Sense of Hearing

                                  

Hearing (or audition) is an organism’s ability to receive mechanical energy in the form of sound waves. Sound wave is thus the stimulus for auditory sensation. Receptor cells of the ear are excited by the sound waves. Frequency and intensity of sound determines the nature of sound. 20 – 20,000 per second sound frequency is possible to denote and distinct.

When an object makes a noise, it sends vibrations (known as sound waves) speeding through the air. Such sound waves from external environment at first reach to outer ear (or pinna). These vibrations are then funneled into ear canal by outer ear. As the vibrations move into middle ear, they hit the eardrum and cause it to vibrate as well. This sets off a chain reaction of   vibrations. Eardrum, which is smaller and thinner than he nail on the pinky finger, vibrates the three smallest bones: hammer, anvil, and the stirrup consecutively. These structure transfer vibrations from eardrum to oval window. The vibration then passes into a coiled tube in the inner ear called the cochlea. The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into message that are sent to the brain through the auditory nerve. The auditory nerve carries message from 25,000 receptors in ear to the brain. The brain then makes sense of the messages and tells what sounds you are hearing.

THE SENSE OF EYE

                      

The most thoroughly studied sensory process is the sense of vision. In visual sensation the light energy (in visible range) enters the eye by passing through cornea, transparent area that allows light to pass into the eye .Then the light energy passes to pupil (the whole center of the iris). When light rays pass through pupil, the muscle called the iris (colored ring) makes the size of the pupil change depending on the amount of light that’s available. You may have noticed this if you have looked at it closely in a mirror. If here is too much light, pupil will shrink to limit the number of light rays that enter. Likewise, if there is very little light available, the pupil will enlarge to let in as many light rays as it can. Just behind the pupil is the lens which focuses the image through a jelly- like substance called the vitreous humor onto the back surface of the eyeball, called the retina. The eye has a complex structure consisting of a transparent lens that focused light on the retina. The retina is covered with two basic types of light-sensitive cells- rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. These cells are located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The point of this connection is called the “blind spot” because it is insensitive to light. Light rays then pass through three layers of neuronal tissue, are transduced into action potentials and are transmitted through the occipital nerve to the visual region of the brain, where hey are registered and interpreted as sights. Many neurons in the visual cortex, called feature detectors, are specialized and are activated only by stimuli of a specific shape or pattern.

The brain combines the input of our two eyes into a single three-dimensional image. In addition, even though the image on the retina is upside-down because of he focusing action of the lens, the brain compensates and provides the right-side-up perception. Experiments have been done with subjects fitted with prisms that invert the images. The subjects go through an initial period of great confusion, but subsequently they perceive the images as right side up.

SENSATION AND PERCEPTION

                      
 

Sensation and perception are fundamental topics in psychology because behavior is the reflection of how one receives, interprets and reacts to stimuli. Sensations regarded as pre-awareness and perceptions regarded as a window to outside world and a preparation for appropriate behavior. Sensation is very simple process and is raw material for perception. Perception is a complex and complete cognitive process. To understand the process of perception it is essential to understand the process sensation. Sensation is regarded as the primary and perception as secondary process. Without sensation perception is not possible

Environment stimulus as such does not enter in the brain directly.  Stimulus is a physical energy and when this physical energy stimulates the sense organs the receptor cells of the sense organs are activated. Each sense organ is programmed to receive a unique form of stimulus. It is termed as appropriate stimuli. For example, eye will never be stimulated by sounds. To receive the physical by sense organs energy conversion process is activated. This process is known as transduction. The receptor cells transduce the physical energy into neural impulses and transmit to the brain via neurons. Usually neural impulses pass through the spinal cord to specific brain centers depending upon the location of sense organs. Simple mental process occurs in the brain center. This process is primary and is called sensation. Thus, sensation is the detection of information about external and internal environment and the transmission of that information to the brain.

Generally, stimulus can excite more than one sense organ e.g., food excites the visual sensory receptor cells of the olfactory cells and gustatory cells. If one touches the food it also excites the cutaneous cell. We get a sensation only when some sense organ is stimulated. A stimulus is any change in outside or inside energy (e.g., muscle pain or hunger) that arouses a sense organ and its receptors. I is a stimulus only when it stimulates. Light is not a stimulus to a blind man or sound to a deaf man.

                                  

Nervous System

                          

Nervous system is the body’s speedy, electrochemical communication system, consisting of all nerve cell of the peripheral and central nervous system. It is the sum totals of tissues that record and distributed information within individual. It is the complex network of neurons that regulates bodily processes and is ultimately responsible for all aspect of conscious experience. The nervous system can broadly be divided into central and peripheral nervous system.

1 Central Nervous System: The central nervous system is that part of the nervous system which consists of the brain and spinal cord. The brain is enclosed in the skull, and the spinal cord within the spinal canal of the vertebral column. Brain and spinal cord are joined at the base of brain so that there is a constant passage of signals to and from the brain. It has also two main parts are Brain and spinal cord.

2 Peripheral Nervous System: All of the nervous system outside the brain and spinal cord is known as peripheral nervous system. It is the portion of nervous system that connects internal organs and glands as well as voluntary and involuntary muscles to central nervous system. It has 31 pairs of spinal nerve and 12 pairs of cranial nerves to carryout it function. It also can be divided into two divisions are Somatic nervous system and Autonomic nervous system

Function of neuron

Communication between neurons: in order o communicate the message  of nervous system, two neurons must communicate information. But the neurons do not actually meet. There is a gap between the axon terminal of one neuron and dendrite of another neuron. This is called synapse. Within the axon terminals of a neuron there are many structures called synaptic vesicles which contain chemical substances called neurotransmitters. When the axon potential reaches to axon terminals the synaptic vesicles release neurotransmitters that that travel across the tiny synaptic gap until they reach specialized receptor sites in the membrane of the other cell. Different neurotransmitters have different receptors sites so that neurotransmitter fit like key into lock. The neurotransmitters either produce excitatory or inhibitory effect depending upon the nature of neurotransmitter. After they complete their tasks neurotransmitters are either taken back for reuse in axon terminals (reuptake) or they are chemically deactivated.