Neural Control and Coordination
Neural control and coordination:
Structure of Neuron:
Nervous tissue originates from ectoderm. Nerve cell –
Cell body or Cyton Centriole is absent or soma or perikaryon: Nissl's granule and Neurofibril are also found in nerve cell Nissl’s Endoplasmic reticulum & ribosome form granules like structure granules: called as Nissl's granules or Tigroid body. They are centre of protein synthesis.
Dendron: • Fine branches of cytoplasm are called dendrites.
• Receptor’s are found on the dendrites. Axon or nerve fibre are longest cell process of cyton, Nissl's granules are absent in the axoplasm.
• Axon is covered by axolemma, part of cyton where arises called axon hillock.
• Terminal end of axon is branched in button shape branches which are called as Telodendria.
• More mitochondria in telodendria which synthesize Acetylcholine (Ach) with the help of choline acetyl transferase enzyme, stored in vesicles.
Axon is covered by phospholipids (sphingomyelin) called as medulla or myelin sheath.
Medulla is covered by neurilemma or sheath of schwann cells, helps in myelinogenesis. Myelin sheath acts as insulator and prevent's leakage of ions.
Myelinogenesis in (PNS) begins with the deposition of myelin sheath in concentric layer around the axon by schwann cells.
Myelin sheath is discontinuous around the Axon. These interruptions are called node of Ranvier
Myelinogenesis in the Central nervous system Neuron (CNS) occurs with the help of oligodendrocytes (Neuroglia) Myelinated Non – Myelinated
Collaterals Small process of axon help in conduction of nerve impulse in more area. of Axon: Gray matter composed of cytons & nonmedullated nerve fibres (Grey fibers).
White matter – It contain myelinated nerve fibres (White fibres).
Group of cyton Group of Nerve fiber
Nuclei for CNS Ganglia for PNS Tract – CNS Nerve – PNS Types of neurons
Unipolar Bipolar Multipolar Single process arises Two process arises from cyton Neuron which have one axon from cyton. (1 Axon) (1Axon & 1 dendron) but many dendrons. e.g. Nervous system e.g. Retina (Rod & cones) e.g. Most of neurons of of embryo Olfactory epithelium vertebrates.
Apolar/Nonpolar • No definite dendron/axon nerve impulse radiates in all directions. Neuron : e.g. Hydra
• Pseudounipolar nerve cell has only axon but a small process act as dendron. e.g. Dorsal root ganglia of spinal cord
Types of Neurons on the basis of function
Sensory of Inter neuron or inter Motor or efferent afferent sensory connecting neuron or CNS → Effector organ → CNS internuncial neuron (organ)
Cerebral cortex contains motor area, sensory area & large area (regions)called associative area responsible for complex function like inter sensory association, memory & communication. Synapse - 1
Synapse: Junctional region between two neurons where information is transferred but no protoplasmic connection.
Synapse = Pre synaptic knob (Telodendria) + synaptic cleft + post synaptic membrane (membrane of dendron).
(i) Axodendritic – b/w axon & dendron Synapse: (ii) Axosomatic – b/w axon & cyton (iii) Axoaxonic – b/w axon & axon
Through neuron At synapse Conduction Fast Slow Synaptic cleft 0.2 nm > 20 nm Neurotransmitter Absent Present Synaptic delay Absent Present Blocking Can not be controlled Controlled by neurotransmitter Synapse – 2 Supporting cells
Supporting cells: Neuroglia/Glial cells
Astrocytes Oligodendrocytes Microgliocytes Origin Ectodermal in origin Ectodermal in origin Mesodermal in origin Morphology Large cell Smaller Smallest Number of process Numerous process Few process With branching Function 1.Provide repair Formation & Scavenger cells of mechanism and preservation of Myelin CNS replace the damage sheath in CNS. phagocytic in nature tissue 2. It forms blood brain barrier. Blood Brain Barrier:
Blood-brain barrier is formed by capillary endothelial cells, which are coupled by tight junctions with extraordinarily high electrical resistance.
Astrocytes are required to produce the barrier which prevents the entry of neurotoxins.
