Overview of the Nervous System Functions and Components

Main function of the nervous system

The nervous system receives sensory input, processes it (integration), and responds via motor output.

Sensory input

The nervous system receives information from sensory receptors in the body.

Integration in the nervous system

The brain interprets and processes sensory input.

Motor output

The nervous system responds by activating muscles or glands.

Central Nervous System (CNS)

The brain and spinal cord; it serves as the integration and command center.

Peripheral Nervous System (PNS)

All neural tissue outside the CNS; includes cranial and spinal nerves.

Two main divisions of the PNS

Sensory (afferent) and Motor (efferent) divisions.

Sensory (afferent) division

Carries impulses from receptors in skin, muscles, and organs to the CNS.

Motor (efferent) division

Transmits impulses from the CNS to muscles and glands (effectors).

Somatic nervous system

A voluntary system that sends impulses to skeletal muscles.

Autonomic nervous system

An involuntary system that sends impulses to cardiac/smooth muscle and glands.

Neurons

Excitable cells that transmit electrical signals.

Neuroglia

Supporting cells that protect and nourish neurons.

Main parts of a neuron

Cell body, dendrites, axon, axon hillock, axon terminals.

Function of the myelin sheath

Insulates axons and speeds up nerve impulse conduction.

Synapse

The junction where a neuron communicates with another cell using neurotransmitters.

Main types of neuroglia in the CNS

Astrocytes, microglia, ependymal cells, oligodendrocytes.

Schwann cells

Form myelin sheath in the PNS and aid in nerve regeneration.

Resting membrane potential (RMP)

A neuron at rest has a charge of -70 mV, with more K+ inside and Na+ outside.

Graded potential

A small, localized change in membrane potential that can initiate an action potential.

Action potential

A large, rapid electrical signal that travels down an axon without losing strength.

Depolarization

Sodium channels open, sodium flows in, and the inside becomes more positive.

Hyperpolarization

The membrane potential becomes more negative than -70 mV, reaching -90 mV briefly.

Saltatory conduction

Nerve impulse 'jumps' from node to node along myelinated axons for faster transmission.

All or none principle

Once the threshold is reached, an action potential always fires with full intensity.

Excitatory post-synaptic potentials (EPSPs)

They open sodium channels, leading to depolarization.

Inhibitory post-synaptic potentials (IPSPs)

They open potassium channels, making the inside more negative.

Neurotransmitters

Chemicals that transmit signals across a synapse.

Three types of ion channels

Chemically-gated, voltage-gated, and mechanically-gated channels.

Axon hillock

The thickened region of the neuron where the axon connects to the cell body; site of action potential initiation.

Perikaryon

The cytoplasm surrounding the nucleus in the neuron's cell body, rich in ribosomes and mitochondria.

Conduction velocity of an action potential

Determined by axon diameter and presence of myelin sheath.

Types of neurotransmitter classifications

Cholinergic (acetylcholine) and adrenergic (norepinephrine).

Absolute refractory period

The neuron cannot fire another action potential regardless of stimulus strength.

Temporal summation

Rapid, repeated impulses from one neuron increase the effect on the postsynaptic cell.

Spatial summation

Multiple neurons stimulate a postsynaptic neuron at the same time, increasing depolarization.