Neurobiological Basis of Behavior

• Neuron/nerve cell- is the basic structural unit of the nervous system.
• Neuron is made up of what?

  Cell body or soma from which arise never processes, viz.., the axon and dendrites
• The cell body or soma contains nucleus that is centrally located.
• It is regarded as a trophic center, i.e. the cell body serves as a center for nourishment
• Axon- described as cellifugal, which, means, it conducts neural impulses away from the cell body
• Dendrites- described as cellulipetal, which means conducts neural impulses away from the cell body
• At the peripheral endings of the axon is a branched terminal portion which is called the end-brush
• The end-brush terminates in knob-like structures known as sypnatic knobs or sypnatic thermal
• Within the sypnatic knobs are synaptic vesicles which contain neurotransmitter substances such as acetylcholine, norepinephrine, and gamma-aminobutyric acid among others
• The neurotransmitter substances released by the sypnatic termals are either excitatory or inhibitory
• These neurotransmitter substances play a significant role in transmission of nerve impulses from one neuron at the junction known as the synapse
• Acetylcholine

  • Facilitates learning and memory

  •Deficiency of Ach disrupts learning and memory
• Norepinephrine

  •Too little of norepinephrine may lead to depression

  •Too much causes hyperactivity
• Dopamine

  • Over supply of dopamine may lead to schizophrenic reaction.

  • undersupply causes Parkinson's Disease ( a neurobiological Disorder disrupting coordinated movement)
• Serotonin

  • lack of serotonin produces insomnia

  • prevent dreaming in the waking state

  • considered as the "worry" chemical in the brain
• GABA (gamma aminobutyric acid)

  • decreases the activity of the neuron; may decrease levels of anxiety
• Neurons are classified according to the function performed
• A sensory or afferent neuron- send neural impulses from the receptor to the brain
• Motor or efferent neuron- sends neural impulses from the brain to the effectors located in the peripheral organs such as muscles and glands
• Sensation of vision, audition, olfaction, gustation and cutaneous sensibilities such as pain, touch, pressure, and thermal senses involve sensory neurons
• Writing, walking, playing the piano, packing up an object, or kicking a ball involve neurons that send efferent signals for muscular contractions and glandular secretions.
• Interneuron- conducts neural impulses from a sensory neuron to a motor nerve cell.
• Interspersed among the neurons are the glial cells which serve as the structural supportive framework of the nervous system
• A mature neuron does not have the capacity to multiply.
• A mature neuron does not possess the cytoplasmic organelle that initiates cell division. It can only regenerate in response to an injury.
• A nerve fiber is covered by a white tissue called myelin sheath
• The myelin sheath runs along the fiber and is interrupted at fairly regular intervals producing the nodes of ranvier
• Due to the insulating effect of the myelin sheath, the large myelinated fiber conduct neural impulses faster than the smaller unmyelinated fibers
• This is due to the saltatory type of nerve impulse transmission, i.e., from node yo node
• A neuron manifested irritably or the ability to respond stimulus
• Once excited, the neuron shows itd irritability by generating and transmitting action potentials or nerve impulses to and from the brain
• These neural impulses (irritability) are electro-chemical in nature and are transmitted from one neuron to another neuron at junction known as the synapse. A neuron is irritable when the membrane is in it's resting membrane potential or in a polarized state.
• This state is characterized by negativity inside the membrane and positivity outside the membrane
• The negativity inside the membrane is due to the preponderance of anions or negatively charged ions while yeh positivity outside the membrane is caused by predominance of cations or positively charged ions
• There are two chief ions which play significant role in the transmission of neural impulses. The extracellular ions and intracellular ion
• The chief extracellular ions are the sodium ion(Na+)
• When a nerve is stimulated, the flow of movement of sodium ions is from the outside where there is greater concentration of sodium ions to the inside of the cell. This movement shows an inward diffusion of sodium ions of what is referred to as Na+ influx
• The chief intracellular ion is the potassium ion (K+) and its movement shows an outward diffusion or what is known as K+ efflux
• The diffusion of this ions causes changes in the electrical membrane potential. Embedded in the cell membrane are numerous ions channels and ion pumps. These ion channels which are protein molecules from porrf across the cell membrane.
• They are selective, allowing only the diffusion of a particular ion. The uneven distribution of ions across the membrane is brought about by ion pumps which are protein structures that cause inflow and outflow of ions across the membrane