Nervous System

Nervous system

Employs electrical and chemical means to send messages from cell to cell.

Endocrine system

Communicates by means of chemical messengers (hormones) secreted into the blood.

CNS (Central Nervous System)

Comprised of the Brain and Spinal cord. Main centers of correlation and integration.

PNS (Peripheral Nervous System)

Includes Spinal nerves and ganglia, Sympathetic and Parasympathetic NS, and Enteric NS; all the nerves outside the brain and the spinal cord.

Sensory Input

The function where receptors from organs respond to external and internal stimuli.

Integration

The function involving combining received data and sending out signals.

Motor Output

The function where impulses from integration go to the effector organs.

Excitability (irritability)

The property of a neuron that responds to environmental changes called stimuli.

Conductivity

The property of a neuron that responds to stimuli by producing electrical signals quickly conducted to other cells at distant locations.

Soma (cell body or neurosoma)

The control center, containing a single, centrally located nucleus with a large nucleolus and Cytoplasm.

Dendrites

Branches off the soma; the primary site for receiving signals from other neurons.

Axon (nerve fiber)

Originates from the axon hillock; specialized for rapid signal conduction.

Axon collaterals

Branches of the axon.

Myelin sheath

Encloses the axon; insulates it and significantly increases the speed of electrical impulse transmission. It is formed by oligodendrocytes in the CNS and Schwann cells in the PNS.

Myelination

The production of the myelin sheath.

Node of Ranvier

Assists in the rapid transmission (saltatory conduction) of nerve impulses along a myelinated axon.

Synaptic knob (terminal button)

Located at the very last segment of the axon.

Multipolar

Most neurons in the CNS.

Bipolar neuron

Found in Olfactory cells, retina, and inner ear.

Pseudounipolar (Unipolar)

Related to the transmission of touch, pressure, and pain.

Sensory (afferent) neurons

Detect stimuli and transmit information toward the CNS.

Interneurons (association neurons)

Carry out integrative functions and make decisions on responses.

Motor (efferent) neuron

Sends signals out to muscles and gland cells (the effectors).

Neuroglia or glial cells

Protect neurons, help them function, bind neurons together, and form a framework for nervous tissue. They outnumber neurons by at least 10 to 1.

Multiple sclerosis

A degenerative disorder where oligodendrocytes and myelin sheaths in the CNS deteriorate, replaced by hardened scar tissue.

Tay–Sachs disease

A hereditary disorder involving the abnormal accumulation of the glycolipid GM2 in the myelin sheath, damaging CNS neurons.

Synapses

Where a nerve signal triggers the release of a neurotransmitter into the space between the presynaptic and postsynaptic neurons.

Presynaptic neuron

The first neuron in the signal path that releases the neurotransmitter.

Postsynaptic neuron

The second neuron that responds to the neurotransmitter.

Neurotransmitters

Major chemical categories include acetylcholine, amino acids (glycine, glutamate, aspartate, GABA), monoamines (Epinephrine, norepinephrine, dopamine, histamine, ATP, serotonin), and neuropeptides (cholecystokinin and substance P).

CNS Anatomy

Coverings and Fluid

Meninges

Membranes covering the brain and spinal cord, including the dura mater, arachnoid mater, and pia mater.

Ventricles of the brain

Four interconnected, fluid-filled cavities that produce and circulate Cerebrospinal Fluid (CSF).

Choroid plexus

A network of specialized capillaries and ependymal cells responsible for continuous CSF secretion.

CSF

A clear, slightly alkaline fluid that supports and protects the brain and spinal cord, maintains uniform pressure, and acts as a cushion/shock absorber.

Cerebrum

The largest part of the brain, divided into two cerebral hemispheres.

Corpus Callosum

A mass of white matter (300 million neuronal axons) that connects the two cerebral hemispheres.

Grey matter (Cerebral cortex)

Consists mainly of neuron cell bodies, dendrites, axon terminals, and glial cells; the "computer of the CNS".

White matter

Primarily bundles of myelinated axons.

Thalamus

The central relay station for sensory and motor signals; the sensory gateway.

Hypothalamus

The body’s control center, regulating the autonomic nervous system, thirst, body temperature, emotional reactions, and biological clocks.

Cerebral Lobes

Frontal (primary motor cortex, decision-making), Parietal (integration center, spatial awareness), Temporal (auditory processing, memory formation via hippocampus), and Occipital (visual processing and interpretation).

Brainstem

The "life support system" including the Midbrain (Mesencephalon), Pons (Metencephalon), and Medulla Oblongata (Myelencephalon); controls vital involuntary functions.

Cerebellum

The "little brain" central to the integration of motor output and sensory perception, coordinating voluntary movement, posture, and balance. Divisions include the vestibulocerebellum, spinacerebellum, and cerebrocerebellum.

Sympathetic

Fight or flight response that activates the body

Parasympathetic

rest and digest system that conserves energy