Neuron/Neurotransmitter and Behaviors – Behavioral sciences explore the cognitive processes within organisms and the behavioral interactions between organisms in the natural world. It involves the systematic analysis and investigation of human and animal behavior through the study of the past, controlled and naturalistic observation of the present and disciplined scientific experimentation and modeling.
It attempts to accomplish legitimate, objective conclusions through rigorous formulations and observation. Generally, behavior science deals primarily with human action and often seeks to generalize about human behavior as it relates to society.
Neuron/Neurotransmitter and Behaviors
Definition of Neuron:
The neuron is the basic unit in the nervous system. It is a specialized conductor cell that receives and transmits electrochemical nerve impulses. A typical neuron has a cell body and long arms that conduct impulses from one body part to another body part.
Parts of Neuron:
There are three different parts of the neuron:
- The cell body
- Dendrites
- Axon
A. Cell body of a neuron
The cell body is like any other cell with a nucleus or control center.
B. Dendrites
The cell body has several highly branched, thick extensions that appear like cables and are called dendrites. The exception is a sensory neuron that has a single, long dendrite instead of many dendrites. Motor neurons have multiple thick dendrites. The dendrite’s function is to carry a nerve impulse into the cell body.
C. Axon
An axon is a long, thin process that carries impulses away from the cell body to another neuron or tissue. There is usually only one axon per neuron.
Classification of Neuron:
According to the number of processes:
➤ Unipolar: Neuron containing single process that is axon. e.g. Mesencephalic nucleus of trigeminal nerve.
➤ Bipolar: Neuron containing two processes, one axon one dendrite. e.g. Bipolar cells of retina.
➤ Multipolar: Neuron containing more than two processes, one axon & other dendrites. e.g. – Dorsal & ventral horn cells of spinal cord.
➤ Pseudounipolar: Originally bipolar but inturn two process fused into one. e.g. Dorsal root ganglia
According to function:
➤ Motor neuron (Efferent neuron): Neurons that carry impulse away from the cell body.
➤ Sensory neuron (Afferent neuron): Neurons that carry impulse towards the cell body.
According to the length of the axon:
➤ Golgi type-I: Neurons having long axon.
➤ Golgi type -II: Neurons having short axon.
According to the position:
➤ Upper motor neuron (UMN): Pyramidal cell and its axon is called UMN
➤ Lower motor neuron (LMN): Anterior horn cells and its axons are called LMN
Figure: Different types of neurons
Definition of Neurosis:
Neurosis is a mental and emotional disorder that affects only part of the personality, is accompanied by a less distorted perception of reality than in a psychosis, does not result in disturbance of the use of language, and is accompanied by various physical, physiological, and mental disturbances (such as visceral symptoms, anxieties, or phobias).
Definition of Neurotransmitter:
Neurotransmitters are chemical substances that are secreted when the axon terminal of a presynaptic neuron is excited and transmit nerve impulse across the synapse (from neuron to neuron and from neuron to effector cells) either to excite or inhibit the target cells.
Characteristics of Neurotransmitter:
To be considered as a post-junctionally acting neuro-humoral transmitter a substance must fulfill the following criteria:
- It should be present in the presynaptic neuron (usually along with enzymes synthesizing it).
- It should be released in the medium following nerve stimulation.
- Its application should produce responses identical to those produced by nerve stimulation.
