NEURON STRUCTURE AND TYPES NEURONS BASIC UNITS OF

NEURON STRUCTURE AND TYPES

NEURONS § BASIC UNITS OF THE NERVOUS SYSTEM § RECEIVE, INTEGRATE, AND TRANSMIT INFORMATION § OPERATE THROUGH ELECTRICAL IMPULSES § COMMUNICATE WITH OTHER NEURONS THROUGH CHEMICAL SIGNALS

BASIC STRUCTURE

THE NERVOUS SYSTEM The Nervous System Central Nervous System (CNS) Brain Peripheral Nervous System (PNS) Spinal Cord Motor Neurons Somatic Nervous System • voluntary movements via skeletal muscles Sympathetic - “Fight-or-Flight” responses Sensory Neurons Autonomic Nervous System • organs, smooth muscles Parasympathetic - maintenance

TYPES

SENSORY NEURONS ARE TYPICALLY CLASSIFIED AS THE NEURONS RESPONSIBLE FOR CONVERTING VARIOUS EXTERNAL STIMULI THAT COMES FROM THE ENVIRONMENT INTO CORRESPONDING INTERNAL STIMULI. THEY ARE ACTIVATED BY SENSORY INPUT (VISION, TOUCH, HEARING, ETC. ), AND SEND PROJECTIONS INTO THE CENTRAL NERVOUS SYSTEM THAT CONVEY SENSORY INFORMATION TO THE BRAIN OR SPINAL CORD. UNLIKE NEURONS OF THE CENTRAL NERVOUS SYSTEM, WHOSE INPUTS COME FROM OTHER NEURONS, SENSORY NEURONS ARE ACTIVATED BY PHYSICAL MODALITIES SUCH AS LIGHT, SOUND, AND TEMPERATURE.

RELAY NEURON A RELAY NEURONIS A NEURON THAT FORMS A CONNECTION BETWEEN SENSORY NEURON AND MOTOR NEURON IN THE CENTRAL NERVOUS SYSTEM.

MOTOR NEURON IN NEUROLOGY, THE TERM MOTOR NEURON APPLIES TO NEURONS LOCATED IN THE CENTRAL NERVOUS SYSTEM THAT PROJECT THEIR AXONS OUTSIDE THE CNS AND DIRECTLY OR INDIRECTLY CONTROL MUSCLES. MOTOR NEURONS ARE NEURONS THAT CARRY SIGNALS FROM THE SPINAL CORD TO THE MUSCLES TO PRODUCE MOVEMENT.

STRUCTURE

CELL BODY THE PART OF A NEURON CONTAINING THE NUCLEUS BUT NOT INCORPORATING THE AXON AND DENDRITES.

AXON AN AXON ALSO KNOWN AS A NERVE FIBER; IS A LONG, SLENDER PROJECTION OF A NERVE CELL, OR NEURON, THAT TYPICALLY CONDUCTS ELECTRICAL IMPULSES AWAY FROM THE NEURON'S CELL BODY. THE FUNCTION OF THE AXON IS TO TRANSMIT INFORMATION TO DIFFERENT NEURONS, MUSCLES AND GLANDS.

• • • AXON FIBERS FORM THE NERVE LONG CYLINDRICAL PROCESS EXTENDS AWAY FROM CELL BODY TRANSMITS OUTPUT SIGNALS (ACTION POTENTIAL ) CONTAINS ORGANELLES , CYTOSKELETON, AXOPLASM AXON HILLOCK - INITIAL SEGMENT PORTION OF NEURON AXON TERMINAL – AXON DIVIDES INTO SEVERAL PROCESSES AND HAS SYNAPTIC KNOBS

DENDRITES ARE THE BRANCHED PROJECTIONS OF A NEURON THAT ACT TO CONDUCT THE ELECTROCHEMICAL STIMULATION RECEIVED FROM OTHER NEURAL CELLS TO THE CELL BODY OF THE NEURON FROM WHICH THE DENDRITES PROJECT.

• NUMEROUS SHORT EXTENSIONS FROM CELL BODY • INCREASING SURFACE AREA • DENDRITIC SPINES FUNCTION OF DENDRITES : • RECEIVE INCOMING SIGNALS AND TRANSMITS THEM • HELPS IN PROTEIN SYNTHESIS • HELPS IN GENERATING ACTION POTENTIAL

NEURILEMMA IS THE OUTERMOST NUCLEATED CYTOPLASMIC LAYER THAT SURROUNDS THE AXON OF THE NEURON. IT FORMS THE OUTERMOST LAYER OF THE NERVE FIBER IN THE PERIPHERAL NERVOUS SYSTEM.

MYELIN SHEATH • FATTY MATERIAL MADE BY GLIAL CELLS • INSULATES THE AXON • ALLOWS FOR RAPID MOVEMENT OF ELECTRICAL IMPULSES ALONG AXON • NODES OF RANVIER: GAPS IN MYELIN SHEATH WHERE ACTION POTENTIALS ARE TRANSMITTED • MULTIPLE SCLEROSIS IS A BREAKDOWN OF MYELIN SHEATH • SPEED OF NEURAL IMPULSE RANGES FROM 2 – 200+ MPH

MYELINATION • IT’S A PROTECTIVE INSULATOR COVERING OF THE AXON • FORMED BY SCHWANN CELLS • DOUBLE LAYER MEMBRANE OF A SINGLE SCHWANN CELL WRAPS ITSELF SEVERAL TIMES AROUND AXON • 1 MM IN LENGTH , 8 -10 MICROMETER INTHICKNESS • SCHWANN CELL NUCLEUS LIES IN THE OUTERMOST LAYER

FUNCTIONS OF MYELINATION • INCREASES SPEED OF CONDUCTION • IT REDUCES ENERGY EXPENDITURE BY THE CELL • PROVIDES PROTECTIVE COVERING OF THE AXON

NODE OF RANVIER • MYELIN SHEATHS AXONS •

SYNAPSE A junction where the axon or some other portion of one cell (= presynaptic cell) terminates on the dendrites, soma, or axon of another neuron (post synaptic cell). The term was introduced in nineteenth century by the British neurophysiologist Charles Sherrington

PART FUNCTION AXON Carry nerve impulses away from cell DENDRITES Carry nerve impulse towards nerve cell SCHWANN’S CELL Protective myelin sheath around the axon of myelinated nerve fibres. NUCLEUS Control the activity of cell MYELIN SHEATH -Protection of the nerve fibre. -Insulation of the nerve fibre. -Increases the rate of transmission of nerve impulses. NODES OF RANVIER -Allowing nutrients and waste products to enter/leave the neurone. -Allowing nerve impulses to move along the neurone through a process of de-polarisation and re-polarisation of the nerve membrane. SYNAPSE Reaching a synapse, an impulse causes the release of a neurotransmitter, which diffuses across the gap and triggers an electrical impulse in the next neurone

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