Neurotransmitters or Neurohormones
Stimulatory Inhibitory ↓ ↓ Stimulates impulse at synapse e.g. Inhibit impulse at synapse e.g. Acetyl choline (anch), nor – epinephrine GABA (gamma amino butyric or nor – adrenaline or sympathetin acid) dopamine glycine Physiology :
The resting membrane potential
Active and passive ion movement across the cell surface of an axon inside the axon called as resting potential
Active transport takes place through the sodium/potassium pump.
Neurons are excitable cells because their membranes are in a polarized.
Resting potential is about – 70 mV. Potassium ions have a membrane permeability greater than that of sodium ions. Due to active transport and diffusion positive charge is more outside and negative charge is more inside.
Action potential in exciting stage:
On stimulus an action potential is generated by a sudden opening of the sodium gates, sodium ions enter by diffusion increases the number of positive ions inside the axon.
10 mV in potential difference from RMP is sufficient to trigger a rapid influx of Na+ ions, 10 mV is threshold stimulus.
(Axolemma) is completely depolarized, called as excited membrane or depolarized membrane.
Membrane potential becomes positive upto +30 to +45 mV called as action potential. Physiology of nerve – Repolarization
Repolarization
Sodium gates closed, potassium gates open, potassium diffuse out of cell makes the cell negative and the process of repolarization.
Repolarization period returns the cell to its resting potential (-70 mV).
The time taken for restoration of resting potential is called refractory period, during this period the membrane is incapable of receiving another impulse.
The whole process of depolarization and repolarization takes only about 1 to 5 milli second (ms). Process Na+-K+ Passive Na+ VGC K+ VGC Potential with Inside Charge pump diffusion value Polarisation 3 3 x x RMP (-60 to - Negative 85 mv) Depolarisation x 3 3 x Neutral Repolarisation 3 3 x 3 - Negative Hyperpolarisation 3 3 x 3 - Negative Saltatory conduction of Nerve Impulse:
Saltatory conduction occur in myelinated fibre.
The combined resistance of the axon membrane and myelin sheath is very high, but nodes of Ranvier, the resistance is low.
Action potential jump from node to node and passes along the ,myelinated axon faster as compared to non – myelinated axon.
Leakage of ions takes place only in nodes of Ranvier and less energy is required for saltatory conduction. Synaptic Transmission
AP develop in pre synaptic membrane, it becomes permeable fro Ca++, Ca++ enter in pre synaptic membrane & vesicles burst and release of neurotransmitters (Ach) in synaptic cleft.
Ach via synaptic cleft & bind to receptors, develops excitatory post synaptic potential (EPSP)
Cholinesterase enzyme in Post synaptic membrane decomposes the Ach into choline & Acetate.
Neuro inhibitory transmitter (GABA) binds with post synaptic membrane to open the Cl– gatted channels and hyperpolarization occurs called inhibitory post synaptic potential (IPSP)
Neuron conducts the impulse in the form of electro chemical wave.
It follow all or none law. Nervous system – Classification :
Classify nervous system Central Nervous System (CNS) Brain and spinal cord Integrative and control centers
Peripheral Nervous System (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of body
Sensory (afferent division) Motor (efferent division) Somatic and visceral sensory Motor nerve fibres nerve fibres Conducts impulses from Conducts impulses from receptors CNS to effectors to the CNS (muscles and glands)
Sympathetic division Mobilizes body systems during Autonomic Nervous Somatic Nervous emergency situations Sysmtem (ANS) Sysmtem (SNS) Involuntary (visceral motor) Voluntary (somatic motor) Parasympathetic division Conducts impulses from the Conducts impulses from the CNS to cardiac muscles CNS to skeletal muscles Conserves energy smooth muscles and glands Promotes nonemergency functions Central nervous system:
Brain: Situated in cranial box made up of 1 frontal bone, 2 parietal bone, 2 temporal bone, 1 occipital bone.
Brain meninges:
Duramater: Outermost membrane made up of collagen fibres.
No space is found between skull & Duramater.
Arachnoid: Middle, thin and delicate membrane, made up of connective tissue. It is found only in mammals.
Arachnoid villi reabsorb the cerebrospinal fluid (CSF) from sub arachnoid space & pour it into cranial venous sinuses. Piamater: • Inner most made up of connective tissue.
• Piamater & arachnoid fuse together to form leptomeninges.
• At some places it directly merges in the brain called telachoroidea form choroid plexus in the ventricles of brain.
