Neural Control and Coordination PDF

Welcome to Neural Control and Coordination Topics Covered 1. Introduction 2. Neural system 3. Human Neural System 4. Neurons 5. Generation of Nerve Inpulse 6. Transmission of Impulses 7. Central Neural System 8. Forebrain 9. Midbrain 10. Hindbrain 11. Sensory Reception and Processing 12. Eye, Mechan...

Welcome to Neural Control and Coordination Topics Covered 1. Introduction 2. Neural system 3. Human Neural System 4. Neurons 5. Generation of Nerve Inpulse 6. Transmission of Impulses 7. Central Neural System 8. Forebrain 9. Midbrain 10. Hindbrain 11. Sensory Reception and Processing 12. Eye, Mechanism of Vision 13. Ear, Mechanism of Hearing Neural System Neural system provides an organised network of point-to-point connection for quick coordination. Endocrine system provides chemical integration through hormones. Control and coordination Nervous system Actions of nervous system are mediated through neurons and these are quick. Endocrine system Actions of endocrine system are slow and are mediated through hormones. Neurons Cell body / Cyton / Soma Cell processes/ Neurite Contains cytoplasm with typical cell organelles and certain granular bodies called Dendrites Short tree like fibres which branch repeatedly and project out of the cell body Axon A long fiber which transmits nerve impulses away from the cell body Neurons are the structural and functional unit of the nervous system. Neurons Dendrites Nissl’s granules: Granular bodies Axon: Each branch terminates into a bulb-like structure called synaptic knob Neurotransmitters: Endogenous chemicals possessed by synaptic vesicles acting as chemical messengers. Soma/ Cell body Nissl's granules Nucleus Node of Ranvier Myelin sheath Axon Synaptic knob Axon terminal Types of Neurons Myelinated axon Non-myelinated nerve fibre Schwann cells form a myelin sheath around the axon Gaps between the adjacent shwann cells are called Nodes of Ranvier ○ Found in cranial and spinal nerves. Myelin sheath throughout its length is to increase the velocity of electrical signals to propagate quickly Myelin sheath Axon Myelin sheath Node of Ranvier Schwann cell It is enclosed by a Schwann cell which does not form a myelin sheath around the axon Conduction of electric impulses in such nerve fibres is slow Commonly found in autonomous and somatic neural systems Types of Neurons Types of neurons (Based on the number of axons and dendrites) Unipolar (Cell body with one axon only) Found usually in the embryonic stage Bipolar (One axon and one dendrite) Found in the retina of eye Multipolar (one axon and two or more dendrites) Found in the cerebral cortex 7 Types of Neurons Types of neurons (Based on function) Sensory neurons (carry signals from the outer parts of your body (periphery) into the central nervous system) Motor neurons (Carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body) Interneurons (Connect various neurons within the brain and spinal cord) 8 Nerve Impulses Neurons are excitable cells and its membrane contains different ion channels which are selectively permeable to different ions. Nerve impulse is the sum total of various biochemical/ electrical changes occurring in a nerve fiber in response to a stimuli. Its propagation along the nerve fiber is called transmission. Nerve impulse Across axon Unmyelinated axon Across synapse Myelinated axon Generation of Nerve Impulse Ion channels Lipid bilayer of axonal membrane is a good electrical insulator so the main paths for current to flow across the membrane are through the ion channels. When ion channels are open, they allow specific ions to move across the plasma membrane, down their electrochemical gradient. As ions move, they create a flow of electrical current that can change the membrane potential. Ion channels open and close due to the presence of “gates”. The gate is a part of the channel protein that can seal the channel pore shut or move aside to open the pore. Resting Membrane Potential (RMP) It exists because of a small buildup of negative ions in the cytosol inside of the membrane and an equal buildup of positive ions in the extracellular fluid. Such a separation of positive and negative electrical charges is a form of potential energy, which is measured in volts or millivolts. In neurons, the resting membrane potential ranges from -40 to -90 mV. A typical value is -70 mV. The minus sign indicates that the inside of the cell is negative relative to the outside. A cell that exhibits a membrane potential is said to be polarized. Extracellular space Resting Membrane Potential (RMP) Na+ Na+ Na+ K+ Na+ Na+ K+ Na+ Na+ K+ K+ K+ Na+ Resting membrane potential K+ Polarized membrane K+ Channel Na+/K+ pump + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Axonal membrane - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Na+ K+ Protein - - - - K+ Na+ K+ K+ Axoplasm - Protein K+ K+ - - Action Potential Resting membrane potential Action Potential An action potential or impulse is a sequence of rapidly