- Its effects should be antagonized or potentiated by other substances which similarly alter effects of nerve stimulation
Classification of Neurotransmitter:
A. Excitatory neurotransmitter:
a) Acetylcholine
b) Nor-adrenaline
c) Adrenaline
d) Glutamate
B. Inhibitory neurotransmitter:
a) GABA (Gamma amino-butyric acid)
b) Dopamine
c) Glycine
d) Serotonin
e) Taurine
f) Alanine
C. Mixed neurotransmitter:
a) Enkephalins
b) 5-HT
c) Histamine
d) Prostaglandin
e) Nor-epinephrine
Other Types of Neurotransmitters
A. Centrally acting:
a) Acetylcholine
b) Dopamine
c) Serotonin
d) Histamine
B. Peripherally acting:
a) Acetylcholine
b) Nor-epinephrine
C. According to chemical nature:
Classical” neurotransmitters
a) Acetylcholine (Ach)
b) Amines:
- Catecholamines:
✓ Epinephrine (E),
✓ Nor epinephrine (NE) and
✓ Dopamine (DA)
- Histamine (H)
- Serotonin (5-HT)
c) Amino acids (in CNS);
- Aspartate (aspartic acid)
- Glutamate (glutamic acid)
- Gamma-aminobutyric acid (GABA) and
- Glycine
Peptide Neurotransmitters:
a) Substance P, Beta endorphin. Enkephalin,
b) Somatostatin, Vasopressin, Angiotensin II,
c) Gastrin, Cholecystokinin.
d) Oxytocin, Neuropeptide Y. etc.
Nice to Know
Major Neurotransmitter:
| Type | Mechanism of Action | Physiologic Effects |
| 1. Dopamine | Excitatory | Controls complex movements, motivation, cognition; regulates emotional response |
| 2. Norepinephrine | Excitatory | Causes changes in attention, learning and memory, sleep and wakefulness, mood |
| 3. Epinephrine | Excitatory | Controls fight-or-flight response |
| 4. Serotonin | Inhibitory | Controls food intake, sleep and wakefulness, temperature regulation, pain control, sexual behaviors, regulation of emotions |
| 5. Histamine | Neuromodulator | Controls alertness, gastric secretions, cardiac stimulation, peripheral allergic responses |
| 6. Acetylcholine | Excitatory or inhibitory | Controls sleep and wakefulness cycle; signals muscles to become alert |
| 7. Neuropeptides | Neuromodulators | Enhance, prolong, inhibit, or limit the effects of principal neurotransmitters |
| 8. Glutamate | Excitatory | Results in neurotoxicity if levels are too high |
| 9. Gamma- aminobutyric acid (GABA) | Inhibitory | Modulates other neurotransmitters |
Functions of Cerebellum:
- Control of voluntary activity (via pyramidal system).
- Control tone, posture & equilibrium (via extra pyramidal system).
- Maintains the motor activity of the distal part of limbs. E.g.- hand, fingers, feet, toes etc.
- Concerned with overall planning & time of the sequential motor activity
Functions of Neo-Cerebellum:
The lateral portions of cerebellar hemispheres are called neo-cerebellum.
The functions of neo-cerebellum are:
- Planning & programming of movements by interacting with the motor cortex.
- Helps in muscular co-ordination.
- Responds to proprioceptive, tectile, visual & auditory stimulation.
Definition of Hypothalamus:
The hypothalamus is a very small, but extremely important part part of the diencephalon that is involved in the mediation of endocrine, autonomic and behavioral functions?
Functions of Hypothalamus:
1. Thermoregulation:
if there is cold environment in the outside
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There is cutaneous vasoconstriction, standing up of the fur (horripilation) and shivering occurs.
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Temperature loss is decreased as well as gaining of temp, occur
Or
When there is hot environment
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There is sweating, cutaneous vasodilatation and relaxation of muscle tone occurs.
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Normal temperature is maintained.
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These functions are maintained by hypothalamus. Thus hypothalamus acts as a thermostat.
2. Behavior & emotions:
This includes-
- Hunger & satiety.
- Sex & mating
- Thirst & drinking
- Defense reactions
- Emotions like rage and panic
3. Control of endocrine gland:
- Various releasing hormones (CRH/GnRH/ TRH/ GHRH etc) of hypothalamus control the anterior pituitary. The anterior pituitary, in turn, control many different endocrine glands.
4. Control of autonomic nervous system!
5. Acts as a biological clock.
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