• Sub Dural space filled with serous fluid.
• Sub arachnoid space filled with C.S.F.
• Inflammation of meninx is called as meningitis.
Cerebrospinal Clear and alkaline has protein glucose, cholesterol, urea, – fluid (CSF): bicarbonates, sulphate and chlorides of Na, K.
• Mainly formed in choroid plexus of lateral ventricles.
• Collection of CSF fro any investigation is done by lumbar
puncture at L3 – L4 region. Functions of It act as shock absorbing medium. C.S.F.: • Excretion of waste products.
• Endocrine medium for the brain to transport hormones. Cerebrum –
Brain
Fore brain (develops Mid brain (mesencephalon) Hind brain (rhombencephalon) from prosencephalon)
Netencephalon Myelencephalon Rinencephalon Telencephalon Diencephalon (pons, cerebellum) (medulla (olfactory lobe) (cerebrum) oblongata)
Cerebrum consist of two cerebral hemispheres on the dorsal surface separated.
Cerebral hemisphere partially connected by corpus callosum.
Frontal lobe (anterior) Partial lobe (middle) Cerebrum: Occipital lobe (posterior) Temporal lobe (lateral) Insula
Central separates frontal lobe from parietal lobe.
Lateral sulcus separate temporal lobe from frontal & parietal.
Parieto occipital sulcus separate occipital lobe from parietal lobe. Ridges in brain are known as gyri while grooves are called sulci.
Corpus callosum is largest commissure of brain. Exclusive feature of mammals.
Anterior truncated part of corpus callosum is genu while posterior is splenium.
A oblique band is formed by body of corpus callosum & goes towards genu called fornix.
Genu & fornix called as Vth ventricle or pseudocoel.
Diencephalon and Mid brain Diencephalon • Thalamus forms upper lateral walls of diencephalon. It receives all sensory impulses from all part of body & send to the cerebral cortex. • Hypothalamus forms lower or ventral part of Diencephalon. • Pituitary is attached to middle part of hypothalamus by infundibulum.
• A cross like structure on anterior surface of hypothalamus called as optic chiasma, it also acts as temperature regulatory center of body.
• Corpous mammillare or corpus albicans or mammalian body posterior part of hypothalamus. It is a character of mammalian brain. • Epithalamus forms the roof of diencephalon. Pineal body (Epiphysis cerebri) is found in epithalamus. • Metathalamus located in floor of diencephalon. Mid brain:
• Anterior part of mid brain contains two longitudinal myelinated nerve fibres peduncles called Cerebral peduncles or crus cerebri or crore cerebri.
• On the posterior part colliculus or optic lobes are found. Four colliculus are collectively called as corpora quadrigemina. Hind brain
Pons or pons varoii: Situated below the midbrain & upper side of the M.O.
It consists of many transverse & longitudinal nerve fibres.
Helps in controlling functions, facial expression, breathing.
Cerebellum: Made up of 2 lateral lobe & 1 vermis.
Lateral lobe of cerebellum are also called hemisphere.
Superior cerebellar peduncle attach with mid brain. Middle cerebellar peduncle attach with pons and Inferior cerebellar peduncle attach with M.O.
Inner white matter is branched like a tree called arbor vitae.
Main functions is balancing and coordination of muscles.
Medulla oblongata It contains 4th ventricle (myelocoel). (M.O.): Roof of 4th ventricle has a pair of foramina of luschka.
Control involuntary functions like breathing, peristalsis, sneezing, vomiting, defecation, urination etc. Ventricles of brain
Except Midbrain, Cerebellum, Pons & olfactory lobe complete brain is hollow cavity lined by ependymal epithelium, Cavities are known as ventricles, filled with cerebrospinal fluid (C.S.F.).
1st and 2nd ventricles are paracoel or Lateral ventricle, combine with each other & open into cavity of Diencephalon through Foramen of Monro.
Cavity of diencephalon is 3rd ventricle or Diocoel.
Cavity between anterior pons, medulla & posterior cerebellum called 4th ventricle.
3rd and 4th ventricle are connected through Iter or Aqueduct of sylvius.
4th ventricle continues in the metacoel and metacoel continues neurocoel or central canal.
