Nervous system Class I M Sc Semester 2

Nervous system Class: I M. Sc. , Semester: 2 Unit: 4 Department of Biochemistry, SJC, Trichy 1

Brain of Human and Different Animals Department of Biochemistry, SJC, Trichy 2

Department of Biochemistry, SJC, Trichy 3

Department of Biochemistry, SJC, Trichy 4

Department of Biochemistry, SJC, Trichy 5

Frontal lobe Executive Anterior Cingulate Effort Parietal lobe Attention Ventrolateral Working frontal Memory cortex Amygdala/ Emotioncortex Orbitofrontal Long term Hippocampus memory Temporal lobe Understanding Department of Biochemistry, SJC, Trichy 6

Corpus collosum Septum pelucidum Midbrain Thalamus Pons Hypothalamus Medulla oblongata Department of Biochemistry, SJC, Trichy 7

Divisions of Nervous System n 2 big initial divisions: 1. Central Nervous System n 2. The brain + the spinal cord ¨ The center of integration and control Peripheral Nervous System n n The nervous system outside of the brain and spinal cord Consists of : ¨ 31 Spinal nerves § Carry info to and from the spinal cord ¨ 12 Cranial nerves § Carry info to and from the brain Department of Biochemistry, SJC, Trichy 8

PNS Spinal Nerves Ganglia Department of Biochemistry, SJC, Trichy 9

PNS Cranial Nerves Department of Biochemistry, SJC, Trichy 10

Peripheral Nervous System Responsible for communication between the CNS and the rest of the body. n Can be divided into: ¨ Sensory Division n Afferent division ¨ Conducts impulses from receptors to the CNS ¨ Informs the CNS of the state of the body interior and exterior ¨ Sensory nerve fibers can be somatic (from skin, skeletal muscles or joints) or visceral (from organs w/i the ventral body cavity) ¨ Motor Division n Efferent division ¨ Conducts impulses from CNS to effectors (muscles/glands) Department of Biochemistry, SJC, 11 Trichy ¨ Motor nerve fibers

Peripheral Nervous System Skeletal (Somatic) Autonomic Sympathetic Parasympathetic Department of Biochemistry, SJC, Trichy 12

Somatic System n n n Nerves to/from spinal cord ¨ control muscle Sensory movements Neuron ¨ somatosensory inputs Both Voluntary and reflex movements Skin receptors Skeletal Reflexes ¨ simplest is spinal reflex arc Department of Biochemistry, SJC, Trichy Brain Motor Neuron Interneuron Muscle 13

Autonomic System n Two divisions: ¨ sympathetic ¨ Parasympatheitic n Control involuntary functions ¨ heartbeat ¨ blood pressure ¨ respiration ¨ perspiration ¨ digestion n Can be influenced by thought and emotion Department of Biochemistry, SJC, Trichy 14

Sympathetic n n n “ Fight or flight” response Release adrenaline and noradrenalin Increases heart rate and blood pressure Increases blood flow to skeletal muscles Inhibits digestive functions CENTRAL NERVOUS SYSTEM SYMPATHETIC Brain Dilates pupil Stimulates salivation Relaxes bronchi Spinal cord Salivary glands Lungs Accelerates heartbeat Inhibits activity Heart Stomach Pancreas Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Liver Adrenal gland Kidney Sympathetic Stimulates ejaculation ganglia in male Department of Biochemistry, SJC, Trichy 15

Parasympathetic CENTRAL NERVOUS SYSTEM PARASYMPATHETIC Brain Contracts pupil n n n “ Rest and digest ” system Calms body to conserve and maintain energy Lowers heartbeat, breathing rate, blood pressure Stimulates salivation Spinal cord Department of Biochemistry, SJC, Trichy Constricts bronchi Slows heartbeat Stimulates activity Stimulates gallbladder Gallbladder Contracts bladder Stimulates erection of sex organs 16

Summary of autonomic differences Autonomic nervous system controls physiological arousal Sympathetic division (arousing) Pupils dilate Parasympathetic division (calming) EYES Decreases Pupils contract SALIVATION Increases Perspires SKIN Dries Increases RESPIRATION Decreases Accelerates HEART Slows Inhibits DIGESTION Activates Secrete stress hormones ADRENAL GLANDS Decrease secretion of stress hormones Department of Biochemistry, SJC, Trichy 17

