Nervous System: Structure, Function, and Cranial Nerves

Nervous System

Two parts: central nervous system (CNS) including brain and spinal cord; peripheral nervous system (PNS) including nerves and sensory receptors.

Neuroglia

Cells that support, nourish, and insulate neurons, but they don't transmit info.

Microglia

Cells that engulf foreign material and bacteria, providing slight immune function.

Oligodendrocytes

Cells in the CNS that insulate axons of neurons.

Schwann cells

Cells in the PNS that insulate axons of neurons.

Ependymal cells

Cells that line the central canals of the brain and spinal cord.

Astrocytes

Cells that pass nutrients between blood capillaries and neurons and help form the blood-brain barrier.

Neurons

Nerve cells that transfer information via electrical stimuli throughout the body.

Cell body

Also known as soma or perikaryon, it is a part of the neuron.

Dendrites

Parts of a neuron that receive nerve signals.

Axons

Parts of a neuron that transmit nerve impulses.

(Pseudo)Unipolar Neuron

Neuron with a single stem that divides into a dendrite and axon.

Bipolar Neuron

Neuron with two processes; one dendrite and one axon.

Multipolar Neuron

Neuron with multiple dendrites and one axon.

Nerve

Bundle of axons in the PNS.

Tract

Bundle of axons in the CNS.

Ganglion

Collection of nerve cell bodies in the PNS.

Nucleus

Collection of nerve cell bodies in the CNS.

Myelin sheath

Thick, whitish, fatty material wrapped around some axons that helps to insulate them.

Myelinated nerves/axons

Nerves/axons that transmit faster signals.

Unmyelinated nerves/axons

Nerves/axons that transmit slower signals.

Nodes of Ranvier

Gaps that let signals propagate along myelinated axons.

Nerve impulse

An electrical signal that is transmitted by a neuron.

Graded potential

Wave of electrical excitation.

Resting potential

Electrical difference across a membrane at rest.

Action potential

All-or-none phenomenon which is the nerve impulse that sends the actual signal to other cells.

Synapse

Junction between a neuron and another cell.

Synaptic cleft

Space between terminal and cell.

Neurotransmitters

Stored chemical signals released by neurons in response to an action potential.

Somatic nerves

Nerves that pass to or from somatic tissues - skeletal muscle, skin, and their derivatives.

Visceral nerves

Nerves that pass to or from viscera (internal organs) - involuntary muscles and glands.

Sensory (afferent) neurons

Neurons that carry info to the CNS.

Motor (efferent) neurons

Neurons that carry info away from the CNS to effectors.

Spinal nerves

Nerves that come off the spinal column in pairs and are sequentially named and numbered.

Dorsal root

Carries afferent fibers from nerves; also has dorsal root ganglion.

Ventral root

Carries efferent fibers to nerves.

Cranial nerves

Nerves that have roots enclosed in the brain case and vary depending on animal groups.

Olfactory Nerve

Nerve that senses smell.

Optic Nerve

Nerve that senses vision.

Oculomotor Nerve

Nerve that controls 4 out of 6 muscles of the eye and constricts the pupil.

Trochlear Nerve

Nerve that moves the superior oblique muscle.

Trigeminal Nerve

Nerve with 3 branches that senses skin of face and moves muscles of mastication.

Facial Nerve

Nerve that senses taste on anterior 2/3rds of tongue and controls muscles of facial expression.

Auditory (Vestibulocochlear) Nerve

Nerve that senses hearing and balance.

Glossopharyngeal Nerve

Nerve that senses taste and feeling on posterior 1/3rd of tongue and controls salivation of parotid gland.

Vagus Nerve

Nerve that senses sensations from thoracic and abdominal organs and controls thoracic and abdominal viscera.

(Spinal) Accessory Nerve

Nerve that moves SCM and trapezius.

Hypoglossal Nerve

Nerve that moves the tongue.

Somatic reflex arc

Usually includes somatic sensory, interneuron (association neuron) and somatic motor; it sometimes doesn't have an interneuron.

Visceral reflex arc

Involves organs and is more complex with a minimum of 4 neurons.

Autonomic Nervous System (ANS)

Part of nervous system that presides over involuntary visceral activities; is poorly understood in most vertebrates except for mammals.

Autonomic sensory fibers

Monitor BP, oxygen and carbon dioxide levels, temperature, and visceral activity.

Autonomic motor fibers

Innervate cardiac muscle, smooth muscle, and glands; therefore, they control the digestive tract, blood vessels, respiratory tree, bladder, sex organs, and other general body viscera.

Control of ANS

Some people can control the ANS to a certain point, but by far, the system operates subconsciously.

Sympathetic nervous system

Fight or flight; has thoracolumbar outflow.

Parasympathetic nervous system

Rest and digest; has craniosacral outflow.

Enteric nervous system

Exclusively in the digestive tract and can be influenced by the sympathetic or parasympathetic; appears to be present in all classes of vertebrates.

Two-neuron system in ANS

The ANS has a two-neuron system most of the time in sending signals, as opposed to the one-neuron system in the somatic nervous system.

Adrenergic

Sympathetic nervous system is adrenergic because the neurotransmitters released during its stimulation are adrenaline (epinephrine) or noradrenaline (norepinephrine).

Cholinergic

Parasympathetic nervous system is cholinergic because the neurotransmitter is acetylcholine, which is also released between pre- and post-ganglionic fibers in both systems.

Dual innervation

Most organs have dual innervation from both systems, with the exception of the adrenal gland, peripheral blood vessels, and sweat glands, which only receive sympathetic innervation.

Central Nervous System (CNS)

Primarily coordinates activities that enable an organism to survive and reproduce in its environment.

Proprioceptor

Informs CNS about position of limbs, degree to which joints are bent and muscles are stretched.

Somatosensory system

Info-processing system which includes proprioceptors and surface receptors within the skin.

Exteroceptors

Gather info from the external environment - includes touch, pressure, temperature, sight, hearing, smell, taste, and other stimuli.

Embryology of CNS

Vertebrate CNS is hollow due to fusion of two raised neural folds in ectoderm.

Prosencephalon

Differentiates into forebrain, cerebrum, and diencephalon.

Mesencephalon

Differentiates into midbrain.

Rhombencephalon

Differentiates into hindbrain, cerebellum, pons, and medulla oblongata.

Meninges

Brain and spinal cord are wrapped in meninges; 3 types in mammals.

Dura mater

Tough, outermost layer of the meninges.

Arachnoid mater

Weblike, middle layer of the meninges.

Pia mater

Inner layer of the meninges.

Cerebrospinal fluid (CSF)

Slightly viscous fluid in brain ventricles, subarachnoid space, and central canal in spinal cord.

Choroid plexus

Small tufts of blood vessels with ependymal cells which produce most CSF.

Gray matter

Includes nerve cell bodies.

White matter

Includes myelinated neurons.

Brainstem

Includes midbrain, pons, and medulla oblongata.