One aperture on dorsal surface of metacoel known as foramen of Magendie. CSF Circulation and Limbic System
Some time Iter or aqueduct become blocked improper circulation of CSF or blockage of CSF cause an increase in intra cranial pressure this condition called Hydrocephalus.
Choroid plexus ⟶ Lateral ventricle ⟶ Foramen of monro ⟶ Diocoel ⟶ Iter ⟶ 4th ventricle ⟶ Metacoel ⟶ Foramen of Magendie and foramen of Luschka ⟶ Arachnoid space ⟶ arachnoid villi ⟶ Cranial venous sinus ⟶ Blood circulation C.S.F. Circulation
Limbic system:
Limbic lobe (area of temporal Lobe) + Hippocampus + Hypothalamus including septum + Part of Thalamus + Mammalary bodies + Amygdaloid complex
Function of limbic system:
Behaviour, Emotion, rage and anger (Hypothalamus, amygdaloid body) Recent memory & short term memory converts into long term memory. (Hippocampal lobe) Food habit. Sexual Behaviour (Hypothalamus) Olfaction (Hippocampal lobe and Limbic lobe) Functions of Various Lobes of Brain -
S.No. Name of Area Location Relation or Analysis 1. Prefrontal cortex Frontal lobe Seat of intelligence, knowledge, ideas, ability (organ of mind).
2. Premotor area Frontal lobe – Written centre – Associated Movement of eye, & body. – Control complex movement of jaw, tongue, pharynx, larynx 3. Motor area Frontal lobe Analysis of all type of voluntary muscle 4. Frontal Eye field Frontal lobe Responsible for conjugate movement of eye. Opening & closing of eye lid 5. Broca's Area Frontal lobe Analysis for speak if injury to this region In Rt handed person present of Lt. inability to speak (aphasia) even though In Lt handed side present of concerned are not paralysed person Rt. side (Motor speech area) 6. Auditory area Temporal Analysis for sound. Functions of Various Lobes of Brain -
S.No Name of Area Location Relation or Analysis . 7. Olfactory Temporal or Analysis for smell. Hippocampal gyrus 8. Wernicke's area Temporal Analysis for language (Sensory area of Sensory analysis for speech speech) 9. Gustatory area Parietal Analysis for Taste 10. Somesthetic Parietal Analysis for touch, pressure, area pain, knowledge about position in space. taking in information from environment etc. 11. Angular gyrus Parietal Sensory analysis for writing
12. Occipital area Occipital Analysis for vision Functions of Brain –
Association area responsible for complex functions like intersensory association, memory and communications.
Olfactory lobe centre of smelling power, sharks and dogs have well developed olfactory lobes.
All the voluntary actions are controlled by cerebral hemispheres.
Cerebral hemispheres regulates different parts of brain, centre of conscious senses, will power, voluntary movements, knowledge, memory, speech and thinking, reasoning etc.
Diencephalon controls the sexual maturity of animal.
Thalamus centre for sensory stimulation. It is related with RAS
Hypothalamus, Thermoregulation, Behaviour and emotion, Endocrine control, Biological clock system, ANS control. • The regulatory hormones of hypothalamus control the activity of endocrine glands.
• Optic chiasma carry optic impulses received from eyes to the cerebral hemispheres.
• Metathalamus related with MGB & LGB, MGB related with hearing & LGB related with vision.
• Four optic lobes or colliculus present, superior optic lobes are the main centres of pupillary light reflexes.
• Inferior optic lobes are related acoustic (sound) reflex action.
• Crura cerebri controls the muscles of limbs.
• Cerebellum maintains the body balance of persons, alcohol in excess, affect cerebellum as a result of they can not maintain their balance.
• Pons regulates breathing reaction through pneumotaxic centre.
• Medulla Oblongata controls involuntary activities of the body e.g. heart beats, respiration , metabolism. • It acts as conduction path for all impulses between spinal cord and remaining portions of brain. • It is also concerned with Reflex– Sneezing reflex , salivation reflex, coughing reflex, swallowing reflex, vomiting reflex, yawning reflex. Spinal cord
Medulla oblongata from foramen of magnum & continues in neural canal known as Spinal cord.
Its lower part is narrow known as conus – medullaris present upto L1 vertebra.
Terminal part of conus medullaris extend, called filum terminale, non – nervous part.
