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Nervous System

The system in the body responsible for receiving sensory input, integrating information, controlling muscles and glands, maintaining homeostasis, and establishing and maintaining mental activity.

Central Nervous System (CNS)

The division of the nervous system that includes the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system that includes all the nervous tissue outside the CNS.

Sensory division

The division of the PNS that conducts action potentials from sensory receptors to the CNS.

Motor division

The division of the PNS that conducts action potentials to effector organs, such as muscles and glands.

Somatic Nervous System

The division of the motor division that transmits action potentials from the CNS to skeletal muscles (voluntary).

Autonomic Nervous System

The division of the motor division that transmits action potentials from the CNS to cardiac muscles, smooth muscle, and glands (involuntary).

Enteric Nervous System

A special nervous system found only in the digestive tract.

Neurons

Cells in the nervous system that receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.

Glial Cells

Supportive cells of the CNS and PNS that enhance neuron function and maintain normal conditions within nervous tissue.

Cell Body

The part of a neuron that contains a single nucleus.

Dendrite

A cytoplasmic extension from the cell body that usually receives information from other neurons and transmits it to the cell body.

Axon

A single-long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS.

Multipolar Neurons

Neurons that have many dendrites and a single axon, most common type of neurons.

Bipolar Neurons

Neurons that have two processes, one dendrite and one axon, located in some sensory organs.

Pseudo-unipolar Neurons

Neurons that have a single process extending from the cell body, which divides into two processes a short distance from the cell body, rare.

Astrocytes

Glial cells that serve as the major supporting cells in the CNS, can stimulate or inhibit the signaling activity of nearby neurons and form the blood-brain barrier.

Ependymal Cells

Glial cells that line the cavities in the brain that contain cerebrospinal fluid.

Microglial Cells

Glial cells that act in an immune function in the CNS by removing bacterial and cell debris.

Oligodendrocytes

Glial cells that provide myelin to neurons in the CNS.

Schwann Cells

Glial cells that provide myelin to neurons in the PNS.

Myelin Sheath

Specialized layers that wrap around the axons of some neurons, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, increases the speed and efficiency of action potential generation along the axon.

Unmyelinated Neurons

Neurons that lack myelin sheaths, rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS.

Gray Matter

Consists of groups of neuron cell bodies and their dendrites, where there is very little myelin.

White Matter

Consists of bundles of parallel axons with their myelin sheaths, which are whitish in color.

Resting Membrane Potential

The electrical potential difference across the cell membrane of a neuron when it is not conducting an action potential.

Action Potential

A rapid change in the membrane potential of a neuron, allowing conductivity along the nerve or muscle membrane.

Leak Channels

Membrane channels that are always open, allowing ions to "leak" across the membrane down their concentration gradient.

Gated Channels

Membrane channels that are generally closed but can be opened due to voltage or chemicals.

Sodium-Potassium Pump

A pump that actively transports K+ into the cell and Na+ out of the cell, maintaining the greater concentration of Na+ outside the cell membrane and K+ inside.

Synapse

A junction where the axon of one neuron interacts with another neuron, neurotransmitters are released and bind to receptors on the postsynaptic membrane, causing stimulation or inhibition of an action potential in the postsynaptic cell.

Norepinephrine

A neurotransmitter that is either transported back into the presynaptic terminal or broken down by enzymes.

Reflex

An involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS.

Reflex Arc

The neuronal pathway by which a reflex occurs, consisting of a sensory receptor, sensory neuron, interneurons, motor neuron, and effect organ.

Neuronal Pathway (Converging)

A simple pathway in which two or more neurons synapse with the same postsynaptic neuron, allowing information from multiple pathways to converge.

Neuronal Pathway (Diverging)

A simple pathway in which an axon from one neuron divides and synapses with more than one other postsynaptic neuron, allowing information from one pathway to diverge into multiple pathways.

Summation

The process of combining multiple subthreshold local potentials to reach threshold and trigger an action potential.

