will rush inside the cell ……. Leading to more +ve charge inside 3. Repolarization: Na+ entry will decline …… K+ channels will open & K+ rush out of the cell …… & so negativity inside the membrane will be restored 4. Na+ K+ pump The ion redistribution will be accomplished by SodiumPotassium pump (Will take K+ ions inside & Na+ ions outside) This action potential will be propagated along the entire axon