NERVOUS SYSTEM AND BEHAVIOR

INTRODUCTION

Living organisms have a unique property of receiving stimuli from environment and respond to change accordingly. The information received by the organism is coordinated through nervous system so that it can act or behave effectively for its survival under any circumstances

Nervous System

There are two divisions….

CNS and PNS

Central Nervous System

Brain

Spinal Cord Central Nervous System

Peripheral Nervous System

Peripheral Nervous System (PNS)

Cranial Nerves – emerge through cranial foramina of the skull.Reptiles, birds, and mammals have only 12 pairs of these.Spinal Nerves – emerge through intervertebral foramina. The number of spinal nerves is directly related to the number of segments in the trunk and tail of vertebrae. e.g, number of spinal nerves in frog is only 10 pairs due to reduced trunk, and no tail in adult.

Ganglia – groups of nerve cell bodies outside of the brain and spinal chord.

Autonomic Nervous System – innervates smooth muscle, cardiac muscle, and glands

Peripheral Nervous System

SpinalCord

Brain

Nerves

Neurons

The functional unit of nervous system is highly specialized cell known as neuron. these are specialized to produce signals that can be communicated over short to relatively long distance, from one part of animal body to another.

Structure of neuron

Nucleus

Cell body

Dendrite

Axon

Schwann cell

Node of Ranvier

Classification of Nerve Cells (Neurons)

A. Sensory (afferent)B. Motor (efferent)C. Interneuron

Sensory neurons act as receptor of stimuli. Change in internal and external environment stimulate sensory neurons which respond by sending signals to major integrating centre where information are processed.

Motor neuron

Motor neurons send the processed information via signals to body effectors e.g., muscles causing them to contract or to glands causing them to secrete.

Interneuron

Comprises integrating centre and receive signals from sensory neuron and transmit them to motor neurons.

Myelinization

Myelin Sheath – The specialized glial cells that wrap around the axon of neurons.

Within the CNS Oligodendrocytes

Within the PNS Schwann Cells

Unmyelinated axons

Sympathetic Nervous – Fight/Flight

Increased Heart Rate

Increased Blood Pressure

Pupil Dilation

Decreased Urination

Increased Sweating

Bronchial Dilation

Decreased Salivation

Parasympathetic – Energy Sparing

Decreased Heart Rate

Decreased Blood Pressure

Pupil Constriction

Increased Urination

Decreased Sweating

Bronchial Constriction

Increased Salivation

Neurotransmitters

Chemicals released by the pre-synaptic neuronSympathetic

Epinephrine,Norepinephrine

ParasympatheticAcetylcholine

What’s the Matter?

Grey Matter – non-myelinated neurons

White Matter – Myelinated neurons

Brain

Cerebrum – made of white and grey matter

Largest part of mammalian brain

Higher order behavior (awareness, learning)

Cerebellum – motor function and coordination

Brain Stem –Medulla Oblongata, Pons, Mid-brain

Autonomic Functions – things you don’t think about

Ventricles and Cerebrospinal Fluid

Ventricles – Open spaces in the brain, filled with fluid, that support and cushion the brain.

Cerebrospinal Fluid – slippery, clear fluid that bathes and cushions the CNS.

Produced by Choroid Plexuses

Reproduced every 24 hours

Reflexes

Spinal Reflex- rapid, automatic response to sensory input

Does not require brainTypes of reflexes

There are three types of reflexesSuperficial reflexesMyotatic reflexesRighting reflexes

Superficial reflexes Reflexes that are involved with the

skin are called Superficial reflexes.

Myotatic reflexes Reflexes that depend on impulse

from muscles are called myotatic reflexes.

Righting reflex

In spite the basic complexity of many behavioral acts controlled by central nervous system, the responses to some stimuli are often automatic and are invariable.

If a cat dropped down from a height , it will land correctly on all four due to righting reflex.

Hypothalamus

It is located in the middle of brain above the Pituitary gland and below the thalamus,and is surrounded by two cerebral hemispheres.Although a small structure,yet it is composed of relatively large number of nuclei.It perform many functions of greatest importance both for survival and for enjoyment of life.

Role of hypothalamus in feeding

Hypothalamus control the intake and output of water and food.Group of neurons in the hypothalamus when stimulated make the animal go around sniffing everything to find out if it is edible or not.The animal eat fastly when a strong current is passed through a particular region of hypothalamus.