occurring events that reverse the membrane potential and then eventually restore it to the resting state. ❖ An action potential has two main phases: ❖ Depolarizing phase ❖ Repolarizing phase ❖ During the depolarizing phase, the negative membrane potential becomes less negative, reaches zero, and then becomes positive. ❑ During the repolarizing phase, the membrane potential is restored to the resting state of -70 mV. ❏ Following the repolarizing phase there may be an after-hyperpolarizing phase, during which the membrane potential temporarily becomes more negative than the resting level. ❑ Transmission of Impulse A synapse is formed by the membranes of a pre-synaptic neuron and a postsynaptic neuron There are two types of Synapse: Synaptic cleft Postsynaptic neuron Synapse Electrical Presynaptic neuron Chemical Transmission of Impulse Neurons communicate with one another at junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron. Impulse is transmitted from one neuron to another at the synapse. Pre-synaptic neuron Post-synaptic neuron Types of Transmission Synapse Electrical Chemical Pre-and post synaptic neurons are in very close proximity. Pre-and post synaptic neurons are separated and fluid-filled space called synaptic cleft. Flow of ions occurs directly from one neuron to another. Chemical transmission involves release of chemical messengers known as neurotransmitters. Impulse transmission across an electrical synapse is faster than chemical synapse. Impulse transmission across a chemical synapse is slower than electrical synapse. Electrical synapses are rare in our system. Chemical transmission is more common, and more complicated, than electrical transmission. Human Neural System The human nervous system is divided into two parts Central neural system (CNS) Peripheral nervous system Peripheral nervous system BRAIN CNS The human neural system Peripheral neural system (PNS) Brain Spinal cord All the nerves associated with CNS Human Neural System The nerve fibres of PNS are divided into types: PNS nerves Efferent nerves Afferent nerves Sensory organ Stimulus Afferent nerve CNS CNS Response Efferent nerve Sensory organ 19 Human Neural System PNS is divided into two divisions Peripheral Neural System (PNS) Autonomic neural system (Transmits impulses from CNS to involuntary organs and smooth muscle) Sympathetic neural system Somatic neural system (Transmits impulses from CNS to skeletal muscle) Parasympathetic neural system Central Neural System Brain is the central information processing organ, it controls: Voluntary organs movement balance of the body functioning of vital involuntary organs thermoregulation hunger and thrust circadian (24-hours) rhyths of the body endocrine glands and human behaviours Central Neural System Brain Cerebrum Cerebral hemisphere Corpus callosum Thalamus Hypothalamus Pituitary gland Cerebral aqueduct Pons Amygdala Cerebellum Medulla Spinal Cord Central Neural System The human skull is composed of the bones and cartilage that surround the brain and make up the upper part of the head. The purpose of the skull is to protect the brain and to support and provide structures for the parts of the face. Brain and spinal cord are protected and supported by three meningeal layers. ○ Protect brain from trauma injury ○ Provide a support system for blood vessels, nerves, cerebrospinal fluids Meninges Dura mater - outermost, toughest and avascular layer Arachnoid mater - Thin middle layer, webby in appearance Pia mater - Innermost, most delicate, has pain receptors and capillaries Central Neural System Brain Forebrain Midbrain Hindbrain Cerebrum Pons Thalamus Cerebellum Hypothalamus Medulla Forebrain Cerebrum Major part of the brain Divided into 2 parts - right and left cerebral hemispheres Right and left hemispheres connected by corpus callosum Corpus callosum is present only in mammals Corpus callosum Left hemisphere Right hemisphere Hemispheres 25 Forebrain Cerebrum Sensory area Motor area Association area Responsible for intersensory association, memory and communication Outer layer is the cerebral cortex and the inner layer is cerebral medulla. Grey matter - Outer layer -neuronal cell bodies White matter - Inner layer- myelinated axon bodies Forebrain Thalamus Cerebrum wraps around a structure called thalamus, which is a major coordinating centre or relay centre for sensory and motor signalling. Cerebral cortex Thalamus Hypothalamus 27 Forebrain Hypothalamus Hypothalamus lies at the base of the thalamus. Neurosecretory structure, secretes hormones called hypothalmic hormones. Has both neural and endocrine functions Hypothalamus Pituitary gland Amygdala Cerebral cortex Corpus callosum Thalamus Hippocampus Anterior pituitary Hypothalamus Neurosecretory Cells Posterior pituitary 28 Forebrain Hypothalamus It is highly vascular & regulates behavior essential for survival of species i.e., feeding, fighting, fleeing, mating (sex desire/ libido). It has ○ Hunger centre (lateral hypothalamus) ○ Satiety centre (ventromedial hypothalamus) ○ Thirst centre ○ Osmoregulatory centre It regulates body temperature i.e., it is thermoregulatory centre. It regulates emotional reactions. 