Plus One Zoology Notes Chapter 10 Neural Control and Coordination is part of Plus One Zoology Notes. Here we have given Kerala Plus One Zoology Notes Chapter 10 Neural Control and Coordination.
|Text Book||NCERT Based|
|Chapter Name||Neural Control and Coordination|
|Category||Kerala Plus One|
Kerala Plus One Zoology Notes Chapter 10 Neural Control and Coordination
The organ system in an animal that serves to coordinate and control the functioning of all other organ systems in the body is known as Nervous system.
Coordination: The process through which two or more organs interact and complement the functions of one another is called Coordination.
The neural system of animals is composed of highly specialized cells called neurons, which can detect, receive and transmit different kinds of stimuli.
Human neural system
The human neural system consists of two parts, Central neural system and Peripheral neural system.
♦ CNS (Central Nervous System)
- Consisting of nerves arising from the brain and spinal cord.
- A site of information processing and control.
- It includes the Brain and Spinal cord.
♦ PNS (Peripheral Nervous System)
- It comprises all the nerves of the body associated with CNS.
- There are two types of nerve fibres in PNS.
i. Afferent fibres It transmits impulses from tissues or organs to CNS.
ii. Efferent fibres It transmits regulatory impulses from the CNS to concerned peripheral tissues or organs.
- PNS has two divisions
a. Somatic neural system (SNS)
- It relays impulses from the CNS to skeletal muscles.
b. Autonomic neural system (ANS)
- It transmits the impulse from the CNS to involuntary organs and smooth muscles of the body.
- ANS is grouped into two
1. Sympathetic neural system.
2. Parasympathetic neural system.
Structure of Neurons
The neuron is the structural and functional unit of the neural system. It composed of: Cell body, Axon and Dendrites.
a. Cell body (Cyton)
It contains, cytoplasm with a nucleus and all other cell organelles and Nissl’s granules.
They are short fibres projecting from the cell body and carry Nissl’s granules. Transmits impulses towards the cell body.
- Axon is ci long fibre which transmits impulses away from the cell body towards neuromuscular junction/synapses.
- Branching of an axon is called aconite or axon terminals.
- Each axon it ends as a bulb-like structure called synaptic knob containing neurotransmitters.
- Axon may or may not be covered by a fatty sheath called myelin sheath. This covering is missing at intervals. These gap between the sheath are known as nodes of Ranvier.
Types of Axon
i. Myelinated axon
ii. Non-myelinated axon
♦ Myelinated axon
- An axon that has myelin sheath is known as the myelinated axon.
- It is enveloped with Schwann cells that form a myelin sheath around the axon.
- It is found in spinal and cranial nerves.
- The gap between two adjacent myelin sheaths is called nodes of Ranvier.
♦ Non-myelinated axon
Axon without myelin sheath is known as the non-myelinated axon. Based on the number of axon and dendrites the neurons are of three types:
i. Unipolar neuron
- Cell body with one axon only found in the ganglion, brain and spinal cord
- Found usually in the embryonic stage.
ii. Bipolar neuron
Cell body with one axon and one dendrite found in the retina of an eye.
iii. Multipolar neuron
Cell body with one axon and 2 or more dendrites found in the cerebral cortex.
Generation and conduction of nerve impulses
- Neurons are excitable cells because their membranes are in a polarised state. The cell membrane separates the inside of a cell from the outside, and all chemicals that get into and out of the cell must go through it. As in all cells, the cell membrane of a neuron is polarized.
- Impulse transmission is electrochemically conducted along a nerve fibre.
- It occurs in three stages.
1. Resting membrane potential.
2. Depolarisation or Action potential
3. Propagation of action potential or polarisation.
♦ Resting membrane potential
Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ( ions. When a neuron is not conducting an impulse, i.e., resting
- Resting membrane potential is the electrical potential difference across the resting neuron.
- During resting condition, the concentration of K+ ions is more inside the axoplasm while the concentration of Na+ ions is more outside the axoplasm.