Lateral hypothalamus

The lateral part of hypothalamus is responsible for feeding.To test its role an experiment was made on male rats,these rats had electrodes implanted in Lateral hypothalamus and were put in cages containing both nice smelling food and females.The males immediately showed intrest in females

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but as the current was passed to stimulate the neurons in Lateral hypothalamus the male rats left the females and started eating.

There are also some other factors that contribute the desire of feeding process and these are food shortage etc

APHAGIA

Bilateral lesions located in the area of the lateral hypothalamus can produce aphagia. Affected animals may starve, even with food and water available

hyperphagia

The lateral hypothalamus had the feeding center and if this center was stimulated it caused excessive eating called as Hyperphagia. It caused Hypothalamic hyperphagia syndrome.

Anand and brobeck observed that if a center in ventromedial hypothalamus stimulated aphagia was caused and its destruction brought about hyperphagia.They named this center as Satiety Center.Hethrington showed that bilateral destruction of the ventromedial hypothalamic nuclei

Satiety centre

Alone produced obesity,this was caused by voracious over eating and was called “ventromedial hypothalamic syndrome”

Role of hypothalamus in reproductive behavior

The hypothalamus control reproductive behavior either through pituitary or directly. The pituitary secrete several hormones concerned with regulation of sexual behavior and reproductive physiology.

Hormones of Pituitary

The gonadotropic hormone stimulate the development of ovaries and secretion of estrogen in the female, it trigger spermatogenesis and secretion of androgen in the males.Luteinizing and lactogenic are involved in the regulation of maternal activities.

Controlling centre for reproductive behavior

The nuclei of the hypothalamus organizing sexual behavior are situiated in anterior hypothalamus.

Fisher and co workers observed that female cats with anterior hypothalamic lesions did not mate.

Role of hypothalamus in reward and punishment

Olds discovered that there are groups of nuclei in posterior hypothalamus which are known as reward and punishment centre.Olds implanted electrodes with the lever which the rat could press,in the pleasure centre of rat. Whenever the rat pressed it excited its own pleasure center.

The rat found it extremely pleasing and pressed it 5000 times in an hour without any pause till he fell with exhaustion. olds kept the same rat in a cage and starved him, later Olds offer the rat nice odorous food, but still the rat prefer pressing the lever to get the pleasure, rats pressed the lever without any pause, though tired still he dragged the body back to lever for more and more pleasure, the rat did almost anything to get at lever, even hopped across a painful electrified grid.

Stimulation of another specific cluster of nuclei in posterior hypothalamus causes the animal to show all the signs of pain,Displeasure and punishment. Prolonged stimulation of such area causes the animal to become severly sick and sometime this may even lead to death.

Role of hypothalamus in fighting and fleeing

Hess discovered that the stimulation of certain nuclei in lateral and posterior hypothalamus caused aggression, attack or fight.He further found that when he stimulated these neurons in hypothalamus with the minimal current the animal just show a state of vigilance,as the current was increased the reaction became more intense, finally when the intensity of the current was..

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Increased more and more at the same locus in hypothalamus the animal showed an actual attack. The cat jumped with rat on experimenter and when the current was switched off, the animal calmed down quickly.

Role of hypothalamus in Sleeping and waking

Sleep wake phenomenon has been of great importance and has drawn attraction of various workers since earlier. A Russian surgeon reported a very interesting case of soldier. On whom he had operated during war time a metal fragment had entered the patient skull and had lodged in the anterior hypothalamus.

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When the surgeon operating under local anesthesia tried to pull the piece of metal out the patient immediately fell of to sleep. the surgeon got upset thinking that the patient had fainted. after sometime the patient woke up and when questioned, said he had an irresistible urge to sleep. the surgeon drive from the incidence that the anterior hypothalamus had the center for sleep.

Hess reestablished posterior hypothalamus is a waking center. In the pathological conditions of epidemic encephalitis the patient go into a state of comma this is due to inhibition in the activity of posterior hypothalamus.

Hypothalamus and other activities

Various component of emotional reactions are organized here. this center is situated in posterior hypothalamus and controls fear, anxiety, pleasure, rage, irritation and attack. Lesion in this center can make a person like a vegetable who is difficult to arouse emotionally.