Spatial Summation

Summation that occurs when local potentials originate from different locations on the postsynaptic neuron, such as from converging pathways.

Temporal Summation

Summation that occurs when local potentials overlap in time, often from a single input firing rapidly.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system consisting of all the nerves and ganglia outside the brain and spinal cord.

Spinal Cord

The part of the CNS that extends from the foramen magnum to the 2nd lumbar vertebra and is responsible for transmitting signals between the brain and the rest of the body.

Gray Matter

The center of the spinal cord, composed of cell bodies and dendrites.

White Matter

The outer region of the spinal cord, composed of myelinated axons.

Reflexes

Involuntary reactions in response to a stimulus, such as the stretch reflex or withdrawal reflex.

Spinal Nerves

Nerves that arise along the spinal cord and contain axons of sensory and somatic neurons.

Dermatome

The area of skin supplied with sensory innervation by a pair of spinal nerves.

Brainstem

The part of the CNS that connects the spinal cord to the rest of the brain and is responsible for basic functions such as breathing and heart rate regulation.

Cerebellum

The part of the brain responsible for balance, muscle tone, and coordination of fine motor movements.

Diencephalon

The part of the brain located between the brainstem and cerebrum, consisting of the thalamus, hypothalamus, and epithalamus.

Cerebrum

The largest part of the brain responsible for higher cognitive functions, divided into two hemispheres and lobes.

Sensory Areas of Cerebral Cortex

Areas of the cerebral cortex where sensations are perceived, such as the primary somatic sensory cortex.

Somatic Motor Functions

Functions of the somatic motor system, which controls voluntary movements and maintains posture and balance.

Motor Areas of Cerebral Cortex

Areas of the cerebral cortex responsible for controlling voluntary motor movements, such as the primary motor cortex and premotor area.

Descending Tracts

Motor tracts carrying impulses down the spinal cord, either terminating there or in the brainstem.

Corticospinal Tracts

Direct motor tracts that extend from upper motor neurons in the cerebral cortex to lower motor neurons in the spinal cord.

Tracts in the ventral columns

These tracts, such as the reticulospinal tract, are important for maintaining posture, balance, and limb position through their control of neck, trunk, and proximal limb muscles.

Crossover of axons

Axons in the brainstem or spinal cord typically cross over to the opposite side of the body in descending pathways.

Left side of the brain controls skeletal muscles on the right side of the body

The left side of the brain is responsible for controlling the skeletal muscles on the right side of the body, and vice versa.

Basal Nuclei

A group of functionally related nuclei that plan, organize, and coordinate motor movements and posture. Includes the corpus striatum (deep in the cerebrum) and substantia nigra (in the midbrain).

Speech

Mainly located in the left hemisphere of the brain. Sensory speech (Wernicke's Area) is in the parietal lobe, where words are heard and comprehended. Motor speech (Broca's Area) is in the frontal lobe, where words are formulated.

Brain Waves and Consciousness

Brain waves are used to diagnose and determine treatment for brain disorders. Electroencephalogram (EEG) is a recording of the brain's electrical activity using electrodes placed on the scalp.

Memory

Encoding is the brief retention of sensory input received by the brain while something is scanned, evaluated, and acted upon. Consolidation refers to data that has been encoded and stored in short-term memory. Storage refers to long-term memory, which can last for a few minutes or permanently. Retrieval is how often information is used.

Types of Memory

Short-term memory retains information for a few seconds or minutes, usually in small bits. Long-term memory can last for a few minutes or permanently. Episodic memory is memory of specific places or events. Learning involves utilizing past memories.

Limbic System and Emotions

The limbic system includes the olfactory cortex, certain deep cortical regions and nuclei of the cerebrum and diencephalon. It influences long-term declarative memory, emotions, visceral responses to emotions, motivation, and mood. It is connected to the hypothalamus and lesions in the limbic system can result in changes in appetite, sexual activity, and emotional responses.