Spinal cord is covered by Duramater, Arachnoid & Piamater, space is found between vertebra & duramater known as Epidural space. Internal structure of spinal cord -
Outer-part of spinal cord is of white matter while inner-part contain gray matter.
The grey matter forms the one pair dorsal & ventral horn divide white matter in 4 segments & known as function or white column.
Dorsal & ventral horn continue in root of Dorsal & Ventral Horn.
In root of dorsal horn, ganglia is present called Dorsal root ganglia contains sensory neurons, pseudopolar in nature. Both root combined at the place of intervertebral foramen.
Motor neurons are found in the ventral root. Both sensory & motor nerve fibers from intervertebral foramen form spinal nerve
Lateral horns nerve fibre come through ventral root & further come into intervertebral foramen. These fibre called Ramus communicans forms ANS.
Group of spinal nerve at the terminal end (L1) form tail like structure called cauda equina (horse tail).
Functions of spinal cord: Bridge between brain & organs of the body. Provides relay path for the impulses coming from brain Regulates and conducts the reflex action. Internal structure of spinal cord - Reflex action
Cranial reflex are completed by brain. These are slow actions e.g. watering of mouth to see good food, pupil reflex etc. Reflex action: Spinal reflex completed by spinal cord. These are very fast actions e.g. displacement of the leg at the time of pinching by any needle.
Reflex action on the basis of pervious experiences:
Conditioned reflex: Previous experience is required e.g. swimming, cycling, dancing, singing etc, studied first by Evan Pavlov on dog.
Unconditioned reflex: These actions do not require previous experience e.g. sneezing, coughing, yawning, sexual behaviour migration in birds etc.
Reflex Arch: The path of completion of reflex action is called reflex arch.
Stimuli → Receptor → Sensory nerve → Spinal cord/Brain → Motor nerve → Effector
Monosynaptic: Direct synapse found between sensory and motor neurons e.g. stretch reflex.
Polysynaptic: One or more small neurons found between sensory and motor neurons. These small neurons are called connector neuron or inter neurons or internuncial neurons e.g. withdrawal reflex. Knee Jerk Reflex - 1 Knee Jerk Reflex - 2
• Sensory neuron supplied the sensation through dorsal root ganglia.
• Terminal branches of axon divide in the gray matter & one is supplied agonist muscle & other is supplied antagonist muscle.
• EPSP (Excitatory postsynaptic potential) develop in synapse between motor fibre of agonist muscle.
• Interconnection of interneuron with antagonist muscle neuron, IPSP (Inhibitory post synaptic potential) develop in synapse between collateral branch of sensory fibre and antagonist muscle.
• Contraction of agonist muscle and relax the fibre of antagonist muscle.
Knee jerk reflex Withdrawal reflex 1. No any involvement of interneuron. Role of interneuron is important. 2. It is an example of monosynaptic reflex. It is an example of polysynaptic reflex. Peripheral Nervous System - 1
Peripheral nervous system
Cranial nerves Spinal nerves
Nerves arising from Nerves arising from brain spinal cord
12 in pairs 31 in pairs
Fibres of autonomous nervous system are found in III, VII, IX & X cranial nerves.
• Longest cranial nerve is Vagus nerve. • Largest cranial nerve is Trigeminal nerve. • Smallest cranial nerve is Abducens cranial nerve.
Autonomic nervous system is also part of PNS controls involuntary activities. Peripheral Nervous System - 2
Each spinal nerve is mixed type and arises from the roots of the horns of gray matter.
In dorsal root only afferent or sensory fibres and in ventral root efferent or motor fibres are found.
Both the roots come out from the Inter vertebral foramen in the form of spinal nerves.
Spinal nerves divide into 3 branches
Ramus – dorsalis Ramus ventralis Ramus communicans → A.N.S.