29 Forebrain Cerebrum The inner parts of cerebral hemispheres and a group of associated structures like amygdala, hippocampus form the limbic system or limbic lobe Limbic System The regulation of sexual behaviour, expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and motivation. Cerebral cortex Hypothalamus Pituitary gland Amygdala Corpus callosum Thalamus Hippocampus Midbrain Brain Forebrain Midbrain Hindbrain Midbrain Midbrain Located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina A canal called the cerebral aqueduct passes through midbrain Contains the cerebrospinal fluid Thalamus Hypothalamus Midbrain Pons Corpora quadrigemina Cerebral aqueduct Parts of the Brain Brain Forebrain Midbrain Hindbrain Pons Medulla Cerebellum 33 Hindbrain Pons connects different areas of brain. It has apneustic area and pneumotaxic area for regulating respiration. Cerebellum is highly developed in humans for maintaining equilibrium and erect posture. Its surface is extremely convoluted to facilitate more neurons Pons Medulla oblongata is continuous with superior part of the spinal cord. It controls several vital functions such as cardiovascular, respiratory and gastric. 34 Hindbrain Cerebellum & Medulla Cerebellum is second largest part of brain (also called little brain). It is highly developed in humans for maintaining ○ equilibrium ○ balance ○ erect posture Regions of medulla regulate vital activities including the cardiovascular center and the medullary rhythmicity area. The cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels. The medullary rhythmicity area of the respiratory center adjusts the basic rhythm of breathing. Cerebellum Medulla 35 Hindbrain Midbrain and parts of hindbrain like pons and medulla form the brainstem Vomiting Thalamus Swallowing Sneezing Coughing Hiccupping Hypothalamus Brain stem Midbrain Pons Medulla 36 Reflex Action and Reflex Arc Reflex action is the process of spontaneous response to a stimulus without intervention of will Automatic mechanical response in response to the stimulus Response to peripheral nervous stimulation Requires involvement of a part of CNS 37 Reflex Action- Mechanism Reflex arc: It is the nerve pathway or chain, between the receptor and the effector organ, which controls a reflex. Reflex action: The process of spontaneous response to a peripheral nervous stimulation that occurs without intervention of will and requires a part of CNS (spinal cord and brain). 2. Afferent neuron 1. Receptor Stimulus 3. Spinal cord (CNS) 4. Efferent neuron 5. Effector Response Reflex arc 38 Sensory Reception and Processing Detect all changes in the environment Send signals to CNS - processed and analysed by brain Major sensory organs: ○ ○ Eyes Ears 39 Eye Paired eyes located in sockets of the skull – Orbits Adult human eye ball- Spherical structure Eye - Structure Wall of the eye ball Sclera Choroid Retina Retina Macula lutea Fovea Optic nerve Blind spot 41 Eye - Structure Sclera External layer Composed of dense connective tissue It is the “white” of the eye. It covers the entire eyeball except the cornea Cornea Anterior portion of sclera layercornea Transparent layer It allows free entry of light. It is curved and helps to focus light onto retina. Cornea provides maximum refraction to light. Eye - Structure Choroid Middle layer which contains blood vessels Bluish in color Thinner posterior part Thicker anterior partciliary body Choroid Ciliary body 43 Eye - Structure Iris Pigmented and opaque structure formed by ciliary body Visible coloured portion of eye It is suspended between cornea and lens and is attached at its outer margin to the ciliary processes. The amount of melanin in the iris determines the eye color. Pupil is the hole in the center of the iris. Muscles of the iris regulate the diameter of the pupil 44 Eye - Structure Retina Has three layers of neural cells Ganglion cells Bipolar cells Photoreceptor cells Bipolar cells Photoreceptor cells Cone Rod Photoreceptor cells: Two types- Rods and cones These are modified bipolar neurons. These cells contain the photopigments (light sensitive pigments). Ganglion cells Eye - Structure Rods Cones Contains purplish-red proteinRhodopsin (Vit A derivative) Contains iodopsin pigment Function of the rodsScotopic vision Functions of cones- Photopic vision and colour vision Inner segment has the main metabolic machinery like mitochondria, Golgi etc. 3 types- respond to green, red and blue lights When stimulated equallywhite light sensation Eye - Structure Retina Optic nerves: ○ Located at the back of the eye ○ Connects eye to brain Blind spot: ○ ○ Posterior pole where optic nerves leave and retinal blood vessels enter Macula lutea Blind spot Optic nerve Photoreceptor cells absent Macula lutea: ○ Yellowish area of retina ○ Image formed at yellow spot 47 Eye - Structure Fovea: Shallow depression