- As a result, K+ ions move faster from inside to outside as compared to Na+ ions. Therefore membrane became positively charged outside and negatively charged inside. This is known as a polarization of membrane.
- The ionic concentration gradient across the resting membrane is maintained by the Na+ K+ pump which transports three Na+ outwards for two K+ into the cells.
♦ Action potential
- When a stimulus is applied at site ‘A’ of the polarised membrane more Na enters the membrane making it more electropositive inside the membrane.
- This reversal of polarity of the membrane is called Depolarization.
- Immediately Na pump becomes active and resting membrane potential is restored repolarization.
- Depolarization and subsequent repolarization together constitute the action potential.
♦ Propagation of action potential or repolarization
- Action potential formed at a point ‘A’ becomes a stimulus for the next region ‘B’, ie current flows on the inner surface from stimulated site to adjacent site. As a result depolarization and repolarization occurs here.
- At the depolarized site the original resting potential is regained by pumping out Na+ this is called repolarization.
- This process is repeated and the action potential travels along the entire length of a neuron as a nerve impulse.
Difference between resting potential and action potential.
|Resting potential||Action Potential|
|it is the potential difference across the nerve fibre when there is no condition of nerve impulse||It is the potential difference across nerve fibre when there is- conduction of nerve impulse.|
|The membrane is more permeable to K ions than to Na+ ions||The membrane is more permeable to Na+ ions than to K+ ions|
Transmission of impulses
Synapse is the functional junction between the axon of one neuron and dendrite of another neuron. Synapse is formed by the membrane of a presynaptic neuron and a postsynaptic neuron.
- It is separated by a small gap known as synaptic cleft filled with synaptic fluid.
- There are two types of synapses.
i. Electrical synapse
ii. Chemical synapse
♦ Electrical synapse
The membranes presynaptic and postsynaptic neurons lie in close proximity.
- Electric current can move directly from one neuron to another across the synapse. It is a faster method of impulse transmission.
- Impulse transmission in the electrical synapse is similar to impulse conduction along a single axon.
- It is very rare in the human system.
♦ Chemical Synapse
- In this, there is a fluid-filled space called synaptic cleft between presynaptic neuron and postsynaptic neuron, which separate these membranes.
- The presynaptic regions have swellings called synaptic knob. They contain synaptic vesicles filled with neurotransmitters (like acetylcholine).
- When a nerve impulse reaches a presynaptic knob stimulates the movement of the synaptic vesicle towards the presynaptic membrane.
- Synaptic vesicle fuse with the presynaptic membrane and break, releasing neurotransmitters.
- The released neurotransmitters bind to their specific receptors found on the postsynaptic neuron.
- This binding opens ion channels allowing the entry of ions and generates an action potential, in the postsynaptic neuron
CNS (Central Neural System)
- A brain is the main coordinating centre of the body. It is a part of the nervous system that controls and monitors every organ of the body.
- It is well protected by cranial meninges with an outer layer dura mater, a middle layer Arachnoid and the inner layer called Pia mater.
- The brain is divided into three parts.
It is the anterior part of the brain. It.has three Parts.
- The largest part of the brain and is divided longitudinally into right and left hem spheres.
- The hemispheres are connected by a tract of nerve fibre called corpus callosum.
- Each hemisphere consists of two parts.
i. Cerebral cortex
ii. Cerebral Medulla
♦ Cerebral Cortex
- The cerebral cortex is referred to as the grey matter due to its greyish appearance. The neuron cell bodies are concentrated here giving the colour.
- the cerebral cortex is divided into three areas.
♦ Motor area:
It Controls voluntary movements.
♦ Sensory area
Concerned with a sense of vision, hearing, taste and sensations of smell.
♦ Association Areas :
Concerned with memory communication and intersensory associations
♦ Cerebral Medulla
It is the inner part of forebrain formed of myelinated nerve fibres with an opaque white appearance and is called white matter.
It is the main centre of coordination for sensory and motor signalling. It is wrapped by cerebrum.