Motor Efferent Divisions n Can be divided further: ¨ Somatic nervous system n VOLUNTARY (generally) n Somatic nerve fibers that conduct impulses from the CNS to skeletal muscles ¨ Autonomic nervous system n INVOLUNTARY (generally) n Conducts impulses from the CNS to smooth muscle, cardiac muscle, and Department of Biochemistry, SJC, glands. Trichy 18

The Neuron n Neuron - a nerve cell; Receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs. ¨ the basic and functional unit of the nervous system Department of Biochemistry, SJC, Trichy 19

The Neuron n 3 types of neurons: ¨ 1. sensory neurons: respond to input from sensory organs (skin, eyes, etc. ) ¨ 2. motor neurons: send signals to muscles to control movement ¨ 3. interneurons: connect the sensory neurons and motor neurons n n most of the neurons in the brain = interneurons average human brain 100 billion neurons ¨ plus 10 x as many glial cells ¨ glial cell: a cell that fills the gaps between neurons, facilitate communication between neurons, and help in the care and upkeep of Department of Biochemistry, SJC, neurons Trichy 20

Structure of the Neuron Department of Biochemistry, SJC, Trichy 21

Structure of the Neuron n cell body (soma): the central part of the neuron, contains the nucleus ¨ n regulates cell functioning dendrites: the branching part of the neuron that receives Biochemistry, SJC, messages from other Department neuronsof. Trichy and relays them to the cell body 22

1. Two cell types ¨ Neurons n Functional, signal conducting cells ¨ Neuroglia n Supporting cells Department of Biochemistry, SJC, Trichy 23

n 6 types of supporting cells ¨ n 4 are found in the CNS: 1. Astrocytes n n n Star-shaped, abundant, and versatile Guide the migration of developing neurons Act as K+ and NT buffers Involved in the formation of the blood brain barrier Function in nutrient transfer Department of Biochemistry, SJC, Trichy 24

n n 2. Microglia n Specialized immune cells that act as the macrophages of the CNS n Why is it important for the CNS to have its own army of immune cells? 3. Ependymal Cells n Low columnar epithelialesque cells that line the ventricles of the brain and the central canal of the spinal cord n Some are ciliated which facilitates the movement Department of Biochemistry, SJC, Trichy of cerebrospinal fluid 25

4. Oligodendrocytes n Produce the myelin sheath which provides the electrical insulation for certain neurons in the CNS Department of Biochemistry, SJC, Trichy 26

Properties of Nerve fiber n Excitability n Conductivity n All-or-None n Summation n Refractory n Adaptation law period n Accommodation n Indefatigability Department of Biochemistry, SJC, Trichy 27

Department of Biochemistry, SJC, Trichy 28

1. Excitability May occur due to mechanical, thermal, chemical or electrical stimulus Changes that a nerve has been excited 1. The muscle or the gland where the nerve ends will respond 2. The responded nerve becomes electrically negative 3. The action potential – An electrical disturbance always accompanies the traveling nerve impulse Department of Biochemistry, SJC, Trichy 29

Development of Action Potential n At rest the n. f remains polarized state and the membrane potential lies within -70 m. V Na + Na+ Na+ Na+ + _ + _ _ K+ K+ K+ K+K+K + _ _ _ _ _ + + + Na+ Na+ Na+ Department of Biochemistry, SJC, Trichy 30

n n n The A. P occurs in successive stages of depolarization, negative after potential and positive after potential. It is postulated that during resting stage Ca ++ ions remains binding to the protein surface of the membrane pores and it blocks Na entering in. During excitation Ca ++ is dislodged from its binding site and the permeability of Na is increased, so depolarization starts with the onset of its entry. Department of Biochemistry, SJC, Trichy 31

Na + Na+ Na+ Na+ + + + - - - K+ K+ K+ K+K+K + - - + + + Na+ Na+ Na+ Department of Biochemistry, SJC, Trichy 32

Na + Na+ Na+ Na+ Pores become permeable to Na and so there is change in AP - - + + + - - - K+ K+ K+ K+K+K + + + - - - - + + + Na+ Na+ Na+ Department of Biochemistry, SJC, Trichy 33