in the middle of macula lutea Thinned out portion of retina Cones densely packed – Greatest visual resolution Fovea Aqueous humor: Space between cornea and lens – Aqueous chamber Aqueous chamber contains thin watery fluid – Aqueous humor Vitreous Chamber Space between lens and retina – Vitreous chamber Vitreous chamber contains transparent gel – Vitreous humor 48 Vitreeous humor Aqueous humor Mechanism of Vision Photopigments (Rhodopsin) = Opsin (Protein) + Retinal (Aldehyde of vitamin A) Light energy Light causes a change in retinal, which initiates a signal to the brain 49 Mechanism of Vision Potential differences are generated at the photoreceptor cells This generates an action potential at the ganglion cells through the bipolar cells. Layer of rods and cones Bipolar neurons Ganglion layer 50 Mechanism of Vision Potential differences are generated at the photoreceptor cells This generates an action potential at the ganglion cells through the bipolar cells. Optic nerves transmit the action potential to the visual cortex of the brain. Here the impulses are processed and analysed and the image is identified based on the earlier memory. Layer of rods and cones Bipolar neurons Ganglion layer Visual cortex 51 Ear Ear Ear External Ear Ear pinna Tympanum Ext. Auditory Canal or Meatus Middle Ear Internal Ear / Labyrinth 3 Ear Ossicles Membranous Labyrinth Bony labyrinth Outer ear Pinna (Auricle) Has fine hair and waxsecreting glands. Collects sound waves Present in mammals except whales, dolphins, etc Many mammals can move their ear pinna in the direction of sound. In humans it is relatively immobile because auricular muscles of pinna are vestigial. External auditory meatus (canal) Has fine hair and wax- secreting glands Extends up to the ear drum Tympanic membrane (Ear drum) Tympanic membrane or eardrum is a thin, semi transparent partition between the external auditory canal and middle ear. It is covered by epidermis and lined by simple cuboidal epithelium. It vibrates in response to sound waves. For tympanum to vibrate freely air pressure must be equal on both sides. Middle ear Malleus Attached to ear drum Incus Stapes Attached to oval window of cochlea Ear ossicles increase efficiency of transmission of sound waves to inner ear 55 Middle ear Eustachian tube Connects middle ear cavity with nasopharynx Helps in equalising pressure on both sides of tympanum. It normally remains closed but opens during chewing, swallowing, yawning, coughing, sneezing and changes in altitude. 56 Inner Ear It is also called labyrinth because of its complicated series of canals. Structurally, it consists of two main divisions: Internal Ear/Labyrinth Bony Labyrinth Membranous Labyrinth Bony labyrinth is a series of cavities in the petrous portion of the temporal bone divided into three areas: ○ Semicircular canals. ○ Vestibule (both of which contain receptors for equilibrium) ○ Cochlea (contains receptors for hearing). Bony labyrinth is lined with periosteum and contains perilymph. Inner Ear Cochlea Endolymph Filled in membranous labyrinth Perilymph Coiled portion of labyrinth Cochlea is a bony spiral canal that resembles a snail’s shell. It makes almost three turns around a central bony core called modiolus. Surrounds membranous labyrinth Bony labyrinth Endolymph Membranous labyrinth Bony labyrinth Membranous labyrinth Perilymph Cochlea 58 Inner Ear Inner ear Scala vestibuli Ends at oval window Scala media Filled with endolymph Scala tympani Terminates at round window Organ of Corti Reissner’s membrane Basilar membrane Divide the surrounding perilymph Inner Ear Tectorial membrane Inner ear Thin elastic membranes Stereo cilia Projected from apical part of hair cell Afferent nerve fibres Present at the base of nerve fibres Hair cells Auditory receptors 60 Inner Ear Inner ear 3 Semi-circular canals At right angles to each other Ampulla Contains projecting ridge – crista ampullaris Otolith organs Contains projecting ridge - macula Utricle Saccule 61 Mechanism of Hearing Mechanism of Hearing Sound wave received by external auditory meatus Eardrum vibrates malleus, incus and stapes amplify the vibration Vibration reaches inner ear through oval window Auditory nerve transmits impulses to brain hair cells of organ of corti get stimulated by vibration in the basilar membrane Movement of fluid by pressure waves Summary - Transmission of Impulse 1. Impulse arrives at the axon terminal 8. Ions generate new potential in the postsynaptic membrane 2. Synaptic vesicles move towards the membrane 7. Entry of ions into the post-synaptic membrane 3. Synaptic vesicles fuse with the plasma membrane 6. The ion channels on the post-synaptic membrane opens up 4. Release of neurotransmitters 5. Neurotransmitters bind to receptors on the postsynaptic membrane Human Nervous System The Human Neural System Peripheral Neural System (PNS) Central Neural System (CNS) Brain Spinal cord Autonomic Neural System Sympathetic Neural System Somatic Neural System Parasympathetic Neural System 65