It lies at the base of the thalamus. Groups of neurosecretory cells, which secrete neurohormones are called hypothalamic hormones.lt also contains nerve centres to control body temperature, hunger and thirst.
♦ Limbic system or limbic lobe
The inner part of cerebral hemisphere and is associated with amygdala and hippocampus, regulate sexual behaviour, emotional reaction and motivation.
It is located between the thalamus of the forebrain and pons region of the hindbrain. It consists of:
a. Cerebral aqueduct A canal passing through the midbrain.
b. Corpora Quadri Gemina A dorsal portion of the midbrain contains four round lobes. Midbrain and hindbrain from the brain stem
Posterior part of the brain and has three regions.
i. Pons Varolii It is the fibre tract that interconnects different regions of the brain.
ii. Cerebellum It has a convoluted surface to accommodate (little cerebrum) more neurons.
iii. Medulla oblongata /medulla
It connects the brain with spinal cord and contains the centres that control respiration, cardiovascular reflexes and gastric secretion.
|Functions of parts of the brain|
|Cerebrum||Centre of intelligencé, memory and imagination. reasoning, judgement, expression of Will power.|
|Thalamus||It acts as a relay centre to receive and transmit general sensation1 of pain, touch and temperature|
|Hypothalamus||Regulation of body temperature, urge for eating and drinking.|
|Midbrain||Co-ordinate ,jsuaI reflex and auditory reflex.|
|Cerebellum||Maintain posture and equilibria urn of the body as well as coordinates and regulates voluntary movement.|
|Pons Varolii||It relays impulses between the medulla oblongata and cerebral hemisphere and between the hemispheres of cerebrum a cerebellum:|
|Medulla oblongata||Control heartbeat, breathing swallowing, salivation, sneeze vomiting coughing.|
Reflex action and Reflex Arc
It is the rapid, involuntary and unconscious actions of the body brought about by any part of the CNS through sudden stimulation from receptors. Path stimulation by an impulse in a reflex action is called a reflex arc.
- It consists of, one afferent and one efferent neuron.
- A receptor organ receiving the stimulus.
- An afferent neuron receives signals from a sensory organ and transmits into the CNS.
- An efferent neuron that conducts impulses from CNS to effector organ.
- An effector organ that responds to impulse.
Sensory Reception And Processing
Receptors are sensory structures present all over the body. They can detect changes in the environment, which are called stimuli and turn them into electrical impulses. They are located in the sense organs such as ear, eye skin etc,
An eye is a visual organ present in the orbit of the skull. The eyeball is a spherical structure and has a three-layered wall, namely
a. Sclera b. Choroid c. Retina
- An outer most layer composed of dense connective tissue.
- if It protects the inner structure and helps to maintain rigidity of the eyeball.
- The transparent anterior portion of this layer is called cornea that lacks blood vessels and is nourished by lymph.
- Conjunctiva A transparent covering protects the cornea.
- A middle layer of the eyeball with blood vessels and looks bluish in colour.
- This layer is thin over the post region and gets thickened in the anterior region to form a ciliary body.
- Iris Pigmented and opaque structure that appears circular through the cornea.
- Pupil It is the small aperture in the iris that regulates the amount of light entering into the eye.
- Innermost photosensitive layer.
- It consists of three layers of cells
i. Inner ganglion cells
ii. Middle bipolar cells
iii. Outermost photoreceptor cells.
- There are two types of photoreceptor cells.
The rods contain the rhodopsin pigment (a purple coloured pigment derived from Vitamin A) that is highly sensitive to dim light.lt is responsible for scotopic vision.
The cones contain the iodopsin pigment (visual pigment) and are highly sensitive to high-intensity light.
- Responsible for photopic vision and colour vision.
- There are three types of cone cells.
- Cone cells respond to green light, to blue light and to red light.
- When these cones are stimulated equally, a sensation of white light is produced.
- Blind Spot is the region of the retina from where optic nerve originates and rods and cones are absent, no vision in this area.