2. Conductivity n n The nerve impulse is conducted along the nerve fiber. Conductivity in both direction Occurs with velocity i. e. . , with definite speed. Various factors affecting are Temperature pressure blood supply Co 2 and narcotics Oxygen lack Department of Biochemistry, SJC, Trichy 34

3. All – or – none law n n If stimulus is adequate a single nerve will always give a maximum response If the strength or duration of the stimulus be further increased no alteration in the response will takes place Department of Biochemistry, SJC, Trichy 35

4. Refractory period Once excited, the nerve fiber will not respond to a second stimulus for a brief period. This period is called ABSOLUTE REFRACTORY PERIOD (0. 5 sec) n Excitability is subnormal but gradually rising after ARP is called Relative refractive period. ( 3 m Sec ) n Department of Biochemistry, SJC, Trichy 36

5. Summation n Summation of two sub maximal stimuli is possible 6. Adaptation n Nerve fiber adapt quickly itself. Due to this adaptation there is no excitation during the passage of a constant current. Unless there is break in current. Department of Biochemistry, SJC, Trichy 37

7. Accommodation n A stimuli with stronger strength is applied very slowly to a nerve, then there is no response only due to lack of attaining the threshold strength. This phenomenon is called Accommodation i. e. . , slowly applied stimulus is accommodated by the nerve no matter how strong the stimulus is applied. Department of Biochemistry, SJC, Trichy 38

8. Indefatigability n If nerve fiber is stimulated repeatedly, then after a certain period the muscle fails to give any response. Now if the nerve is isolated from the muscle and placed on afresh muscle, then application of stimulus will excite the muscle. This shows that nerve is not fatigued. Department of Biochemistry, SJC, Trichy 39

Synapse n n It is the junctional region where one neuron ends and the other begins. The terminal branches of the axon (presynaptic) of other neurons come in contact with the cell body of the another (postsynaptic) Department of Biochemistry, SJC, Trichy 40

Types of synapse connections) n n n (Based on Axosomatic synapse Axodentrite synapse Axo-axonic synapse Nature of synapse n n Chemical synapse Electrical synapse Department of Biochemistry, SJC, Trichy 41

Types of Synapses n Axo-dendritic synapse n Axo-axo synapse n Axo-soma synapse Department of Biochemistry, SJC, Trichy 42

Chemical synapse CNS synapse are of this type. n Neuron secrete a chemical substance called NT (Neurotransmitters) at the synapse. n The NT act on receptor proteins in the membrane of the next neuron to excite the neuron, inhibit it or modify its sensitivity in some other way. n Conduction is ONE-WAY at chemical synapse (Pre to Post synaptic) n Department of Biochemistry, SJC, Trichy 43

More than 50 NT have been discovered. n Some of the best known are : Acetylcholine Norepinephrine Histamine Gamma-amino butyric acid Glycine Serotonin and Glutamate. n Department of Biochemistry, SJC, Trichy 44

Electrical Synapse Characterized by the direct fluid channels that conduct electricity from one cell to the next. n Most of these synapse consists of small protein tubular structures called Gap Junctions n Gap junctions transmit impulses from one muscle fiber to other and one cardiac muscle to other. n Department of Biochemistry, SJC, Trichy 45

Structure of synapse Department of Biochemistry, SJC, Trichy 46

Anatomy of the Synapse Department of Biochemistry, SJC, Trichy 47

NT Binding n n n NT bind to specialized - receptors NT-receptor Binding opens specific ion channels Opening of specific ion channels initiate EPSP and IPSP Department of Biochemistry, SJC, Trichy 48

NT – Receptor Binding Two Types of Post synaptic Receptors: ¨ Ionotropic receptors: NT binding results in direct opening of specific ion channels ¨ Metabotropic receptors: binding of NT initiates a sequence of internal molecular events which in turn open specific ion channels Department of Biochemistry, SJC, Trichy 49

NT binding - Membrane Potential Response Department of Biochemistry, SJC, Trichy 50

Mechanism of Neurotransmission Department of Biochemistry, SJC, Trichy 51

References n Arthur C. Guyton, 2005, Text Book of Medical Physiology, WB Saunders’s, USA. n C. C Chatterjee, 1985, Human Physiology Vol I & Vol II. 11 th. Edn, Kalyani Mukerjee Publications, Kolkata, India. Department of Biochemistry, SJC, Trichy 52

END Department of Biochemistry, SJC, Trichy 53