Sympathetic nervous system Parasympathetic nervous system Cranial nerves -
Name Origin Distribution Nature Function I.Olfactory Olfactory Enters Olfactory lobe, Sensory Smell II.Optic epithelium Extends to temporal lobe. Sensory Sight III.Oculomotor Retina Leads to occipital lobe. Motor Movement of eyeball IV.Trochlear Midbrain Four eye muscles Motor Movement of eyeball. (Pathetic) Midbrain Superior oblique eye Mixed Sensory Trigeminal Pons muscle. Sensory Sensory (Dentist nerve) – Skin of nose, upper eyelids, Sensory Supply to concerning (i) Ophthalmic – forehead, scalp, conjunctiva, Mixed part (ii) Maxillary – lacrhymal gland. Motor – (iii) Mandibular Pons Mucous membrane of Mixed Muscle of Mastication VI. Abducens Pons cheeks and upper lip and Sensory of eyeball VII. Facial Pons lower eyelid ------VIII. Auditory ------Lower jaw, lower lip, pinna. ------(i) Cochlear ------lateral rectus eye muscle Mixed (ii) Vestibular Medulla Face, neck, taste buds, Mixed salivary gland Name Origin Distribution Nature Function VIII. Auditory - cheeks and upper lip and - - Cochlear - Mixed Vestibular Medulla Lower jaw, lower lip, pinna. lateral Mixed rectus eye muscle. Face, neck, taste buds, salivary gland IX Glossopharyngeal Medulla Internal ear Motor Taste (antr 2/3 part of X Vagus Medulla ------Motor Tongue) (Pneumogastric) Medulla ------Facial expression, Saliva XI Accessory spinal Muscles and mucous secretion. XII Hypoglossal membrane of pharynx Hearing and equilibrium. and tongue. Taste (postr 1/3 part of Larynx, lungs, heart, tongue) & saliva secretion stomach, intestine Visceral sensations and Muscles of pharynx, larynx movements. Muscles of tongue Movement of pharynx, larynx. Movement of tongue Autonomic nervous system –
It consists of motor neuron passing to the smooth muscle of internal organs.
Most of the activities of the autonomic nervous system is controlled within the spinal cord or brain by reflexes known as visceral reflexes
Overall control of the autonomic nervous system is maintained by medulla and hypothalamus.
ANS also maintain (homeostasis) neurons.
Preganglionic neuron (myelinated) which leaves the central nervous system Neurons Postganglionic neurons (nonmyelinated) leading to effector (concerning organs) Origin of Sympathetic and Parasympathetic Nervous System:
Sympathetic NS Parasympathetic NS 1. Thoracico lumbar outflow (T1 to L3) (Ramus communicans of 1. Cranio sacral outflow T1 to L3) (cranial nerves) 3, 7,9, 10 2. Just lateral to vertebral column sympathetic trunks are there and sacral's ramus on both sides (each made up of 22 ganglia) (Rabbit = 18 communicans ganglia) 2. Ganglia are situated 3. Preganglionic nerve fibres (Ramus communicans of spinal separately either near the nerves) are smaller than post ganglionic nerve fibres (arises organ or surface of organ from sympathetic trunk or ganglia to organs) 3. Preganglionic nerve fibres 4. Preganglionic nerve fibres are cholinergic are longer postganglionic (filled with acetylcholine). and post ganglionic nerve fibres are nerve fibres. adrenergic (filled with noradrenaline) except sweat gland which 4. Both pre and post have cholinergic postganglionic nerve fibres. ganglionic nerve fiber 5. Preganglionic nerve fibres are made up of white ramus cholinergic communicans and postganglionic nerve fibres are made up of gray ramus communicans
Important points:
Cerebral – cortex
Sensory area Motor area Associated area
Detect shape, colour, sound, taste and smell. Regulates muscular – contraction
Broca’s area motor speech area translates the written words into speech. Temporal- lobes of cerebrum regulates the mechanism of hearing. Diencephalon is the centre of carbohydrate - metabolism and fat – metabolism. Acetylcholinesterase enzyme helps in the dissociation of Acetylcholine. Acetylcholine is synthesized by the Mitochondria. Inhibitory neuro- hormones GABA- gamma amino butyric –acid. The marking of brain- waves is done through E. E. G i.e. Electro- encephalon gram. Alzheimer's disease cerebral cortex is atrophied and ultimately the ventricle enlarges Alzheimer disease is more common in down syndrome. Epilepsy is short, recurrent periodic attack of motor, sensory or psychological malfunction. Symptoms – seizures, unconsciousness, Involuntary contraction of muscle. Malathione destroy the acetyl cholinesterase in synapse area. Curare blocks acetylcholine receptor on skeletal muscle used by a surgeon for keeping a muscle relaxed during operation.