Category: 12th Zoology

Hypothalamus

Hypothalamus represents the central part between the nervous system and endocrine system. Though pituitary is designated as the master
gland controlling the functions of other endocrines, the pituitary itself is
controlled by the hypothalamus. The above control is effected by means of
releasing hormones or factors and inhibitory hormones or factors.

The hypothalamus is connected to the posterior lobe of pituitary by the
neural tissue and to the anterior lobe of pituitary by the epithelial tissue.
The releasing factors from the hypothalamic cells reach the anterior pituitary
through their axons. The hormones from the pituitary enter the blood stream.

Chemical co-ordination – Functions of Endocrine glands

Post author By Mr. Padeepz
Post date September 23, 2018
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Chemical co-ordination

The two major systems of the human body that coordinate, regulate
and integrate almost all physiological functions are the nervous system and
the endocrine system. The information transmitted by the nervous system in
the form of electric impulses is conducted rapidly in the neurons. The signals
from the endocrine glands or ductless glands are communicated by means of
chemical substances called hormones. The hormones are secreted into and
carried by the blood stream from their point of origin to the target organs or
tissues. In the target tissues, the hormone action is manifested.

A hormone may be defined as a chemical substance synthesized by
the cells of endocrine glands and carried by blood to the site of action where
it exerts its physiological effects. Hormones are considered as chemical
messengers.

Functions of Endocrine glands

Endocrine glands play an important role in maintaining the constancy
of internal environment (milieu interior) and hormones integrate and
regulate various physiological functions. They regulate the general
metabolism viz., the metabolism of carbohydrates, proteins, fats, minerals
and water. The endocrine glands also control the reproductive functions of
animals. The adrenal hormones prepare the body to meet emergency and
stressful situations. The hormones are also responsible for intercellular
communication.

Each endocrine gland may secrete excess quantities of its own
hormone. However, once the normal physiological response is over, this
information is fed back to the endocrine gland. As a result, its secretion
decreases or inhibited. Conversely, if the secretion of the hormone is
subnormal and the physiological effects or responses are reduced, the
information is taken to the gland and it secretes the hormone at an increased
rate. Thus, homeostatic equilibrium is restored.

Spinal cord functioning

The spinal cord remains as a connecting, functional nervous structure
in between the brain and sensory / effector organs. The sensory inputs
received by sense organs are conducted towards appropriate regions of the
brain. Similarly from the brain motor sensations are transmitted towards
effector structures. Further as the brain, the spinal cord can effect motor
initiation and bring about an effect. This activity is known as reflex action.

Reflex action

Reflex action is the spontaneously involuntary response caused due
to stimulation of receptor organ. E.g. The quick closure of eye lid when
some object touches the eyelashes.; the sudden withdrawl of hand when the
hand touches hot pan.

A reflex action is an involuntary process and does not involve the
intervention of consciousness. The anatomical basis of reflex action is the
reflex arc. It is a nerve chain between receptor organ and effector organ.
The reflex arc has the following route.
Sensory organ ® sensory or afferent neuron ® grey matter of the
spinal cord ® intermediary or relay neuron ® efferent or motor neuron ®
effector organ.

Cerebro Spinal Fluid (CSF)

The ventricle of the brain and the central canal of the spinal cord
contain, a clear fluid similar to plasma called cerebrospinal fluid (CSF).
CSF is formed by a group of cells called the choroid plexus located inside
the four ventricles. In human the volume of CSF is 150 ml and the rate of its
secretion is 550 ml/day. (Spinal cord)

Functions (Spinal cord)

1. CSF cushions the brain against mechanical shock when the head moves.
2. It acts as a protective covering for the CNS and confers buoyancy to
brain.
3. The CSF also provides a reservoir of hormones and nutrition for the brain
and spinal cord.
4. It acts as a mechanical buffer. Remaining inside and outside the CNS, it
equalizes the mechanical pressure. If the intracranial pressure tends to rise
the CSF is pressured out. If the pressure tends to fall, more CSF is retained.

Right and Left brain concept

Post author By Mr. Padeepz
Post date September 22, 2018
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Right and Left brain concept

In the cerebral cortex, the left hemisphere is connected to the skin
receptors in the right half of the body. It also controls the muscles on the right side of the body.

The right hemisphere is connected to the sensory receptors on the
left half of the body. Further, it controls muscles on the left side. Both the hemispheres are also connected to the eyes. The sensory nerve tracts of the left eye is connected to the right hemisphere and the right eye to the left hemisphere through the optic chiasma.

Thus the left half sees the right half of the world while the right half sees only the left half of the world.