- Yellow spot/Macula lutea is the tiny yellow area, lateral to a blind spot having cones. As it contains a yellow pigmented spot hence it is a yellow spot.
- Fovea Centralis It is a shallow depression in the centre of the yellow spot having densely grouped cones. It is a region of visual resolution.
- Space between the cornea and lens is called aqueous chamber and is filled with a thin watery fluid called aqueous humour.
- Space between the lens and the retina is called Vitreous chamber and is filled with a transparent gel called Vitreous humour.
Mechanism of Vision
- When light rays are focused on the retina through the cornea, it generates impulses in rods and cones.
- Photopigments in the human eye are composed of opsin (a protein) and retinal [an aldehyde of vitamin A].
- Light induces dissociation of the retinal from opsin. As a resulting structure of opsin changes and potential differences are generated in photoreceptor cells.
- These signal generate action potentials in the ganglion cells through bipolar cells
- Optic nerve transmits an impulse to the visual cortex where it is analysed and the image formed is recognised.
|Difference between rods & cones|
|Helps in twilight vision||Helps in colour vision|
|Visual purple pigment present called rhodopsin||A visual violet pigment called iodopsin|
|Photoreceptor cells sensitive to dim light||Photoreceptor cells sensitive to bright light|
The ear performs two sensory functions, hearing and maintenance of body balance. Anatomically, the ear can be divided into three major sections called the outer ear, the middle ear, the inner ear.
♦ Outer ear
- Consists of, Pinna, External auditory canal and Tympanic membrane (eardrum).
- Pinna is a sensitive structure that collects and directs the vibrations into the ear to produce sound.
- External auditory canal is a tubular passage supported by cartilage in the outer ear.
- It contains ceruminous glands which secrete wax.
- Hairs are present at the opening of the ear canal, which prevent the entry of foreign objects.
♦ Middle ear
- It is an air-filled tympanic cavity that is connected with pharynx through eustachian tube, which helps to equalize pressure in both sides of the tympanic membrane.
- The middle ear contains ear ossicles. The I three ear ossicles are malleus, incus and stapes that are attached to each [ other.
- Malleus is attached to the tympanic j membrane.
- Stapes is attached to the oval window of the cochlea.
- Ear ossicles act as a lever that transmits sound waves from external ear to internal ear.
♦ Inner ear
- Also called labyrinth and consists of two parts, bony labyrinth and membranous labyrinth. !
- Bony labyrinth is filled with a fluid called perilymph and a membranous labyrinth is filled with a fluid called endolymph.
- The coiled portion of the labyrinth is called cochlea. It is the main hearing organ.
- Internally, the prisoners and basilar membranes of cochlea consist of three fluid-filled chambers or canals. The upper scale vestibule, the lower scale tympani and the middle chamber called scala media.
- Scala media, bears an upper membrane, the Reissner’s membrane, and lower membrane, basilar membrane.
- The Organ of Corti present on the basilar membrane consists of hair cells that act as auditory receptors.
- The basal end of the hair cells is in close contact with the afferent nerve fibres.
- Above the rows of the hair cells is a thin elastic membrane called the tectorial membrane.
- The inner ear also contains a complex system called the vestibular apparatus.
- Vestibular apparatus is composed of three semicircular canals and the otolith consisting of the utricle and saccule.
- Bony labyrinth consists of three semicircular canals, the base of the canal is swollen and is called ampulla.
- The lower end of each semicircular canal contains a projecting ridge called crista ampullaris.
- Crista and macula are specific receptors of vestibular apparatus responsible for maintenance of a balance of the body and posture,
♦ Mechanism of Hearing
- The outer ear receives sound waves and directs them to the tympanic membrane(eardrum).
- The tympanic membrane vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles to the oval window.
- The vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymph which induces a ripple in the basilar membrane.
- These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane.
- As a result nerve impulses are generated in the associated afferent neurons and are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain.
- Where the impulses are analysed and the sound is recognised.
Flow chart showing the Mechanism of hearing
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