Meninges

The meninges are three connective tissue layers that surround the brain and spinal cord. The dura mater is the outermost and toughest layer. The arachnoid mater is a thin, wispy membrane. The pia mater is tightly bound to the surface of the brain and spinal cord.

Ventricles

The CNS contains fluid-filled cavities called ventricles. The lateral ventricles are located in each cerebral hemisphere. The third ventricle is in the center of the diencephalon. The fourth ventricle is at the base of the cerebellum and is continuous with the central canal of the spinal cord.

Cerebrospinal Fluid

CSF bathes the brain and spinal cord, providing a protective cushion. It is produced by ependymal cells in the choroid plexuses of the ventricles. CSF flows through the ventricles and subarachnoid space. It is absorbed into the blood through arachnoid granulations.

Cranial Nerves

There are 12 pairs of cranial nerves, each with sensory and motor functions. They are named using Roman numerals. Examples include the olfactory nerve (I) for smell, optic nerve (II) for vision, and facial nerve (VII) for taste and facial expression.

Autonomic Nervous System

The autonomic nervous system innervates smooth muscle, cardiac muscle, and glands. It controls unconscious functions. It consists of the sympathetic division (fight-or-flight) and the parasympathetic division (rest-and-digest).

Senses

Senses allow us to perceive stimuli. Sensation is the conscious awareness of stimuli received by sensory neurons. Sensory receptors are nerve endings that respond to stimuli by developing action potentials.

Classification of Senses

Senses can be classified as general or special. General senses include touch, pressure, pain, temperature, and itch. Special senses include smell, taste, sight, hearing, and balance.

Types of Receptors

Mechanoreceptors detect movement, chemoreceptors detect chemicals, photoreceptors detect light, thermoreceptors detect temperature changes, and nociceptors detect pain.

Sensory Receptors in the Skin

There are different types of touch receptors in the skin, including Merkel's disks, hair follicle receptors, Meissner corpuscles, Ruffini corpuscles, and Pacinian corpuscles

Taste buds

Certain taste buds are more sensitive to certain tastes.

Taste and smell

Taste is also linked to smell.

Eyebrow

Protects from sweat and shades from the sun.

Eyelid/Eyelashes

Protects from foreign objects and lubricated by blinking.

Conjunctiva

Thin membrane that covers the inner surface of the eyelid.

Lacrimal Apparatus

Produces tears.

Extrinsic eye muscles

Help move the eyeball.

Fibrous Tunic

Outermost tunic of the eye, composed of the sclera and cornea.

Vascular Tunic

Middle tunic of the eye, contains the choroid, ciliary body, suspensory ligaments, lens, iris, and pupil.

Nervous Tunic

Innermost tunic of the eye, contains the retina, pigmented retina, and sensory retina.

Rods

Photoreceptors sensitive to light, function in dim light.

Cones

Photoreceptors that provide color vision, three types:blue, green, and red.

Rhodopsin

Photosensitive pigment in rod cells.

Retina

Covers the posterior 5/6 of the eye, contains photoreceptors (rods and cones).

Macula

Small spot near the center of the retina.

Fovea Centralis

Center of the macula, contains only cones and enables the ability to discriminate fine images.

Optic Disk

White spot medial to the macula, called the blind spot as it contains no photoreceptors.

Anterior Chamber

Located between the cornea and lens, filled with aqueous humor.

Posterior Chamber

Located behind the anterior chamber, also contains aqueous humor.

Vitreous Chamber

Located in the retina region, filled with vitreous humor.

Light Refraction

Bending of light.

Focal Point

Point where light rays converge, occurs anterior to the retina.

Myopia

Nearsightedness, image is in front of the retina.

Hyperopia

Farsightedness, image is behind the retina.

Presbyopia

Lens becomes less elastic, reading glasses required.

Astigmatism

Irregular curvature of the lens, glasses or contacts required to correct.