The left and right hemispheres exchange information through a set of
axons called the corpus callosum, and also through anterior commissure and hippocampal commissure.

The two hemispheres have their own specific functions and the above division of functions or labour between the two
hemisphere is called ‘lateralization’. (Right and Left brain concept)

The corpus callosum enables the right and left half of the brain to
operate cooperatively, instead of independently. The anterior commissure plays an important role in unifying the emotional responses of two sides of brain.

Damage to the corpus callosum blocks the exchange of information
between the two hemispheres.

The left brain is concerned with language, number skills, reasoning,
spoken language, scientific skills and right hand control.

The right brain is concerned with art awareness, imagination, visual
functions, emotions, music awareness, 3D forms and left hand controls. The left brain is meant for analytical tasks while the right brain is for creative tasks. (Right and Left brain concept)

Electroencephalography EEG

Post author By Mr. Padeepz
Post date September 22, 2018
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Electroencephalography (EEG)

The tissues of the cerebral cortex consists of a vast range of neuronal elements. The brain tissue is characterized by a continuous rhythmic oscillation of electric potential. EEG is a device to record electrical activity of the brain via electrodes attached to the scalp. It displays a net average of all the neuron’s potential. Electroencephalography EEG yields information about the brain function in health and disease. It provides data about brain functions during various functional or behavioral activities such as sleeping or waking states. It is also used in the diagnosis of brain disease such as tumour, lesions and also in
epilepsy.

Conditioned reflex

Conditioned reflexes

The Russian Physiologist Ivan Pavlov first demonstrated ‘the
conditioned reflexes’ phenomenon. The cerebral cortex controls the
conditioned reflexes. It is also called the classical conditioning, in which a
stimulus comes to elicit a response similar to the response produced by some
other stimulus.

In his experiment, Pavlov presented a dog with a sound of a bell
(Neutral stimulus) followed by meat (Unconditioned stimulus). This
combined stimuli stimulated the dog to salivate (unconditioned response).
After many such conditioned pairings the sound alone (Conditioned
stimulus) would stimulate the dog to salivate (Conditioned response – CR).

The bell sound initially called the neutral stimulus which after a
number of trials pairing with the unconditioned stimulus viz., the meat piece,
becomes the conditioned stimulus. Similarly the salivation of the dog during
the initial trials of pairing (NS + UCS) is called Unconditioned Response
(UR).

This unconditioned response later on becomes designated into a
conditioned response (CR). It will be elicited just by bell sound (CS).
The conditioned reflexes are developed in animal’s life in association
with previously established reflexes. This is the basis of learning and memory.

Alzheimer – Meningitis (Brain fever)

Post author By Mr. Padeepz
Post date September 22, 2018
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Alzheimer Disease

Alzheimer disease is otherwise called Chronic brain syndrome.
It is characterized by progressive loss of memory followed by general loss
of cognitive functions and death. This disease becomes more and more
prevalent among aged persons. Occasionally people develop the disease
before 50 or even before the age of 40. It affects less than 5 per cent of the
population between 65 – 74. In the aged people beyond 80 almost 50 per
cent are affected invariably.

Alzheimer disease is associated with the atrophy of cerebral
cortex. Neurons undergo degeneration. In the damaged regions, plaques
formed by the degeneration of axons and dendrites, appear.
Alzheimer’s disease is commonly attributed to genetic mutation.
People with Down syndrome are invariably affected with this disease. It is
presumed that atleast two or three genes in chromosome 21 are linked to
this disease. However genetics is not the only etiological factor, for this
disease.

Meningitis (Brain fever)

The term Meningitis refers to the inflammatory condition of the brain
membranes and the sub-arachnoid space. Meningitis may be caused by
bacterial infection, or viral infection or fungal infection. The clinical
symptoms of meningitis include headache, photophobia, irritability, stiffness
of the neck, fever and other neurological symptoms.

Stroke – Brain haemorrhage

Post author By Mr. Padeepz
Post date September 21, 2018
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Stroke Brain haemorrhage:

“Stroke is a rapidly developed clinical sign of focal disturbances of
cerebral function lasting more than 24 hours or leading to death”. (WHO)
Inspite of the presence of factors inhibiting the coagulation of blood
within vessels, clotting may occur at times. Such clots frequently are formed
in veins than in arteries.

The blood clot or thrombus formed in the streaming
blood is called thrombosis. A clot in the cerebral vessel is called stroke or
cerebral thrombosis. Stroke may be caused due to vascular occlusion, which
is a blockage in the cerebral artery. The occlusion and stroke lead to
infarction. The infarction leads to abnormal symptoms in the brain.
Vascular occlusion is of two types viz., Thrombotic and embolic. An
embolus is a portion of the thrombus clot that becomes detached and enters
into circulating blood. An embolus may block the circulation to vital parts
leading to serious consequences.

