Download Nervous System Chap49

Nervous System Chapter 49
1. The nervous system is the main system to communicate and coordinate body activities by
sending electrical impulses. Nervous system forms a communication network in whole body.
2. Central nervous system CNS consists of Brain and Spinal Cord. The human brain contains about
100 billion neurons, organized into circuits more complex than the most powerful
supercomputers.
3. Peripheral nervous system PNS consists of cranial nerves arising from brain and spinal nerves
connected to spinal cord. These nerves bring information into or out of Central nervous System.
PNS has also Somatic NS to pass instructions to skeletal muscles and ANS to pass instructions to
visceral organs like heart, intestine etc. ANS has 2 divisions Sympathetic and Parasympathetic.
Sympathetic division increases heart rate, breathing rate, blood pressure and is FIGHT or FLIGHT
response. Parasympathetic is antagonistic to sympathetic and induces rest by lowering heart
rate, breathing rate, blood pressure. It increases digestive activity by increasing secretions and
bowl movements. It acts by REST and DIGEST response.
4. Specialized nerve cells are called Neurons. Supporting cells are Glial cells.
5. Glial cells nourish and anchor neurons. Some are phagocytes and others build myelin sheath
around axons.
6. Sensory neurons bring information from sensory receptors like eyes to CNS.
7. Motor neurons take information from CNS to effectors like muscles or glands.
8. Association neurons receive information from sensory neurons and integrate it, interpret the
meaning and pass instructions to motor neurons to act.
9. A neuron has a cell body. Many smaller branched appendages are called Dendrites. Dendrites
bring in information (nerve impulse) to the cell body. A single longer appendage is called Axon. It
takes information away from cell body. It branches at the end into terminal knobs. A terminal
knob secretes a chemical called Neurotransmitter in the gap to the next neuron or muscle
membrane. Most common neurotransmitter secreted is Acetylcholine.
10. Resting Potential: is when a nerve fiber has more positive ions outside and more negative ions
inside (-70mV). It is not conducting any electrical impulse.
11. Action Potential (depolarization): is the sudden change on stimulation. Na+ ions move in. Now
nerve fiber has more + ions inside (+30mV). Action potential or nerve impulse travels from cell
body side to terminal knob side of axon. When the impulse reaches a part it becomes + inside
and the part just behind it, returns to resting potential, Repolarization, due to outward
movement of K+ ions.
Comparison of Nervous System in animal phyla
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Porifera does not have nerve cells.
Cnidaria have nerve cells making a nerve net. There is no CNS.
Cephalization, differentiation of head at anterior end, started in bilateral animals.
Platyhelminthes have brain at anterior end and 2 lateral nerve cords joined by nerves. A nerve is
only a bundle of nerve fibers. A ganglion is a cluster of neurons in PNS. A nerve cord has ganglia
joined by bundles of nerve fibers.
Annelida has CNS, a nerve ring with ganglia surrounding alimentary canal, at anterior end and a
solid ventral nerve cord. Each segment has one ganglion in the nerve cord.
Arthropoda also like annelids have a nerve ring surrounding alimentary canal. It is connected 2
solid ventral nerve cords with fused ganglia in each segment.
Echinoderms have a nerve ring in the central disc around alimentary canal. A radial nerve enters
each arm.
Vertebrates have well defined CNS and PNS.
Brain: has external Gray matter formed of neurons with unmyelinated axons. White matter lies
deeper to gray matter in brain and has bundles of myelinated nerve fibers. Medulla and spinal
cord have gray matter internal and white matter internal.
Brain has 3 main parts.
Fore Brain has cerebrum and diencephalon.
Cerebrum is the largest part of brain. It is divided into 2 cerebral hemispheres. Each hemisphere
has 4 lobes. It has cerebral cortex, gray matter of the folded surface. Cerebral cortex has special
primary area for different functions. It is the seat of sensory input and motor output, language
intelligence, imagination, calculations or processing. Most of the times we use word brain to
mean cerebrum.
Diencephalon has thalamus, lateral thick walls. Thalamus is the relay switch and direct
information to different centers in cerebral cortex. Hypothalamus is the floor. Pituitary gland is
attached to it. Hypothalamus controls hunger, thirst, sex drive, ANS and homeostasis like body
temperature and water/salt balance.
Cerebellum is the 2nd largest part of brain and is responsible for maintaining body posture and
balance of body.
26. Brain Stem The remaining part of brain is the Brain Stem. It has Pons and Medulla parts which
have the cardiac and breathing centers to regulate heart beat and rate of breathing.
Spinal Cord
27. The spinal cord conveys information to and from the brain and generates basic patterns of
locomotion
28. The spinal cord also produces reflexes independently of the brain
29. A reflex is the body’s automatic response to a stimulus. For example, a doctor uses a mallet to
trigger a knee-jerk reflex
30. Arousal and Sleep
31. The brainstem and cerebrum control arousal and sleep
32. The core of the brainstem has a diffuse network of neurons called the reticular formation
33. These neurons control the timing of sleep periods characterized by rapid eye movements
(REMs) and by vivid dreams.
34. Sleep is essential and may play a role in the consolidation of learning and memory
35. Emotions: Limbic System
36. Generation and experience of emotions involve many brain structures, including the amygdala,
hippocampus, and parts of the thalamus
37. These structures are grouped as the limbic system
38. Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss
39. Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in
the brain
Sensory System:
40. Human body has 5 main sensory organs which collect information about environment. Some
receptors also collect internal information like hunger, joint movement etc.
41. Skin: It gives us information about Touch, Pressure, Heat, Cold and Pain. Most receptors in skin
are present inside dermis just below epidermis.
42. Nose: It has special sensory cells which collect information about smells of vapors.
43. Tongue: It has groups of sensory cells called taste-buds. Taste-buds detect 4 main types of taste
salt, sweet, sour and bitter.
44. Eyes: Eyes collect visual information. Front of the eye is transparent to allow light to enter inside
eye. It has to pass through a diaphragm called Iris, the colored part of eye. Iris has an opening at
center called Pupil. If we get out in bright sunlight pupil quickly gets small to reduce the light
entering eye. If we enter a dark room the pupil gets bigger to increase the light entering the eye.
Eyes focus on far and near objects by changing the thickness of lens in the eye. The image is
focused on Retina, the photo-sensitive layer. Retina has cone cells – give us colored vision in
bright light and Rod Cells – give us black and white vision in dim light.
45. Ears: are the sensory organs for hearing and equilibrium. The external ear collects sound waves.
After passing a duct sound wave hit Tympanum.
46. Middle ear: Tympanum passes vibrations to auditory ossicles, small bones in middle ear. These
small bones pass vibrations to cochlea in inner ear.
47. Inner ear has 2 main parts cochlea and vestibule.
48. Cochlea a coiled duct has sensory cells that send impulses to brain. Brain interprets the meaning
of sounds.
49. Vestibule is upper part of internal ear detects changes in body position and sends impulses to
Cerebellum of brain. Cerebellum with the help of ears maintains balance = equilibrium of the
body at rest or during motion.
50. Fishes have no auditory ossicles and ear does not hear sounds. Amphibians and reptiles have
one auditory ossicle in middle ear. Mammals have 3 auditory ossicles in middle ear.