Brain haemorrhage:

Haemorrhage or bleeding of brain vessels may be
caused by hypertension which results in bursting of blood vessels or due to
aneurysm wherein the arterial wall bulges and forms a sac like structure and
ruptures later. The stroke and the haemorrhage are also due to vascular
malformations.

Stroke causes both physical; and mental crippling. It is a worldwide
health problem. It can occur at any age. Several risk factors may lead to
stroke and brain haemorrhage. They are cardiac abnormalities, diabetes,
elevated blood lipids, hypertension, obesity, smoking and stenosis (narrowing
of valvular orifice), etc.
One can control stroke by controlling the above risk factors.

Sleep – Types of sleep

Sleep

Sleep is defined as a state of unconsciousness from which a person can
be aroused by appropriate sensory or other stimuli.

Types of sleep

During each night a person goes thorugh two stages of sleep that
alternate with each other. They are (1) Slow wave sleep and (2) REM sleep.

Slow wave sleep

In this type of sleep the brain waves are very slow.
Though this sleep is frequently called “dreamless sleep”, dreams actually occur
very often and even nightmares occur during this sleep. During this sleep the
process of consolidation of the dreams in memory does not occur. This sleep
is highly useful in decreasing blood pressure, respiratory rate and basal
metabolic rate.

REM sleep or Rapid eye movement sleep

In a normal night sleep, REM sleep lasting 5-30 minutes usually appear on an average every 90 minutes. It is usually associated with active dreaming. The muscle tone throughout the body is exceedingly depressed during this sleep
indicating strong inhibition of the spinal projections from the reticular
formation of the brain stem.

The heart rate and respiration usually become irregular, which is
characteristic of the dream state. During REM sleep, the brain is quite
active. But, the brain activity is not channeled in the proper direction for
persons to be aware of their surroundings and therefore to be awake.

Physiological effects of sleep

Sleep restores both normal sensitivities of nervous system and “balance” among the different parts of the central nervous system. Due to good sleep arterial blood pressure falls, pulse rate decreases, skin vessels dilate, muscles fall into relaxed state and overall metabolic rate of the body falls by 10-30 percent.

Unit 2 – Microbiology Topic List Zoology

12th Zoology

Memory – Types of memory

Memory

The term ‘memory” denotes a specific brain function of storing and
retrieving of informations related to experiences. The duration of memory
varies from few seconds or hours, to several years.

Types of memory

Sensory memory

It means the ability to retain sensory signals in the sensory areas of the brain for a short interval of time following the actual sensory experience. This is the initial stage of memory process.

Primary memory

It is the memory of facts, words, numbers, letters or other information. The information in this memory is instantaneously made available so that a person need not search through his or her mind for it.

Secondary memory

It is the storage in the brain of information that can be recalled at some later time(hours, days, months or years later). This is also called long-term memory, fixed memory or permanent memory.

Physiology of memory

Certain anatomical, physical or chemical changes occur in the pre synaptic terminals (a part in the neuron) or perhaps in whole neurons that permanently facilitate the transmission of impulses at the synapses.

All the synapses (nerves junctions) are thus facilitated in a thought
circuit. This circuit can be re-excited by any one of many diverse signals at
later dates thereby causing memory. The overall facilitated circuit is called a memory engram or a memory trace.

Amnesia

Amnesia means memory loss. It is the inability to recall memories from the past.

Hypothalamus

Related Topics in Zoology:

Chemical co-ordination

Functions of Endocrine glands

Related Topics in Zoology:

Spinal cord functioning

Reflex action

Cerebro Spinal Fluid (CSF)

Functions (Spinal cord)

Related Topics in Zoology:

Right and Left brain concept

Related Topics in Zoology:

Electroencephalography (EEG)

Related Topics in Zoology:

Conditioned reflexes

Related Topics in Zoology:

Alzheimer Disease

Meningitis (Brain fever)

Related Topics in Zoology:

Stroke Brain haemorrhage:

Brain haemorrhage:

Related Topics in Zoology:

Sleep

Types of sleep

Slow wave sleep

REM sleep or Rapid eye movement sleep

Physiological effects of sleep

Related Topics in Zoology:

Unit 2 – Microbiology Topic List Zoology

Memory

Types of memory

Sensory memory

Primary memory

Secondary memory

Physiology of memory

Amnesia

Related Topics in Zoology:

Unit 2 – Microbiology Topic List Zoology